Multi-physics analysis of a supercritical water reactor with improved MCNP modeling

Supercritical water reactors (SCWR) are proposed Generation IV light water reactors where supercritical water acts as the working fluid. Due to the large density gradients in the coolant, evaluation of reactor designs requires a detailed multi-physics analysis. In this work, MCNP is coupled to a single channel analysis tool to analyze a fuel assembly design whose neutronics performance has been experimentally validated. Accurate modeling of the reactor physics in a SCWR requires a detailed temperature treatment, including the effects of Doppler broadening (TMP cards in MCNP), thermal scattering (MT cards), and fully temperature-dependent cross-section sets for fuel and coolant (using the MAKXSF code). There is a $2 difference in keff between this highest-fidelity approach and a conventional treatment that addresses only Doppler broadening. An analysis is performed to determine the size of the temperature intervals for custom-developed cross-section sets, which indicated the necessity of 50 K bins in the fuel and 10 K bins in the coolant.