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This may account for the peak releases of radionuclides seen at the last stage of the active period. Approximately nine days after the accident, the corium began to lose its ability to interact with the surrounding materials.

It solidified relatively rapidly, causing little damage to metallic piping in the lower regions of the reactor building. The chemistry of the corium was altered by the large mass of the lower biological shield taken up into the molten corium about of the 1,t shield of stainless steel construction and serpentine filler material.

The decayheat was significantly lowered, and the radionuclide releases dropped by two to three orders of magnitude.

Visual evidence of the disposition of the corium supports this sequence of events. On the basis of an extensive series of measurements in of heat flux and radiation intensities and from an analysis of photographs, an approximate mass balance of the reactor fuel distribution was established data reported by Borovoi and Sich [B16, S1].

Different estimates of the reactor fuel distribution have been proposed byothers. Purvis [P4] indicated that the amount of fuel in the lava, plus fragments of the reactor core under the level of the bottom of the reactor, is between 27 and t and that the total amount of the fuel in the reactor hall area is between 77 and t.

Kisselev et al. It may be that most of the fuel is on the roof of the reactor hall and is covered by the material that was dropped on it from helicopters.

Only the removal of this layer of material will allow making a better determination of the reactor fuel distribution. Two basic methods were used to estimate the release of radionuclides in the accident.

The first method consists in evaluating separately the inventory of radionuclides in the reactor core at the time of the accident and the fraction of the inventory of each radionuclide that was released into the atmosphere; the products of those two quantities are the amounts released.

The second method consists in measuring the radionuclide deposition density on the ground all around the reactor; if it is assumed that all of the released amounts deposited within the area where the measurements were made, the amounts deposited are equal to the amounts released.

In both methods, air samples taken over the reactor or at various distances from the reactor were analysed for radionuclide content to determine or to confirm the radionuclide distribution in the materials released.

The analysis of air samples and of fallout also led to information on the physical and chemical properties of the radioactive materials that were released into the atmosphere.

It is worth noting, however, that the doses were estimated on the basis of environmental and human measurements and that the knowledge of the quantities released was not needed for that purpose.

Estimation of radionuclide amounts released From the radiological point of view, I and Cs are the most important radionuclides to consider, because they are responsible for most of the radiation exposure received by the general population.

Several estimates have been made of the radionuclide core inventory at the time of the accident.

Some of these estimates are based on the burn-up of individual fuel assemblies that has been made available [B1, S1].

The average burn-up of In the case of Te and of the shortlived radioiodines, Khrouch et al. An extended list of radionuclides present in the core at the time of the accident is presented in Table 1.

The values used by the Committee in this Annex are those presented in the last column on the right.

For comparison purposes, the initial estimates of the core inventory as presented in [I2], which were used by the Committee in the UNSCEAR Report [U4], are also presented in Table 1; these estimates, however, have been decaycorrected to 6 May , that is, 10 days after the beginning of the accident.

The large differences observed between initial and recent estimates for short-lived radionuclides radioactive half-lives of less than 10 days are mainly due to radioactive decay between the actual day of release and 6 May, while minor differences may have been caused by the use of different computer codes to calculate the build-up of activity in the reactor core.

For Cs, the and current estimates of core inventory at the time of the accident are and PBq, respectively.

For I, the corresponding values are 1, and 3, PBq, respectively. There are several estimates of radionuclides released in the accident based on recent evaluations.

Three such listings, including two taken from the IAEA international conference that took place at Vienna in [D8], are given in Table 2 and compared to the original estimates of [I2].

The estimates of Buzulukov and Dobrynin [B4], as well as those of Kruger et al. There is general agreement on the releases of most radionuclides, and in particular those of Cs and I, presented in the evaluations.

From average deposition densities of Cs and the areas of land and ocean regions, the total Cs deposit in the northern hemisphere was estimated to be 70 PBq, which is in fairly good agreement with the current estimate.

This, however, was the inventory of I at the end of the release period 6 May It would have been higher at the beginning of the accident.

The results presented in Table 2 are incomplete with respect to the releases of Te and of the short-lived radioiodines I to I.

In this Annex, the releases of those radionuclides have been scaled to the releases of I, using the radionuclide inventories presented in Table 1 and taking into account the radioactive half-lives of the radionuclides.

The following procedure was used: a the release rates at the time of the steam explosion were estimated from the radionuclide inventories presented in Table 1, assuming no fractionation for the short-lived radioiodines I, I and I with respect to I, a value of 0.

The activity ratios to I in the initial release rates are therefore estimated to have been 1. The estimated daily releases of I are presented in Table 3; and c the variation with time of the release rates of the short-lived radioiodines and of Te has been assumed to be the same as that of I, but a correction was made to take into account the differences in radioactive half-lives.

Daily release of iodine, iodine, tellurium and caesium from the Chernobyl reactor. The overall releases of short-lived radioiodines and of Te are presented in Table 4; they are found to be substantially lower than those of I.

This is due to the fact that most of the short-lived radioiodines decayed in the reactor instead of being released.

Additional, qualitative information on the pattern of release of radionuclides from the reactor is given in Figure III.

The concentrations of radionuclides in air were determined in air samples collected by helicopter above the damaged reactor [B4]. Although the releases were considerably reduced on 5 and 6 May days 9 and 10 after the accident , continuing low-level releases occurred in the following week and for up to 40 days after the accident.

Particularly on 15 and 16 May, higher concentrations were observed, attributable to continuing outbreaks of fires or to hot areas of the reactor [I6].

These later releases can be correlated with increased concentrations of radionuclides in air measured at Kiev and Vilnius [I6, I35, U16].

Physical and chemical properties of the radioactive materials released There were only a few measurements of the aerodynamic size of the radioactive particles released during the first days of the accident.

A crude analysis of air samples, taken at m above the ground in the vicinity of the Chernobyl power plant on 27 April , indicated that large radioactive particles, varying in size from several to tens of micrometers, were found, together with an abundance of smaller particles [I6].

In a carefully designed experiment, aerosol samples taken on 14 and 16 May with a device installed on an aircraft that flew above the damaged reactor were analysed by spectrometry [B6, G14].

Concentration of radionuclides in air measured above the damaged Chernobyl reactor [B6]. The geometric sizes of the fuel particles collected in Hungary, Finland and Bulgaria ranged from 0.

Taking the density of fuel particles to be 9 g cm3, their aerodynamic diameter therefore ranged from 1. Similar average values were obtained for fuel particles collected in May in southern Germany [R20] and for those collected in the km zone in September [G27].

It was observed that Chernobyl fallout consisted of hot particles in addition to more homogeneouslydistributed radioactive material [D6, D7, K34, S26, S27, S28].

These hot particles can be classified into two broad categories: a fuel fragments with a mixture of fission products bound to a matrix of uranium oxide, similar to the composition of the fuel in the core, but sometimes strongly depleted in caesium, iodine and ruthenium, and b particles consisting of one dominant element ruthenium or barium but sometimes having traces of other elements [D6, J3, J4, K35, K36, S27].

These monoelemental particles may have originated from embedments of these elements produced in the fuel during reactor operation and released during the fragmentation of the fuel [D7].

Typical activities per hot particle are 0. Hot particles deposited in the pulmonary region will have a long retention time, leading to considerable local doses [B33, L23].

In the immediate vicinity of a 1 kBq ruthenium particle, the dose rate is about 1, Gy h1, which causes cell killing; however, sublethal doses are received by cells within a few millimetres of the hot particle.

Although it was demonstrated in the s that radiation doses from alpha-emitting hot particles are not more radiotoxic than the same activity uniformly distributed in the whole lung [B28, L33, L34, L35, R15], it is not clear whether the same conclusion can be reached for beta-emitting hot particles [B33, S27].

Areas of the former Soviet Union Radioactive contamination of the ground was found to some extent in practically every country of the northern hemisphere [U4].

In this Annex, contaminated areas are defined as areas where the average Cs deposition densities exceeded 37 kBq m2 1 Ci km2.

Caesium was chosen as a reference radionuclide for the ground contamination resulting from the Chernobyl accident for several reasons: its substantial contribution to the lifetime effective dose, its long radioactive half-life, and its ease of measurement.

As shown in Table 5, the contaminated areas were found mainly in Belarus, in the Russian Federation and in Ukraine [I24].

The radionuclides released in the accident deposited over most of the European territory of the former Soviet Union.

A map of this territory is presented in Figure IV. The main city gives its name to each region. The regions oblasts are subdivided into districts raions.

The important releases lasted 10 days; during that time, the wind changed direction often, so that all areas surrounding the reactor site received some fallout at one time or another.

The initial plumes of materials released from the Chernobyl reactor moved towards the west. On 27 April, the winds shifted towards the northwest, then on 28 April towards the east.

Administrative regions surrounding the Chernobyl reactor. Plume formation by meteorological conditions for instantaneous releases on dates and times GMT indicated [B7].

The contamination of Ukrainian territorysouth of Chernobyl occurred after 28 April Figure V, traces 4, 5 and 6.

Rainfall occurred in an inhomogeneous pattern, causing uneven contamination areas. The general pattern of Cs deposition based on calculations from meteorological conditions has been shown to match the measured contamination pattern rather well [B7].

Surface ground deposition of caesium released in the Chernobyl accident [I1, I3]. Surface ground deposition of caesium in the immediate vicinity of the Chernobyl reactor [I1, I24].

The distances of 30 km and 60 km from the nuclear power plant are indicated. The detailed contamination patterns have been established from extensive monitoring of the affected territory.

The contamination of soil with Cs in the most affected areas of Belarus, the Russian Federation and Ukraine is shown in Figure VI, and the Cs contamination of soil in the immediate area surrounding the reactor is shown in Figure VII.

The deposition of 90Sr and of nuclear fuel particles, usuallyrepresented as the deposition oftheir marker, 95 Zr or Ce, were relatively localized.

An important deposition map to be established is that of I. Because there were not enough measurements at the time of deposition, the I deposition pattern can be only approximated from limited data and relationships inferred from Cs deposition.

Because the I to Cs ratio was observed to vary from 5 to 60, the I deposition densities estimated for areas without I measurements are not very reliable.

Measurements of the current concentrations of I in soil could provide valuable information on the I deposition pattern [S45].

The principal physico-chemical form of the deposited radionuclides are: a dispersed fuel particles, b condensation-generated particles, and c mixed-type particles, including the adsorption-generated ones [I22].

Deposition in the near zone reflected the radionuclide composition of the fuel. Larger particles, which were primarily fuel particles, and the refractory elements Zr, Mo, Ce and Np were to a large extent deposited in the near zone.

Intermediate elements Ru, Ba, Sr and fuel elements Pu, U were also deposited largely in the near zone.

The volatile elements I, Te and Cs in the form of condensation-generated particles, were more widely dispersed into the far zone [I6].

Of course, this characterization oversimplifies the actual dispersion pattern. Areas of high contamination from Cs occurred throughout the far zone, depending primarilyon rainfall at the time the plume passed over.

The composition of the deposited radionuclides in these highly contaminated areas was relatively similar. Some ratios of radionuclides in different districts of the near and far zones are given in Table 6.

The Central area is in the near zone, predominantly to the west and northwest of the reactor. Outside these three main contaminated areas there were manyareas where the Cs deposition densitywas in the range kBq m2.

Rather detailed surveys of the contamination of the entire European part of the former Soviet Union have been completed [I3, I6, I24].

A map of measured Cs deposition is presented in Figure VI. The areas affected by Cs contamination are listed in Table 7.

As can be seen, , km2 experienced a Cs deposition density greater than 37 kBq m2 1 Ci km2. The total quantity of Cs deposited as a result of the accident in the contaminated areas of the former Soviet Union, including in areas of lesser deposition, is estimated in Table 8 to be 43 PBq.

A Cs background of 24 kBq m2 attributable toresidual levels from atmospheric nuclear weapons testing from earlier years must be subtracted to obtain the total deposit attributable to the Chernobyl accident.

When this is done, the total Cs deposit from the accident is found to be approximately 40 PBq Table 8.

Dernovichi Savici Pirki Dovlyady The Gomel-Mogilev-Bryansk contamination area is centred km to the north-northeast of the reactor at the boundary of the Gomel and Mogilev regions of Belarus and of the Bryansk region of the Russian Federation.

In some areas contamination was comparable to that in the Central area; deposition densities even reached 5 MBq m2 in some villages of the Mogilev and Bryansk regions.

The Kaluga-Tula-Orel area is located km to the northeast of the reactor. Contamination there came from the same radioactive cloud that caused contamination in the Gomel-Mogilev-Bryansk area as a result of rainfall on April.

The Cs deposition density was, however, lower in this area, generally less than kBq m2. The Cs deposition was highest within the km-radius area surrounding the reactor, known as the km zone.

Deposition densities exceeded 1, kBq m2 40 Ci km2 in this zone and also in some areas of the near zone to the west and northwest of the reactor, in the Gomel, Kiev and Zhitomir regions Figure VII.

Surface ground deposition of strontium released in the Chernobyl accident [I1]. Surface ground deposition of plutonium and plutonium released in the Chernobyl accident at levels exceeding 3.

Estimated surface ground deposition in Belarus and western Russia of iodine released in the Chernobyl accident [B25, P19]. Surface ground deposition of caesium released in Europe after the Chernobyl accident [D13].

During the first weeks after the accident, most of the activity deposited on the ground consisted of short-lived radionuclides, of which I was the most important radiologically.

As indicated in paragraph 35, these maps are based on the limited number of measurements of I deposition density available in the former Soviet Union, and they use Cs measurements as a guide in areas where I was not measured.

These maps must be regarded with caution, as the ratio of the I to Cs deposition densities was found to vary in a relatively large range, at least in Belarus.

Interhemispheric transfer also occurred to a small extent through human activities, such as shipping of foods or materials to the southern hemisphere.

Therefore, only very low levels of radioactive materials originating from the Chernobyl accident have been present in the biosphere of the southern hemisphere, and the resulting doses have been negligible.

Deposition of 90Sr was mostly limited to the near zone of the accident. Only a few separate sites with 90Sr deposition density in the range kBq m2 were found in the Gomel-Mogilev-Bryansk area, i.

The environmental behaviour of deposited radionuclides depends on the physical and chemical characteristics of the radionuclide considered, on the type of fallout i.

Special attention will be devoted to I, Cs and 90Sr and their pathways of exposure to humans. Deposition can occur on the ground or on water surfaces.

The terrestrial environment will be considered first. Information on the deposition of plutonium isotopes is not as extensive because of difficulties in detecting these radionuclides.

The only area with plutonium levels exceeding 4 kBq m2 was located within the km zone Figure IX. In the Gomel-Mogilev-Bryansk area, the ,Pu deposition density ranged from 0.

At Korosten, located in Ukraine about km southwest of the Chernobyl power plant, where the Cs deposition density was about kBq m2, the ,Pu deposition density due to the Chernobyl accident derived from data in [H8] is found to be only about 0.

Terrestrial environment 2. Remainder of northern and southern hemisphere As shown in Table 5, there are also other areas, in Europe, where the Cs deposition density exceeded 37 kBq m2, notably, the three Scandinavian countries Finland, Norway and Sweden , Austria and Bulgaria.

Small amounts of radiocaesium and of radioiodine penetrated the lower stratosphere of the northern hemisphere during the first few days after the accident [J6, K43].

Subsequently, transfer of radiocaesium to the lower atmospheric layers of the southern hemisphere may have occurred as a result of interhemispheric air movements from the northern to the southern stratosphere, followed by subsidence in the troposphere [D11].

However, radioactive contamination was not detected in the southern hemisphere D. For short-lived radionuclides such as I, the main pathway of exposure of humans is the transfer of the amounts deposited on leafy vegetables that are consumed within a few days, or on pasture grass that is grazed by cows or goats, giving rise to the contamination of milk.

The amounts deposited on vegetation are retained with a half-time of about two weeks before removal to the ground surface and to the soil.

Long-term transfer of I from deposition on soil to dietary products that are consumed several weeks after the deposition has occurred need not be considered, because I has a physical half-life of only 8 days.

Radionuclides deposited on soil migrate downwards and are partially absorbed by plant roots, leading in turn to upward migration into the vegetation.

These processes should be considered for long-lived radionuclides, such as Cs and 90Sr. The rate and direction of the radionuclide migration into the soil-plant pathway are determined by a number of natural phenomena, including relief features, the type of plant, the structure and makeup of the soil, hydrological conditions and weather patterns, particularly at the time that deposition occurred.

The vertical migration of Cs and 90Sr in soil of different types of natural meadows has been rather slow, and the greater fraction of radionuclides is still contained in its upper layer cm.

The effective half-time of clearance from the root layer in meadows cm in mineral soils has been estimated to range from 10 to 25 years for Cs and to be 1.

For a given initial contamination of soil, the transfer from soil to plant varies with time as the radionuclide is removed from the root layer and as its availability in exchangeable form changes.

The Cs content in plants was maximum in , when the contamination was due to direct deposition on aerial surfaces. In , Cs in plants was 36 times lower than in , as the contamination of the plants was then mainly due to root uptake.

Since , the transfer coefficients from deposition to plant have continued to decrease, although the rate of decrease has slowed: from to , the transfer coefficients of Cs decreased by 1.

Later on, ageing processes led to similar mobility values for Cs from the Chernobyl accident and from global fallout.

The variability of the transfer coefficient from deposition to pasture grass for Cs is indicated in Table 9 for natural meadows in the Polissya area of Ukraine [S40].

The type of soil and the water content both have an influence on the transfer coefficient, the values of which were found to range from 0.

The variability as a function of time after the accident in the Russian Federation has been studied and reported on by Shutov et al.

Contrary to Cs, it seems that the exchangeability of Sr does not keep decreasing with time after the accident and may even be increasing [B36, S41].

In the Russian Federation, no statistically significant change was found in the 90Sr transfer coefficient from deposition to grass during the first 4 to 5 years following the accident [S41].

This is attributable to two competing processes: a 90Sr conversion from a poorly soluble form, which characterized the fuel particles, to a soluble form, which is easily assimilated by plant roots, and b the vertical migration of 90Sr into deeper layers of soil, hindering its assimilation by vegetation [S41].

The contamination of milk, meat and potatoes usually accounts for the bulk of the dietary intake of Cs.

However, for the residents of rural regions, mushrooms and berries from forests occupy an important place.

The decrease with time of the Cs concentrations in those foodstuffs has been extremely slow, with variations from one year to another depending on weather conditions [I22].

Aquatic environment Deposition of radioactive materials also occurred on water surfaces. Deposition on the surfaces of seas and oceans resulted in low levels of dose because the radioactive materials were rapidly diluted into very large volumes of water.

In rivers and small lakes, the radioactive contamination resulted mainly from erosion of the surface layers of soil in the watershed, followed by runoff in the water bodies.

In the km zone, where relatively high levels of ground deposition of 90Sr and Cs occurred, the largest surface water contaminant was found to be 90Sr, as Cs was strongly adsorbed by clay minerals [A15, M19].

Much of the 90Sr in water was found in dissolved form; low levels of plutonium isotopes and of Am were also measured in the rivers of the km zone [A15, M19].

The contribution of aquatic pathways to the dietary intake of Cs and 90Sr is usually quite small. However, the Cs concentration in the muscle of predator fish, like perch or pike, may be quite high in lakes with long water retention times, as found in Scandinavia and in Russia [H16, K47, R21, T23].

For example, concentration of Cs in the water of lakes Kozhanyand Svyatoe located in severely contaminated part of the Bryansk region of Russia was still high in because of special hydrological conditions: Bq l1 of Cs and 0.

Concentration of Cs in the muscles of crucian Carassius auratus gibeio sampled in the lake Kozhany was in the range of kBq kg1 and in pike Esox lucius in the range kBq kg1 [K47, T23].

Activity of Cs in inhabitants of the village Kozhany located along the coast of lake Kozhany measured by whole-body counters in summer was 7.

Taking into account seasonal changes in the Cs whole-body activity, the average annual internal doses were estimated to be 0.

Also, the relative importance of the aquatic pathways, in comparison to terrestrial pathways, may be high in areas downstream of the reactor site where ground deposition was small.

Improper, unstable operation of the reactor allowed an uncontrollable power surge to occur, resulting in successive steam explosions that severely damaged the reactor building and completely destroyed the reactor.

It is worth noting, however, that the doses were estimated on the basis of environmental and thyroid or body measurements and that knowledge of the quantities released was not needed for that purpose.

The three main areas of contamination, defined as those with Cs deposition density greater than 37 kBq m2 1 Ci km2 , are in Belarus, the Russian Federation and Ukraine; they have been designated the Central, GomelMogilev-Bryansk and Kaluga-Tula-Orel areas.

The Central area is within about km of the reactor, predominantly to the west and northwest. The Gomel-Mogilev-Bryansk contamination area is centred km to the northnortheast of the reactor at the boundary of the Gomel and Mogilev regions of Belarus and of the Bryansk region of the Russian Federation.

The Kaluga-Tula-Orel area is located in the Russian Federation, about km to the northeast of the reactor.

All together, as shown in Table 7 and in Figure XI, territories with an area of approximately , km2 were contaminated in the former Soviet Union.

Outside the former Soviet Union, there were many areas in northern and eastern Europe with Cs deposition density in the range kBq m2.

These regions represent an area of 45, km2, or about one third of the contaminated areas found in the former Soviet Union.

For short-lived radionuclides such as I, the main pathway of exposure to humans is the transfer of amounts deposited on leafy vegetables that are consumed by humans within a few days, or on pasture grass that is grazed by cows or goats, giving rise to the contamination of milk.

For long-lived radionuclides such as Cs, the long-term transfer processes from soil to foods consumed several weeks or more after deposition need to be considered.

It is convenient to classify into three categories the populations who were exposed to radiation following the Chernobyl accident: a the workers involved in the accident, either during the emergency period or during the clean-up phase; b inhabitants of evacuated areas; and c inhabitants of contaminated areas who were not evacuated.

The available information on the doses received by the three categories of exposed populations will be presented and discussed in turn.

Doses from external irradiation and from internal irradiation will be presented separately. The external exposures due to gamma radiation were relatively uniform over all organs and tissues of the body, as their main contributors were TeI, I and BaLa for evacuees, Cs and Cs for inhabitants of contaminated areas who were not evacuated, and radionuclides emitting photons of moderatelyhigh energy for workers.

These external doses from gamma radiation have been expressed in terms of effective dose. With regard to internal irradiation, absorbed doses in the thyroid have been estimated for exposures to radioiodines and effective doses have been estimated for exposures to radiocaesiums.

Doses have in almost all cases been estimated by means of physical dosimetrytechniques. Biological indicators of dose has been mainly used, within days or weeks after the accident, to estimate doses received by the emergency workers, who received high doses from external irradiation and for whom dosemeters were either not operational nor available.

Unlike physical dosimetry, biological dosimetric methods are generally not applicable to doses below 0. Soon after the accident, biological dosimetry is usually based on the measurement of the frequency of unstable chromosome aberrations dicentric and centric rings.

By comparing the rate of dicentric chromosomes and centric rings with a standard dose-effect curve obtained in an experiment in vitro, it is possible to determine a radiation dose.

However, the use of dicentric as well as other aberrations of the unstable type for the purposes of biological dosimetry is not always possible, since the frequency of cells containing such aberrations declines in time after exposure.

For retrospective dosimetry long after the exposure, biological dosimetry can be a complement to physical dosimetry, but only techniques where radiation damage to the biological indicator is stable and persistent and not subject to biochemical, physiological or immunological turnover, repair or depletion are useful.

In that respect, the analysis of stable aberrations translocations , the frequency of which remains constant for a long time after exposure to radiation, is promising.

The probability of occurrence of stable translocations and unstable dicentrics aberrations after exposure is the same.

However, translocations are not subjected to selection during cell proliferation, in contrast to dicentrics.

Fluorescence in situ hybridization FISH or Fast-FISH in conjunction with chromosome painting may be useful in retrospective dosimetry for several decades after exposure.

Other biological or biophysical techniques for measuring doses are electron spin resonance ESR or opticallystimulated luminescence OSL.

These techniques are used in retrospective dosimetry to measure the radiation damage accumulated in biological tissue such as bone, teeth, fingernails and hair.

Also, the gene mutation glycophorin A that is associated with blood cells may be used. Most of them were at the reactor site at the time of the accident or arrived at the plant during the few first hours.

The numbers of accident witnesses and emergency workers are listed in Table According to Table 10, on the morning of 26 April, about emergency workers were on the site of the Chernobyl power plant.

The workers involved in various ways in the accident can be divided into two groups: a those involved in emergency measures during the first day of the accident 26 April , who will be referred to as emergency workers in this Annex, and b those active in at the power station or in the zone surrounding it for the decontamination work, sarcophagus construction and other clean-up operations.

This second group of workers is referred to as recovery operation workers in this Annex, although the term liquidator gained common usage in the former Soviet Union.

The power plant personnel wore only film badges that could not register doses in excess of 20 mSv. All of these badges were overexposed.

The firemen had no dosimeters and no dosimetric control. Dose rates on the roof and in the rooms of the reactor block reached hundreds of gray per hour.

Measured exposure rates in the vicinity of the reactor at the time of the accident are shown in Figure XII.

Emergency workers Measured exposure rates in air on 26 April in the local area of the Chernobyl reactor. The highest doses were received by the firemen and the personnel of the power station on the night of the accident.

Some symptoms of acute radiation sickness were observed in workers. Following clinical tests, an initial diagnosis of acute radiation sickness was made in of these persons.

On further analysis of the clinical data, acute radiation sickness was confirmed later in in individuals. The most important exposures were due to external irradiation relatively uniform whole-body gamma irradiation and beta irradiation of extensive body surfaces , as the intake of radionuclides through inhalation was relatively small except in two cases [U4].

Because all of the dosimeters worn by the workers were overexposed, they could not be used to estimate the gamma doses received via external irradiation.

The estimated ranges of doses for the emergency workers with confirmed acute radiation sickness are given in Table Forty-one of these patients received whole-body doses from external irradiation of less than 2.

Ninety-three patients received higher doses and had more severe acute radiation sickness: 50 persons with doses between 2. The skin doses from beta exposures evaluated for eight patients with acute radiation sickness ranged from 10 to 30 times the dose from whole-body gamma radiation [B10].

Internal doses were determined from thyroid and wholebody measurements performed on the persons under treatment, as well as from urine analysis and from post-mortem analysis of organs and tissues.

For most of the patients, more than 20 radionuclides were detectable in the whole-body gamma measurements; however, apart from the radioiodines and radiocaesiums, the contribution to the internal doses from the other radionuclides was negligible [U4].

Internal doses evaluated for 23 persons who died of acute radiation sickness are shown in Table The lung and thyroid doses, calculated to the time of death, are estimated to have ranged from 0.

Some of the low thyroid doses may be due to the fact that stable iodine pills were distributed among the reactor staff less than half an hour after the beginning of the accident.

It is also speculated that the internal doses received by the emergency workers who were outdoors were much lower than those received by the emergency workers who stayed indoors.

For comparison purposes, the estimated external doses are also presented in Table The external doses, which range from 2. Internal dose reconstruction was also carried out for surviving emergency workers who were examined in Moscow; the results are presented in Table The average doses were estimated to vary from 36 mGy to bone marrow to mGy to bone surfaces, the maximum doses being about 10 times greater than the average doses.

Also, thyroid doses were estimated for the emergency workers admitted to Hospital 6 in Moscow within 34 weeks after the accident Table 15 ; most of the thyroid doses were less than 1 Gy, but three exceeded 20 Gy.

The thyroid doses due to internal exposures are estimated to be in the range from several percent to several hundred percent of the external whole-body doses.

The median value of the ratio of the thyroid to the whole-body dose was estimated to be 0. Recovery operation workers About , persons civilian and military have received special certificates confirming their status as liquidators, according to laws promulgated in Belarus, the Russian Federation and Ukraine.

Of those, about , were militaryservicemen [C7]. The principal tasks carried out by the recovery operation workers liquidators included decontamination of the reactor block, reactor site, and roads and construction of the sarcophagus MayNovember , a settlement for reactor personnel MayOctober , the town of Slavutich , , waste repositories , and dams and water filtration systems July-September , [K19].

During the entire period, radiation monitoring and securityoperations were also carried out. Of particular interest are the , recoveryoperation workers who were employed in the km zone in , as it is in this period that the highest doses were received; information concerning these workers is provided in Table About half of these persons were civilian and half were military servicemen brought in for the special and shortterm work.

The workers were all adults, mostly males aged years. The construction workers were those participating in building the sarcophagus around the damaged reactor.

Other workers included those involved in transport and security, scientists and medical staff. The distributions of the external doses for the categories of workers listed in Table 16, as well as for the emergency workers and accident witnesses, are shown in Table The remainder of the recovery operation workers about , , who generally received lower doses, includes those who worked inside the km zone in a small number of workers are still involved , those who decontaminated areas outside the km zone, and other categories of people.

In a state registry of persons exposed to radiation was established at Obninsk. This included not only recovery operation workers but evacuees and residents of contaminated areas as well.

The registry existed until the end of Starting in , national registries of Belarus, the Russian Federation and Ukraine replaced the all-union registry.

The number of recovery operation workers in the national registries of Belarus, the Russian Federation and Ukraine is listed in Table Some , workers from these countries were involved in the years To this must be added the 17, recovery operation workers recorded in the registries of the Baltic countries, including 7, from Lithuania, 5, from Latvia and 4, from Estonia [K13].

More detailed information on the registries is provided in Chapter IV. This number is likely to increase in the future, as some organizations may not have provided all their information to the central registries; in addition, individuals may on their own initiative ask to be registered in order to benefit from certain privileges.

However, the number of recoveryoperation workers recorded in the national registries is well below the figure of about ,, which corresponds to the number of people who have received special certificates confirming their status as liquidators.

The doses to the recovery operation workers who participated in mitigation activities within two months after the accident are not known with much certainty.

Attempts to establish a dosimetric service were inadequate until the middle of June. TLDs and condenser-type dosimeters that had been secured by 28 April were insufficient in number and, in the case of the latter type, largely nonfunctioning, and records were lost when the dosimetric service was transferred from temporary to more permanent quarters.

In June, TLD dosimeters were available in large numbers, and a databank of recorded values could be established. From July onwards, individual dose monitoring was performed for all non-military workers, using either TLDs or film dosimeters.

The dose limits for external irradiation varied with time and with the category of personnel.

According to national regulations established before the accident [M1], for civilian workers, during , the dose limit, 0.

The maximum dose allowed during the year was, therefore, 0. In , the annual dose limits for civilian personnel were lowered to 0.

However, a dose of up to 0. In , the annual dose limit was set at 0. From onwards, the annual dose limit was set at 0.

For military workers, a dose limit of 0. From onwards, the dose limits were the same for military and civilian personnel.

Methods b and c were used for the civilian workers before June , when the number of individual dosimeters was insufficient, and for the majority of the military personnel at any time.

For example, effective doses from external irradiation have been reconstructed by physical means for the staff of the reactor, as well as for the workers who had been detailed to assist them, exposed from 26 April to 5 May [K19].

Personnel location record cards filled in by workers were analysed by experts who had reliable information on the radiation conditions and who had personally participated in ensuring the radiation safety of all operations following the accident.

Using this method, two values were determined: the maximum possible dose and the expected dose. The maximum possible effective doses ranged from less than 0.

It seems that in most cases the maximum possible effective doses are those that were officially recorded. The main sources of uncertainty associated with the different methods of dose estimation were as follows: a individual dosimetry: incorrect use of the dosimeters inadvertent or deliberate actions leading to either overexposure or underexposure of the dosimeters ; b group dosimetry: very high gradient of exposure rate at the working places at the reactor site; and c time-and-motion studies: deficiencies in data on itineraries and time spent at the various working places, combined with uncertainties in the exposure rates.

The registry data show that the annual averages of the officially recorded doses decreased from year to year, being about mSv in , mSv in , 30 mSv in , and 15 mSv in [I34, S14, T9].

It is, however, difficult to assess the validity of the results that have been reported for a variety of reasons, including a the fact that different dosimeters were used by different organizations without any intercalibration; b the high number of recorded doses very close to the dose limit; and c the high number of rounded values such as 0.

However, the doses do not seem to have been systematicallyoverestimated, because biological dosimetry performed on limited numbers of workers produced results that are also very uncertain but compatible nonetheless with the physical dose estimates [L18].

Using the numbers presented in Table 18, the collective effective dose is estimated to be about 40, man Sv. A particular group of workers who may have been exposed to substantial doses from external irradiation is made up of the 1, helicopter pilots who were involved in mitigation activities at the power plant in the first three months after the accident [U15].

The doses to pilots were estimated using either personal dosimeters or, less reliably, calculations in which the damaged reactor was treated as a collimated point source of radiation [U15].

The doses obtained by calculation were checked against the results derived from the personal dosimeters for about pilots.

That comparison showed a discrepancy of a less 0. The simplification used to describe the origin of the radiation emitted from the damaged reactor is the main source of uncertainty in the assessment of the doses received by the helicopter pilots.

The average dose estimates are 0. Another group of workers that may have been exposed to substantial doses from external irradiation is the workers from the Kurchatov Institute, a group that includes those who were assigned special tasks inside the damaged unit 4 before and after the construction of the sarcophagus [S36].

A number of nuclear research specialists worked in high-radiation areas of the sarcophagus, without formal recording of doses, on their own personal initiative, and were exposed to annual levels greater than the dose limit of 0.

Doses for this group of 29 persons have been estimated using electron spin resonance analysis of tooth enamel as well as stable and unstable chromosome aberration techniques [S42, S47].

It was found that 14 of those 29 persons received doses lower than 0. Additional analyses by means of the FISH technique for three of those nuclear research specialists resulted in doses of 0.

Biological dosimetry. Chromosome aberration levels among Chernobyl recovery operation workers were analysed in a number of additional studies.

A good correlation was found, however, for group rather than individual doses. Blood samples of 52 Chernobyl recovery operation workers were analysed by FISH [S32] and simultaneously by conventional chromosome analysis.

Based on FISH measurements, individual biodosimetry estimates between 0. Pooled data for the total group of 52 workers provided an average estimate of 0.

For a group of 34 workers with documented doses, the mean dose estimate of 0. Comparison between the conventional scoring and FISH analyses showed no significant difference.

In a study of Estonian workers, Littlefield et al. In conclusion, FISH does not currently appear to be a sufficiently sensitive and specific technique to allow the estimation of individual doses in the low dose range received by the majority of recovery operation workers.

Lazutka et al. When transformed data were analysed by analysis of variance, alcohol abuse made a significant contribution to total aberrations, chromatid breaks, and chromatid exchanges.

Smoking was associated with frequency of chromatid exchanges, and age was significantly associated with rates of chromatid exchanges and chromosome exchanges [L31].

In another study [S37], the frequency of chromosomal aberrations was evaluated in more than recovery operation workers.

Blood samples were taken from several days to three months after exposure to radiation. The mean frequencies of aberrations for different groups of workers were associated with doses varying from 0.

Glycophorin A assay GPA was used as a possible biological dosimeter on subjects from Estonia, Latvia and Lithuania with recorded physical dose estimates [B17].

Although a slight increase in the frequency of erythrocytes with loss of the GPA allele was seen among these subjects compared to control subjects from the same countries, this difference was not significant.

The pooled results indicate that the average exposures of these workers were unlikely to greatly exceed mGy, the approximate minimum radiation dose detectable by this assay.

In addition to effective doses from external gamma irradiation, recovery operation workers received skin doses from external beta irradiation as well as thyroid and effective doses from internal irradiation.

The dose to unprotected skin from beta exposures is estimated to have been several times greater than the gamma dose.

Because of the abundance of I and of shorterlived radioiodines in the environment of the reactor during the accident, the recovery operation workers who were on the site during the first few weeks after the accident may have received substantial thyroid doses from internal irradiation.

Information on the thyroid doses is very limited and imprecise. From 30 April through 7 May , in vivo thyroid measurements were carried out on more than recovery operation workers.

These in vivo measurements, which are measurements of the radiation emitted by the thyroid using detectors held or placed against the neck, were used to derive the I thyroidal contents at the time of measurement.

The thyroid doses were derived from the measured I thyroidal contents, using assumptions on the dynamics of intake of I and short-lived radioiodines and on the possible influence of stable iodine prophylaxis.

The average thyroid dose estimate for those workers is about 0. The thyroid doses from internal irradiation are estimated to range from several percent to several hundred percent of the effective doses from external irradiation.

The median value of the ratio of the internal thyroid dose to the external effective dose was estimated to be 0. It is important to note that information on the influence of stable iodine prophylaxis is limited, as iodine prophylaxis among the recoveryoperation workers was not mandatory nor was it proposed to everybody.

The decision to take stable iodine for prophylactic reasons was made by the individual worker or by the supervisor.

The results of interviews of workers including emergencyworkers and recoveryoperation workers who arrived at the plant at the ealy stage of the accident concerning the time when theytook stable iodine for prophylaxis is presented in Table The internal doses resulting from intakes of radionuclides such as 90Sr, Cs, Cs, ,Pu, and others have been assessed for about recovery operation workers who were monitored from April to April [K2, K8, P13, S11].

The majority of them were staff of the power plant who took part in the recovery work starting on days 3 and 4 after the accident.

The dose assessment was based on the analysis of whole-body measurements and of radionuclide concentrations in excreta.

The average value of the effective dose committed by the radionuclide intakes was estimated on the basis of ICRP Publication 30 [I17] to be 85 mSv.

The part of the effective dose received between June and September was estimated to have been about 30 mSv.

The evacuation of the nearby residents was carried out at different times after the accident on the basis of the radiation situation and of the distance of the populated areas from the damaged reactor.

The initial evacuations were from the town of Pripyat, located just 3 km from the damaged reactor, then from the km zone and from the km zone around the reactor located mostly in Ukraine but also in Belarus.

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Emergency workers. Recovery operation workers. Doses from external exposure. Doses from internal exposure.

Residual and averted collective doses. Thyroid doses. Bone-marrow doses. Collective doses from external exposure. Collective doses from internal exposure.

Total collective doses. The Chernobyl registries. Specialized registries. Cancer incidence. Specialized cancer registries. Registers of exposed populations.

Registers of the general population. The International Chernobyl Project. Thyroid cancer. Other solid tumours.

Thyroid abnormalities. Somatic disorders other than thyroid. Immunological effects. The accident of 26 April at the Chernobyl nuclear power plant, located in Ukraine about 20 km south of the border with Belarus, was the most severe ever to have occurred in the nuclear industry.

The objective of this Annex is a to review in greater detail the exposures of those most closely involved in the accident and the residents of the local areas most affected by the residual contamination and b to consider the health consequences that are or could be associated with these radiation exposures.

The impact of the accident on the workers and local residents has indeed been both serious and enormous. The accident caused the deaths within a few days or weeks of 30 power plant employees and firemen including 28 deaths that were due to radiation exposure , brought about the evacuation of about , people from areas surrounding the reactor during , and the relocation, after , of about , people from what were at that time three constituent republics of the Soviet Union: Belorussia, the Russian Soviet Federated Socialist Republic RSFSR and the Ukraine [K23, R11, V2, V3] these republics will hereinafter be called by their present-day country names: Belarus, the Russian Federation and Ukraine.

Vast territories of those three republics were contaminated, and trace deposition of released radionuclides was measurable in all countries of the northern hemisphere.

Stratospheric interhemispheric transfer may also have led to some environmental contamination in the southern hemisphere [D11].

The radiation exposures resulting from the Chernobyl accident were due initially to I and short-lived radionuclides and subsequently to radiocaesiums Cs and Cs from both external exposure and the consumption of foods contaminated with these radionuclides.

It was estimated in the UNSCEAR Report [U4] that, outside the regions of Belarus, the Russian Federation and Ukraine that were most affected by the accident, thyroid doses averaged over large portions of European countries were at most 25 mGy for one-year old infants.

It was recognized, however, that the dose distribution was veryheterogeneous, especially in countries close to the reactor site. For example, in Poland, although the countrywide populationweighted average thyroid dose was estimated to be approximately 8 mGy, the mean thyroid doses for the populations of particular districts were in the range from 0.

It was also estimated in the UNSCEAR Report [U4] that effective doses averaged over large portions of European countries were 1 mSv or less in the first year after the accident and approximately two to five times the first-year dose over a lifetime.

The doses to population groups in Belarus, the Russian Federation and Ukraine living nearest the accident site and to the workers involved in mitigating the accident are, however, of particular interest, because these people have had the highest exposures and have been monitored for health effects that might be related to the radiation exposures.

Research on possible health effects is focussed on, but not limited to, the investigation of leukaemia among workers involved in the accident and of thyroid cancer among children.

Other health effects that are considered are non-cancer somatic disorders e. Epidemiological studies have been undertaken among the populations of Belarus, the Russian Federation and Ukraine that were most affected by the accident to investigate whether dose-effect relationships can be obtained, notably with respect to the induction of thyroid cancer resulting from internal irradiation by I and other radioiodines in young children and to the induction of leukaemia among workers resulting from external irradiation at low dose rates.

The dose estimates that are currently available are of a preliminary nature and must be refined by means of difficult and timeconsuming dose reconstruction efforts.

The accumulation of health statistics will also require some years of effort. Because of the questions that have arisen about the local exposures and effects of the Chernobyl accident, the Committee feels that a review of information at this stage, almost 15 years after the accident, is warranted.

Of course, even longer-term studies will be needed to determine the full consequences of the accident. It is the intention to evaluate in this Annex the data thus far collected on the local doses and effects in relation to and as a contribution to the broader knowledge of radiation effects in humans.

Within the last few years, several international conferences were held to review the aftermath of the accident, and extensive use can be made of the proceedings of these conferences [E3, I15, T22, W7]; also, use was made of books, e.

The populations considered in this Annex are a the workers involved in the mitigation of the accident, either during the accident itself including firemen and power plant personnel who received doses leading to deterministic effects or after the accident recovery operation workers ; b members of the general public who were evacuated to avert excessive radiation exposures; and c inhabitants of contaminated areas who were not evacuated.

The contaminated areas, which are defined in this Annex as being those where the average Cs ground deposition density exceeded 37 kBq m2 1 Ci km2 , are found mainly in Belarus, in the Russian Federation and in Ukraine.

Information on the contamination levels and radiation doses in other countries will be presented only if it is related to epidemiological studies conducted in those countries.

The accident at the Chernobyl nuclear power station occurred during a low-power engineering test of the Unit 4 reactor.

Safety systems had been switched off, and improper, unstable operation of the reactor allowed an uncontrollable power surge to occur, resulting in successive steam explosions that severely damaged the reactor building and completely destroyed the reactor.

An account of the accident and of the quantities of radionuclides released, to the extent that they could be known at the time, were presented by Soviet experts at the Post-Accident Review Meeting at Vienna in August [I2].

The information that has become available since will be summarized in this Chapter. The radionuclide releases from the damaged reactor occurred mainly over a day period, but with varying release rates.

An initial high release rate on the first day was caused by mechanical discharge as a result of the explosions in the reactor.

There followed a five-day period of declining releases associated with the hot air and fumes from the burning graphite core material.

In the next few days, the release rate of radionuclides increased until day 10, when the releases dropped abruptly, thus ending the period of intense release.

The radionuclides released in the accident deposited with greatest density in the regions surrounding the reactor in the European part of the former Soviet Union.

The events leading to the accident at the Chernobyl Unit 4 reactor at about 1. Actions taken during this exercise resulted in a significant variation in the temperature and flow rate of the inlet water to the reactor core beginning at about 1.

The unstable state of the reactor before the accident is due both to basic engineering deficiencies large positive coefficient of reactivity under certain conditions and to faulty actions of the operators e.

Other actions resulted in a rapid increase in the power level of the reactor [I7], which caused fuel fragmentation and the rapid transfer of heat from these fuel fragments to the coolant between 1.

This generated a shock wave in the cooling water, which led to the failure of most of the lower transition joints. As a result of the failure of these transition joints, the pressurized cooling water in the primary system was released, and it immediately flashed into steam.

The Chernobyl reactor is of the type RBMK, which is an abbreviation of Russian terms meaning reactor of high output, multichannel type.

It is a pressurized water reactor using light water as a coolant and graphite as a moderator. A simplified description of the events leading to the accident and of the measures taken to control its consequences is provided in the following paragraphs.

As is the case in an The steam explosion occurred at 1. It is surmised that the reactor core might have been lifted up by the explosion [P4], during which time all water left the reactor core.

This resulted in an extremely rapid increase in reactivity, which led to vaporization of part of the fuel at the centre of some fuel assemblies and which was terminated by a large explosion attributable to rapid expansion of the fuel vapour disassembling the core.

This explosion, which occurred at about 1. Fuel, core components, and structural items were blown from the reactor hall onto the roof of adjacent buildings and the ground around the reactor building.

A major release of radioactive materials into the environment also occurred as a result of this explosion. The core debris dispersed by the explosion started multiple more than 30 fires on the roofs of the reactor building and the machine hall, which were covered with highly flammable tar.

Some of those fires spread to the machine hall and, through cable tubes, to the vicinity of the Unit 3 reactor. A first group of 14 firemen arrived on the scene of the accident at 1.

Reinforcements were brought in until about 4 a. These activities were carried out at up to 70 m above the ground under harsh conditions of high radiation levels and dense smoke.

By about 4. These actions caused the deaths of five firefighters. It is unclear whether fires were originating from the reactor cavity during the first 20 h after the explosion.

However, there was considerable steam and water because of the actions of both the firefighters and the reactor plant personnel.

Approximately 20 h after the explosion, at 9. The fire made noise when it started some witnesses called it an explosion and burned with a large flame that initially reached at least 50 m above the top of the destroyed reactor hall [P4].

The first measures taken to control the fire and the radionuclide releases consisted ofdumping neutron-absorbing compounds and fire-control materials into the crater formed bythe destruction of the reactor.

The total amount of materials dumped on the reactor was approximately 5, t, including about 40 t of boron compounds, 2, t of lead, 1, t of sand and clay, and t of dolomite, as well as sodium phosphate and polymer liquids [B4].

About t of materials were dumped on 27 April, followed by t on 28 April, t on 29 April, 1, t on 30 April, 1, t on 1 May, and t on 2 May.

About 1, helicopter flights were carried out to dump materials onto the reactor. During the first flights, the helicopters remained stationary over the reactor while dumping the materials.

However, as the dose rates received by the helicopter pilots during this procedure were judged to be too high, it was decided that the materials should be dumped while the helicopters travelled over the reactor.

This procedure, which had a poor accuracy, caused additional destruction of the standing structures and spread the contamination. In fact, much of the material delivered by the helicopters was dumped on the roof of the reactor hall, where a glowing fire was observed, because the reactor core was partially obstructed by the upper biological shield, broken piping, and other debris, and rising smoke made it difficult to see and identify the core location see Figure I.

The material dumping campaign was stopped on day 7 2 May through day 10 5 May after the accident because of fears that the building support structures could be compromised.

If that happened, it would allow the core to be less restrained from possible meltdown, and steam explosions would occur if the core were to interact with the pressure suppression pool beneath the reactor.

The increasing release rates on days 7 through 10 were associated with the rising temperature of the fuel in the core.

Cooling of the reactor structure with liquid nitrogen using pipelines originating from Unit 3 was initiated only at late stages after the accident.

The abrupt ending of the releases was said to occur upon extinguishing the fire and through transformation of the fission products into more chemically stable compounds [I2].

Reactor cover Core region empty Materials dropped from helicopter Spent fuel pool Location of fuel "lava" 69 m Figure I. Cross-section view of damaged Unit 4 Chernobyl reactor building.

The further sequence of events is still somewhat speculative, but the following description conforms with the observations of residual damage to the reactor [S1, S18].

It is suggested that the melted core materials also called fuelcontaining masses, corium, or lava settled to the bottom of the core shaft, with the fuel forming a metallic layer below the graphite.

The graphite layer had a filtering effect on the release of volatile compounds. The very high temperatures in the core shaft would have suppressed plate-out of radionuclides and maintained high release rates of penetrating gases and aerosols.

After about 6. This is evidenced by the absence of carbon or carboncontaining compounds in the corium.

On day 8 after the accident, it would appear that the corium melted through the lower biological shield LBS and flowed onto the floor of the sub-reactor region see Figure I.

This rapid redistribution of the corium and increase in surface area as it spread horizontally would have enhanced the radionuclide releases.

The corium produced steam on contact with the water remaining in the pressure suppression pool, causing an increase in aerosols.

This may account for the peak releases of radionuclides seen at the last stage of the active period. Approximately nine days after the accident, the corium began to lose its ability to interact with the surrounding materials.

It solidified relatively rapidly, causing little damage to metallic piping in the lower regions of the reactor building.

The chemistry of the corium was altered by the large mass of the lower biological shield taken up into the molten corium about of the 1,t shield of stainless steel construction and serpentine filler material.

The decayheat was significantly lowered, and the radionuclide releases dropped by two to three orders of magnitude.

Visual evidence of the disposition of the corium supports this sequence of events. On the basis of an extensive series of measurements in of heat flux and radiation intensities and from an analysis of photographs, an approximate mass balance of the reactor fuel distribution was established data reported by Borovoi and Sich [B16, S1].

Different estimates of the reactor fuel distribution have been proposed byothers. Purvis [P4] indicated that the amount of fuel in the lava, plus fragments of the reactor core under the level of the bottom of the reactor, is between 27 and t and that the total amount of the fuel in the reactor hall area is between 77 and t.

Kisselev et al. It may be that most of the fuel is on the roof of the reactor hall and is covered by the material that was dropped on it from helicopters.

Only the removal of this layer of material will allow making a better determination of the reactor fuel distribution.

Two basic methods were used to estimate the release of radionuclides in the accident. The first method consists in evaluating separately the inventory of radionuclides in the reactor core at the time of the accident and the fraction of the inventory of each radionuclide that was released into the atmosphere; the products of those two quantities are the amounts released.

The second method consists in measuring the radionuclide deposition density on the ground all around the reactor; if it is assumed that all of the released amounts deposited within the area where the measurements were made, the amounts deposited are equal to the amounts released.

In both methods, air samples taken over the reactor or at various distances from the reactor were analysed for radionuclide content to determine or to confirm the radionuclide distribution in the materials released.

The analysis of air samples and of fallout also led to information on the physical and chemical properties of the radioactive materials that were released into the atmosphere.

It is worth noting, however, that the doses were estimated on the basis of environmental and human measurements and that the knowledge of the quantities released was not needed for that purpose.

Estimation of radionuclide amounts released From the radiological point of view, I and Cs are the most important radionuclides to consider, because they are responsible for most of the radiation exposure received by the general population.

Several estimates have been made of the radionuclide core inventory at the time of the accident. Some of these estimates are based on the burn-up of individual fuel assemblies that has been made available [B1, S1].

The average burn-up of In the case of Te and of the shortlived radioiodines, Khrouch et al. An extended list of radionuclides present in the core at the time of the accident is presented in Table 1.

The values used by the Committee in this Annex are those presented in the last column on the right. For comparison purposes, the initial estimates of the core inventory as presented in [I2], which were used by the Committee in the UNSCEAR Report [U4], are also presented in Table 1; these estimates, however, have been decaycorrected to 6 May , that is, 10 days after the beginning of the accident.

The large differences observed between initial and recent estimates for short-lived radionuclides radioactive half-lives of less than 10 days are mainly due to radioactive decay between the actual day of release and 6 May, while minor differences may have been caused by the use of different computer codes to calculate the build-up of activity in the reactor core.

For Cs, the and current estimates of core inventory at the time of the accident are and PBq, respectively.

For I, the corresponding values are 1, and 3, PBq, respectively. There are several estimates of radionuclides released in the accident based on recent evaluations.

Three such listings, including two taken from the IAEA international conference that took place at Vienna in [D8], are given in Table 2 and compared to the original estimates of [I2].

The estimates of Buzulukov and Dobrynin [B4], as well as those of Kruger et al. There is general agreement on the releases of most radionuclides, and in particular those of Cs and I, presented in the evaluations.

From average deposition densities of Cs and the areas of land and ocean regions, the total Cs deposit in the northern hemisphere was estimated to be 70 PBq, which is in fairly good agreement with the current estimate.

This, however, was the inventory of I at the end of the release period 6 May It would have been higher at the beginning of the accident.

The results presented in Table 2 are incomplete with respect to the releases of Te and of the short-lived radioiodines I to I.

In this Annex, the releases of those radionuclides have been scaled to the releases of I, using the radionuclide inventories presented in Table 1 and taking into account the radioactive half-lives of the radionuclides.

The following procedure was used: a the release rates at the time of the steam explosion were estimated from the radionuclide inventories presented in Table 1, assuming no fractionation for the short-lived radioiodines I, I and I with respect to I, a value of 0.

The activity ratios to I in the initial release rates are therefore estimated to have been 1. The estimated daily releases of I are presented in Table 3; and c the variation with time of the release rates of the short-lived radioiodines and of Te has been assumed to be the same as that of I, but a correction was made to take into account the differences in radioactive half-lives.

Daily release of iodine, iodine, tellurium and caesium from the Chernobyl reactor. The overall releases of short-lived radioiodines and of Te are presented in Table 4; they are found to be substantially lower than those of I.

This is due to the fact that most of the short-lived radioiodines decayed in the reactor instead of being released.

Additional, qualitative information on the pattern of release of radionuclides from the reactor is given in Figure III.

The concentrations of radionuclides in air were determined in air samples collected by helicopter above the damaged reactor [B4].

Although the releases were considerably reduced on 5 and 6 May days 9 and 10 after the accident , continuing low-level releases occurred in the following week and for up to 40 days after the accident.

Particularly on 15 and 16 May, higher concentrations were observed, attributable to continuing outbreaks of fires or to hot areas of the reactor [I6].

These later releases can be correlated with increased concentrations of radionuclides in air measured at Kiev and Vilnius [I6, I35, U16].

Physical and chemical properties of the radioactive materials released There were only a few measurements of the aerodynamic size of the radioactive particles released during the first days of the accident.

A crude analysis of air samples, taken at m above the ground in the vicinity of the Chernobyl power plant on 27 April , indicated that large radioactive particles, varying in size from several to tens of micrometers, were found, together with an abundance of smaller particles [I6].

In a carefully designed experiment, aerosol samples taken on 14 and 16 May with a device installed on an aircraft that flew above the damaged reactor were analysed by spectrometry [B6, G14].

Concentration of radionuclides in air measured above the damaged Chernobyl reactor [B6]. The geometric sizes of the fuel particles collected in Hungary, Finland and Bulgaria ranged from 0.

Taking the density of fuel particles to be 9 g cm3, their aerodynamic diameter therefore ranged from 1. Similar average values were obtained for fuel particles collected in May in southern Germany [R20] and for those collected in the km zone in September [G27].

It was observed that Chernobyl fallout consisted of hot particles in addition to more homogeneouslydistributed radioactive material [D6, D7, K34, S26, S27, S28].

These hot particles can be classified into two broad categories: a fuel fragments with a mixture of fission products bound to a matrix of uranium oxide, similar to the composition of the fuel in the core, but sometimes strongly depleted in caesium, iodine and ruthenium, and b particles consisting of one dominant element ruthenium or barium but sometimes having traces of other elements [D6, J3, J4, K35, K36, S27].

These monoelemental particles may have originated from embedments of these elements produced in the fuel during reactor operation and released during the fragmentation of the fuel [D7].

Typical activities per hot particle are 0. Hot particles deposited in the pulmonary region will have a long retention time, leading to considerable local doses [B33, L23].

In the immediate vicinity of a 1 kBq ruthenium particle, the dose rate is about 1, Gy h1, which causes cell killing; however, sublethal doses are received by cells within a few millimetres of the hot particle.

Although it was demonstrated in the s that radiation doses from alpha-emitting hot particles are not more radiotoxic than the same activity uniformly distributed in the whole lung [B28, L33, L34, L35, R15], it is not clear whether the same conclusion can be reached for beta-emitting hot particles [B33, S27].

Areas of the former Soviet Union Radioactive contamination of the ground was found to some extent in practically every country of the northern hemisphere [U4].

In this Annex, contaminated areas are defined as areas where the average Cs deposition densities exceeded 37 kBq m2 1 Ci km2. Caesium was chosen as a reference radionuclide for the ground contamination resulting from the Chernobyl accident for several reasons: its substantial contribution to the lifetime effective dose, its long radioactive half-life, and its ease of measurement.

As shown in Table 5, the contaminated areas were found mainly in Belarus, in the Russian Federation and in Ukraine [I24].

The radionuclides released in the accident deposited over most of the European territory of the former Soviet Union.

A map of this territory is presented in Figure IV. The main city gives its name to each region. The regions oblasts are subdivided into districts raions.

The important releases lasted 10 days; during that time, the wind changed direction often, so that all areas surrounding the reactor site received some fallout at one time or another.

The initial plumes of materials released from the Chernobyl reactor moved towards the west. On 27 April, the winds shifted towards the northwest, then on 28 April towards the east.

Administrative regions surrounding the Chernobyl reactor. Plume formation by meteorological conditions for instantaneous releases on dates and times GMT indicated [B7].

The contamination of Ukrainian territorysouth of Chernobyl occurred after 28 April Figure V, traces 4, 5 and 6.

Rainfall occurred in an inhomogeneous pattern, causing uneven contamination areas. The general pattern of Cs deposition based on calculations from meteorological conditions has been shown to match the measured contamination pattern rather well [B7].

Surface ground deposition of caesium released in the Chernobyl accident [I1, I3]. Surface ground deposition of caesium in the immediate vicinity of the Chernobyl reactor [I1, I24].

The distances of 30 km and 60 km from the nuclear power plant are indicated. The detailed contamination patterns have been established from extensive monitoring of the affected territory.

The contamination of soil with Cs in the most affected areas of Belarus, the Russian Federation and Ukraine is shown in Figure VI, and the Cs contamination of soil in the immediate area surrounding the reactor is shown in Figure VII.

The deposition of 90Sr and of nuclear fuel particles, usuallyrepresented as the deposition oftheir marker, 95 Zr or Ce, were relatively localized.

An important deposition map to be established is that of I. Because there were not enough measurements at the time of deposition, the I deposition pattern can be only approximated from limited data and relationships inferred from Cs deposition.

Because the I to Cs ratio was observed to vary from 5 to 60, the I deposition densities estimated for areas without I measurements are not very reliable.

Measurements of the current concentrations of I in soil could provide valuable information on the I deposition pattern [S45].

The principal physico-chemical form of the deposited radionuclides are: a dispersed fuel particles, b condensation-generated particles, and c mixed-type particles, including the adsorption-generated ones [I22].

Deposition in the near zone reflected the radionuclide composition of the fuel. Larger particles, which were primarily fuel particles, and the refractory elements Zr, Mo, Ce and Np were to a large extent deposited in the near zone.

Intermediate elements Ru, Ba, Sr and fuel elements Pu, U were also deposited largely in the near zone. The volatile elements I, Te and Cs in the form of condensation-generated particles, were more widely dispersed into the far zone [I6].

Of course, this characterization oversimplifies the actual dispersion pattern. Areas of high contamination from Cs occurred throughout the far zone, depending primarilyon rainfall at the time the plume passed over.

The composition of the deposited radionuclides in these highly contaminated areas was relatively similar. Some ratios of radionuclides in different districts of the near and far zones are given in Table 6.

The Central area is in the near zone, predominantly to the west and northwest of the reactor. Outside these three main contaminated areas there were manyareas where the Cs deposition densitywas in the range kBq m2.

Rather detailed surveys of the contamination of the entire European part of the former Soviet Union have been completed [I3, I6, I24].

A map of measured Cs deposition is presented in Figure VI. The areas affected by Cs contamination are listed in Table 7. As can be seen, , km2 experienced a Cs deposition density greater than 37 kBq m2 1 Ci km2.

The total quantity of Cs deposited as a result of the accident in the contaminated areas of the former Soviet Union, including in areas of lesser deposition, is estimated in Table 8 to be 43 PBq.

A Cs background of 24 kBq m2 attributable toresidual levels from atmospheric nuclear weapons testing from earlier years must be subtracted to obtain the total deposit attributable to the Chernobyl accident.

When this is done, the total Cs deposit from the accident is found to be approximately 40 PBq Table 8. Dernovichi Savici Pirki Dovlyady The Gomel-Mogilev-Bryansk contamination area is centred km to the north-northeast of the reactor at the boundary of the Gomel and Mogilev regions of Belarus and of the Bryansk region of the Russian Federation.

In some areas contamination was comparable to that in the Central area; deposition densities even reached 5 MBq m2 in some villages of the Mogilev and Bryansk regions.

The Kaluga-Tula-Orel area is located km to the northeast of the reactor. Contamination there came from the same radioactive cloud that caused contamination in the Gomel-Mogilev-Bryansk area as a result of rainfall on April.

The Cs deposition density was, however, lower in this area, generally less than kBq m2. The Cs deposition was highest within the km-radius area surrounding the reactor, known as the km zone.

Deposition densities exceeded 1, kBq m2 40 Ci km2 in this zone and also in some areas of the near zone to the west and northwest of the reactor, in the Gomel, Kiev and Zhitomir regions Figure VII.

Surface ground deposition of strontium released in the Chernobyl accident [I1]. Surface ground deposition of plutonium and plutonium released in the Chernobyl accident at levels exceeding 3.

Estimated surface ground deposition in Belarus and western Russia of iodine released in the Chernobyl accident [B25, P19].

Surface ground deposition of caesium released in Europe after the Chernobyl accident [D13]. During the first weeks after the accident, most of the activity deposited on the ground consisted of short-lived radionuclides, of which I was the most important radiologically.

As indicated in paragraph 35, these maps are based on the limited number of measurements of I deposition density available in the former Soviet Union, and they use Cs measurements as a guide in areas where I was not measured.

These maps must be regarded with caution, as the ratio of the I to Cs deposition densities was found to vary in a relatively large range, at least in Belarus.

Interhemispheric transfer also occurred to a small extent through human activities, such as shipping of foods or materials to the southern hemisphere.

Therefore, only very low levels of radioactive materials originating from the Chernobyl accident have been present in the biosphere of the southern hemisphere, and the resulting doses have been negligible.

Deposition of 90Sr was mostly limited to the near zone of the accident. Only a few separate sites with 90Sr deposition density in the range kBq m2 were found in the Gomel-Mogilev-Bryansk area, i.

The environmental behaviour of deposited radionuclides depends on the physical and chemical characteristics of the radionuclide considered, on the type of fallout i.

Special attention will be devoted to I, Cs and 90Sr and their pathways of exposure to humans.

Deposition can occur on the ground or on water surfaces. The terrestrial environment will be considered first.

Information on the deposition of plutonium isotopes is not as extensive because of difficulties in detecting these radionuclides.

The only area with plutonium levels exceeding 4 kBq m2 was located within the km zone Figure IX.

In the Gomel-Mogilev-Bryansk area, the ,Pu deposition density ranged from 0. At Korosten, located in Ukraine about km southwest of the Chernobyl power plant, where the Cs deposition density was about kBq m2, the ,Pu deposition density due to the Chernobyl accident derived from data in [H8] is found to be only about 0.

Terrestrial environment 2. Remainder of northern and southern hemisphere As shown in Table 5, there are also other areas, in Europe, where the Cs deposition density exceeded 37 kBq m2, notably, the three Scandinavian countries Finland, Norway and Sweden , Austria and Bulgaria.

Small amounts of radiocaesium and of radioiodine penetrated the lower stratosphere of the northern hemisphere during the first few days after the accident [J6, K43].

Subsequently, transfer of radiocaesium to the lower atmospheric layers of the southern hemisphere may have occurred as a result of interhemispheric air movements from the northern to the southern stratosphere, followed by subsidence in the troposphere [D11].

However, radioactive contamination was not detected in the southern hemisphere D. For short-lived radionuclides such as I, the main pathway of exposure of humans is the transfer of the amounts deposited on leafy vegetables that are consumed within a few days, or on pasture grass that is grazed by cows or goats, giving rise to the contamination of milk.

The amounts deposited on vegetation are retained with a half-time of about two weeks before removal to the ground surface and to the soil.

Long-term transfer of I from deposition on soil to dietary products that are consumed several weeks after the deposition has occurred need not be considered, because I has a physical half-life of only 8 days.

Radionuclides deposited on soil migrate downwards and are partially absorbed by plant roots, leading in turn to upward migration into the vegetation.

These processes should be considered for long-lived radionuclides, such as Cs and 90Sr. The rate and direction of the radionuclide migration into the soil-plant pathway are determined by a number of natural phenomena, including relief features, the type of plant, the structure and makeup of the soil, hydrological conditions and weather patterns, particularly at the time that deposition occurred.

The vertical migration of Cs and 90Sr in soil of different types of natural meadows has been rather slow, and the greater fraction of radionuclides is still contained in its upper layer cm.

The effective half-time of clearance from the root layer in meadows cm in mineral soils has been estimated to range from 10 to 25 years for Cs and to be 1.

For a given initial contamination of soil, the transfer from soil to plant varies with time as the radionuclide is removed from the root layer and as its availability in exchangeable form changes.

The Cs content in plants was maximum in , when the contamination was due to direct deposition on aerial surfaces. In , Cs in plants was 36 times lower than in , as the contamination of the plants was then mainly due to root uptake.

Since , the transfer coefficients from deposition to plant have continued to decrease, although the rate of decrease has slowed: from to , the transfer coefficients of Cs decreased by 1.

Later on, ageing processes led to similar mobility values for Cs from the Chernobyl accident and from global fallout.

The variability of the transfer coefficient from deposition to pasture grass for Cs is indicated in Table 9 for natural meadows in the Polissya area of Ukraine [S40].

The type of soil and the water content both have an influence on the transfer coefficient, the values of which were found to range from 0.

The variability as a function of time after the accident in the Russian Federation has been studied and reported on by Shutov et al.

Contrary to Cs, it seems that the exchangeability of Sr does not keep decreasing with time after the accident and may even be increasing [B36, S41].

In the Russian Federation, no statistically significant change was found in the 90Sr transfer coefficient from deposition to grass during the first 4 to 5 years following the accident [S41].

This is attributable to two competing processes: a 90Sr conversion from a poorly soluble form, which characterized the fuel particles, to a soluble form, which is easily assimilated by plant roots, and b the vertical migration of 90Sr into deeper layers of soil, hindering its assimilation by vegetation [S41].

The contamination of milk, meat and potatoes usually accounts for the bulk of the dietary intake of Cs. However, for the residents of rural regions, mushrooms and berries from forests occupy an important place.

The decrease with time of the Cs concentrations in those foodstuffs has been extremely slow, with variations from one year to another depending on weather conditions [I22].

Aquatic environment Deposition of radioactive materials also occurred on water surfaces. Deposition on the surfaces of seas and oceans resulted in low levels of dose because the radioactive materials were rapidly diluted into very large volumes of water.

In rivers and small lakes, the radioactive contamination resulted mainly from erosion of the surface layers of soil in the watershed, followed by runoff in the water bodies.

In the km zone, where relatively high levels of ground deposition of 90Sr and Cs occurred, the largest surface water contaminant was found to be 90Sr, as Cs was strongly adsorbed by clay minerals [A15, M19].

Much of the 90Sr in water was found in dissolved form; low levels of plutonium isotopes and of Am were also measured in the rivers of the km zone [A15, M19].

The contribution of aquatic pathways to the dietary intake of Cs and 90Sr is usually quite small. However, the Cs concentration in the muscle of predator fish, like perch or pike, may be quite high in lakes with long water retention times, as found in Scandinavia and in Russia [H16, K47, R21, T23].

For example, concentration of Cs in the water of lakes Kozhanyand Svyatoe located in severely contaminated part of the Bryansk region of Russia was still high in because of special hydrological conditions: Bq l1 of Cs and 0.

Concentration of Cs in the muscles of crucian Carassius auratus gibeio sampled in the lake Kozhany was in the range of kBq kg1 and in pike Esox lucius in the range kBq kg1 [K47, T23].

Activity of Cs in inhabitants of the village Kozhany located along the coast of lake Kozhany measured by whole-body counters in summer was 7.

Taking into account seasonal changes in the Cs whole-body activity, the average annual internal doses were estimated to be 0. Also, the relative importance of the aquatic pathways, in comparison to terrestrial pathways, may be high in areas downstream of the reactor site where ground deposition was small.

Improper, unstable operation of the reactor allowed an uncontrollable power surge to occur, resulting in successive steam explosions that severely damaged the reactor building and completely destroyed the reactor.

It is worth noting, however, that the doses were estimated on the basis of environmental and thyroid or body measurements and that knowledge of the quantities released was not needed for that purpose.

The three main areas of contamination, defined as those with Cs deposition density greater than 37 kBq m2 1 Ci km2 , are in Belarus, the Russian Federation and Ukraine; they have been designated the Central, GomelMogilev-Bryansk and Kaluga-Tula-Orel areas.

The Central area is within about km of the reactor, predominantly to the west and northwest. The Gomel-Mogilev-Bryansk contamination area is centred km to the northnortheast of the reactor at the boundary of the Gomel and Mogilev regions of Belarus and of the Bryansk region of the Russian Federation.

The Kaluga-Tula-Orel area is located in the Russian Federation, about km to the northeast of the reactor. All together, as shown in Table 7 and in Figure XI, territories with an area of approximately , km2 were contaminated in the former Soviet Union.

Outside the former Soviet Union, there were many areas in northern and eastern Europe with Cs deposition density in the range kBq m2.

These regions represent an area of 45, km2, or about one third of the contaminated areas found in the former Soviet Union. For short-lived radionuclides such as I, the main pathway of exposure to humans is the transfer of amounts deposited on leafy vegetables that are consumed by humans within a few days, or on pasture grass that is grazed by cows or goats, giving rise to the contamination of milk.

For long-lived radionuclides such as Cs, the long-term transfer processes from soil to foods consumed several weeks or more after deposition need to be considered.

It is convenient to classify into three categories the populations who were exposed to radiation following the Chernobyl accident: a the workers involved in the accident, either during the emergency period or during the clean-up phase; b inhabitants of evacuated areas; and c inhabitants of contaminated areas who were not evacuated.

The available information on the doses received by the three categories of exposed populations will be presented and discussed in turn.

Doses from external irradiation and from internal irradiation will be presented separately. The external exposures due to gamma radiation were relatively uniform over all organs and tissues of the body, as their main contributors were TeI, I and BaLa for evacuees, Cs and Cs for inhabitants of contaminated areas who were not evacuated, and radionuclides emitting photons of moderatelyhigh energy for workers.

These external doses from gamma radiation have been expressed in terms of effective dose. With regard to internal irradiation, absorbed doses in the thyroid have been estimated for exposures to radioiodines and effective doses have been estimated for exposures to radiocaesiums.

Doses have in almost all cases been estimated by means of physical dosimetrytechniques. Biological indicators of dose has been mainly used, within days or weeks after the accident, to estimate doses received by the emergency workers, who received high doses from external irradiation and for whom dosemeters were either not operational nor available.

Unlike physical dosimetry, biological dosimetric methods are generally not applicable to doses below 0.

Soon after the accident, biological dosimetry is usually based on the measurement of the frequency of unstable chromosome aberrations dicentric and centric rings.

By comparing the rate of dicentric chromosomes and centric rings with a standard dose-effect curve obtained in an experiment in vitro, it is possible to determine a radiation dose.

However, the use of dicentric as well as other aberrations of the unstable type for the purposes of biological dosimetry is not always possible, since the frequency of cells containing such aberrations declines in time after exposure.

For retrospective dosimetry long after the exposure, biological dosimetry can be a complement to physical dosimetry, but only techniques where radiation damage to the biological indicator is stable and persistent and not subject to biochemical, physiological or immunological turnover, repair or depletion are useful.

In that respect, the analysis of stable aberrations translocations , the frequency of which remains constant for a long time after exposure to radiation, is promising.

The probability of occurrence of stable translocations and unstable dicentrics aberrations after exposure is the same.

However, translocations are not subjected to selection during cell proliferation, in contrast to dicentrics. Fluorescence in situ hybridization FISH or Fast-FISH in conjunction with chromosome painting may be useful in retrospective dosimetry for several decades after exposure.

Other biological or biophysical techniques for measuring doses are electron spin resonance ESR or opticallystimulated luminescence OSL.

These techniques are used in retrospective dosimetry to measure the radiation damage accumulated in biological tissue such as bone, teeth, fingernails and hair.

Also, the gene mutation glycophorin A that is associated with blood cells may be used. Most of them were at the reactor site at the time of the accident or arrived at the plant during the few first hours.

The numbers of accident witnesses and emergency workers are listed in Table According to Table 10, on the morning of 26 April, about emergency workers were on the site of the Chernobyl power plant.

The workers involved in various ways in the accident can be divided into two groups: a those involved in emergency measures during the first day of the accident 26 April , who will be referred to as emergency workers in this Annex, and b those active in at the power station or in the zone surrounding it for the decontamination work, sarcophagus construction and other clean-up operations.

This second group of workers is referred to as recovery operation workers in this Annex, although the term liquidator gained common usage in the former Soviet Union.

The power plant personnel wore only film badges that could not register doses in excess of 20 mSv. All of these badges were overexposed.

The firemen had no dosimeters and no dosimetric control. Dose rates on the roof and in the rooms of the reactor block reached hundreds of gray per hour.

Measured exposure rates in the vicinity of the reactor at the time of the accident are shown in Figure XII.

Emergency workers Measured exposure rates in air on 26 April in the local area of the Chernobyl reactor. The highest doses were received by the firemen and the personnel of the power station on the night of the accident.

Some symptoms of acute radiation sickness were observed in workers. Following clinical tests, an initial diagnosis of acute radiation sickness was made in of these persons.

On further analysis of the clinical data, acute radiation sickness was confirmed later in in individuals. The most important exposures were due to external irradiation relatively uniform whole-body gamma irradiation and beta irradiation of extensive body surfaces , as the intake of radionuclides through inhalation was relatively small except in two cases [U4].

Because all of the dosimeters worn by the workers were overexposed, they could not be used to estimate the gamma doses received via external irradiation.

The estimated ranges of doses for the emergency workers with confirmed acute radiation sickness are given in Table Forty-one of these patients received whole-body doses from external irradiation of less than 2.

Ninety-three patients received higher doses and had more severe acute radiation sickness: 50 persons with doses between 2. The skin doses from beta exposures evaluated for eight patients with acute radiation sickness ranged from 10 to 30 times the dose from whole-body gamma radiation [B10].

Internal doses were determined from thyroid and wholebody measurements performed on the persons under treatment, as well as from urine analysis and from post-mortem analysis of organs and tissues.

For most of the patients, more than 20 radionuclides were detectable in the whole-body gamma measurements; however, apart from the radioiodines and radiocaesiums, the contribution to the internal doses from the other radionuclides was negligible [U4].

Internal doses evaluated for 23 persons who died of acute radiation sickness are shown in Table The lung and thyroid doses, calculated to the time of death, are estimated to have ranged from 0.

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