Analysis of Uncertainties in Summation Calculations of Decay Heat Using JNDC FP Nuclear Data Library.

Abstract

Uncertainties of decay heat summation calculations are derived for the thermal fission of 235 U and 239 Pu and the fast fission of 238 U through sensitivity analyses using data given in the JNDC FP nuclear data library. The uncertainties analyzed are those relevant to decay energies, fission yields and decay constants among the nuclear data contained in the summation calculation. For nuclides lacking complete experimental data, the uncertainties of the decay energies are theoretically calculated. Thus analyzed, the maximum uncertainties of burst fission are 2.8% for 235 U, 3.2% for 239 Pu and 4.2% for 238 U in the range of cooling time between 1 and 10 9 s, and in the case of infinite irradiation, the corresponding level of maximum uncertainty is below 1.6% for all three fissioning nuclides.

Uncertainty analyses of decay heat summation calculations using JENDL, JEFF, and ENDF files

“…In the cases of JEFF and ENDF, the uncertainties at 0.1 s are about 8% and go down to about 1% at 10,000 s. The present calculations are for a burst fission. It has been indicated that the uncertainty of the decay heat calculation for finite irradiation is much smaller than that for burst fission [22,23]. Then it is expected that the uncertainty of practical case is much smaller than the present one.…”

“…In the previous analysis using JNDC library [23], the correlation of the yield data was not considered, but the uncertainties of the independent yields were modified to reproduce the uncertainty of the mass yield. When the squares of the uncertainties of the independent yields were summed up in a mass chain, the squared uncertainty of the mass yield was obtained.…”

“…The uncertainty analyses of the decay heat power of the major fissioning nuclides have been performed previously by several authors [20][21][22][23]. The analyses, however, were based on a kind of the simplification of the decay chains or the assumption of the unavailable decay data, as the evaluated decay data were not fully developed at that time.…”

Estimation of239Pu independent and cumulative fission product yields from the chain yield data using a Bayesian technique

“…Increasing demands on reliable fission product yield (FPY) data come primarily from the recent, and growing, fission studies supporting a fundamental understanding of fission physics and for energy applications, such as decay heat calculations [1][2][3], prompt fission neutron spectrum calculations [4][5][6][7], and the fission modeling [8]. The FPY data of 239 Pu at fast and at 14-MeV neutron incident energies were updated recently, and they were released as a part of the evaluated nuclear data library ENDF/B-VII.1 [9] in December 2011.…”

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

“…As a result the committee decided that a conservative margin should be added in order to compensate this effect when the AESJ-recommendation is applied to LOCA analyses of light water reactors. This recommendationC 8 ), proposed by the Atomic Energy Society of Japan (AESJ), is composed of the ascalculated decay-heat values with the JNDC FP Nuclear Data Library-Version 2 (hereafter JNDC-V2) (1) and the pertinent uncertainty analysis ( 9 ). Identifying the origin of this )'-ray discrepancy, therefore, could have considerable impact not only from the academic but also from the legislative, the safety, and the economic points of view.…”