VVER-1000 MOX Core Computational Benchmark analysis using indigenous codes EXCEL, TRIHEX-FA and HEXPIN

Validation studies based on the analysis of theoretical benchmarks play a key role in the identification of deficiencies in the reactor physics design computational codes and the associated nuclear data libraries. Implementation of improvements, if any, in theoretical models and the choice of appropriate nuclear data libraries help in enhancing the accuracy of calculations. As part of the effort for the validation of computer codes for plutonium utilization in VVER type reactors, the indigenous codes EXCEL, TRIHEX-FA and HEXPIN, developed at Light Water Reactor Physics Section (LWRPS), RPDD, BARC, and the associated nuclear data library (JEF22XS), were employed to analyse “VVER-1000 MOX Core Computational Benchmark”. The few group homogenized parameters of assembly cell or individual lattice cells were obtained by the hexagonal lattice burn-up code EXCEL and the core diffusion calculations were then performed using hexagonal assembly geometric code TRIHEX-FA or the pin-by-pin diffusion code HEXPIN. VVER-1000 reactor core loaded with 2/3rd of Low-Enriched Uranium (LEU) fuel assemblies (FAs) and 1/3rd of weapons grade MOX FAs was investigated. Effective multiplication factors and assembly average fission reaction rate distributions have been calculated for various reactor state descriptions using 3-D diffusion theory codes TRIHEX-FA and HEXPIN. Further, estimate of detailed pin-by-pin fission reaction rate distributions of a few selected assemblies were made for the normal working state of the reactor using pin-by-pin core simulation code HEXPIN. A comparison of results was done with the reported Monte Carlo (MC) values of the benchmark and in most cases good agreement was observed with the benchmark results.