Neighbor-informed burnup correction for gadolinia depletion in pin-homogenized core calculation

Abstract

The neighbor-informed burnup correction (NIBC) method is proposed to improve the accuracy of gadolinia depletion in pin-wise two-step calculations. The inability to capture severe heterogeneous depletion behaviors inside the gadolinia absorber with pin-homogenized quantities leads to inaccurate prediction of the burnup of the gadolinia pins, which is worsened throughout depletion by positive feedback between burnup and power. As a practical means to resolve this problem, the NIBC method represents the burnup of a gadolinia fuel pin using the average burnup of its neighboring ordinary fuel pins. This method is implemented in a GPU-based pin-wise two-step nodal code VANGARD. Verification results demonstrate significant improvements in accuracy. In the APR1400 two-dimensional core depletion problem, the maximum and RMS pin power errors are reduced from 8% and 2.1% to 2.7% and 0.7%, respectively. In a small modular reactor core depletion problem, those are reduced from 6% and 2% to 3% and 1%, respectively.