NASA on building nuclear reactors in space and what's next

Earlier this year, the U.S. Department of Energy (DOE) awarded three contracts worth about $5 million each to three companies to obtain designs for nuclear fission surface power systems that could be deployed to the moon. According to NASA, such technology could be deployed to the moon by the end of the century.

The money awarded under the DOE contract will be used to develop a preliminary design concept for a 40-kilowatt fission power system that should last at least 10 years in the harsh lunar environment. Lockheed-martin, Westinghouse, and IX were selected for the contract, and all three will collaborate with other companies on design development.

Because nuclear fission systems are relatively small and light, they are ideal for the lunar environment. They can also generate electricity reliably, independent of location, available sunlight, and other natural conditions. If successfully developed and deployed, such technology could pave the way for long-term missions to the moon, Mars and beyond.

Tofel, program manager for fission surface power at NASA's Glenn Research Center, spoke with the media about the issue.

Nuclear reactors on Earth are usually housed in large containment buildings, but descriptions of reactors on the moon do not appear to have such a structure. What is the reason for this?

Tofel: A reactor on the moon does have a containment vessel, but it's much smaller than what's needed for a reactor on land. A typical land-based nuclear reactor would produce 1,000 megawatts of energy, while a lunar reactor would produce 40 kilowatts, or 0.04 megawatts. Because a lunar reactor contains much less nuclear material, its structure, including containment and shielding, is much smaller than that required for a typical Earth-based reactor.

NASA on building nuclear reactors in space and what's next

Safety is a core principle of every NASA activity on Earth and in space, and is incorporated into every stage of the design, testing, manufacture, and operation of space nuclear power systems. The lunar system design will provide the same protection and safety standards that apply to terrestrial systems.

What are the biggest challenges to overcome before such a reactor can be deployed to the moon?

Tofel: One challenge is that the launch and ascent to the moon involves intense vibrations and shocks, as the rocket stages separate after burning their fuel. A space reactor must have a robust and durable structure, electronics, communication equipment, and power conversion equipment designed to survive the launch environment. Another challenge of operating on the lunar surface is to reject the power generated by the reactor to handle the heat. Water or air cooling systems like those used on Earth are not possible on the moon.

Instead, NASA will need thermal radiators to cool the reactors by pouring waste heat into space. It's the same process used to manage heat on the International Space Station. Finally, another challenge is operating a power plant 250,000 miles from Earth, where autonomous control systems must be developed and tested to ensure safe operation and fault detection. All of these challenges are solvable and will be overcome through detailed design and testing activities.

How much harder would it be to deal with a nuclear leak in space compared to one on Earth?

Tofel: The chances of that happening are extremely slim. The safety analysis will cover all aspects, including normal and abnormal operation phases of the system. NASA takes safety very seriously, and safety issues are integrated into every stage of the design, testing, manufacturing and operation of space nuclear power systems.

This includes several layers of protection features within the power system to minimize the possibility of failure during operation, as well as backup safety controls in the event of failure. For example, the lunar surface fission power system will have redundant controls to detect failures and shut down the reactor before its operation becomes critical. The control subsystem will have active and passive measures to ensure that the reactor core can return to subcriticality and that the reactor fuel is always operating at a stable temperature.

How would fluctuating ambient temperatures on the moon affect the operation of such a reactor?

Tofel: The thermal management of the system was designed to allow for fluctuations in ambient temperatures on the lunar surface. Cooling panels are used to drain waste heat into space over the entire range of operating temperatures. The thermal radiant plates will be sized to handle the most extreme lunar conditions.

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