Regular Article

Preservation of kinetics parameters generated by Monte Carlo calculations in two-step deterministic calculations

¹ North Carolina State University, 3140 Burlington Engineering Labs, 2500 Stinson Drive, Raleigh, NC, 27696-7909, USA
² Idaho National Laboratory, 2525 Fremont Ave., Idaho Falls, ID, 83415, USA

^* e-mail: cntakasu@ncsu.edu

Received: 30 March 2022
Received in final form: 19 July 2022
Accepted: 20 December 2022
Published online: 27 February 2023

Abstract

The generation of accurate kinetic parameters such as mean generation time Λ and effective delayed neutron fraction β_eff via Monte Carlo codes is established. Employing these in downstream deterministic codes warrants another step to ensure no additional error is introduced by the low-order transport operator when computing forward and adjoint fluxes for bilinear weighting of these parameters. Another complexity stems from applying superhomogenization (SPH) equivalence in non-fundamental mode approximations, where reference and low-order calculations rely on a 3D full core model. In these cases, SPH factors can optionally be computed for only part of the geometry while preserving reaction rates and K-effective, but the impact of such approximations on kinetics parameters has not been thoroughly studied. This paper aims at studying the preservation of bilinearly-weighted quantities in the Serpent–Griffin calculation procedure. Diffusion and transport evaluations of IPEN/MB-01, Godiva, and Flattop were carried out with the Griffin reactor physics code, testing available modeling options using Serpent-generated multigroup cross sections and equivalence data. Verifying Griffin against Serpent indicates sensitivities to multigroup energy grid selection and regional application of SPH equivalence, introducing significant errors; these were demonstrated to be reduced through the use of a transport method together with a finer energy grid.