Optimization of Core Regions and Fuel Fractions for Better Power Peaking Factor of 150, 450 and 1,000 MWth Molten Salt Reactor

The power peaking factor (PPF) is an important parameter that needs to be considered to maintain the reactor's stability, safety and efficiency. The present study discusses the power density distribution in the reactor core by calculating the PPF to increase the reactor safety margin and minimize the possibility of a high power density at a certain point causing core failure in the Molten Salt Reactor (MSR), which is one of the Generation-IV reactors with fuel and coolant dissolved in molten salt. Important parameters discussed in the present study are the distribution of the reactor core region and the fuel composition in each region during the reactor operation time of 2,000 days. Analysis was performed for 3 different thermal power: 150, 450 and 1,000 MWth as a representative to determine the behavior of PPF at small to large power by taking the reference design of the FUJI U3 reactor developed by ITMSF (International Thorium Molten-Salt Forum) Japan. FliBe (Lithium and Beryllium Fluoride) is used as the coolant, and the fuel mixture is 233UF4-ThF4. The calculation was conducted using SRAC2006 with PIJ and CITATION modules that solve the neutron diffusion equation providing power distribution values and effective multiplication factors. As a result, the MSR with 4 core regions produces a more balanced power distribution, a better PPF value, and a good effective multiplication factor for 2,000 days of operation time compared to the reference design.