Energy From Thorium Discussion Forum

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 Post subject: Re: Protactinium-233
PostPosted: Apr 17, 2012 10:16 pm 
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USPWR_SRO wrote:
Steve Brown wrote:
Lars wrote:
...The ratio of Pa to thorium in the blanket will be more like 75kg / 40 tonnes....


Really? The ratio 75:40,000 reduces to 1:533, or 1 part Pa to 533 parts Th in the banket salt, even after extended running and equilibrium is attained. That makes neutron capture by Pa-233 insignificant, not worthy of any special design features to make it less. Are you sure that 1:533 ratio is correct, or approximately so?

My fields of expertise are computer science and electronics. When it comes to nuclear reactor design, I'm an interested observer.


Be careful using a simple ratio, neutron cross sections for absorbtion will make a big difference.

From the previous post. The cross-section of Pa is about 4x that of thorium so the effective ratio is smaller than you think but still the point is still the same.


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 Post subject: Re: Protactinium-233
PostPosted: Apr 19, 2012 9:54 am 
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I think that U234 should be treated as an inevitable nuisance, just like Pu240. The system, at least the initial few machines, should not be made complicated if,
a. Criticality is achieved.
b. Breeding ratio of 1 or more can be achieved at any enrichment (fissile inventory).
If, however the fast spectrum chloride reactor is used, Pa233 will boil off at working temperature and can be rested for 180-270 days for 99-99.9% conversion to U233.


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 Post subject: Re: Protactinium-233
PostPosted: Apr 22, 2012 5:12 pm 
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An interested question from a layman...

Assuming that Th-232 to Pa-233 production occurs in greater concentration closer to the core, would it be possible to create a circulation in the blanket that gradually moved material nearest the core to the outside of the blanket and set up a flow from the outside inwards? Following the initial assumption, the Pa-233 thereby moved would be less likely to absorb neutrons before decaying to U-233. The exterior of the blanket could then provide a function somewhat analogous to Steve's holding tank, without the additional costs and other concerns of extracting the blanket material for that purpose.

With more U-233 dispersed toward the blanket's exterior, however, I suppose this might reduce its effectiveness as shielding for the vessel walls.

All of this presumes that there is not some sort of flow already in the design of the blanket -- in which case, never mind.


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 Post subject: Re: Protactinium-233
PostPosted: Apr 23, 2012 7:44 am 
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jubal8 wrote:
An interested question from a layman...

Assuming that Th-232 to Pa-233 production occurs in greater concentration closer to the core, would it be possible to create a circulation in the blanket that gradually moved material nearest the core to the outside of the blanket and set up a flow from the outside inwards? Following the initial assumption, the Pa-233 thereby moved would be less likely to absorb neutrons before decaying to U-233. The exterior of the blanket could then provide a function somewhat analogous to Steve's holding tank, without the additional costs and other concerns of extracting the blanket material for that purpose.

With more U-233 dispersed toward the blanket's exterior, however, I suppose this might reduce its effectiveness as shielding for the vessel walls.

All of this presumes that there is not some sort of flow already in the design of the blanket -- in which case, never mind.


I am not 100%, but I believe if continuous treatment of the blanket salt to remove the U-233 is the idea, there will be flow within the blanket, hopefully enough to disperse the Pa-233 from concentrating at the core surface. If this is still a problem, I don't think it would not be overly difficult to force convection within the blanket salt.


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 Post subject: Re: Protactinium-233
PostPosted: Apr 23, 2012 7:53 am 
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Production does occur to a greater extent near the core, but any produced Pa or U is soluble so very rapidly diffuses into the blanket salt. It mixes very rapidly. Also the heat production isn't negligible so the time constant for natural or forced circulation is much shorter than Pa extraction/decay. It is therefore also not possible to do anything with this.


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 Post subject: Re: Protactinium-233
PostPosted: Apr 23, 2012 10:46 am 
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gcarlin wrote:
I am not 100%, but I believe if continuous treatment of the blanket salt to remove the U-233 is the idea, there will be flow within the blanket, hopefully enough to disperse the Pa-233 from concentrating at the core surface. If this is still a problem, I don't think it would not be overly difficult to force convection within the blanket salt.

There must be a thread or three about this, but what are the radiation, handling, proliferation and other concerns re extracting/separating the U-233? You obviously have to do it at some point if you are going to move U-233 to the core or use it to seed another reactor.

As I understood it, however, the main concern Steve was addressing with his holding tank was the adverse effect on neutron economy of having Pa-233 in the blanket. His suggested remedy was to extract it to allow it to 'age in the bottle'. As the thread progressed, it seemed that the Pa/Th ratio was low enough that the cost for the additional equipment and process might not be justifiable.

Being ignernt of much about all this, but somehow wanting to contribute anyway, I thought that modifying the blanket container with some simple baffles, tubes and convective flow -- or maybe pumps -- might achieve most of Steve's purpose at little cost and with no additional processes needed. Though given the non-negligible heat, as Cyril points out, I did wonder how actively the blanket solution would be turning over. But that's about where the being ignernt really kicked in.

Speaking of ignernce... apart from the always enjoyable and informative browsing of the EFT forum, are there whole books/documents available that describe in concise yet nerdy detail a LFTR design and operations, e.g. the ORNL reactor. And how different might Kirk's, or China's, or anyone else's LFTR design be?


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 Post subject: Re: Protactinium-233
PostPosted: Apr 25, 2012 2:28 pm 
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jubal8 wrote:
There must be a thread or three about this, but what are the radiation, handling, proliferation and other concerns re extracting/separating the U-233? You obviously have to do it at some point if you are going to move U-233 to the core or use it to seed another reactor.
I was under the impression that for anti-proliferation reasons you DON'T want to remove the Pa233 since the Pa233 (n,2n) Pa232 reaction is one of the ways that U232 winds up in the mix. And folks seem to thing that U232 is good for A-P purposes. No?

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 Post subject: Re: Protactinium-233
PostPosted: Apr 25, 2012 8:11 pm 
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Mostly it is that having the equipment present to separate protactinium means you can extract a modest amount of almost pure 233U (about 50kg or so per GWe reactor). So a country that had several GWe of LFTRs could withdraw from the anti-proliferation treaty and within a few months have several time 50kg of nearly pure 233U.


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 Post subject: Re: Protactinium-233
PostPosted: Apr 25, 2012 8:49 pm 
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Lars wrote:
Mostly it is that having the equipment present to separate protactinium means you can extract a modest amount of almost pure 233U (about 50kg or so per GWe reactor). So a country that had several GWe of LFTRs could withdraw from the anti-proliferation treaty and within a few months have several time 50kg of nearly pure 233U.

Considering that only about 6kg of U233 is enough for a high-yield fusion-boosted weapon, there is plenty of incentive to discourage MSR designs involving Pa233 separation.


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 Post subject: Re: Protactinium-233
PostPosted: Apr 26, 2012 1:37 pm 
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A fast spectrum reactor could burn U234 like transuranics. Go for a Th-U233 fast breeder if possible.


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 Post subject: Re: Protactinium-233
PostPosted: Feb 08, 2014 6:33 am 
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Is Pa only tetravalent ? If it has any other valency states, none of them as gas at LFTR operating temperatures ?
I read somewhere somebody saying Pa as a tetra and penta valent states.
If there was a PaF5 that was a gas, that would move the Pa into the core, which would be a waste of neutrons at a minimum.

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 Post subject: Re: Protactinium-233
PostPosted: Feb 08, 2014 2:25 pm 
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Protactinium is typically tetravalent in fluorides and pentavalent in oxides.


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