Void Reactivity Predictions for an Infinite Lattice of 37-Element CANDU Fuel

Abstract

In this study, a comparison between the reactivity predictions of several deterministic lattice codes and the Monte-Carlo code MCNP is presented. Superficially, it appears that there is a significant discrepancy between the void reactivity predictions of the lattice codes WIMS-AECL and LATREP when compared with the MCNP3B version of the Monte-Carlo code. However, it is noted that when the WIMS-AECL and LATREP codes' predictions of void reactivity are compared with the newer version MCNP, the situation improves; that is, WIMS-AECL, LATREP and MCNP4 are in good accord. The reason for the discrepancy between the two versions of MCNP will be explained in terms of the certainty that the older version MCNP3B contains a "defect" that has never been properly appreciated. By making allowance for this defect, it can be shown that both versions of MCNP are in accord with one another and with both deterministic lattice codes.