ICONE23-1403 EXAMINATION OF RADIOACTIVITY DETERMINATION METHOD FOR RADIOACTIVE WASTE GENERATED FROM THE ROKKASHO REPROCESSING PLANT

Abstract

The reprocessing of spent nuclear fuels at the Rokkasho reprocessing plant generates radioactive wastes in solid and liquid forms. These wastes contain a mixture of radioactive nuclides such as Transuranium (TRU) elements, fission products (FP), and corrosion products (CP). The waste processing methods prior to disposal depend upon the waste characteristics (solid, liquid, or gas), and the disposal methods (shallow land disposal at a few tens of meters below ground level, mid-depth disposal at 50 to 100 meters below ground level, or geological disposal at more than 300 meters below ground level) depend upon the type and extent of radioactivity in Japan. In the Rokkasho waste management program, radioactive waste is segregated into vitrified high-level liquid waste, iodine waste absorbed on silver, waste from cutting spent fuel assemblies, low-level liquid waste, and miscellaneous solid waste. The last one is difficult to characterize as this waste is generated from various locations in the plant. Japan Nuclear Fuel Limited (JNFL) is developing a method for determining the radioactivity of radioactive waste generated from the Rokkasho Reprocessing Plant. Miscellaneous solid waste in particular is generated in large volumes and has a wide distribution of radioactivity. Therefore, the establishment of a radioactivity determination method for this waste is an urgent issue. Important nuclides were selected from the viewpoint of waste classification for individual disposal and safety assessments. The behavior of some important nuclides at the Rokkasho Reprocessing Plant, such as C-14, Sr-90, Tc-99, I-129 and actinides, was examined. A radionuclide inventory of the spent nuclear fuel was calculated by combustion calculation code ORIGEN 2.2, and nuclide compositions at each processing line were evaluated by using the "Reprocessing Process Activity Balance Evaluation System" under development by JGC Corporation. As a result, the "Reference Nuclide Spectral Method" can be applied to miscellaneous solid waste as if the Rokkasho Reprocessing Plant is sectioned into several areas.