The impact of homogenized cross-section correction mechanisms in OSCAR-4 as applied to SAFARI-1 research reactor

Abstract

The nodal solver OSCAR-4 reactor analysis system contains a series of approximations (nonlinear extensions) which aim to correct the full-core nodal calculation (mostly via corrections to the homogenised cross-sections) for typical errors induced during coarse-mesh homogenisation and group condensation. These schemes are intended to correct the nodal diffusion result as compared to an idealised full-core transport solution, which is in practice seldom performed or even practical to attempt. These schemes were developed for PWRs and the application and relevance of these schemes to highly heterogeneous research reactor designs have not as yet been fully quantified. This work focuses on the analysis of the cross-section re-homogenisation correction scheme. The purpose of this work is to perform an evaluation of this non-linear model as implemented in OSCAR-4, specifically with respect to the newly proposed OSCAR-4 SAFARI-1 core model. The new model is based in part on nodal cross-sections generated from the Monte Carlo based Serpent code. Serpent is a consistent reference transport solution against which the capability of the re-homogenisation scheme is measured. The SAFARI-1 mini-core model results show that the scheme is applicable in some cases, like the fuel-follower. In the full-core model, the environmental error due to infinite lattice approximation was 252 pcm, 2.30 % in average assembly power and 4.59 % in maximum power. The scheme reduced these to 88 pcm, 1.69 % and 3.52 % respectively. The scheme should therefore be applied selectively in the full-core to maximise it's capability. The work will support both the verification and validation of SAFARI-1 reactor models.