Possible Origin of the Gamma-ray Discrepancy in the Summation Calculations of Fission Product Decay Heat

• Published in: Journal of nuclear science and technology Vol. 36; no. 2; pp. 135 - 142
• Main Authors: YOSHIDA, Tadashi, TACHIBANA, Takahiro, STORRER, François, OYAMATSU, Kazuhiro, KATAKURA, Jun-ichi
• Format: Journal Article
• Language: English
• Published: Tokyo Taylor & Francis 01.02.1999; Atomic Energy Society of Japan
• Subjects: after-heat; Applied sciences; beta decay; beta-strength function; branching ratios; decay heat; Energy; Energy. Thermal use of fuels; Exact sciences and technology; Fission nuclear power plants; fission products; fission yield; gross theory; Installations for energy generation and conversion: thermal and electrical energy; loss of coolant; Gamma radiation; Fission product; Reactor core; Irradiated nuclear fuel; Heat liberation; Nuclear reactor
• ISSN: 0022-3131; 1881-1248
• DOI: 10.1080/18811248.1999.9726191

In order to identify the origin of the ubiquitous and long-standing discrepancy seen in the γ-ray component of the FP decay heat in the cooling time range 300-3,000 s, a comprehensive analysis of the differences between the summation calculations and the experiments has been carried out. There may be some missing of the β-strength in the high energy region of the FPs in the mass region A=100-110. Especially, 102 Tc, 104 Tc, 105 Tc and 108 Rh are potentially responsible for the γ-ray discrepancy seen in the three major fissioning nuclides, 235 U, 238 U and 239 Pu, systematically. The β-strength functions are theoretically calculated in order to validate this possibility. It is proved that the chance for finding the additional β-strength required to solve the discrepancy is not so large but still exists, and the exact β-feed from Tc to the highly excited levels in Rb should be identified experimentally. Finally, the impact of the β-ray discrepancy on the reactor-core decay heat is evaluated quantitatively for the first time. It may introduce 0.5-1% underestimation of the total FP decay heat from 1 to 2,000 s after reactor shutdown, and the underestimation may reach 3% at the maximum when the γ-ray component of the decay heat is separately taken into consideration.