Japan Nuclear Fuel Limited has carried out environmental monitoring in order to ascertain that the dose of radiation to which the public is exposed around the Rokkasho Reprocessing Plant (RRP) is much lower than the annual dose limit. This report presents the point of view of selection of the monitoring items for dose estimation and the point of view of the dose estimation from the monitoring results. As measurement items of the monitoring for dose estimation, the objects and nuclides are selected in consideration of main exposure pathways. Estimation of the public dose is based on these monitoring data. However, when it is difficult to make such estimation, it is calculated by the dose estimation model, using discharge data from the RRP and meteorological data around the site, etc. In the monitoring items for dose estimation, in 85Kr, although frequency of appearance was very few, a transitory variation considered to be effect of the facilities accompanied by the active testing was observed. Except the monitoring items for dose estimation, the results considered to be effect by the discharge from the facilities were obtained in the samples from rain water and lake water. The effective dose from April, 2007 to March, 2008 by RRP was estimated about 0.0013 mSv/year from the measurement results of discharge, etc.
Radon (222Rn) generated within the grains of rocks, soils, building materials and other materials by the radioactive decay of radium (226Ra) can migrate to the atmosphere. This paper reviews the emanation coefficient, diffusion coefficient, and exhalation rate, and the factors that control the rate at which radon can enter atmosphere. The emanation coefficient which is the fraction of radon generated within the grains of materials and escaped to the pore space, varied from 2.1 to 32% for rocks, from 0.14 to 80% for soil, and from 0.10 to 58% in case of building materials. In addition, measurement methods used to evaluate emanation coefficient and its influence factors are also reviewed. The diffusion of radon is a process determined by radon concentration gradient across the radon sources and the surrounding air. The effective diffusion coefficient of some materials is summarized. Moreover, the radon exhalation rate process and the main influencing factors on the variation of exhalation rate data are reviewed. The exhalation rate varied in the range of 0.11 to 80 mBq m-2 s-1, 2.0×10-3 to 5.0×104 mBq m-2 s-1 and 4.0×10-3 to 5.0×101 mBq m-2 s-1 for rocks, soils and building materials, respectively.
Long-term fluctuation of the yield and ash content of muscle dissected from marine organisms were investigated for establishing a standard of pretreatment procedure based on the data on radioactivity analyses of various biological samples such as fish and shellfish which were collected from 15 sea areas adjacent to nuclear power stations in Japan. The muscle yield in terms of the percentage of muscle weight to the whole raw weight as well as ash content were obtained for 53 species during the period from 1983 to 2007 and subjected to a statistical scrutiny. There was no significant change in general in the muscle yield and ash content, with the exception of some species due to modification of pretreatment method. However those exceptions would not have resulted in a critical change of the level of 137Cs concentration in marine organisms as a whole in the sea areas of concern, because it was usually expressed as the average for three different species in the present study. The ash content would be useful, nevertheless, as an index to assure the comparability of sample preparation technique. The 137Cs radioactivity concentration in muscle of marine organisms gradually decreased year by year from 1990 after the Chernobyl nuclear accident, and would not be more than 0.24 Bq/kg-wet, the maximum level during 2003 to 2007, in the future from the viewpoint of fail-safe approaching.
We surveyed the concentration levels of Transuranium (TRU) nuclides in the effluent discharged from the Tokai Reprocessing Plant (TRP) from 1998 to 2003 for Light Water Reactor (LWR) Fuel Reprocessing. The survey was performed for upcoming the effluent monitoring in Fast Breeder Reactor (FBR) Fuel Reprocessing. It was confirmed that the TRU nuclides concentration discharged from the TRP was 1/150∼1/106 much lower than the concentration limits authorized in governmental notification. Then, we compared the normalized discharge amounts by the unit of generated energy from the TRP with those from the foreign reprocessing plants. As a result, the TRP has reduced the amounts of discharged nuclides, by the order of 1/100-1/107 compared with foreign ones. This survey provided the important and basic data in order to compare the effluent of TRU nuclides in FBR and the present nuclear fuel cycles.