Energy From Thorium Discussion Forum

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PostPosted: May 31, 2017 9:57 pm 
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https://whatisnuclear.com/articles/thorium.html

"Protactinium can be chemically separated shortly after it is produced and removed from the neutron flux (the path to U-233 is Th-232 -> Th-233 -> Pa-233 -> U-233). Then, it will decay directly to pure U-233. "

My understanding is that even if Protactinium is removed immediately and placed into a decay tank that there will always be some degree U232 contamination, no matter what.

Is this not correct?

Whatisnuclear seems adamant that absolutely pure U233 with zero U232 contamination can be produced over on reddit.

Are there any sources to rebuke this?


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PostPosted: May 31, 2017 10:44 pm 
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I've already explained it to him, repeatedly. He only damages his own credibility if he continues to say this.


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PostPosted: Jun 04, 2017 6:56 pm 
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https://www.reddit.com/r/Documentaries/ ... ?context=3

"I must have missed Kirk's explanations. I bumped into him a few months ago at a DOE workshop and he didn't mention it then. Maybe you can point me to the counterargument?"


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PostPosted: Jun 04, 2017 7:28 pm 
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Tell him to check the emails I sent him.


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PostPosted: Jun 04, 2017 7:36 pm 
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Is there anyone I can read the explanation?
Is there some sort of carryover of 232Pa or similar?
Or is it simply an issue with not being able to obtain high enough decontamination factors between 232U and Pa?


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PostPosted: Jun 05, 2017 8:46 am 
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I remember there being an explanation in Hargraves book about this, but I am having trouble finding it.


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PostPosted: Jun 05, 2017 11:12 am 
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This is how I understand the claim of being able to produce "pure" U-233 from a thorium MSR. I apologize for not keeping my references for this, I don't recall where I saw this argument made since it was lost in my shuffle of web pages as I was verifying the math.

Pa-232 has a half life of 1.3 days after which it decays to U-232 and a small portion of Th-232, Pa-233 has a half life of 26.9 days and then decays to U-233. In normal operation the typical thorium MSR will have this uranium separation as a continuous process, protactinium separated into the decay tank and uranium drawn from the decay tank and returned to the reactor core. If this protactinium is allowed to sit for a large number of Pa-232 half-lives, but a small number or fraction of Pa-233 half-lives, then the protactinium in the decay tank will be highly pure Pa-233.

For example if the protactinium is allowed to decay for something like 26 or 27 days then 20 Pa-232 half-lives would have passed but only one for Pa-233. At that time the protactinium can be drawn off and stored in a different tank. If this allowed to sit for time on the order of several months then a large portion of the Pa-233 would have decayed to U-233. There would still be some U-232 in this but several orders of magnitude smaller than there would be if taken directly from the thorium MSR by most other means.

The purity of the U-233 after the process I described would be very high. Depending on the chemical separation processes used the threat of isotopes that produce spontaneous neutrons and decay heat that would render it useless for making weapons could be nearly non-existent. Whether or not this can be called "pure" U-233 or not at this point is a matter of defining "pure". As someone that did some coin trading I think of the definition of purity with "nines". A "three nines pure" gold or silver coin is 99.9% pure. Getting beyond "four nines pure" (99.99%) is difficult and only the snobbiest of coin collectors care of purity this high. In many cases once one gets to three nines it's considered "100% pure". How one defines "weapon grade" is more complex than specifying the "nines" of purity but I assume (perhaps wrongly) that if one can achieve two or three nines purity of any fissile material that it could be considered both "pure" and "weapon grade".

There's two big problems with using a thorium MSR to produce weapon grade material. First is that to make up for the loss of U-233 in your reactor those valuable neutrons have to be made up with more fissile material or your reactor will shutdown. As pointed out in the articles I've read (again I apologize for no citations) that would have to be done with reactor grade uranium or plutonium. A person would have to start with having access to some pretty high grade reactor fuel before using a thorium MSR to purify it further.

The second problem I see, and I believe this is huge, is that a U-233 bomb is still theoretical. People claim U-233 was used successfully in weapons before but every test I have been able to find were considered failures. The bombs did in fact "go boom" but at a yield much lower than expected. None of these weapons used pure (by any definition) U-233 in the core, it was a mix of U-233 with U-235 or Pu-239. No one knows for sure if a pure U-233 bomb is even practical.

Thorium as a fuel is not considered weapon proliferation resistant because it is theoretically impossible to make a weapon from it. It's considered a non-issue in making weapons because it would be easier to make a weapon by other means. If someone has access to reactor grade uranium or plutonium and proceeds to use it to siphon off some highly pure U-233 and hope no one notices then they are going about it the wrong way. It would take much less time and effort to use that material in centrifuges and/or a solid fuel reactor to get what they want.

I have some theories on how one could design a thorium fueled reactor that could produce weapon grade material but it would be very obvious that the reactor was not a typical civilian reactor. It would have multiple decay tanks and chemical separators that would not be needed in a civil power reactor. It would also produce weapon grade material very slowly.

If my thought experiment above is insufficient to convince people on the difficulty on making weapon grade material from thorium then I'll come back when I have time to cite some sources. I will say that if you want some more insight on this then Mr. Sorensen's blog entries on this website is a good place to start. http://energyfromthorium.com/category/blog/

This blog post explains some of the problems (and includes citations): http://energyfromthorium.com/2015/04/10 ... -response/

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Disclaimer: I am an engineer but not a nuclear engineer, mechanical engineer, chemical engineer, or industrial engineer. My education included electrical, computer, and software engineering.


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PostPosted: Jun 06, 2017 10:46 am 
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Hi Kirk,

I apologize for bothering you again.

Whatisnuclear responded with:

https://www.reddit.com/r/Documentaries/ ... e/diiiz9d/

I have 21 emails from Kirk Sorensen in my archives from the Dec 2015-August 2016 range, mostly a back-and-forth exchange about compiling an old Fortran program related to supercritical CO2. I cannot find anything related to this topic with his name on it.
Maybe he wrote in on my webpage's contact form under a different name?


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PostPosted: Jun 10, 2017 5:33 am 
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U-233 is in case radioactive and needs handling as such. More radioactive inclusions require more protection which is easier than separation. The utility is limited.


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