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Science news: a “new,” safe, clean nuclear tech that’s actually decades old!

February 27, 2019 1 comment

It’s been a while since I did a science-themed post around here, partly because of generally neglecting my blog but partly because I’ve fallen out of the habit of reading science magazines online — something that I fear has been affecting my professional writing as well, since I’ve been having trouble thinking up new story ideas in recent years, and maybe the lack of inspiration from science articles is part of the problem. But recently, when the Firefox browser discontinued its inbuilt support for RSS feeds, I found a separate add-on that worked even better, in that it notified me of new posts and made it easier to keep current. So I decided to take advantage of that to subscribe to some science sites’ feeds so I could stay more current with the news.

Anyway, Discover Magazine just posted the following article, which is quite interesting:

Nuclear Technology Abandoned Decades Ago Might Give Us Safer, Smaller Reactors

It’s a long article rather than the short colums the feed usually gives me, so I’m not sure if it’ll stay permanently available or go behind a paywall at some point. So I’ll summarize here.

It turns out that, in the early days of nuclear research, scientists had examined various options for generating power from atomic fission, including a system called a molten salt reactor. Per the article:

Every other reactor design in history had used fuel that’s solid, not liquid. This thing was basically a pot of hot nuclear soup. The recipe called for taking a mix of salts — compounds whose molecules are held together electrostatically, the way sodium and chloride ions are in table salt — and heating them up until they melted. This gave you a clear, hot liquid that was about the consistency of water. Then you stirred in a salt such as uranium tetrafluoride, which produced a lovely green tint, and let the uranium undergo nuclear fission right there in the melt — a reaction that would not only keep the salts nice and hot, but could power a city or two besides.

Weird or not, molten salt technology was viable; the Oak Ridge National Laboratory in Tennessee had successfully operated a demonstration reactor back in the 1960s. And more to the point…, the liquid nature of the fuel meant that they could potentially build molten salt reactors that were cheap enough for poor countries to buy; compact enough to deliver on a flatbed truck; green enough to burn our existing stockpiles of nuclear waste instead of generating more — and safe enough to put in cities and factories. That’s because Fukushima-style meltdowns would be physically impossible in a mix that’s molten already. Better still, these reactors would be proliferation resistant, because their hot, liquid contents would be very hard for rogue states or terrorists to hijack for making nuclear weapons.

Molten salt reactors might just turn nuclear power into the greenest energy source on the planet.

It sounds paradoxical — they’re safe from meltdowns because they’re already molten? But the thing is, they’re designed to contain material at that temperature to begin with, and since it’s already liquid, any temperature runaway would just make it expand until the reaction shut down. Plus the coolant wouldn’t need to be under pressure so there’d be no risk of a steam explosion, and there’s a failsafe built in that would drain the molten salts into an underground tank so they wouldn’t be released into the environment. The one real problem, it seems, was finding a sufficiently corrosion-resistant material to make the tanks and pipes from.

Better yet, the liquid nature of the nuclear fuel means that it could be continuously filtered, purified, and cycled back into use like the liver cleansing the bloodstream, so eventually all the nuclear material would be used up and there’d be no nuclear waste — or rather, what little waste there was would have a short enough half-life to be safe after about 300 years rather than a quarter of a million. What’s more, it could use some of our existing nuclear waste as fuel and help reduce that problem too.

So why was this superior technology abandoned decades ago in favor of the riskier water-cooled, solid-fuel nuclear plants? Largely just industrial and political inertia, it seems. The solid-fuel design was already in use on nuclear subs when the effort to build civilian nuclear power plants got underway, and the molten salt design was still experimental. So by the time molten salt technology was experimentally proven viable, the industry was already fully committed to solid-fuel reactors, with a big infrastructure built up to support them and deal with their fuel. And there were big plans to recycle their fuel in breeder reactors and create more and more plutonium to power future reactors, which seemed like a great idea until it turned out you could build bombs from the spent fuel, which meant the recycling plan was shut down and we were stuck with a bunch of nuclear waste we didn’t know what to do with, and that problem plus Three Mile Island and Chernobyl soured people on any nuclear-fission research, even something like molten salt reactors that would be far safer and cleaner and have none of the drawbacks that made people so afraid of fission power. But now, people (at least those who aren’t in denial) are more afraid of climate change and are looking for green energy sources, and this might be one of the best.

Then again, MSRs are not a perfect technology. I looked around and found another site talking about the tech:

Molten Salt Reactors

This article is more cynical about the downsides of the tech than the Discover article, asserting that it could be used to create weapons after all, and that there are a number of unknowns yet to be addressed.

And here’s the World Nuclear Association’s assessment, which mentions that MSR research is already pretty big in China, something the Discover article doesn’t mention:

Molten Salt Reactors – World Nuclear Association

Although it doesn’t seem to agree with the previous article about the weapons risk, barely mentioning the issue in its discussion, and suggesting that the early research into the technology was specifically focused on finding a form of nuclear power that would minimize the proliferation risk. So evidently there are differing points of view on this, which is why it’s always a good idea to look beyond a single source.

This is informative stuff for a science fiction writer like me. For decades, SF writers have assumed that the future of clean nuclear power would be fusion rather than fission. I’ve long been a believer in the aneutronic form of fusion that would react deuterium with helium-3 (which is abundant on the Moon due to being deposited by the solar wind) and react without neutron radiation. But it turns out there’s been a viable, safe, fairly compact fission technology that’s been known about this whole time and largely ignored — already pretty much proven viable, while fusion has remained just out of reach (they’ve been predicting it was 30-40 years away for the past 50-60 years now). I mean, sure, a reactor based on what’s essentially a pit of radioactive lava sounds scary, but no more so than a starship engine based on constantly annihilating matter and antimatter.

It’s also a good reminder that technology doesn’t always develop in a straight line — that viable advances can be sidelined for a generation or more because industries choose to concentrate all their attention elsewhere, or because the political will to explore them is lacking. Of course, there’s no shortage of SF stories about scientists (often of the mad persuasion) trying to prove to Those Fools at the Institute that a discredited fringe idea is viable after all, but it might also be worth exploring what comes after that, when the fringe idea finally starts to get acceptance — or when it was never really discredited to begin with, just overshadowed and forgotten until the hero of the story tried digging into old research and turned up an overlooked gem.

By the way, it’s amusing to read that the molten uranium-salt mixture has “a lovely green tint,” given that the public has long associated radioactivity with a green glow. That myth arose as a result of the glow-in-the-dark radium clock and watch faces that were common back in the days before it was understood how dangerous radioactivity was. The green glow wasn’t from the radium itself, whose emissions (like those of all radioactive isotopes) are invisible; rather, the radioactivity excited luminescence in the phosphor dyes the radium was mixed with. But since such items were common in the early 20th century, people assumed that anything radioactive would glow green, which is part of why the Incredible Hulk is that color (although it’s largely because his original gray hue was hard to reproduce consistently with cheap 1960s printing methods), along with various vintage monsters like those in The Green Slime and Doctor Who‘s “The Green Death,” and why the nuclear rod prominently featured in the titles of The Simpsons glows green. It’s also probably why kryptonite is green. So anyway, given that I’ve grown used to thinking of “green radiation” as a total myth, it’s ironic that the molten salt fuel in this case actually is green in color (though presumably not glowing except thermally) — not to mention that it’s a “green” power source in the environmental sense!