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PostPosted: Dec 06, 2012 1:38 am 
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see


http://phys.org/news/2012-12-thorium-pr ... -fuel.html

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PostPosted: Dec 06, 2012 5:13 am 
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KitemanSA wrote:
To me, the least resistant system would be a DMSR. With the U238 there, it would be easy to use simple chemical means to remove high purity Pu239 for bomb making. This is why I prefer FLiBe Energy's dump and dilute plan to add the U238 at the last moment, only if needed.


It's not easy at all. If only it were easy. Plutonium is difficult to seperate from lanthanides and thorium, and thorium makes lots of Pu238 that produces heat and spontaneous neutrons.

The blanket fluorinator produces highly decontaminated HEU. This is a fact.

A dump and dilute plan would be easy to sabotage or otherwise disable - it's an engineered system. This is especially true for a global LFTR buildout, with LFTRs in every country.

Not that any of this actually matters. If we were concerned about proliferation, we'd be interested in stopping the proliferation of enrichment technology, and more importantly, we'd be interested in destroying actual nuclear weapons that have already been fabricated. These are the biggest threats.


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PostPosted: Dec 06, 2012 5:16 am 
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Axil wrote:


The oceans and seas have often been touted as wonderful things, but it's not correct to state that it's inherently proliferation proof. The debate about the ocean is rather one-sided. No one seems to worry about the 28 million tonnes of U-235 in it, accessible to most countries in the world. A simple chemical process can easily remove enough U-235 for a bomb, with a simple centrifuge or a simple graphite moderated bomb reactor (needs only natural uranium).


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PostPosted: Dec 06, 2012 8:39 am 
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Cyril R wrote:
KitemanSA wrote:
To me, the least resistant system would be a DMSR. With the U238 there, it would be easy to use simple chemical means to remove high purity Pu239 for bomb making. This is why I prefer FLiBe Energy's dump and dilute plan to add the U238 at the last moment, only if needed.


It's not easy at all. If only it were easy. Plutonium is difficult to seperate from lanthanides and thorium, and thorium makes lots of Pu238 that produces heat and spontaneous neutrons.
FV of the fuel salts of a DMSR can remove the Np so Pu238 could be limited. Also it will remove the Pu239 bred from the U239. Seems simple enough to me. What am I missing?

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PostPosted: Dec 06, 2012 8:49 am 
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The thing everyone is missing is perspective, which I tried to add with my earlier posts.

Enrichment and plutonium separation are far easier than anything to do with thorium or protactinium. A thorium fuel cycle is not an added proliferation risk.


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PostPosted: Dec 06, 2012 8:57 am 
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KitemanSA wrote:
Cyril R wrote:
KitemanSA wrote:
To me, the least resistant system would be a DMSR. With the U238 there, it would be easy to use simple chemical means to remove high purity Pu239 for bomb making. This is why I prefer FLiBe Energy's dump and dilute plan to add the U238 at the last moment, only if needed.


It's not easy at all. If only it were easy. Plutonium is difficult to seperate from lanthanides and thorium, and thorium makes lots of Pu238 that produces heat and spontaneous neutrons.
FV of the fuel salts of a DMSR can remove the Np so Pu238 could be limited. Also it will remove the Pu239 bred from the U239. Seems simple enough to me. What am I missing?


Np is about as good a bomb material as U233 - without the U232 to protect it. Removing it from any reactor, DMSR or LFTR, will result in increased proliferation weakness. Sure no one has ever built a pure Np bomb but the same is true for U233.

It follows that fluoride volatility would be even more proliferation-sensitive. So another big hit for a 2 or 1.5 fluid, which need onsite fluorinators, and another advantage for DMSR - which has no fluorinator onsite. Contrary to what some people here think, fluorinators - especially Pu fluorinators - are not that simple, and bringing one in on a DMSR that isn't designed to have one is a major undertaking.

Another thing is that a 1.5 or 2 fluid reactor has a blanket with much less U232 in the fluorinated uranium. Another hit for a 1.5 or 2 fluid.

A hybrid U238 (LEU) + TRUs + Th DMSR with no onsite fuel processing would be the most proliferation proof design. U232 and U238 to protect U233 and U235, and Pu238 + TRUs to protect Pu239, and no fluorinator available to grab anything. If you believe that sort of proliferation thinking, of course.


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PostPosted: Dec 06, 2012 8:59 am 
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Kirk Sorensen wrote:
The thing everyone is missing is perspective, which I tried to add with my earlier posts.

Enrichment and plutonium separation are far easier than anything to do with thorium or protactinium. A thorium fuel cycle is not an added proliferation risk.


Well said Kirk. Enrichment and tiny Pu production reactors are the 2 proliferation super-highways. Everyone criticising the thorium cycle is focusing on a tiny little proliferation backroad that is theoretical, full of potholes and swamps. Why would people take the tiny road through the poor quality road through the swamp, risking to get stuck, when there are 2 proliferation super highways?


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PostPosted: Dec 06, 2012 9:07 am 
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Isotopically pure neptunium-237 is produced in every reactor in the world. There is nothing unique to the thorium fuel cycle therein. LWRs produce copious amounts of Np-237 every day, isotopically pure and chemically separable. If there was weapons potential there, it would have been exploited.

The question is--does a LFTR present an added proliferation risk? To which I would emphatically contend--no.


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PostPosted: Dec 06, 2012 9:17 am 
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Kirk Sorensen wrote:
Isotopically pure neptunium-237 is produced in every reactor in the world. There is nothing unique to the thorium fuel cycle therein. LWRs produce copious amounts of Np-237 every day, isotopically pure and chemically separable. If there was weapons potential there, it would have been exploited.

The question is--does a LFTR present an added proliferation risk? To which I would emphatically contend--no.


The only valid point that the anti-proliferationists could make is that LFTRs, using fluorinators, include by design the means to seperate and almost fully decontaminate the Np237, while LWRs decidedly do not.


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PostPosted: Dec 06, 2012 9:50 am 
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There is already large amounts of spent nuclear fuel with isotopically pure Np-237 present that could be obtained and fluorinated. Natural uranium could be burnt in a CANDU or graphite-moderated reactor, yielding Np-237. The thorium fuel cycle is no added risk.


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PostPosted: Dec 06, 2012 9:57 am 
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Kirk Sorensen wrote:
There is already large amounts of spent nuclear fuel with isotopically pure Np-237 present that could be obtained and fluorinated. Natural uranium could be burnt in a CANDU or graphite-moderated reactor, yielding Np-237. The thorium fuel cycle is no added risk.


This is true, though the anti's could argue that a LFTR has the fluorinator onsite by design, and decontaminate it by design (it gets stuck in certain fluoride pellet beds), whereas the legacy stockpile of Np-237 is safeguarded by highly radioactive fission products and transuranics, and U-238, inside the fuel rods.

So they could argue that the thorium cycle poses no added threat, but the fluorinator onsite of every reactor could. I disagree that it is meaningful but it is something that could follow from their myopic, terribly predictable logic.


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PostPosted: Dec 06, 2012 10:10 am 
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Well, anti-nukes think fissile material's very existence on Earth is some sort of cruel cosmic trick so what can be done with them?


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PostPosted: Dec 06, 2012 11:07 am 
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Kirk Sorensen wrote:
Well, anti-nukes think fissile material's very existence on Earth is some sort of cruel cosmic trick so what can be done with them?


I don't know, it's an anti-everything-nuclear attitude that has resulted in real problems, ironically including inhibiting development of new fuel cycles and reactor technologies that actually help close the proliferation super highway of enrichment (fuel cycles that don't need enrichment) and can eat bombs (arguably the single biggest proliferation threat if ever there was one - just steal an exisiting nuclear weapon). We could already have closed down 2 of the 3 biggest proliferation threats, but it wasn't allowed. We could also have made high purity graphite a regulated material, effectively closing down the last proliferation super highway.

The fact that we didn't do any of this shows that the anti-proliferationists don't really care about proliferation, they just use this as an excuse to stop anything nuclear. They think all nuclear things are evil, uniquely corporately corrupt, unnatural, and avoidable. Of course all these things are not true, but the anti's have such a strong influence on policy that they've convinced politicians of things like killing Gen IV reactor programs (such as IFRs).


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PostPosted: Dec 06, 2012 1:41 pm 
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with the possible exception of shortly after start up,
the isotopic quality of Pu in a DMSR stinks as bomb making material.
Worse than a LWR due to all the Pu-238.
See ORNL-7207.

If the start-up period is deemed a problem,
the initial fuel load can be spiked with reactor grade Pu.


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PostPosted: Dec 06, 2012 6:47 pm 
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I agree with Cyril, a DMSR running on a feed of 75% Th-232 and 25% Light Water Reactor (LWR) Spent Nuclear Fuel (SNF) seems like the most proliferation-proof solution. There is enough U-238 to enable the breeding of a significant amount of U-233 while staying under the 12% fissile uranium limit. There is enough Th-232 to enable thorium's better thermal breeding to get the system near breakeven. By starting with Pu-240 and Pu-242 in the mix, there is never chemically separable weapons-usable Pu-239. By starting with SNF, we get our fissile feed without requiring any new uranium mining or enrichment.

Every year, drain off some core salt, evaporate out and recycle the FLiBe, fluorinate out and recycle the U-233 and U-238 (and whatever Np and Pu that will come willingly). The recycled FLiBe is cheaper than new stuff, since you have to enrich the lithium. Recycling U, Np, and Pu is optional -- it greatly reduces the amount of SNF needed to keep the reactor going. Hold whatever is left from the two reprocessing stages for 10 years aboveground, then sink 800 kg/year of fission products along with 1-2 tons of FLiBe, 5-10 tons of thorium, and some non-weaponizable TRU in glass logs in clutch of six boreholes drilled right on site.

And be done. No material in the system can be chemically diverted for weapons use, at any point, ever. No caveats. No need to transport waste off-site -- you bring SNF to this reactor. No need for enrichment anymore (we can start all the DMSRs we need off the SNF we've already got). If you don't add the SNF at first, you don't have any fissile and the reactor doesn't start. If you don't add it later, you can dilute the U-238 in the reactor eventually but it will take decades to get the U-238 down to a level low enough to use the uranium for weapons.

Perhaps this sounds overly hopeful, because I'm talking about fuelling a reactor with SNF, where the Oak Ridge DMSR documents were contemplating enriching the uranium to the highest possible levels.

Here's why I think a DMSR can be started on SNF: the stuff was once critical in a LWR. When it left the LWR, there were other rods there with more reactivity, so the rods that are removed might not be able to achieve criticality by themselves in an LWR core. Those removed rods still have plenty of fissile, it's just mixed with fission products that are poisoning it. We'll strip out 1/3 of the fission products when we turn the stuff into a salt, put it into a better-moderated and better-reflected core, and add enough thorium to bring the reactivity down to about unity.

Finally, I don't know about chemically separating Neptunium. Maybe this is a bug with the above scheme.

-Iain


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