U.S. Government Finds that Reactor for Moon Does Not Require Bomb-Grade Uranium Fuel
NPPP Obtains Report under Freedom of Information Act
AUSTIN (NPPP PR) – The nuclear reactor that NASA plans to launch to the Moon’s surface later this decade to power a manned mission would not require weapons-grade, highly enriched uranium (HEU) fuel, according to a government study released yesterday that contradicts previous assertions. The report, “Analysis of Alternative Core Designs for Fission Surface Power Capability Demonstration Mission,” was released to the Nuclear Proliferation Prevention Project at the University of Texas at Austin, in response to a Freedom of Information Act request.
As recently as 2018, U.S. officials had claimed that bomb-grade fuel was necessary to reduce the weight of space power reactors and had tested such a reactor at a national laboratory. By contrast, the new report reveals that using low-enriched uranium (LEU) fuel, which is unsuitable for nuclear weapons, would not increase the total weight of the reactor system if a “moderator” were used to slow down the neutrons to facilitate nuclear fission.
The report compares the weight of reactor systems including fuel, moderator, and radiation shield. It finds that two alternative LEU designs have similar weight ranges as the HEU baseline design, and the lightest estimate is actually for one of the LEU versions. The report says the two proposed moderators, yttrium hydride (YH) and zirconium hydride (ZrH), still require some research and development – but there is time because NASA’s deadline for launching a power reactor is not until 2027.
Space Reactor Weight Comparison: Moderated LEU vs Fast HEU
| Fuel (moderator) | Kg including shield |
|---|---|
| HEU (none) | 900 – 1100 |
| LEU (YH) | 800 – 1200 |
| LEU (ZrH) | 900 – 1200 |
Before being finalized this year, the report was distributed within the U.S. government in February 2020 as a “final draft.” This may explain why the U.S. government’s Space Policy Directive–6, in December 2020, effectively banned bomb-grade uranium fuel in space reactors by declaring that, “The use of HEU in space nuclear power and propulsion systems should be limited to applications for which the mission would not be viable with other nuclear fuels or non-nuclear power sources.” Last month, the Department of Energy confirmed that space nuclear power reactors must comply with Space Policy Directive–6.
The U.S. government’s rapid evolution from viewing bomb-grade uranium fuel as essential for space nuclear power in 2018, to effectively banning it in 2020, is analyzed in NPPP’s April 2021 presentation to a national laboratory. In October 2019, NPPP hosted a symposium on space reactors and proliferation, including participation by officials from NASA and Congress. The national-security importance of avoiding HEU in space reactors also was analyzed in a 2020 project by UT-Austin graduate students.
7 responses to “U.S. Government Finds that Reactor for Moon Does Not Require Bomb-Grade Uranium Fuel”
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There’s no way they were going to get a bunch of HEU for a civilian space mission. Even aside from objections from the non-proliferation people, the stuff isn’t exactly cheap and most of it is being hoarded for nuclear weapons, new carriers, and new nuclear submarines.
Using moderators for an LEU reactor gets you the same power to mass ratio as the HEU reactor, but it also increases the complexity and shortens the useful life of the reactor. You could probably design an HEU reactor to last 20-30 years before replacement (Kilopower’s proposed reactor was 15 years). A moderated LEU reactor is not going to last that long unless you increase the relative amount of fuel and thus mass.
Maybe that’s okay, though. If they have to replace them every 5 years, then you’ve at least got something resembling a production line to get the costs down versus bespoke construction of a reactor.
It is notable that if we do another design using molten salt reactors, and sCO2 turbines, and dynamic radiators, then we could get rid of most of the lifetime worries, … and lower total system mass as well. Maybe do it as a second generation device?
It’d have to be a second-generation device, at least. It’d be more complex than a moderated LEU reactor, and while I don’t think it would be an issue on the Moon itself, testing it could be a challenge – the Thorium Fuel Cycle produces U-233, which is fissile in bombs if extracted and concentrated from the reactor. That might mandate a lot more extra security on any test reactors you have.
“That might mandate a lot more extra security on any test reactors you have.”
Ahhh! Finally, … A job for the Space Marines! /s
*Any* ability to use the vast majority of fission nuclear power’s potential will require breeding! Thus it will require security, and that should be specified. No security will ever be enough for many, because it is all that energy being available without them being in control of it, and the industrial society it enables, that frightens them.
Nucleophobia will take *many* forms, at the political need of those who I remember pronouncing that even “Cold Fusion”, back in the 1980s, was, “Like handing machine guns to to infant children”. That was specifically because it was supposedly capable of producing the energy needs of an industrial civilization not under the control of the University-certified philosopher kings, who should be in control of society’s resources.
To me… the Moon should be the ONLY home of HEU
It seems this increment of mass increase percentage is exactly what Starship will make into a minor shipping change, rather than a major design problem. I wonder if the original teams were banned from assuming a launch on Starship?
I’m with you in spirit, but I think banning would have been superfluous. This is a government program which, so far as I know, has yet to bend any metal on a prototype. That almost certainly means it has been ongoing for far longer than Starship has been a real enough thing to merit consideration as transportation.