Non-destructive measurement method for the amount of fission product gas released

Purpose: To perform, in a reactor site, non-destructive measurement of the amount of fission product gas released within a nuclear fuel element without requiring a prolonged cooling period and with high sensitivity. Method: A fission product gas is radiated by re-irradiating the plenum section within an irradiated fuel element by thermal neutrons, etc. Then, of gamma rays released from the fission product gas radiated, the intensity of gamma rays having an energy not affected by the induced radioactivity of the plenum spring and zircaloy-2 clad tubes, namely, gamma rays in the vicinity of about 2560 KeV released by krypton 87 is measured. From a measured value thus obtained the quantity of krypton-86 is know and the amount of fission product gas can be evaluated. According to this method, unlike the measurement of gamma rays of krypton-85, the non-destructive measurement can be made without requiring a long period of cooling after irradiation. (Kamimura, M.)