Trends in americium detection during work in reprocessing facilities

Yoshinaka, Kazuyuki 

In the decommissioning of reprocessing facilities, one of the reasons why a safe storage period is usually not set is that Pu-241 decays into Am-241, which accumulates in the process. As eighteen years have passed since the Tokai Reprocessing Plant finished its operation in 2007, it was considered during recent work that the relative proportion of Am-241 has increased compared to earlier measurements. Therefore, this trend was investigated using records of nuclide analyses conducted during operations. In this investigation, we focused on and discussed the relative proportion of the major nuclide, Cs-137 and Am-241. The survey confirmed that the proportion of Am-241 tended to increase in all process equipment, though the extent of the increase varied depending on the process. In operations related to spent fuel storage systems, decontaminating when moving fuel, and the solubility of Cs-137 have an effect. In recent years, there have even been cases where Am-241 accounted for 80 % to 90 % of the nuclides detected. In operations related to mechanical processes, including the shearing equipment, the increase appears to correspond to the composition of the spent fuel, and the proportion of Am-241 in all nuclides can exceed 40 % in some cases. In operations related to vitrification process, while the increase seems to correspond to the composition of the high-level radioactive waste, the proportion of Am-241 among all nuclides has not exceeded 10 % in any case. In operations related to radioactive liquid waste processes, the precipitate components at the bottom of storage tanks have an effect and Am-241 tends to be detected at a high proportion. In operations related to incineration processing of radioactive solid waste, the overall trend is thought to correspond to the type of waste handled, but relatively high proportions of Am-241 have been detected on internal walls of incinerators and similar areas.