Unified Monte Carlo: Evaluation, Uncertainty Quantification and Propagation of the Prompt Fission Neutron Spectrum

¹ XCP-5 Division, Los Alamos National Lab, Los Alamos, NM 87545
² T-2 Division, Los Alamos National Lab, Los Alamos, NM 87545
³ Chemical and Nuclear Engineering Department, University of New Mexico, Albuquerque, NM 87131

Abstract

The unified Monte Carlo (UMC) method is used for the quantification of uncertainties associated with the evaluation of the prompt fission neutron spectrum (PFNS) for the n(0.5 MeV)+²³⁹Pu fission reaction and compared to the Kalman filter. Ultimately, the UMC and Kalman filter approaches lead to very similar evaluated PFNS while UMC is also capable of capturing the nonlinearities present in the Los Alamos (LA) model used to calculate the PFNS. Next, the unified Monte Carlo + total Monte Carlo (UMC+TMC) method is implemented to propagate uncertainties from the prior LA model parameters through the Flattop critical assemblies. Due to the fact that cross-experiment correlations are neglected in the present evaluation work, the UMC+TMC method predicts uncertainties in the integral quantities smaller by an order of magnitude or more compared to direct sampling from the posterior LA model parameters. Last, the UMC method is proposed for use as an evaluation tool that can be used with the new prompt fission Monte Carlo Hauser-Feshbach codes that are currently under development.