Predicting Spectrum Averaged Cross Sections in Prompt Fission Neutron Fields

Abstract

New non-model evaluations of prompt fission neutron spectra (PFNS) for thermal neutron induced fission on 233,235U and 239Pu targets have been recently proposed based on an available experimental database. The evaluated PFNS have been validated using measured spectrum averaged cross sections (SACS) and evaluated dosimetry cross sections from the International Reactor Dosimetry and Fusion File v1.05 library. A systematic is derived that predicts the SACS ratio in different PFNS as a function of the E50 % energy for each reaction. The proposed systematic is used to predict difficult to measure or discrepant values of (n,p) and (n,2n) threshold dosimetry reactions in 235U(nth,f) and 252Cf(sf) prompt fission neutron fields based on existing measurements. Parabolic dependence of selected SACS on the average energy of the neutron field is proposed and used to predict the expected SACS in the 239Pu(nth,f) prompt fission neutron field. Independence of the SACS ratio on the neutron field is experimentally confirmed for reactions with E50 % approximately equal to the PFNS average energy. Such independence is used to predict SACS for 235U(n,f), 239Pu(n,f), 10B(n,α), and 237Np(n,f) reactions in 233U(nth,f) and 239Pu(nth,f) prompt fission neutron fields.