MULE -- A Co-Generation Fission Power Plant Concept to Support Lunar In-Situ Resource Utilisation

TL;DR

This paper presents the MULE concept: a co-generation, very-high-temperature fission microreactor designed to heat lunar ISRU feedstock via molten salt electrolysis and to provide electrical power to a small lunar base. Using Serpent 2 neutronic simulations with a fully ceramic SiC/TRISO core and BeO-based moderator/reflector, the authors show feasible shutdown margins and a long neutronically viable lifetime at about 100 kW_th, with potential lifetimes extending to decades. The study outlines a hardware design that minimizes mass (dry mass ~2.1 t) and proposes coupling with a Brayton cycle and thermal energy storage to ensure operation through the lunar night. Next steps include detailed thermal-hydraulic CFD, system modeling in Modelica, and transient analyses to validate performance and safety for future lunar missions.

Abstract

For a sustained human presence on the Moon, robust in-situ resource utilisation supply chains to provide consumables and propellant are necessary. A promising process is molten salt electrolysis, which typically requires temperatures in excess of 900°C. Fission reactors do not depend on solar irradiance and are thus well suited for power generation on the Moon, especially during the 14-day lunar night. As of now, fission reactors have only been considered for electric power generation, but the reactor coolant could also be used directly to heat those processes to their required temperatures. In this work, a concept for a co-generation fission power plant on the Moon that can directly heat a MSE plant to the required temperatures and provide a surplus of electrical energy for the lunar base is presented. The neutron transport code Serpent 2 is used to model a ceramic core, gas-cooled very-high-temperature microreactor design and estimate its lifetime with a burnup simulation in hot conditions with an integrated step-wise criticality search. Calculations show a neutronically feasible operation time of at least 10 years at 100kW thermal power. The obtained power distributions lay a basis for further thermal-hydraulic studies on the technical feasibility of the reactor design and the power plant.

Figures (6)

• Figure 1: Schematic of the mule co-generation fission power plant concept with adjacent lunar base modules. "T" stands for turbine, "G" for generator and "C" for compressor. Dashed lines indicate the focus of the individual tasks. The flowchart on the top right corner with exemplary temperatures indicates expected temperature levels for each component.
• Figure 2: Sectional cut through length of proposed mule reactor design in its shutdown position. The right picture is a horizontal cut near the fuel midplane. Notable parts are annotated and a scale for radial and axial dimensions is given. Electrical motors at the shaft ends and piping flanges are not depicted.
• Figure 3: Neutronic model of the mule reactor. (a) is a $y$-$z$ cut through one of the control drums with coolant inlet on the left and outlet on the right hand side. (b) is an $x$-$y$ cut near the fuel midplane with control drums facing inwards ($\varphi_{\mathrm{CD}} = \ang{0}$). (c) shows a fuel compact with its triso particles, which are magnified in (d).
• Figure 4: Assumed temperature distribution in the reactor for the neutronic model.
• Figure 5: Power deposition per fuel element for bol, eol and extended eol. The background features the geometrical configuration of the control drums at the respective burnup step.