I’m sure it is, but it was too long with too many full blown nerds (as testified by their haircuts) to keep me watching.
These sort of guys are the reason high school kids don’t want to study science.
Damn it! Science is exciting, and amazing and sexy and doesn’t deserve these Professor Frink stereotypes.
Spiny Norman said:
Pretty cool
This is brilliantly informative – if you cut it up into appropriate small chunks and expand the important chunks.
Several things I wished I knew before designing my super-high temperature nuclear reactor for space propulsion. For example, one driver for the original work was to investigate the possibility of a nuclear-powered aircraft, I looked into that myself, and like them concluded that it isn’t feasible.
In another example, In my super-high temperature reactor design I was running into the problem that I needed really high thermal conductivity but at the same time very low corrosion. They go into that in this video in a lot of detail – using molten salt gives a very high heat transfer rate because of the low viscosity but at the same time adding beryllium to the mix makes it reducing, which minimises corrosion. Very nice.
45 minute doco.
I’ll watch it later tonight perhaps.
mollwollfumble said:
Spiny Norman said:
Pretty cool
This is brilliantly informative – if you cut it up into appropriate small chunks and expand the important chunks.
Several things I wished I knew before designing my super-high temperature nuclear reactor for space propulsion. For example, one driver for the original work was to investigate the possibility of a nuclear-powered aircraft, I looked into that myself, and like them concluded that it isn’t feasible.
In another example, In my super-high temperature reactor design I was running into the problem that I needed really high thermal conductivity but at the same time very low corrosion. They go into that in this video in a lot of detail – using molten salt gives a very high heat transfer rate because of the low viscosity but at the same time adding beryllium to the mix makes it reducing, which minimises corrosion. Very nice.
We really need to work together at some point, our knowledge supplements each other quite well.
FWIW I’m trying to get into Griffith Uni here on the Gold Coast next year to do Mechanical Engineering.
All this is ORNL, “Oak ridge national laboratory”, I have heaps of respect for those guys.
“Homogeneous reactors tend to be chemically unstable”, pity because they’re by far the easiest and smallest nuclear reactors to build. “The second one worked fairly well.”
“Manually operating parts of the reactor by means of very long-handled tools”, I agree with them in that everything these days would be done remotely and so the overall design would look very different.
“Hotter → molten salt less dense → fewer reactions → cools down again” = inherently stable. Other types of reactors (heavy water, boiling water, pressurised water) tend to be inherently stable too. The other stability they didn’t mention was that Hotter → neutrons too hot for maximum absorption → cools down.
“232Th → 233U” which is fissile. This is a breeder reaction analogous to “238U → 239Pu”
Spiny Norman said:
We really need to work together at some point, our knowledge supplements each other quite well.
FWIW I’m trying to get into Griffith Uni here on the Gold Coast next year to do Mechanical Engineering.
I’m all theoretical, on the impractical side of practical. You’re great at practical. Yes we really need to work together.
for an aircraft the fuel could be in the wing I suppose
thermo electric devices could use the air running over the wings to create the cool side
wings have a large area and the fuel could be spread out inside , you’d need a neutron source that could be removed when not flying
the aircraft would have electric driven propellers designed for high speed flight – it would be very quiet inside – no engine noise
you go for a low temperature , high surface area generator
for a spacecraft the thermoelectric device could be the hull
mollwollfumble said:
Spiny Norman said:
We really need to work together at some point, our knowledge supplements each other quite well.
FWIW I’m trying to get into Griffith Uni here on the Gold Coast next year to do Mechanical Engineering.
I’m all theoretical, on the impractical side of practical. You’re great at practical. Yes we really need to work together.
mollwollfumble said:
“232Th → 233U” which is fissile. This is a breeder reaction analogous to “238U → 239Pu”
“Shaw at Washington was sold on the alternative Na cooled fast breeder reactor 238U → 239Pu at Argonne”.
“Tritium would have to be captured”. I didn’t know that. Why? Where would it have come from?
Ah, I see, from neutron interactions with Lithium 6 and Lithium 7. They could have run “molten salt” without lithium.
Later on in video I see 46.5% LiF, 11.5% NaF, 42% KF. Presumably there’s a good reason for choosing that mix.
Later, tritium was highly valued in nuclear weapons, now we just use it as a keychain light.
Some documents were saved after program termination in 1972 in private hands. I wish I could see those.
“You don’t get taught this stuff in nuclear engineering school?” Why not? Some molten salt + thorium breeder stuff, together with diagrams and calculations, has been written up in a book that is one of my prize possessions. “Elementary introduction to nuclear reactor physics” by S.E.Liverhant, 1960. This was before the molten salt reactor program was cancelled, a diagram of the Oak Ridge reactor assembly is shown in Fig 7.7. By the way, the words “elementary introduction” in 1960 don’t mean the same as they do now, for example a knowledge of partial differential equations and how to solve them is a prerequisite for understanding some chapters.
“Nickel alloys, inconel 600, ideally Hastelloy”, interesting, chosen because of resistance to corrosion. Hastelloy is more difficult to get in complex shapes.
“Above about 600 C it becomes technologically very difficult to transfer heat effectively”. Hmm. “Corrosion tests at 700 C”.
Screenshot of corrosion testing billboard.
Testing a pebble bed reactor. The pebbles are of silicon carbide and contain solid fuel “TRISO”
Screenshot of billboard for flow diagram for pebble bed high temperature reactor.
Thinking further, I know why they have Lithium Fluoride as the main salt, of all the salts it’s the one with the greatest neutron-slowing action because the elements Lithium and Fluorine are lightweight. The melting point of LiF is 845 °C, of NaF is 993 °C, of KF2 858 °C. These are all too high! Mixing them together in the correct proportions lowers the melting point. The eutectic LiF–NaF–KF (46.5; 11.5; 42.0 mol%) has a melting point at or below 520 °C. The melting point of of BeF2 is 554 °C.
> Testing a pebble bed reactor. The pebbles are of silicon carbide and contain solid fuel “TRISO”
These pebbles are less than 1 mm in diameter. The silicon carbide coating of the pebbles contain gaseous fission products. I think another of the coating layers is graphite.
“Molten salt the only material trialled capable of high temperature at low pressure, which is the unique combination”. “Boiling point could be as high as 815 Celsius”, well, it had better be higher than the temperature of 700 Celsius used in corrosion testing. About 600 degrees in the main reactor, that makes it a high temperature reactor (HTR).
“In homogeneous reactors the expensive process of producing fuel pellets is bypassed” but in Pebble bed reactors the problem is still there. “making a fluoride salt is trivial”. (PS, my idea for an extremely high temperature reactor, too hot for molten salt, was also a homogeneous reactor).
“In the conventional (water-based) reactor design with solid UO2 fuel pellets, a problem is that the solid UO2 is a particularly bad heat conductor, so that means that the centres of the fuel rods get very hot, “about 1000 degrees hotter than the surface, which puts enormous thermal stresses on the assembly”, “you can’t even get close to 100% burn”.
“Hexagonal grid of plates for fuel assembly cooled by liquid salt F+Li+Be”.
“Conventional solid fuel the fuel doesn’t move. Pebble bed if a halfway house where the fuel does move, but not fully with the liquid. Then a slurry where the fuel is in particulates that move with the flow. The final step has the fuel in solution.”
“CASL” is the name for overcoming problems associated with nuclear reactors, problems like power-level-shift, corrosion, mechanical failure, unwanted chemical reactions, geometric distortion, and safety problems.
————————————————
mollwollfumble’s private thoughts on this.
1) I don’t see molten salt reactors replacing water-based reactors for large public power facilities.
2) Keeping in mind that molten salt was initially started as a solution to the “minimum weight” nuclear power source, I see a use for in small power plants such as ships, submarines, possibly trains, and scientific applications that require other properties such as high neutron flux for doping computer chips and for neutron-based imaging. Neutrons penetrate materials better than X-rays and gamma rays, and unlike gamma rays are stopped by the presence of light elements such as hydrogen, helium and carbon.
3) The 232Th to 233U breeder technology is the best long-term power source, simply because 232Th is cheaper and much more plentiful than natural uranium. Clean-up of the radioactive waste is slightly easier, but not much easier. A breeder reactor of any sort requires a reprocessing facility.
4) On the other hand, 232Th technology can be implemented with more conventional types of reactor, it doesn’t have to be a molten salt reactor.
5) I’m not keen on the pebble-bed idea because the pebble manufacture is complicated and expensive. I’d prefer to see the fuel dissolved in the liquid salt, despite the more complicated chemistry.
Checking up what the heck “TRISO” is.
“TRISO is a shortened version of TRIstructural-ISOtropic. TRISO fuel is tiny balls of uranium coated with carbon, then silicon carbide, then carbon. The Germans first developed it in the 1980s and several countries have considered it for various next generation reactors. It works particularly well in High Temperature Gas-cooled Reactors HTGRs”.
Um, what’s a HTGR? Checking web again. Helium circulated through the reactor transfers the heat across to a steam circuit. The process generates hydrogen. Applications proposed include cogeneration of electricity and steam, heat for petroleum refining, heat for shale-oil and oil sand processing, coal gasification (requiring all three of hydrogen, steam and heat), and natural gas reforming.
So where does the hydrogen come from? I see now, high temperature steam plus electric power feeds into a hydrolysis unit that produces hydrogen. Not a particularly good use of electric power IMHO, but could be worse.
All of the above applications apart from coal gasification are also suitable applications for molten salt reactors (MSR). Coal gasification works better above 800 °C.
A molten salt reactor (MSR) operates at about 600 °C. A HTGR operates “conceptually” up to a temperature of 1000 °C. The two can use the same pebble-type fuel. Hmm, corrosion problems would be much less with gaseous helium coolant.
party_pants said:
45 minute doco.I’ll watch it later tonight perhaps.
I’ve watched it now, very interesting, worth a look if you got the time.
I have nothing to contribute to the ongoing discussion though, that’s a bit beyond me,.
> Um, what’s a HTGR (High Temperature Gas Reactor)? Checking web again. Helium circulated through the nuclear reactor transfers the heat across to a steam circuit. The process together with the electricity from the reactor generates hydrogen from electrolysis of water.
(Hobbyhorse warning). There’s an annoying doublethink about hydrogen in the public and hence political mind. One that is illustrated sharply in HTGRs.
On the one hand, hydrogen as a fuel is seen as the best thing since sliced bread.
On the other hand, hydrogen in the Hindenberg is seen as the deadliest thing since Jaws.
We see both annoying attitudes together here. An HTGR would be significantly cheaper and work better if the helium circulating through the reactor was replaced by hydrogen. Hydrogen is more than twice as good as helium as a moderator for neutrons for starters, is far less rare, and is much less expensive. But no, that’s seen as too dangerous. It’s no more dangerous than the attached plant that generates hydrogen by electrolysis, possibly even less dangerous because the electrolysis plant has pure oxygen in close proximity to the hydrogen.
Couple that annoyance with the annoyance of where our helium actually comes from. Helium is a rare byproduct that is separated out of natural gas. But natural gas is also a much better source of hydrogen than electrolysis of water. Better (less wasteful of energy) overall would be to generate the hydrogen from natural gas, use that hydrogen in the HTGR reactor in place of helium, and scrap the hydrogen plant that’s run off the electricity of the nuclear reactor.
PS. I prefer the pebble bed HTGR to the pebble bed molten salt reactor for large-scale nuclear power plants, because the HTGR has higher temperature and less corrosion risk. A molten salt pebble bed plant would only have the advantage of compactness, useful for small-scale reactors. A molten salt with dissolved fuel is another ballpark.