Decay heat calculations based on theoretical estimation of average beta-and gamma-energies released from short-lived fission products

Abstract

Fission product decay heat of235U was calculated for short cooling-time on the basis of a preliminary version of a new decay data library recently completed by the Japanese Nuclear Data Committee. It was shown that a full adoption of recent publications of decay schemes to derive average energies of β-and γ-rays, Ēβ and Ēγ, leads to a large underestimation of the γ-ray component of the decay heat and to an overestimation of the β-ray component. In order to remedy this, theoretical values of Ēβ and Ēγ were introduced for high Q-value decays, which were obtained with a gross theory of β-decay. It improved remarkably the agreement between calculation and experiment not only for the235U decay heat but for239Pu and241Pu as well. It was concluded that a large part of decay schemes recently published for high Q-value nuclides are inappropriate to use in calculations of Ēβ and Ēγ, because they fail to reproduce the effect of β-strengths at high excitations, which makes Ēβ small and Ēγ large. The use of the gross theory introduces this effect correctly into the values of Ēβ and Ēγ and, hence, leads to a quite good prediction of both β-and γ-ray components of the decay heat. © 1981 Taylor and Francis Group, LLC.