The Fast Capacitance (Fat Cat) program addresses one of the most challenging logistics problems faced by government and industry: Reliably and persistently powering systems in extreme, remote environments, such as space or undersea. A new class of small, lightweight fast fission reactors shows promise, but achieving autonomy in reactor control systems is essential to operate these reactors independently, without human intervention.
Scope and objectives
Fat Cat will develop and experimentally validate groundbreaking models to understand and control fast reactor transients, enabling fully autonomous operation. The program will progress from simulation to real-world testing, focusing on the following key areas:
- Physics modeling: Cataloging all probable and highly probable nuclear transient conditions with high certainty
- Enhanced reactor control: Advancing nuclear reactor physics models to improve control capabilities and ensure safer operations through predictive methods
- Design tools: Creating models and tools to help nuclear engineers understand complex physical conditions, regardless of reactor scale
- Experimental validation: Building hardware, developing software, and designing reactor experiments to test automated control systems
Fat Cat aims to accelerate nuclear innovation writ large. By focusing on understanding and proving out the most difficult physics for fast reactors, Fat Cat will create models to allow the broader nuclear power ecosystem to safely design and gain approvals for new types of reactors.
Fat Cat plans to make history by demonstrating autonomous nuclear control on a fully functional fast reactor in conjunction with Los Alamos National Laboratory at the Device Assembly Facility.
Leveraging small reactor technology
Demonstrating Fat Cat on a small, fast reactor will serve as a testbed for autonomy breakthroughs.
Unlike large, steady-state reactors with basic human-controlled mechanisms, reactors designed for propulsion systems (e.g., spacecraft or submarines) must rapidly throttle power generation to meet dynamic energy demands while maximizing reliability and longevity. Current on-demand controllable reactors, such as those in nuclear submarines, are prohibitively large, and their controllers lack the speed to manage the nimble dynamics of small fast reactors. Fat Cat aims to overcome these limitations by developing autonomous controllers capable of handling the rapid neutronics and physical transients unique to small reactors.
Autonomous reactor controllers must be proficient in nuclear physics
In 2018, a NASA-led program successfully demonstrated the viability of small-scale, steady-state nuclear fission under laboratory conditions using the KRUSTY (Kilopower Reactor Using Stirling TechnologY) fast reactor. However, missionizing autonomy for small reactors in remote environments requires new tools.
Control rods in reactor cores absorb neutrons to regulate fission reactions — lowering reactivity when inserted and increasing it when withdrawn. Unlike conventional thermal spectrum reactors, which use moderators (e.g., graphite or water) to slow neutrons, small fast reactors like KRUSTY operate without moderators, reducing size and weight.
The absence of moderators, combined with faster neutrons and smaller control rods, makes small reactors highly responsive. Yet this agility introduces rapid physical transients, such as temperature gradients and material geometry changes, which are too complex for human operators to manage independently. Autonomous controllers must rely on updated physics models to anticipate the full spectrum of reactor transients, enabling real-time predictions and adjustments for smooth, safe, and continuous power operations.
Fat Cat’s vision for reactor autonomy
Fat Cat aims to master the complete spectrum of reactor physics, creating comprehensive models that ensure the highest levels of safety and reliability for current designs like KRUSTY and for future reactors. By pioneering autonomous control systems, Fat Cat will enable small reactors to power mission-critical systems in remote environments, revolutionizing energy solutions for space exploration, undersea operations, and beyond.
