Humanity is on the verge of a giant leap: establishing the first long-term settlements in space. The first will almost certainly be on the moon. But how will lunar pioneers keep themselves warm and fed, without diesel for generators? How will they power their lunar rovers and light their labs, without wind for turbines? 

One novel technology—microreactors fuelled by encapsulated pellets—may be the answer. And it could also provide power to hard to reach corners of the earth.

Powering the places other fuels can’t reach

Powering these with a low-carbon, high-energy source would be vital. Micro-reactors are a type of nuclear reactor that is smaller and simpler than traditional nuclear reactors. “A microreactor is a totally different set of technology” explains Gary Jones, head of manufacturing at Rolls Royce, “It’s more of a solid-state, a much simpler system, it doesn’t pump water around as a coolant, it doesn’t have large backup systems, you can fit this thing into a footprint of a small family car.” 

Rolls Royce engineers have been building nuclear reactors to power the Royal Navy’s submarine fleet for decades. They know how to design reactors for long-term use in challenging environments, but for a much smaller reactor, a new type of nuclear fuel is needed. 

The idea of a micro-reactor isn’t a new concept either. Jones says, “In the 70s, the US launched a micro-reactor called Snap 10” but it only functioned as a test to see if it was possible. Earlier experiments dated back to the early 1960s.

One of the primary applications of micro-reactors is off-grid power generation. These reactors can be used to provide electricity to remote communities that are not connected to the main power grid. 

That could be “remote communities in Alaska that are currently dependent on barges shipping in diesel for three months of the year” says Catherine Harvey, a business development manager for Rolls Royce’s novel nuclear business. Or in developing countries, where a significant portion of the population lacks access to reliable electricity. Micro-reactors can also be used to power microgrids, which are small, isolated power grids that can provide backup power during outages.

Another use of micro-reactors is for heat generation. Thermal energy is generated through the controlled fission of nuclear fuel. For the whole system to be efficient, says Jones, “We’ll be looking to transfer that into an exchanger, and then into a turbine: we will be probably looking at gas.” A gas-powering system to produce electricity from excess waste heat would allow for this whole system to be more efficient. 

Micro-reactors can also be used to desalinate seawater. This is a critical process for providing clean drinking water to coastal communities that rely on desalination. Micro-reactors can provide the energy needed to heat seawater to the point where the salt can be separated, making it drinkable. 

Made for the moon

Micro-reactors can also be used to provide clean sustainable energy on the moon. Harvey says, “For space, we’re focusing on developing lunar surface power, or something that could be used for lunar surface power.”

If the lunar surface had a sustainable power source, it could power exploration, and even colonisation, of the moon. The idea of space colonies is not new, however, it is not feasible until we have reliable power sources. Micro-reactors could be the first step on this path. It is an untapped market. Jones says, “There’s no micro reactors on the moon or, or anywhere else. And we believe there’s a market for that, and therefore there should be volume to that.”

Space exploration and colonisation could help us learn more about the planetary systems, and harness new resources we haven’t seen before, or get a surplus of resources that are limited to our planet. 

Turning an idea safely into reality

Jones explains that the project is in a “concept phase at the moment”, with innovation going towards optimising the heat energy transfer, as well as working through the practical requirements of this new market. 

This has been the focus of engineer Katy Jarman, an expert in heat transfer. Jarman and her colleagues are looking at how different technologies can be used to move heat from the core, to be used directly or converted into electricity. The challenges of heat transfer, in Jarman’s words, are “from a size and weight perspective.” 

Two types of solutions are being looked at to figure out how to transfer heat effectively. 

The first is to look at gas cooling “where you run gas, Helium, Xenon, through the core, and then you run that gas through a power conversion system and use the heating of the gas to transfer the energy,” Jarman explains. 

The second option Jarman is researching is to use “heat pipes, which are quite a well-established technology.” Heat pipes are a highly efficient and versatile device used for transferring heat between two surfaces. They work by utilising the latent heat of vaporisation of a working fluid, which is a liquid that can easily evaporate and condense.

As the development of microreactors continues, it is important to prioritise safety at all stages of the testing process. Jarman says that “We’re designing for safety, we’re making sure that all of those barriers, and all of those defence in depth mechanisms are in there from the start, both from a design and technological perspective, and also from a people perspective.”

Focusing on safety requirements is vital for innovative nuclear technology. Jarman says, “It’s really important that each one of those people involved in the project understand their individual role in product safety, and we will have a collective responsibility to make sure that the product that we are designing, and that will go into service, is as safe as it possibly can be.” The team is putting in place product safety review boards, with appropriate safety management plans and training schemes, Jarman explains. And the company has a long track record of managing nuclear safety in the confines of submarines. 

A new industry for the UK

Commercialising micro-reactors would allow for the technology to be tested and refined in a real-world setting. This would help to identify any potential problems or safety concerns that could arise during operation on the Moon. It would also bring down the costs of the technology, helping simplify the design. Rolls Royce aims for a terrestrial variant that would fit in a lorry. “That’ll be one to five, maybe 10 megawatts,” says Jones. 

Harvey believes that “There are options to commercialise in the UK. The UK is quite uniquely positioned in that we have nuclear capability that we— in the civil sector—paused for a bit. But in the defence sector, we’ve carried that on and we’ve got that heritage in the UK of designing, manufacturing, commissioning, and then supporting and service, through to decommissioning, small nuclear reactors.”