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PostPosted: May 17, 2010 7:48 pm 
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Lars wrote:
The strongest evidence against using u233 to create a nuclear weapon is that no one does this. So far, I've heard of one test where the US tried and it was a fizzil and they did not try again.


Not quite true. From http://nuclearweaponarchive.org/Nwfaq/Nfaq6.html , Despite the gamma and neutron emission drawbacks, U-233 is otherwise an excellent primary fissile material. It has a much smaller critical mass than U-235, and its nuclear characteristics are similar to plutonium. The U.S. conducted its first test of a U-233 bomb core in Teapot MET in 1957 and has conducted quite a number of bomb tests using this isotope, although the purpose of these tests is not clear. India is believed to have produced U-233 as part of its weapons research and development, and officially includes U-233 breeding as part of its nuclear power program.

From http://nuclearweaponarchive.org/Usa/Tests/Teapot.html , MET stands either for "Military Effects Test" or "Military Effects Tower" (according to Frank Shelton). This was a LASL test of a composite U-233/plutonium bomb core (the first test by the U.S. to use U-233) in a Mk 7 HE assembly. The 30 inch diameter spherical implosion system weighed 800 lb.

The primary purpose was to evaluate the destructive effects of nuclear explosions for military purposes. For this reason, the DOD specified that a device must be used that had a yield calibrated to within +/- 10%, and the Buster Easy device design was selected (this test gave 31 kt and used a plutonium/U-235 core). LASL weapon designers however decided to conduct a weapon design experiment with this shot, and unbeknownst to the test effect personnel substituted the untried U-233 core. The predicted yield was 33 kt. The actual 22 kt was 33% below this, seriously compromising the data collected.


I don't think a yield of 22 kt qualifies as a fizzle, although it was a third less than desired.

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PostPosted: May 17, 2010 8:56 pm 
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I'm guilty of repeating what others have said.

I could only find one test referenced. The reference to India is a "belief" of an unknown person. I could not find any references to "other tests" the US did. Since the test was a mix of plutonium and u233 in an undetermined quantity it is hard to say how successful the u233 portion was - except to say that it was less successful than the u235.

So while I don't have the references to back up what I repeated this site doesn't directly contradict it either.

I'm sticking with the idea that a future, widely deployable, reactor should be a sealed, unity conversion machine, with a fail-safe to denature the u233 inside, and continuous feedback to a central monitoring site to detect any abnormal operations. Kirk's concept of a submarine deployment certainly helps provide a layer of physical security as well.


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PostPosted: May 18, 2010 1:00 am 
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Axil wrote:
Reactors don’t make bombs, the type of fuel that they burn may or may not be used for bombs; it depends.


LFTR breeds fissile material. That's weapons-useful, period.

Quote:
The primary disincentive for weapons use involves OSHA issues due to personnel radiation exposure from U-232, which can be avoided by choosing weapons grade plutonium or HEU instead of U-232.


If you can handle it at a power plant you can handle it at a bomb factory.

-Carl


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PostPosted: May 18, 2010 1:25 am 
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clumma wrote:
Axil wrote:
Reactors don’t make bombs, the type of fuel that they burn may or may not be used for bombs; it depends.


LFTR breeds fissile material. That's weapons-useful, period.

But if LFTR breeds no more fuel than it burns then the only way to get fissile is to shutdown your reactor. If you are very concerned about proliferation and believe a nuclear power plant is a threat then you could use the heavily graphite moderated DMSR. In that case, even if a country decided to shutdown its reactor to gain access to the fuel they will still need to first cleanse it of the fission products, then enrich it. Doing so will announce to the world their intentions - without even a fig leaf to hide behind.

Quote:
The primary disincentive for weapons use involves OSHA issues due to personnel radiation exposure from U-232, which can be avoided by choosing weapons grade plutonium or HEU instead of U-232.


Quote:
If you can handle it at a power plant you can handle it at a bomb factory.

Not quite that simple. In the power plant we can afford any weight penalty for shielding - not so in a weapon. In a power plant we can use long shaft tools so that the electronics can be 20 feet away - not so in a weapon. These things make it difficult to use the uranium from the reactor in a weapon. If you clean the uranium you can get rid of the u232 decay products that generate the intense radiation. This will give you a window of opportunity where you can build your weapon and deploy it. But after a while (a yearish?) the radioactivity builds up again and starts to destroy your electronics.

Certainly one could use pure u233 which you can get in modest quantity by stripping the protactinium. But if the LFTR is a unity conversion machine then you only get to grab the protactinium present when you shutdown the reactor. IF you built a chemical plant capable of stripping the protactinum (or uranium) from the salt instantly then you could grab the entire inventory and get yourself around 80kg of clean u233. You get to do this once for each GWe reactor you shutdown. That's some pretty pricey fuel. If your chemical plant takes 60 days to process the fuel you only get 40 kg. Note that normally people let the fuel cool a while to reduce the radioactivity during processing. The PUREX process for example uses chemicals that get destroyed by the intense radioactivity so it would be completely useless here.

Not to say it is completely impossible. Just much easier to go the road that others have already traveled with either enrichment or plutonium.


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PostPosted: May 18, 2010 2:12 am 
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Quote:
LFTR breeds fissile material. That's weapons-useful, period.


Per Peterson’s hot cell description has not made an impression on you yet.

I think that you don’t understand the secure hot cell concept yet. Here are some pictures to show how people manipulate stuff inside a hot cell.

Image

Image

Image

Nothing can exit a hot cell. No one can enter. The walls are two meters thick. Life is not possible inside an Lftr hot cell. There is no air inside the hot cell. The radiation and heat inside is intense and killing. The hot cell is hell on earth. No one can steal fresh U233. There are armed guards to protect the hot cell and IAEA inspectors are there to keep an eye on everything.

Also see the hot cell at INL
http://www.facebook.com/video/video.php?v=1106122749832

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PostPosted: May 18, 2010 2:38 am 
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Axil wrote:
I think that you don’t yet understand the secure hot cell concept yet.


??


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PostPosted: May 18, 2010 2:50 am 
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clumma wrote:
Axil wrote:
I think that you don’t yet understand the secure hot cell concept yet.


??



Everybody makes mistakes. I try to fix mine as best I can. Keep up the good work; we all need an anvil to temper our steel.

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PostPosted: May 18, 2010 3:33 am 
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Can someone split the proliferation stuff out into a seperate thread?

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Self-referential - see circular logic

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PostPosted: May 18, 2010 3:51 pm 
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[sorry about the doubled post]

-Carl


Last edited by clumma on May 18, 2010 3:56 pm, edited 1 time in total.

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PostPosted: May 18, 2010 3:55 pm 
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Axil wrote:
Everybody makes mistakes. I try to fix mine as best I can. Keep up the good work; we all need an anvil to temper our steel.


I mean, I don't understand. Your claim boils down to "security". Any reactor can be secured. It says nothing about proliferation risk inherent to the design.

Lars wrote:
Not quite that simple. In the power plant we can afford any weight penalty for shielding - not so in a weapon.


Fat Man was a 20kT device containing ~ 5kg Pu. A similar mass of U233 would produce a similar result. According to
http://www.torium.se/res/Documents/9_1kang.pdf
one needs a spherical shell of lead weighing about 90kg to reduce the rad dose from 5kg of U233 (year-old, starting @ 5ppm U232) to that of Pu. As a ball, that much lead is 10" in diameter. Eyeballing the Fat Man diagrams on wikipedia, its tamper was bigger than this.

Granted, a French-style LFTR apparently operates more around 200-300ppm U232. For 1kg of material @ 100ppm, it still takes 3 months to get to 60mrem/hr, unshielded, if I'm reading their plot right. A U.S. worker could spend 80hr with it. People on suicide missions, considerably more.

You mentioned testing earlier. If optimal yield and accurate delivery by missile aren't design goals, a design can be fully tested with inert pits, and size and weight are irrelevant. It could be built and detonated in somebody's basement, within days of obtaining fissile.

All reactors improve access to nuclear materials. However, power reactors should reduce the desire to build and use bombs. That's about all I think we can say about proliferation.

-Carl


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PostPosted: May 18, 2010 7:30 pm 
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Alex Goodwin wrote:
Can someone split the proliferation stuff out into a seperate thread?


Good idea. This proliferation tangent is important, and popular - this thread has 25,000+ views (!) and I don't think it had anywhere near that many a week ago. I'd split it off to a new thread myself if I knew how.

(Yo, webmaster! Little help?)

Perhaps the new thread title could be: "LFTRs: Proliferation-Proof, or Proliferation-Resistant?"

The proliferation tangent started in earnest on page 14 of this thread with clumma's 2:25am posting in which he rebutted an idea that I have come across many times in the blogosphere, to the effect that you can't make a bomb with a LFTR.

He's right - We don't want to oversell LFTRs. And "you can't make a bomb with a LFTR" has been one of LFTR's big selling points. So this topic should be thoroughly batted around.


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PostPosted: May 18, 2010 9:08 pm 
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its not that you can not its that its easier to use u235 and plutonium.

Another thing to think about. Is it easier to detect a hot nuke?


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PostPosted: May 18, 2010 10:51 pm 
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Ida-Russkie wrote:
its not that you can not its that its easier to use u235 and plutonium.

Another thing to think about. Is it easier to detect a hot nuke?


clumma made the point that a terrorist doesn't need to have a deliverable weapon. The thing could be as big as a locomotive. He could just build it in a warehouse and blow it up and take the city with him. As for tracking the material, it could be stashed in a lead container, on a flatbed if needed. A bad guy could assemble the weapon sans the nuclear material, then open the container, install the material into the device, kiss his irradiated butt goodbye, and push the button before Jack Bauer arrives.

So the key question is not, is it practical to make a nuke from LFTR material? But rather, how feasible is it to remove material from a LFTR, and concentrate it or filter it or clean it or whatever, and install the result into a pre-assembled device? And then push the button and have more than a fizzle?


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PostPosted: May 19, 2010 12:31 am 
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People who think about proliferation more seriously divide the terrorist threat from the rogue state threat. I think there is a reasonable consensus that the terrorist threat is from theft of existing weapons or highly enriched material in transit - not from operating reactors. It is hard to conceive of a terrorist organization capturing a reactor, waiting for the reactor to cool enough to get access to the salt, processing the salt to separate the uranium from the fission products, and then making a get-away.

The more serious problem for a LFTR would be the rogue state. In this case we can make it harder (a single fluid DMSR is pretty hard to use) but not impossible. It is noticeably harder to use a DMSR to get weapons material than it would be to use an LWR - but with modifications and knowledge of how to separate plutonium from fission products you could use either one to produce plutonium. What we can provide is obvious indicators that they are trying to build weapons. I argue that the biggest proliferation technical risk is enrichment technology. LFTR can allow for a dramatic expansion of nuclear power without any expansion in our current enrichment capacity and eventually it can eliminate the commercial market for enrichment services. So, in that sense I consider it will reduce proliferation risks over time.

DMSR has the ugly side of lots of graphite wastes so I tend to prefer the graphite less design.


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PostPosted: May 19, 2010 1:25 am 
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Lars wrote:
The more serious problem for a LFTR would be the rogue state. In this case we can make it harder (a single fluid DMSR is pretty hard to use) but not impossible. It is noticeably harder to use a DMSR to get weapons material than it would be to use an LWR - but with modifications and knowledge of how to separate plutonium from fission products you could use either one to produce plutonium.


But wouldn't those modifications mostly be the fuel that was used? And wouldn't that be the tip-off that the rogue state was up to no good, rather than their use of a LFTR per se?

A 1Gw thorium-fueled LFTR only makes about 90 grams of Pu/year, according to the ppt slides I saw on the Google Tech talks. However, according to the proliferation pdf that David posted on another thread, a 1 Gw thorium MSR could make 25kg of Pu/year. But to do so, it would require 17.5 MT of 20% LEU for the initial core, and 1MT/year 20% LEU after that. Which would be damn near impossible for a rogue state to hide.
(http://www.cissm.umd.edu/papers/files/f ... _power.pdf)

Which enforces your argument that enrichment technology, not LFTR technology, is a proliferation problem.


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