Garbage Alert: Fusion Fuel “Crisis”

I’ve never had much faith in nuclear fusion as a “boundless source of clean energy for the future”. That vision has been around for over 50 years, and has yet to bear fruit. I did flirt with the vision, many years ago when I was a senior at Michigan State. I took a graduate class in plasma physics, dabbling my toes in the field. The course was interesting; I still have the textbook. But the more I learned, the more skeptical I grew. I couldn’t see fusion as having any prospects for becoming a practical source of electrical power in the remotely foreseeable future. It wasn’t the scientific challenge of confining a sufficiently hot and sufficiently dense plasma long enough to achieve net energy production. That was indeed a challenging problem, but it was the problems that would follow afterward that put me off. The practical engineering issues with building a working power plant around fusion energy – and doing so in a design that would be competitive with conventional nuclear power – looked insurmountable. At least with the technologies of the time.

I mention all that as context for what I’m about to say. I’m about to defend fusion energy against an attack campaign of disinformation. The campaign is based on a supposed inability to supply the tritium fuel that fusion reactors will require. I want to make it clear that I’m reacting to the attacks because they’re garbage, not because I feel obligated to defend a pet concept to which I’m committed. As they say, “I have no horse in this race and no dog in this fight”. It just annoys me to see blatant misinformation masquerading as objective science reporting.

Here's a key article that popped up in my Google news feed this morning: The Failure to Plan for Fusion Fuel. It asserts that the fusion research community has blundered by having no plans for how to provide tritium, the fuel needed to operate fusion power plants, once they begin to move into the engineering development phase. It goes further, to suggest that in fact there is no viable way to produce tritium in the quantities needed, and that the whole idea of fusion as a source of carbon-free energy is therefore fundamentally flawed.

I could point out that not all fusion energy schemes that are being explored require tritium for half their fuel. At least one aims for aneutronic proton-boron fusion. But let that pass. Tritium is indeed intended to be half the operational fuel for ITER and most other Tokamak-class reactors under development elsewhere.

I could also point out that even in the class of reactors expected to use it, tritium isn’t actually essential to be able to build a working reactor. A 50-50 mix of deuterium and tritium is optimal for fusion, and should make for the most compact and least expensive working reactors. But if the various plasma heating and stability problems that have blocked practical fusion energy to date can be overcome for the “easy” case of D+T fusion, then they can be overcome for the harder case of straight D+D fusion also. Once one has achieved the ability to control the plasma, it’s only a matter of reactor scaling. A commercial D+D reactor would be larger and more expensive than the smallest workable D+T reactor, but it could still work. Never mind though. We’ll let that point pass as well.

The attack article is correct, AFAIK, that no plans have as yet been set in place to ramp up the tritium supply to meet the needs of a substantial fusion energy industry, should one somehow spring to life over the next 10 years. But it’s not because fusion energy researchers are all idiots who failed to anticipate the issue. No plans for large-scale production of tritium have been put in place because there hasn’t been – and still isn’t – any need. The plans would be premature.

There have been major breakthroughs lately that have advanced fusion much closer to commercial feasibility, but there’s still a long way to go. We’ll be very lucky indeed if development proceeds quickly enough that we’ll need to worry about tritium supplies over the next five years. And when we do need to ramp the supply, it shouldn’t be all that difficult.

As the article is at pains to emphasize, tritium does not exist in nature in any usable concentration. It’s radioactive, undergoing low energy beta decay to ³He with a half life of 12.3 years. But there are two practical ways it can be produced. Some tritium is produced as a byproduct in heavy water nuclear reactors, when deuterium atoms in the heavy water coolant / moderator manage to absorb a neutron. Every couple of years, the heavy water is processed to purge the tritium. That’s done for safety, to reduce the amount of tritium that could get released in a coolant leak. The purged tritium is sold. According to another article by the same author, Canada’s heavy water reactors are the only commercial source of tritium. It’s not a large amount, and the reactors that produce it are scheduled to be shut down over the next couple of decades.

I don’t know if he’s right about CANDU reactors being the only commercial source, but it’s of little consequence. There is an easier way to produce tritium on demand. It can be bred from the isotope ⁶Li by neutron activation. The author of the article acknowledges that fact, but seems to labor under the impression that it’s somehow a showstopper. It’s not.

The isotope ⁶Li makes up 6.94% of natural lithium, which in turn has an average abundance of 20 ppm in the earth’s crust. That makes lithium the 25th most common element on earth. We’re not about to run out of it, however much we might use to produce tritium. Even though only 6.94% of it – the ⁶Li portion – can be used for that purpose, there’d still be enough to power civilization for millennia to come. If it were to somehow become a limitation far down the road, all that our descendents would have to do – if there are any still residing on Earth – is to build bigger reactors that can run on straight deuterium.

The author displays considerable confusion about breeding tritium from ⁶Li. To begin with, he assumes that it requires pure ⁶Li, and avers that there are no facilities for separating ⁶Li from its more abundant ⁷Li sister isotope – or at least none outside of secret military facilities. He’s wrong on both counts. Plain lithium with no isotopic enrichment can be exposed to a neutron flux, and the ⁶Li fraction will breed tritium without regard for the ⁷Li fraction around it. The sample will simply be less concentrated, and it will take longer to breed a given amount of tritium.

All of which is moot, because isotopic separation of ⁶Li and ⁷Li is not difficult – and not a military secret. It can be accomplished by chemical means that don’t require fancy centrifuges or lasers. It’s done routinely for production of ⁶Li-depleted lithium hydroxide as an additive to the cooling water in pressurized water reactors. See this article about lithium from the World Nuclear Association for details.

So does this mean I think it’s now smooth sailing to a bright future of clean fusion energy? No, of course not. We’ve only just gotten to the point where those hard engineering problems that scared me away from a career in fusion energy research all those years ago need to be addressed. All I’m saying is that obtaining an adequate supply of tritium isn’t one of those problems, and anyone who asserts that it is simply doesn’t know what they're talking about.

Do I think that the bright young MIT graduates and others now beavering away on those hard engineering problems will be successful? Damned if I know. But I wish them luck. I’m sure they’re smarter than I am now, in my doddering old age. I certainly won’t be betting against them.