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Comment by OisinMoran | Hacker News Reader

If this interests you, I would highly recommend reading this article on molten salt reactors [0].

TL;DR: Molten salt reactors are safer (can't have a meltdown if it's already melted), smaller (could fit on the back of a truck), able to run on more abundant materials like Thorium (which in turn come from more politically stable regions), and to top it all off: not only do they leave much less nuclear waste, they can actually use up current nuclear waste, turning it into much less harmful and shorter lived stuff in the process!

Also, Mike Shellenberger [1] is a great proponent of nuclear power and has some great points on why the current focus on renewables is damaging. Well worth the follow on Twitter.

[0] https://www.knowablemagazine.org/article/technology/2019/nuc...

[1] https://twitter.com/ShellenbergerMD

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The advantage of MSRs is not that they can't melt down (or that they could use thorium; that's vastly overhyped), it's that there's no volatile material in the containment building.

The containment of a LWR has to be large because it fills with radioactive steam in an accident. It has to be able to contain this steam, which means at least a certain amount of structure to withstand its pressure.

But MSRs don't use water as a coolant. They circulate salt in and out of the building. They can be designed to remain at low pressure even in a bad accident, just from heat transfer that occurs from thermal radiation at elevated temperature. As a result, the cost of the containment could be as much as 1/5th that of a LWR.

Unfortunately, MSRs are not available today, and likely will not be for decades (especially if new materials must be qualified; no one will buy an MSR if there is any question about the materials not lasting their projected lifespans.) By that time, renewables will have marched down their experience curves to an economic position that will likely be unassailable.

I'm pretty convinced that they're worth working on today because in 20 years when we have vast renewable deployment we'll either have solved the storage/intermittency problem with no unexpected environmental or economic costs, or we'll desperately need advanced nuclear. It's kind of a Pascal's Wager type of thing: worst case if you work on advanced reactors is that you learn new things about reactors and maybe they'll be useful in deep space (far from the sun). Worse case if you don't work on advanced reactors is you get screwed by climate change when running into logistical issues with renewable intermittency.

Yes. MSRs are an insurance policy in case renewables suddenly stop getting cheaper. They might have niche uses (very high latitudes, actinide destruction), but that won't be earthshattering if we don't have it.

Yes, for reactors operating at atmospheric pressure like MSR or metal cooled reactors, the containment building is much cheaper. And by not needing stuff that stands up to 15 MPa, you can frickin' stamp out the reactors from sheet metal. Well, not quite, but a lot simpler and faster than building large pressure vessels capable of LWR pressures with 25cm thick walls.

> By that time, renewables will have marched down their experience curves to an economic position that will likely be unassailable.

You're posting this and statements like it all over this thread without a lot of supporting evidence that indicates very strong probability of it happening. Hacker News currently has a highly-ranked article on the main page regarding how there are massive battery and energy storage problems, and this particular issue is raised weekly here and in the news.

Why are you so optimistic that seemingly significant blockers will be for sure eliminated in the short decades to come?

The reason to be optimistic about renewables is they have a proven track record of improvement. These experience curve effects are somewhat mysterious, but they've been shown to occur in a wide variety of industries.

https://en.wikipedia.org/wiki/Experience_curve_effects#The_e...

Solar has declined in price by 20% (or perhaps a bit more) for each doubling of cumulative production. This empirical observation has been sustained over a history during which solar's cost has declined by more than two orders of magnitude. Wind has showed similar learning effects.

Nuclear, on the other hand, has not shown consistent experience effects (or, arguably, any, if one discard as unreliable the numbers from South Korea).

Talk is cheap, but renewables have actually demonstrated, in the real world, that they get cheaper as they are built out (and, if anything, the learning rate has increased recently). Nuclear proponents are hanging the future of their technology on the assumption, unsupported by much of anything, that these real world trends will suddenly switch places.

Also Molten salt reactors don't exist yet appart from a few research reactors, which you forgot to mention.

While it would certainly be welcome to get our electricity from something more modern than steam engines, it is also important to note that fundamental material science breakthroughs are required to actually build these things.

Molten salt reactors are interesting but more in the context of funding research than how we should put together the energy mix of a country. Especially considering how much funding fusion power have gotten, which is still in the basic physics stage and things like materials breakdown and heat transport is largely not even a known problem yet.

A quibble:

The point about meltdowns is cute, but probably wrong; the insurance against meltdown is a negative thermal coefficient of reactivity, if I understand correctly. In other words, the thermal expansion drives the fuel out into the piping as the reaction heats up, away from the compact reacting core, and also reduces the density in the core, allowing more neutrons to escape.

All reactors have negative temperature coefficients of reactivity, including LWRs (the water moderator boils away), SFRs (the core thermally expands), and MSRs (the fuel density decreases). The key to avoiding radiation leakage out of any nuclear plant is decay heat removal [1]. If you can passively remove decay heat, your reactor is very safe. MSRs do this easily, as do other reactors with low-pressure coolants (like sodium metal-cooled reactors).

[1] https://whatisnuclear.com/decay-heat.html

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