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PostPosted: Jan 28, 2008 11:17 pm 
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Here is a series of comments on NNadirs blog on Daily Kos

In light of the points NNadir raises, is the Chloride reactor worth the trouble?
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Waste burning reactors

We could make a start on it by putting (slightly) used Light Water Reactor fuel through CANDUs using the DUPIC process.

To really get rid of the Pu239 put it through liquid chloride reactors with a thorium blanket to breed U233 for starting up liquid fluoride reactors.

See http://thoriumenergy.blogspot.com/ & the connected discussion forum for technical details.

by Jim Baerg on Sun Jan 27, 2008 at 08:49:48 PM PST
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I don't know why anyone would use chlorine in a

MSR.

Of the 4 available halogens, I think it's the worst one because of the longevity of Cl-36.

Every time I think about nuclear chemistry, particularly where there are potential neutron fluxes, I try to stay away from chlorine.

What is the justification for using chlorine in your mind?

Ignorance Kills.

by NNadir on Sun Jan 27, 2008 at 09:08:03 PM PST
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Chloride reactors

Kirk Sorenson who runs that website is particularly enthusiastic about fluoride reactors for use in the Thorium-U233 fuel cycle, but he is also looking at using some sort of fast neutron reactor to fission the trans-uranics & breed start-up charges of U233 for the fluoride reactors. Molten chloride is one that is considered.

IIRC there is some mention of doing chloride isotope separation so only Cl-37 is used in the reactor & no Cl-36 is generated. I don't know what advantages that would have over using bromides & iodides.

Perhaps some variant of the IFR to fission plutonium & breed U233 would be better.

by Jim Baerg on Mon Jan 28, 2008 at 09:09:58 AM PST
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Kirk and I briefly corresponded off line - Rod

Adams put us in touch.

He asked me about this point and I can't recall exactly in response what I said, but here is what I think about this subject.

Isotope separations add a layer of cost. In order to justify the expense, there should be a compelling reason for doing it. Moreover, the heavier the isotope, the smaller the isotope effects, and the more difficult the matter becomes.

In fact, were this 1940 and someone were to ask me, I would insist that the matter is well nigh impossible for an element as heavy as uranium. In fact, according to the Farm Hall transcripts obtained by bugging the captured German nuclear scientist's reaction to Hiroshima, that was their immediate reaction: "My God! These fellows have separated uranium isotopes!" It is almost certainly the case that if fluorine had two stable isotopes rather than one, the effort would have failed in any case, because UF6 contains 6 flourines, which would have easily overwhelmed the U-235/U-238 isotope effect.

One might argue - and I do - that one can prevent, even in modern times, the utility of isotope seperations today merely by adding U-236 to the mix - something that continuous recycling on a thorium based cycle will almost certainly do. That is, in my view, a good thing, since it tends to make uranium based weapons design extremely difficult.

It is relatively easy, and justifiable in my view, to separate deuterium from protium to make CANDU type reactors, but less so for chloride reactors. The isotope effect between protium and deuterium is the largest for any element.

The neutronic efficiency of chlorine-37 is not as good as fluorine and while there might be a small corrosion resistance advantage, it's not all that huge - especially for anyone who has looked at a piece of metal that's been under seawater for a few decades. Further, chlorine, unlike fluoride has very few insoluble aqueous compounds. Those that are available are expensive (silver) or extremely toxic (mercury I).

By contrast, it is trivial to remove fluoride (as the calcium salt, for instance). Iodine can be removed by selective volatilization (along with technetium, uranium, some neptunium and some plutonium,) by direct fluroination with distillation. (This is true of chlorine as well, but in both cases a very interesting salt is formed if cesium is the counter ion.)

Chlorine-37 has some huge absorption resonances, and while iodine is also inefficient from a neutronic standpoint, the product of neutron capture in iodine is very valuable, the gas xenon. For chlorine is is argon, which is cheaply available constituent of air. Moreover, it is inevitable that the chlorine separations will not be completely efficient and that thus one will needlessly end up with some chlorine-36 contamination - and this with a completely soluble ion. (Silver halides decay photochemically accounting for a long time, for almost all photography.) By contrast flourine has no long lived radioisotopes.

In any case, in order to separate (chemically) chlorine from iodine, a fission product, tricky chemistry is involved. I can't see why one would want to bother.

The main motivation in my mind for considering iodides is the xenon matter and the fact that I-129 is an inconvenient - at least politically - fission product. I-129 is considered by some - without much rational justification - a long term radiation hazard. (I once wrote a fun diary here about I-129 found in the Mississippi River as a result of operations at La Hague and Sellafield.) That said, iodine is not particularly corrosive when compared with its cogeners and this is a big advantage. Iodine in its free state can be handled as a solid and not as a gas, and that it a big thing in my mind as well.

Iodine, last I looked, was fairly expensive, about $13/kg on a metric ton scale, so expensive that it is rarely used in industrial pharmaceutical chemistry, even though it has wonderful properties.

I'm not sure what Kirk is getting at with this, but these are my impressions.

Ignorance Kills.

by NNadir on Mon Jan 28, 2008 at 05:32:28 PM PST

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PostPosted: Jan 29, 2008 12:14 am 
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I've got a few papers on chlorine isotope separation and it doesn't look too hard. It's not like we're going to build thousands of chloride reactors--just a few. They're going to chew up all that nasty transuranic waste and breed clean beautiful U-233 from a thorium blanket.


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PostPosted: Jan 29, 2008 12:16 am 
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NNadir wrote:
I don't know why anyone would use chlorine in a MSR.


Really hard neutron spectrum, that's why. A hard spectrum like that makes the capture-to-fission ratio of all your TRUs get really attractive and allows you to burn them up in a neutronically favorable way.


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PostPosted: Jan 29, 2008 7:54 am 
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Kirk Sorensen wrote:
NNadir wrote:
I don't know why anyone would use chlorine in a MSR.


Really hard neutron spectrum, that's why. A hard spectrum like that makes the capture-to-fission ratio of all your TRUs get really attractive and allows you to burn them up in a neutronically favorable way.


It also generally lowers the absorption cross section of everything. This means fission products are less of a problem, so is structural material and so is Protactinium. If you run a Thorium breeder in a fast spectrum, you might get away with a Hastelloy vessel and without Protactinium removal, and still breed. See Eric Ottewitte's thesis for more on that topic (somewhere in Kirk's document repository). A dual breeding cycle (Th/U + U/Pu) may also be possible, such a breeder might be fed with ordinary rocks.

Besides, how much Cl-36 would be formed anyway? Cl-37 has only a small cross section for the (n,2n) reaction, so Cl-36 will come mostly from capture in Cl-35, which has a cross section of around 1 barn. Does anyone know cross sections for Cl-36? Much of it will burn out, and so will the Cl-35 if a reactor runs for long enough and/or the Chlorine is recycled (which makes sense, since it is enriched in Cl-37). So what will be the equilibrium concentration? And what's the impact of Cl-36, should it be released? Worse than, say, C-14?


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PostPosted: Jan 29, 2008 9:24 am 
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If you've got a spectrum as hard as a chloride reactor, you can easily breed in uranium and plutonium--in fact, it would be more favorable than thorium. Not that I'm advocating that, because I think chloride reactors represent a significant proliferation risk, but just pointing out that it could be done.


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PostPosted: Jan 29, 2008 10:35 am 
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Kirk Sorensen wrote:
If you've got a spectrum as hard as a chloride reactor, you can easily breed in uranium and plutonium.


Of course. I understand that's the main idea behind a fast molten salt reactor, and Ottewitte seems to be the only advocate for a fast neutron Thorium cycle. BTW, I think a U/Pu cycle is a good idea (independently of any Th/U cycles running or being developed in parallel), chiefly because the fuel has already been mined. Burying all that depleted uranium (how much is it? must be close to a million tons) would truly be a waste.


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Udo Stenzel wrote:
BTW, I think a U/Pu cycle is a good idea (independently of any Th/U cycles running or being developed in parallel), chiefly because the fuel has already been mined. Burying all that depleted uranium (how much is it? must be close to a million tons) would truly be a waste.


Yeah, but the fact the material is mined isn't really a good argument for thorium or U-238. If thorium is used in an LFTR, or if U238 is used in an LCFR, the costs of mining the original material is so tiny compared to the other costs that it can be safely ignored.

That's one of the reasons when I get breathless emails from someone telling me to invest in some thorium mining operation, I tell them I'm not interested. It's just not where the money (or the problem) is.

But having the chloride reactor as a "deployed" reactor (vs. a handful of them on secure sites destroying TRUs) troubles me. If they had a U238 blanket breeding Pu239 (instead of a thorium blanket breeding U233) they would make a LOT of Pu239 and it would be of super high isotopic quality. Smells a lot like trouble.


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PostPosted: Jan 29, 2008 3:01 pm 
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Kirk Sorensen wrote:
But having the chloride reactor as a "deployed" reactor (vs. a handful of them on secure sites destroying TRUs) troubles me. If they had a U238 blanket breeding Pu239 (instead of a thorium blanket breeding U233) they would make a LOT of Pu239 and it would be of super high isotopic quality. Smells a lot like trouble.


The actual proliferation risk is PUREX processing, so I wouldn't worry about a reactor type. And if you think that having dangerous reactors only in the US, the only nation that ever used nuclear weapons in warfare, is reassuring to most people on earth, you're also wrong. But since this no longer has anything to do with chlorine, I won't argue that further.


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PostPosted: Jan 30, 2008 1:44 pm 
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Kirk Sorensen wrote:
NNadir wrote:
I don't know why anyone would use chlorine in a MSR.


Really hard neutron spectrum, that's why. A hard spectrum like that makes the capture-to-fission ratio of all your TRUs get really attractive and allows you to burn them up in a neutronically favorable way.


I really think there is too much emphasis on the capture-to-fission ratio of TRUs. If all you want to do is burn off as much TRUs as possible you can accomplish things in a more thermal spectrum fluoride based reactor. Yes, you`ll be forced to clean out fission products at a higher rate but otherwise you burn TRUs just as fast in a thermal spectrum since a gigawatt year of energy will mean the same number of TRUs fissioned no matter the spectrum. The chain will go higher up the transplutonium ladder but as long as you keep them in the flux, everything will eventually fission.

A fast spectrum will need several tonnes of TRUs to start up and have criticality issues in spills or accidents. A thermalized spectrum will only need a few hundred kilograms to start. This is due to the enormous cross sections of TRUs at lower neutron energies. If a hard spectrum really is that attractive, you can get a pretty hard one from fluoride salts as well, at least according to the French studies.

I think the R&D needed to get a functioning chloride based reactor going is better spent elsewhere if you are just thinking to use them for U233 production or TRU burning. Fluoride reactors, in their variety of forms with and without added moderator can do all the jobs we need, in my opinion.


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PostPosted: Jan 30, 2008 1:55 pm 
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David wrote:
I think the R&D needed to get a functioning chloride based reactor going is better spent elsewhere if you are just thinking to use them for U233 production or TRU burning. Fluoride reactors, in their variety of forms with and without added moderator can do all the jobs we need, in my opinion.


I may be overly simplistic in this statement, so please forgive me, but if we had a fluoride-TRU burner there really wouldn't be any extra neutrons to breed U233 from thorium, would there? The capture-to-fission ratio is so much less favorable at thermal/epithermal energies that all of your "excess" neutrons would just be going into moving TRUs up the ladder, so to speak.

In a hard spectrum, however, we would blast apart those TRUs and make enough neutrons to comfortably breed a lot of U233.

You're absolutely right--a gigawatt*year is a gigawatt*year, thermal or fast, but the fast version can probably make a whole lot more U233 than the thermal version, if it can make any.

High inventory doesn't trouble me too much, because we're only talking about a handful of chloride reactors and we've got LOTS of TRUs.


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PostPosted: Jan 30, 2008 10:16 pm 
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Kirk Sorensen wrote:
David wrote:
I think the R&D needed to get a functioning chloride based reactor going is better spent elsewhere if you are just thinking to use them for U233 production or TRU burning. Fluoride reactors, in their variety of forms with and without added moderator can do all the jobs we need, in my opinion.


I may be overly simplistic in this statement, so please forgive me, but if we had a fluoride-TRU burner there really wouldn't be any extra neutrons to breed U233 from thorium, would there? The capture-to-fission ratio is so much less favorable at thermal/epithermal energies that all of your "excess" neutrons would just be going into moving TRUs up the ladder, so to speak.

In a hard spectrum, however, we would blast apart those TRUs and make enough neutrons to comfortably breed a lot of U233.

You're absolutely right--a gigawatt*year is a gigawatt*year, thermal or fast, but the fast version can probably make a whole lot more U233 than the thermal version, if it can make any.

High inventory doesn't trouble me too much, because we're only talking about a handful of chloride reactors and we've got LOTS of TRUs.


As long as you have a neutronically good carrier salt like Flibe or 73%LiF-27%ThF4 like the French group proposes, you do have enough excess reactivity and neutrons when burning TRUs in a fluoride molten salt reactor.

If you go the harder spectrum route like the French you can get a nice high production rate of U233. However they are relying on a pretty high concentration of PuF3 and that might pose a problem. It is a shame that no one is doing the experiments to pin down the solubility properly as the published data available varies greatly.

If you have a more thermal spectrum like the standard 1970s Single Fluid design you can certainly startup on LWR wastes. There is a ton of data on this in most of the late 60s and early 70s MSBR progress reports and it is also discussed in the "Reactor Physics" paper in the 1970s Nuclear Applications and Technology issue. Plutonium is so incredibly reactive in a thermalized spectrum that they could mix in plenty of thorium and perform a nice transition from burning LWR wastes to the U233-Thorium cycle. One thing to be clarify though is they never looked at including the transplutonium actinides, that might degrade the prospects a bit.

Yes, it is certainly true that if all you want your reactor for is to burn TRUs and breed U233 that a hard spectrum is better but you can certainly start up most any reactor design with reactor grade plutonium and then transition to U233 later.


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PostPosted: Aug 22, 2010 7:00 am 
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In any case, in order to separate (chemically) chlorine from iodine, a fission product, tricky chemistry is involved. I can't see why one would want to bother.


Why the need for chemical seperation? In fact there isn't much need for fission product removal at all in a very fast chlorides reactor. It is convenient to remove noble gasses, and much iodine will come with it because chlorine will displace iodine as salt. Halogen shortage will lead to some remaining iodides, but this isn't a problem in neutron budget and can probably be sold as good PR - waste eating. (iodine-129 transmutation).


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PostPosted: Aug 22, 2010 1:14 pm 
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Cyril R wrote:
... in a very fast chlorides reactor. It is convenient to remove noble gasses, and much iodine will come with it because chlorine will displace iodine as salt ...


If high-fissile-content fuel rods are bathed in a low-melting alloy of PbCl2 and RbCl and leak fission fragments, or actinide chlorides are dissolved in it to begin with, what happens with newborn iodine and cesium?

<code>2 CsI + PbCl2(l) ---> 2 CsCl + PbI2(l)
-673.624 -344.25 -885.66912 -157.68</code>

Delta 'H' -25.47512 kJ/mol. So this will tend to happen. But the iodine isn't going anywhere. Chlorine would not displace less electrophilic halogens from the pot unless it were present as the free element.

Chlorine-36 may be a minor nuisance, but it is not the only nuisance that neutron irradiation of chlorine-35 produces. There's also a lot, not sure metric or imperial, of (n, p)-produced sulphur.

One of the nice things about fast chloride reactors is that the coolant can be transparent.

(How fire can be domesticated)


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PostPosted: Aug 22, 2010 2:05 pm 
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PbCl2 is less stable than NaCl and has more parasitic chlorine captures, having two chlorines attached. I'd rather go for MgCl2 then, but NaCl is really good overall.

Certainly true that sulphur is a major problem. One of the reasons KCl is much less attractive than NaCl, though it has reduced inelastic scattering advantages. I don't think isotope seperation for Cl-37 is all that hard, using HCl or CCl4 methods. Costs probably of similar magnitude to D2O production of equal purity. More weight difference for H/D but three orders of magnitude less of it compared to the abundance of Cl-37. I think we can burn out Cl-36 faster than Cl-37, and maybe with some calcium to regenerate the burnt out Cl-37, Cl-36 will ultimately vanish.


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PostPosted: Aug 23, 2010 7:32 am 
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Chloride reactors are basically for hard spectrum. Metallic fuel is even better for this purpose. Why not extend it to fluid fuel?
A Pb-Pu eutectic could be used as fluid fuel. Other TRU's can join Pu or be filtered out. Fertile feed, Uranium or thorium, need not be fully dissolved and could be placed as rolls of metallic U or Th perforated sheet or wire gauze. If there is thorium, it could be electro-refined to recover U-233 with protective U-232
Could a reactor get critical with Pb-Pu in voids of Uranium-238 pebbles?. Fertile/Fissile ratio could be low and smaller quantity of fertile with higher space for fissile as described may be necessary.


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