Tubular radiation source measurement for verification of the FP plate-out activities in the OGL-1 primary cooling system

Activities and distribution of fission products (FPs), which plated-out in the primary cooling system of the High Temperature Engineering Test Reactor (HTTR), are important for the design, maintenance and accident analysis of the reactor. In the department of JMTR project, the distribution of FPs plated-out on inner surface of the primary cooling system piping of the high temperature gas cooling in-pile loop facility (OGL-1) has been measured during reactor operation and after shutdown. The OGL-1 is utilized for irradiation tests of the HTTR fuels. It became clear in the measurement that a large amount of 137Cs plated-out on the piping whose operation temperature was around 500degC, and 137Cs plated-out on the 500degC piping was released with decrease of FPs release from fuel to primary gas and redeposited on the piping in temperature range of 200-300degC. It was also found that 131I release rate from HTTR fuels in irradiation was 2x10-7-4x10-5. In this report, tubular radiation source measurement for verification of the FP plated-out activities in the OGL-1 primary cooling system was shown. Measurement error of plated-out activities in the OGL-1 primary cooling system was evaluated to be within 20%. (author)