13 ms·

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 wo

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?

sophacles 4y ago
> 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!)
- nine_k 4y ago
  Exactly. In other variants of reactors the inner contour could circulate molten slightly radioactive sodium instead.
- dangerlibrary 4y ago
  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.
  - ethbr0 4y ago
    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.
- marcosdumay 4y ago
  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.
- philipkglass 4y ago
  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 https://en.wikipedia.org/wiki/Boiling_water_reactor
- tadfisher 4y ago
  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-educators/04.pdf https://www.nrc.gov/reading-rm/basic-ref/students/for-educat...
ortusdux 4y ago
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.
- politician 4y ago
  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.
  - throwaway894345 4y ago
    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?
    - phire 4y ago
      I believe they use active cooling to keep the plug frozen. If the power fails, the cooling fails and the plug melts.
      - ortusdux 4y ago
        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.
PaulHoule 4y ago
People thought this stuff https://haynesintl.com/docs/default-source/pdfs/new-alloy-brochures/corrosion-resistant-alloys/brochures/n-brochure.pdf?sfvrsn=18 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#Results 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.
- HPsquared 4y ago
  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.
  - mulmen 4y ago
    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.
    - HPsquared 4y ago
      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.
rich_sasha 4y ago
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.
p1mrx 4y ago
> 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 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.
- acidburnNSA 4y ago
  LANL built a reactor like that, with liquid fuel in tungsten capsules. It was called LAMPRE. https://www.osti.gov/biblio/4368180-operation-plutonium-fueled-fast-reactor-lampre https://www.osti.gov/biblio/4368180-operation-plutonium-fuel...
  - pfdietz 4y ago
    Tantalum capsules. Molten plutonium is darn corrosive.
    - acidburnNSA 4y ago
      Even better.
ars 4y ago
> 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.
- YakBizzarro 4y ago
  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
  - ars 4y ago
    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.
  - credit_guy 4y ago
    > 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.
    - japanuspus 4y ago
      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.
mjul 4y ago
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/ https://www.copenhagenatomics.com/ [2] https://www.copenhagenatomics.com/products/molten-salt-loop/ https://www.copenhagenatomics.com/products/molten-salt-loop/ [3] https://www.seaborg.com/ https://www.seaborg.com/ [4] https://www.seaborg.com/press-release-hyme https://www.seaborg.com/press-release-hyme
- japanuspus 4y ago
  Thanks for posting, this sounds super cool. Now I just really wished I had a reason to order a molten salt loop.
  - panick21_ 4y ago
    I would love to rip the gas heating out of the house and have little nuclear reactor there.
Manuel_D 4y ago
> 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) https://en.wikipedia.org/wiki/Steam_generator_(nuclear_power...
- acidburnNSA 4y ago
  > 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-development-of-the-boiling-water-reactor https://whatisnuclear.com/reactor_history.html#the-developme...
pnw 4y ago
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.
- PaulHoule 4y ago
  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 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.
- panick21_ 4y ago
  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.
ortusdux 4y ago
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.
- HPsquared 4y ago
  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?
  - kenned3 4y ago
    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.
pfdietz 4y ago
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-OverviewofMSRTechnologyandConceptsML17331B114.pdf 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)
- jabl 4y ago
  > "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.
  - pfdietz 4y ago
    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.
    - jabl 4y ago
      > 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. :)
runarberg 4y ago
> 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/ https://ambri.com/ 2: https://www.youtube.com/watch?v=-PL32ea0MqM https://www.youtube.com/watch?v=-PL32ea0MqM
- marcosdumay 4y ago
  Molten salt / liquid metal batteries normally use alkaline salts, so steel holds it pretty well.
  - runarberg 4y ago
    I see. So there is a pretty simple explanation. Thanks.
samstave 4y ago
https://i.imgur.com/qX2d2qg.jpg https://i.imgur.com/qX2d2qg.jpg https://i.imgur.com/InQHoSI.png https://i.imgur.com/InQHoSI.png https://i.imgur.com/go5v5QL.jpg https://i.imgur.com/go5v5QL.jpg

sophacles 4y ago

> 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!)

nine_k 4y ago
Exactly. In other variants of reactors the inner contour could circulate molten slightly radioactive sodium instead.
dangerlibrary 4y ago
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.
- ethbr0 4y ago
  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.
marcosdumay 4y ago
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.
philipkglass 4y ago
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 https://en.wikipedia.org/wiki/Boiling_water_reactor
tadfisher 4y ago
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-educators/04.pdf https://www.nrc.gov/reading-rm/basic-ref/students/for-educat...

ortusdux 4y ago

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.

politician 4y ago
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.
- throwaway894345 4y ago
  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?
  - phire 4y ago
    I believe they use active cooling to keep the plug frozen. If the power fails, the cooling fails and the plug melts.
    - ortusdux 4y ago
      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.

PaulHoule 4y ago

People thought this stuff https://haynesintl.com/docs/default-source/pdfs/new-alloy-brochures/corrosion-resistant-alloys/brochures/n-brochure.pdf?sfvrsn=18 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#Results 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.

HPsquared 4y ago
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.
- mulmen 4y ago
  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.
  - HPsquared 4y ago
    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.

rich_sasha 4y ago

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.

p1mrx 4y ago

> 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 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.

acidburnNSA 4y ago
LANL built a reactor like that, with liquid fuel in tungsten capsules. It was called LAMPRE. https://www.osti.gov/biblio/4368180-operation-plutonium-fueled-fast-reactor-lampre https://www.osti.gov/biblio/4368180-operation-plutonium-fuel...
- pfdietz 4y ago
  Tantalum capsules. Molten plutonium is darn corrosive.
  - acidburnNSA 4y ago
    Even better.

ars 4y ago

> 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.

YakBizzarro 4y ago
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
- ars 4y ago
  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.
- credit_guy 4y ago
  > 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.
  - japanuspus 4y ago
    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.

mjul 4y ago

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

japanuspus 4y ago
Thanks for posting, this sounds super cool. Now I just really wished I had a reason to order a molten salt loop.
- panick21_ 4y ago
  I would love to rip the gas heating out of the house and have little nuclear reactor there.

Manuel_D 4y ago

> 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) https://en.wikipedia.org/wiki/Steam_generator_(nuclear_power...

acidburnNSA 4y ago
> 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-development-of-the-boiling-water-reactor https://whatisnuclear.com/reactor_history.html#the-developme...

pnw 4y ago

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.

PaulHoule 4y ago
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 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.
panick21_ 4y ago
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.

ortusdux 4y ago

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.

HPsquared 4y ago
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?
- kenned3 4y ago
  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.

pfdietz 4y ago

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-OverviewofMSRTechnologyandConceptsML17331B114.pdf 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)

jabl 4y ago
> "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.
- pfdietz 4y ago
  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.
  - jabl 4y ago
    > 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. :)

runarberg 4y ago

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

marcosdumay 4y ago
Molten salt / liquid metal batteries normally use alkaline salts, so steel holds it pretty well.
- runarberg 4y ago
  I see. So there is a pretty simple explanation. Thanks.

samstave 4y ago

https://i.imgur.com/qX2d2qg.jpg https://i.imgur.com/qX2d2qg.jpg https://i.imgur.com/InQHoSI.png https://i.imgur.com/InQHoSI.png https://i.imgur.com/go5v5QL.jpg https://i.imgur.com/go5v5QL.jpg