Neutronics and thermal–hydraulics analysis of a liquid metal fast reactor for expandable lunar surface power

This paper presents a liquid NaK-78 cooled, fast spectrum nuclear reactor for lunar surface power. The reactor nominally operates at 500 kWth–1000 kWth and same inlet and exit temperatures of 850 and 900 K, but different coolant circulation rates. Depending on the type of energy conversion technology employed, the power system could generate 30–270 kWe for operation lives of 20–40 years. The reactor core is comprised of 6 hydraulically independent, but thermally and neutronically coupled sectors loaded with highly enriched UN fuel pins in a triangle lattice. Each sector has a separate pair of primary loop with energy conversion unit(s) and secondary loop with heat rejection radiator panels. The liquid metal coolant is circulated through the primary and secondary loops using separate electromagnetic pumps powered with separate thermoelectric conversion assemblies. The pumps continue to operate after reactor shutdown, effectively and safely removing the decay heat. Presented are the results of a multi-physics neutronics and 3-D thermal–hydraulic design optimization analysis performed to satisfy launch safety subcriticality requirement, determine beginning-of-life excess reactivity and the reactor full power operation lives, and ensure proper coolant distribution in the reactor core sectors and mixing in the upper plenums.

► We developed a nuclear reactor design with long operation life for expandable lunar surface power.
► On the moon, the liquid NaK-78 cooled reactor is placed below grade and surrounded by regolith.
► The six reactor core sectors are loaded with UN Fuel pins in a triangular lattice.
► Lunar regolith supplementary reflector decrease the reactor launch mass.
► Reactor design optimization is based on multi-physics, neutronics, thermal-hydraulics and reactivity depletion analysis.