Current Topics about the Radiological Consequences by the Chernobyl
Accident
Tetsuji IMANAKA
Research Reactor Institute, Kyoto University
Kumatori-cho, Sennan-gun, Osaka, 590-0494 Japan: imanaka@rri.kyoto-u.ac.jp

Abstract
Basic radiological factors of the Chernobyl accident are reviewed such as radioactivity
discharge, the size of contaminated area, radiation dose, radiation risk assessment etc. Roughly
estimating, 50-60 % of 131I and 30-50 % of 137Cs in the reactor core were released into theenvironment, which correspond to 40-50 MCi and 2-4 MCi, respectively, as the activities at the timeof the accident. The total area in 13 European countries with the 137Cs contamination more than 1
Ci/km2 amounts to 190,000 km2. The collective thyroid dose for the entire populations in the mostaffected three countries (Belarus, Ukraine and Russia) is estimated 1.6 × 106 person-Gy. The
collective effective dose (excluding thyroid dose) for 5.16 million people living in the maincontaminated territories in three countries is estimated 4.26 × 104 person-Sv during 10 years after
the accident. Using these collective doses together with radiation risk coefficients of ICRP (1990),
13,000 thyroid cancer and 2,100 other cancer deaths are expected among the corresponding
populations.
Other articles in this report indicate the followings. About 4,400 cases of radiation-induced
thyroid cancer were observed in Belarus by the end of 2000. There are also observed someincreasing tendencies of other cancers among inhabitants in the contaminated areas and liquidators.
Health deteriorations and mental retardations are observed among the children living in thecontaminated areas and having received irradiation in utero. All these findings suggest the necessityof well organized epidemiological studies before giving conclusions about the health consequencesof the Chernobyl accident as well as applicability of ICRP radiation risks to the related populations.
An interesting map is shown representing dose rate around the Chernobyl NPP on June 1, 1986.
Using the dose rate in this map for reconstructing radiation dose for evacuees, the possibility ofacute radiation sickness was confirmed among a substantial part of evacuees from some villages
within the 30 km zone.

1. Introduction
It was more than a quarter of century ago that our group, Nuclear Safety Research Group of Kyoto
University began to raise the alarm for catastrophic consequences in case of large nuclear accidents inJapan. According to our assessment based on the methodology developed by Reactor Safety Study of
USNRC (1975), about 5,000 acute deaths were forecast when a severe loss-of-coolant accident would
happen at the Ikata-1 NPP (560 MW, PWR) [1]. The high level of radioactive contamination was expected
to extend more than 100 km along the wind stream. The Japanese authorities, however, neglected
possibilities of such accidents, saying every time that nuclear power plants were designed and constructedunder conceptions; “Fail Safe” and “Fool Proof”.
In March 1979, a large loss-of-coolant accident happened at Three Mile Island-2 NPP (1,000 MW,
PWR) in USA, which resulted in a partial meltdown of the reactor core. Fortunately, the containment of
TMI-2 could keep radioactive particulates from escaping although a large amount of radioactive gases
were released [2]. The radiological consequences due to the TMI-2 accident were considered rather small

1

in comparison with the worst ones. This accident, however, demonstrated the reality of possible
catastrophic accidents at NPPs.
On April 26, 1986 an excursion accident occurred at the Chernobyl-4 (1,000 MW, RBMK) in theformer USSR and destroyed the reactor and the building at a moment, which released a huge amount ofradioactivity into the environment. Sixteen years have already passed since the occurrence of theChernobyl accident. There remain, however, many questions that were not yet answered. For example,
according to Malko’s article [3], the primary causes of the Chernobyl accident were design defects of thereactor and inadequate operation manuals, while unprofessional actions of the operators of the Unit-4 were
responsible for the accident, according to Gorbachev’s article [4].
In this article, current topics about the radiological consequences of the Chernobyl accident aresummarized, referring to activities of our group and the contents of the other articles in this report.
2. Radioactivity release
The amount of radioactivities released into the environment is the basic factor characterizing thescale of nuclear accidents. So far a number of estimations have been made by various authors about theradioactivity discharge by the Chernobyl accident [5-12]. Table 1 summarizes several estimations for mainradionuclides.
USSR 1986 Report:
In August 1986 the Soviet government sent a delegation to the post-accident review meeting on the
Chernobyl accident held in Vienna by IAEA. According to the report of the Soviet delegation [5], the total
release of non-gaseous radionuclides and gaseous ones were estimated to be 50 MCi and 50 MCi,
respectively. These figures were decay-corrected to the activities on May 5. The USSR 1986 Report
included valuable information, but the detailed methods of their estimation were not clear. I would like tonote one episode of our group with the USSR report. Our group was independently involved in the task toestimate the radioactivity release by the Chernobyl accident. In October 1986, after reading through the
USSR Report extensively, Seo of our group wrote a letter to Legasov, the head of the Soviet delegation in
Vienna, asking various unclearness and inconsistencies in the Soviet estimations. More than one year later,in January 1988, Seo received a kind answer from Legasov, writing “the discharge estimate has beenobtained measuring fall-outs from the initial discharge, radionuclide concentration in the air in the
direction of air mass motion and on the basis of model calculations” [13].
Estimation by our group:
By the end of 1986, we could collect radioactive deposition data by the Chernobyl accident from allover the northern hemisphere except for the Soviet territories. Our primary attention was directed to theground deposition of 137Cs. It was strange that our estimate for the 137Cs deposition on all European
countries except USSR was about 1 MCi, which was the same as the total release of 137Cs estimated in the
USSR 1986 Report.
Using the level of 137Cs deposition as the reference nuclide of the radioactive contamination, we haveanalyzed dependencies of radionuclide composition on the direction and the distance from Chernobyl.
Table 1. Estimates of released radioactivity of major nuclides by the Chernobyl accident.
Estimated released radioactivity, MCi (% of core inventory)
Inventory,
Nuclide Half life
USSR
reportSeo
Imanaka
UkraineBorovoiMCi(1986) [5](1988) [7](1993) [9] (1996) [10] (2001) [12]131I
8.05 d36.5
7.3 (20)
25.40 (70)(49)
(50-60)(50-60)137
Cs
30.2 y7.7
1.0 (13)
4.35 (57)(31)(20-40)(33±10)
95
Zr
64 d
119
3.8 (3.2)
5.60 (4.7)
(5.0)
(3.5)
90
Sr
28 y
5.5
0.23 (4.0)
0.53 (9.6)(4-6)- All activities are decay-normalized to values on May 6, 1986.
- Values of reactor inventory are cited from the USSR 1986 Report.

2

Then, by integrating the deposition functions, the total depositions were calculated up to 3,000 km from
Chernobyl [7]. The obtained results showed larger depositions than the USSR 1986 Report by factors of
4.4 and 3.5 for 137Cs and 131I, respectively (Table 1).
In our first estimation, only small data in the USSR 1986 Report were used for the contamination
within the USSR territories. The collapse of USSR at the end of 1991 changed the situation around
Chernobyl problems. In 1993 we organized a collaborative study with Belarusian scientists under aresearch-grant from the Toyota foundation [14]. We made new estimation using more data provided from
Belarusian side [9]. Our new estimates were smaller than the previous ones and by 2.4 and 2.5 times larger
than the USSR 1986 Report for 137Cs and 131I, respectively (Table 1).
Estimation based on the radioactivities remaining within Sarcophagus:
Another method for estimation of radionuclide discharge is to investigate the amounts ofradioactivities that remain within “Sarcophagus” (the concrete building containing the destroyed 4th unit).
Pavlovych’s article [15] describes the current situation of nuclear fuel within Sarcophagus. 190 ton of
uranium was loaded in the reactor core at the time of the accident. Now within Sarcophagus, uranium fuelexists mainly in three forms: fuel fragments, LFCM (Lava-like Fuel Containing Material) and dusts. The
amount of uranium in LFCM is estimated about 120 ton (min; 65, max; 165) [15]. According to Borovoi
and Gagarinsky [12], it was found that 60 % of 137Cs escaped from LFCM from the analysis of LFCM
samples, while no amount of 129I was detected in LFCM. Concerning fuel fragments dispersed from thereactor core at the time of the explosions, 25 – 37 % of 129I remain within them and 137Cs was retained as it
was in the core. Based on these data, they concluded that 33 ± 10 % of 137Cs and 50 – 60 % of 131I werereleased from the reactor core of the Chernobyl-4.
Looking at the values in Table 1, we can roughly say that 50 - 60 % of 131I, 30 - 50 % of 137Cs andabout 5 % of non-volatile nuclides in the reactor inventory were discharged into the environment by the
Chernobyl accident. These values correspond to round estimates of radioactivities: 40 - 50 MCi of 131I, 2 4 MCi of 137Cs and 0.3 MCi of 90Sr. These activities are adjusted at the time of the accident.
3. Radioactive contamination
One of unexpected features of the Chernobyl accident is that the contamination extended over a vast
area on the Earth. This was caused partly by the fact that radioactive plumes reached high altitude of theatmosphere by the first explosions and the consequent fire, and partly by the fact that the radioactive
discharge continued more than 10 days changing the direction of the radioactive plumes. These conditions
can not be supposed in case of accidents at water power reactors such as PWR and BWR.
Cesium-137 is the most important nuclide from the point of the long-term effects of radioactive
contamination. The areas of 137Cs contamination more than 1 Ci/km2 in European countries are
summarized in Table 2 [16]. As the value of the total deposition on the northern hemisphere, 70 PBq (1.9MCi) of 137Cs is given in UNSCEAR 1988 Report [8]. This value is near the lower limit of our roundestimate of 137Cs release (2-4 MCi). The following two points should be noted about the estimate in
UNSCEAR 1988. At first, UNSCEAR 1988 was made before the detailed information about the highly
contaminated within USSR was disclosed in 1989. Based on the more recent 137Cs contamination data in
Table 2, the amount of total 137Cs deposition in the most affected three countries (Belarus, Russia,
Ukraine) is calculated to be 1.2 MCi, which is 0.5 MCi larger than the value given for the USSR territories
in UNSCEAR 1988. At second, the UNCEAER 1988 estimate did not seem to include the radioactivities
in the 30 km zone. The 137Cs activity in the Ukrainian territory within the 30 km zone is reported to beabout 0.5 MCi: 0.11 MCi on soil and 0.41 MCi in radioactive waste pits [10]. Considering these factors,
the UNSCEAR 1988 estimate should be revised to 2.9 MCi, which lies in the middle of our round range.
Meanwhile, according to Nasvit’s article [17], 137Cs activity contained in the lake sediments of the cooling3

Table 2 Area of 137Cs contamination in European countries with more than 1 Ci/km2 (km2) [16]Country
Belarus
RussiaUkraineSwedenFinland
Bulgaria
Austria
NorwayGreeceSlovenia
Italy
Moldova
Switzerland
Total

Area
(km2)
208,000
17,075,000
604,000
450,000
337,000
111,000
84,000324,000
132,000
20,000301,000
34,00041,000

10 - 2060,000300,000
150,000
37,40048,80027,50027,60051,80016,6008,600
10,90020,0005,900
765,100

Level of 137Cs contamination, kBq/m2 (Ci/km2)
37 - 185
185 - 555 555 - 1480
20 - 37(1 - 5)(5 – 15)(15 - 40)
30,00029,900
10,200
4,200
100,000
48,8005,700
2,100
65,00037,2003,200
90042,60012,00037,40011,50040,4004,800
24,7008,600
13,000
5,200
6,400
1,200
8,000
300
5,600
300
100
60
1,900
1,300
375,100
161,160
19,100
7,200

>1480
(>40)
2,200
300
600
3,100

Note-1: 137Cs level in European countries due to global fallouts by nuclear test was 2 - 3 kBq/m2 in early 1990s.
Note-2: According to Chernobyl laws in Belarus, Russia and Ukraine, the contaminated territories are legallydivided into the following categories depending on 137Cs density:(1) 1-5 Ci/km2 - zone of radiation control, (2) 5-15 Ci/km2 - zone of guaranteed voluntary resettlement,(3) 15-40 Ci/km2 - zone of obligatory resettlement, (4) > 40 Ci/km2 - zone of alienation.

pond of the Chernobyl NPP is estimated to be 4,400 Ci.
The processes forming radioactive contamination around the territories adjacent to the Chernobyl
NPP and their nuclide compositions were extensively analyzed in Gaydar’s article [18], taking into
considerations geological features of the contaminated territories. Detailed contamination maps were
presented for 137Cs and Pu isotopes and 241Am. Interesting data are presented in Stepaneko’s article [19]about the radioactive plume arrival and departure in contaminated settlements in Bryask, Tula and Kaluga
regions of Russia. According to Stepanenko’s article [19], about 80 % of the total 131I deposition wasformed during the first week after the accident.
Recent data about the food contamination of 137Cs and 90Sr in Belarus are reviewed in Matsko’s
article [20]. They noted that special attention should be paid to non-farm products such as mushrooms,
berries and meat of wild animals. For example, about 37,000 Bq/kg of 137Cs in fresh mushroom wasregistered in a settlement of Gomel region in 1999. Tykhyy’s article [21] presents the results of two seriesof measurements that were conducted in 1992 and in 2001 at the same village in Zhytomyr region,
Ukraine. The 137Cs activity in milk in the village was decreased by 9 times in 2001 in comparison with
1992, while the 90Sr concentration was 3 times higher in 2001 than in 1992.
Dynamics of 137Cs accumulation in fish in various water bodies are described in Ryabov’s article [22].
Although a general decreasing trend of 137Cs accumulation has been observed, lowering rates are quite
different, depending on fish species and conditions of water bodies. High levels of 137Cs accumulation are
still observed in some lakes with stagnant water. Nasvit’s article [17] provides the results of recent
radioecological monitoring of the cooling pond of the Chernobyl NPP.
3. Radiation dose and risk assessment
UNSCEAR 2000 report [11] provides a series of interesting information about radioactive
contamination, dose reconstruction and health effects due to the Chernobyl accident.

4

Table 3. Thyroid dose for the population in the main contaminated areas.
Collective thyroid dose,
Average individual thyroid
Country
Population
person-Gydose, mGy
Belarus [11]3,100,000
402,000
130
Russia [19]3,100,000
106,000
34
Ukraine [11]3,500,000
300,00086
Total
9,700,000
808,000
83
Note; Belarus- Gomel and Brest regions. Russia - territories with 137Cs contamination more than 1 Ci/km2
in Bryansk, Orel, Tula and Kaluga regions. Ukraine - 8 districts around Chernobyl and Kiev city.
Thyroid dose and thyroid cancer risk:
Thyroid dose for the populations in the main contaminated areas in the most affected three countries
is summarized in Table 3 [11, 19]. The highest average thyroid of 130 mSv is given in Belarus, while thelowest of 34 mSv is in Russia. Thyroid dose in Table 3 are given for the population including all ages. As
is well known, thyroid dose to children is larger than adults. For example, among 1,988 children less than
1 year old living in the contaminated district of Gomel region, Belarus, 667 children (34 %) received
thyroid dose more than 2 Gy [11]. For the evacuees from Ukrainian villages within the 30 km zone, themean thyroid dose of 3.9 Gy is estimated for 369 children less than 1 year old, while the average thyroid
dose for the people more than 18 years old is 0.40 Gy [11].
Collective thyroid dose for the entire populations of three countries are given as follows: 5.53 × 105
person-Gy for Belarus, 7.4 × 105 person-Gy for Ukraine and (2 - 3) × 105 person-Gy for Russia. Using thetotal collective thyroid dose of 1.6 × 106 person-Gy for three countries and the radiation risk factor forthyroid cancer of 8 × 10-2 Gy-1 from ICRP Publication 60 [23], about 13,000 thyroid cancer cases are
expected in these countries as the consequences by the Chernobyl accident. 10 % of them, that is, 1,300
cases will be fatal.
UNSCEAR 2000 Report [11] presents the data that about 1,800 thyroid cancers were observed during
1990 – 1998 in children 0 – 17 years old at the time of the Chernobyl accident: 1,067 cases in Belarus, 205
cases in Russia and 519 cases in Ukraine.
According to Malko’s article [24], 4,400 cases of radiation-induced thyroid cancer have been alreadyobserved in the whole population of Belarus by the end of 2000: about 700 cases in children under 15
years old and 3,700 cases in adolescents and adults at the time of diagnosis. The number of additional
thyroid cancer in Ukraine and Russia can be calculated using the ratio of their collective thyroid dose to
Belarus. Thus, about 12,000 cases of thyroid cancer are considered to have already appeared in theaffected three countries. Anyway, we have to carefully watch the results of future follow-up studies inorder to give conclusions about the total outcome of thyroid cancer by the Chernobyl accident.
Knatko’s article [25] describes a method to estimate thyroid dose from 131I inhalation in thecontaminated territories in Belarus. Average thyroid dose from inhalation for adults are estimated to be 20
and 130 mSv for the eastern and southern contaminated areas, respectively. The difference between twoareas was mainly due to the differences of the 131I/137Cs ratio and the type of 131I deposition (dry depositionin the southern and wet deposition in the eastern).
Effective dose and health effects other than thyroid cancer:
Estimates of effective dose for the total body (excluding thyroid dose) during the period 1986-1995
for the populations living in the contaminated areas with more than 1 Ci/km2 are summarized in Table 4[11]. Compared with the values for thyroid dose in Table 3, about 10 times less values are shown for
effective dose. The difference among three countries is rather small. In addition, age dependency ofeffective dose is reported to be small compared with the case of thyroid dose [11].
Forecasts of effective dose for 70 years after the accident (1986 – 2056) are also shown in5

Table 4. Effective dose for the population living in the contaminated territories more than 1
Ci/km2 of 137Cs for the period 1986-1995 (excluding thyroid dose) [11].
Collective effective dose
Average effective doseCountry Population(person-Sv)(mSv)
External
Internal
Total
External
Internal
Total
Belarus1,880,000
9,600
5,500
15,100
5.1
2.9
8.0
Russia1,980,000
8,500
5,000
13,500
4.3
2.5
6.8
Ukraine1,300,000
6,100
7,900
14,000
4.7
6.1
10.8
Total
5,160,000
24,20018,40042,600
4.7
3.5
8.2
UNSCEAR 2000 [11]. Effective dose during 10 years after the accident (1986 -1995) consists of 60 –70 % of the 70 years dose, within which the first year (1986) contributed 23 – 28 %.
Using the collective dose of 42,600 person-Sv in Table 4 and the radiation risk coefficient for cancer
mortality of 5 × 10-2 Sv-1 from ICRP [23], we can expect 2,100 cancer deaths among the 5.16 million
people other than thyroid cancer. Assuming that 15 % of this population will die of spontaneous cancer,
the number of cancer deaths without irradiation will amount around 770,000. Therefore, 2,100 cases ofradiation-induced cancer deaths will increase the cancer death rate about 0.3 %. If the cancer risk
coefficient from ICRP is applicable to the population suffering from the Chernobyl accident, it will beabsolutely impossible to observe such small increase of cancer death by means of epidemiological studies.
A new cancer risk model based on recent knowledge about dose-effect relationship is proposed in
Knatko’s article [26]. According to their cancer risk assessment for 250,000 inhabitants (average effective
dose, 43 mSv) living in the contaminated areas in Belarus more than 5 Ci/km2 of 137Cs, 5 – 6 % of ERR(excess relative risk) is expected during the whole life, which is about 6 times larger than the value basedon the risk coefficient from ICRP. In this case 2,200 cancer deaths will be added on 37,000 spontaneouscancer deaths.
Meanwhile, a significant increase of cancer deaths among 66,000 Russian liquidators (the mean dose,about 100 mSv) is reported for the observation period 1991 – 1998 in Maksioutov’s article [27]. The ERR
coefficient is estimated to be 2.04 Sv-1 (95%CI: 0.45, 4.31). This value is about 60 % higher than thecorresponding coefficient derived from ERR in Kantko’s article [26]. It should be noted that a significant
increase of deaths from cardiovascular diseases (0.79 Sv-1, 95%CI: 0.07 – 1.64) is also observed among
Russian liquidators in Maksioutov’s article [27].
Prysyazhnyuk’s article [28] presents analysis of medical statistics in Ukraine mainly based on the
National Cancer Registry that was established in 1989. The results suggest increasing tendencies of female
breast cancer among women liquidators, inhabitants in the most contaminated districts and evacuees fromthe 30 km zone. Arynchyn’s article [29] reports the results of a prospective cohort study of children in
Belarus: the main group consists of 133 children living in the contaminated territories and the control
group is 186 children in clean territories. Through clinical examinations they found significantly highrelative risks of the main group for diseases such as arterial hypotension and cardic metabolic dysfunction.
Nyagu’s article [30] presents the results of medical investigation concerning brain functions of 100
children prenatally irradiated at the time of the accident and born to mothers evacuated to Kiev from the
30 km zone. Bain damages expressed as decreases of IQ indices, mental disorders etc. were observed
among the prenatally irradiated children, compared with the control children consisting of theirclassmates.
Considering the findings shown in a series of epidemiological studies performed in Belarus, Ukraine
and Russia, it is early to say that the radiation risk from ICRP is applicable to the populations sufferingfrom irradiation due to the Chernobyl accident. The author would like to address the necessity of welldesigned and organized epidemiological studies in order to conclude about the radiation consequences by
the Chernobyl accident.
Concerning the efforts to reconstruct effective dose more precisely, Chumak’s article [31] overviews
6the current situation in Ukraine about EPR dosimetry using tooth enamel. Based on the EPR
measurements of 465 Ukrainian liquidators who worked in 1986-1987, the average dose of 110 mSv isobtained. This value is comparative to the average value of 130 mSv for Russian liquidators in 1986-1987
based on official records. Application of EPR dosimetry in Russia for the population living in thecontaminated territories is described in Ivannikov’s article [32]. From the regression analysys between
EPR dose and 137Cs contamination density, the normalized dose of 0.068 mGy per kBq/m2 of 137Cs was
obtained during 8 years after the accident, while UNSCEAR 2000 [11] gives the value of 0.037 mSv per
kBq/m2 of 137Cs for the rural area in Russia.
4. Cytogenetic research
Cytogenetic disturbances in cells are primary markers of irradiation effects on biological organism.
Geraskin’s article [33] presents the results of a cytogenetic experiment on plants in the first years after theaccident within the 30 km zone of Chernobyl. They observed chromosome aberration in rye and wheat.
Through the experiment of subsequent generations for 3 years, an increasing tendency of radiation
sensitivity of chromosome aberration was observed both for rye and wheat.
Chromosome aberrations in human lymphocyte have been investigated for more than 1,500
liquidators in Snigiryova’s article [34]. Even 15 years after the accident a significantly higher level ofdicentrics frequencies is still observed among liquidators although there is a general tendency of decrease
for this index. In Slozina’s article [35], an incresed level of chromosome abberation in lymphocyte is also
observed among the liquidators. An interesting tendency is reported that the dicentric frequency among
the liquidators shows an increase for the period 8-12 years after irradiation. Bezdrobna's article [36]presents the results of a cytogenetic examination of 33 self-settlers in the 30 km zone of the Chernobyl
NPP. The frequencies of chromosome abberation among the self-settlers were found to be significantly
higher than the control group living in relatively clean territories.
5. New information about radiation situation within the 30 km zone
According to UNSCEAR 2000 [11], 49,614 people in Pripyat city and Yanov railway station were
evacuated on April 27, 1986, the next day of the Chernobyl accident. Another 41,792 people evacuatedfrom Ukrainian territory within the 30 km zone, mainly in May 3 – 7. From the Belarusian territory within
the 30 km zone, 24,725 people evacuated mainly in May 2 – 7. In total, 116,231 people were evacuatedfrom the 30 km zone. A large part of evacuees stayed at their places for 6 – 11 days before evacuation.
There are two confronting opinions about acute radiation syndromes among the inhabitants. The firstone is official opinions beginning from USSR 1986 Report up to UNSCEAR 2000 Report that no case of
acute radiation disease occurred among the inhabitants around the Chernobyl NPP. According to thesecond opinion, there should be a lot of acute radiation sicknesses among inhabitants. For example,
according to the secret protocols of the Special Operative Group of the Central Committee of the USSR
Communist Party [37, 38], the number of patient with radiation sickness was periodically reported to
Moscow, including cases of children. Acute radiation syndromes were also confirmed from theinvestigation of medical records made in May – June 1986 at the Central Hospital of Khoyniki district
adjacent to the Chernobyl NPP [39, 40].
The level of radiation dose to evacuees is crucial in order to judge which side of two confronting
opinions is reflecting the real fact. According to UNSCEAR 2000 Report [11], the average external dose
for the Ukrainian evacuees is estimated 17 mSv with the maximum individual dose of 380 mSv.
Concerning Belarusian evacuees, the average eternal dose of 31 mSv is given for the whole evacuees,
while the highest average dose of about 300 mSv is estimated for the population in two villages; Chamkov
and Masany. These pieces of information are supporting the official opinion that no cases of acuteradiation sickness occurred among the inhabitants.
7

50

Radin

Prypyat R.
Ulasi
KryukiBorshchevka

200

200

Mashevo

Usov

50
500

Khatki

Krasnoe

Railway
Prypyat C.
500

Tolsty Less

Korogod
Chernobyl C.
0

5

10km

Fig. 1. Dose rate around the Chernobyl NPP on June 1, 1986; mR/h [44 ].
On the other hand, Imanaka [41, 42] suggested a possibility that a substantial fraction of evacuees
from the most contaminated villages could receive effective dose more than 1 Sv, which is a criteria for
acute radiation sickness, using the dose rate map on May 1, 1986 presented at CIS/EC Minsk conferencein 1996 [43] and temporal changes of dose rate until the evacuation.
After these works Imanaka happened to find another map representing the radiation situation around
Chernobyl on June 1, 1986 compiled by USSR scientists in 1991 (Fig. 1) [44]. As seen in Fig. 1, the dose
rate in Usov village on June 1 was around 200 mR/h. Our previous calculations [41, 42] indicate that thedose rate on May 1 was about 10 times higher than June 1, which means that a dose rate about 2 R/h canbe supposed in Usov village on May 1, 1986, from where inhabitants were evacuated on May 3.
In our previous works the average external dose of 0.32 Sv was estimated for the evacuees from Usovvillage based on a dose rate of 350 mR/h on May 1 in the previous map [43]. If a dose rate of 2 R/h is used
for May 1 instead of 350 mR/h, the average external dose for the inhabitants in Usov village becomes
about 2 Sv before the evacuation. In this case, the following description in the secret protocols of the
USSR Communist is seriously realistic: “By the situation at 9:00 on May 6, the total number ofhospitalized reached 3,454 persons. Among them, 2,609 persons are in hospital for treatment, including
471 infants. According to confirmed data, the number of radiation disease is 367 cases, including 19
children.” (from the protocol of the meeting on May 6, 1986).
6. Final remarks
For these 16 years our group has been studying the radiological consequences by the Chernobyl
accident, the worst accident in the history of nuclear energy development. We have visited contaminatedareas, measured radiation, took samples, discussed with scientists, met people and participated in meetings.
Then we clearly understood that the radiological aspect of the accident is only a small part of the tragedy
that happened to the people around Chernobyl.
8

We were overwhelmed by the followings. Just after the accident about 120,000 people were
evacuated from the 30 km zone. Several years later, resettlement of much more people began from thehighly contaminated areas. The total area for evacuation and resettlement amounted to 10,000 km2. About
500 villages and towns within the 30 km zone and in highly contaminated areas disappeared. We can say
the local societies have entirely vanished. A recent report [45] indicates that totally 350,400 people had toleave their homes.
We are sure that the Chernobyl tragedy can not be described without referring the pain of thesepeople. We should not consider that the whole aspect of the Chernobyl accident can be revealed byscientific approaches. Of course, the pain of these people is not the direct target of our scientific works.
We are thinking that scientific efforts, only by cooperating with other efforts such as films, photos,
documentaries, novels and so on, can be successful to draw the whole aspect of the Chernobyl tragedy.
Acknowledgement
The author should be grateful to Koide H., Kawano S., Kobayashi K. and Ebisawa T. of Nuclear
Safety Research Group for their encouragement in promoting the present studies. The leadership by late
Seo T. should be noted to begin collaborative works with former USSR scientists. This study is supported
by Grant-in-Aid for Scientific Research from Japan Society for Promotion of Science.
References
1.

Seo T. et.al.; “Safety Problems of Nuclear Power Plants. Vol.1”, pp.113-131, Nuclear Energy Information
Center, Osaka (1976) (in Japanese).
2. Seo. T and Imanaka T.; Discharge of Radioactive Rare Gases by the NPP Accident: In case of TMI-2, kagaku,
52 No.1 (1982) 42-52 (in Japanese).
3. Malko M. V.; The Chernobyl Reactor: Design Features and Reasons for Accident, in this report, p.11-27.
4. Gorbachev B. I.; The Causes and Scenario of the Chernobyl Accident, and Radioactive Release on the CHNPP
Unit-4 Site, in this report, p.11-27.
5. USSR State Committee on the Utilization of Atomic Energy; “The Accident at the Chernobyl Nuclear Power
Plant and Its Consequences”, August 1986.
6. S. A. Khan; The Chernobyl Source Term: A Critical Review, Nuclear Safety, 31, No.3 (1990) 353-74.
7. Seo T., Imanaka T. and Koide H.; Released Radioactivity by the Chernobyl Accident, Kagaku, 58 No.2
(1988)108-117 (in Japanese).
8. United Nations Scientific Committee on the Effects of Atomic Radiation; UNSCEAR 1988 Report, Annex D(1988).
9. Imanaka T. et.al.; The Final Report of the Research Grant of the Toyota Foundation in 1993 (in Japanese).
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11. United Nations Scientific Committee on the Effects of Atomic Radiation; UNSCEAR 2000 Report, Annex J(2000).
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Atomnaya Energiya, 90 No.2 (2001) 137-45 (in Russian).
13. Letter from Legasov to Seo received on January 6, 1988.
14. Imanaka T.; Research Activities of the Nuclear Safety Research Group of KURRI with Belarusian, Russian andUkrainian Colleagues about the Chernobyl Accident, in “Research Activities about the RadiologicalConsequences of the Chernobyl NPS Accident and Social Activities to Assist the Sufferers by the Accident”,
KURRI-KR-21, p.1-4, 1998.
15. Pavlovych V. M.; Nuclear Fuel in the Destroyed 4th Unit of Chernobyl NPP, in this report, p.45-58.
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plant accident", EC/CIS international scientific collaboration, EUR 16542 EN (1996).
17. Nasvit O.; Radioecological Situation in the Cooling Pond of Chornobyl NPP, in this report, p.74-85.
18. Gaydar A. and Nasvit O.; Analysis of Radioactive Contamination in the Near Zone of Chornobyl NPP, in thisreport, p.59-73.

919. Stepanenko V. F. et.al.; Iodine-131 Contamination, Thyroid Doses and Thyroid Cancer in the Contaminated
Areas of Russia, in this report, p.86-96.
20. Matsko V. P. and Imanaka T.; Content of Radionuclides of Chernobyl Origin in Food Products for the
Belarusian Population, in this report, p.105-113.
21. Tykhyy V.; Radioactive Contamination of Food in Stepanivka Village, Zhytomyr Region, Ukraine: in 1992 andin 2001, in this report, p.97-104.
22. Ryabov I. N.; Long-Term Observation of Radioactivity Contamination in Fish around Chernobyl, in this report,
p.114-124.
23. 1990 Recommendation of ICRP, ICRP Publication 60 (1990).
24. Malko M. V.; Chernobyl Radiation-induced Thyroid Cancers in Belarus, in this report, p.242-257.
25. Knatko V. A. and Dorzhok I. N.; Estimation of Thyroid Doses from Inhalation of 131I for Population ofContaminated Regions of Belarus, in this report, p.154-161.
26. Knatko V. A., M. M. Komochkov M. M. and Yanush A. E.; Estimations of Radiation Risk for the Population ofContaminated Territory of Belarus, in this report, p.162-169.
27. Maksioutov M. M.; Radiation Epidemiological Studies in Russian National Medical and Dosimetric Registry:
Estimation of Cancer and Non-cancer Consequences Observed among Chernobyl Liquidators in this report,
p.11-27.
28. Pryshazhnyuk A. Ye et.al.; Review of Epidemiological Finding in Study of Medical Consequences of theChernobyl Accident in Ukrainian Population, in this report, p.190-203.
29. Arynchyn A. N. et.al.; Health State of Belarusian Children Suffering from the Chernobyl Accident: Sixteen
Years after the Catastrophe, in this report, p.233-241.
30. Nyagu A. I. et.al.; Intelligence and Brain Damage in Children Acutely Irradiated in Utero As a Result of theChernobyl Accident, in this report, p.204-232
31. Chumak V.; EPR Dosimetry of Chernobyl Liquidators, in this report, p.125-143.
32. Ivannikov A., Skvortsov V. G. and Valeri F. STtepanenko V. F.; Retrospective Dose Assessment of
Inhabitants in the Contaminated Areas of Russia by EPR Measurement of Tooth Enamel, in this report,
p.144-153.
33. Geraskin S. A. et.al.; Cytogenetic Effects of Radiation on Agricultural Plants Observed in the Chernobyl region
during the First Years after the Accident, in this report, p.289-298.
34. Snigryova G. and Shevchenko V.; Analysis of Chromosome Aberrations in Human Lymphocytes after
Accidental Exposure to Ionizing Radiation, in this report, p.258-269.
35. Slozina N. M. and Neronova E. G.; he Follow-up Study of Chromosomal aberrations in Chernobyl Clean-up
Workers, in this report, p.270-278.
36. Bezdrovna L. et.al.; Chromosomal Aberrations in Blood Lymphocytes of the Residents of 30-km Chornobyl
NPP Exclusion Zone, in this report, p.279-288.
37. A. Yaroshinskaya, “Chernobyl: Top Secret”, Drugie-berega, Moscow, 1992. (in Russian).
38. A Yaroshinskaya; Impact of Radiation on the Population during the First Weeks and Months after the Chernobyl
Accident and Health State of the Population 10 Years Later, KURRI-KR-21, p.104-107, 1998.
39. V. Lupandin, Invisible Victims, NABAT 36, Minsk, October 1992.
40. V. Lupandin; Chernobyl 1996: New Materials concerning Acute Radiation Syndrome around Chernobyl
KURRI-KR-21, p.108-113, 1998.
41. T. Imanaka and H. Koide; Dose Assessment for Inhabitants Evacuated from the 30-km Zone Soon after the
Chernobyl Accident, KURRI-KR-21, p.121-126, 1998.
42. T. Imanaka and H. Koide; Assessment of External Dose to Inhabitants Evacuated from the 30-km Zone soonafter the Chernobyl Accident, Radiation Biology Radioecology, 40 (2000) 582-588.
43. I.K.Baliff and V.Stepanenko ed., “Retrospective Dosimetry and Dose Reconstruction”, Experimantal
Collaboration Project ECP-10. EUR 16540, EC, 1996.
44. G. M. Kozubov et.al.; The Map-scheme of Radiation Damage of Coniferous Forests in the Region of Accident
on the Chernobyl Nuclear Power Plant, Institute of Biology, Komi Scientific Center, Ural Division of USSR
Academy of Sciences, 1991.
45. UNDP and UNICEFF; The human consequences of the Chernobyl nuclear accident: A strategy for recovery, 25January 2002.

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