Energy From Thorium Discussion Forum

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PostPosted: Dec 29, 2008 6:04 pm 
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GRLCowan wrote:
But the non-graphical summaries at http://www.matpack.de/Info/Nuclear/Nuclids/C/Cl37.html and
http://www.matpack.de/Info/Nuclear/Nuclids/C/Cl35.html show that the lighter isotope has a number of ways of, with significant probability, making a neutron useless besides just capturing it.

In fission-spectrum neutrons: (n, alpha) 56.45 mb, (n, p) 96.25 mb, ... OK, that's not "a number" of ways, it's two, unless two can be considered a number. Resonance integrals, for whatever they might mean here, 466.3 mb and 965.1 mb, respectively. That (n, alpha) process makes loads of sulphur.

I've been reading up on this because I think fast reactors may have been missing out on the advantage water reactors have of a transparent coolant with high volumetric heat capacity. If they could be cooled with some alloy of Na(37-Cl), Rb(37-Cl), and Pb(37-Cl)2, maybe they could gain that advantage.


--- G.R.L. Cowan (How fire can be domesticated)


There are a number of researchers looking into that concept in the U.S., more so for using fluoride salts to cool TRISO fueled thermal reactors but they also mention the possibilities of chloride salts for cooling fast reactors. They have been going by the term, Liquid Salt Very High Temperature Reactor (LS VHTR) lately so if you Google that term, perhaps along with Forsberg (the leading proponent) you can get some reading material to start.

My view is that molten salts as coolants is certainly an interesting option that might improve existing designs but there are just so many more advantages to actually having the fuel in the salt itself.

David L.


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PostPosted: Dec 29, 2008 8:40 pm 
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David wrote:
My view is that molten salts as coolants is certainly an interesting option that might improve existing designs but there are just so many more advantages to actually having the fuel in the salt itself.

Not to mention it avoids the non-trivial issue of positive coolant void coefficients that plague these salt-cooled designs.


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PostPosted: Jun 27, 2009 10:36 am 
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Hi,

Also how desirable is it that the reactor be breakeven in breeding? Can't we have a single fluid reactor with a breeding ratio in the .9 range and supply the extra fissile load from spent light water reactor fuel? Perhaps separating the transuranics out so that the uranium 235/238 mix can be sent back to light water reactor fuels... but I'm entering areas of seriously sketchy economics.

I realize that transuranics are less soluble in FLiBe, and FLiNaK is more corrosive against hastelloy, and can complicate fuel processing.


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PostPosted: Jun 27, 2009 11:19 am 
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Either can be attractive.
If it is break-even, then we have a couple of strong selling points:
1) fuel shipments are now simple thorium no fissile shipments at all. This is attractive in a world of 10,000 GWe worth of reactors (assuming we are massively successful).
2) buyer countries could be absolutely certain no country can hold back fuel as a means of control. It will be much easier for countries to depend on nuclear as 80% of their primary energy if they know that they have an assured supply. This would be in the sense that they could go mine their own thorium quite readily if need be OR that they could simply buy a lifetime supply of thorium. Assuming we are successful one might expect thorium prices in the same neighborhood as todays natural uranium prices (roughly $160/kgU). Thorium to last the life of the power plant (60 years @ 1 ton/year) would then cost around $10M/GWe. So if a country were completely devoid of thorium inside their borders and trusted no one in the world they could still provide an assured supply simply by buying a lifetime supply and storing it.

If it is not break-even then we need to talk about how much makeup fissile is required and in what form. Using u235 as makeup fissile will mean that we get a lot of u238 in the bargain. This can work but the u238 will mean a higher production of plutonium etc. in such a reactor. Using u233 as the makeup fuel is just as bad assuming we are not allowed to ship HEU around the world (pretty safe assumption). Using SNF/Pu would avoid generating extra Pu but if it means shipping either SNF or Pu around then there will be extra protests to put up with.

So this is actually an area of proper engineering tradeoffs with no clear winner in my book yet. For my part, I still need to get a better handle on the efficacy and costs of various fission product removal techniques and the importance of each fission product.


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PostPosted: Jun 27, 2009 12:11 pm 
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Lars wrote:
...Using u233 as the makeup fuel is just as bad assuming we are not allowed to ship HEU around the world (pretty safe assumption)....


Does this assumption included HEU that is self protecting?

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PostPosted: Jun 27, 2009 12:56 pm 
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Lars wrote:
I still need to get a better handle on the efficacy and costs of various fission product removal techniques and the importance of each fission product.

Whatever the "costs of various fission product removal techniques", its a safe bet that the costs of the engineered hardware will be nothing like the costs of various red tape issues (fuel procurement, plant licensing, etc.).
Thousands of radiopharmaceutical purification machines are currently in use around the world, and hundreds more are sold every year.
This is an utterly phony issue.
Engineering is much cheaper than lawyers!

Here's the schematic for your typical F-18 labeled FDG production machine, used for PET scans in large hospitals in every major city.....

Image

Image


Last edited by jaro on Jun 27, 2009 7:02 pm, edited 1 time in total.

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PostPosted: Jun 27, 2009 1:56 pm 
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I hear that the complexity and cost of the fuel salt processing makes LFTR a non-starter numerous times by people who don't know what is involved with LFTR fuel processing. They tend to base their opinions on PUREX processing complexity so their experience isn't directly relevant. I think it would help if I could respond with how the flow would be different and how well it would do.

I look at the complexity of the ORNL MSRE equipment and I think they are quite reasonable to build.
The He sparge, and vacuum distillation processes seemed to work well in ORNL's experiments.
The fluorination has some challenges with corrosion but they had reasonable ideas on how to fix this.
The equipment for fluorination and vacuum distilling was modest in size so that I'm confident it will be a minor minor cost in a real plant.

The main technique that did not work for them was the liquid metal exchange process.
So far I haven't found a good technique for extracting thorium from the fuel salt before trying to isolate the salt seeking fission products.
Liquid metal exchange is the presumed solution by ORNL and by the French team - but I haven't found papers describing positive enough results in the lab.

The other area of concern is where the noble metals go. When running u233 MSRE sent (90% IIRC) of the noble metals into the off-gas or overflow system.

I do not have a good feel for how much we gain neutronically with each processing step. The order of difficulty seems pretty clear:
1) He sparge to remove especially Xe.
2) noble metal removal
3) salt seeking

What I plan to work on when I get a couple of weeks is to write a program to track the yield, decay and extraction rates of all the fission products to generate a profile of the fission product flows, and heat generation for each of the extraction paths and for the fission products in the salt. And finally the neutronic benefits of each step.

Is there a massive regulatory cost component to on-site fuel processing?


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PostPosted: Jun 27, 2009 5:11 pm 
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Lars wrote:
Is there a massive regulatory cost component to on-site fuel processing?

Good question.

But a better one might be: How do we avoid having a massive regulatory cost component to on-site fuel processing?

I think that the answer must lie in highlighting the differences of fluoride processes, versus the aqueous PUREX process (including mechanical reduction of fuel assemblies & pins, plus subsequent re-fabrication....).

A good start might be comparing chemical process risk mitigation: PUREX must deal with combustible gas byproduct generation (due to acids and radiolytic decomposition of water), combined with heating that could potentially lead to explosion & dispersion of radioactive material, etc.
Fluoride processes should be pretty much inert, by comparison.


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PostPosted: Jun 27, 2009 6:15 pm 
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So, watch out for processes that could possibly explode or do exciting things.
He sparge should be fine.
Vacuum distill should be fine.

The fluorination step (and then reducing the UF6) does involve some potentially exciting reactions that we need to watch for in combining hydrogen and fluorine.

But I get the point. If there are no safety issues then there should be much less regulation.

So far as I know the liquid metal exchange process also does not involve anything exciting (it just doesn't seem to be too effective in the lab yet).


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PostPosted: Jun 27, 2009 7:07 pm 
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Salt reprocessing is no cakewalk either.
http://www.energyfromthorium.com/ans09/ ... essing.pdf
A liquid metal as solvent could be an interesting system. Filtration, washing, electrolysis (electrowinning) should do the job.


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PostPosted: Jan 17, 2010 12:38 am 
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David
Quote:
In terms of using chloride based salts to get protactinium out, there are about 3 threads discussing the issue of protactinium removal in the other "Reprocessing" section. Many of us feel that it just adds too much proliferation risk and financial cost to justify employing it. If your idea of protactinium chloride bubbling out is correct that could change the financial cost side of the equation but I still think proliferation concerns win out.

I guess it boils down to this "how difficult is it to remove all of Thoriums Isotopes?" But leave the Th232.

Besides, if you could make a weapon from U233, it would have been done. Just look at the thermal breeding cross section. Over 92% of the U233 atoms would fission if given the chance. Pu wishes it had a cross section that wonderful.


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PostPosted: Apr 20, 2010 11:41 pm 
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I agree with redbat. Anti-proliferation design is not an issue; the Lftr and like reactor types will have on site IAEA inspectors in place 24/7/365. I think the IAEA inspector crew will number 7; two per shift with a supervisor to cover vacations and sickness.

The Lftr will be a source of a lot of jobs, good jobs, high paying jobs… at least for IAEA inspectors and their cost will be worth it.

Bubbling protactinium will provide the highest possible breeding ratio with the smallest possible U234 conversion probability…I like it.

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