Theoretical Treatment of the Asymptotic Behavior of Fission Product Decay Heat toward Very Short Cooling-Time

Abstract

The asymptotic behavior of the FP decay heat has been studied toward the very short cooling-time range down to 0.1s after a fission event. For this purpose we apply the second generation of the gross theory of β-decay and estimate the decay properties of short-lived FP nuclides. In order to reproduce the recent measurements adequately, we introduce a new parameter named the Q₀₀-factor, and optimize it in terms of the calculation of the half-lives and the average β- and γ-ray energy releases per decay (E _β- and E _γ-values). The favorable value of the Q₀₀-factor is 1.0 for the half-lives and about 0.4 for the E _β- and E _γ-values. The E _β and E _γ-values thus calculated for the short-lived nuclides, whose β-decay Q-values are larger than 3–4 MeV, guarantee a good reproduction of asymptotic behavior of the measured decay heat toward the very short cooling-time range. Adoption of the present calculation to data files for the summation calculations is recommended from a practical point of view.

KEYWORDS:

• decay heat
• fission products
• beta decay
• beta strength function
• gross theory
• short-lived nuclides
• evaluation method
• evaluated data
• Q-value