High power density reactor core design for civil nuclear marine propulsion. Part II: Whole-core analysis

In this reactor physics study, we attempt to design a high power density core that fulfills the objective of providing ∼15 effective full-power-years life at 333 MWth using 19% ²³⁵U enriched micro-heterogeneous ThO₂-UO₂duplex fuel and 16% ²³⁵U enriched homogeneously mixed all-UO₂fuel. We use W1MS to develop subassembly designs and PANTHER to examine whole-core arrangements. In a companion (Part I) paper, three core designs with power densities between 82 and 111 MW/m³were selected on the basis of achieving the target ∼15-year core lifetime. Our analyses in this paper (Part II) show that higher power density cases require less burnable absorber than lower power density cases for both candidate fuels. Reactivity coefficients [moderator temperature coefficient (MTC) and fuel temperature (Doppler) coefficient (FTC)] values for the higher power density cases are lower (more negative) than for the lower power density cores. In addition, higher power density cases exhibit higher axial offset (AO). It is observed that a duplex fuel lattice needs less burnable absorber than uranium-only fuel to achieve the same poison performance. MTC and FTC values of the duplex core are generally considerably more negative than those of the UO₂core. It is possible to increase the power density by at least 30% above that for the reference core design (63 MW/m³) while satisfying the core neutronic safety constraints and providing a core life of ∼ 15 years. Ultimately the most successful design, in terms of whole-core neutronic performance, is the duplex core with an average power density of 120 MW/m³, which exhibits a reactivity swing of less than 4000 pcm, while obtaining a core life of ∼15 years. The average core power density is increased by ∼50% compared to the reference core design and now is equivalent to the Sizewell B PWR (101.6 MW/m³).