an exciting new concept - the fluoride salt based "fast" MSR

Threads relating to the design of liquid-fluoride reactors.
darryl siemer
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Re: an exciting new concept - the fluoride salt based "fast"

Post by darryl siemer » Dec 09, 2013 2:21 pm

Cyril R wrote:You mean PWR, not BWR. BWRs don't use Li7.

Also, the 300 kg per year is for all US PWRs. So more like throwing away 45 dollars a day per PWR.

You can't even wipe the desks in the offices of a PWR for 45 dollars. Peanuts.

The total 300 kg/year market in the US would be swamped by even a single prototype MSFR.

I full well understand why an industry of less than a million a year can't survive domestically. You can't operate a domestic li7 facility for a million bucks a year. You couldn't run the sales and marketing office with a million dollars.

I also find the talk about a shortage for Li7 for PWRs to be complete nonsense. The amount used is tiny and can easily be replaced by sodium if necessary. The fact that it isn't suggests it isn't necessary.

You're right it is PWRs. I've edited/corrected.

The rest of your posting is "right" too but irrelevant - my object was to put the 7-Li cost "issue" of my MSFR scenario into perspective. It would be no problem for the same reason that the cost of zirconium hasn't been a problem since Rickover decided to create a market for it.
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Cyril R
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Re: an exciting new concept - the fluoride salt based "fast"

Post by Cyril R » Dec 09, 2013 2:46 pm

The total cost of the inventory must also be considered, even at a high "specialty" price of $3000/kg.

MSBR needed 18 tonnes of Li7. A $3 million/ton it makes only $54 million, for a 1 GWe plant, only $54/kWe. Perhaps 2% of the plant capital investment.

Hardly worth fussing about cost.

More fundamentally to do with "can we get it in the first place". Once a demand exists people will start building plants. After all no radioactive enrichment is involved, it is not much different from any other chemical plant, where the plant will get built if a demand exists.

Note that this is a potential showstopper for a prototype MSR though. It's not likely that a high Li7 enrichment facility will be built just to satisfy a one off 1 ton market and no guarantee of future market beyond that.

A would be MSR developer planning to use Li7 may end up having to build their own Li7 plant as part of the cost of building a prototype. That may be acceptable, considering a simple and mundane lithium crown ether process plant.

darryl siemer
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Re: an exciting new concept - the fluoride salt based "fast"

Post by darryl siemer » Dec 09, 2013 3:52 pm

Cyril R wrote:The total cost....
You are right again. The real problem is that there's no one who thinks like Rickover left anywhere in the USA's NE R&D decision making structure. Like General Groves, he could & did commit to doing things that needed to be done before it was totally "safe" to do so.
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jaro
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Re: an exciting new concept - the fluoride salt based "fast"

Post by jaro » Dec 09, 2013 10:43 pm

darryl siemer wrote:Since my much-simplified MSFR implementation scenario would discard roughly 1 kg of pure 7-Li/day....
Would you mind please reiterating why Li7 is needed in an MSFR ? (sorry if I missed it the first time)

E Ireland
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Re: an exciting new concept - the fluoride salt based "fast"

Post by E Ireland » Dec 10, 2013 2:03 am

IIRC 7Li is rather less to start throwing out tritium under a reactor's neutron flux, it takes fusion neutrons to do it, whereas 6Li will do it far more easily.
Last edited by E Ireland on Dec 10, 2013 4:12 am, edited 1 time in total.

Lars
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Re: an exciting new concept - the fluoride salt based "fast"

Post by Lars » Dec 10, 2013 2:34 am

Jaro's point is that in a thermal reactor the neutronic and moderating advantages of FLiBe (over other fuel salts) make it worth the effort but in a fast reactor the neutronic losses to the fuel salt are noticeably less so there is less need to use 7Li. This has two big advantages, first we might avoid isotropic enrichment (which has a very uncertain cost structure) and second it avoids tritium generation.

Avoiding isotropic enrichment will help reduce the R&D costs and schedule at least. Whether it saves anything significant in the production is very uncertain. (Personally this sounds like a pretty solvable problem to me).

Tritium containment is a PR challenge for us. Somehow the nuclear power industry has totally failed to convince the public that tritium leaks from a power plant are non-issues. One attack on LFTR is certainly going to be that it produces XXX times as much tritium as LWRs. And it will take some heroic efforts to avoid the tritium release to the atmosphere from being XXX times as much as leaks from an LWR. (This is much worse for fusion by the way). Containing tritium in a hot environment is a challenge.

Cyril R
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Re: an exciting new concept - the fluoride salt based "fast"

Post by Cyril R » Dec 10, 2013 4:19 am

There are other considerations than just neutronics and tritium.

For me, they are primarily thermal/hydraulics related. Li based salt eutectics have the best heat transfer properties and the lowest melting points.

If tritium is to be avoided then Be must be avoided too.

With no Li and Be, basically only the heavy salts are left. That is where it gets ugly in terms of heat transfer.

A Na/Zr/Rb based salt could be used, at the cost of much worse heat transfer (bigger pumps, HXs, and such) and a much higher melting point. The neutronics are not very good compared to Li7 even for a fastish fluoride reactor.

It is very difficult to find a high thorium fluoride eutectic with reasonable melting point without Li and Be. The salts that have reasonable melting points and high thorium fluoride proportions have terrible neutronics and heat transfer properties (these are the Rb/K based salts).

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Re: an exciting new concept - the fluoride salt based "fast"

Post by E Ireland » Dec 10, 2013 4:23 am

Beryllium has its own problems as well (its horrendously toxic and difficult/expensive to handle even outside of the radiological problems with handling fuel salt).
Lithium fluoride can almost be handled with bare hands before it is introduced with a reactor, doing that with Beryllium will get you poisoned rather fast.

Which leaves us with just lithium if you are sold on the idea of a fluoride MSR.

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Re: an exciting new concept - the fluoride salt based "fast"

Post by Cyril R » Dec 10, 2013 5:30 am

The toxicity of beryllium seems rather a joke to me. Considering the ionizing radiation flux from the fuel salt. It is only an advantage when first preparing the salt, I never got the idea that those initial cost were meaningful. Gloves and gas masks are not expensive, even full HAZMAT gear isn't a big cost for a large powerplant. Tritium seems much more tricky in handling, and any fuel salt with Li in it makes tritium, some of that will inevitably get into the secondary coolant loop. Tritium in the secondary loop means it needs a tight containment. So beryllium in it will be contained along with whatever containment there is for the tritium, plus any activated atoms produced from the neutrons in the primary HXs.

Beryllium is a good moderator, so in a fast spectrum reactor you may not want that.

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Jim L.
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Re: an exciting new concept - the fluoride salt based "fast"

Post by Jim L. » Dec 10, 2013 9:36 am

Toxicity from beryllium is from breathing it in powder form, and beryllium fluoride is very chemically stable therefore you should have few concerns. Also, the cost issue of beryllium is a bit of a nonstarter as well - the cost of beryllium metal is high but beryllium fluoride (which we want) is a precursor to metallic beryllium and the steps converting from the fluoride to the metal are a significant cost adder. So, concerns about toxicity and cost are inflated.

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jaro
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Re: an exciting new concept - the fluoride salt based "fast"

Post by jaro » Dec 10, 2013 3:00 pm

I don't see a lot of difference between Li6 and Li7 in the fast spectrum:
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Lars
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Re: an exciting new concept - the fluoride salt based "fast"

Post by Lars » Dec 10, 2013 3:14 pm

What percentage of the neutrons get below 1keV?

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jaro
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Re: an exciting new concept - the fluoride salt based "fast"

Post by jaro » Dec 10, 2013 5:49 pm

I think you're missing the point: An MSFR with even pure Li7 would be producing almost as much tritium as if it was natural un-enriched Li.

This, by the way, is what caused the unexpectedly high (3x) yield of the Castle Bravo thermonuclear bomb test in Bikini back in the 1950s: It was not known then that in the fast spectrum, ordinary Li produces almost as much tritium as pure Li6.
http://en.wikipedia.org/wiki/Castle_Bra ... high_yield

Cyril R
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Re: an exciting new concept - the fluoride salt based "fast"

Post by Cyril R » Dec 10, 2013 5:59 pm

I think Lars' point is that if you have light elements such as fluorine and lithium in your reactor, some of the neutrons will be slower, these then going into the Li6 to capture neutrons parasitically and making more tritium.

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jaro
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Re: an exciting new concept - the fluoride salt based "fast"

Post by jaro » Dec 10, 2013 6:26 pm

Lars wrote:What percentage of the neutrons get below 1keV?
Maybe 10% ?
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