Energy From Thorium Discussion Forum

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PostPosted: Sep 30, 2010 11:56 am 
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Lars wrote:
If one values minimizing waste over proliferation risk then you might be reluctant to put 100 tonnes of graphite inside the reactor and thus avoid the largest flow of waste (around 3 tonnes / GWe-yr).


Shouldn't graphite be only low level waste? I don't think that pure carbon gets activated, and even if one makes C-14, graphite is very durable and insoluble. The salt can be washed off or baked off. Wouldn't it be less toxic than uranium ore tailings?


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PostPosted: Sep 30, 2010 9:16 pm 
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jaro wrote:
Axil wrote:
Both the PB-AHTR and the Indian CHTR will use pure thorium fuel cycle TRISO fuel. What is the problem?
Not sure what you mean Axil -- PB-AHTR uses 10% LEU.

Dr. Peterson has said that alternative fuel cycles are for the PB-AHTR are still under study. He has hinted that the pure thorium cycles might be too expensive due to frequent reprocessing (unless extra make-up fissile is added).

However, I think there is a variation in which the used fuel pebbles are discarded, and the blanket pebbles (which contain thorium and undiluted U233) would be recycled. The plan would be to have a reactor on-site at the fuel processing plant to pre-irradiate the U233 pebbles, so that they would be self-protected for their journey to the off-site power plants.

But in any case, I agree that the DMSR is much better than what we have now, and nearly as good as the 2-fluid thorium cycle LFTR, and much easier to sell politically. It's a great reactor for the export market (which is currently much bigger than the US market). It works fine with off-site (and long deferred) reprocessing, and the reprocessed salt can easily be blended with a bit of dirty salt to deter theft during shipment. It can burn essentially all of its TRansUranics. It provides energy security, since it is possible to cheaply stockpile a decade or more of fuel.

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Last edited by Nathan2go on Sep 30, 2010 9:26 pm, edited 1 time in total.

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PostPosted: Sep 30, 2010 9:22 pm 
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Lars wrote:
If one values minimizing waste over proliferation risk then you might be reluctant to put 100 tonnes of graphite inside the reactor and thus avoid the largest flow of waste (around 3 tonnes / GWe-yr).


I don't see how this is a big deal. Of course for coal, the comparison would be 3 million tons of waste.

But even for a graphite-free LFTR, your one-ton/GWE-yr of fission products surely must turn into 10 tons once it's vitrified? What about the gaseous fission products?

Graphite at least is ready to bury, with no vitrification required (I assume).


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PostPosted: Sep 30, 2010 9:47 pm 
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Waste is associated with U238 burning

The pure thorium fuel cycle waste only goes up to U238. Yes, there is some NP237 but not much Pu239.

I don’t believe pure thorium cycle waste needs to be vitrified?

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PostPosted: Sep 30, 2010 10:04 pm 
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It provides energy security, since it is possible to cheaply stockpile a decade or more of fuel.


Very good point Nathan. Even without improving the 1980 DMSR design, if you had the customer purchase about half as much fissile U235 as a fast breeder (9 tonnes per GWe) as a stockpile and startup, you could run over 35 years before you'd need to buy more (much longer or with a smaller stockpile if you improve the standard design). Over ninety years if you bought the full 18 tonnes! The economics of interest rates always work against this but a good way for the customer to feel reassured.

David L.


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PostPosted: Oct 01, 2010 8:55 pm 
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Axil wrote:
Waste ...
I don’t believe pure thorium cycle waste needs to be vitrified?

As David has pointed out elsewhere, pure thorium cycle waste (going to disposal) and DMSR waste (to disposal) are about the same. Both types can burn all their TRUs to the extent that their reprocessing sytems can put the TRUs back into the fuel. So in both cases, waste means leakage. The DMSR will have larger TRU inventory, but also reprocess the fuel 100x less often, probably the result will be similar leakage.

If you were going to put the waste in a really good repository (like a salt formation), it wouldn't matter whether you vitrified it.

But if your goal was to provide DMSR fuel reprocessing services to almost every country in the world, and ship the waste back to the user nation for disposal, you'll have to assume some in-perfect disposal will occur. If you thought much of the waste would simply be dumped in shallow land fills or coastal waters, then you'd better vitrify everything, so no country feels discrimated against.

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