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Hello, and welcome to this week’s Fix the Planet, the weekly climate change newsletter that reminds you there are reasons for hope in science and technology around the world. To receive this free, monthly newsletter in your inbox, sign up here.

I’ve just about recovered from the COP26 summit in Glasgow, where 196 countries agreed to ramp up action on climate change. While wind and solar power often get a big airing at UN climate summits, nuclear has historically had little presence, despite offering a steady supply of low-carbon power.

Unusually, nuclear power did have a showing in Glasgow, at official events in the conference, deals on the sidelines and cropping up as a subject during press briefings.

One new technology popped up a few times: small modular reactors (SMRs), mini nuclear plants that would be built in a factory and transported to a site for assembly. A UK consortium led by Rolls-Royce wants to build a fleet in the country to export around the world as a low carbon complement to renewables. During COP26 the consortium . More private investment is expected soon.

Yet questions abound. Why should this technology succeed where large nuclear plants have failed to take off in recent years, beyond China? If they are small, will they make a sizeable enough dent in emissions? And will they arrive in time to make a difference to a rapidly warming world? Read on.

What’s the pitch?

Large new nuclear plants, such as Olkiluoto 3 in Finland and Hinkley Point C in the UK, are infamous for running over schedule and over-budget. Assuming Olkiluoto 3 achieves full power next year as planned, . And the huge upfront costs – around £23 billion in Hinkley’s case – means it can take a long time to get a final investment decision on new plants, as shown by the .

Advocates for SMRs argue they solve these problems, because building them in a factory and assembling them on-site will be faster and cheaper. Moreover, they say the technology will be more flexible, an important quality in energy systems increasingly dominated by the variable nature of renewables. “The big push here is pace,” says Alastair Evans at . “These are not large scale nuclear projects, we are not building the world’s biggest steam turbine, the world’s biggest crane, .”

What exactly is planned?

The reactors that Rolls-Royce SMR wants to build have been six years in development, with their roots in ones the company previously built for nuclear submarines. Despite being billed as small, the new reactor design is fairly large. Each would have 470 megawatts of capacity, a good deal bigger than the . The consortium hopes to initially build four plants on existing nuclear sites around the UK. Ultimately it wants a fleet of 16 , enough to replace the amount of nuclear capacity expected to be lost in the UK this decade as ageing atomic plants retire. Later down the line, the SMRs could be exported around the world too.

Evans says the first SMR would cost about £2.3 billion and could be operational by 2031. Later versions may fall to £1.8 billion, he claims. That may seem cheap compared to Hinkley, but an offshore wind farm with twice the capacity costs about £1 billion today, and that figure will be even lower in a decade’s time.

Why might the plan succeed?

“I think it’s got quite a lot of potential,” says Richard Howard of analysts Aurora Energy Research. For one, the expected subsidy cost for Rolls-Royce SMR is significantly lower than obvious alternative ways of providing a continuous supply of low-carbon power:  large-scale nuclear and gas plants fitted with carbon capture and storage. Secondly, he notes SMRs should be more flexible – able to dial up and down their output as needed – compared with large nuclear plants, which are usually always on. “What SMRs are providing  is complementing renewables really well,” says Howard.

He thinks there are two reasons the Rolls-Royce SMR vision may become reality. One is the private sector is putting in significant amounts of money for development. The other is growing international interest in the technology. While France is committed to reducing the share of nuclear in its energy mix, . Romania and Bulgaria with US SMR developers that could pave the way for Europe’s first SMRs towards the end of this decade. Canada and the US have long shown interest.

What might trip them up?

SMRs have been in development for years but have made little inroads to date. The UK government has been talking about them for much of the past decade, with nothing to show. Progress elsewhere around the world has been slow, too. Outside of Russia there are no commercial SMRs connected to power grids. Even China, one of the few countries that has built new nuclear plants in recent years, , four years late. It wasn’t until last year that leading US firm NuScale .

Paul Dorfman at the non-profit Nuclear Consulting Group, a body of academics critical of nuclear power, says the nuclear industry has always argued economies of scale will bring down costs so it is hard to see why going small will work. He says modularisation – making the reactors in factories – will only bring down costs if those factories have a full order book, which may not materialise. “It’s chicken and egg on the supply chain,” he says. He also notes the plants will still create radioactive waste (something another potential next gen nuclear technology, fusion, does not). And he fears nuclear sites near coasts and rivers will be increasingly vulnerable to the impacts of climate change, such as storm surges as seas rise.

What’s next?

The Rolls-Royce SMR group by the UK nuclear regulator, a process that could take around five years. It now needs to pick three locations for factories and start constructing them. The group also needs to win a Contract for Difference from the UK government, a guaranteed floor price for the electricity generated by the SMRs. Given the government’s support for the technology so far, that doesn’t seem like a huge obstacle.

The technology is also still young and may have hiccups. The much-vaunted cost savings from modularisation may fail to materialise. The planning process may throw up problems. Nonetheless, says Howard: “While there are challenges, I think they are surmountable.”

Whether SMRs play an important role in helping renewables decarbonise power grids remains to be seen, but observers think they will have a part to play. “My summary is we can’t get to net zero based on renewables alone. SMRs on paper seem to offer an attractive proposition,” says Howard.

MORE FIXES

• How much did COP26 change the course of warming this century? One analysis during the summit suggested pledges for Glasgow put the world on track for 2.4°C. But published in Nature Climate Change on Monday says we need to stop looking for such levels of precision and a range of 2.2°C to 2.9°C is a better way to consider the outcome.
• Talking of Glasgow, a wind farm near the city is to get a new neighbour an electrolyser to use water and the turbines’ renewable electricity to make “green hydrogen”. More on hydrogen in this New Ů��С��Ƶ article.
• Rainwater could be used to help microorganisms generate electricity with a microbial fuel cell, a team of researchers have shown. Full details in .
• Wind and solar power reign dominant in UK renewables, but tidal power is set to get a boost with the UK government .
• The number of countries and companies with a net zero pledge has grown dramatically – but shows that about half of companies have failed to be clear about their plans for the .

Elsewhere in the New Ů��С��Ƶ universe, you might be interested in this story on what UK energy firm Bulb’s collapse means for the renewables revolution, and to know Discovery Tours has a new wildlife tour in Sri Lanka.