What nuclear microreactors bring to the energy table

Can we go even further and even smaller than the concept of SMRs? Possibly even into space? As plans move ahead for bases on the Moon and even mining and forging operations in orbit, energy is going to be the limiting factor. So why not a mini nuke?! Rolls-Royce are also working on those too with a line-up of reactors that are even smaller than their smallest modular reactors. They’re called microreactors, and to explain how they work, here’s Katie Jarman, assistant chief engineer at Space, Rolls-Royce Novel Nuclear…

Katie - A microreactor is a pretty general term for any sort of small scale nuclear, and they vary in size and they vary in power depending on what the application is. Our Rolls-Royce microreactors go from about 40 kilowatts from a space perspective, powering moon bases for humans to live there, to, at the upper limit, about 20 megawatts. That’s enough to power a small town but transportable by lorry or shipping container.

Chris - So you could have something capable of powering a town that would fit in a shipping container?

Katie - That's the plan.

Chris - How much would something like that weigh?

Katie - We are talking about under 10 tonnes. Obviously, to launch a microreactor and then land it on the moon and make it easily transportable around the moon, making it as light as possible is the answer. So every gram, every kilogram that you're putting on that rocket makes it more expensive, makes it more difficult. Getting it under 7 or 8 tonnes would be a really good thing.

Chris - Can you tell me what's inside the box, as it were? When we've got this shipping container sized thing, this is a self-contained micro reactor, what's actually going on in there? How does it work?

Katie - It works very similarly to large scale nuclear power plants. Ultimately, it's generating heat through nuclear fission, transporting that heat to a turbine or another way of generating electricity. The microreactors specifically have a choice of different technologies and the main decision that you are making is how you're transferring that heat from the nuclear core, from the uranium atoms, into your gas turbine to generate the electricity. Some use molten salt, some use liquid metal, and heat pipes have been a really compelling technology to be able to do that. We've chosen to use gas because it enables us to leverage our nuclear experience as well as our industrial heritage in gas turbines for airplanes to make it as small, as compact as possible.

Chris - Is the idea that these are, to take a battery analogy, the equivalent of a rechargeable battery where you could go in and replace the fuel in them to give them a longer life?

Katie - It depends, and it will vary from design to design depending on how big it is, what its actual application is, how easy it is to get to wherever you are positioning it. There are benefits in both ways. One of the main things around microreactors is that the whole thing is pretty compact and is designed to be pretty self-sufficient and flexible, so it might be easier to just replace the whole thing.

Chris - It sounds amazing as a technology. You could see, if you've got a big building or a big site or something, you could just put one of these in and you wouldn't have to worry about having massive connections to the grid or whatever. You'd have a self-contained reliable power supply at the place you needed it.

Katie - Absolutely, and I don't think anyone is saying that this is going to replace large scale nuclear, but nuclear has obviously got a really important role to play in combating the climate emergency. Small nuclear also has a really important role to play exactly for that reason: it doesn't need grid connection. You've got it exactly where you need it. It's really useful to decarbonise the traditionally hard to decarbonise industries, whether it's hydrogen production, whether it's data centres. If you look at Ireland, I think about 20% of the national electricity consumption is data centres, and that puts an enormous strain on the infrastructure. It also means that the data centre companies are really sensitive to the price of electricity. Now, if instead of being reliant on the grid they had their own entirely predictable, very reliable source of energy from a microreactor, for example, that is a complete game changer.

Chris - I suppose, by investing in doing this in space, if you can do it in space, you can do it anywhere. It will help to drive the implementation of this technology on Earth as well as up there on the moon base or whatever?

Katie - Absolutely. I think they've shown, going way back to the Apollo missions, that one of the main benefits of doing those missions was all of the technology that it really kicked off back on Earth. Things like microprocessors came out of the Apollo missions, something like a microreactor could be the Artemis generation's opportunity for really benefiting our lives here on Earth. This isn't sci-fi, this is what we are working on here and now. The Artemis missions go out to the early 2030's, and the intent is that fission power on the moon will be part of those.

Chris - And just to finish Katie, because obviously when we talk about nuclear, people are always concerned about safety. If we are into the realms where we're going to put these things into space, there's therefore a burden of proof that this is going to be safe on the part of the manufacturers and those using these sorts of devices. How will you approach that? How are you going to safeguard this?

Katie - That's a really good question. We all know that space launches are fraught with risk. One of the things that we are doing is making sure that the reactor has never gone critical and is not radioactive on launch. It won't be turned on until it's in situ on the moon. Other things that we'll do is demonstrate that it’s impact resistant. There are examples where they've put trains into transport containers to demonstrate that, even under such a significant impact, they aren't scratched, they're not damaged in any way. We'll be building up the confidence that we've got in its safety under those extreme circumstances throughout the design programme and into manufacturing and test.