Validation of the MCNP5 core model of the PSU breazeale research reactor

The Monte Carlo method is currently one of the new methodologies under development to be employed as a fuel management tool for the Pennsylvania State University Breazeale research reactor (PSBR). This paper discusses the effort to analyze the current core loading of the PSBR by the MCNP5 code. Since the initially loaded fresh fuel has been depleted due to the long operation history of the PSBR, the fuel material composition of each fuel element is needed to be determined in order to model the current PSBR core. The HELIOS code was used in this research to obtain the fuel material composition change of each fuel element. In addition, the decay calculation was introduced to the PSBR core model by the ORIGEN2.2 code to take into account of the effect of the Xe ¹³⁵ decay after reactor shutdown. The X ¹³⁵ decay was found to have a significant impact on the core excess reactivity. Subsequently, the MCNP5 core model was compared to the current core analysis methodology and it was also validated against measurements. Good agreements were observed from the code-to-code comparison and the measurement comparison.