Could small nuclear reactors power our towns and cities?

Thanks to Simon Taylor for the answer!

James - Nuclear reactors split the nuclei of heavier atoms from the periodic table, most commonly uranium, in what's known as a fission reaction. The energy released from this process can be used to generate electricity for national grids. Unlike coal, oil or gas stations, nuclear power plants do not produce CO2 during their operation and they're expected to play an increasingly vital role in the clean energy transition. You're right that nuclear reactions are also being harnessed to generate the energy needed on board long missions to the depths of the ocean and the surface of Mars. So, is nuclear power the fix-all to every energy challenge? Here's Simon Taylor, Research Associate at the Energy Policy Group at the University of Cambridge.

Simon - It's possible to create a workable nuclear reaction that allows you to generate electricity on a variety of scales including very small. The idea of putting them on a Mars rover or indeed on submarines and some ships is because they can provide energy over a very long period of time in a very reliable way, in a way that you couldn't achieve with fossil fuels. If you're thinking about a Mars rover or even on a nuclear submarine, cost is not the main consideration but if we're thinking about providing electricity for homes and businesses, cost is pretty important.

James - Mars rovers use something called radioisotope power. Radioactive plutonium gives off heat as it decays, designed to produce 110 watts of power, about the same used by a light bulb. This powers the rover's instruments and keeps it warm during the freezing nights and winters on Mars and, as the isotope of plutonium being used has a half-life of 88 years, it will provide energy for as long as the mission needs. But meanwhile if we're talking about nuclear reactors to power our towns and cities, that's very different. We need them to be affordable, to work at scale, and produce much more energy. But recently there has been interest in using smaller reactors to be able to do this.

Simon - The history of not just nuclear power stations but also coal and gas is that bigger has generally been better. There are quite good reasons for believing that there are economies of scale. There are really two parts to this. First, there are a lot of fixed costs to doing any project to build a new power station, things like siting and permissions and so on. Those are the same pretty much whether you're asking for a 10 megawatt power station or 1000 megawatts. Secondly, a lot of the equipment that goes into nuclear power stations is the same as for other power stations, other thermal power stations, and generally speaking it doesn't cost three times as much to build a reactor three times as big. What's new now is the idea of small modular reactors. Big nuclear reactors, at least in Europe and the US, have proven in recent years to be extremely expensive to build. It's the construction cost that's been the problem. Smaller modular reactors hope to be able to overcome this by being made from more modular components, that's to say essentially a smaller number of relatively standardized components which can be produced at cheaper cost because you're mass producing them, maybe not mass producing in the sense of a car, but producing far more units. Also, which allows you to benefit from the quality control that you get in a factory as opposed to building out on location.

James - So Laurie, while the technology on board Mars rovers and nuclear submarines are very cool applications of nuclear physics, this model isn't right for powering our towns and cities when it comes to the economy. But smaller nuclear reactors are being explored and at least in principle small modular reactors may allow us to have affordable cheaper nuclear power for the grid than traditional nuclear power stations. There are a number of small reactors in operation but to test the theory properly on their claimed economies of scale we need to see a few more be constructed and the effects of that mass production.