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PostPosted: Oct 23, 2012 11:59 am 
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Lars wrote:
The 90Sr is mixed with all the other salt seekers. Any idea how to separate them?
Nope, I are a enganere, not an alchemist. :P

I said I got a use, not a way to extract it.

Anyone got any ideas?

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PostPosted: Oct 23, 2012 9:31 pm 
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Sorry, it seems to me that 137Cs and 90Sr are just too dang useful to throw away.



I have never looked at the numbers but I suspect talk of using 137Cs and 90Sr might be a little like similar talk of Pu238 and Moly99. The entire world's needs of either Pu238 or Moly99 could be supplied by one modestly sized reactor so one can't really use this a business case (but does give a nice goal for perhaps the first reactor built). I suspect the market and/or uses for Cs and Sr might also be easily flooded if one is proposing working recovery schemes into numerous reactors.

David LeBlanc


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PostPosted: Oct 23, 2012 10:08 pm 
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Given the difficulty, and thus expense, of obtaining the subject materials, it does not surprise me that there is little market. But providing power 24/7 via 90Sr heated SRGs in lieu of $200 - $500 trucked in fuel seems like a good idea for army consideration. And they need LOTS of said power.

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PostPosted: Oct 26, 2012 6:03 am 
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Lars wrote:
You are very welcome to take the both the 137Cs and 90Sr. The 137Cs we can likely give you mixed together will all other isotopes of Cs and other decay products from Kr and Xe. A second batch of Cs comes from the distiller combined with fluorination so it would contain a mix of Cs and Zr with a bit of Be and Li. The 90Sr is mixed with all the other salt seekers. Any idea how to separate them? It would be good news for me if you could because then the remaining fission products would have a short half-life so they could be glassified and buried without any concern about heat load underground.


SrF2 is the most stable and highest boiling fluoride of the salt seekers. In the reprocessing idea that is suggested here, it would stay behind last in a reducing operation, though some BaF2 would probably come along.

Thankfully, the form needed for strontium in RTGs is the fluoride, so no further chemical steps than partioning are needed.

This would be a great material for marine and remote terrestrial RTGs, where weight is less important than space applications, and the insolubility, low volatility and chemical stability of SrF2 are big advantages. There would be very large military and research/ROV submarine markets if the cost is reasonable.


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PostPosted: Oct 26, 2012 6:31 am 
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David wrote:
Quote:
Sorry, it seems to me that 137Cs and 90Sr are just too dang useful to throw away.



I have never looked at the numbers but I suspect talk of using 137Cs and 90Sr might be a little like similar talk of Pu238 and Moly99. The entire world's needs of either Pu238 or Moly99 could be supplied by one modestly sized reactor so one can't really use this a business case (but does give a nice goal for perhaps the first reactor built). I suspect the market and/or uses for Cs and Sr might also be easily flooded if one is proposing working recovery schemes into numerous reactors.

David LeBlanc


The current markets are small, but the potential markets are large. Military bases in remote or frontier areas for example, could be powered by RTGs on SrF2. The RTG needn't be very cheap for this, it has to compete with the logistics of diesel fuel (sometimes more than $1/kWh just in delivery cost) or solar panels with oversized battery (to get to a high reliability level for military bases). Diesel delivery and solar panels are themselves vulnerable, soft targets, so an RTG in a bunker would compare favorably in security. In terms of cost and issues with dealing with large amounts of radioactive material, this is much less an issue for a military base, obviously.

If the RTG is under $20/Watt electric it could already compare very well against other options. Free piston, zero maintenance, Stirling engines could be used for improved efficiency.


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PostPosted: Oct 26, 2012 1:53 pm 
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Cyril R wrote:
Lars wrote:
You are very welcome to take the both the 137Cs and 90Sr. The 137Cs we can likely give you mixed together will all other isotopes of Cs and other decay products from Kr and Xe. A second batch of Cs comes from the distiller combined with fluorination so it would contain a mix of Cs and Zr with a bit of Be and Li. The 90Sr is mixed with all the other salt seekers. Any idea how to separate them? It would be good news for me if you could because then the remaining fission products would have a short half-life so they could be glassified and buried without any concern about heat load underground.


SrF2 is the most stable and highest boiling fluoride of the salt seekers. In the reprocessing idea that is suggested here, it would stay behind last in a reducing operation, though some BaF2 would probably come along.

Thankfully, the form needed for strontium in RTGs is the fluoride, so no further chemical steps than partioning are needed.

This would be a great material for marine and remote terrestrial RTGs, where weight is less important than space applications, and the insolubility, low volatility and chemical stability of SrF2 are big advantages. There would be very large military and research/ROV submarine markets if the cost is reasonable.


This sounds like basically keeping most of the salt seekers together with the Sr90 after aging a bit to clear out the most intense, short lived heat. We probably generate 300kg of such material per GWe-yr (plus mass of fluorides and vitrification material). At 3 years we are at 0.06% of full power or 144 kWth for 1 years worth of all fission products. I believe this power is mostly split between 137Cs and 90Sr. It would be great to have a market for this material. How concerned do you think folks should be about possible dirty bombs made from the stuff or accidents like happened in the past with RTGs?


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PostPosted: Oct 26, 2012 3:18 pm 
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Lars wrote:
This sounds like basically keeping most of the salt seekers together with the Sr90 after aging a bit to clear out the most intense, short lived heat. We probably generate 300kg of such material per GWe-yr (plus mass of fluorides and vitrification material). At 3 years we are at 0.06% of full power or 144 kWth for 1 years worth of all fission products. I believe this power is mostly split between 137Cs and 90Sr. It would be great to have a market for this material. How concerned do you think folks should be about possible dirty bombs made from the stuff or accidents like happened in the past with RTGs?
Since CsF is water soluble, it should be fairly easy to separate the two. My use for the Cs is for the gamma emission while the Sr is for the heat. I'd prefer not to mix the two in a SRG (Stirling Radiothermal Generator) as Sr requires almost no shielding while Cs needs a lot.

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PostPosted: Oct 26, 2012 3:31 pm 
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I say again. The 137-Cs and 90-Sr are already split.
Almost all the cesium will be in the offgas stream, the 90-Sr is the fuelsalt.

The dirty bomb issue will be a big player in some circles.
but making and trasnporting a 137-Cs bomb will be a dicey proposition.


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PostPosted: Oct 26, 2012 4:01 pm 
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Xe decays quickly enough that SOME Cs-137 will be in the salt before the Xenon can be extracted. I read somewhere that about 1/4 of it will remain in the salt. So there is still an issue with it. However, with fractional distillation, the CsF should come out before the FLiBe components, so you are correct in essence if not in detail. Thanks for the reminder.

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PostPosted: Oct 26, 2012 4:11 pm 
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Yes, most Cs-137 would be in the offgas system, but not clean enough in terms of CsF in the fuel salt to be no hazard or concern in partioning! Though in a vacuum distillation operation, almost all the CsF will come along in the product stream. The resulting distillation bottoms would indeed contain almost no CsF at all, and CsF's lower stability than SrF2 means it won't come remain in the later reducing operation partioning.

Now, Cs-137 is less suited for RTGs due to its great solubility and greater volatility. SrF2 is much more suitable. Very stable, very low volatility, very low solubility in water.

Re dirty bombs. There can be no doubt, that Cs-137 and Sr-90 are very toxic materials. Hence the idea of military bases as initial market. Heavy rockets, high explosives and weapons at military bases already require high security, so the added requirement for the RTG could be accomodated.

It's not a good idea to remove the shielding of such large RTGs, containing kilogram quantities of SrF2, and then playing around with the fissioin product as if they were toys. There have been cases where people were killed, that removed the shielding of a Cs RTG. It is toxic and dangerous. It's not a good idea to take a bath in cyanide either. In both cases industrial safety is needed in handling and recycling.

Industrial food sterilization and such as later application. Industries routinely handle high toxicity materials such as botulin toxin, cyanides and such. Various extremely toxic materials that could much easier be converted for use in dirty bombs (just need skin and lung protection as opposed to also needing heavy radiation shielding).

As proven by decades of industrial and military good practice, it is possible to handle high toxicity materials safely, to a level where it is much safer than eating peanut butter. Of course there is the public opinion and poor journalism that is against anything toxic, industrial, radioactive, and/or corporative. But strictly speaking, SrF2 RTGs have good inherent properties that allow safe use and recycling for terrestrial and marine applications.

The experience with consumer equipment is not at all so good, and I wouldn't want to see fission product batteries in consumer electronics or some such things, that's too much optimism and naïvety for my tastes.


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PostPosted: Oct 26, 2012 6:40 pm 
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OK, so when we did distillation to recover the Li and Be we also removed the Zr and Cs so our still bottoms contain none of these. They likely also go through fluorination after aging so we collect any Pa that decays to 233U and as a side effect will remove any of the fission products that are volatile in fluorine.

What remains then are the rare earths including Sr and possibly the higher actinides curium and americium. Plausibly the higher actinides could be removed with a liquid metal exchange - for the moment let's assume either they are acceptable or the higher actinides are removed.

If we have 144kWth total then perhaps we have 50-70kWth in the Sr90. This is in around 300kg of fission products which after adding fluoride and vitrification might be expanded 5-10x. So is 10-20Wth per kg an interesting power supply?


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PostPosted: Oct 27, 2012 6:21 am 
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The Wiki entry on RTGs says 460 W/kg for Sr-90.

Quote:
Strontium-90 also requires little shielding, as it decays by B emission, with negligible G emission. While its half life of 28.8 years is much shorter than that of 238Pu, it also has a much lower decay energy. Thus its power density is only 0.46 kilowatts per kilogram. Because the energy output is lower it reaches lower temperatures than 238Pu, which results in lower RTG efficiency. 90Sr is a high yield waste product of nuclear fission and is available in large quantities at a low price


http://en.wikipedia.org/wiki/Radioisoto ... _generator

If that 460 W/kg is for Sr (elemental) then SrF2 (much safer) would result in 324 W/kg. At the quoted 23% efficiency for the Stirling variant, this means 74 W electric per kg. A large unit would definately be more efficient, though (30-40%). So >100 W electric/kg should be feasible.

It isn't a high power density, a 100 kWe unit would need a ton of SrF2. But that is still quite compact (with casing and the Stirling, similar to a diesel generator assembly). For some military bases the fuel delivery cost is so high, it could actually be economical.


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PostPosted: Oct 27, 2012 7:38 am 
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I wonder if it would be worth fluorinating recent SNF and going thru the processes just to get the 90Sr.

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PostPosted: Oct 27, 2012 8:12 am 
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KitemanSA wrote:
I wonder if it would be worth fluorinating recent SNF and going thru the processes just to get the 90Sr.


That would also be the best way to test the process. The Wiki article asserts that it isn't too hard to recover the Sr from SNF.


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PostPosted: Oct 27, 2012 9:08 am 
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Is anyone conversant enough with this all to put together a research proposal? Maybe "we" (or you) can get so $ from the Yucca Fund to pay for it. At least one NPP operator would like to see a solution to the SNF issue.

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