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1st Generation (gen1) Systems
SpaceNukes’ Gen1 reactors do not require technology development or new infrastructure. They are designed to be passively safe under all nominal and accident conditions, providing the simplest path to gaining launch approval. Most importantly, they are designed to perform and operate almost identically to KRUSTY, so no additional nuclear-powered testing is required.
These features are what make SpaceNukes’ Gen1 reactors the only space reactor systems ready for flight – no other proposed systems are remotely close.
1 to 20 kWe Gen1 HEU Space Reactors
Courtesy of NASA
The quickest reactor to production for space flight is a 1 to 20-kilowatt electric (kWe) HEU space reactor (the original Kilopower design) that would be essentially identical to the nuclear-powered “KRUSTY” test.
Figure 1 shows the basic layout of a 1-kWe Kilopower reactor with a highly enriched Uranium (HEU) core. The reactor shown has eight heat pipes attached to eight 125-watt Stirling engines – KRUSTY was a prototype of this reactor.
Figure 1 - 1 kWe Space Reactor with HEU core
With an HEU core, 1 to-20 kWe Gen1 reactors are small enough and light enough to fit a range of deep space missions. Of particular excitement are Nuclear Electric Propulsion (NEP) missions that could orbit outer solar system planets and moons, with abundant power for science and high data transmission rates.
These reactors would have all the qualities of a SpaceNukes design including load following, high uranium atom density, low burnup, and low power density. The reactors are designed to operate for decades without any control commands, except for ~monthly minor reactivity changes to account for small decreases in temperature.
These Gen1 Kilopower power systems could be ready for flight in approximately 3 years. No major technical issues remain; the long pole in the schedule would be the launch safety approval. The 1-kWe power system is approximately 400 kg and is 58 cm in diameter and 145 cm in length (without heat rejection). The 1-kWe reactor can be readily upsized to 10- kWe by increasing the weight and size of the reactor to approximately 1300 kg with an HEU core. These designs are ready for deep-space applications without additional terrestrial nuclear testing.
20 to 50 kWe Gen1 HALEU Surface Reactors
The proven Kilopower approach (i.e. KRUSTY) can be applied to powers up to 50 kWe with the use of HALEU fuel (19.75% enriched uranium).
Courtesy of NASA
Figure 2 shows a schematic of a potential SpaceNukes 30-kWe surface reactor. The configuration shown uses a direct one-to-one heat-pipe-to-Striling approach (lots of smaller converters), but alternate designs use intermediate heat exchangers and/or fewer larger Stiling converters. Each configuration has pros-and-cons that can be suited to a customer’s requirements and risk posture.
Figure 2 - 35 kWe Surface Reactor with LEU core
First generation Kilopower surface power systems use between 400 and 500 kg of HALEU. Unlike terrestrial reactors, fuel cost is not a primary driver for space reactors – there are many more-significant costs and risks. This relatively high mass of fuel is what enables the proven, low-cost KRUSTY-based technology to scale to up to 50 kWe. HEU Kilopower surface reactor concepts are conservatively limited to ~20-kWe to keep uranium atom burnup < 1.0%, because at ~1% burnup swelling of the metal fuel might significantly impact design performance. By using HALEU instead of HEU, the burnup can be extended (more total uranium atoms are available) and the power raised up to 50 kWe.
The weight of the Gen1 HALEU surface system would nominally be ~600 kg heavier than a Gen1 HEU system, but the allowable increase in power can more than offset the increased weight. The alpha (power to weight ratio) of the 10 kWe HEU surface reactor is about 8 Watts/kg. The 30 kWe HALEU system would also have an alpha of about 8 Watts/kg. A 30-kWe Gen1 HALEU surface reactor could be ready for flight in approximately 4 years.
