Comment by ortusdux | Hacker News Reader

Comment by ortusdux | Hacker News Reader

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It doesn't, but any material used needs to withstand 4 extremes - high temperatures (650-850 C), corrosion (dissolves uranium), very high neutron flux, and US govt. regulation.

Graphite is the current favorite non-metal option. It is already widely used in traditional reactors, so it is approved, and its interaction with radiation is well understood. On the other hand, its interaction with radiation and molten salt is not as well understood, but hopefully this test reactor and others like it will solve that.

One of my favorite solutions seals the reactor in with a crane and 8 graphite containment vessels. The best estimate of the lifespan of structural graphite in this environment is ~7 years, so the plan would be to monitor the system and move the reactor to a new vessel as needed. The goal is 50 year life-span for these reactors.

Anyway, there is research into alternate materials, but to really test them you need to expose them to both molten salts and radiation. And if they pass, you need to get government approval. The last material to get govt approval was Hastelloy N, and I heard the process was a slog.

Well, one thing about liquid fuel vs solid fuel is that you can move the fuel to a new reactor and, uh... ?"recycle"? / ?"overhaul"? the old one. So you could use one for 7 years why the other is retrofitted. You'd need two reactors... or... you'd need 8 and seven are online while 1 is replaced per year.

So unless materials is solved, you need scalability and replacement. At least the OTHER problem with solid fuel, lots of waste, is generally not a problem with breeder reactors and liquids. You remove the fission products from the fluid and feed it back in. I'm no chemist so I don't know all the separation nastiness involved, but it's better than carting ten thousand year waste across the country to Yucca.

So the question is, what about the other reactor designs, don't they need replacement with respect to the vessel? And as I understand it, fusion reactors also have issues with high speed neutrons so their vessels would need periodic replacement, even if they get to sustained ignition and positive energy.

Your replacement containment layers seems like the "constant replacement" strategy. What if you could simply inject a new layer that hardens and pushes out the older layer?

Also, why not have solid uranium or some similar material as the inner container? Could simple saturation of the existing uranium in the salt prevent excessive wear?

I wonder how much of this approval is because the Chinese brought one online.

There are a lot of options, I'm no nuclear engineer but looking at all the different companies, they all have different approaches:

Terrestrial Energy: The whole reactor, including heat exchanges and so on is defined for 7 years of life. After that a second reactor is running. After a few years the original reactor is put into a storage silo and then a new reactor is placed their ready to be switch to.

From memory they don't seem to pump the fuel from 1 to the other.

Flibe Energy: They are doing the famous lifter. Simular concept, 2 reactor cores with graphite moderation, after 7 years the fuel is pumped to the second reactor, the first is getting its graphite core replaced. This will have longer lead time to deployment.

Moltex Energy: They have totally different approach. Instead of 7 year lift-time they are building a traditional reactor with much longer life. They are basically building a sodium cooled fast reactor, but replace sodium with salt solution. And then in the fuel assemblies are also like those in sodium reactor, but contain liquid salt with uranium in them. They want to produce the fuel salt from spent Canadian CANDU fuel.

Kairos energy: This is a molten salt cooled reactor that uses pellet fuel but little balls instead of the traditional pellets.

I've been thinking about the dumb idea of using solid uranium/thorium as the (closest) salt containment layer: you have a solid uranium (melting point 2000C) or thorium layer (3000C) around the salt, which may not degrade it that quickly if the salts (which are a solution basically, if it's a liquid?) are more or less saturated. Or even if it isn't, how long would a layer of uranium or thorium last? I guess that's the big question.

You don't care if the thorium or uranium captures neutrons I would think. Thorium neutron capture is a good thing.

So depending on how long the solid "breeder" inner shell hold up, when you "recondition" the inner shell, I assume you can just dissolve it into salt, feed it into the normal fission products processing that the salt fuel use, and put in a new solid uranium/thorium salt shell.

Or maybe thorium could be alloyed for more endurance properties as the containment. Of course I have no idea about the various cracking / strength / fatigue properties of thorium as a metal.

I wonder if pellets/spheres could use thorium as a surrounding material.

So how nuts is all of that?

Maybe you could do a weekly monthly re-coat of the inner layer with more thorium or uranium to replace that which gets dissolved/degraded.

Edit: ORNL on thorium properties in a nuclear environment

https://www.osti.gov/servlets/purl/4622065

I don't know enough to answer any of that.

> weekly monthly re-coat

Any operation inside the reactor is a bad idea.

Ah yes, the most extreme thing one withstands is U.S. regulation.

Nothing requires this research to to be carried out in the US specifically beyond funding being available here. It’s really the inherent difficulties which is holding back progress.

My understanding is that you are not allowed to build a research reactor that is bigger then a university reactor but isn't a full scale energy producing reactor. My understanding is that for such a reactor you would need the full operating license just as a grid connected PWR.

And since in the US its essentially impossible to get a license for anything but a PWR, that isn't rally possible.

Technology independent regulatory framework is one of the main reasons Canada has so many reactor startup, even those that started in other countries.

https://nuclearsafety.gc.ca/eng/reactors/power-plants/pre-li...

> Technology independent regulatory framework is one of the main reasons Canada has so many reactor startup

Canada's vast tracts of land wouldn't hurt either. If a meltdown or containment breach happens, and no population centers are within 400km, that's a much better bad scenario.

yeah im not exactly mad about it being hard / impossible for people to set up a lab-based experimental nuclear reactor near me due to regulations

Those reactors will be much safer then the street in front of your house.

Prove it.

And thus the reason for all this regulation.

We have prove how unsafe the streets are and yet ...

In fact, nuclear reactor to be built have a higher barrier of 'prove of safety' then almost anything else.

In fact, nobody in the US ever died because of civilian nuclear reactor research or at least not in the last 40+ years.

The street is too dangerous, you are right. An experimental nuclear reactor, however, does not make the street safer.

Additionally, the public is relatively unaware of how nuclear plants fail. If people at nuclear reactor research labs suddenly stop showing up to work - what happens? People kind of assume it will explode, or become a radiation hot-zone rendering the local area unusable for a hundred+ years.

And considering the experimental reactors being discussed need parts replacement due to corrosion, what happens if those replacements dont happen?

The dangers of human inaction seem much higher for nuclear than other things. With standard fuel sources, if people stop showing up to work then power simply stops being made - that's pretty much it. And while they are at work, the process is pretty simple and robust (compared to nuclear) with a lot of room for error.

I know I've been surprised (in a good way) to learn about some of the safety mechanisms existing within nuclear reactors, but I still only sort of understand what anything means that I read - and the safety mechanisms that gave me some sense of relief is based on a lot of assumptions I had to make about the way nuclear works as a lay person.

how about nuclear scientist stop saying "trust me bro" and more aggressively educate people on nuclear fail-safes? People have trouble voting for things they do not understand. And educating the public on something they are either uninterested in or incapable of understanding is an unfair burden to put on nuclear scientists, but they are the only ones qualified to do so.

the ball will move a lot faster once lay people can exchange stories about nuclear safety that go beyond "we barely use nuclear, and no one has died yet, it's actually really safe because ... reasons? scientists said so?"

I mean you don't build reactors somewhere out of in the middle of no-where, you need a labor force and infrastructure to build them.

Pure speculation here but what about using salt to contain the salt? Make a big block of salt (possibly foamed) and melt a puddle in the middle?

Which of these do you think ACU's NEXT project is pursuing?

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