In good news for future planetary missions, NASA and the US Department of Energy's National Nuclear Security Administration (NNSA) have announced that the next-generation Kilopower Reactor Using Stirling Technology (KRUSTY) nuclear reactor has passed its initial demonstration tests.

Nuclear energy in space isn't new. In fact, the Curiosity Mars rover and almost every deep space mission to the outer Solar System depend completely on nuclear sources. The problem is that, with mission plans becoming steadily more ambitious and stocks of space-grade plutonium almost exhausted, the present systems simply are not up to the increasing demand.

To meet this challenge, NASA is developing its Kilopower system, which is a 10-kilowatt reactor that can run for a decade before refuelling. To avoid the plutonium shortage, it uses a solid-cast uranium 235 reactor core 6 inches in diameter surrounded by a beryllium oxide reflector. A mechanism at one end removes and inserts a single rod of boron carbide that starts and stops the reactor, while the reflector catches escaping neutrons and bounces them back into the core, improving the efficiency of the self-regulating fission reaction. Until activated, the core is only mildly radioactive.

Artist's concept of new fission power system on the lunar surface(Credit: NASA)

Kilopower is designed to be modular, so the self-contained reactor units and their Stirling generators can be hooked together to provide as much power as needed, whether it's a deep space probe or a Martian outpost. The latter would only require four units for full power and the reactors work independent of their environment, which gives them a broad range of applications and, unlike solar power, darkness has no effect on them, so they are ideal for lunar missions where night lasts 14 days.

The Kilopower experiment was carried out at the Nevada National Security Site from November 2017 through March of this year. David Poston, chief reactor designer at NNSA's Los Alamos National Laboratory, says the Nevada tests were intended to both demonstrate that the reactor works and that it is safe under abnormal circumstances. Two tests were conducted without the reactor generating power to test the components and a third increased power in stages. The final test was a 28-hour, full-power mission simulation that included reactor startup, ramp to full power, steady operation, and shutdown.

At present, the project is still largely conceptual, but it's hoped that the success of the demonstration will lead to its progressing to inclusion in the Technology Demonstration Mission program in Fiscal Year 2020.

"We put the system through its paces," says Marc Gibson, lead Kilopower engineer at NASA's Glenn Research Center in Cleveland, Ohio. "We understand the reactor very well, and this test proved that the system works the way we designed it to work. No matter what environment we expose it to, the reactor performs very well."

Source: NASA

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