The United States, Russia and China are racing to build nuclear reactors on the moon, as scientists warn about the possible risk of a radioactive mishap.

In January, NASA, the US space agency, announced plans to develop a nuclear reactor on the moon by the end of 2030. Russia, working with China, aims to do the same by 2036 as they strive to advance space exploration.

The reactors will be needed to power mining of frozen water trapped deep in the moon’s craters, which scientists believe could supply drinking water, air, and rocket fuel for future bases. The reactors would also provide power for lunar bases. Here is what we know. Which countries want to put nuclear reactors on the moon?

The US said NASA’s Lunar Reactor 1 would produce 20 kilowatts of electricity, creating enough power to run on its own for five years without maintenance.

NASA’s reactor is designed to be compact, weighing under 6,000kg (13,200 lbs) and will fit inside a rocket compartment measuring 3.7 metres (12 feet) long by 5.5 metres (18 ft) wide.

Russia is also building a nuclear reactor, which is expected to produce 10 kilowatts. The reactor, called Selena, will be able to run for a decade without maintenance. It will be ready to power a Chinese-led moon base by about 2036.

The Selena reactor is expected to be even lighter than NASA’s, weighing about 1,100 to 1,300kg (2,400 to 2,800 lbs) for an easier and softer landing on the lunar surface. This would not be the first time nuclear reactors have been placed in outer space.

The Soviet Union launched more than 30 nuclear fission reactors into Earth’s orbit between the late 1960s and the 1980s to power spy satellites during the Cold War.

The small, 1,000kg (2,200 lbs) reactors powered radar-tracking spy satellites using heat from splitting uranium atoms into 3 to 5 kilowatts of electricity. They are no longer operational, and no other country has sent nuclear reactors into space.

The US has spent $20bn on advanced space nuclear programmes over the past 70 years, but has never successfully launched a nuclear reactor into space since an experiment in 1965.

That experiment was carried out to see if nuclear energy could power a satellite. It worked at first but accidentally shut down after just 43 days because a non-nuclear electrical part of the satellite broke down. It is still floating up in space today.

Previous attempts by the US to develop nuclear projects have stalled due to shifting budget priorities How do you put nuclear reactors on the moon?

First, scientists will have to build a reactor on Earth, which will then be transported to the moon using a robotic spacecraft that fires rocket engines for a slow and gentle touchdown.

Both the US and Russia say they would keep their reactors switched off until they reach the moon, to keep radioactive risk at a minimum until the last step.

Once set up on the moon, the reactors would be designed to run without maintenance for years, supplying power to bases engaged in mining on the lunar surface. Why does the moon need a nuclear reactor?

The US, China and Russia want to build bases near the moon’s south pole, close to the known sources of water ice. The ice sits in the permanently shadowed craters, where sunlight has not reached for millions of years.

As well as powering the moon bases, the reactors would also supply enough power for mining. So far, the US, Russia and China want to mine for frozen water which, once released, could be used to support life on the moon at bases where people could live and conduct research.

Tech billionaire Elon Musk has also said he wants to extract minerals such as aluminium, titanium, and silicon, required for manufacturing satellites.

Solar power for such endeavours would be limited as the sun shines on any one spot on the moon only half the time, so solar panels would go dark for about two weeks every month.

Simon Middleburgh, director of Bangor University’s Nuclear Futures Institute (NFI), told Al Jazeera that solar power is too limited to provide the steady flow of energy a moon base would need, while batteries and diesel are too costly, because everything has to be launched from Earth.

Nuclear energy is the “obvious choice”, Middleburgh said, adding that it must be used “responsibly”.

It is likely that three or four reactors working together would be required to provide sufficient energy for mining lunar ice as well as supporting a moon base, he added. Why the rush? It comes down to geopolitics.

In a December 2025 executive order US President Donald Trump ordered NASA to build a lunar reactor ready to launch by 2030. Chinese President Xi Jinping and Russian President Vladimir Putin have revealed similar plans.

In August this year, Sean Duffy, the US transportation secretary, said the US is in a “race to the moon, in a race with China”.

Middleburgh said the 2030 deadline is likely for building the reactor itself, but the harder part will be landing on the moon and safely setting up the system.

“The biggest challenge isn’t really the nuclear technology at all; it is the regulation for launch, the availability of a launch platform itself, and the landing and setting up the system on the lunar surface ready for it to be operated sustainably and safely,” he said.

The race to the moon also comes amid growing military competition beyond Earth. In September, the US announced it had deployed weapons into orbit which officials said would be used to defend US forces.

While the US did not provide details about these “weapons”, experts say they are likely to be space-based communications jammers, rather than kinetic ones that launch strikes.

The announcement raised concerns about the concept of “space weapons” or the use of space for military purposes, including the potential targeting of satellites that provide GPS, communications and intelligence. What could go wrong?

Middleburgh told Al Jazeera that an accident during the launch of the reactors would be less frightening than it sounds because uranium alone, before it is used in a reactor, is not very radioactive. However, that changes once the reactor is switched on. The risk is bigger if a running reactor falls back onto Earth, analysts say.

In 1978, a Soviet satellite carrying a reactor, Kosmos 954, scattered radioactive material across nearly 124,300 square km (48,000sq miles) of northern Canada.

The accident forced an expensive military cleanup of the highly radioactive fragments and microscopic particles.

On the moon, Middleburgh says, any contaminated area would be “extremely localised” if there were to be a similar accident. Who has sovereignty over the moon?

Legally, no one. The 1967 Outer Space Treaty bans countries from “claiming” the moon or any part of it, though they have ownership of the equipment they send there. The treaty does not ban nuclear power in space.

Antonino Salmeri, director of the Lunar Policy Platform, a nonprofit, told Al Jazeera that a reactor can be lawful if it follows the treaty’s principles, including peaceful use and avoiding harmful contamination.

Norbert Schorghofer, a senior scientist at the Planetary Science Institute in Arizona, US, told Al Jazeera all signatories “have the right to mine the lunar surface as long as it is for peaceful purposes”.

Whichever country’s reactor gets to the “best” water ice first could claim a “safety zone”, which would not be a land claim but could operate like one. Salmeri said declaring one creates no territorial rights, but a reactor shuts others out anyway, because nobody wants to enter a radioactive area.

A Lunar Policy Platform report released last month points to another problem: Who is responsible if something goes wrong? The report says existing liability rules have not been designed to regulate the use of long-term hazardous equipment on another celestial body.