The average value of annual 7Be deposition in Japan from 1989 to 1995 was 1, 500Bq/m2, the overall range being 290-6, 500Bq/m2. The 7Be concentration in rain obtained by dividing the annual amount of 7Be deposition by annual precipitation was 0.2-2.8 Bq/l, giving an average of 1.0±0.4Bq/l. A large amount of 7Be deposition was found along the Japan Sea, such as in the prefectures of Ishikawa, Toyama, and Fukui, while lesser amounts were found along the Pacific Ocean, and the lowest amounts were found inland and/or in the Setonaikai area. In the areas along the Japan Sea, both precipitation and 7Be concentration in the rain peak during the winter months, which causes large amounts of 7Be to be deposited. Along the Pacific Ocean-side of eastern Japan, an increase in 7Be deposition was observed during spring and autumn, while 7Be deposition in western Japan was in the spring. In the basins of central Japan, as well as in the Setouchi district, only slight 7Be deposition was seen throughout the year.
Dose rates due to cosmic rays at all municipalities in Japan are estimated using a computer code (PLOTINUS) developed by K. O'BRIEN. Latitude, longitude and altitude data for all municipalities are assumed to be represented by the location of the city office and categorized into 417 data sets every degree for latitude, every two degrees for longitude, and every 50-m for altitude as input data for computation. The outputs for each cosmic ray component are grouped into two categories, ionizing component including photons and neutron component. The population weighted average dose in Japan is estimated to be 29.2nSv h-1 for the ionizing component, 6.1nSv h-1 for the neutron component and 35.3nSv h-1 for the total. The highest value among prefecture averages is found in Nagano Prefecture to be 44.0nSv h-1 although it is not located at the highest latitude but at the highest altitude. Based on the assumption in the UNSCEAR 2000 Report for dose estimation due to cosmic rays, the doses in Japan are estimated to be 0.21mSv a-1 for the ionizing component, 0.045mSv a-1 for the neutron component and 0.26mSv a-1 for the total.
The first large-scale commercial nuclear fuel cycle facilities in Japan are now under construction in Rokkasho-mura, Aomori Prefecture. Prior to the implementation of operations, we conducted this study to collect sociological data in relation to the estimation of radiation dose by radionuclides released from the facilities. Food intake in Aomori Prefecture was surveyed by dividing the prefecture into four areas and having the residents answer a questionnaire. The results of the survey in the final area (Shimokita Peninsula area) are reported in this paper, together with the combined results for the whole prefecture. The 50 families surveyed in Shimokita Peninsula area were divided into three different groups based on primary occupation: fishery worker, farmer and other occupation. The average total daily food consumption of the whole survey group was 2, 238 grams/day/person (g/d/p), and showed no significant seasonal variation. The consumption rates for marine, agricultural and livestock products were 244, 1, 205 and 372g/d/p, respectively, and were relatively constant year-round. The consumption rate of other products was 417g/d/p, with a slightly higher value during the summer. The category of other products included confectioneries, drinks and seasonings. The foods with the highest consumption rates in the area were: (a) squid, salmon and wakame among marine products, (b) rice, radish, tofu (soybean curd), cucumber, apple and potato among agricultural products, and (c) milk, eggs and pork among livestock products. The average total daily food consumption rate in the whole prefecture was 2, 117g/d/p, which was weighted by proportion of types of occupations in Aomori Prefecture. Some slight but statistically significant differences were recognized in the consumption patterns of families as determined by occupation and area of residency in the prefecture. The consumption of marine products was the highest for fishery workers, and that of agricultural products was higher for farmers than fishery workers. The food consumption data were compared with the results of a nationwide nutrition survey carried out by the Japanese Ministry of Health and Welfare. The present intakes were re-calculated applying the method used in the national nutrition survey for comparison. The re-calculated results were approximately 10% higher than the national average. This indicates that specific data are important for evaluating food intake in local areas. Food intake rates were used to assess the safety of the reprocessing plant in Rokkasho. In comparing the present data with that used in the safety assessment, the present results were mostly lower than that applied in the assessment.