Passive Gamma Spectrometry of Low-Volatile FPs for Accountancy of Special Nuclear Material in Molten Core Material of Fukushima Daiichi Nuclear Power Plant: Numerical Simulation of Leakage Gamma-ray from Molten Core Materials in Hypothetical Canister

摘要

For the nuclear material accountancy of molten core material in Fukushima Daiichi unit 1, 2 and 3(1F1, 1F2 and 1F3), feasibility studies of variety of technologies are being performed. As one of the technologies, feasibility study of passive gamma spectroscopy of low-volatile fission products (FPs) for nuclear material accountancy in molten core material has been performed with reviewing TM1-2 experience, and the correlation of actinides and FPs inventory in core of 1F1, 1F2 and 1F3, considering the sensitivity of axial neutron spectrum, void, burnup, enrichment distribution unique to BWR fuel, and also leakage gamma-ray from molten core materials sphere model. In the present paper, numerical simulation of leakage gamma-ray from molten core materials in hypothetical canister is dealt for determination of radioactivity of low-volatile high-energy emission FPs, which could be utilized for sensitive nuclear material(SNM) quantity estimation coupling with SNM/FPs ratio derived from core inventory calculation.