SpaceNukes will design, build and ground test a kilopower reactor with Los Alamos National Laboratory under an other transaction agreement from DARPA, the Space Nuclear Power Corporation said. The award falls under DARPA's Fast Capacitance program, known as Fat Cat, which seeks to advance reactor operations, including reactors designed for propulsion systems, as a source of reliable power for systems in extreme, remote environments.

A 5-kWt prototype ran in 2017 and 2018

The design descends from KRUSTY, the Kilopower Reactor Using Stirling Technology, the prototype in the NASA-led Kilopower Project, which aimed to power planetary missions and deep space travel. KRUSTY was a 5-kWt solid fuel uranium-235 reactor that used boron carbide control rods. It was tested in phases in 2017 and 2018 and was found to be highly tolerant of failure conditions and operational transients.

Small, fast reactors such as KRUSTY operate without a moderator, according to the Fat Cat program website. Faster neutrons and smaller control rods make them highly responsive while reducing size and weight. Rapid physical transients can be too complex for human operators to manage independently, requiring reliable autonomous controllers.

The new test will move control rods actively

SpaceNukes and LANL will design an autonomous reactor and take the project through procurement, integration and a ground demonstration. The work will include active control rod operation, compared with the passively controlled architecture used in the 2018 KRUSTY test. Integration will be led by Marc Gibson, SpaceNukes' chief engineer, who was previously lead engineer for the Kilopower Project at NASA. Chief technical officer David Poston and chief operational officer Patrick McClure worked on the Kilopower Project at LANL as chief reactor designer and project lead, respectively.

Fat Cat targets reactors too fast for human operators

Fat Cat is managed by Tabitha Dodson in DARPA's Defense Sciences Office. The program seeks to address a lack of small, on-demand controllable reactors while developing systems capable of managing the dynamic behavior of small, fast reactors, and aims to demonstrate autonomous nuclear control on a fully functional fast reactor with LANL at the Device Assembly Facility. It also aims to catalogue nuclear transient conditions, develop reactor physics models, evolve design tools for nuclear engineers and progress to real-world testing, including building hardware, developing software and designing reactor experiments.