Analysis Methods for Thermal Research and Test Reactors

HE-3 AND LI-6 POISONING OF THE MARIA REACTOR BERYLLIUM MATRIX

Teresa Kulikowska, Krzysztof Andrzejewski
Institute of Atomic Energy, Swierk, Poland


Manuel M. Bretscher
Argonne National Laboratory, USA

Abstract

This report discusses methods used to evaluate ⁶Li and ³He poison concentrations, initiated by the ⁹Be(n,a ) reaction, in the beryllium blocks of the MARIA reactor. The results are based on ENDF/B-VI neutron cross sections, 3D diffusion neutron fluxes, and solutions to the differential equations which describe the time-dependent poison concentrations as function of reactor operation and shutdown periods. MCNP Monte Carlo calculations were used to verify calculated poison levels for observed critical configurations. Previous evaluations used somewhat less refined methods based on asymptotic solutions for the poison concentrations. It was found that ³He and ⁶Li in the beryllium blocks limit the available excess reactivities and alter flux and power distributions. Based on analyses of critical cores, it was determined that poison concentrations need be evaluated for only an in-core region and for an ex-core region and not for each beryllium block.