NEUTRONIC PERFORMANCE OF HIGH POWER DENSITY MARINE PROPULSION CORES USING UO_2 AND MICRO-HETEROGENEOUS ThO_2-UO_2 DUPLEX FUELS

摘要

In an effort to de-carbonise commercial freight shipping, there is growing interest in the possibility of using nuclear propulsion systems. Reactor cores for such an application would need to be fundamentally different from land-based power generation systems. For marine propulsion reactors, where weight and hence size are at a premium, power density is an important figure of merit and characterizes design performance. This paper investigates the effect of high power density on core lifetime while satisfying the neutronic safety constraints. 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 (EFPY) life at 333 MWth using 15% U-235 enriched micro-heterogeneous ThO_2-UO_2 duplex fuel and 18% U-235 enriched homogeneously mixed all-UO_2 fuel. We use WIMS to develop subassembly designs and PANTHER to examine whole-core arrangements. In order to design cores with power densities between 90 and 250 MW/m~3, five cases have been chosen by optimizing the fuel pin diameter (D), pin pitch (P) and pitch-to-diameter ratio (P/D). Taking advantage of self-shielding effects, the duplex option shows greater promise in the final burnable poison design for all the high power density cases. For the final poison design with ZrB_2, duplex fuel contributes ～5% more initial reactivity suppression and ～20% lower reactivity swing. Our analyses show that it is possible to increase the power density by at least 40% above that for the "standard geometry fuel" while satisfying the core neutronic safety constraints and providing a core life of at least 15 years. Finally, optimised assemblies for all the high power density cases are loaded into a 3D reactor model in PANTHER. PANTHER results confirm that at the end of the 15-year cycle, the candidate cores are on the border of criticality for both fuels, so the fissile loading is well-designed for the desired lifetime.