The Hater’s Guide to Thorium Reactors

Programming note: I made the mistake of promising a Twitter thread on thorium reactors today. I ain’t got time for a 14-tweet thread and f***ing CHARACTER LIMITS. So have this blog post instead. I’ve got six beers and a few hours to pound this one out. Enjoy!

It’s time to have The Talk, friends. You’ve read about thorium reactors on the internet by now, I’m sure. Heard whispers from your classmates about how great they are. Maybe you opened up an incognito tab after mom and dad went to sleep to see what “hot LFTR reactors” looks like with SafeSearch off. This curiosity is natural, of course – it’s all part of the process of becoming a true nuclear power stan. But before you find yourself all hot and sweaty in containment, wearing a double set of protective clothing and screaming at the heavens “who on earth decided to try pyroprocessing at power?!”, there are some things you should know about thorium reactors. They’re not all they’re cracked up to be.

Beer #1: New Glarus’ Kid Kolsch

New Glarus Brewing Co. is a real American treasure. A German-style brewery in Wisconsin (northern US), their beer is good, solid, everyday stuff. And it’s not sold outside of Wisconsin, giving what few beers I bring back from my parents’ house a special significance. You might have heard of their flagship beer Spotted Cow (which is priced like Budweiser on draft but much better) – but this Kid Kolsch is pretty nice. Nice carbonation, clean finish. Bit of grain. I’m acutely aware of the spot on the roof of my mouth where I burned my mouth on a late-night pizza last night. It’s a no-frills beer and a good palate cleanser before I get deeper into the muck here.

Topic #1: What is a thorium reactor, anyway?

In the broadest sense, a thorium reactor is a nuclear reactor that derives some or all of its energy from the fission of thorium rather than the fission of uranium. Thorium sits down on the bottom of the periodic table near uranium and plutonium, so it certainly seems nuclear at first glance. But we need to talk a bit of nuclear science first, about how thorium becomes a source of energy.

Nuclear binding energy - Wikipedia
Only one chart in this one, I promise…

There is energy contained in the nucleus of an atom – binding the neutrons and protons together. Atoms bigger than iron-56 release energy when you split them into smaller chunks, while atoms smaller than iron-56 release energy when you fuse them to make bigger atoms (e.g. why hydrogen fusion makes energy). Up on the right side of that chart, next to uranium, is thorium-232, which is the only naturally-occurring isotope of thorium.

So in the wide world of atomic physics, we know that if we split thorium into smaller pieces, we will get energy out. But how do we actually fission atoms? In short, with neutrons. And some atoms fission more easily than others.

Consider two similar statements:

  • if we hit this atom with a neutron of a specific speed, then there is a probability that it will split into two or more pieces
  • if we hit this atom with a neutron of a specific speed, then there is a probability that it will absorb the neutron into its nucleus

In reality, for uranium and thorium isotopes, there are big ranges in which different isotopes can absorb neutrons for “keeps” or for fission. There’s legit physics behind the squiggly (resonance) region on the graph below – but suffice to say that we have a good handle on why this happens, even if I would have trouble explaining it.

Comparison of the capture and fission cross sections of 238 U and 232 Th. 
I lied.

The graph (neutron speed on x-axis, probability on y-axis) above shows two things:

  • In blue and red: uranium-238 and thorium-232 have similar behavior when it comes to absorbing neutrons to form uranium-239 and thorium-233
  • In green and purple: uranium-238 and thorium-232 have similar behavior when it comes to fission, unlikely at high neutron speeds and very unlikely at anything less

So what happens when uranium-238 and thorium-232 successfully absorb a neutron? They decay into plutonium-239 and uranium-233. Like uranium-235, Pu-239 and U-233 are good candidates for fission at low neutron energies. Th-232 and U-238 are fertile, meaning they absorb neutrons and decay into something easier to fission at lower neutron energies. In a lot of ways, thorium-232 simply substitutes for uranium-238 in the “breeder” role, but it’s hard to find a compelling reason of why other than some mystical energy about thorium. [There are many proposed uranium breeder reactors out there.]

File:Fission cross section of 4 nuclides.png - Wikimedia Commons
This isn’t going well, is it?
  • In blue, red, and purple – Pu-239, U-235, and U-233 have pretty similar properties when it comes to fission
  • In green, look at U-238! Isn’t it sad? It’s not very good at fission at all.

So, to summarize all of this up: the fundamental “thorium-ness” of a thorium reactor is that it has a good probability to absorb fast neutrons and decay into uranium-233, which in turn is likely to fission via collision with slower (“thermal”) neutrons and release energy.

Reactors with water as coolant slow down neutrons to slower (thermal) speeds to cause fission in uranium-235. The standard thorium reactor is not water-cooled, so neutrons stay fast (i.e. on the right side of charts above) and the thorium-232/uranium-233 tandem produces the energy through uranium-233 fission. You’ll see thorium reactors proposed with both solid and liquid (yes, liquid!) fuel – but we’ll talk about that later.

Beer #2: Walnut River’s WARBEARD

When I moved to the heartland, I went on a big kick for local beers. Warbeard is made by Walnut River Brewing Company in El Dorado [el duh-RAY-doh], Kansas, and it’s a delightful little Irish Red. Maltier and toastier than your basic red, it’s a big comfort beer for me and just light enough that you can get away with drinking more than two. If you come visit me, I’ll buy you one.

Topic #2: Every Hero Needs a Good Villain

I’m a big comic book movie guy – and it’s fair to say that most of our favorite heroes are as good at solving problems as they are at creating new ones for themselves. The Joker exists as a response to Batman’s brand of justice. Ivan Vanko doesn’t build that bootleg arc reactor and (very kinky) Whiplash suit if Tony Stark isn’t parading around the stage in armor. Stay away from the damn Speed Force, Barry Allen!

Proponents of thorium reactors (and really, all advanced reactors) usually start by telling you what thorium reactors are not – and what they are not are light water reactors. Light water reactors – LWRs – are the 450-ish boiling and pressurized water reactors that generate the ultramajority of our nuclear energy today. And by being notLWRs, the discussion often turns to a litany of reasons why LWRs are bad.

I’m going to talk about a few of these reasons in turn, but the one at the absolute top of my list is the concept of safety. You’ll hear this a lot – “our reactor reactor design is very safe!” But too often it comes across like a chef proclaiming “there are no rats in our kitchen.” What are you hiding, chef? Is your crab and lobster ravioli neither crab nor lobster? [Confession: I may have sold you canned crab and/or imitation lobster ravioli sometime c. 2015-2017)]

When proponents of thorium reactors talk about how their reactor can’t “do a Fukushima” or that some design feature is meltdown-proof, the implication is that existing reactors are dangerous, are going to melt down, are going to explode. That they need to be fixed or shut down. And while the designs of our 1970s/1980s-vintage reactors aren’t perfect (have you ever heard of an ice condenser?), it’s important to discuss how new reactors enhance nuclear technology, or how they offer new features or efficiencies, rather than framing it in the language of fixing problems. We’re all in this together – and success of one nuclear technology over another can’t be a zero-sum game for this reason.

So light water reactors are often cast as an imperfect technology with serious downside, whereas thorium reactors (or breeder reactors as a whole) are perfectly safe. Frankly, it’s a lot easier to do that when thorium reactors mostly exist on paper…

Beer #3: Old Backus Barleywine, Free State Brewing Co.

This beer rocks. Free State is in Lawrence, Kansas – a delightful spot if there weren’t a global pandemic on. Every so often they distribute a four-pack of something dense, and Old Backus continues the grand tradition. I’m not cultured enough to know the difference between a barleywine and a “barleywine ale,” but I’m not too particular when it comes to this style. With two digits to the left of the decimal point on the ABV, I may not be long for this blog post.

Topic #3: The Official Reactor of Dudes Who Voted for Yang

There’s a necessary simplicity to slogans. Catchy, repeatable, riffable. But “tax the rich” isn’t a fiscal policy. “Build the wall” is not an immigration policy. “Ban fracking and coal” is not the solution to climate change, nor is “just say no” a good drug policy. So when my pet issue (nuclear energy) finally got its time in the sun during the 2020 American presidential campaign, imagine my surprise when we wasted our collective shot on “Andrew Yang says build thorium reactors.”

Seriously? This f***ing guy?

I get bombarded with thorium questions at family barbeques and bars because made thorium reactors a thing with a certain demographic of Extremely Online Men. Let’s take a look at Andrew Yang’s thoughts on thorium reactors (I had to use the Wayback Machine for this one):

I tire of my vision.

I’ll admit that I wasn’t expecting much when I absentmindedly searched for an archive of this page, but it truly has everything! Follow me down the list here.

Thorium can produce more energy than uranium – can it produce more energy than natural uranium? Enriched uranium? In different reactor types? I need to see your work.

There is more thorium than uranium out there – this is going to break the heart of many of my readers, but uranium isn’t particular rare. Cheap uranium, found at very high grades, is the rare thing. So saying “there is more thorium than uranium on earth” is a function of the supernova of that provided our solar system’s heavy elements, not a real indicator of scarcity. Quantity IS NOT value. [Looking at you, EV per pound guys.] tl;dr: uranium not rare, thorium less rare

Thorium is a byproduct of other mining – turns out, so is uranium. Did the Yang campaign do its research with Bing instead of Google? The Olympic Dam copper mine is one of the largest single sources of uranium in the world, despite the fact that it is not a uranium mine. In fact, with higher uranium prices, we’d be stripping uranium out of all kinds of things – rare earth mines, phosphate plants, gold tailings. It’s just not economical right now.

Thorium is retrievable from monazite ore – as it turns out, so is uranium!

Thorium can be mined from open pits – THE LANGER HEINRICH MINE WOULD LIKE A WORD

Paladin eyes $50/lb pricepoint for restart
Pictured: uranium, open pits, probably some scorpions

Thorium reactors produce less waste than uranium reactors – even if we assume this is true, we’ve got to dig a bit deeper here. We think of nuclear waste less in terms of volume and more in terms of its longevity and its activity (i.e. how radioactive it is). While it’s possible that a well-executed thorium nuclear fuel cycle could reduce waste longevity, it is unlikely to have significantly less radioactive waste on account of most of the activity coming from fission products (i.e. the things uranium splits into when it fissions). This is a long way of me saying “press X to doubt.”

Thorium MSRs are safer than the earlier generation nuclear reactors – see above.

NUCLEAR ISN’T A PERFECT SOLUTION” – why respond to this when I can post this four-second Sam Kinison clip which perfectly encapsulates how I feel:


It’s cheap to score points by dissecting the policy positions of a failed (primary) presidential candidate, but a win is a win. When I think of The Discourse on thorium reactors, I think of this sort of list. Well-meaning, technocratic, directionally correct – but misguided. I don’t want to shame thorium guys too badly, I want to bring them out to the plant for a tour (and maybe an internship or a job!). I would, however, like them to stop posting.

Beer #4: The Stuff of Legend, Boulevard

Boulevard. Kansas City, Missouri. Barrel-aged stout with vanilla and cocoa flavors. They’re called legends because someone forgot the original truth. At 13.3%, this beer seems more capable of making legends than memories.

Topic #4: You Can’t Build [REDACTED] with Thorium

One thing not listed above, but commonplace elsewhere, is the idea that the thorium fuel cycle cannot be used to make nuclear weapons, whereas the uranium fuel cycle is inherently tied to nuclear weapons.

Just kidding, of course it’s on Yang’s old website.

Shout out to whichever unpaid intern wrote my blog post for me.

There’s a certain attitude about thorium power – that the US government conspired (or is actively conspiring) against thorium energy because you can’t make bombs with it

I’ll spell it out very clearly: of course you f***ing can. Thorium-232 is just a gateway to uranium-233, after all, and that stuff is most definitely explosive.

The Indians built the Shakti V nuclear device with a U-233 core. The US government has a stockpile of U-233 in Tennessee, ostensibly for the same purpose. This stuff is on Wikipedia – for all to see – and yet people keep talking about how you can’t divert thorium power for nuclear weapons. It’s probably not as “good” as plutonium at going boom, but it ain’t inert.

The US government did attempt some thorium reactors or thorium-fueled cores back in the day, but like many of the other “fast” reactors, it wasn’t a successful technology class for making commercial power. Fast reactors were great at breeding material for bombs, but a handful of the early test reactors were slight or total failures and the technology for naval propulsion and commercial power reactors diverged to water. And with a uranium enrichment infrastructure to enrich material for bombs already in place, it certainly didn’t hurt the momentum towards uranium-fueled nuclear reactors.

That said, inertia is currently conspiring against thorium. There’s a much shallower technical knowledge in the area. We know how to design efficient cores with uranium fuel and know all the tricks. We’ve got a dozen fuel cycle facilities designed to make uranium fuel, to process uranium, to handle uranium wastes. We’ve got years of environmental knowledge on how to safely (or unsafely) mine for uranium. For thorium? It’s simply behind uranium in scientific knowledge. That’s a disadvantage, even if it’s not inherent to the technology.

To boot, the intersection of allegedly well-meaning non-proliferation activity and the anti-nuclear movement is notorious and deeply unproductive, and this “thorium is no good for bombs” bit feels cut from the same cloth as the anti-nukes who killed many 1970s/1980s nuclear projects that gave us coal instead. Just say no.

Topic #5: Designing a reactor is hard, running one is harder

Even if we took the most generous approach to every one of the things above, the fact still remains that the world has sixty-plus years of operating experience with water/uranium reactors. We know what components break, when they do, and how they do it. We know how to design high-performing uranium/zirconium fuel (it took many years of trial and error). We’ve done countless studies on how to dispose of light water reactor waste. And the safety analysis that enables the licensing and safe operation of our existing nuclear fuel is enormously complex, borne of years of experiments, models, and tests (and paperwork!).

There’s just so much labor built into the regulatory status quo that doing anything different becomes an enormously difficult exercise. Want to license a reactor that uses liquid metal as a coolant? First, invent the universe (kidding, but not really). I’m not endorsing this regulatory fait accompli, I wish it were otherwise, but it is what it is. So not only is the knowledge deck stacked against a thorium reactor, so is a speedy trip through the licensing phase. Because many thorium-based designs use higher temperatures, new coolants, or liquid fuel, there are just so many seemingly-benign materials questions that are not yet satisfactorily answered.

And that’s maybe my chief gripe with all those outside of the insular nuclear industry. Building a reactor is hard. Running a reactor is harder. Safety takes vigilance and effort. And so I’m skeptical of those who nonchalantly advocate for major technological changes. Building a new reactor isn’t easy peasy lemon squeezy – it’s difficult difficult lemon difficult.

Beer #5/#6: 2021 Goose Island Bourbon County Stout

Line Analysis: “You've met with a terrible fate, haven't you?” | With A Terrible  Fate
Pray for me

Topic #6: That’s a lotta gamma

Admittedly this is the most niche thing that I have discussed, but any thorium fuel cycle is going to, as a side effect, generate some uranium-232. Uranium-232 is unstable, and so it decays and produces (eventually, but somewhat quickly) thallium-208. Tl-208 isn’t critically (heh heh) important, except that it emits a very powerful gamma ray when it decays. I’m no health physicist, but a big gamma can be big trouble when trying to shield workers from unnecessary radiation dose. This is a minor thing in the context of everything else I’ve discussed, but it’s an interesting microcosm of the hypothetical problems we might face if we wanted to operate a reactor with thorium fuel. Would we need to refuel remotely? How would that effect cost? Dose? Reliability?

If I know about this highly specific problem, what else could be lurking under the surface?

Coda: I’m not totally cold on thorium, ya know

To summarize all of this technobabble, let’s cover a couple of quick points:

  • There’s not a clear fuel cycle or non-proliferation advantage to thorium fuel
  • Thorium knowledge – fuel, reactors, otherwise – is much less mature than the current state of the art in uranium
  • Thorium is often sold as the panacea to uranium, but that exclusionary thinking just doesn’t feel like a constructive approach when we’re struggling to fight climate change
  • The most popular thorium reactor design – the liquid fluoride thorium reactor – relies on a lot of unproven/not yet deployed materials and fuel reprocessing technologies that are dealbreakers if not properly solved
  • I work at a light water reactor, so I’m biased

But I do want to end this on as kind a note as I can muster.

Folks interested in thorium reactors – just like folks who are strictly interested in uranium as an investment – agree on the promise of nuclear technology as a solution to climate change. They’re not scared of it, at least, and they’re part of the nuclear family (even if they’re a little smelly). And so, this cynical Hater’s Guide aside, I want to engage with thorium bros. I want to bring them to events and tours and get their hands on the steel and concrete (but perhaps not the uranium) of our existing fleet of reactors. I want to redirect their enthusiasm to our near-term needs – saving existing reactors like Diablo Canyon and setting policies which spur the construction of new reactors in the West.

It’s fair to call much of the interest in thorium reactors pseudo-snake oil, but if the last year has taught us anything, maybe we’ll get more done with kindness and patience than The Hater’s Guide to Thorium Reactors.


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