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Post by David B. Benson on Feb 12, 2020 17:33:36 GMT 9.5
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Post by engineerpoet on Feb 15, 2020 11:16:41 GMT 9.5
But do we know if salt domes will still be stable if they have heat-generators planted in them?
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Post by David B. Benson on Feb 15, 2020 13:03:52 GMT 9.5
But ... heat-generators ...? The melting point of sodium chloride is 801 °C. The once-through nuclear assemblies are kept in local storage until the generated temperature is but 50 °C, considered adequate for safe transport.
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Post by engineerpoet on Feb 15, 2020 19:11:33 GMT 9.5
The melting point of sodium chloride is 801 °C. The once-through nuclear assemblies are kept in local storage until the generated temperature is but 50 °C Do you think SNF stops generating heat when it reaches some particular temperature? Do you understand the concepts of "thermal resistance" and "water migration"? Something buried in a salt dome will heat to a far higher temperature than one in water or air, and a heat source in salt will attract water, which can boil and create pressure. All must be accounted for. One way to account for the heat is to remove it. All significant heat comes from isotopes with half-lives far too short to require burial in salt domes. Separate those isotopes and dispose of (or employ) them differently. End of problem. I suspect that deep borehole disposal also deals with the heat problem (by dispersion into a large thermal mass) but again, all must be accounted for. IMO the sheer scale of our need for energy to ameliorate our escalating climactic disaster precludes burying significant amounts of actinides, so that points more toward reprocessing.
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Post by David B. Benson on Feb 15, 2020 19:33:19 GMT 9.5
Yes, reprocessing is to be preferred.
However, there is no water to be "attracted" in the salt domes mentioned in the Conca article. Furthermore, the once-through nuclear pins can be stored indefinitely above ground until cool enough to be buried.
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Post by engineerpoet on Feb 15, 2020 21:44:27 GMT 9.5
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Post by David B. Benson on Feb 15, 2020 22:09:39 GMT 9.5
The salt domes work well enough for the clean up of the Hanford plutonium processing. Surely that is more stringent than mere once-through nuclear pin storage.
This has been well-studied. Conca summarized.
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Post by David B. Benson on May 1, 2020 10:36:58 GMT 9.5
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Post by cyrilr on May 1, 2020 15:28:35 GMT 9.5
The salt domes work well enough for the clean up of the Hanford plutonium processing. Surely that is more stringent than mere once-through nuclear pin storage. This has been well-studied. Conca summarized. EP did point out the heat load issue, which is likely the biggest uncertainty compared to what's been done so far at WIPP. Heat load is typically the limiting constraint on any geologic repository. However, on first principles we shouldn't expect serious issues with heat load for salt formations: 1. salt has higher thermal conductivity (lower thermal resistance) than typical rocks. 2. salt formation storage actually relies on instability - plastic creep sealing the storage cavity over time, a leak-tight seal in fact. Because of the creep-down sealing of any cavity or fissure, salt domes are so tight you can safely store high pressure natural gas and likely even hydrogen in them. Adding heat load likely accellerates the creep-down sealing so probably a good thing. It's a matter of validation though - testing. I suppose one might stick a big electric heater in a mockup cask and put it in a salt formation for a few years, then see if salt strains are acceptable and comply with computer models. Something else that is of relevance to study would be the "sinking" of the casks in the salt formation. Spent fuel casks have much higher density than rock salt. Because of the plastic creep phenomenon there could be an issue with the cask slowly "sinking" to the bottom of the salt formation. Then there could be faults and such where a leakage path may exist. Perhaps the casks could be loaded on a platform of sorts that acts as a raft/barge.
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Post by cyrilr on May 1, 2020 15:35:05 GMT 9.5
I don't like it when people say Yucca Mountain is a "dump". As Cohen pointed out in the 80's and 90's, clearly a "dump" would not cost billions of dollars. What is involved here is a highly engineered deep repository with many layers of containment both engineered and natural, in a remote site with little preciptitation far from groundwater and even from used groundwater sources. There is no credible, even hypothetical way the stored materials could harm even a single person, bird or animal. A fact that seems to have been lost on all the opponents. Conca is pretty good though. A real light in the darkness. Always love reading his stuff.
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Post by David B. Benson on May 1, 2020 15:50:27 GMT 9.5
... Yucca Mountain is ... in a remote site with little preciptitation far from groundwater and even from used groundwater sources. There is no credible, even hypothetical way the stored materials could harm even a single person, bird or animal. ... Yes there is. Yucca Mountain is the headwaters of the underground river, flowing south, with the various species of blind pupfish unique to that water source.
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Post by cyrilr on May 1, 2020 17:12:03 GMT 9.5
... Yucca Mountain is ... in a remote site with little preciptitation far from groundwater and even from used groundwater sources. There is no credible, even hypothetical way the stored materials could harm even a single person, bird or animal. ... Yes there is. Yucca Mountain is the headwaters of the underground river, flowing south, with the various species of blind pupfish unique to that water source. That does not follow as a risk. You seem completely unfamiliar with the geotechnics of the repository site. The Yucca Mountain site is way above ground water, and even if the casks fail and would somehow get to hypothetically elevated groundwater, it would take forever for any nuclides to transport, due to rock sorption dynamics. There is no meaningful dose left by the time it gets to the nearest fish. Read Cohen's book, The Nuclear Energy Option for more information. There is no way, even hypothetically, that you can get lethal doses to a fish.
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Post by cyrilr on May 1, 2020 17:49:55 GMT 9.5
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Post by David B. Benson on May 5, 2020 13:33:54 GMT 9.5
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Post by cyrilr on May 5, 2020 15:12:32 GMT 9.5
Interesting, but what happens to the fission products? To what extent are they incorporated into, or stick to, the crystals? What is the decontamination factor?
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Post by David B. Benson on May 5, 2020 15:27:54 GMT 9.5
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Post by cyrilr on May 5, 2020 15:46:36 GMT 9.5
Cs is just one fp. What about rare earths and noble metals? Any single stage process will require a high decontamination factor for all fp.
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Post by David B. Benson on May 5, 2020 16:18:13 GMT 9.5
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Post by Roger Clifton on May 6, 2020 20:01:29 GMT 9.5
Just use 'red,fuming' nitric acid plus moderate heat. It is hard to see that a process that creates an aqueous solution of plutonium from unspecified fuel rods is anything but proliferating. Several years ago, CyrilR proposed – correct me if I'm wrong – that (oxide?) fuel could be heated to high temperatures that separated off the most volatile fission products, leaving the plutonium still in the uranium matrix. Non-proliferating. Since the baked fuel is still in pellet form it can go directly into a fresh fuel assembly and returned to the reactor.
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Post by cyrilr on May 7, 2020 3:23:42 GMT 9.5
Just use 'red,fuming' nitric acid plus moderate heat. It is hard to see that a process that creates an aqueous solution of plutonium from unspecified fuel rods is anything but proliferating. Several years ago, CyrilR proposed – correct me if I'm wrong – that (oxide?) fuel could be heated to high temperatures that separated off the most volatile fission products, leaving the plutonium still in the uranium matrix. Non-proliferating. Since the baked fuel is still in pellet form it can go directly into a fresh fuel assembly and returned to the reactor. Correct. And don't remind me of the endless flow - tempus fugit and all that. But that idea still has merits, in my opinion. If we want to recycle oxide fuel into oxide fuel, why not point out the obvious and stay with oxides. Not that anyone listens to me. Even OREOX, as proposed for DUPIC, which comes close, is too complicated with valence-state changes. Some sort of simple low speed grinding and attrition process should suffice. We have UO2, we want UO2, why not stay with UO2. Indeed, major issues of PUREX and its cousins have arisen from the obvious facts: * criticality problems (acid is mainly water) * radiolysis problems (acids are NOT radiation resistant) * secondary waste generation and contamination problems (plutonium has extremely complex chemistry and will go all over the place, in the waste bin, in the product bin, on your equipment) which then cost a fortune to clean up and generate secondary wastes that cost even more to clean up. *etc. etc. What can I say? I'm shouting in the desert. Them chemists love their acid. Perhaps they are ON acid. Or just being deliberately obtuse - one hardly sees strategy in proposals that make oneself (and your program managers) redundant. If you're a hammer everything looks like a nail, and if your business is selling hammers you won't be promoting screws even if they are superior to nails. I'm sure that if a nuclear chemist were in charge of designing a steel recycling plant, he/she would suggest we start by dissolving the steel in acid, and then... The idea could also be applied to other fuels: alloy fuel such as used in the IFR, where possibly one would melt the fuel in an electrically heated, vacuum furnace (perhaps in a thoria crucible or such). Be a lot simpler than the electrochemical process with cathode processing and nasty biles of electrolyte, anode slime... yuck. Better than acid I guess, but that's not a high standard. In metal fuel there would be less concern about the lanthanides staying behind - up to a point. At some point one does end up with too much physical concentration of lanthanide in the fuel and another process would have to be used - zone refining, perhaps, keeping with the no chemical change theme.
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Post by David B. Benson on May 7, 2020 10:45:01 GMT 9.5
Just use 'red,fuming' nitric acid plus moderate heat. ... an aqueous solution of plutonium ... Not aqueous en.m.wikipedia.org/wiki/Red_fuming_nitric_acidAt the higher temperature all the constituents of the nuclear fuel oxide pellet are in solution. As the temperature drops various elements precipitate nitrate crystals with all of the actinides forming impurities in the primarily uranium nitrate. There is never any separate only plutonium phase.
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Post by cyrilr on May 7, 2020 16:25:58 GMT 9.5
It contains water, and tons of hydrogen. Let’s not split hairs here. Rocket propellant isn’t the first thing that comes to mind we should use to recycle spent fuel!!! That is just another example of the craziness of nuclear chemists.
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Post by David B. Benson on May 7, 2020 16:46:15 GMT 9.5
It contains water, and tons of hydrogen. ... Actually in freshman Chem lab, 6 hours per week for 3 quarters, we used pubchem.ncbi.nlm.nih.gov/compound/Nitric-15N-acid-solutionwhich also has a tiny bit of water. Either way, the oxygen in the oxides will instead combine with the hydrogen, once everything is cool and so all the actinides and the interesting fission products have formed separate precipitates. Except those elements that remain in solution,the solution being less acidic. I don't know whether or not this is a good idea for nuclear waste management, but it certainly offers possibilities.
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Post by cyrilr on May 7, 2020 17:33:18 GMT 9.5
It contains water, and tons of hydrogen. ... Actually in freshman Chem lab, 6 hours per week for 3 quarters, we used pubchem.ncbi.nlm.nih.gov/compound/Nitric-15N-acid-solutionwhich also has a tiny bit of water. Either way, the oxygen in the oxides will instead combine with the hydrogen, once everything is cool and so all the actinides and the interesting fission products have formed separate precipitates. Except those elements that remain in solution,the solution being less acidic. I don't know whether or not this is a good idea for nuclear waste management, but it certainly offers possibilities. You mean if it doesn't radiolyse and form combustible gasses, or go critical with all that hydrogen, and if no water enters into it accidentally which will cause it to explode. You do realise this stuff is rocket propellant right? It's unstable? Not radiation resistant? We need to make nuclear reprocessing safer so it can be cheaper. Starting off with mixing rocket propellant in with the spent fuel is not a good start.
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Post by David B. Benson on May 7, 2020 17:47:30 GMT 9.5
cyrilr, I state once again that all of us freshmen chemistry students used as much 15 formel nitric acid as we needed, being quite careful when diluting with water.
Once-through nuclear fuel pins are not very radioactive. I don't see any remarkable hazard. I just see this as a way, quite clever really, to separate actinides from fission products.
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Post by cyril r on May 7, 2020 20:03:46 GMT 9.5
cyrilr, I state once again that all of us freshmen chemistry students used as much 15 formel nitric acid as we needed, being quite careful when diluting with water. Once-through nuclear fuel pins are not very radioactive. I don't see any remarkable hazard. I just see this as a way, quite clever really, to separate actinides from fission products. Well over 10e16 Bq/ton for 10 year cooldown of typical PWR SNF. Yeah, >1000 TBq is "not very radioactive". I happen to know a thing or two about the high costs of reprocessing facilities, including construction, operation, safety against criticality, diversion, security, cleanup. We can agree to disagree.
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Post by engineerpoet on May 7, 2020 23:13:55 GMT 9.5
You do realise this stuff is rocket propellant right? It's unstable? Not radiation resistant? Oxidizer, to be specific. It's not going to catch fire by itself or with SNF, and it's not like anyone's going to be throwing UDMH into the mix. The radiolysis products are going to be nitrogen, oxygen and water. This is about as harmless as you could ask for. So a bit of it breaks down and you have to add more; no big deal. The safeguards you need to protect against the radiation are more than enough to deal with the chemical hazards. As I wrote elsewhere, the issue with using this to "recycle" LWR fuel is that there isn't enough fissile content to make it re-usable in an LWR again. You'd have to re-enrich the uranium, which requires separating it. You also have the issue that the accumulation of non-fissile Am, Cm and so forth is a neutron sink. The real use for this might be to help make FBR fuel. Fluorinate enough of the uranium off as UF6 and what remains could be just what the doctor ordered.
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Post by cyrilr on May 8, 2020 0:29:29 GMT 9.5
Thanks for the additions, E-P. You are correct, as usual.
Not too sure about the radiolysis being trivial; generating oxygen in a closed loop system (can't just vent to atmosphere, obviously!) and water that reacts exothermically with the rocket propellant oxidizer... depending on the rate it could probably be designed for.
My point being rather to attempt to avoid hydrogen chemistries (including water, HNO3 compounds etc.). So to me things like vacuum baking, vacuum distillation and zone refining (latter two more for metal fuels) are better avenues of approach.
Of course there is not sufficient reactivity left with the uranium and TRUs left together. The idea is to either add some 5% LEU for a hybrid fuel-repo fuel mix, or to use the fuel for CANDUs.
An interesting option I think would be to add some ThO2 and make a CANDU fuel mix; even with the lanthanides in there is actually more reactivity than natural uranium, the ThO2 brings that down while yielding good fuel burnup later via U233. The ThO2 could be varied radially and axially across the CANDU core for power flattening, equivalent to enrichment zoning, yielding at least a 20% uprate to reactor power. All without any more uranium having to be mined...
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Post by engineerpoet on May 8, 2020 1:51:13 GMT 9.5
Thanks for the additions, E-P. You are correct, as usual. You're gonna make me blush here. I don't know how many HNO3 molecules a single beta particle or gamma ray can break up, but I have a sneaking suspicion that the heat of dissolution of the water isn't going to compare to the fractional MeV of the decay. If I was going to dig into this I'd look at getters for the oxygen. You'll get nitrogen too, and maybe some free hydrogen. IIUC, LWRs generate some radiolytic hydrogen. A catalyst can recombine the hydrogen before it gets to combustible levels. Let a thousand reprocessing chemistries bloom... as long as at least one goes commercial. If you add 5% fissile to 2% fissile to make 3.5% fissile, you've just doubled your fuel volume. The point is to get rid of the "waste problem", not just cut it in half. I admit, I've been wondering for a while why ThO2 hasn't been used as a "breedable poison" in lieu of gadolinium or dysprosium. You'd make plenty of U-234 at anything like an economic neutron flux, but that would actually be an advantage in that application. I just plain don't know enough about this stuff to do more than speculate. It's fun to think about, though.
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Post by cyrilr on May 8, 2020 5:04:37 GMT 9.5
Let a thousand chemistries bloom... very poetic, spoken like a true mad chemist! Though one can't go too crazy - in a regulated industry like nuclear, having too many options leads to lack of focus and cost efficiency. As the French proved with their PWR focus - you can pick between big, bigger and biggest PWR! Not a huge fan of their PUREX MOx work though, it's a dead end old dog tech, too big too messy.
As for cutting it in half... sounds like a decent start. Perfect is the enemy of done. I'll say that in favor of the French MOx work even. In any other industry, doubling the amount of energy you can generate from a resource, with the same amount of waste, would be considered a big achievement.
But you're right, the CANDU path seems more promising. Any engineer would be able to appreciate the entropic advantage of adding ThO2 to the recovered spent fuel rather than diluting enriched uranium into it.
As to why ThO2 is not used as a burnable poison - it does have some downsides for that particular application. Gad is really high worth so little is needed. Thorium is very low cross section by comparison, so a bunch would be needed. That then displaces natural uranium so it lowers the fissile loading. It also generates U233, a rather superb fissile. Good for fuel economy but maybe not for a poison application - one can end up with too much worth at end of life. For a recovered fuel mix it makes a good deal of sense to me as the recovered U + TRUs have a higher worth than natural uranium.
Plus one can do the opposite trick of enrichment zoning. This has always been an issue with CANDUs. Reactors have a natural Guassian power distribution, so the edge channels don't want to make much power. Since thermal-hydraulics limit power output, the leading pins become limiting. With natural uranium one is limited to the 0.7% U235. While ideally one would have more fissile in the central pins of a channel, and in the outer channels of the core. By using slightly enriched uranium, or a more reactive fuel mix with poison (thorium) added variously one may better optimize the power output. This could mean a 20% power increase. Combined with a square calandria (why not, there's no pressure) one can generate another 25% more power for a 50% power uprate. 900 MWe out of a 600 MWe reactor with the same core width sounds like a big deal.
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