A cross-section correction model for history effect treatment in pin-by-pin code NECP-Bamboo2.0

Abstract

The consideration of the history effect is one of the foundations for ensuring the precision of the two-step calculation scheme. Since the actual condition could not be predicted in advance, the standard approach of the lattice calculation adopts the branch-based model in which the variations of nuclide number densities with burnup are only considered in averaged operating conditions. Consequently, the nuclide number densities associated with actual operating conditions are not considered properly in the 3D whole-core calculation, and the problem of the history effect arises then. The microscopic depletion method and serval correction methods based on different lattice calculation structures were developed to solve this problem and have been employed in pin-by-pin two-step calculation codes. This paper introduces a new spectral history correction method with the implementation of a new bidirectional branch model, a pin-cell burnup correction model, and a multiscale cross-section correction model. The work was carried out based on the pin-by-pin fuel management calculation code system NECP-Bamboo2.0 developed by Xi'an Jiaotong University. Encouraging conclusions have been obtained from the numerical results. For the heterogeneous history effect caused by CR movement, the bias of keff given by the classical corrections will exceed ± 1000pcm. In contrast, the improved method can reduce it to be smaller than ± 250pcm. For the histories triggered by the changes of other state parameters, including boron concentration, fuel, and/or moderator temperature(s), the new cross-section correction method is comparable in accuracy to the traditional microscopic cross-section correction method, both better than the microscopic depletion correction method.