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PostPosted: May 19, 2010 1:28 am 
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The info re: Pu production of 25kg/year that I was referring to is in Table 4.1 on page 11 of the proliferation pdf.


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PostPosted: May 19, 2010 2:33 am 
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How much plutonium is present is a strong function of the reactor details.
A pure thorium fueled machine will generate around 20kg Pu per GWe-yr but it is mostly Pu238 and would be a royal pain to use for weapons - maybe not impossible for someone really expert but not a concern in my opinion for terrorists or a rogue nation.

A DMSR burns both u233 and plutonium and has a large inventory of plutonium. I believe the isotropic mix is even poorer than an LWR. The plutonium is mixed with fission products so it is at least as safe as an LWR. The report you referenced used an MSR design that was a conversion machine. You could likely make it come real close or even break-even if you cleaned the fuel once per decade instead of once per 30 years.


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PostPosted: May 19, 2010 2:53 am 
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Ida-Russkie wrote:
its not that you can not its that its easier to use u235 and plutonium.


In at least one sense, the reverse is true. Let's have another look at the post of Per Peterson's, which Axil quoted from earlier:

Quote:
On the proliferation side, U-233 has roughly the same bare-sphere critical mass as plutonium, almost no spontaneous neutron generation, and almost no heat generation. This is excellent from the perspective of weapons use. ... the major barrier to use of U-233 in weapons involves OSHA rules rather than actual physical limits. ... [LFTRs] will have similar non-proliferation issues with other fission reactors... As is commonly said, no technologies will offer a silver bullet to eliminate proliferation risks...


First, note he says the same things I've been saying. Second, the part about U233's lower spontaneous neutron generation. One of the biggest problems with Pu for makeshift bomb designers is its spontaneous fission rate, which necessitates a high-precision implosion mechanism. Like U235, U233 could be used in a gun-type weapon, but with a much smaller subcritical mass (on the order of Pu's). So it's an ideal weapons material, if making precision shaped-charge assemblies is a bottleneck and you don't care about weapon shelf-life.

-Carl


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PostPosted: May 19, 2010 10:49 am 
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But it is very difficult to come by pure u233. You could do it if you build a reactor for that purpose with sufficient excess reactivity, fissile material source, and protactinium extraction. But in a power reactor the u233 will be used to fission. Once you use some of the u233 for fission you will also generate u232 and u234. These are so close in mass that they would be much harder to enrich than to get u235 from natural uranium - especially so since you have elements you don't want just one AMU way in both directions. In a liquid fuel reactor all the various isotopes of uranium will be well mixed so the properties of pure u233 are irrelevant to the discussion of proliferation risks generated by a LFTR.

In a solid fuel reactor there is more risk in that one could have fuel rods that are pulled out of the reactor quick enough that very little fission occurs in those fuel rods. I presume that is how the US got its supply of u233 in the first place (and also I would guess this is how folks get their supply of weapons grade plutonium as well).

Bottom line - a LFTR with protactinium extraction and breeding could pose a risk of a rogue nation openly converting it to other uses if they had sufficient skill and equipment to modify the reactor. Making the reactor a sealed unit with a sword of damaclese ready to denature the fuel upon intrusion would be an engineered way to reduce this risk. In any event, I doubt this would be the easiest route available to such a nation.

A LFTR with no protactinium extraction and no breeding is even more difficult since now the only fissile source in the mix of uranium isotopes not pure u233 and the fissile is available only one time. Again the sword is a means to reduce such a risk.

Finally, a DMSR with no protactinium extraction means you only have denatured uranium available that is much less useful than natural uranium and even the plutonium that gets generated is contaminated with pu238 and is pu239 poor due to the large thermal cross-section of pu239 - so the plutonium is less useful than reactor grade plutonium.


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PostPosted: May 19, 2010 1:51 pm 
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Lars, maybe you missed my earlier post, where I asked whether it is so easy to enforce a breeding ratio of 1. I don't know where the throttle is on a LFTR, but I presume there are ways an operator could improve neutron economy so that some Pa could be removed to produce U233 for a weapon. (Please note, I am playing devil's advocate here.)

Maybe you could explain briefly about this... do we want a faster or slower spectrum? What would be the effect of...

1. pumping the salt faster/slower
2. increasing the concentration of fissile in the salt
3. being more aggressive about cleaning the salt
4. adding graphite pellets to the salt (or other moderator)
5. wrapping the core and/or plumbing with beryllium (or other neutron reflector)

?

-Carl


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PostPosted: May 19, 2010 2:54 pm 
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clumma wrote:
Lars, maybe you missed my earlier post, where I asked whether it is so easy to enforce a breeding ratio of 1. I don't know where the throttle is on a LFTR, but I presume there are ways an operator could improve neutron economy so that some Pa could be removed to produce U233 for a weapon. (Please note, I am playing devil's advocate here.)

Maybe you could explain briefly about this... do we want a faster or slower spectrum? What would be the effect of...

1. pumping the salt faster/slower.

Pumping the salt faster will decrease the delta temperature between the hot and cold outlet. I do not think it will have any effect on the breeding.
Quote:
2. increasing the concentration of fissile in the salt

Increasing both the fissile and fertile concentration in the salt will harden the spectrum. For a graphite-less reactor this will generally increase the breeding.. But if I own fissile that I don't need to run the reactor then I already have the material for a weapon. I'd likely be shot by the dictator if I dumped that precious fissile into the reactor.
Quote:
3. being more aggressive about cleaning the salt

This will increase breeding - but the capacity and technique of cleaning the salt would be part of the initial design.
Quote:
4. adding graphite pellets to the salt (or other moderator)

Sounds like a good way to clog the pump, HX, etc. Yes adding graphite to the reactor will increase its reactivity and hence would require rebalancing the fissile/fertile mix or you could destroy the reactor. So I suppose one could try to remove some fissile, then add a fixed moderator like graphite to restore the reactor to operation. But frankly I think this would be harder than to build a reactor from scratch.
Quote:
5. wrapping the core and/or plumbing with beryllium (or other neutron reflector)

Again you are suggesting major modifications to the reactor on a scale that would be quite challenging. It would be easier to build a new reactor.

It is difficult to design for exactly unity breeding. So I would include a feedback mechanism on the Xe extraction rate to allow it to be adjusted. The nominal reactor with Xe extraction operating at its best would then have a breeding ratio of 1 plus the uncertainty. The reactor operations would then tone done the Xe extraction adaptively to accomplish unity breeding. This information along with the many continuous monitor readings would be transmitted in real time to IAEA or a similar organization. Tampering with the reactor would cause a dump of u238 into the reactor - effectively destroying the fuel (about $200M/GWe worth). The reactor would function as a GWe, multidecade, sealed battery.

Kirk would further park the reactor under a hundred feet of sea water making any physical assault more difficult and making it possible to simple remove the reactor if the country became obstinate about following the rules.


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PostPosted: May 19, 2010 3:18 pm 
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Thanks Lars. But again, many different kinds of reactors can be designed as sealed batteries, and any reactor can be secured via international law. I just read again today, via facebook, that 'Thorium can't be used for weapons, so it was abandoned'. This story is completely false and we should stop telling it.

-Carl


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PostPosted: May 19, 2010 3:55 pm 
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I won't argue with you there. To say it "can't" be used is overstating things and we should not do that.

But I do think it is easier to use other material than u233.
Consider how many nuclear weapons have been built so far - and none of them are u233 based (granted there has been at least one test using u233).


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PostPosted: May 19, 2010 4:13 pm 
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Quote:
But it is very difficult to come by pure u233.


It is impossible to produce pure U233. Pure U233 cannot exist, it never has been produced and it never will. The devil is in the details as follows:


Chronology of Important FOIA Documents: Hanford’s Semi-Secret Thorium to U-233 Production Campaign

You need a custom built ultra low neutron spectrum breeder reactor and thorium feed stock without any Th230 impurities to produce U233 with low contamination levels. The Lftr is an epithermal reactor that uses thorium-232 heavily contaminated with Th230. This will result in the production of U233 with a few hundred PPM of U232 contamination at a minimum and maybe more.

U232 is profoundly disruptive of weapons function as shown by the teapot bomb. The designers of that test would have used U233 with the lowest u232 contamination level available; about 2PPM. Even at that low level spontaneous neutrons production from U232 caused a fizzle.

A pure U233 bomb has never been made. A rogue state would take a foolish and futile chance to try to build a bomb out of U233 from an Lftr. It would have very little if any chance of success. The purported Indian U233 bomb test had no power. It was said to have displaced a sandbag or two just a few inches.

Since any type of U233 fission produces U232…even background fission outside of a reactor, U232 contamination in that bomb material would increase over time as the weapon sits in storage as proved by what has happen to the US U233 stockpile. The containers shielding the U233 weapons grade material that had been produced in the 50’s and 60’s stored in that stockpile cannot even be safely inspected without the use of a hot cell. The spontaneous alpha production is now very high…dangerously high. This fact does not bode well for U233 bomb storage.

Quote:
Once you use some of the U233 for fission you will also generate u232 and u234. These are so close in mass that they would be much harder to enrich than to get u235 from natural uranium - especially so since you have elements you don't want just one AMU way in both directions. In a liquid fuel reactor all the various isotopes of uranium will be well mixed so the properties of pure u233 are irrelevant to the discussion of proliferation risks generated by a LFTR.


This statement implies that U233 enrichment is possible. It is not. U232 contamination will destroy any type of enrichment equipment in short order. If U233 enrichment were possible, the US would have done it to produce U232 purified U233 bomb material. They never tried enrichment even though they struggled for 30 years to eliminate U232 from U233 as documented by the reference listed above.

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Last edited by Axil on May 19, 2010 4:35 pm, edited 1 time in total.

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PostPosted: May 19, 2010 4:33 pm 
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Lars wrote:
Consider how many nuclear weapons have been built so far - and none of them are u233 based (granted there has been at least one test using u233).


I think this is better explained by invoking the usual technology head-start or lock-in scenarios. It happens that an isotope of Uranium is the only fissile material found naturally on Earth, so it was the logical place to start. Then you breed Plutonium quite readily. Pretty simple. As for IFR vs MSR, I've posted on this in the past (in another thread)... you've got the guy who built the first reactor in history telling you that U/Pu fast-spectrum is required from a neutronics point of view. And to explain the subsequent failure of the IFR, simply what I posted earlier in this thread on the economics of resource exhaustion and breeders.
Edit: Jess Gehin agrees: viewtopic.php?f=8&t=322&p=29970#p29970

I'm obviously not a weapons expert but U233 looks pretty good. One needs a source of Pa-233, and an MSR is definitely the most convenient way to obtain that. The weapons we used against Japan would have been much higher-yield, since they both exploded too rapidly to fission completely. Once one gets better at weapon design -- certainly once one gets into fusion-boosted weapons -- Pu allows warheads to be more compact. 233 would still be useful for nuclear artillery, which are usually gun-type. We used U235 for those until they were retired in the '90s. Not that the idea of firing nuclear bombs from a rifle isn't completely ridiculous.

I'll go on. Watching the mating contests of the animal kingdom, it's clear that, while injuries do occur, most of the deadliness has evolved away -- sometimes nothing is left but a dance. Even if one isn't the peace-loving type, it seems to me that nuclear weapons completely exceed the design goals for human violence.

-Carl


Last edited by clumma on May 22, 2010 3:25 am, edited 1 time in total.

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PostPosted: May 19, 2010 5:07 pm 
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Quote:
I'm obviously not a weapons expert but U233 looks pretty good.


Any reference to pure U233 is dishonest. Pure U233 does not exist and cannot exist.

Quote:
One needs a source of Pa-233, and an MSR is definitely the most convenient way to obtain that.


Pa-233 will be mixed with Pa-231 as a result of Th230 contamination in Th232. Th230 produces U232 via Pa231. Most nations cannot remove Th230 contamination from Th232. Most Th232 deposits contain Th230. It is safe to say that pure Th232 does not exist. This implies that pure U233 does not exist and cannot exist.

Since any type of U233 fission produces U232…even background fission outside of a reactor, U232 contamination will spontaneously erupt in pure U233 if it existed.

In more detail, U233 fission has a neutron spectrum described by a Gaussian distribution of neutron energies. At the high energy tail of this Gaussian distribution, neutrons over 6MeV are produced. 2.6% of those high energy neutrons have energies over 6 MeV and are subject to the (n,2n) reaction. This reaction produces U232 from U233.

U233 decay from fission will ALWAYS produce U232 no matter what. It is a fact of nature. If U233 exists it will always contain U232 contamination and that contamination level will increase over time.

U232 cannot be avoided. This is the reason why nations … any nation … will not use U233 for a weapon.

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PostPosted: May 19, 2010 6:51 pm 
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Axil wrote:
Any reference to pure U233 is dishonest. Pure U233 does not exist and cannot exist.


I already gave a plausible argument that U233 with 5% U232 is perfectly suitable for a weapon, even if the material is a year old.

Quote:
Pa-233 will be mixed with Pa-231 as a result of Th230 contamination in Th232. Th230 produces U232 via Pa231. Most nations cannot remove Th230 contamination from Th232. Most Th232 deposits contain Th230. It is safe to say that pure Th232 does not exist. This implies that pure U233 does not exist and cannot exist.


...Meaningless without rates and quantities. Th230 is exceedingly rare in nature, owing to its 75Kyr half-life.

Quote:
In more detail, U233 fission has a neutron spectrum described by a Gaussian distribution of neutron energies. At the high energy tail of this Gaussian distribution, neutrons over 6MeV are produced. 2.6% of those high energy neutrons have energies over 6 MeV and are subject to the (n,2n) reaction. This reaction produces U232 from U233.


Again, meaningless without quantities. U233 spontaneous fissions are 0.5/kg*s. Very few produce fast neutrons... let's accept your 2.6% for now. Not all of those neutrons will produce U232 from U233. etc.

-Carl


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PostPosted: May 19, 2010 8:33 pm 
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Quote:
I already gave a plausible argument that U233 with 5% U232 is perfectly suitable for a weapon, even if the material is a year old.


U232 peak alpha activity is 5.8x10e12 disintegrations/s-g (157 curies/g) at the 10 year mark. This corresponds to 5 W/g of thermal energy. For 500 grams of U232, 2500 watts/s will be produced. That is 8536 btu/hr. This will make 10 Kgs of U233 white hot. This is not compatible with a functional U233 weapon.

Even if the U232 was fresh, 416 watts or 1420 btu/hr would be produced. Extensive heat removal would be required to keep the U233 cool. But long term storage of the U233 weapon would require engineering for the worse case heat load(white hot U233) to keep the high explosives from deterioration or unintended ignition.


With 1 spontaneous neutron produced for each 1,000,000 alpha decays, about 10e9 N/s would be produced. This will cause preignition (aka fizzle).


Without extensive lead shielding, this weapon would be detectible through gamma emissions from a distance of many kilometers and vulnerable to counter measures.

The gamma radiation from the proximity of this U233 weapon would be lethal in seconds.


Have you considered these factors?


Quote:
Again, meaningless without quantities. U233 spontaneous fissions are 0.5/kg*s. Very few produce fast neutrons... let's accept your 2.6% for now. Not all of those neutrons will produce U232 from U233. etc.



The result of this reaction can be quantified by the state of the US U233 stockpile. It is real, significant, and undeniable.

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PostPosted: May 19, 2010 10:14 pm 
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clumma wrote:

I'm obviously not a weapons expert but U233 looks pretty good.


I'll agree with the first part of your statement: you are not a weapons expert. Having worked over three decades at one of the nuclear priesthood labs, you can be assured they are not selecting materials and designs to make their life hard.

And any nation (or rogue state or terrorist) that wants to pursue materials and designs for nuclear weapons is grateful for all the expenditures by the U.S. in exploring the nuclear material and design space so they do not have to. Ditto for the efforts of the Russians, French, and Brits.

Considering that in the golden age of nuclear design (varieties of designs & materials, including small quantities of boutique weapons), if U233 was so great there would surely be a device physicist that would want their name on one. Didn't happen, and it is not going to happen.


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PostPosted: May 19, 2010 10:50 pm 
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Axil wrote:
Have you considered these factors?


When you post something coherent, I'll certainly consider it.

arcs_n_sparks wrote:
I'll agree with the first part of your statement: you are not a weapons expert. Having worked over three decades at one of the nuclear priesthood labs, you can be assured they are not selecting materials and designs to make their life hard.


Sorry, are you saying you know something about weapon design?

-Carl


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