IMPLEMENTATION OF GENERALIZED INCORE DETECTOR RESPONSES IN MPACT

In this paper, the performance of a new detector response methodology is examined. The new capability, implemented in the MPACT deterministic neutron transport solver, allows for incore detector responses to be calculated on an arbitrary axial mesh that is not limited to the computational axial meshing. A single miniaturized 3D fuel assembly is used to compare the old and new methods. The 3×3 assembly had radial reflective boundary conditions and contained five spacer grids along its axial length. The results from this study show that the new methodology allows the calculation of finer incore detector responses, which can better describe localized flux shapes without increasing the simulation runtime. The axial reflection at the top and bottom of the core, as well as the flux depression in the area surrounding spacer grids, are more accurately represented using this new methodology. In addition to the test problem, a full-core model is compared with measured 600-level data from the Catawba Nuclear Station Unit 1 for cycle 19. This comparison resulted in a 3D RMS of 4.8% at the start of the cycle, which was reduced to 2.2% at the end of cycle. Owing to the uncertainty in the measurement, these results demonstrate good agreement with the simulated MPACT response. Although these results are only marginally better than linearly interpolating data using the existing methodology, more work is ongoing to further improve the calculated detector response.