Research Activities of the Nuclear Safety Research Group of KURRI withBelarussian, Russian and Ukrainian Colleagues about the Chernobyl Accident
Tetsuji IMANAKA
Research Reactor Institute, Kyoto University
Kumatori-cho, Sennan-gun, Osaka 590-04, Japan; imanaka@rri.kyoto-u.ac.jp
Sarcophagus, the containment of the destroyedreactor): 600,000 - 800,000 persons
Evacuees from the 30-km zone during the firstweeks after the accident: 135,000 persons
People resettled from the contaminated areas: morethan 115,000 persons
Residents in the contaminated areas: over 6 million
persons (Table 2)

The 12th anniversary is coming soon since theChernobyl accident on April 26, 1986, the worst
accident in the history of the commercial use of
nuclear energy. In Japan we say ″JUNEN
HITO-MUKASHI″. It means that a period of ten years
is one era. Literally, there happened a series ofhistorical events during these 12 years which brought
drastic changes in the world. The USSR, which had totake the primary responsibility for the Chernobyl
accident, disappeared at the end of 1991. ″JUNEN
HITO-MUKASHI″ also means that we tend to forget
events in the past. The concern of the world toChernobyl seems to become gradually diminishing as
time goes on. However, a vast amount ofcontaminated territories remains and will remain
regardless of the main events in the world (Table 1).
The sufferers by the Chernobyl accident are
categorized into the followings:
Staffs of the Chernobyl NPP and firemen directly
involved in the accident: 1,000 - 2,000 persons
Liquidators who worked for elimination of theconsequences of the accident (including soldiers
and workers for construction of so-calledIn April 1996, at the time of the 10th anniversaryof the Chernobyl accident, an international conference
was held in Vienna by IAEA together with EC andWHO [6]. One of main purposes of the conference
was announced to distinguish ′myths′ and′speculations′ from scientific facts about theconsequences of the Chernobyl accident. Conclusionsof the conference can be summarized as follows.
<The only long-term health effect that could beobserved so far due to the Chernobyl accident was theincrease of thyroid cancer among inhabitants around
Chernobyl. Other health effects were difficult to beobserved even with following-up investigations ofwide-scale. Reports indicating health deterioration ofChernobyl sufferers were made by scientists in theTable 1. Areas contaminated with 137Cs in three affected countries, km2 [1].
Level of 137Cs density (Ci/km2)
1-5

5 - 1515 - 40>40>1 total

Russia48,800

5,720

2,100

300

56,920Belarus29,900

10,200

4,200

2,200

46,500

Ukraine37,200

3,200

900

600

41,900Total

115,900

19,120

7,200

3,100

145,320- According to Chernobyl laws in these countries, the contaminated territories are divided into the following
categories depending on 137Cs density: higher than 40 Ci/km2 - zone of alienation, 15-40 Ci/km2 - zone of obligatory
resettlement, 5-15 Ci/km2 - zone of guaranteed voluntary resettlement, 1-5 Ci/km2 - zone of radiation control.

Table 2. Number of people living in the contaminated territory, thousands of persons.
Level of 137Cs density (Ci/km2)
Country (year of data)
1-55 - 15
15 - 40>40>1 total
Russia(1991.1.1) [2]
1,883
347
93
2,323
Belarus(1995) [3]1,485314
41
0.283
1,840
Ukraine(1995.1.1) [4]1,732653
192,404
Total
5,100
1,314
153
0.283
6,567
- According to the GOSPLAN report in 1990 [5], the numbers of residents in the area of 15-40 Ci/km2 and over 40
Ci/km2 were 234 thousands and 33.8 thousands, respectively. So, 115 thousands were at least resettled since 1990.

1

works, our group has been providing the public withinformation about risks accompanied with thecommercial use of nuclear energy.
It was quite natural for us, when the Chernobyl
accident happened, to begin one more task toinvestigate its consequences from our point of view.
We measured radioactivity from Chernobyl in Japan,
collected information on all aspects of the accident
including contamination data from all over the world,and made the assessment of radioactivities released by
the accident [12-15].
By the end of 1986, we succeeded in making
outline of radioactive contamination in the northernhemisphere except in the territory of the former USSR.
Our estimates of irradiation dose in Japan due tofallouts from Chernobyl are shown in Table 3. Table 4
includes our assessment of released activities made in
the first years after the accident. Although the resultsof our analysis, which was made based on small data
presented in the 1986 USSR report on the accident[16], indicated a very high level of contamination in
the territory of Belarus, we did not have measures toconfirm it for several years. The fact should be kept inmind that there was a vacant period of information forabout three years, when we retrospectively try toinvestigate the Chernobyl accident.
In the process of perestroika and glasnost within
the USSR, the first detailed map of contamination waspublished in Belarus in February 1989 [17]. A vast
amount of contaminated areas showed the validity of
our assessment in the first years. We were also
surprised to know that high levels of contamination
extended even to 200 - 300 km from the Chernobyl
site, which could not be supposed from our accident
assessment for light water reactors.
Imanaka and his colleague Seo (deceased in 1994)
made the first visit to the USSR in the summer of1990[18,19].
Throughthevisit
toMoscow/Minsk/Kyiv, we knew that there wereamounts of data about radioactive contamination
taken by Soviet scientists at the initial stage of theaffected countries, but they were not reliable from thescientific point of view.>
We can interpret the above conclusion as follows:
the health effects of the Chernobyl accident were verysmall except thyroid cancer, mortality of which isrelatively low, although the Chernobyl accident was
the worst one. The fact in 1991 at the conference ofInternational Chernobyl Project by IAEA [7],however, should be remembered that experts of IAEA
neglected protests of Belarussian and Ukrainianscientists insisting serious increase of child thyroid
diseases around Chernobyl against the conclusion of
the International Chernobyl Project that there was nohealth effect there. Five years later the same experts of
IAEA had to recognize ′myth′ of thyroid diseases tobe facts.
In this report of our international collaborative
project, we have included reports and information thatthe experts of IAEA would see as ′myths′ or′speculations′. The present author believes that there
are ′myths′ reflecting the truth, and that one importanttask of science is to find out the truth hidden behindfragmentary information.
By the way, during these years the number ofnuclear power plants in Japan increased to 53 reactors(total 45GWe) in January 1998 from 33 reactors (total25 GWe) at the moment of the Chernobyl accident.
Activity of Japanese members before thecollaborative project
The Nuclear Safety Research Group of Research
Reactor Institute, Kyoto University (KURRI), towhich the present author belongs, has been working
on safety problems of nuclear facilities for more than
20 years. Main tasks of our group have been thefollowings: analyses of engineering problems of PWR
and other reactors, assessment of radiologicalconsequences by hypothetical severe accidents atnuclear power plants in Japan, measurements ofradioactive contamination in the environment,investigation of the Three Mile Island NPP accident
in March 1979 in the USA, etc. [8-11]. Through these

Table 3. Estimates of irradiation dose in Japan due to fallouts from Chernobyl for the 1st year
after the accident [13].
Thyroid Organ Dose, µSv
Path
Total
Inhalation
Tap water
Leafy vegetable
Milk
Children60
14290
43~400Adults
30
4110
6~150
Total Body Dose: µSv
External
Internal
Total
CloudGround
Inhalation Tap water Leafy vegetable
Milk
Children0.02
30.20.070.7
1.2~5Adults
0.02
30.2
0.04
0.5
0.4~42

Table 4. Estimates of released radioactivity of major nuclides by the Chernobyl accident.
Estimated released radioactivity, MCi
Inventory,
USSR
reportNuclideHalf life
Seo [14]
Dobrynin [21]ImanakaMCi[16](1988)(1993)
1993 [20](1986)
I-131
8.05 d36.5
7.3 (20)*
25.40
19.0
17.0
Cs-13730.2 y7.7
1.0 (13)
4.35
2.3
2.5
Ru-10339.3 d110
3.2 (2.9)
10.40
3.8
3.3
Zr-95
64 d
119
3.8 (3.2)
5.60
4.0
5.9Ce-144
284 d
85.7
2.4 (2.8)
4.60
3.6
3.4
- All activities are decay-normalized to values on May 6, 1986.
- Values of reactor inventory are cited from the 1986 USSR report.
* Values in () are released percentage to inventory.

between members to preparing reports by eachmember for his own themes.
In 1995 we received a new research grant under
the title, ″Investigation of Research Activities about
the Radiological Consequences of the Chernobyl
Accident in Russia, Belarus and Ukraine after theCollapse of the USSR″. At the time of the application
to the Toyota foundation, the members were limited toImanaka and Matsko in Minsk in order to keep aflexibility of the project. Then, three members, Koide
at KURRI, Ryabzev in Moscow and Nasvit in Kyiv
joined the project. The members in CIS countries
were expected to make their report concerning thesituation of research activities in each country about
the radiological consequences of the Chernobylaccident. In addition, Imanaka asked preparation of
special reports for our project to several scientists whoare engaged in interesting studies. Through the 1995
project, we succeeded in making 8 reports, including
4 special reports. Four of them were published in
English or Japanese [22-25].
In 1996 we succeeded in extending our research
grant under the title, ″Investigation of Research
Activities about Radiological Consequences of theChernobyl Accident and Social Activities to Assist Its
Sufferers in Russia, Belarus and Ukraine″. A theme
concerning social aspects of Chernobyl problems wasadded in this year. The following 4 new members
joined the project; Malko in Minsk, Yaroshinskaya inMoscow, Tykhyi in Kyiv and Sugiura in Minsk. InJanuary 1997, we had a meeting of all members inMoscow to discuss the contents of the project anddecided the following 5 sub-themes (names ofresponsible member):A. General description of research activities
concerning the radiological consequences of theaccident (Matsko, Ryabzev, Nasvit, Malko).
B. Investigation of the current situation of
epidemiological studies in each country (Matsko,Ryabzev, Nasvit).
C. Investigation of acute radiation syndrome among
inhabitants around Chernobyl (Yaroshinskaya,accident.
″Toyota″″ project in 1993-1994The collapse of the USSR at the end of 1991
changed the situation around Chernobyl problems.
This allowed as a possibility to start a collaborative
work with former USSR scientists.
In 1993, we succeeded in getting a research grantof the Toyota foundation for a collaborative projectwith Belarussian scientists under the title,″Radioactivity Releases from the Chernobyl-4
Accident and Dose Estimates in Its Early Stage″(leader Seo T.). The Japanese side consisted of 4
members of the Nuclear Safety Research Group. TheBelarussian side includes 5 scientists of Academy ofSciences of Belarus, Belarussian State University andHydrometeorology Committee. The Japanese side wasgoing to refine the old analysis of contamination
patterns around Chernobyl and reevaluate released
activities on the basis of the new data that wereobtained from the Belarussian side. In the course ofthis project, frankly speaking, the Japanese side met a
lot of difficulties: differences in the tradition how topromote cooperative researches, difficulties to keep
close communication (e-mail was not available, airmail was not a sure way, fax was relatively expensive),differences in the tradition how to manage the finance,etc. In addition, the team leader, Seo T. unexpectedly
died of lung cancer during the project. In spite ofthese difficulties, some valuable results were obtainedby this first project [20]. Our new estimates ofreleased radioactivities are shown in Table 4 together
with old values and by others. Our new estimates are
consistent with the estimation by Dobrynin et.al. [21].
″Toyota″″ project in 1995-1997
We have passed over the application to the Toyota
foundation in 1994 and rearranged the frame ofcooperation during this period. Considering theexperiences through the first project, the base ofcollaboration was converted from a relation between
groups of equal partnership into a network of personal
relation coordinated by Imanaka. The way of working
was also changed from face-to-face discussion

3April 8-12, 1996, STI/PUB/1001.
7. IAC/IAEA, The International Chernobyl Project: AnOverview, Technical Report, Proceedings of anInternational Conference, IAEA, 1991.
8. Kume S. et.al., Defective Safety Devices of Nuclear
Power Plants, Daisanshokan, Tokyo, 1979 (inJapanese).
9. Kobayashi K., Fast Breeder Reactor MONJU:Dreams and Actuality of a Giant Nuclear Technology,Nanatsumori-shokan, Tokyo, 1994 (in Japanese).
10. Seo T. The Nuclear Power Plant Accident: What
Are You Going to Do Then?, Fubaisha, Nagoya, 1995(in Japanese).
11. Koide H. et.al., Environment and Human Society:Lessons from Pollution, Tpkyo-kyogakusha, 1995 (inJapanese).
12. Imanaka T. and Koide H, Fallout in Japan from
Chernobyl, J. Environ. Radioactivity 4 (1986)149-53.
13. Imanaka T., Irradiation Dose in Japan due to theRadioactive Contamination from Chernobyl, Keisemi
Dec1986, pp.120-130 (in Japanese)
14. Seo T. et.al., Released Radioactivity by the
Chernobyl Accident, Kagaku, 58 No.2 (1988)108-117(in Japanese).
15. Imanaka T., Radioactive Contamination and theSufferers by the Chernobyl Accident (1)-(4),Gijutsu-to-Ningen, May-Aug 1992 (in Japanese).
16. USSR State Committee on the Utilization of Atomic
Energy, Report to IAEA, Aug 1986.
17. Sovetskaya Belorussiya, Feb 9, 1989 (in Russian).
18. Seo T., Diary during Travel to Chernobyl, Fubaisha,Nagoya, 1992 (in Japanese).
19. Imanaka T. et.al., Radioactivity in the Highly
Contaminated Area near the Chernobyl Site,J.Radioanal.Nucl.Chem., 154 (1991)111-9.
20. Imanaka T. et.al., The Final Report of the Research
Grant of the Toyota Foundation in 1993 (in Japanese).
21. Dobrynin
Yu.L.
et.al.,
Data
Verification
Methodology and New Data for Chernobyl Source
Term, Radiation Prot. Dosimetry, 50 (1993)307-10.
22. Matsko V.P. and Imanaka T., J. Health Physics 32(1997) 81-96.
23. Ryabtsev I.A. and Imanaka T., J. Health Physics, 32(1997)211-25.
24. Imanaka T., Recent Atmosphere in Minsk (4),Gijutsu-to-Ningen, Jun 1996, pp.23-33 (in Japanese).
25. Yaroshinskaya A., Gijutsu-to-Ningen, Apr 1997
pp.28-34 (in Japanese)
26. Sugenoya A. et.al., ibid., Nov 1997 pp.36-40 (inJapanese).
27. Lazjuk G. et.al, ibid., Jan/Feb 1998, pp.26-32 8inJapanese).
28. Lupandin V., ibid., Mar 1998, pp.58-68 (inJapanese)
29. Tykhyi V., ibid., Apr 1998, (in Japanese) inpreparation.

Imanaka, Koide).
D. Overview of social activities to assist sufferers by
the accident (Yaroshinskaya, Malko, Tykhyi,Sugiura).
E. Preparation of special reports of interesting studies(Imanaka and all others).
The 1996 project formally finished at the end ofOctober 1997.
Here in this KURRI report we present 32 papers
we could prepare through the collaborative works in1995-1997. They are classified into the following
categories by the report number in CONTENTS:- Member reports in the 1995 project; 4, 5, 6 and 7,- Special reports in the 1995 project; 8, 11, 22 and 25,- Member reports in the 1996 project; 1, 2, 13, 14, 15,16, 28, 29, 30 and 32,
Special reports in the 1996 project; 3, 9, 10, 12, 17, 18,
19, 20, 21, 23, 24, 26, 27 and 31.
Besides already mentioned, No. 19 by Sugenoya,
No. 21 by Lazjuk and No.12 by Lupandin were
published in Japanese [26-28]. No. 28 by Tykhyi will
be published soon [29].
Acknowledgement
Our work was supported by the research grant of
the Toyota foundation (93-II-260, 95-B3-031,96-B3-034). We are deeply grateful to Kusumi-san of
the foundation for his encouragement and advises toour project. Kamio-san of Catalogue House Inc. isalso acknowledged for her kind arrangement for ourtrip to CIS. Ignatovich A. and Malko V. should begreatly acknowledged for their contribution oftranslating Russian manuscripts into English. Imanaka
expresses his deep gratitude to his colleagues of
Kobayashi-san, Ebisawa-san and Kawano-san for
their continuous concern and encouragement to ourproject. It should be especially noted that ourcollaborative project was started by the initiative ofthe late Seo-san.
References
1. Izrael Yu.A. et.al., Global and Regional Radioactive
Contamination with Cs137 in the European Territoryof the former USSR, Meteorology and Hydrology,
1994, No.5, pp.5-9 (in Russian)
2. Stepanenko V.F. et.al., Proc. 2nd Hiroshima Intern.
Symp. July 23-25, 1996, ed. Hoshi M., RIRBM,
Hiroshima Univ., pp.31-84.
3. Malko M.V., No. 29 of this report.
4. Ten Years after the Accident at the Chernobyl NPP;
National Report of Ukraine, MinChernobyl, 1996 (inRussian).
5. Firsova D., Chernobyl: Catastrophe Continues,Moskva, 1990, No.11 pp.138-48 (in Russian)
6. IAEA, One Decade after Chernobyl: Summing up theConsequences of the Accident: Proc. Intern. Conf.,

4