A Monte Carlo technique for sensitivity analysis of alpha-eigenvalue with the differential operator sampling method

A method for Monte Carlo sensitivity analyses of alpha-eigenvalue (prompt neutron time decay constant) in a subcritical system is developed using the first-order differential operator sampling (DOS) method. The first-order derivative of alpha-eigenvalue with respect to nuclear data is calculated using the DOS method that includes the capability of calculating perturbed source effect. This paper is an extension of the author's previous work for development of the sensitivity analysis method for k(eff)-eigenvalue. Unlike the conventional Monte Carlo method for alpha-eigenvalue calculation that uses the power iteration of fission sources, this paper introduces a recently developed time source method. The time source method has a weakness for a void-containing subcritical system, which is overcome by assigning a virtual total cross section in the void region. The perturbed source effect, which is caused by the change of nuclear data in a subcritical system, can be calculated by two methods, the source perturbation iteration method and the superhistory method. The source perturbation iteration method is superior in terms of computation efficiency, but a huge computer memory is required. The superhistory method dramatically reduces the memory requirement, although it worsens the variance of the sensitivity coefficients. The method developed in this paper is applied to some numerical tests that use multi-group constants, and it is verified by comparing to the results obtained by a deterministic perturbation theory. (C) 2018 Elsevier Ltd. All rights reserved.