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Is fusion better than fission?

The answer may depend – not on technology – but on creating a differentiated niche for public perception and regulation


  • Why might fusion be better than fission?

  • Why might fusion not be better than fission?

  • The Big Question – Regulation

Why might fusion be better than fission?

Two potentially significant advantages of fusion are:

  1. Catastrophic meltdown. Fusion has a lower chance of the plant catastrophically melting down.

  2. Short-lived waste. The byproducts from fusion have a much lower half-life than byproducts from fission.

Catastrophic meltdown

Fusion works by allowing small atoms (e.g. isotopes of hydrogen) to combine, and, in that combination, tiny amounts of mass are converted into energy. For fusion to happen, a threshold amount of energy needs to be added to get the atoms to react. A nuclear fusion reactor slowly adds small amounts of fuel to the reaction. If something breaks in the system, then the reaction tends to slow down because fuel runs out, and the threshold level of energy needed to keep fusion going is no longer provided.

By contrast, in fission you start by putting all of the fuel inside the reactor. The idea is to have large radioactive compounds (e.g. uranium) split up into smaller compounds and release energy in the process. Importantly, the energy required to start a fission reaction is a lot smaller than to start a fusion reaction. Once a fission reaction starts (and all of the fuel is loaded) it tends to build upon itself and accelerate. Control rods are used inside the reactor to slow down neutrons that reactions product, thus controlling the rate of reaction. If something bad happens (and well-designed fission plants have many ways of preventing this), there is much more of a tendency for the nuclear reaction to escalate out of control – resulting in a melt-down.

Long-lived waste

Fission splits large atoms into what are still quite large atoms that have have long half-lives – meaning they remain radioactive for hundreds or thousands of years. In fusion, small atoms are combined to produce other small atoms that typically have short half-lives. In fusion, the waste can be more radioactive in the short-term, but the radioactivity dies down substantially within decades.

Why might fusion not be much better than fission?

The goals of fusion and fission are the same in the sense that they both generate lots of heat that is used to produce steam to drives a turbine and produce electricity.

The steam generation and turbine aspects of fission and fusion are similar in design and cost.

The design of fission and fusion reactors themselves – the things that emit heat – differ very substantially. Both are highly complex to build and maintain. Fusion reactors don’t exist for power generation today, so predicting costs is tough. It’s not clear to me whether there is a clear advantage for fission or fusion in cost here.

To grossly oversimplify – while fusion might have a lower meltdown risk and fusion waste is easier to dispose of – fusion and fission do the same thing in that they are complicated ways to create a ball of heat that is converted to steam and then electrical power. Perhaps not as differentiated then as they might seem? This brings me to…

The Big Question – Regulation

Construction costs are the main portion of electricity generated from nuclear fission. This will likely be the case for fusion as well. A huge problem for fission has been wildly varying and upward spiral costs of construction. Here is the 2016 study from Lovering, Yip and Nordhaus that compares the costs of building a nuclear fission plant per kW of power, all brought to a 2010 cost basis. Take a look, individually, at the US, France, South Korea and Japan.

Why is there such a variance in construction costs, and in some cases wildly increasing costs? My best guess is – somewhat similar to large desalination plant projects – is long planning and permitting periods, followed by project delays due to design changes mid-project.

But why would there be such delays, and why would delays have such strongly variable impact across projects and – in the case of the US and Japan – cause costs that continue to increase?

One potential explanation is that nuclear fission kept discovering more and more safety problems over time and had to add more safety features. But then why were some countries – like South Korea – able to keep costs low?

The best explanation I can come up with is variances in regulatory regimes between countries, which drive different regulations (although not necessarily different levels of safety – e.g. are South Korean reactors less safe than US reactors, I think not). Further, the large variance in costs is potentially explained by unclear regulation or retrospective regulation, which makes project costs unpredictable and tends to result in changes mid-project that are costly.

Note: The chart above looks purely at construction costs, so differences in government financing for projects (which is a cost on top of construction costs) shouldn’t be an explainer for differences in trends. One might also argue that these construction costs don’t capture the true cost of nuclear, e.g. they exclude costs of waste handling. This may be true, but it still doesn’t explain why non-waste handling costs vary so much.

The big question is … What kind of regulatory environment will nuclear fusion earn and be granted?

True, the chances of a meltdown are lower with fusion (although, for well built fission plants, I think meltdown risks are managed to a safe enough level for me to be comfortable living nearby), and waste disposal issues are more straightforward with fusion. However, that certainly doesn’t guarantee fusion a safety-conscious but systematic and thoughtful and regulatory environment.

Regulations often address new technologies by squeezing them into old buckets. So, perhaps the biggest impact to be had by fusion entrepreneurs is to create new and differentiated public perception and regulatory environments for their innovation.

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