General Reseach

Safety Analysis Unit

This Unit was established in 1984 as an organ to overview the result of experimental researches relevant to the assessment of environmental radiation risks and to integrate them into a comprehensive and consistent entity in order to provide a scientific basis for control and management of radiation exposure by regulatory bodies. The area of research for safety analysis is illustrated in Fig. 1. The unit consists of three sections: the first section is responsible for compilation of data base with regard to current estimates of (1) doses from environmental radiation sources and (2) biological risk factors, as well as the estimates of social and occupational risk levels (Fig. 2); the second section is responsible for evaluation and development of methodology, mainly with regard to computer codes for dose and risk assessment as well as epidemiological approaches; and the third section deals with risk analysis utilizing currently available methods and data. Main subject being pursed by this section are (1) quantitative assessment of risk perception by the public. (2) formulation of health effects models for barious scenarios of radiation exposure, (3) cost-benefit evaluation of various energy sources. (4) assessment of does from environmental radiation with emphasis on the internally deposited naturally occurring radionuclides.

Some examples are given on the results of researches relevant to risk analysis as follows.

[Fig. 1] Structure of risk analysis study.
large size image is here. (25 kbyte)

[Fig. 2] Comparision of various risks on a risk scale.
large size image is here. (35 kbyte)

Occupational Risk

Assessment is made on the yearly trend of change in the age-specific accidental fatality rates due to occupational work in seven categories of industries in Japan during the period from 1973 to 1990. Accidental deaths in occupational workers showed a rather wide distribuiton ranging from 1000-1500 per million per year in mining to tens per million per year in manufacturing or electricity and others supply, all of which indicated tendency of decrease by year (Fig. 3). Age-specific fatality rates showed a trend of increase with the age in all pccupations except for fisheries. Fatality rates from occupational accidents in various industries in Japan are within the same order of levels which were observed in order countries as cited in ICRP Reports (Publ. 27 & 45).

[Fig. 3] Trend in the death rates per million per year for seven industries in Japan (1973-1990)
large size image is here. (34 kbyte)

Radioligical Consequences of the Chernobyl Accident

Assessment was made on the health consequences in the Japanese population of 131I, 134Cs and 137Cs due to the Chernobyl nuclear power plant accident.

thyroid dose from 131I was estimated to be 38¦ĚSv per year as the population weighted average. The critical group was found to be that of 10 years old. The internal dose from 137Cs was estimated to be 0.6¦ĚSv as the population weighted average. This dose corresponds to 0.35% of the internal dose of 170 ¦ĚSv per year from the body burden of natural 40K. The results are indicated in Fig. 4 in terms of effective dose equivalent received during one year after the accident by each of the three age group and the population as a whole for deferent intake routes and the total.

[Fig. 4] Age-related effective dose equivalent for japanese form 131I 134Cs and 137Cs for one year after the Chernobyl nuclear power plant accident.
large size image is here. (18 kbyte)

Indoor Radon

Naturally occurring radon and its daughters indoors contribute the largest dose to the general population. A nationwide survey of radon concentration in dwellings is conducted since 1985 to 1991,covering about 6,300 houses throughout Japan to obtain the population dose due to radon progeny so as to compare its risk with others. The results of the entire country with a median value of 23 Bq m-3 and a geometric standard deviation of 1.6. The average indoor radon concentration by prefecture ranged from 19 to 57 Bq m-3 with the highest in Hiroshima lacerated in the Chugoku district, geologically a typical granite region in the western part of Japan (Fig. 5).

In the view of the possibly significant contribution of Rn-220 to lung the dose in certain areas of Japan, a new passive dosimeter was developed which can discriminatively measure Rn-220. This dosemeter has now been used to evaluate Rn-220 concentration both indoors and outdoors.

[Fig. 5] Distribution of indoor radon concentration (interim results)
large size image is here. (35 kbyte)

Major Publications

Iwasaki, T., Nishizawa, K.: Risk of the occupational injuries in industry of Japan. II. Yearly trend in the occupational deaths between 1984-1990 in seven categories of industry, J.Jpn. Health Phys. Soc., 28 173-178, 1993.
Iwasaki, T., Ichikawa, M., Takeda, a. and Kobayashi, S. Data Base for Occupational Health Risk in Japan. Incidence of Accidental Injury and Death (1970-1983), Safety Analysis Report, NIRS-M-59, 1986.
Kobayashi, S. et al. Nation wide survey of indoor radon concentration in Japan. Proceeding of the Third International Symposium on Advanced Nuclear Energy Research. JAERI, Mito JAPAN, 63-67, 1991.
Uchiyama, M. and Kobayashi,S. Increased Body Burden of Radiocesium in Four Cases of Japanese after the Chernobyl Reactor Accident. J. Nucl. Scr. Technol., 25, 413-416, 1988.
Uchiyama, M., Suzuki, Y., Nakamura, R., Ichikawa, R. and Shiraishi, Y. Effect on International dose to Thyroid from Radioiodine in Foodstuff by Rat. In Age-related Factors in Radionuclide Metabolism and Dosimetry (ed. Gerber G. B. et al. ) Martinus Nijhoff Publishers, DORDRE CHT/BOSTON?LANCASTER, 1987.
Uchiyama, M., Nakamura, Y., Kankura, T., Iwasaki, T., Fujimoto, K., and Kobayashi, S. Environmental and Health Consequences in Japan due to the Accident at Chernobyl Nuclear Reactor Plant. Safety Analysis Report, NIRS-M-69, 1988.

Home Page

General Reseach