Radiation-induced cancer is one of the key issues in a consequence analysis on a Nuclear Power Plant accident. U. S. Nuclear Regulatory Commission (USNRC) developed the estimation model of those risks for the use of accident consequence analysis in 1980s and 1990s. This model is still used as a leading model in this field. In this paper, we aimed to explore the differences between the results of risk prediction from the model of USNRC and those from a latest model. To achieve this aim, radiation-induced cancer risks were projected based on the Japanese population statistics using the models developed by USNRC and the latest model, which was developed by U. S. Environmental Protection Agency (USEPA). As compared to the model of USEPA, the lifetime attributable risks of all cancers projected by the model of USNRC were about 30% higher for male and about 35% lower for female in both morbidity and mortality. When the sex-averaged values were compared between them, the difference is within 10%.
Intercomparison of in situ gamma spectrometry was organized at a site contaminated by the radioactive fallout that originated from the Fukushima Dai-ichi Nuclear Power Plant accident. This intercomparison was conducted by eight teams from four different institutions, which have contributed to the government-led project to construct distribution maps of radionuclides deposited on the ground soil. The resultant 134Cs and 137Cs inventories evaluated by the participants agreed within 6% of the coefficient of variation, after correction for inhomogeneous distribution of the dose rate in air. The evaluated 40K inventories agreed within 4% of the coefficient of variation. The authors estimated that these results were in good agreement for creating distribution maps of the radionuclide inventory in the ground soil.
Various radionuclides, including radioactive tellurium (Te), were released to the environment by the Fukushima nuclear power plant accident. The total amount of Te-127m released from the power plant was estimated to be 1.1 × 1015 Bq. The radioactive Te may have contributed to the internal radiation dose at the initial stage of the accident. However, data on the environmental behavior of radioactive Te are limited. In this study, therefore, the uptake of Te in plants was investigated. Radishes (Raphanus sativus var. sativus) were cultivated into a nutrient solution, grown for 20-30 days, and then their fine roots (taproots in the plant anatomy) and a part of fleshy roots (hypocotyls in the plant anatomy) were immersed for two hours into nutrient solutions with different Te and Cs concentrations. After soaking, plants were returned to the initial Te- and Cs-free nutrient solution for further maturation. ICP-MS measurements were made to assess concentrations of Te and Cs in the plants' leaves and fleshy roots (the fine roots were removed). Resulting differences among the individual plants were large. The leaf/fleshy root ratios of the concentration of Te and Cs were 0.09-1.14 and 1.59-5.00 on a fresh-matter basis, respectively. Both Te and Cs were absorbed by the radishes through the fine roots. There was a general tendency for Te to be retained in the fleshy roots, whereas Cs was mainly absorbed by the fine roots and then transferred to the leaves.
Three different types of soil were collected at each of three locations: a persimmon orchard, an ume (Prunus mume, so to speak, ‘a Japanese apricot’) orchard, and a paddy field located 50-55 km northwest from Fukushima Daiichi Nuclear Power Plant. The goal was to investigate the involvement of microbes inhabiting these soils on the behavior of 137Cs. The soils were sterilized with gamma ray irradiation for 30 hours (absorbed dose of 60 kGy) or with high-pressure steam (autoclave sterilization) at 121°C for 20 minutes. A radish cultivar (Raphanus sativus var. sativus) was then cultivated in those soils for 45 days, and the harvested taproots and leaves were testing using a Ge semiconductor detector for concentration of 137Cs. The result showed that the concentration of 137Cs in radishes cultivated in the sterilized soils with autoclave sterilization or gamma ray irradiation were significantly higher than in those cultivated in the unsterilized soils. An increase in the plant available 137Cs could be caused by NH4+ arisen from the multiple effects of the structural change of the soil, decomposition of organic matter, and/or extinction of the microbes by sterilization.