Applicability of the first-order adjoint-weighted perturbation method for estimating beta-effective sensitivity to nuclear data

This study formulated equations in operator form using the first-order Adjoint-Weighted Perturbation (AWP) method. These equations are designed to calculate the relative change of reactor parameters—such as the multiplication factor (k), general reaction rates, and the effective delayed neutron fraction (βeff)—in a perturbed system during a steady-state Monte Carlo eigenvalue calculation. A new module for calculating the relative change in βeff was specifically implemented in McCARD, a continuous-energy neutron transport Monte Carlo code. This module was applied to a two-group infinite homogeneous problem, as well as the GODIVA and KRUSTY problems from the ICSBEP benchmark suite, to verify its performance. The results obtained from the AWP method were compared with analytic solutions or those from the Direct Subtraction method to verify its applicability and limitations.