Multi-physics Assessment of Reduced-moderation Pressurized Water Reactor using Thorium Fuel

Reduced-moderation pressurized water reactor (RMPWR) utilised thorium (Th) as the fuel in exchange for uranium (U) due to its huge advantages in term of neutronics characteristics, including low void and moderator temperature coefficient, and the potential of breeding into fissile fuel 233U. In RMPWR, the water to fuel ratio is reduced to 50% of the normal value to allow for transuranic (TRU) isotopes burning contained in the Th-TRU pin. This corresponds to the implementation of larger fuel pin (11 mm in RMPWR and 9.5 mm in normal PWRs). This work is aimed to develop a single 3D fuel assembly (FA) model and a 3D whole core model of the RMPWR. These are then used to assess the feasibility of RMPWR to sustain an equilibrium cycle and to satisfy the safety criteria. The assesment of a single 3D FA is performed using Monte Carlo code MCS, developed at Ulsan National Institute of Science and Technology and then confirmed using SERPENT 2. The criticality and pin-by-pin power distribution calculation for a single 3D FA at beginning-of-cycle (BOC) shows that the MCS model has a great agreement with the SERPENT 2 model within ~1% average difference. The calculation time for SERPENT 2 is significantly less than MCS due to the different memory usage. A coupled neutronic/TH model has also been developed to perform coupling calculation using MCS/TH1D. The objective is to provide a better result by accounting for the thermal-hydraulic feedback. The coupled whole core model of RMPWR is then employed to calculate the safety parameters, which include the reactivity coefficients and control rod worth.