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 Post subject: End Game
PostPosted: Oct 31, 2008 5:43 pm 
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When we complete the fission age we will need to shut the reactors down.
There is a substantial inventory of TRUs in the reactor fleet at that time.
I'm looking at an orderly fleet shutdown to minimize long term waste.
Is the U from a LFTR fuel salt of any particular concern for radioactive waste or proliferation?
The inventory in a fast reactor initially is 5t U233, 2t U234, 0.5t U235, 0.5t U236.
I'm thinking that the radioactivity isn't a big concern for the same reasons that natural U or depleted U or spent LWR U aren't big concerns unless it is due to the U232.

Proliferation sounds worse since it is rather rich in U233 but with u234 (and some U232) is it practical to isotropical enhance it or are these so close in mass that they can't really be separated?

As I shutdown more reactors the mix of U isotopes gets heavier and eventually poisons the reactor. So I was wondering if I can just set the U aside.


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 Post subject: Re: End Game
PostPosted: Oct 31, 2008 5:50 pm 
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I don't think we will ever "complete the fission age"...I think fission (thru thorium) will supply planetary energy demands for hundreds of thousands of years.


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 Post subject: Re: End Game
PostPosted: Oct 31, 2008 7:33 pm 
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My crystal ball gets rather fuzzy around 200 years out. ;)
One (of several) places LFTR shines is the flexibility to deal with different fuel mixes and that we do not require precise fuel.
During operating life LFTR and other gen IV closed cycle systems will have similar waste flows.
End of life is harder for the solid fuel folks though and for fast reactors the inventory is substantial.
So, whether even if there is no end to the fission age it helps win the arguments now to do the R&D to launch LFTR.
(At least compared to other gen IV ideas).


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 Post subject: Re: End Game
PostPosted: Nov 01, 2008 12:09 pm 
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Here is a paper I'm developing. Still needs work but the idea and graph may prove useful for Kirk on Monday and Robert later.

The chart is up to date, the table at the end needs to be revised yet.
Note that this is based on a simplictic evolution model that presumes the neutron spectrum stays constant. I added fuel to the core to keep the macro-crosssections of fissile and absorbing material constant figuring that this would keep the neutron spectrum constant. The results approximately match the published French results.

The conclusion is substantially different than the French. I had similar results to their claimed end-game when I tried to burn off the inventory U. The build up of >233 U eventually causes the reactor to go below critical. By shipping the inventory U as low level waste (after being diluted) I avoided this problem and could reduce the waste flow to leakage during the chemical process. I made rather conservative estimates for the leakage.

Hope this is interesting to folks.


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 Post subject: Re: End Game
PostPosted: Nov 02, 2008 7:52 am 
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Lars, here's your (hopefully very early draft) paper, with some cleanup and editing done, and somewhat closer to idiomatic Australian English.


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File comment: "First, it is a plot device, not a plot bomb. Second, plot devices initiate, they do not explode."
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 Post subject: Re: End Game
PostPosted: Nov 03, 2008 7:26 am 
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Holly Mackerel! I just calculated how much electricity Lars' "End Game" NM-TMSRs would produce. Lars calculates that his fleet of NM-TMSRs would produce "1,638,400 GW-yr (1.6 PW-yr) of electricity". @ a rate of 500 GWy of electricity consumed in the the United States, that would last the country 3276 years. If the fleet were to provide the energy for the entire national economy, it would provide the country with energy for over 1000 years. Obviously Lars needs to rethink the time range of his project. Holly Mackerel!


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 Post subject: Re: End Game
PostPosted: Nov 03, 2008 10:09 am 
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Lars had it in there, I just made it explicit.

Btw, who's this "Holly Mackerel" woman, CB? :mrgreen:

I don't particularly agree with his 200 year lifetime assumption for his NM-TMSR, and would dearly love to see how he developed some of his numbers.

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 Post subject: Re: End Game
PostPosted: Nov 03, 2008 10:36 am 
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The "massive deployment" isn't intended to be limited to the US.
Roughly here is the maximal deployment scenario:
Current "first world" economy population around 1 billion people.
Future total world population around 9 billion people.
Assume 50% energy consumption reduction of first world through efficiency gains (LED lights, plug in hybrids, etc.).
Assume that eventually the rest of the world will enjoy a standard of living similar to our current one.
Current US nuclear is around 100GWe, total electric is around 500GWe.
Electricity is around 50% of US energy consumption.

Combining these you get 15,000 GW electric

If you anticipate new demands like significant water desalination you could make the case for even higher numbers.

Note that this will not happen overnight, over a decade, or even over five decades but it will happen.

I chose a nice power of two and 50% market share. The results are very easily scalable to different forecasts. The key point is not how many plants will be operating in the future as no one can predict that very well. The key point is - this is a technology that can actually meet even the highest demand, and while we are at it eliminate 50% of the current transuranic waste and move almost all the rest from the waste pile to being inside operating reactors. Eventually, when we shutdown the entire fleet we can do so in a way that eliminates almost all the TRU waste. At the end of several centuries, we have supplied the energy AND cleaned up 95% of the currently existing transuranic wastes.


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 Post subject: Re: End Game
PostPosted: Nov 03, 2008 10:41 am 
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fnord wrote:

I don't particularly agree with his 200 year lifetime assumption for his NM-TMSR, and would dearly love to see how he developed some of his numbers.



The design target for a plant lifetime is 60 years. The nice thing about MSRs is that we can transfer the salt from a plant being decommissioned to a new one with almost no transuranic waste. When analysing the TRU waste flow then the lifetime of an individual plant becomes irrelevant. What is important is how long society depends on these type of plants for its energy. I picked 200 years rather arbitrarily.


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 Post subject: Re: End Game
PostPosted: Nov 03, 2008 10:45 am 
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fnord wrote:
Lars, here's your (hopefully very early draft) paper, with some cleanup and editing done, and somewhat closer to idiomatic Australian English.



Thank you. Yes it is a decidedly VERY early draft. I finished the simulations on Sunday and wanted to make the curve and conclusions available to Kirk and Robert in case they would be useful this week.


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 Post subject: Re: End Game
PostPosted: Nov 03, 2008 11:03 am 
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fnord wrote:
Lars had it in there, I just made it explicit.

Btw, who's this "Holly Mackerel" woman, CB? :mrgreen:

I don't particularly agree with his 200 year lifetime assumption for his NM-TMSR, and would dearly love to see how he developed some of his numbers.

The Mackerel is doubly holy. I suspect that Lars had not run the numbers on his electrical output, Clearly he needs to. I would love to post Lars paper when he finishes it.


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 Post subject: Re: End Game
PostPosted: Nov 03, 2008 11:21 am 
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Same here, Lars. If you want me to proof read later drafts of your paper, I'd be happy to do so. So your central thesis is that a given actual plant is practically irrelevant, it's the GW-yr that counts?

My professional education is in mathematics and finance - nuclear reactors (of the very-high-neutron-energy one-use self-disassembling kind as well as the kinds we're talking about on this site) are a hobby for me.

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 Post subject: Re: End Game
PostPosted: Nov 05, 2008 12:13 pm 
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Here is take two on the paper - I would appreciate any comments or questions.
The quick summary is:
We can use the TRU from current LWR spent fuel to start the reactors.
We can generate enough electricity to allow everyone (9 billion people) to enjoy a standard of living similar to ours.
Suppose after 200 years (3+ reactor lifetimes) we chose to shut them down.
We can shutdown 95% of them within a decade. Then by shutting down the rest in an orderly fashion over a period of 83 years we can minimize residual wastes.
The net effect is that we will have eliminated >95% of the TRUs while generating enormous amounts of electricity.

My target audience - beyond this forum is the French team. I want to convince them to evaluate this strategy using industry standard codes that I don't have access to. My work was done using home brew s/w that correlates reasonably enough with published results but won't (and frankly shouldn't) generally be accepted.

I'm thinking clearing the shut down inventories is going to be a significant advantage for any MSR versus any solid fuel reactor.

Lars


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 Post subject: Re: End Game
PostPosted: Nov 06, 2008 10:42 am 
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Great stuff Lars. We should be able to do better than 0.3% loss during processing but we don't have much proof what it would be. Keep in mind that any process that simply tries to pull TRUs out of the salt directly (such as fluorination) should always be able to getting better and better efficiencies if we just keep repeating the process (because what we miss is still in the salt). If we need pyroprocessing or liquid bismuth extraction for the minor actinides like Am and Cm then a certain fraction might get tied up in the intermediate steps. The minor actinides will be a much lower quantity though than Pu and Np which we can deal with through fluorination (Np easily, Pu with more effort).

David L.


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 Post subject: Re: End Game
PostPosted: Nov 06, 2008 11:42 am 
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David,

I hope we can do better the 0.3% but this seems to be an area where hopes often fall short. As best as I know, so far 1% is about has been achieved in fluorination or pyroprocessing. PUREX gets down to 0.01% but at the expense of diluting the fission products into a mess of chemicals and is expensive. Liquid bismuth may do better but so far I think it has only been done in simulations.

I learned some things in this exercise:
1) the TRU inventory remains about the same regardless of the neutron spectrum
2) the production of neutrons is pretty much flat as well
3) the absorbtion of neutrons by the fission products goes down rapidly with a faster spectrum
4) running Th/U rather than U/Pu means dramatically (20x) lower inventories of Pu and hence roughly 20x lower leakage rates.

The conclusion I draw is that the faster spectrum allows me to have slower onsite processing to remove fission products.
I'll call the material stored in the cooling ponds (or dry casks) thorium spent nuclear fuel (TSNF) to distinguish from the LWR SNF we use to start up with.
The thorium spent nuclear fuel then has less U/Np/Pu in it since we can process much less frequently.
I suspect our limit for processing rate will not be set by neutronics but rather by some chemical property of some fission product.

I make an assumption that a slower processing rate means: lower onsite processing costs, lower leakage, and the less painful leakage (since we do it fewer times).
In the end the leakage that really matters is the offsite reprocessing leakage rate.
Unfortunately, unless the central reprocessing is a money maker itself (seems rather wishful thinking to me) our society will likely neglect to get around to building a reprocessing station for a long time (100 years?).
So, for me there is value in reducing the Np/Pu in the TSNF beyond quickly feeding back the fuel to the core.


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