Nodal cross section corrections with the apec method in an SMR core analysis

Abstract

A new method for correcting the homogenized two-group cross sections (XSs) by taking into account the neutron leakage, which is named the albedo-corrected parameterized equivalence constants (APEC) method, has been developed to reduce the two-group XS error in the conventional homogenization method. In the APEC method, the homogenized two-group XSs generated from several color-set calculations as well as a single fuel assembly (FA) calculation are parameterized in terms of an integrated albedo information current-to-flux ratio (CFR). In addition, the neutron spectrum change in an FA can be considered by introducing a spectral index (SI) defined as the fast-to-thermal flux ratio. In our previous study, the new method was implemented into an in-house nodal code and its performance was tested only for benchmark problems based on the initial core state. The results demonstrate that the nodal accuracy can be improved significantly with a small amount of additional computing cost. In this paper, the APEC method is implemented into the practical nuclear design code MASTER, and validation is performed with two-dimensional problems based not only on the fresh state but also the burned condition of a small modular reactor (SMR) core. It was verified that the APEC XS corrections can lead to a noticeable improvement in the nodal accuracy of the fresh core, while relatively marginal in the depleted core.