Mar 27 2023

Nuclear Microreactors

The first nuclear powered vessel was completed in 1959. Since then there have been nuclear powered vessels in the oceans, including many nuclear submarines. The obvious advantage is that such vessels can stay at sea for long periods of time without refueling. These ships use what are called nuclear microreactors, those that produce <50 MW of electricity (small modular reactors create 50-300 MW, and large traditional reactors about 1,000 MW).

There has been renewed interest in these nuclear microreactors recently as we explore new possible solutions to global warming. Nuclear power is a great option, because it produces a large amount of power in a small footprint and does not product CO2 as a waste product. It also serves as either baseload or increasingly on-demand energy, which makes it more useful than intermittent sources.

But nuclear also has some challenges, namely that it takes a long time to get a new plant up and running, and the initial investment can be very high (in the billions for a traditional reactor). For this reason the nuclear industry is moving in the direction of small modular reactors which are quicker and cheaper to build (although they may lose some of the economy of scale of larger reactors). But we may be able to go beyond small modular reactors and repurpose the microreactors used by naval vessels as power for the grid. Such reactors may also serve as the core of nuclear engines for spaceflight, or be used to power off-world bases and settlements.

Rolls-Royce Holdings (not the car company – that split off decades ago) recently unveiled their designs for its own microreactor. They have been producing nuclear reactors for submarines since the 1960s, so they are an old player in this technology space. Their goal is to do exactly what I said – to repurpose the technology they have been developing for ships to be used for grid energy, and eventually nuclear rockets and power bases on the Moon and Mars. Rolls-Royce is also getting into the small modular reactor business, but that’s a separate story.

The potential advantages are numerous. Such reactors may produce 30 MW or even as much as 50-60 MW of electricity. That is not much compared to a large nuclear plant, but only 20 of them would be the equivalent, and they can be more easily placed closer to where the power is used. This may also allow for recapturing waste heat to use as heating, adding to their efficiency. For comparison a large wind turbine is rated at 2-3 MW, but typically operates at about 50% capacity. So one microreactor may produce over time as much as 10-20 wind turbines.

Microreactors may not have to be refueled any more often than every 10 years. They are relatively easy to operate, and therefore require less crew to staff. They can be entirely built inside a factory and then moved to their location. They can be swapped out easily for upgrades or to replace ones that have malfunctioned. They are also very safe by design. The uranium is encased in multiple layers of protection.

We can look at the experience of nuclear subs to get some idea of the safety record of nuclear microreactors. The US has had nothing but minor mishaps, with no serious nuclear incidents. The Russians have had several nuclear submarine accidents, but none involving a meltdown of the reactors. A submarine is a much more challenging environment than a stationary reactor in a hardened facility on land.

The idea is also to develop nuclear microreactors optimized for the grid. Hopefully these would be even safer than their submarine counterparts, which are pretty safe. But this still leaves the big question, and that is cost. None of the above will matter if they are too expensive. There are two primary variables here – how much power does the reactor generate, and where are you placing it. The larger microreactors are more cost-effective, so perhaps we should be focusing on the 50-60MW designs. But even the smaller reactors can be cost competitive in some locations, specifically remote communities. Electricity cost will likely be greater than the best grid power available now, but less expensive than options used by many remote communities. Of course, as I have discussed many times, cost of power is partly a choice – how much do we value environmental and health protection?

At the very least, microreactors could become the most cost-effective and convenient option for many parts of the world. As I have said – we should not be thinking of energy production in terms of what is the single best solution, but rather how can we leverage every solution in the best way. This is very location and use specific. Put each type of energy production where it is most cost effective and environmentally safe. Microreactors might become the preferred solution for remote energy needs.

This can have a couple of positive impacts. First, remote communities now largely rely on diesel generators to make their energy, and/or use natural gas for heating. Replacing those fossil fuels with anything carbon neutral would be great. Some communities might do better with solar panels or wind turbines, but again, that depends on terrain, climate (solar panels are not great in Alaska), and other considerations. For small microgrids, relying entirely on intermittent sources could be problematic, and would almost require large amounts of battery storage. Or you could bury one microreactor in the ground and have enough power to serve a community for 20 years.

Second, having more options for remote energy production would allow for more communities to develop, without having to bootstrap their standard of living with fossil fuels. We don’t want to tell communities they cannot climb out of poverty because we already used the world’s carbon budget. We should give them climate-friendly options for development.

There very likely, therefore, are cost-competitive applications for nuclear microreactors. They will be the early adopters that allow the industry to continue to develop this technology. The hope is that the tech will become increasingly reliable and efficient, to the point that it can become cost effective as grid energy. Essentially more and more locations will become cost competitive, until microreactors settle in to their optimal place in our energy production infrastructure (if they have one).

It would be good news if they do turn out to be economically viable, because that will help fuel the development of these reactors for use in aerospace. We definitely need to make the move from chemical to nuclear rockets, which should at least cut travel times in half. This is critical if we ever want to send people to Mars, or have a vibrant cis-lunar space infrastructure. Also, microreactors are probably the best option to power settlements on the Moon or Mars. Solar power is difficult on the Moon, as there are 15 days of night everywhere except the poles. Solar radiation is only 50% as strong on Mars as on Earth – not a dealkiller, but a challenge. Dust is also a challenge. Power is also not a luxury on Mars. Having extremely reliable power is a must.

The bottom line is that this is an extremely useful technology to develop, with several possible key applications. There are multiple initiatives to develop microreactors, Rolls-Royce just being one. I’m hoping this will be a stealth technology that doesn’t get a lot of attention until suddenly it turns out to be a great option helping us get to net zero.

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