Adaptation of SUBCAL subchannel code for square-lattice rod bundles using PSBT benchmark

Subchannel analysis is a commonly used approach for simulating heat transfer and coolant flow in nuclear reactor cores. This paper presents the adaptation of the SUBCAL computational code, originally developed for reactors with a triangular lattice, to configurations with a square lattice. Geometry-dependent computational relations, models and correlations were identified and analyzed based on the research. The selected relations for the square lattice were implemented into the SUBCAL code, and the computational model was optimized for the recalculation of the PSBT benchmark. Verification of the proposed changes was carried out by evaluating the results of the benchmark recalculation against experimental data and through code-to-code comparisons with results from other participating organizations. These modifications and the recalculated PSBT benchmark represent the starting point for validating the SUBCAL code for this type of analysis.