Energy From Thorium Discussion Forum

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PostPosted: Feb 16, 2010 2:15 pm 

Joined: Jul 14, 2008 3:12 pm
Posts: 5045
Lars wrote:
Cyril R wrote:
As for the wall life, it sounds plausible that the 1 1/2 fluid has a longer wall lifetime but this really requires testing, with various different materials. It may not be a big enough difference to warrant more complicated reprocessing.

Maybe not but this is the area that I'm most concerned about. It appears it is OK for a graphite filled reactor like MSBR. The last I saw from the French was that the wall in their fast 1 1/2 fluid design had to be periodically replaced.

With a 1 1/2 fluid the worst case in the processing is that we have a spent fuel pool for decades. The spent fuel pool would contain the salt-seeking fission products + 238Pu + a small amount of 239Pu + tonnes of thorium. It would be a job for the future to separate the stuff. The thing of particular value would be to extract the plutonium. The thorium would have modest value and likely would be extract primarily to reduce the volume of waste storage.

In my view the wall lifetime is a show stopper for some designs. The spent fuel pool is not, though as a policy I would want to guarantee the future extraction of the Pu and funding it as it is generated.

I think we should test a wider array of materials for the wall, since even the French have to replace their 1 1/2 fluid wall. You do make a good case for the 1 1/2 fluid design, though it will be a hard sell - getting rid of spent fuel waste must be, in the eyes of the public, a 'raison d'etre' for a LFTR revival programme.

PostPosted: Feb 16, 2010 3:08 pm 

Joined: Jul 28, 2008 10:44 pm
Posts: 3063
I agree it would be better from a waste perspective to recycle on site.
But we have to balance the waste and proliferation angles for selling to the public.

In regards to the waste:
We get a 90% reduction in plutonium production just by using 233U as our main fuel.
Further, the half-life of 238Pu is only 88 years - and the space program wants it and is willing to spend hundreds of millions to get it.
In fresh reactors we could easily accept an initial loading with plutonium (be it reactor or weapons grade) up to a few tonnes / GWe. This is a place where we could permanently destroy the plutonium.

In regards to proliferation:
The plutonium that is produced is USELESS as a weapon material and in fact can be used to destroy the weapons usefulness of 239Pu. It is never separated from fission products except at a centralized, secure location.

In regards to the wall lifetime:
The French use a fast spectrum to enhance breeding. Breeding is not a goal for me so I am comfortable going to a softer spectrum. This also has the benefit of reducing the fissile inventory needed for startup. The wall damage in the French design is from the fast neutrons so going to a softer spectrum will increase the lifetime of the wall. I haven't figured out how to calculate the resulting lifetime though.

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