NASA is proposing to develop a reactor called Kilopower that could be ready to support lunar bases in the latter half of the 2020s, but the choice of fuel for that reactor worries nuclear nonproliferation experts. (credit: NASA)
Space nuclear power is enjoying something of a renaissance in recent years. Congress has directed money to NASA to work on nuclear thermal propulsion, including $125 million in the House version of a fiscal year 2020 spending bill for NASA that calls for a flight demonstration of such technology in 2024.
“If we are to fulfill the objectives of President Trump’s first space policy directive to establish a long-term presence on the Moon and send the first crewed mission to Mars, nuclear power is arguably the most important technology to enable these bold national goals,” Rex Geveden, president and chief executive of BWX Technologies and a former NASA associate administrator, said at the most recent meeting of the National Space Council in August.
At that meeting, the White House announced a new policy for reviewing missions that plan to use nuclear power. Kelvin Droegemeier, director of the Office of Science and Technology Policy, described that policy as a “forward-looking” authorization process for both government and commercial missions that plan on using nuclear power.
Nuclear thermal propulsion is often cited as a key technology for missions to Mars, shortening the travel time for crews. It’s not necessary for near-term missions to the Moon, where the focus instead is on nuclear power systems. The two-week lunar night means that, for extended-duration stays on the lunar surface as contemplated for later in the 2020s, solar power alone likely won’t be sufficient.
To that end, NASA has been working on a technology called Kilopower for small nuclear reactors that can produce one to ten kilowatts of power. Last year, NASA and the Department of Energy announced the successful test of a prototype of such a system, called the Kilowatt Reactor Using Stirling Technology, or KRUSTY. The success of KRUSTY, NASA said then, could lead to a flight demonstration of a Kilopower reactor, perhaps carried to the Moon on a mid-sized lunar lander, some time in the mid-2020s.
For advocates of lunar exploration, Kilopower seems like a boon. However, Kilopower is raising concerns in the nuclear nonproliferation community because of the type of fuel that reactor may use.
“I’m concerned about a program for a power reactor using weapons-grade uranium, or HEU,” said Rep. Bill Foster (D-IL) during an October 17 forum on nonproliferation risks of space nuclear power in Washington. The KRUSTY test last year used highly enriched uranium at a time when many other terrestrial applications of HEU are being phased out because that material could be used in nuclear weapons.
That issue has not generally been discussed when NASA talks about space nuclear power. “NASA is a very different world from the nonproliferation community. It is not surprising folks at NASA may not initially have realized how much effort the US government has put into minimizing the use of HEU in civilian applications,” said Alan Kuperman, associate professor at the University of Texas at Austin and organizer of the event. At the same time, he said, nonproliferation experts have not have realized “how serious NASA was about using HEU in civilian applications for space reactors.”
He and other nonproliferation experts said using HEU in space would send the wrong message to other countries about the development and use of such fuels. “No one should be under the delusion that the US can go for HEU reactors and the rest of the world will continue to minimize HEU,” he said. “If the rest of the world goes for HEU reactors, one day some of that HEU is going to go into a bomb.”
Edwin Lyman of the Union of Concerned Scientists said the use of HEU in space raised a number of issues, including increased security costs and stimulating demand for the production of more HEU fuel. It might even require, he argued, deployment of international inspectors in space to ensure the HEU is not being used for weapons.
Others noted that the growing commercialization of space brings other complications. “Elon Musk wants to go to Mars, and that means Elon Musk is somewhere thinking about nuclear reactors,” said Jeffrey King, an associate professor at the Colorado School of Mines. “One of the things in the cyberpunk dystopia that I think about, in reading and other things, is transnational corporations armed with nuclear weapons, or with the capability to develop nuclear weapons. That seems like something we should avoid.”
So, given all those concerns, why is NASA considering using HEU in space nuclear power reactors? Jeffrey Sheehy, chief engineer in NASA’s Space Technology Mission Directorate and the only agency official speaking at the event, said that decision to use HEU in KRUSTY was driven by practical concerns. “There was an enriched uranium fuel that was readily available that we could use in the reactor,” he said. “We could run a test and do a validation of the ability to develop and test a space reactor in today’s environment.”
KRUSTY was done in the cheap, relatively speaking: NASA spent $12.7 million on the project in cooperation with the Department of Energy, whose National Nuclear Security Administration provided $5 million for the test and “a lot of in-kind support,” Sheehy said.
HEU might be considered for Kilopower reactors in the future because it would allow the reactors to be smaller and simpler than those that use low-enriched uranium (LEU), which is not suitable for weapons but produces less power. “Everything in spaceflight is complicated, but we’re still looking for the least complex, the least costly, and the least massive system almost every time,” he said. “Every kilogram helps.”
An LEU reactor would be heavier and more complex than an HEU one, but by how much was a subject of debate. King estimated that an LEU reactor with the same power as an HEU one might weight twice as much, but also have a shorter lifetime.
Sheehy said NASA and the Department of Energy are currently doing trade studies on a ten-kilowatt reactor for surface nuclear power applications. That study, scheduled to be completed in early 2020, is considering both LEU and HEU fuels. “There are a lot of constraints, a lot of design requirements that will feed into that,” he said. “LEU and HEU are both in the trade space at this point.”
The study would be at the level of a NASA “mission concept review,” or a very early-stage study, he said, leading to a reactor that could be flown in 2027. “That’s plus or minus a year, but it’s certainly not going to be minus.”
Kuperman later asked if that trade study would include policy issues associated with using HEU. “Are we considering the broad ramification of the utilization of HEU in terms of policy, nonproliferation, political risk, in the design trade studies that we’re doing? The direct answer is no,” Sheehy responded. The study is focused on the technical issues and laying out various options, he argued, leaving the policy issues to others.
That could include Congress. Foster praised NASA for considering LEU for its nuclear thermal propulsion work (although it’s still an open question if LEU can work for such systems.) He noted he offered an amendment during consideration of the fiscal year 2020 appropriations bill that includes NASA that directed the agency to work on LEU power reactors. “I understand it is, in fact, easier to design with HEU, but technical ease is not a good reason to threaten global security,” he said.
Foster serves on the House Science Committee, which has been working on a new NASA authorization bill. However, when asked if he might seek language in that act directing NASA to only use LEU for nuclear power systems, he stopped short of a strict prohibition. “We’re not going to succeed at saying that we should permanently foreswear all uses of HEU,” he said. “Right now, we’re just trying to say, ‘Let’s develop a good alternative for what we anticipate to be the high-volume uses of power reactors.’”
That could, he argued, allow for some use of HEU reactors in space in the near term, but he clearly believed the future involved the use of reactors that don’t require weapons-grade uranium. “It is my feeling that you can do a lot of R&D before you’ll need many reactors in space,” he said. “There may be a very limited window for one or two or a small handful or missions.”
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