I’m not entirely closed to the idea that nuclear energy might have a role in a decarbonising world, but the recent claims that Ineos had held talks with Rolls-Royce on using its nuclear technology to provide zero-carbon energy to the Grangemouth refinery was not a winner for me.

Small Modular Reactor (SMR) nuclear appears to be knocking at Scotland’s door – and less for the purpose of fuelling our homes but in order to solve the problem of what’s considered to be a hard-to-abate industry, the production of petrochemicals, many of which are the building blocks of plastic. For, to create the high heats needed in, for instance, Grangemouth’s ethane cracker, the temperatures are beyond what an electrical heat source could provide, and nuclear is being seen as part of a system that creates hydrogen for the process.

Of course, Scotland’s door, as yet, is not open – and last year the First Minister ruled out any new nuclear power stations in Scotland, insisting that they “represent poor value for consumers”.

But with the UK Government already heavily backing the technology, the idea is unlikely to go away – despite renewed concerns, linked to the war in Ukraine, around security risks.

Across the world, the idea that nuclear has a role to play in decarbonising our energy systems is being increasingly promoted. It is touted as the fallback when the wind drops. It is seen as a tool in hard-to-abate industries. We are told a Rolls-Royce SMR needs 10,000x less land than equivalent wind energy.

The idea that nuclear might save us is not new. Some leading climate-change scientists – from James Lovelock to James Hansen – have seen it as an essential element in decarbonising our energy system. James Hansen, for instance, estimated in 2013 that over the past 40 years the use of nuclear power to replace fossil fuels had prevented 1.8 million deaths from air pollution and the emission of 64 billion tonnes of CO2 equivalent.

But, what’s clear, when you look at the arguments for nuclear is that, for the most part, they have been made in opposition to fossil fuels.

We are told nuclear is relatively safe – and has caused 97.6 per cent fewer human deaths than, for instance, gas – and also very low emissions. In the face of such a binary, who could not choose this safer, cleaner option, even if the instinct is to worry over disasters like Fukushima?

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But energy, in a renewables age, is no longer about nuclear versus coal. The problem for nuclear is that, as many reports are showing, just as the cost of renewables is falling, its costs look to be rising. Costs of the Hinkley C double reactor, for instance, have been estimated to have increased fourfold since a 2008 UK Government white paper. In the United States, modular reactor costs have nearly doubled. Meanwhile, a recent Oxford University study noted that nuclear was unlikely to be cost competitive, but predicted that not only would renewables costs continue to fall but that costs for key storage technologies, were also likely to fall dramatically.

One of the factors that can make these new nuclear plants seem more friendly is that appealing word “small”. But it’s worth noting that, as energy expert and chair of the Nuclear Consulting Group Dr Paul Dorfman has pointed out, the Rolls-Royce SMRs are hardly that small.

Previously the ceiling for an SMR was deemed to be around 300 MW of capacity, but these reactors are much larger, at 470 MW – and that, according to Dorfman matters because of waste and safety. “The Rolls-Royce design is simply not an SMR,” he said, speaking at a recent UK All-Part Parliamentary Group on Energy Costs. “It’s more than half the size of the 900 MW reactors that make up the bulk of the French fleet.”

How much nuclear waste are we talking about? Tom Samson, CEO of Rolls-Royce SMR, observes that if any human were to be fuelled for a lifetime by a Rolls-Royce SMR the waste produced would fill no more than a can of Irn-Bru.

I find that of little comfort, particularly given a recent report by Stanford University found that SMRs “will actually increase the volume of nuclear waste in need of management and disposal, by factors of 2 to 30”.

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A further risk, pointed out by Dorfman, is that currently two out of five power plants are located on the coast, and, as oceans rise, their safety could be compromised. Maps of predicted sea level rise suggest that Grangemouth is a key risk area.

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Advocates of nuclear often point to France, which is a world leader in terms of the low carbon intensity of its electricity due to the fact that it generates 70 percent from nuclear power. It’s worth noting, however, there is a growing scepticism - due to cost of replacement of an ageing fleet - over nuclear as a prime power source, even in France. A study published by Ademe, Frances’s energy transition agency, predicted that purely based on economics, renewables could take an 85 percent share in the country’s electricity mix by 2050.

Perhaps, though, Grangemouth is  a perfect targeted example of where nuclear could still be needed. Certainly, the emissions from Ineos need to be addressed. If growth in the plastic industry continues it has been estimated that emissions, globally, from plastic production would consume at least 12% of the planet’s remaining carbon budget by 2050.

Ineos has to find a way to avoid producing emissions. But isn’t growth in plastics itself something we should be addressing? Do we want petrochemicals, themselves a problem, to be the reason we bring next generation nuclear onto our land?

This proposal feels like two negatives hoping to come together and make themselves into a positive.

And, outside of mathematics, I don’t believe that ever adds up.