Preliminary design and neutronic characterisation of a 200 kWt HALEU fueled heat-pipe reactor for space applications

Nuclear reactors represent a key technology for advancing space exploration and utilisation, providing a reliable, continuous, and environmentally independent energy source essential for long-duration missions beyond Earth. This capability is crucial for ensuring uninterrupted operation of spacecraft systems, sustaining lunar habitats, and supporting energy-intensive scientific experiments. Nuclear energy, particularly fission, is renowned for its high energy density and reliability, making it a key element in the design of space missions where mass minimisation is a critical requirement for feasibility and economic viability. While designs like KRUSTY have demonstrated compactness and simplicity, it is desirable to develop reactors with higher power levels, lower enrichment, and compatibility with non-proliferation concepts. The objective of this work is to propose a preliminary design for a heat-pipe reactor conceived for both lunar surface applications and low-power electric propulsion and to conduct a comprehensive neutronic analysis. The proposed reactor combines the simplicity of a KRUSTY-type reactor with increased power to 200 kWt (40-50 kWe assuming 20%–25% conversion efficiency) and reduced enrichment (from HEU to HALEU). The preliminary design is characterised by an epithermal spectrum, a nominal operating temperature between 1000 K and 1100 K, and has a mass of 1139 kg, resulting in a specific power of 176 Wt/kg. A neutronic analysis was performed to characterise the reactor, extracting information such as power and flux distributions, feedback coefficients, reactivity control, burnup, and addressing safety aspects, demonstrating that the reactor maintains sufficient reactivity margin under certain accidental criticality condition. All the criticality calculations were performed using OpenMC Monte Carlo code.