Application submitted for US molten salt research reactor | Hacker News Reader

Application submitted for US molten salt research reactor

world-nuclear-news.org

446 pointsPaulHoule210 comments

So, in a conventional reactor, you use nuclear fission to heat/pressurize water and then use your hot, slightly radioactive steam turn a turbine. This mostly works because moving even very hot, very high pressure water around is kind of a solved problem in industry.

In a molten salt reactor, you use nuclear fission to melt various corrosive salts into a fluid, and this is good because molten salts store a lot more energy per unit (volume, presumably?) at low pressures, so you can transfer heat indirectly to nearby turbine-turning water without irradiating the water or relying on high-pressure water to cool your reactor. Cool.

But I was under the impression that the main stumbling block for molten salt reactors was that high-energy corrosion resistant materials for containing / moving molten salt simply don't exist (yet). I suppose this is less of a problem for a research reactor, but it doesn't sound like there's been a materials breakthrough here that's allowing them to get started. Are they just plowing forward and they'll need to replace the containment infrastructure every few years?

> So, in a conventional reactor, you use nuclear fission to heat/pressurize water and then use your hot, slightly radioactive steam turn a turbine.

I was under the impression that there was a heat exchanger in the path - that is the reactor turns water into slightly radioacive steam, which is sent through a heat exchanger to turn different water into non (or way less anyway)- radioactive steam for the turbines. So both are indirect.

(This is just a nit comment, I think your main points about efficiency still hold, and your materials questions are good!)

Exactly. In other variants of reactors the inner contour could circulate molten slightly radioactive sodium instead.

That makes a lot of sense.

I think I was confused by news stories about situations where the reactor has failed in some way, and then there are stories of how radioactive water needs to be stored / disposed of somehow.

In those historical cases, the priority was cooling the core, the easiest method (especially if a substantial amount of plumbing is wrecked or questionable) is dumping water into it.

Which then becomes irradiated, and pools via gravity in any lower voids, and then eventually needs to be dealt with.

Also, AFAIK, those high-temperature reactors are normally made with a molten metal intermediate cycle (normally sodium) and a gas-only external cycle (normally CO2).

Water enters only to cools the cold side of the external cycle.

There are two kinds of conventional light water reactor. In the pressurized water reactor (PWR), the most common, there is indeed an additional heat exchanger between the water in the core and the water that turns to steam. In the boiling water reactor (BWR), the second most common, the slightly radioactive steam from the core goes directly to a turbine.

https://en.wikipedia.org/wiki/Boiling_water_reactor

Correct, in a PWR or BWR the hot side is in a closed loop. There's a great PDF here: https://www.nrc.gov/reading-rm/basic-ref/students/for-educat...

Annoyingly, "molten salt reactor" is used to describe two different technologies. What you describe is a traditional reactor that uses molten salt to move heat. This typically leads to higher efficiencies, but does have corrosion issues. Other power generation systems can also benefit from molten salt loops - namely solar energy collectors.

In the research field, "molten salt reactors" (MSRs) usually means the other tech - a reactor where the fissile material is dissolved in a salt. This not only brings efficiency increases, but many safety improvements. Many designs also use a 2nd molten salt loop as a temperature step-down before steam power generation.

One of those safety improvements -- a freeze plug -- passively halts the reaction in the event of a power cut. The reactor sits on top of a vault that has a larger volume separated by a narrow tube containing molten salt that has been frozen into a plug by cryocoolers powered by the turbines themselves. If the pumps stop for any reason, then the plug quickly melts and the molten fluid from the reactor drains into the larger vault via gravity at which point it cools and freezes into a solid.

Freeze plugs sound super cool, but this part breaks my brain:

> containing molten salt that has been frozen into a plug

Presumably salt can't be both molten and frozen at once, or is there something about this domain that I don't understand?

I believe they use active cooling to keep the plug frozen.

If the power fails, the cooling fails and the plug melts.

It is literally just a tube with a fan blowing over it. Most designs just barely solidify it, so any over-temperature events also cause a passive shutdown.

Yeah, I got that (and it seems like a really elegant solution! very cool, pun intended, etc). My question was about how salt (or any other matter, really) can simultaneously be molten and frozen.

It can't. Well, maybe at its triple-point, but that is another story. It is just a quirk of the language due to it being know as molten salt. For example, my drink is full of molten water that has been frozen into cubes.

Part of it is molten (above the plug), part of it is frozen (the plug).

Think pipes in a house in winter, where one little part of the pipe gets frozen while the rest of the pipes have liquid water in them.

And in Spring, when the broken pipe plugged with solid molten ice thaws, your house's molten ice circuit performs an emergency evacuation into the yard, saving you from the convenience of adequate molten ice pressure

Hah! Well, we usually think of salt in the solid state (i.e. frozen) and not in the liquid state, so it's not so strange to be explicit in this case. For H2O, we do have pretty common encounters with three of its phase states, so there's less need to be explicit (or, rather, we have separate words for each state: steam, water, ice).

Water is actually a very unusual substance in that it expands upon freezing. (Plutonium being another)

Most materials instead contract when freezing.

Think of a lake in the winter. Just the top layer of water is frozen, exposed to the cold air above the lake. Some of the lake water is frozen and some is liquid, depending on its position in the lake.

I think it was just a clumsy phrasing, with the point being that it's a solid plug of whatever salt is molten and circulating above.

I wrote it that way to aid the reader in understanding what the plug material was composed of. I didn't want the reader to think that the material was water ice.

Yes, the material is the frozen state of the once liquid reactor fluid.

I hope that clears it up, and would welcome a better way of explaining it!

Yes, that makes a lot of sense. I wasn't trying to nit-pick your phrasing, I was just curious if I was misunderstanding something as a lay person. :)

Are freeze plug failures recoverable? Or is is this a final failsafe that toasts the reactor?

Easily recoverable. The tube drains into a collection tank filled with control rods, so any reactions are halted. You can just reheat the salt and pump it back into the reactor. Reportedly, one of the first test reactors in the 50's was shut off every Friday and restarted on Monday. A full power loss, what would be catastrophic for any other reactor, was tested weekly for a year without issue.

I love the image of some guy before going home hitting the red button and some guy on Monday just hitting the green button.

One of my favorite safety elements is often over-looked: they operate at 1 atmosphere. So much of the cost and bulk of a traditional reactor is the shielding needed to protect from an over-pressure event.

And even better, most of the things that are dangerous in a traditional reactor is chemically bound to the salt. So even if there is some kind of explosion, these materials would not be vaporized and transported in the air with wind.

So no crazy misinformed graphics all over the news.

So even if you drop a hand-grande into that reactor, it just gone be like throwing a rock into a bucket full of toothpaste. Its gone be a mess but its not gone result in a lot of airborne materials.

It seems like that might suggest a potential option in the search for appropriate materials to build the containment vessel and piping to hold in the salt: just make the whole thing out of salt. Anything that needs to be solid can have built-in channels with coolant piped through. The rest can maintain a sort of steady state.

I'm sure there's all sorts of practical reasons why that wouldn't work, but it's an interesting thing to think about.

Nice hack! That sounds so easy that I wonder what the catch is.

Maybe it would need more energy for cooling than what it generates? So it would have to be scaled up to a size where the surface-to-content ratio becomes favourable. There might not be enough salt for that :-)

I suppose one problem might be selecting an appropriate coolant that doesn't dissolve the salt on contact. Presumably water would, but google says that salt doesn't dissolve in oil so maybe that's an option.

Ideally you wouldn't need to expend energy to keep the coolant cold enough; rather, you'd use the coolant to boil water to run your steam generator.

“Vessel built out of nothing but heat transfer interface and freeze plug". Do some of the materials problems get easier while it's only touching the salt in frozen state?

Ok so I recently watched a video that went into some of this, and I had know idea how crazy some of these nuclear fuels are in terms of physical requirements.

If I recall the video correctly, solid metal oxide fuel produces offgas at a 50:1 ratio, while being insanely dense. This produces pretty insane internal pressures if the goal of the fuel design is to keep everything contained. Like strong enough to eventually cause mechanical failure of the fuel.

I think there's a lot of really difficult constraints intersecting in these fuel assembly designs, and something that seems obviously simple probably isn't.

There have been quite a few solar energy concentrator test beds based on molten salt in order to try to get to 24/7 solar power. It is an interesting technology but afaik it's not at the stage where it can be rolled out reliably and maintenance free.

It also simply couldn't compete with plummeting cost in silicon panels.

People thought this stuff

https://haynesintl.com/docs/default-source/pdfs/new-alloy-br...

(which is practically stainless steel without the steel) was good for this use but when it was tried in this system it did not hold up very well

https://en.wikipedia.org/wiki/Molten-Salt_Reactor_Experiment...

but it was believed that some small change in the formula such as adding Niobium could clear the problem up. What's needed to move forward is not a big conceptual breakthrough but rather testing of materials under realistic conditions... A new test reactor.

What is more problematic with the MSRE design is that it incorporates graphite as a moderator and the graphite swells and goes bad over time. Possibly you can take the graphite core out every few years and replace it with a new one, but people have also found designs that don't require a moderator outside the fuel salt.

When I went to the first conference on Thorium Energy years ago David Leblanc had done some very simple calculations that showed you didn't need the graphite -- it works just fine with a faster spectrum. He's refined that idea and is running with it. Others are pursuing chloride salts and plutonium fuel with a very fast spectrum.

Fast spectrum MSRs bring a whole litany of other problems. Chlorine has more oxidation states and the chemistry with fission products is much more complex.

Starting with graphite makes sense imho for a university.

If it's designed with replacement in mind, a graphite moderator isn't all that bad. It can even be a safety advantage, in that if you drain the fuel out of the vessel it's taken away from its moderator.

I must not be parsing this correctly. Taking fuel away from the moderator sounds like a safety disadvantage. Maybe I don't know what a moderator does.

If the fuel is designed such that it needs a graphite moderator to sustain a reaction, then if the fuel is removed from the reactor it's less likely to go critical than if the fuel was "higher-grade". It's less likely to have a criticality accident.

I'm not a nuke physicist, but I recall LFTR presentations on the "safety plug" to stop meltdown: basically a plug melts and the fluid flows into a shallow pool.

Since the fluid is "thinned", neutron economy plummets and chain reactions stop.

In addition, I though the fluid would expand a bit under high heat in the reactor, which would drop neutron economy as well, so a fluid can somewhat self-moderate.

So unless the fluid is in a ball or tank where the neutron economy is maintained in three dimensions, if you drain it out it no longer has the neutron economy.

So what they probably are saying is that since the fuel is fluid, and if you need to replace the moderator, you drain the fuel (and as stated above, that stops the reaction as well) and replace the moderator.

A moderator is a material that slows neutrons down. Slow neutrons are more likely to initiate fission in a Uranium (or other fissile) nucleus that they hit, so a moderator increases the reactivity of the reactor.

Thanks, that’s exactly the detail I was misunderstanding.

I think one key aspect is that they are less susceptible / immune to loss of coolant incidents. In a PWR if there is a loss of pressure, or coolant in any other way, and emergency cooling doesn't work, the core overheats and might melt down.

An uncooled pool of molten salt will keep on generating heat even after the reaction is stopped, so will continue heating up, but it is possible to design the reactor so that the whole thing remains stable. Since the pressure is low, there is no risk of explosion, or release of the radioactive materials.

So the energy density is i think a secondary benefit, if at all.

> corrosion resistant materials for containing / moving molten salt

I'm interested to see what Moltex can do to simplify matters:

https://www.youtube.com/watch?v=7qJpVClxzVM&t=758s

Instead of pumping the salt around, they plan to leave it sitting in stainless steel tubes, and use simple convection to extract the heat. Oak Ridge rejected this idea in the 1950s because they were trying to power an aircraft, but convection makes more sense when the reactor isn't moving.

LANL built a reactor like that, with liquid fuel in tungsten capsules. It was called LAMPRE.

https://www.osti.gov/biblio/4368180-operation-plutonium-fuel...

Tantalum capsules. Molten plutonium is darn corrosive.

Even better.

> slightly radioactive steam

For anyone worried about this, the longest lived unstable isotope of oxygen (that is heavier than stable oxygen) has a half life of 26 seconds. Hydrogen can become deuterium which is stable, and finally tritium which is not.

Tritium has a long half life of 12 years, but is low energy and very easily shielded (just don't eat it).

There is very very little tritium - first you'd have to make deuterium (there isn't much), and then a deuterium would have to become a tritium, i.e. a rare event on top of a rare event.

Not compltly accurate. It's true that the half-life of tritium is short compared to long lived actinides. However, like hydrogen, it diffuses very easily and it's not easy to contain. In fact, it's one of the few things emitted in the environment during normal reactor operations. As beta emitter, you are right that it's dangerous only when ingested, but it's very easy to breath of to get it from other ambient sources

Very little tritium will diffuse, because it's bound with oxygen as water.

However some water does come out of the reactor you are correct.

> you are right that it's dangerous only when ingested

Not really. Tritium is Hydrogen. It cannot bioaccumulate. Each atom of Tritium will spread out to become one among the quadrillions of atoms of Hydrogen in our body. Most will get out of the body in a matter of days, long before they've had a chance to decay. Even when they decay, they undergo beta decay, which is not very damaging. But even if it were damaging, the damage would be very localized, it would affect at most one cell, and the immune system is easily able to handle that.

One tidbit on information damage that has stuck with me is that carcinogenic radiation damage is a second order process: to get a cancerous mutation you need both copies of DNA damaged, which would in most cases require two separate events.

To the extend this is true, it implies that it is the square of the radiation dose that determines carcinogenic effects: Half the dose would cause only a fourth of damage.

> Not really.... But even if it were damaging, the damage would be very localized, it would affect at most one cell, and the immune system is easily able to handle that.

you could not be more wrong about this. Alpha and Beta are fairly safe OUTSIDE the body. In the case of Alpha it is not able to penetrate the layer of dead skin on your hands.

Internal, it is VERY damaging because there is no "dead skin" to protect the internal organs.

https://www.epa.gov/radiation/radiation-basics

"Some beta particles are capable of penetrating the skin and causing damage such as skin burns. However, as with alpha-emitters, beta-emitters are most hazardous when they are inhaled or swallowed."

I stand by what I said. Yes, beta-emitters are most hazardous when they are inside your body, if they are together and stay there for a long time. The main examples are Strontium-90 and Caesium-137. The problem with them is that they bioaccumulate. Strontium accumulates in the bones (it is chemically similar to Calcium) and Caesium in the pancreas (it's not clear why. it is chemically similar to Potasium, but it's not obvious why it should accumulate in the pancreas).

Tritium is very different. It is chemically just Hydrogen, which is present everywhere in the body. It just can't bioaccumulate.

In any case, if you don't believe me, here's a statement from the FDA regarding the tritiated water released by Fukushima:

  Tritium presents an extremely low human and animal health risk if consumed and any health risk would be further minimized with the dilution effects of discharge into the ocean.

[1] https://www.fda.gov/news-events/public-health-focus/fda-resp...

Your view really depends on the design.

CANDU (Canadian reactor design) is moderated via deuterium in which case there is a LOT of it circulating in the reactor core.

The heavy water is syphoned off to a tritium separation unit for recovery. With a market value of $30,000 a gram, there is a clear incentive to recover it ;)

Some buddies who work on CANDU tell me they have tritium contamination everywhere as a result of this. From what they tell me it's not really a big safety issue, mostly more annoying than anything.

It is annoying because it is detectable!

Molten salt loops are not as difficult with current technology as they were when they were first introduced.

There are some very interesting startups in this field working on delivering these reactors on an industrial scale rather than the "artisanal" reactors that dominate today:

Copenhagen Atomics [1] is one. They offer a molten salt loop for rapid prototyping [2] if you want to try it yourself.

Seaborg Technologies is also building a compact molten salt reactor. [3] They have a subsidiary, Hyme, to use the same molten-salt technology to provide grid-scale energy storage to balance electricity grids with variable generation from e.g. wind and solar power. [4]

[1] https://www.copenhagenatomics.com/ [2] https://www.copenhagenatomics.com/products/molten-salt-loop/ [3] https://www.seaborg.com/ [4] https://www.seaborg.com/press-release-hyme

Thanks for posting, this sounds super cool. Now I just really wished I had a reason to order a molten salt loop.

I would love to rip the gas heating out of the house and have little nuclear reactor there.

> So, in a conventional reactor, you use nuclear fission to heat/pressurize water and then use your hot, slightly radioactive steam turn a turbine.

Only in the more primitive reactor designs (BWR, Boiling Water Reactor). Most are of the PWR, Pressurized Water Reactor, design. In these, the water in the reactor is still liquid due to being held at pressure. This pressurized water is run through a steam generator [1] that boils non-radioactive water that never comes into contact with the reactor.

1. https://en.wikipedia.org/wiki/Steam_generator_(nuclear_power...

> Only in the more primitive reactor designs (BWR, Boiling Water Reactor).

TRIGGERED :).

The BWR was developed after the PWR specifically to be more economical for terrestrial large-scale power generation. The PWR was designed to be compact and to work on a submarine. So the BWR is the more advanced design for power plants, arguably.

https://whatisnuclear.com/reactor_history.html#the-developme...

I hope we manage to improve the design over the 1960s version MSRE which cost $130m to clean up due to unforeseen problems including a near-criticality incident. Certainly there is a lot of research to be done.

The cause of the criticality accident was that they did not remove the uranium when they were done with it. This is straightforward to do, you pump F2 gas into the salt and this gas is produced

https://en.wikipedia.org/wiki/Uranium_hexafluoride

which can be stored in tanks. Instead of removing it they let the salt sit, and radioactive decay led to F2 gas being produced by the salt, which caused UF6 to be produced slowly and then migrate.

This mistake won't happen again.

Even with that issue, it was still a project that was amazing, they did incredible work, and the cost was very small. Almost hilariously so compared to other nuclear reactor projects.

Had that same team received the funding for a next large commercial prototype, the world would be different now.

But sadly Nixon preferred to spend money for nuclear research in California, Tennessee not exactly a priority.

Alvin M. Weinberg also didn't make himself any friends with government higher ups when he criticized PWR programs for civilian nuclear.

You are correct about the corrosion issue. I've done some work developing molten salt resistant claddings. The main culprit is chromium leaching, which de-alloys most of the metals approved for reactor design. The leeching happens at the grain boundaries, so you will hear 'intergranular attack' as a research focus.

A close second problem is the radiation itself. Elements in both the containment vessel and salt transmute. One study I read estimated that pure tungsten (a viable salt resistant material) would transmute to rhenium at a rate of 1% a year. The radiation also causes void-swelling in both the metals and pure graphite.

The standard way to test material's resistance to molten salt is to put a coupon in a crucible full of salt for a few hundred hours. A paper from 2015 showed that the material the testing crucible is made of greatly effects the rate of chromium leeching. They found that both graphite and nickel act as chromium sinks. Many designs call for graphite or nickel parts to be used alongside chromium containing steels. This reactor appears to be stainless steel with graphite moderators.

Another paper strongly suggested that radiation induced void-swelling can squeeze together the grain boundaries, greatly slowing down intergranular attack. Very little corrosion testing has been done under exposure to radiation as it is logistically difficult.

Basically, the next best step is test reactors. You can only get so far testing things in isolation.

Does it even need to be a metal? (Since the pressure is so low strength requirements are lower)... How about ceramic or glass (or quartz), or something else non-metal?

non-metals have their own problems and glass tends to have some really weird properties.

I would think a major one would be their failure mode. Metals flex and expand before they eventually fail. Glass/ceramic is fine until suddenly it isn't and has a total failure.

Think of a window being hit. If it were metal it would probably deform but if it is glass it shatters.

Next would be joining them on-site. If needed, metal piping can be bent and welded in-place. what do you do with a glass pipe that needs a join? what do you do if there is a small variation in the plans and the pipe needs an adjustment?

I think there are a host of reasons why glass is not used for pipes.

what about glass pipes encased in said metals :-)

Glass-lined vessels and pipes are already used in the chemical industry so it's a somewhat proven technology.

Not sure if it's suited to the chemistry and temperatures (and radiation) of a molten salt reactor, but it seems like an interesting technology.

Composites? Such as the stuff used in Aviation?

Most of those contain plastics which are usually not good for high temperatures but also have long chain molecules which get broken by neutrons and other particles and cannot heal defects the way metals can.

Glass is already basically welded, or maybe it's more like brazing. But an oxyacetylene torch can be used to work with glass just as well as to cut or weld metal.

Metals also have weird properties. Like tempering and hardening based on temperature. In an industrial setting you need expert welders with deep knowledge of the materials or a weld is going to fail and ruin your day.

So it doesn't seem like a huge leap to me actually, assuming ceramics or glass actually have desirable properties.

Doesn't glass.... melt?

At 3100 F.

Salt melts at 1474 F.

1704C

801C

(or

1978K

1074K)

So does metal. Welding is just melting two parts together.

https://en.wikipedia.org/wiki/Cold_welding

https://en.m.wikipedia.org/wiki/Welding

What point are you trying to make here?

no heat, no melting. just welding

Perhaps it would have been better to say "melting two parts together is just welding".

We can do this with glass, however, lapping is incredibly expensive for something as simple as joining two pieces of glass together.

I noticed you focused almost exclusively on the welding while ignoring the brittle nature of glass?

I would think that putting liquid salt in a a glass pipe is somewhat asking for trouble. One of the many issues with glass is "thermal shock".

Let's say there is a fire and water based sprinklers are activated.. what will the 1,400F glass do once water touches it?

Or there is an accident and someone bangs into the glass. Metal can deform and not fail, glass cant.

“Glass” is a generic term for a wide variety of materials. So is “metal”. Metal can be brittle, sometimes that’s even desirable. That’s what tempering and hardening are about.

A molten salt reactor is a material science problem. Conventional “metal” doesn’t work because of the corrosion. If glass has some desirable property then we can overcome the “bumping in to it” problem. Maybe with a hand rail. Or staying away from the operational nuclear reactor.

I’m not suggesting glass actually be used. I’m saying if it was I wouldn’t be surprised.

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.

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.

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

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.

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?

What about using molten lead or something that can act like a lubricant/insulation at that temperature away from the corrosion in the same way airflow is used over jet turbine blades to stop them melting? It there any high temperature liquid that is molten salt phobic like oil and water?

> The standard way to test material's resistance to molten salt is to put a coupon in a crucible full of salt for a few hundred hours.

Q: What is a coupon in this context?

Great Q: maybe? https://www.researchgate.net/figure/a-MAR-M247Nb-coupon-b-Al...

A coupon is an informal term for a small sample of material, most often metal. It’s perhaps most commonly used in welding where practice welds for people first training to weld are done on pieces of metal often referred to as coupons. :)

It is usually an artifact of materials like metal which are hard to cut, and can’t efficiently just be cut as needed during a task, but are prepared and pre-cut into small pieces you can grab easily. Each of those pieces is called a coupon.

I used to store mine in a Chinese takeout container box.

In the mid 1970s, in my welding class, the school was located down the street from a small manufacturer that formed various metal alloys.

They would provide the school with bins of scrap from their manufacturing free of charge. Those were our practice coupons in class. We had to be careful to return the welded scraps back to the proper bin so the manufacturer could recycle them.

Our class was just a very small part of their recycling flow. It was a great relationship, we needed practice materials, and they hired welders.

It's used 2 ways in metallurgy. Mainly it is a term for test pieces cut from a batch of metal and used for proof testing. Tensile, elongation, fatigue, weldability, and many other tests require destructive testing coupons. When you take welding certification tests, you weld two coupons together, and then submit your coupon for testing.

It is also a term for strips of metal that you mount in a corrosive environment as a way to monitor corrosion of other susceptible components. So if you were worried about your bronze bushings, you would buy some matching bronze coupons, put them in an area of similar flow, and measure their thickness periodically.

https://www.alspi.com/coupons.htm https://en.wikipedia.org/wiki/Fatigue_testing#Coupon_tests

>test pieces cut from a batch of metal

>strips of metal

I mean in essence you just have to look at the word. Coupon is from French couper, which means to cut. So it's a cut-out. It has the same meaning when you look at extreme couponing and metal testing.

Yeah, I didn't think of it as an overly obscure usage, but neither Merriam-Webster or Wikipedia list the definition. Dictionary.com does. Maybe its time to edit Wikipedia over lunch =)

Coupon is used in metalworking to mean a sample you can submit for destructive testing that is representative of the whole piece under test.

A weld coupon, for example, is a piece of test material of the same thickness and weld preparation as the main part being welded but is not integral to the part itself. That coupon is then sawed off and submitted for destructive tests like impact testing (to determine minimum operating temperature), tensile strength testing (specimen is pulled apart to find how strong and stretchy it is), and crystallographic etching (looking at the crystal structure of the metal to see if it has defects).

The corrosion issue is part of what drove Moltex to their rather interesting design (sterile coolant salt is a fluoride; fuel salt in tubes is chloride; this is a fast reactor.) The absence of uranium in the fluoride allows it to be operated at a redox potential where chromium does not dissolve.

Yes, one of the reason I like that reactor design. They basically put something in the fluoride that is basically designed to corrode so that the actual reactor vessel doesn't. If I understand correctly.

Their design doesn't require the 7 year swap cycle most MSR do.

Right! They've got the same thing going that ordinary LWRs do: the neutrons lose their energy in a surround liquid rather than in a solid moderator or solid structural materials other than the fuel rods (which are designed to be replaced often anyway). The design even adds some hafnium to the coolant salt (substituting for zirconium, which is the sacrificial metal you refer to there); hafnium serves to shield the reactor walls from thermalized neutrons.

One additional advantage of separating the fuel salt from the coolant salt is that the coolant salt volume can be increased as desired, making the thermal inertia of the reactor as large as one likes independent of reactor power or size of the fuel load.

> One additional advantage

The problem with that is that you would likely require a different design and go threw full licensing. So in practice this will likely not be used.

Presumably it would happen at design time and a large, high thermal inertia design would be the one licensed.

There are a number of obstacles. Neutron damage to the reactor structure is more of a problem, since the fuel is dissolved in salt in direct contact with that structure (unlike a reactor with solid fuel rods, which are separated from the reactor vessel by a thickness of moderator, in the case of LWRs is water.)

See here for a (somewhat old) list of some technical issues:

https://gain.inl.gov/SiteAssets/MoltenSaltReactor/Module2-Ov...

"Nickel-based alloys embrittle under high neutron fluxes at high temperature"

"Over 40% of [fission products] leave core [in offgas]"

"Large fraction of cesium, strontium, and iodine end up in offgas"

"MSRE was approaching end of allowable service life when shut down" (after four years at 40% capacity factor)

> "Over 40% of [fission products] leave core [in offgas]" "Large fraction of cesium, strontium, and iodine end up in offgas"

That could, in theory at least, be an advantage if you have a good process for capturing and storing that offgas (reacting it with something to make it solid and then glassifying it, for instance).

In a traditional fission reactor, gaseous fission products cause swelling and cracking of fuel pellets, and builds up pressure in the fuel tubes, which is one of the factors limiting fuel burnup.

It means the offgas storage system has to be designed for a large heat load, even in accident scenarios. It also means the common MSR talking point that the FPs stay in the salt is not correct.

> common MSR talking point

Well, a lot of 'common MSR talking points' are overblown, firmly detached from reality. Or at least conveniently ignoring all the significant challenges remaining in industrializing MSR technology. MSR fanboys are the most tedious of the pro-nuclear side of the energy debate, perhaps beaten only by the "this entirely unproven aneutronic fusion concept will imminently solve all our energy woes" crowd. :)

This is why I refer to Helion as the "least dubious" fusion concept. :)

Moltex Energy talks a lot about that. It is actually pretty nice, some things stay in the salt, some leave it. The most dangerous stuff that shows up in the news a big scary cloud coming over from Japan to the US would still be in the salt.

Some other things that you really don't in your fuel, like Xenon and Krypton will bubble out.

So I think overall it is an advantage.

Moltex's design keeps the relevant isotopes of Xe/Kr in the fuel tubes long enough for them to (mostly) decay, so the Cs and Sr produced from the decay (mostly) stays in the fuel salt.

> But I was under the impression that the main stumbling block for molten salt reactors was that high-energy corrosion resistant materials for containing / moving molten salt simply don't exist (yet).

Is this also an issue for molten salt / liquid metal batteries[1][2] that have been proposed as a grid scale energy storage solution for renewables?

The way I understand it, molten salt is used as the membrane separating the electrode and electrolyte layers. But I was under the impression that there are actual molten salt batteries prototypes with industrial scale facilities currently under construction.

Are the requirements to contain the molten salt in a battery different from a nuclear reactors? Or do they have the same challenges and are simply able to overcome economic feasibility whereas nuclear reactors aren’t?

1: https://ambri.com/

2: https://www.youtube.com/watch?v=-PL32ea0MqM

Molten salt / liquid metal batteries normally use alkaline salts, so steel holds it pretty well.

I see. So there is a pretty simple explanation. Thanks.

https://i.imgur.com/qX2d2qg.jpg

https://i.imgur.com/InQHoSI.png

https://i.imgur.com/go5v5QL.jpg

Way, way overdue! China has taken all of our research from the 50's and has been charging ahead. Very sad that politics and ignorance has severely kneecapped our nuclear industry :(

It's also sad that industry completely failed to convince the population that they can provide a safe solution. For all the credit we give BigCo for creating propaganda, it's curious that they were unable to be successful here, given the stakes.

They are up against big fossil fuel tycoons like the Kochs. If we are strictly talking corporate propaganda, the fossil fuel industry has plenty of that.

It seems to me that companies like GE and Westinghouse have tons of money. Add that to the billions pro-nuclear folks have in SV and you've got quite the war chest to fund effective pro-nuke campaigns.

Those folks might not want to waste that money in a propaganda race against the entire fossil fuel industry and the emerging renewable energy industry. GE and Westinghouse are large and successful companies, but is nuclear a major part of their portfolio such that they would take such a big risk (compared to fossil fuel industry which views clean energy as an existential threat)?

Westinghouse went bankrupt a few years ago[0]...and GE hasn't been doing well and is splitting up[1]...

[0] https://www.nytimes.com/2017/03/29/business/westinghouse-tos...

[1] https://www.usnews.com/news/business/articles/2022-07-18/ge-...

I'm out of date, lol. Well, GE, even post-breakup, has a huge energy business that would benefit from increasing nuclear production. Assuming they really can make safe, cost-effective power, anyway.

GE is one of the big names in gas turbines, and AFAIK they make wind turbines as well, in addition to nuclear power plants. So whatever the customer wants they can offer. ;)

As much as people portrayed an epic battle between renewables and nuclear the real winner from the move away from nuclear was natural gas fired gas turbines.

The most obnoxious thing about the energy literature is that it frequently reads like a stopped clock. People still compare the cost of nuclear energy to the cost of coal, but it's no accident that the US stopped building coal plants at the same time it stopped building nuclear plants because it stopped both for the same reason... The capital cost of a gas turbine generator (even in a hybrid cycle including a steam turbine) is dramatically smaller than the steam turbines used in coal and nuclear plants.

Since molten salt reactors run a lot hotter than LWRs they could drive

https://en.wikipedia.org/wiki/Closed-cycle_gas_turbine

but it's a technology that is not very well developed. If nuclear energy is going to compete with natural gas, however, they need to ditch the steam turbine.

Do the gas turbines use the brayton cycle? As I understand gas turbines are around 64% efficient with various tricks. I recall a LFTR presentation talking about how they could use the Brayton cycle because of... ?high temps I think?.

Is the closed cycle gas turbine also using a superior cycle like the Brayton? Oh it's in the third sentence, CTRL-F failed me.

> As I understand gas turbines are around 64% efficient with various tricks.

These super-high efficiency gas turbines are not 'pure' gas turbines, but so-called combined cycle plants. Basically you first have a 'normal' gas turbine driving a generator (which, by itself, maybe gives you ~45% efficiency), but then you take the host exhaust of that gas turbine and use that to drive a secondary steam cycle driving another generator.

I'm not sure such a thing is doable in a closed Brayton cycle, at least I haven't read anything about anything like that.

An interesting thing with closed cycle Brayton is that instead of air you can use another fluid as the working fluid. Supercritical CO2, for instance, has some nice properties leading to extremely compact machinery. Of course there's an uphill battle in commercializing this technology; if you use air (or nitrogen) you can just adapt one of the many existing gas turbine cores with $zillions of R&D and decades of experience behind them.

For sure. In theory, I'm in favor of nuclear power; especially as we try get to zero/negative net carbon emissions, nuclear plants have real advantages. But when I think about American business culture, I have a hard time imagining the company I'd trust with something that requires an extremely long-term focus (plants run for decades) and deep social responsibility.

Energy too cheap to meter doesn't sound like a good investment from a capitalistic viewpoint.

Not for the companies that build and design reactors

You don't understand capitalism then. And you fell for propaganda and fantasy of the nuclear industry apparently.

Nuclear power isn't that cheap. Certainly not without subsidies and once you price in all the externalities.

And you fell for the fossil fuels propaganda claiming nuclear is too expensive to without subsidies. Seriously.. new nuclear is on the drawing board with huge investments in the UK, France and Sweden.

Nuclear will be cheap when the industry grows and reactor designs are standardized.

It's really simply the superior technology any way you look at it and the "nuclear is too expensive" is just a tired and arguably false argument against it. I'm so sick and tired of people saying that it's too expensive to save the planet..

In reality there is a lot of research pointing to nuclear power certainly not being anywhere near as cheap as "too cheap to meter". Claiming this is all "fossil fuel propaganda" is stupid and lazy. So far, there has rarely ever been a nuclear power plant built on budget and on time. Most run way over. And often the costs for cleanup and decommissioning are not priced in properly or even at all. Most industries have to pay insurance for their risks, the - actually uncomputable - risk of nuclear power rests on the whole society, while the profits accumulate with the shareholders of the power company. Ask Japan how that is working out for them currently...

"Drawing board" is the operational term. Nuclear power is always late and it's always more expensive than promised. Why is the nuclear power industry subsidized so much everywhere when it's actually a good investment? Have government agencies suddenly become good at investing or are they just charities for corporate interests?

I'm not even saying it's "too expensive", by the way. I'm not totally against nuclear power, I do see the benefits. It has its place, probably. But I know about fat tail distributions and the unpredictability of the future. You really don't want anybody shooting rockets and artillery shells around a nuclear facility a few hundred miles near you. Today that's Ukraine and much of eastern Europe, who says that in the next fourty or fifty years, the lifespan of a typical plant, that's not you either? In Mossul ISIS hunted around for nuclear material to build a dirty bomb, luckily they didn't find the stuff that actually was there. Who says your country will not have a rogue militia like that in the next fifty years?

And then the nuclear industry is unwieldy. It requires a large and expensive specialized infrastructure. Which can be amortized eventually, yes. But much of that investment is upfront and the recuperation is dependent on a lot of things going exactly right for a very long time. Also it requires a huge labor force that has to be trained for this specific task and then can hardly do anything else. France has the problem of a shortage. In short: It's hard and expensive to get into nuclear technology and it's even harder to get out of it.

And in order to solve the climate crisis using nuclear power there are two major problems: First, it's already too late, because nuclear power is so slow. Secondly, you'd need to nuclearize much of the world, including countries with questionable regulatory regimes to say the least. This makes all the problems we see now a lot worse...

I wasn't saying that nuclear IS "too cheap to meter" I'm saying it could be. And my statement about fossil fuels propaganda was merely a jab back at your snarky comment. Your absolutely right that most of the new reactors that have been built in the west has been delayed and exceeded budget and all I'm saying is that this wouldn't have been the case of the industry had kept growing and evolving back in the 80s. Japan is way overreacting with Fukushima and that plant was old as fuck and was literally built on a fault line without taking proper precautions. Tell me how many died as result of the Fukushima incident and how much radioactive water has polluted the surroundings ? I'd urge you to go look it up, but you probably won't.

Sorry i meant all those countries are planning to invest billions of euros into building new reactors now that the EU has deemed nuclear power green. You are talking like other power generation like wind, solar etc is not subsidized ? Hope is the unique to nuclear? Nuclear is subsidized and tightly controlled/regulated for obvious reasons and honestly imho all energy infrastructure should be tightly tied to government as is the case in most of Europe.

Even if Russia was too hot the nuclear power plant in Ukraine with a cruise missile the damage and contamination would be fairly local and I'd imagine hitting a coal or gas power plant with a cruise missile would be just as bad. Besides that hitting a nuclear power plant with cruise missile would be considered firing a nuke and don't think Russia is ready to do that yet. Taking about dirty bombs is just plain stupid, why the hell would you through all that trouble when there's much much cheaper and simpler ways to do damage?

Yes it requires some new infrastructure but in many cases you can switch coal, gas and oil plants almost 1:1 with nuclear. What's wrong with having lots of highly educated people working with supplying the world with energy ? And how is it different from solar, wind etc? France has problems because they still have a huge anti nuclear movement making it very hard to invest properly in maintenance and new plants, besides that France's shortage is because Germany suddenly requires allot more electricity because of stupid investments.

It's never too late.. sure we can also build what is the fastest solution but nuclear is the best bet long term.

Ah yes, "it could be". An unrefutable and unprovable statement without proof. It's purely wishful thinking that nuclear power will become any easier in the future. Japan is not "overreacting", it has to clean up the damn mess not just to one day use that area again, but also to avoid spreading the contamination. Just because nobody dies immediately from the exposure doesn't mean the ground is safe to handle or live on. Case in point: The Russian soldiers in Tschernobyl digging in contaminated ground and spreading it further. Your point about a low immediate death count after Fukushima is just as dishonest, stupid and lazy: People would have had their lifes cut shorter by the radiation exposure, if they hadn't been evacuated at great cost.

Most of your arguments are entire bullshit and I really don't have the time to waste. No, if one of the nuclear plants in Ukraine blows up, the effects are not "very local" and I suspect the locals do care. So should you when a nuclear plant near where you live goes online. Also the biggest nuclear plant in Europe is hurting Ukraine's defense just by sitting there and doing its job perfectly: The Russians discovered that they can shoot artillery from there without anyone shooting back. Nuclear plants are defensive weak points under any circumstance.

A dirty bomb is a viable terror weapon. You can spread radioactive material quite far with an amount of explosives that wouldn't be able to cause near as much death and terror. Good deal, especially when you got the Plutonium and what not for free...

People like you are lying through your teeth by saying the only alternative to nuclear is fossil fuels. I don't even know anyone who believes this.

And no, we can't wait for nuclear power. A world full of nuclear power plants is unsafe. Maybe in Norway or Finland with the most honest and least corrupt governments (at presents) and no immediate threats from the outside it seems safe. But really, betting on nuclear power means betting on a perfect world during the next few decades at least.

You just continue to profess to a profound ignorance on how radiation exposure work, what happened and is happening right now in Tschernobyl and Fukushima, and make hand wavy arguments "Such accidents are never going to happen and aren't actually that bad, for real this time, pinky promise with cherry on top".

And you can just continue fear mongering trying to hold the world back further. The world is going nuclear wether you like it or not, America's biggest enemies Russia and China already have it big time and there's a very big limit to what countries America can hold back line they've tried to do with Iran. If anyone is had bullshit arguments it's you; you clearly haven't done any research into Tjernobyl and Fukushima and fear mongering about dirty bombs is just beyond stupid. Så thank you for ending the conversation. Glad the world has started moving on and had started seeing through bullshit like what you have presented in this argument. Write me back in 10 years and let's see what technology won.

There's no evidence or reality to "nuclear is coming back". Some politicians talk a big talk, that's all. Nor did or do I say it's not going to happen, but in most of the developed/semi-developed world except China it's currently definitely not happening. Just another nuclear fanboy fantasy ignoring reality.

You know who cares about dirty bombs? Every intelligence agency and counter terrorism unit in the world. So far it hasn't happened, but if nuclear power is scaled up, this stuff will be way more accessible. A lot like the gun violence problem in the US, but I guess the denialism around those topics is similar.

I personally care most about the closest nuclear facilities, not so much those in China. And in reality, neither Tschernobyl nor Fukushima have been cleaned up yet and continue to be a problem to be felt financially at the very least. I know quite a bit about it, but some people apparently think it's only bad if you die instantly... But it certainly makes some weak arguments easier, doesn't it? Who cares about people losing decades of their life...

The problem wasn't the safety, the problem was they couldn't deliver a cheap solution. And recently when they tried to come back they completely fucked it up.

Safety isn't a technical problem, it's a human problem. Over long periods safety measures end up being cut and introduce risk. There's also design decisions revolved around cost even though better solutions exist. Then there's just plain oversights. For example we all know earthquakes and tsunamis exist and yet the Fukushima still happened.

> It's also sad that industry completely failed to convince the population that they can provide a safe solution.

I don't really think the population matters. The problem is that after the NRC was replaced AEC was replaced, regulation became totally technology depended. Doing anything other then PWR was essentially impossible.

The DoD is only now undertaking efforts to change this, but its turning a large ship.

The existing technology isn't actually that safe. The safe technology isn't that existing, actually.

The "population" tends to not believe claims about certain accidents being impossible if they keep happening. The safety of nuclear power is a fantasy. No, the track record is not enough. Given the enormous potential for catastrophe and the timespans for nuclear power project, questioning assumptions like "nobody is going to shoot rockets and shells around the plant" is entirely valid.

OTOH if you used bayesian reasoning like your username suggests, you'd understand that nuclear energy is the safest form of energy there is.

https://ourworldindata.org/safest-sources-of-energy

And that's exactly the wrong reasoning in this case. Because you want to predict the future from the past, over a really long time span and with the adverse events being extremely catastrophic. Just read up on how the Fukushima cleanup is going and how the cost estimates have risen...

Bayesian reasoning would require you to argue about priors. You want to take priors from the past. Fine and dandy, when trying to predict the weather or even where the stock market is going. But when talking about how likely it is that something blows up and contaminates a huge area, maybe there are higher standards. And philosophizing about the average is all nice and well, until you happen to live near the site of an accident. And in Ukraine the assumption "nobody is going to shoot around a nuclear plant", which most assurance of nuclear safety depend upon, doesn't hold anymore.

Why does that matter?

Particle physics dominated US research grants for several decades with some results to show for it. Now that the focus has shifted elsewhere (e.g. material science) and another country is leading in nuclear research, we will be able to observe their results and act accordingly (just like China did in the 50s). Why is it so important which government is facilitating which research?

> Why is it so important which government is facilitating which research?

For better or worse, the world doesn't work such that everyone who reads a research paper is on an equal footing to industrialize/commercialize the technology. The ones who got their hands dirty are far ahead. Thus governments do something called 'industrial policy' (a somewhat dirty word in the West these days, to our detriment I think) where they try to build 'value chains' (or whatever you wanna call it) where they spend money on pure research, applied research, early stage spinoffs, etc. to kickstart an industry around a particular technology.

For an example, consider how decades-long investment by the US government into electronic warfare and military electronics kickstarted Silicon Valley.

So China is gearing up to be a dominant player in the global nuclear power market. So does that matter? In a way it's better somebody does it than nobody and we continue burning fossils, but being one of these hopeless romantics who think things like democracy and human rights are incredibly important I'd rather see 'our team' on the field as well. Energy extortion isn't pretty, see Europe and Russia at the moment.

A 1MW research reactor.

Anyway, why is it always a fluoride salt? Is it because of the melting point or because of some nuclear property?

I imagine there is some very relevant reason, because a less reactive anion (even chlorine) would be much easier to work with.

https://en.wikipedia.org/wiki/Molten_salt_reactor#Fused_salt...

Good question - here's a paper and quote on this:

"Molten Salt Reactor (MSR) was designed to operate at high temperature in range 700 - 800°C and its fuel is dissolved in a circulating molten fluoride salt mixture. Molten fluoride salts are stable at high temperature, have good heat transfer properties and can dissolve high concentration of actinides and fission product."

https://aip.scitation.org/doi/10.1063/1.4972932

Without knowing the specifics as apply to nukes, anion reactivity is inversely proportional to atomic reactivity, fluoride is far less reactive than chloride or bromide or iodide, respectively in order of increasing reactivity. Ergo fluoride and fluoride containing anions are quite common in molten salts/ionic liquids.

In English: the flouride, having so voraciously devoured that 8th electron it was missing, really doesn't want to give it up, whereas chlorine et al have lots of spares.)

The concern is not so much about the fluoride losing an electron, but about whatever reacted to it stealing electrons from the reactor.

Which is less likely with fluorine because what fluorine reacts with to form the salt, say Na as in NaF, wants to give up an electron, not receive one. And with fluorine as a partner, Na will have the hardest* time retrieving that electron to give to something else. This can be easily validated by comparing enthalpy of reaction and formation for the various halide salts.

The properties of broad chemical stability are not limited to ionically bonded fluorine either, see PTFE, which also derives its stability from the extreme reactivity of fluorine. Compared to say PTIE (polytetraiodoethylene), which if you could even make would rapidly yellow and degrade in open air/mild sunlight, as iodine compounds are wont to do.

*for a loose definition of hardest.

It is very stable both chemically and atomically.

Fluoride salts are good for fissile uranium + fertile thorium. If you want to work with a plutonium/uranium 238 cycle then chloride salts are a better choice. Plutonium doesn't dissolve very well in fluorides.

Molten chloride reactors can have performance characteristics right out of science fiction, it seems possible for such a reactor to not only breed more fuel but to destroy the long-lived (500 year) fission products such as cesium and strontium.

It never gets upvoted on HN when I link it but I've been following MSRs for a while and even spoke at the first thorium energy conference and I've been watching people's thoughts about designs evolve and this one

https://www.moltexenergy.com/

is well ahead of the others.

While at it, I never understood the worry about the plutonium surfacing in the MSR cycle. Of course it can be diverted to make nuclear warheads. But countries like the US, or France, or Russia, or China, or India already are able to produce nuclear warheads, even from plutonium extracted from more conventional reactors. I don't understand where is the risk of proliferation.

Is this about international treaties and ease of inspection? About currently non-nuclear countries obtaining nuclear weapons more easily?

Perhaps it's just how much more careful you have to be with plutonium products because of proliferation concerns, or possibly diplomacy concerns "legitimizing", or perhaps just paranoia. Or the basic concern of a bunch more plutonium hanging around even if secure.

(1) There is fear that any advance in nuclear power technology will lead to corresponding advances in nuclear weapons technology. For instance, if somebody built a perfect system for separating out protactinium from a thorium MSR, that protactinium could be allowed to decay outside the reactor and produce pure U233 that could be used to make weapons. That perfect system is probably not practical, but in general there is fear that any new approach to fuel processing could have unintended consequences. Would it be possible, for instance, to make something like the EBR-II that breeds weapon grade plutonium in a blanket and uses some form of pyroprocessing to produce pure metallic plutonium? Such a system might be able to make enough material to build several weapons a year.

(2) The published information about nuclear proliferation is incomplete and the mental models behind it are broken. For instance, the "little boy" bomb was made with uranium produced with a

https://en.wikipedia.org/wiki/Calutron

but for all the fear that countries like Iran would develop centrifuges, there has been little fear expressed about Calutrons... Except that when Iraq tried to develop a bomb it used the exact same approach used by the US! A scientist at CERN had been contacted by an Iraqi scientist who was interested in a magnet which could have been used for a Calutron and the proliferation authorities just blew him off.

See https://nuclearweaponarchive.org/Iraq/andre/ISRI-95-03.pdf

A country like Japan has large amounts of plutonium which is contaminated with Pu240 and Pu241 and not weapons usable but it's plausible that a modified Calutron could be used to purify non-weapons grade plutonium and make it weapons grade.

Although the conventional model is that a threat would make plutonium by irradiating uranium with neutrons from a fission reactor, it's also possible that a fusion reactor or particle accelerator could be used as a neutron source to do the same. The later would actually have less heat output per unit of Pu and might be an easier device to hide. Current particle accelerators aren't reliable or economical enough for this purpose, but this is just one of many paths to proliferation which are ignored.

I can't find a source, but my recollection is that the majority of the U-235 for Little Boy was generated by gaseous diffusion? I know the original process was gaseous-diffusion followed by Calutron and that once gaseous diffusion was improved they shut down all of the Calutrons, and the timing is such that all but the first little boy bomb must have been made by gaseous diffusion, but it's unclear how the fissile material for the bomb dropped on Hiroshima was generated.

> There is fear that any advance in nuclear power technology will lead to corresponding advances in nuclear weapons technology.

It seems like it would be a good idea to get the United Nations’ Treaty on the Prohibition of Nuclear Weapons (https://www.un.org/disarmament/wmd/nuclear/tpnw/) signed by more nations then, so that this technology could be safely developed without a risk of nations weaponizing it.

Ukraine let go its Soviet-era nuclear weapons in 1991. In 2014 Russia occupied a large part of it, and in 2022 is trying to occupy it entirely. Aster this, I suppose no other nation will ever voluntarily relinquish their existing nuclear weapons, and many nations that don't have nukes will try hard to obtain them.

This ship has sailed, to my mind.

I think one fear is about the proliferation of reprocessing technology. So currently, with a traditional LWR, you buy X fuel rods, then later IAEA inspectors come by and check that those X rods are in the spent fuel pool. Reprocessing, to the very little extent it's done at all, is done by countries that already have nuclear weapons (except maybe Japan?), so the horse has already left the barn.

But a MSR, at least for some of the more advanced concepts, would have online reprocessing on site (continually siphoning off fission products and adding small amounts of fresh fuel). Additionally, since the fuel wouldn't be in discrete bundles, I think there's a fear that small amounts of fuel could be diverted to a clandestine weapons program.

Are there any MSR designs that require NO reprocessing (whether online, batch or other)?

I'd love to find actual data but, anecdotally, it seems like a large amount (vast majority?) of the nuclear legacy costs for countries like the UK, at least, come from the back-end - ie reprocessing. If you just store used rods (in perpetuity) near the reactor they were used in then the overall legacy footprint is pretty modest. Indeed, I think that's what the UK does now - our reprocessing facilities are now in decommissioning mode and the US did the same a long time ago.

Yes - part of the decision to stop reprocessing was proliferation risk. But I think it's also because reprocessing is so insanely messy and so easy to get wrong.

This is because if you 'reprocess' fuel, the waste problem just balloons... the rods have to be chopped up, dissolved in nitric acid, taken through a complex chemical process and you end up with vast amounts of liquid waste, various bits of undissolved gunk, a fiendishly difficult-to-decommission reprocessing facility and all the rest. Reprocessing plants are some of the most complicated chemical plants in the world... and when they go wrong (eg the UK's Thorp leak) they're almost impossible to repair owing to the radioactivity.

In the past, the purpose of the early reactors was to generate plutonium for weapons and so reprocessing was, in reality, the key activity, with the reactors just the tedious thing you had to build to provide feedstuff for this extraction process.

But if we don't want any new plutonium then there's no need to reprocess and the waste problem just becomes insanely easier.

To see what I mean, google the history of the UK's Sellafield (specifically the B.205 and Thorp plants) or Russia's Mayak or France's La Hague. So many leaks and accidents, all totally unnecessary if they hadn't been trying to reprocess the fuel. The idea of taking something small and stable (a rod) and turning it into a dangerous liquid and then trying to run it through a fiendishly complex chemical plant just seems nuts on its face.

Hence my question about MSRs... can you build one that doesn't require any of this tricky chemical engineering, whether 'online' or otherwise? If so, great. If not, why isn't this whole avenue just shut down as DOA?

> Are there any MSR designs that require NO reprocessing (whether online, batch or other)?

I think the Terrestrial IMSR (which is probably the one closest to commercializing in the West) is designed for a once-through uranium cycle, similar to current LWR plants. The idea, IIRC, is to replace the entire reactor vessel (including the fuel salt) every 7 years.

Not sure what the plan is for dealing with the spent fuel. If the fuel salt is water soluble (not sure, but salts tend to be, right?) I'd think some form of processing is necessary before geological disposal. But maybe that can be a cleaner and simpler process than a full PUREX.

> We can produce heat for hydrogen, replacing the need for fossil fuels in heating, transport and industry.

What does it mean to produce "heat for hydrogen"? Why is heating hydrogen a useful property (how does hot hydrogen replace fossil fuels in heating, transport, and industry?)? That seems oddly specific, so I assume I'm misreading something?

Thermochemical water cracking.

I think it means we can produce heat that can power the generation of hydrogen, e.g. from water.

Yeah, I didn't realize thermalchemical water splitting was a thing.

It's pretty cool that they designed their plants with a heat reservoir and oversized turbine generators. This allows them to turn the turbines on and off at will, complementing wind and solar. The nuclear plant "charges" the heat reservoir during the day when the turbines are idle.

From your perspective, given that Thorium salt reactors are part of India's 3rd stage Nuclear plan, where is this technology in general? I assume that they're leading the pack, but I don't really know.

The problem with India is that they started with redoing the whole solid fuel thing first and that took a very long time.

Its hard to find information, but based on some talks I saw a couple years ago I don't think they are close to liquid fueled reactors.

They are still working mostly on creating thorium pellets to put into reactors.

They are not really ahead.

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

Terrestrial Energy Inc. is the furthest along in terms of the regulatory process.

And for Moltex to work they also need to get a CANDU fuel reprocessing facility online.

But I do think its a great and practical design.

They say they have a version that can be a thorium breeder but they have released little to no information.

Because fluorine has a low neutron capture cross section.

Chlorine has a rather high capture cross section for thermal neutrons, so it could only be used in fast reactors.

This video has a fair amount of information on exactly that question:

https://www.youtube.com/watch?v=bkZ0ZBAVDu4

Anyone know of any software work being done around Nuclear? I don't care what it is, just looking to play a bit more with the space, Open Source, data sourcing. I really mean I don't care what it is, just wanna learn a bit more about it and be a bit more involved.

Same question here!

This is so fantastic. That a 'Christian' university would do this is kind of insane to me, but I take it.

So many problems with nuclear in the last 50 years are that there simply are not enough experiments and research reactors.

If you don't have them, then how can you ever test new materials.

The original molten salt experiment reactor was only not that much bigger then this university reactor and didn't cost a huge amount, but it lead to such amazing research results including new materials that were designed when making it.

New materials can't easily be qualified without having the necessary research infrastructure.

This is really exciting. Fission tech is largely stuck in with incremental improvements from the 1950s. The last time the NRC got an application for a research reactor was 30 years ago.

The reactor is a graphite-moderated, fluoride salt flowing fluid design. If this works well, fission will have a very bright future as it should be more efficient and much safer to operate than current reactor designs.

Forgive me if this is a naive question, but how are molten salt reactors different from the reactor in the 1959 Sodium Reactor Experiment [1]?

[1] https://www.etec.energy.gov/Operations/Major_Operations/SRE....

[Layman, but I've read up quite a bit on thorium and molten salt reactor designs]

The 1959 Sodium Reactor experiment was to demonstrate the feasibility of a sodium-cooled reactor as the heat source for a commercial power reactor to produce electricity. It used fuel rods similar to rods used in reactors in operation today.

Conversely the The Molten Salt Reactor experiment[1] used uranium fuel dissolved into a salt as both fuel and coolant for the reactor - this design enables significant advantages over traditional reactors powered by solid fuel.

[1] https://en.wikipedia.org/wiki/Molten-Salt_Reactor_Experiment

I'm surprised the reactor needs a moderator, I would assume that a liquid fuel reactor could be controlled far better by controlling flow into and out of the critical mass. It's all at normal pressures, just hot (temperature and radiation wise), so just bog standard plumbing practices for handling fluid levels should work.

Being able to scramble the reactor by just dumping the contents through a set of diverters into separate flat bottom chambers to cool and eventually freeze is an awesome safety feature.

A moderator is not used to control the reaction, but to make it possible. The neutrons produced by fission, have high kinetic energy, and fuel has a small cross section for neutrons at such high energy. A neutron moderator slows down the neutrons, making them more likely to interact with the uranium and split them. typically water is a good moderator, but here they use graphite for obvious reason (high temperature salts doesn't play well with water)

That makes a lot of sense... thanks!

As for molten salts and water... oh yeah. That gets into very dangerous territory.[1] A very similar reaction seems to happen even with just molten table salt, where it "shouldn't".

  1 - https://www.youtube.com/watch?v=LmlAYnFF_s8

One of the great practical challenges with molten salt is to design a reliable valve. At temperatures this high and with the high corrosive properties of the medium, this is not trivial.

I didn't realize that the viscosity stays high for molten salt[1], that makes everything abrasive, along with dealing with possible phase change if the salt solidifies... yikes!

So, what we're dealing with is highly radioactive corrosive molasses with a constant stream of radioactive decay product gasses bubbling out of it, like Xenon and Iodine. Yeah, that seems more challenging that I first thought.

  1 - https://www.powermotiontech.com/home/article/21144640/armoring-a-valve-against-molten-salt

Here's an excellent documentary on molten salt reactors if someone is interested in learning more about it.: https://www.youtube.com/watch?v=l08Qzz4j-I0&ab_channel=gordo....

Yey! About time :) hopefully this gains serious traction

Related. Others?

DOE digs up molten salt nuclear reactor tech, Los Alamos to lead the way back - https://news.ycombinator.com/item?id=32423177 - Aug 2022 (1 comment)

Chinese molten-salt reactor cleared for start up - https://news.ycombinator.com/item?id=32406435 - Aug 2022 (9 comments)

Stable Salt Reactor - https://news.ycombinator.com/item?id=32233485 - July 2022 (2 comments)

What is a molten salt reactor? - https://news.ycombinator.com/item?id=31187423 - April 2022 (101 comments)

1MW Molten-Salt Test Reactor by Copenhagen Atomic for €88k [video] - https://news.ycombinator.com/item?id=25388343 - Dec 2020 (198 comments)

New Design Molten Salt Reactor Is Cheaper to Run, Consumes Nuclear Waste - https://news.ycombinator.com/item?id=24771306 - Oct 2020 (2 comments)

ThorCon 2019 500MW molten salt modular tow-able nuclear reactor [pdf] - https://news.ycombinator.com/item?id=21307378 - Oct 2019 (2 comments)

Molten Salt Reactors - https://news.ycombinator.com/item?id=20424841 - July 2019 (120 comments)

What Is Called Nuclear Waste Is Mostly Fuel for Molten Salt and Fast Reactors - https://news.ycombinator.com/item?id=20191064 - June 2019 (49 comments)

Open source Molten salt nuclear reactor design - https://news.ycombinator.com/item?id=18892919 - Jan 2019 (88 comments)

Remote Maintenance of Molten Salt Reactors [video] - https://news.ycombinator.com/item?id=15543428 - Oct 2017 (6 comments)

A Thorium-Salt Reactor Has Fired Up for the First Time in Four Decades - https://news.ycombinator.com/item?id=15084215 - Aug 2017 (161 comments)

Molten Salt Reactor Claims Melt Down Under Scrutiny - https://news.ycombinator.com/item?id=13863626 - March 2017 (137 comments)

The 500MW molten salt nuclear reactor - https://news.ycombinator.com/item?id=5371659 - March 2013 (22 comments)

Nuclear power is great. If you have a few billions to invest and a few decades time to wait.

So did the Chinese beat us to this one? :)

Yes they're turning on their graphite moderated MSR reactor that's fully constructed in the next few days? weeks? not entirely sure, but soon.

https://www.world-nuclear-news.org/Articles/Chinese-molten-s...

It's cool to see what the hottest research is in NA these days, even if they're being so salty about it.

I thought these were outlawed, per a LFTR video I saw once. To emphasize, I'm asking if that is the case, or was the LFTR video was engaging in misinformation, or if something changed in regulations.

I believe it's less outlawed and more not really approved for use due to insufficient research.

The process for licensing a LWR is well established. Commercial LMFBR (Fermi 1) and HTGR (Peach Bottom 1) reactors have been approved in the US but those were a very long time ago. Anybody who wants to license a new reactor type is going to work through an extensive process with the NRC to determine how exactly it is done.

They built an MSR in Wuwei, China and just got approval to start it.

https://www.world-nuclear-news.org/Articles/Chinese-molten-s...

AFAICT materials research is a big part of it. At 800°C even water is pretty reactive; the salt is much more so. Even though an MSR does not need the high pressure of water-based reactors, you can't make all the piping from graphite or platinum.

I believe that the video was misinformed or your recollection is a bit fuzzy. The closest true approximation I can muster is "there is no commercial molten salt reactor design yet approved by the NRC, and the NRC approval process may need updates to consider reactor designs that significantly deviate from the common water-moderated types."

Yes, they are illegal to build.

LFTR?

Liquid Fluoride Thorium Reactor but I believe this reactor is using uranium[1].

[1] https://www.nrc.gov/docs/ML2024/ML20241A071.pdf

LFTR is just a trade name from a guy named Kirk who tried to rebrand the Thorium fueled Molten Salt Reactor.

So basically yes but like all thorium reactors it has to start with enriched uranium first.

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