Measurement and evaluation of decay heat on the "JOYO" spent fuel; Decay heat of short term cooled spent fuel

Torimaru, Tadahiko; Yoshida, Akihiro ; Nagasaki, Hideaki*; Suzuki, Soju

Decay heat measurement system for the JOYO spent fuels was developed to obtain the decay heat data of the fuel assemblies as a non-destructive examination method. Since then, decay heat of the JOYO Mk-II fuels, which were cooled for more than 70 days, was measured in the spent fuel storage pond. The measurement of the short term cooled spent fuels, which were discharged without cooling in the reactor vessel, was performed in order to obtain the higher decay heat of the spent fuels. The burn-up of the measured fuels was about 60GWd/t, and the shortest cooling time was 24 days. The experimental data were compared with calculated values of ORIGEN2 using new libraries based on latest nuclear data library "JENDL-3.2". The main results are as follows; (1) The measured decay heat at 24 days after the reactor shut down was approximately 1.250.3 kW. (2) The ratio between calculated and experimental values, C/E, was approximately 0.9 and indicated a cool down time dependence. (3) The heat generated by Pu and Am, which amount to 1% of initial composition of fresh fuel, reached 7 - 19% of decay heat at 24-160 days after the reactor shut down.