A review of nuclear electric fission space reactor technologies for achieving high-power output and operating with HALEU fuel

Considerable attention is currently directed towards space nuclear reactor systems with significantly higher power outputs, catering to applications like nuclear electric propulsion and fission surface power, in contrast to past historic designs, which were predominantly ≤0.1 MWe. In addition, many previous designs have used Highly Enriched Uranium (HEU), although there is a recent drive to consider only High Assay Low Enriched Uranium (HALEU) for non-proliferation reasons. This requirement in particular motivates a contemporary review. In this paper, we highlight the drivers for high-power outputs (≥1 MWe), provide a comprehensive overview of previously-proposed space fission power system technologies and outline the attractiveness of various technologies. Unlike previous reviews that focused on nuclear thermal propulsion or lower power nuclear electric systems with HEU fuel, this study focuses on higher power nuclear electric systems operating with HALEU and key design considerations. While the reactor core technologies (i.e. coolants, fuels, and core materials) are the focus of this paper, it is important to recognise the interplay between the reactor core, heat rejection, and power conversion systems. Therefore, a systematic and cross-cutting review of the underpinning technologies associated with such space reactor systems is performed, and the technical maturity of relevant technologies is assessed. The most promising technologies for high-power HALEU designs are outlined and important areas for research are also identified.