Delayed Neutron Precursor Data Uncertainty and Sensitivities in Microscopic Calculations

Abstract

This paper presents an analysis of the uncertainty-weighted sensitivities of the delayed neutron precursor (DNP) group parameters, consisting of half-lives τk and yields νd,k, with their nuclear data. This analysis was conducted using the thermal fission of 235U from various data sets: the International Atomic Energy Agency (IAEA) β-delayed neutron emission database, ENDF/B-VII.1, ENDF/B-VIII.0, JEFF-3.1.1, and JENDL-5.These uncertainty-weighted sensitivities provide a detailed view of which DNPs need more accurate data, particularly for microscopic group parameter formulation and summation calculations. Improving the accuracy of these data is of particular importance for kinetics simulations and microscopic calculations. The microscopic approach for the group parameter calculation, which provides insights into how each DNP contributes to delayed neutron emission, requires accurate nuclear data.The analyses conducted in this work identified individual DNPs with a large impact on the DNP group parameters and large uncertainties in their nuclear data. There are also DNPs that have large uncertainties and that vary significantly between data sets, which also warrant additional attention.This work revealed large discrepancies in the ENDF data sets for 85As, 86As, 100Rb, and 137Sb; the underprediction of the delayed neutron yield νd in JEFF-3.1.1 due to many small discrepancies in various DNPs; and good agreement with experimental and calculated delayed neutron yields when using the JENDL-5 data set.