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 Post subject: Re: Thorium production
PostPosted: Jun 01, 2009 7:32 am 
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Interesting enough, even an uranium fuelled (non thorium) MSR can achieve enormous fuel savings, based on Denatured or Converter MSR technology
Assuming they consume something in the range of only 30 or 45 tonn per GWyear of natural uranium
Mission: Resource Extension
and we still have at least 35 milions tonns of low cost reserves of natural uranium (considering the high efficiency of the fuel is even a quite conservative assumption), so we have enough low cost uranium to produce worldwide more than 80 PWh/year for at least ~ 100 years

I wonder if it's possible (as intermediate step, before switching to a full U-233/thorium cycle) to design/build a Denatured/Converter uranium fuelled MSR with a thorium blanket, in order if necessary to produce the uranium 233 in the blanket or it's only an useless and very costly complication


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 Post subject: Re: Thorium production
PostPosted: Jun 01, 2009 12:28 pm 
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Alex P wrote:
Interesting enough, even an uranium fuelled (non thorium) MSR can achieve enormous fuel savings, based on Denatured or Converter MSR technology
Assuming they consume something in the range of only 30 or 45 tonn per GWyear of natural uranium
Mission: Resource Extension
and we still have at least 35 milions tonns of low cost reserves of natural uranium (considering the high efficiency of the fuel is even a quite conservative assumption), so we have enough low cost uranium to produce worldwide more than 80 PWh/year for at least ~ 100 years

I wonder if it's possible (as intermediate step, before switching to a full U-233/thorium cycle) to design/build a Denatured/Converter uranium fuelled MSR with a thorium blanket, in order if necessary to produce the uranium 233 in the blanket or it's only an useless and very costly complication


First a quick point. Even the uranium fueled DMSR (30 Year Once Through) mainly burns thorium, not uranium. It keeps the U233 + U235 content denatured but still tries to get as much of the fissions as possible from the thorium to U233 chain. These designs easily do 5 to 10 times better than PWRs for uranium utilization which also means we could pay almost anything per kg for natural uranium and still not be a big part of the cost of electricity from these. For example, 30 tonnes of natural uranium per year at even $5000/kg still is only 150 million plus a few million for enrichment or about 2 cents per kwh. That is more than a hundred fold increase from today's price, no one can tell me we don't have huge reserves at that price.

The current annual fueling cost of a DMSR design would be about 6 million for 150 kg of U235 from 30 tonnes nat U, added as low enriched uranium (based on 40$ per gram U235 content enriched). Sure, one can claim a break even design only needs $40,000 per GWe year of thorium but when you factor in the capital and O&M costs of fuel processing it is likely well above 6 million. When you are selling hundreds of millions of dollars worth of electricity per year, 6 million is almost nothing.

Putting a blanket around a DMSR design wouldn't be too helpful since there is only a very small percentage of neutrons that normally would leak out (0.8 to 1.5%). As well, you'd have the complication of assuring a leak proof barrier and you'd also have to have fluorination equipment on site which goes against some of the proliferation resistance of the simple DMSR design with no on site chemical processing.

David L.


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 Post subject: Re: Thorium production
PostPosted: Jun 01, 2009 7:01 pm 
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David wrote:

First a quick point. Even the uranium fueled DMSR (30 Year Once Through) mainly burns thorium, not uranium. It keeps the U233 + U235 content denatured but still tries to get as much of the fissions as possible from the thorium to U233 chain. These designs easily do 5 to 10 times better than PWRs for uranium utilization which also means we could pay almost anything per kg for natural uranium and still not be a big part of the cost of electricity from these. For example, 30 tonnes of natural uranium per year at even $5000/kg still is only 150 million plus a few million for enrichment or about 2 cents per kwh. That is more than a hundred fold increase from today's price, no one can tell me we don't have huge reserves at that price.

The current annual fueling cost of a DMSR design would be about 6 million for 150 kg of U235 from 30 tonnes nat U, added as low enriched uranium (based on 40$ per gram U235 content enriched). Sure, one can claim a break even design only needs $40,000 per GWe year of thorium but when you factor in the capital and O&M costs of fuel processing it is likely well above 6 million. When you are selling hundreds of millions of dollars worth of electricity per year, 6 million is almost nothing

David L.


Ok, I realize it. I'm not particurally concerned of the fact that the DMSR is not a real thorium breeder (or it produces anyway some TRU waste, even if much lower than a LWR), rather that is a quite different technology in comparison with thorium LFTR breeders, that could cut space and resources to them - though I understand that the DMSR is much simpler and potentially more economic in the short time than the LFTR breeder and it can be an interesting intermediate solution, before we will be successful to handle the LFTR breeder technology


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 Post subject: Re: Thorium production
PostPosted: Jun 01, 2009 8:03 pm 
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David wrote:
Putting a blanket around a DMSR design wouldn't be too helpful since there is only a very small percentage of neutrons that normally would leak out (0.8 to 1.5%). As well, you'd have the complication of assuring a leak proof barrier and you'd also have to have fluorination equipment on site which goes against some of the proliferation resistance of the simple DMSR design with no on site chemical processing.

David L.


Is this a single fluid configuration with graphite moderator that heavily moderates the neutrons in the center and has very little moderation around the edges of the core? Even at that I'm surprised at the very low leakage. At the walls designed to be reflectors? If so, what percentage of neutrons get saved for use in the fuel due to their reflection?

Lars


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 Post subject: Re: Thorium production
PostPosted: Jun 02, 2009 3:10 am 
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The Indian PFBR has a thorium blanket for conversion to U233. The same should be possible with a fast version of MSR (no graphite). The moderated reactor also requires isotope separation of Lithium for isotope Li7. The fast type shall require separation of isotope Cl37. Light elements Li and Be shall not be required for moderation. A neutron economic salt eutectic may be used.
Such a fast MSR could easily replace current Sodium cooled fire prone fast reactors and irradiate thorium.


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 Post subject: Re: Thorium production
PostPosted: Jun 02, 2009 9:14 am 
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Lars wrote:
David wrote:
Putting a blanket around a DMSR design wouldn't be too helpful since there is only a very small percentage of neutrons that normally would leak out (0.8 to 1.5%). As well, you'd have the complication of assuring a leak proof barrier and you'd also have to have fluorination equipment on site which goes against some of the proliferation resistance of the simple DMSR design with no on site chemical processing.

David L.


Is this a single fluid configuration with graphite moderator that heavily moderates the neutrons in the center and has very little moderation around the edges of the core? Even at that I'm surprised at the very low leakage. At the walls designed to be reflectors? If so, what percentage of neutrons get saved for use in the fuel due to their reflection?

Lars


Yes, for a DMSR probably the only way is going to be quite close to Oak Ridge's design which was basically just a much bigger version of the MSRE. I have been looking at pure salt versions but the huge resonance absorption cross sections of U238 make this really hard. The Oak Ridge DMSR that needs top up of low enriched uranium had a small leakage of 1.5% and that is WITHOUT the usual trick of having less moderation near the edge. If they used that trick they calculated the leakage would drop to 0.8% but then they'd need a larger starting fissile load. If your core is pretty big as the DMSR is (8.3m by 8.3m) then leakage is quite small. They did have the usual 2 feet of graphite at the outer edge to act as a reflector but the main job of this is just to protect the outer vessel, as I've mentioned before, reflectors actually do weird things for you and often don't help lower leakage (most often they increase it! Again because they increase power density at the outer edge of the core).

One of the exciting things about the brief work on the DMSR is that it was in no way optimized and even still, the great results shocked the Oak Ridge workers. I've been having fun for the last several months looking into various new options for this basic idea.

David L.

P.S. Alex P, the R&D needed for a simple Denatured Molten Salt Converter (DMSR) would be completely relevant to any other molten salt design (just there is so much less of it needed!). I'm also a firm believer that more than one design will go to market in the next 20 years, I'm just making the case that a DMSR without fuel processing will likely be one of them.


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 Post subject: Re: Thorium production
PostPosted: Jun 02, 2009 12:51 pm 
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Just an extra comment to my last post. The other reason that graphite moderated cores typically include graphite reflectors around them is to flatten the power and flux levels across the cores. This is an effective way to increase the lifetime of the graphite since otherwise the centre of the core would have a much higher power density and shorter graphite lifetime.

David L.


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 Post subject: Re: Thorium production
PostPosted: Jun 03, 2009 1:56 pm 
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David wrote:

First a quick point. Even the uranium fueled DMSR (30 Year Once Through) mainly burns thorium, not uranium. It keeps the U233 + U235 content denatured but still tries to get as much of the fissions as possible from the thorium to U233 chain. These designs easily do 5 to 10 times better than PWRs for uranium utilization which also means we could pay almost anything per kg for natural uranium and still not be a big part of the cost of electricity from these. For example, 30 tonnes of natural uranium per year at even $5000/kg still is only 150 million plus a few million for enrichment or about 2 cents per kwh. That is more than a hundred fold increase from today's price, no one can tell me we don't have huge reserves at that price.

David L.


Actually, according to the ORNL reference the natural uranium need is about 1800 tonn for 22,5 GWyear, or 80 tonn/GWyear, excluding the final further reprocessing step (that halving the nat U need)


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 Post subject: Re: Thorium production
PostPosted: Jun 05, 2009 9:44 am 
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Alex P wrote:
David wrote:

First a quick point. Even the uranium fueled DMSR (30 Year Once Through) mainly burns thorium, not uranium. It keeps the U233 + U235 content denatured but still tries to get as much of the fissions as possible from the thorium to U233 chain. These designs easily do 5 to 10 times better than PWRs for uranium utilization which also means we could pay almost anything per kg for natural uranium and still not be a big part of the cost of electricity from these. For example, 30 tonnes of natural uranium per year at even $5000/kg still is only 150 million plus a few million for enrichment or about 2 cents per kwh. That is more than a hundred fold increase from today's price, no one can tell me we don't have huge reserves at that price.

David L.


Actually, according to the ORNL reference the natural uranium need is about 1800 tonn for 22,5 GWyear, or 80 tonn/GWyear, excluding the final further reprocessing step (that halving the nat U need)


In the 1800 tonne ore for 22GWeyear (30 years at 0.75 capacity factor) about half of that is just for the initial startup load of LEU. You can recover the same amount of fissile uranium at the end of the 30 years by a simple fluorination of the salt, we don't have to do it but at 30 to 50$/g for fissile content these days that is upwards of 175$ million dollars we could easily recover. If you assume the initial fissile is recovered, then you need 34 tonnes ore per year averaged over the 30 year life. Ore is 85% uranium so the value is actually about 29 tonnes nat U per year (again at 0.75 capacity factor, I'm sure we can easily get that above 0.9 though which would raise those numbers).

I think any new reactor needs to have a lifetime of more than 30 years. We can stretch the graphite to more years by making them bigger or just accept the fact that every 10, 20 or 30 years etc we shut down and replace graphite (I've also been working on pebbles for the graphite which makes this almost trivial but there are lots of issues with pebble beds, it is looking good though and these systems were surprizingly well studed at ORNL). Anyhow, it is pretty obvious to me that we'd want to change the salt now and then too, if you simply do this a little more frequently (say every 15 years) the average conversion ratio goes way up and your annual uranium needs drop (easily to 20 tonnes uranium per year). Changing the salt means fluorinating out the Uranium (easy) and likely also processing out 99.99% of the transuranics to also put back into the next salt (much harder, not economically needed but the right thing to do). The salt with all the soluble fission products can then be processed to whatever degree is felt necessary to prepare the fission products for medium term disposal (i.e. 500 years, not 100,000). You'd also want to recover the carrier salt but that is only an economic question, nothing more. Same thing for the 100 tonnes or so of thorium in the salt, we don't need to recover it but nice if we do.

David L.


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 Post subject: Re: Thorium production
PostPosted: Jun 05, 2009 3:31 pm 
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David wrote:

In the 1800 tonne ore for 22GWeyear (30 years at 0.75 capacity factor) about half of that is just for the initial startup load of LEU. You can recover the same amount of fissile uranium at the end of the 30 years by a simple fluorination of the salt, we don't have to do it but at 30 to 50$/g for fissile content these days that is upwards of 175$ million dollars we could easily recover. If you assume the initial fissile is recovered, then you need 34 tonnes ore per year averaged over the 30 year life. Ore is 85% uranium so the value is actually about 29 tonnes nat U per year (again at 0.75 capacity factor, I'm sure we can easily get that above 0.9 though which would raise those numbers).


I doubt a lot at Ornl they have considered the difference between natural uranium weight and heavy metal weight fraction in NU (if I rightly understand what you mean), anyway...

Instead, I have an thought about your post
What about the transuranics production for GWyear in a DMSR?

I mean, given the fact that many countries don't have enough TRU to start a large fleet of MSR breeders and considering the superiority (at least for many of you) of moderator free, epithermal spectrum MSR version (because it avoids irradiated graphite/heavy water (***) waste at the end of the life and allow the use of both neutron economy poorer, cleaner and more economic salts, achieving at the same time break even breeding), it could be wise as intermediate solution to use low enriched uranium in DMSR while waiting for a total switch to thorium breeders, building up meanwhile as much TRUs as possible for future "pure" thorium breeders. Has it any sense or the TRU production in DMSRs is anyway too low ?


(***) I understand that, unfortunately, it's pratically impossible to avoid graphite use at least in DMSRs, due to the presence of uranium


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 Post subject: Re: Thorium production
PostPosted: Jun 06, 2009 1:37 am 
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Alex P wrote:
Has it any sense or the TRU production in DMSRs is anyway too low ?


80+% of people in all the EU countries claim the "nuclear waste issue" has to be addressed now, rather than left over to future generations. To get the nuclear off the grounds with politicians, this issue therefore has to be addressed...


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 Post subject: Re: Thorium production
PostPosted: Jun 06, 2009 10:36 am 
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ondrejch wrote:
Alex P wrote:
Has it any sense or the TRU production in DMSRs is anyway too low ?


80+% of people in all the EU countries claim the "nuclear waste issue" has to be addressed now, rather than left over to future generations. To get the nuclear off the grounds with politicians, this issue therefore has to be addressed...



I also suspect that the TRU production from a DMSR is too low to start up new thorium breeders


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 Post subject: Re: Thorium production
PostPosted: Jun 06, 2009 12:26 pm 
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TRU production from a DMSR is part of its normal way to generate its own fuel to achieve a high conversion.
There were a variety of designs. The strongest non-proliferation design did not include a full chemical processing plant - it did include He bubbling and noble metal extraction. In such a design the reactor did not break even but had to be fed a continual stream of fissile (much lower than an LWR). At the end of 30 years one could refresh the salt and keep going (with new graphite etc) but there wasn't sufficient fissile TRU or uranium to start multiple similar reactors.


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 Post subject: Re: Thorium production
PostPosted: Jun 06, 2009 2:25 pm 
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When you all say that DMSR didn' t include a processing plant, you mean only the fuel (uranium + thorium + actinides), not the fission or the activation products, otherwise I don' t undserstand how safety is assured, in case of loss of coolant/fuel accident, if the FPs are not extracted from the reactor (maybe the TRUs are not so dangerous...)


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 Post subject: Re: Thorium production
PostPosted: Jun 06, 2009 3:21 pm 
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Alex,

The key nuclide relating to safety is Xe-135 as it has a huge cross-section and can fairly rapidly (8 hours) change the reactivity of the core. This is removed by He bubbling.

Here is a summary of what I understand about the fuel processing (corrections welcomed). About 20% of the fission products are removed by He bubbling, another 40% by noble metal extraction. Most of the last 40% are removed by the liquid metal exchange system. If you want to get only clean salt then you need to use the vacuum distilling method.

The fission products pose issues for a couple of reasons:
1) they give off decay heat that we can not turn off, we must make provision for removing this heat under any circumstance
2) they give off serious radioactivity - this is actually key to anti-proliferation - but it also requires extreme safety mindedness in the design and operation of the plant.

There is no additional safety concerns with the DMSR compared to other LFTR designs that I can think of.


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