Explainer: What is a small modular nuclear reactor?

As our energy systems focus more on renewables, and coal and oil are phased out, there’s been increasing talk about nuclear power – specifically about “small modular reactors”.

So, what exactly is a small modular reactor? Cosmos explains.

What is a small modular reactor?

A small modular reactor, or SMR, is a nuclear reactor, generally with a capacity of 300 megawatts (MW) or less.

For comparison, the smallest conventional nuclear reactors at present are at least 400 MW, and most are over 1000 MW.

The “modular” part refers to the construction of the reactors: they’re designed to be made in factories, ready for transportation to their sites. Modules could also be added once the reactor is running, if more energy is needed.

At the moment, there are two SMRs in operation: one 70 MW “floating” reactor on a barge in northeastern Russia, and one 200 MW high temperature gas reactor in northeastern China.

The Russian SMR began being built in 2007 and came online in 2019, while the Chinese began construction in 2012 and came online in 2021.

The USA and Canada also both have plans for SMRs, with plants proposed to come online in 2029 and 2028, respectively.

“There are several projects that will definitely be operating before 2030,” says Tony Irwin, an honorary associate professor at the Australian National University and technical director of SMR Nuclear Technology.

Irwin says that most of the proposed SMRs are pressurised water reactors (PWRs): the most common type of nuclear reactor. PWRs use the heat from nuclear fission to turn pressurised water into steam, which then spins a turbine and creates electricity. This makes water the “coolant”.

“There’s also one or two advanced SMRs, which are interesting, but obviously have more of a licensing challenge,” says Irwin.

These include high-temperature gas reactors like the one just opened in China, which uses gas as a coolant, and molten salt reactors, which use melted salts as a coolant.

Rolls-Royce has proposed plans for SMR factories in the UK, building 16 SMRs that could then be transported and assembled onsite. Each reactor would be 470 MW, making them much larger than other plants deemed ‘SMRs’.

Are SMRs safe?

“Really, modern large nuclear power plants are very safe, because they use now what’s called passive safety features – so they don’t rely on external electricity supplies, external water supplies, or operator action,” says Irwin.

“Something like a Westinghouse AP1000, which has been built in China and the US, would have survived even the Fukushima type action.”

Irwin says that SMRs use less nuclear material and might therefore be deemed “safer” than big nuclear power stations.

He cites the SMR proposed for Idaho, US, which if approved will be a pressurised water reactor built by American company NuScale.

“It has got what’s called indefinite coping time. It’ll keep safe forever,” says Irwin.

“It doesn’t need any outside electrical supplies, water, or operator action to keep it safe. It basically sits in a large pool of water – it’s very much like ANSTO [the Australian Nuclear Science and Technology Organisation]’s OPAL research reactor at Lucas Heights.”

So SMRs are safe to operate. But they still have some similar risks to conventional plants. Professor Ian Lowe, an emeritus professor of science, technology and society at Griffith University, points out that SMRs pose problems when it comes to waste and security.

“The two fundamental problems of nuclear energy are that the fissile material can be used for weapons, and they produce radioactive waste that has to be stored for geological time,” says Lowe.

“Whether the reactor is large or small, those problems still apply: that the fissile material requires military scale security to ensure it’s not misused, and at the end of the life of the reactors is high level radioactive waste that needs to be stored for certainly tens of thousands of years, if not longer.”

Will they be economically competitive?

Solar and wind have plummeted in price over the past decade. Can nuclear compete with renewables in Australia?

“I haven’t seen many credible calculations that suggest they’ll be cheaper,” says Lowe.

“Historically, the only situations in which the economics of nuclear power is credible is where there have been massive cross-subsidies from the [nuclear] defence program,” he adds, pointing out that Australia does not have such a program, nor any plans to get there.

Lowe is also not convinced that smaller nuclear power stations will be cheaper than large ones, because of the national security and waste management costs.

Successive GenCost reports from the CSIRO and the Australian Energy Market Operator (AEMO) have consistently found that, even factoring storage into account, solar and wind power have been the cheapest energy sources in Australia for years. They come in at about a quarter of the price of nuclear SMRs, according to the reports.

Irwin, however, points out that these reports aren’t comparing apples with apples when it comes to nuclear power.

“The nuclear SMR figures in the [2023 GenCost] report, are based on 2018 figures. And these have been disputed in numerous reports and inquiries,” he says.

Irwin adds that, taking into account capacity factor (the amount of time an energy plant is running), the lifetime of a plant (nuclear plants generally have lifespans about twice that of solar and wind), and transmission costs, nuclear power be seen as cheaper.

“When we say nuclear is too expensive, we’re not looking at the total system costs of running a system with these technologies. Because of the things like capacity factor and lifetime, and transmission and storage,” he says.

Are SMRs a viable option for Australia?

The AUKUS agreement, which hinges on nuclear submarines, has reopened the debate about the viability of nuclear energy in Australia.

Irwin says that SMRs could be switched in for retiring coal-fired power stations, citing Bill Gates’ proposed SMR in Wyoming, US, as an example.

“You’ve already got the infrastructure, the transmission’s already there, you’ve got the cooling water supplies already. Importantly, you’ve got the staff, who you can retrain.”

In its 2022 Integrated Systems Plan, AEMO predicts that 60% of coal-fired power stations will be closed by 2030 on current trends.

While the two SMRs currently operating took about a decade to build, ANSTO estimates that SMRs could take 3-5 years to construct. SMRs in Canada and the US, both already nuclear nations, are expected to come online by 2028 and 2029 at the earliest. Australia could expect to take years longer to do things like get community support and build approval and environmental impact plans.

“The other problem the industry has had is that they keep coming up with new designs, rather than having a learning curve, which gradually improves the economics,” says Lowe.

“All of the three [conventional nuclear power stations] being built in Western Europe at the moment are all one-off, and they’re all years behind schedule, and billions over budget.”

But Irwin thinks that the skillset demanded by AUKUS could open up a new industry for Australia.

“We’ve got an opportunity to manufacture SMRs in Australia, for our region. We could supply ourselves, but also our position in this region would be very good for a manufacturing centre for SMRs.”

Lowe disagrees, saying that while nuclear might make sense for other countries, it’s not necessary in Australia.

“I’ve seen studies that show that almost everywhere, getting to 80% renewables is pretty straightforward. But the last 20% is difficult in countries that don’t have the sort of solar and wind resources we do, and have larger populations, so greater demand for energy,” says Lowe.

“There will be countries, I think, that have to consider nuclear, but we’re fortunately not in that position.”