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A design study of ultra-long cycle fast reactor with a rated power of 1000 MWe (UCFR-1000) was performed to flatten its radial power distribution throughout the cycle depletion of the core. It is expected that the flattening of the radial power distribution lowers the power peak factor at the center and consequently the maximum peak temperature of the fuel and clad. Thorium fuel has lower reproduction factor than uranium; thus, thorium-loaded fuel zone has relatively lower power. A lot of test cases were introduced that have thorium-loaded fuel in the inner fuel region to lower the center power peak. Each test case had a different zoning strategy; different fuel forms were loaded for both the upper blanket region and the lower low enrichment uranium (LEU) region. The final evaluation models were designed by loading the thorium-loaded fuel only in the inner blanket for the 1-zone case, in both blanket and LEU regions for the 2-zone case, and in an additional zone for the other cases. It was demonstrated that the fuel zoning has a significant impact on the power flattening, and a gradual fuel zoning can achieve a flattened radial power distribution, and can consequently reduce the maximum power peak.

This paper proposes a new control rod material for a boron-free small modular pressurized water reactor (SMPWR) to compensate the loss of the soluble boron. To design control rod for SMPWR is difficult due to the large amount of reactivity control necessity and the multiple roles of control rod, i.e., the excess reactivity control, the coarse/fine power control, and the axial shape control and shutdown. This paper presents a study of various control rod materials: B4C, Ag-In-Cd, and HfB2. The rod worth and the excess reactivity control capability will be assessed for the SMPWR using Studsvik’s reactor core design code system, CASMO-4E/SIMULATE-3.