Energy From Thorium Discussion Forum

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PostPosted: Feb 10, 2011 5:47 pm 
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From what I've read U-233 is required to kickstart the fission process in LFTRs. I also know that the US has a small stock pile of U-233 which they're looking at "destroying". If this does happen then what other options are there for 1) producing more U-233 and 2) firing up LFTRs without U-233.

Thanks


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PostPosted: Feb 10, 2011 6:14 pm 
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Getting the startup charge needed to launch a new LFTR is a topic that has received considerable attention. Alternatives include:
a) use traditional uranium mining and enrichment and gradually burn off the u238 while adding thorium. This will work better for more thermal designs but for the fastest neutron spectrum designs this isn't viable. Roughly you will need as much fissile uranium as is used in 1-3 years of operation for a similar sized LWR.
b) use traditional uranium and create u233 in the blanket, then after a time remove the uranium in the fuel salt and replace it with the u233 that has been created in the blanket.
c) use plutonium from weapons or from spent nuclear fuel.
d) build LFTRs that actually produce more 233U than they use. Over time save up the extra 233U to be used to start another LFTR. The time required to build up enough surplus fuel to start a second machine (while keeping the first one running) is called the doubling time.

My personal favorite is a) or a combination of a) and c).


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PostPosted: Feb 10, 2011 7:00 pm 
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Lars wrote:
Getting the startup charge needed to launch a new LFTR is a topic that has received considerable attention. Alternatives include:
a) use traditional uranium mining and enrichment and gradually burn off the u238 while adding thorium. This will work better for more thermal designs but for the fastest neutron spectrum designs this isn't viable. Roughly you will need as much fissile uranium as is used in 1-3 years of operation for a similar sized LWR.
b) use traditional uranium and create u233 in the blanket, then after a time remove the uranium in the fuel salt and replace it with the u233 that has been created in the blanket.
c) use plutonium from weapons or from spent nuclear fuel.
d) build LFTRs that actually produce more 233U than they use. Over time save up the extra 233U to be used to start another LFTR. The time required to build up enough surplus fuel to start a second machine (while keeping the first one running) is called the doubling time.

My personal favorite is a) or a combination of a) and c).


So we can fire up a LFTR using just weapons grade plutonium? That's pretty awesome if my understanding is correct. A major win/win situation. Disarm the bombs to make energy for peace.


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PostPosted: Feb 10, 2011 8:20 pm 
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Yes you could but I think that is only relevant for the military. Great for PR purposes though - we will destroy the plutonium rather than just bury it. I don't expect we will be using weapons grade anything to start up civilian power reactors.

Beside the volume of weapons grade plutonium (200 tonnes worldwide) is rather modest compared to our needs (perhaps 20,000-30,000 tonnes) to have LFTR become the energy source for the world.


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PostPosted: Feb 10, 2011 9:12 pm 
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Lars wrote:
Yes you could but I think that is only relevant for the military. Great for PR purposes though - we will destroy the plutonium rather than just bury it. I don't expect we will be using weapons grade anything to start up civilian power reactors.

Beside the volume of weapons grade plutonium (200 tonnes worldwide) is rather modest compared to our needs (perhaps 20,000-30,000 tonnes) to have LFTR become the energy source for the world.


Hmm, I'm guessing all this must have been discussed a zillion times already on this forum. Looks like this is a bit of a sticking point for getting LFTR off the ground, no pun intended. ;-)


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PostPosted: Feb 10, 2011 11:04 pm 
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One could also breed U233 in CANDU or perhaps in LWR (reprocessing used Lightbridge fuel..). Or use actinides from LWR spent fuel. Yes it was discussed earlier.


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PostPosted: Feb 11, 2011 1:46 am 
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It is much discussed but the problem isn't severe for thermal LFTRs assuming you can get LEU enriched to 20% (or even 10%). You need 0.5 to 2 tonnes fissile to get a 1GWe reactor started. This is the equivalent of 1-2 years fuel for a LWR. There is some 400 GWe worth of nuclear reactors around now. We have enrichment capacity to handle these (well almost - we've been living off of weapons inventory for a while but new enrichment capacity and mining will be coming online to keep those reactors running). You could use that same capacity to start around 200 GWe worth of new LFTRs each year.

I should also point out that expanding ANY energy source at this pace will strain existing supply systems. This should not be an argument against thermal LFTRs.

A fastish LFTR needs more startup fissile and then this becomes more of a consideration.

Start up charge is a more serious problem for fast plutonium machines like IFR or TerraPower. These system will need to breed their fuel to expand their fleet if they are to provide a serious portion of the world's energy needs.


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PostPosted: Feb 11, 2011 2:20 am 
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Fastest way to obtain the fissile feed for fast (uranium or thorium) or thermal (thorium fueled) breeders is to separate reactor grade plutonium from existing thermal reactors. This could be as a major part of the cocktail of Transuranics. UK, France and Russia have stocks available. The French are expending it as MOX fuel for their LWR's. US has maximum stocks in the spent fuel. Japanese are doing it on a small scale. Indians are investing their modest stocks in the fast reactors for creating U233 for thorium use.
The best way for existing LWR users is to reprocess and invest the plutonium directly in the breeders of their choice. It can be LFTR if they want to.


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PostPosted: Feb 11, 2011 2:33 am 
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Countries that want to have a nuclear energy independent future will opt for thorium and avoid U235. China and India have already done so. Cheap U235 is shaky ground to build a national nuclear industry on. Necessity is the mother of invention. Another source for U233 will be found when the cost of U235 is sufficiently high. Prudent nuclear planning must look towards new ways and means to produce cost effective U233.

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PostPosted: Feb 11, 2011 2:51 am 
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19 or 20% enriched uranium with thorium can act as fuel for all thermal reactors with different ratios. Designs of fuel to enable separate processing of Thorium are also feasible.
Only possibility of producing U33 without uranium fueled reactors is use of accelerator driven systems. Success seems distant.


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PostPosted: Feb 12, 2011 8:16 am 
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Lars wrote:
Yes you could but I think that is only relevant for the military. Great for PR purposes though - we will destroy the plutonium rather than just bury it. I don't expect we will be using weapons grade anything to start up civilian power reactors.

Beside the volume of weapons grade plutonium (200 tonnes worldwide) is rather modest compared to our needs (perhaps 20,000-30,000 tonnes) to have LFTR become the energy source for the world.


Can MOX fuel be used?


There appears to be a misinformed article in the Telegraph today,
http://www.telegraph.co.uk/earth/earthc ... -yard.html

Britain's MOX plant has failed to date, but they're considering building a new one.
Britain has 112 tons of Plutonium, though I'm not sure if it's all the right isotope.

Can some one technical clarify this?


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PostPosted: Feb 12, 2011 9:16 am 
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alexterrell wrote:
.......Can MOX fuel be used?


There appears to be a misinformed article in the Telegraph today,
http://www.telegraph.co.uk/earth/earthc ... -yard.html

Britain's MOX plant has failed to date, but they're considering building a new one.
Britain has 112 tons of Plutonium, though I'm not sure if it's all the right isotope.

Can some one technical clarify this?
Reactor grade plutonium that could be used for MOX fuel could be used to start LFTRs instead, you just need a bit more of it. See comment on the other thread for a very rough calculation.

'MOX plutonium' usually refers to the Pu content of spent MOX fuel, which is no use for anything much as most of the fissile isotopes are gone.

That Telegraph article is a terrible piece of fear-mongering. Five minutes on Google would have cleared up most of the silly errors.


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PostPosted: Feb 12, 2011 10:06 am 
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The Telegraph article is indeed fear mongering. The ignorant can cry the sky is falling with the greatest conviction.

However the conclusion that MOx fuel plants are a bad idea is correct, for factual reasons. It ruins good quality plutonium by putting it in inefficient once through cycles. Or rather, the 'one more time' cycle. At the end of the 'one more time' cycle the fissile quality of the remaining plutonium is so poor it can not be used economically anymore. Then, it truely is a 100,000 year waste with no economical solution but to store it forever. What's more, the fission products are now in a big messy bath and costly waste conversion (vitrification) is required for long term storage. Making big messes, pointlessly. Using thorium oxide in the MOx makes it even harder.

In stead, use the transuraniums as startup for faster spectra MSRs that do breakeven breeding. For options and details see:

http://hal.archives-ouvertes.fr/docs/00 ... 6_TMSR.pdf

http://hal.in2p3.fr/docs/00/02/55/18/PD ... 021905.pdf


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PostPosted: Feb 13, 2011 2:49 pm 
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My thinking is that reprocessing is expansive and involves transporting the nations spent fuel over the rails and highways to a central reprocessing plant and then the return trip..................
this idea is in the category of economicly and politically not feasible.
So can a LFTR be started with DUPIC fuel?( I should be saying spent fuel dissolved in Florine, but not reprocessed)
is DUPIC fuel from a heavy water reactor of any use to a LFTR?( a PWR/CANDU/LFTR fuel cycle ?)
The goal is the spent fuel does not leave the PWR reactor site, but is processed on site and burned again onsite
does it make any sense in a PWR/CANDU/LFTER fuel cycle to add Thorium at the PWR/CANDU stage of the cycle?
IE would there be any synergy with a Lightbridge fueled PWR where the spent fuel ends up in a CANDU next door?

This paper posted above seems exciting, but it seems to talk about reprocessing PWR fuel for the breeder and the molten salt reactor something to be avoided unless it can be done on site or regionally.Only DUPIC might be able to be done on site.

http://hal.in2p3.fr/docs/00/02/55/18/PD ... 021905.pdf


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PostPosted: Feb 13, 2011 6:33 pm 
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As a reactor gets more thermal the cross-section of all components gets larger. The fissile elements cross section grows larger faster than any others as the spectrum slows down (gets more thermal). A LWR has a fairly thermal spectrum. A CANDU has a very thermal spectrum. So, fuel that can NOT be used in an LWR anymore still has enough fissile left in it to be used in a CANDU. This is the gist of DUPIC.

In general, LFTRs have a faster spectrum than LWRs so no you could not use spent LWR fuel directly to start a LFTR. With one exception, Jaro advocates a heavy water LFTR. This, being a very thermal machine could run on spent fuel.


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