Estimation of adjoint-weighted kinectics parameters in Monte Carlo forward calculations

Abstract

The effective delayed neutron fraction, βeff, and the prompt neutron generation time, Λ, in the point kinetics equation are adjoint-weighted quantities. There have been some approaches to estimating them based on the use of either the constant source adjoint function or the self-consistent adjoint function. In this paper, we derive the MC algorithms for computing βeff and Λ weighted by using two kinds of the adjoint functions that can be obtained from the MC forward eigenvalue calculations. The results of applications for the infinite homogeneous 2-group problems and some critical facilities are compared with analytic solutions and experimental measurements, respectively. It is demonstrated that βeff and Λ from the use of the self-consistent adjoint function as the weighting function agree better with measurements within a 3% error.