Validation of the Monte Carlo Model of the Greek Research Reactor Core

The aim of this study was to validate a Monte Carlo-based model of the Greek Research Reactor-1 (GRR-1) developed with the MCNP5 code. The GRR-1 core was modeled in detail using the exact geometry without approximations. The inventory of the core was derived using the WIMS-ANL code, taking into account the different ²³⁵U burnup of each fuel assembly. The model was validated against experimentally determined control rod reactivity worth and neutron flux measurements performed in various irradiation positions. The ratio of the calculated-to-measured integral reactivity of each of the five control rods was found to be 0.972 ± 0.151, 1.083 ± 0.168, 1.156 ± 0.179, 0.874 ± 0.137, and 1.097 ± 0.170. The calculated-to-measured thermal neutron flux ratios ranged from 0.83 ± 0.04 to 1.22 ± 0.07. Therefore, good agreement between MCNP calculated and experimental values was observed. The GRR-1 core model will be fully implemented in the design of material irradiation experiments along with reactor safety and fuel management studies.