U.S. Government Finds that Reactor for Moon Does Not Require Bomb-Grade Uranium Fuel

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.