Analysis and Flattening of Power Distribution During the Whole Life of the Micro Reactor Based on SiC Coated Fuel Particles

[Background] As a clean power source, nuclear power can meet diverse energy demands. Micro reactor has broad application prospects and irreplaceable advantages with small size, high flexibility and security, strong adaptability, and less maintenance requirement, which can provide power for the areas that large power grid cannot reach. The SiC-based Vehicular Micro Reactor (SVMR) is mainly used to provide power for remote areas and has the advantages of high fuel loading and high burnup depth due to its compact core design. However, SVMR has distortion phenomenon of sharp rise of power density at the edge of the active zone, resulting in the radial Power Peak Factor (PPF) exceeding the safety limit of 2.10, which threatens the reactor safety seriously. [Purpose] Therefore, this study aims to optimize the power distribution of SVMR to meet the thermal design criteria without compromising the fuel utilization efficiency of the core. [Methods] Firstly, the power distribution throughout the lifetime of the SVMR core was calculated under critical conditions. It was found that the rotation of control drums has a great influence on the radial power distribution. Thus, based on the critical conditions of control drum rotating, four methods were adopted to flatten the power distribution of SVMR during its lifetime, including changing the reflector thickness, adding burnable poison, fuel enrichment partition and fuel loading partition.[Results] The calculation results show that (1) reducing the reflector thickness leads to increased neutron leakage and seriously deteriorates the depletion characteristics of SVMR; (2) adding burnable poisons can reduce the radial PPF to less than 2.03, and achieves more than 10 years of lifetime and 75.53 MWd/kgU of burnup depth; (3) fuel enrichment partition can reduce the radial PPF of SVMR below 2.10, but the lower neutron utilization of fuel results in poor burnup performance; (4) fuel loading partition can achieve different power flattening targets and ensure the burnup depth greater than 77.70 MWd/kgU, in which the radial PPF can be less than 1.44. [Conclusion] In contrast, fuel load zoning offers greater flexibility, allowing adjustments to be made according to the specific needs of the user to achieve the desired power flattening effect, which can provides theoretical reference for the subsequent research work.