Plate-out distribution of 137Cs in the OGL-1 primary loop

In order to reflect on safety evaluation of HTTR (High Temperature Engineering Test Reactor), measurements of fission products plate-out distribution have been done on the primary circuit of OGL-1 (Oarai Gas Loop No.1) which has been operated in the simular gas flow condition with the HTTR. The measurements have been performed since 46th till 73rd operation cycles of the JMTR (Japan Materials Testing Reactor) in which from 3rd to 9th fuel specimens of OGL-1 were irradiated. It became clear that 137Cs plated-out well on the piping at 400 ∼ 500 deg C. It was also observed that 137Cs released from the pipe at higher than 500 deg C and deposited again on the pipe at lower than 400 deg C when the release rate of 137Cs from irradiation fuel decreased. (author)