Saturday, September 25, 2010

Why the LFTR is Still Needed

A new MiT report, The Future of the Nuclear Fuel Cycle, argues that
Uranium supplies will not limit the expansion of nuclear power in the US or around the world for the foreseeable futurer . . .
This should quiet the anti-nuclear power camp on that particular issue, but it won/t. Critics of nuclear power have a tin ear when it comes to evidence. Any evidence that discredits their position simply does not exist, in their minds, and thus they will discount the MiT Report, and continue to tell us that we are running out of uranium.

If we are not running out of uranium is their any justification for the LFTR, a reactor that operates on an alternative - Thorium - fuel cycle? The answer is that there are several good reasons for adopting LFTR technology, even though there may be a large supply of accessible uranium.

One major reason for choosing the LFTR is that it invites far lower fuel cycle related capital investments. If the future reactor fleet is to be entirely uranium fueled, very large capital investments will have to go into uranium mines, processing facilities, enrichment facilities, and spent fuel management. in addition all of these facilities have significant operation costs attached.

Now consider fuel related the capital costs associated with a fluoride salt thorium reactor deployment compared to that of a massive deployment of uranium fueled molten salt reactors. First thorium is a bye product of rare earth mining, and with increasing rare earth use in the economy, more and more thorium will be coming out of the ground anyway. Thus, unlike uranium which is often mined in costly uranium only mines, thorium basically comes out of the earth at no added cost, from mines that would exist whether or not we wanted to recover thorium.

Secondly, while the milling expenses for thorium and uranium would probably be similar, 200 times more uranium would have to be milled, because uranium reactors operate on a once through fuel cycle reactors, which consumes less than 0.5% of the milled uranium, while nearly 100% of the milled thorium will be consumed in closed fuel cycle LFTR.

Secondly, the uranium must be enriched, and this involves another costly, energy intense process. With thorium the enrichment process can be skipped. Following enrichment uranium oxide must be prepared fabricated into reactor fuel pellets. in contrast thorium would be prepared for reactor use by fluoridation, a simple, inexpensive and well understood chemical process. At that point the thorium would be inserted into a reactor blanket where it would be bombarded with neutrons. After thorium absorbs a neutron it is transformed into protactinium 233, which will be separated from the blanket salts by fluoride chemical processes, that will be performed by processing equipment that is directly attached to the reactor. Then the p
rotactinium is stored for a few months, while it undergoes nuclear transformation to fissionable U-233. Once that occurs, the U-233 is automatically inserted into the reactor core by another reactor mechanism. All of these processes are low cost.

The advantage of the Thorium Fuel cycle LFTR is that it requires a fuel infrastructure that is 200 times smaller than a fleet of once through uranium cycle reactors would require. The added cost of the uranium infrastructure is not the primary problem. Rather it is the enormous task of building the infrastructure. The LFTR will require a large infra structure as well, but the infrastructure that will be required to keep LFTRs fueled will be tiny compared to that of a once through uranium fueled reactor fleet.

If we draw the comparison between LFTRs and LWRs, even more U-235 has to be prepared per GWh of power delivered. LWRs waste about 17% of the U-235 that goes into the core, as well as an even larger percentage of the plutonium created in the core. These inefficiencies mean that more U-235 has to be produced relative to the fuel requirements of LFTRs.

LFTRs produce little or no nuclear waste, and indeed can be significant consumers of actinides, which are the most troubling components of LWR nuclear waste. LFTR waste products reach benign levels of radioactivity after 300 years, but many useful and valuable fission products become safe after a few years, and can be mined from the fission product stream for use in industry. Long half life fission products have uses in medicine, and industry. Thus the fission products from LFTRs can be viewed as material resources rather than nuclear waste.

Although Fast Breeder Reactors share many of the advantages of the LFTR, they are likely to be considerably more expensive to build and deploy in large numbers. In addition, FBRs require 10 times the fissile inventory of LFTRs or even more, thus limiting the size of the initial deployment of FBRs. FBR advocates argue that the higher breeding ratio of the FBR will make up for the disadvantage. But it will take time to breed up to the size of an initial LFTR deployment. Supplementing the FBR start up stock with freshly separated U-235 would require the same sort of uranium mining, processing and seperating facilities that would be required by a uranium fueled reactor deployment. Using the nuclear fuel inventory in existing LWR waste stockpiles, more than enough LFTRs could be started to provide 100% of American electricity. If the LFTRs simply replaced the fuel they consumed through nuclear breeding, no further reactors would only be required except to meet added electrical demand.

The LFTR offers both lower cost and significant deployment advantages over the FBR.

Thus the LFTR offers economic and deployment advantages over any of its competitors including Light Water Reactors, Uranium fueled Molten Salt Reactors, and fast breeder reactors. It would be far cheaper to invest in LFTR development and deployment than to build the new uranium mines, mills, isotope separation and fuel fabrications facilities that would be needed to support a uranium fueled reactor deployment. Clearly then even given adequate uranium supplies, the LFTR continues to offer significant advantages for a large scale nuclear deployment.


13 comments:

Martin Burkle said...

Since nuclear reactor operating costs are already low and the fuel costs are part of the operating cost, a lowering of the fuel cost does not seem to me to be very important. The story about lower construction costs and shorter, more certain construction time should be the main theme.
The 3rd 10 meter ring of the Sanmen AP1000 was lowered into place. It is about 2 inches thick. Sanmen is now about 30 meters tall. Would a LFTR need a 2 inch thick containment vessel and the world's largest crane to lower it into place?

Colin Megson said...

Charles,

I greatly appreciate you covering my 'Answer to our energy problems' letter. I'm trying to stir up debate over here in the UK and I've already been contacted as a result of your efforts.

I've just made the first couple of posts on my brand new Blog: http://lftrsuk.blogspot.com/ Would you be kind enough to link to it, to help me get in touch with the wider UK audience?

Great work you're doing! I'm sure we're more than half way up the hill on this one.

Regards, Colin.

LarryD said...

"... thorium basically comes out of the earth at no added cost, from mines that would exist whether or not we wanted to recover thorium."

Well, it's not quite that simple. One one hand, the thorium will have to be extracted from the ore, on the other hand, I believe this would render the tailings non-radioactive, which should reduce costs. Hard to tell how that works out in advance, before the fuel value of the thorium is factored in.

"...200 times more uranium would have to be milled, because uranium reactors operate on a once through fuel cycle reactors ..."

But it's not fair to compare the LWR fuel cycle to the LFTR, when the MSR design can use uranium too.

I would expect to see a transition period, starting with MSRs using SNF, switching to depleted uranium and then to thorium as the thorium infrastructure is developed. It's not like we don't have a lot of SNF on hand, and disposing of it is an issue. Also remediation of comtaminated water will produce some uranium, which should become part of the fuel stock.

Anonymous said...

I just a bit confused Charles. By your term "uranium fueled molten salt reactors" do you mean the work on salt cooled, solid fueled of Berkeley and current ORNL work or do you mean the DMSR approach of Oak Ridge circa 1980 (or both?). The DMSR approach that consumes a mix of thorium and low enriched uranium certainly wouldn't need any sort of massive increase in mining or enrichment since it needs only a small fraction the uranium of a Light Water Reactor. In fact you could have about 2500 GWe of DMSRs running on current mining and enrichment facilities.

Otherwise I agree with your point, building either LFTR (pure Th-U233 break even MSRs) or DMSRs (Denatured converters without fuel processing) is a whole lot easier than the infrastructure needed to support thousands of new LWRs.

David LeBlanc

P.S. Charles, say it isn't so! You think a Two Fluid LFTR should have protactinium removal as well? It adds a huge amount of chemical processing and adds significant proliferation problems all for saving a small number of neutrons. I know ORNL proposed it for their Two Fluid version in the 1960s but I'm sure it was only because their funding was so dependent on keeping up to the doubling times of sodium fast breeder. The whole idea of Two Fluid is to simplify salt processing. Pa removal has to process the entire blanket salt every few days with a more difficult processing method than needed to get rid the fuel salt of fission products (which only need removal on a few months timescale).

Bill Hannahan said...

I think David has it right. For a PWR the uranium cost is about 1/3 cent per kWh. For the simplest uranium burning MSR it is about 1/15 cent per kWh. For a breeder it is approximately zero. The potential savings with a breeder is tiny but the potential downside is much larger due to the added complexity of the breeder system. Longer R&D time, longer licensing time, longer time to build mass production factories, longer time to build each plant. The cost of each of these steps will go up due to the additional time and complexity with a breeder. The added complexity also means higher potential for an undetected design error in the R&D phase that could bite hard later on.

The initial cost of kWh's from a breeder will be higher than those from a simple DMSR, and the key to a fast transition is making kWh's that are cheaper than burning fossil fuel; the cheaper the better.

In 100-300 years the breeder might make cheaper kWh's than the simplest MSR, but for now we should focus on building the Model T of MSR’s and leave the GT-40 for later.

Charles Barton said...

My view is that the LFTR can be deployed faster, because it would not require a huge and time consuming buildup in uranium processing technology. One of the advantages of the 2 fluid core is the ability to extract U-233 or protactinium when you choose too.

The LFTR does have a significant political advantage over a U-235 uranium fuel cycle MSR, unless you believe that public discomfort with nuclear waste is going to disappear overnight. I don't.

Utilities will also covet that fraction of a cent per kWh that the LFTR will save. It will add up to billions of dollars a year going to the bottom line.

Anonymous said...

Charles said:

The LFTR does have a significant political advantage over a U-235 uranium fuel cycle MSR, unless you believe that public discomfort with nuclear waste is going to disappear overnight. I don't.

Please remember Charles, a uranium and thorium burning MSR converter design (i.e. the DMSR) has just as good (actually slightly better) a waste profile as the pure cycle.

Once a batch of salt is finished in a DMSR (10 to 30 years) we would likely want to pay for a one time only removal and recycle of all the actinides (with 10 to 30 years of revenue to help pay). If this is done (a nation's choice) then the waste stream is as good or better than a pure Th-U233 LFTR.

We typically assume a tiny bit of loss in any chemical process (0.1% is typical) for the DMSR we have to process 3 to 10 times as much actinides out of the salt BUT we only do it one time every 10 to 30 years as opposed to needing to do so every 10 days to a year in the pure cycle.

In fact, in a DMSR we could likely have spare neutrons to help transmute some of the few long lived fission products (at the price of some extra annual uranium). A pure cycle typically doesn't have this ability and still break even on breeding.

I am not against the pure Th-U233 cycle but the DMSR is looking more and more attractive the more we study it. It might be a first step or maybe all we'll need.

David LeBlanc

Kirk Sorensen said...

David, could you please tell me what depletion code(s) you are using to arrive at these conclusions? My modeling has not reached that level of fidelity.

Anonymous said...

The simplest answer Kirk is we could just talk like the IFR folks and say that as long as we are removing and recycling the actinides then the only waste is fission products and everyone is the same. However, as you might know they had the goal of 0.1% loss of higher actinides. Even if they could reach that (by throwing a lot more R&D money at the process since they never reached that goal) they would still have a modest amount of transuranic waste because you have to process so much Pu etc in a IFR. I.e. 0.1% of several tonnes a year is several kg a year (per GWe). Great compared to about 250 kg per year from a PWR once through but room for improvement.

Getting back to a DMSR (that processes at the end of each batch) versus the pure Th-U233 cycle they are both amazing. The standard DMSR design of ORNL would have a little under 1000 kg of transuranics (Np,Pu,Am,Cm)in the salt after 30 years (ORNL TM 2707). If you process to recover and recycle the TRUs and lose 0.1% this is just 1 kg in 30 years or tens of grams per GWe year.

A pure Th-U233 that also doesn't want to throw away TRUs means you keep recovering and recycling them each time you process the salt to remove fission products. In this case they actually do build up to significant levels. From French studies (Ph.d of either Mathieu or Nuttin) when they still examined a wide range of graphite fractions it was 89 kg for a really thermalized (more thermal than MSBR) to 395 kg for a more epithermal case to 427 kg for graphite free (table 7.3 of Mathieu). For their two graphite cases, they could push things to a max of 3 to 6 months between processing. I often assume a 200 kg TRU load and 6 months processing time. If 0.1% slip out with the fission products this is 400 grams per GWe year. Still amazingly low but I stand by my statement that DMSR can also be so great.

Now if you want to split hairs we get back to a discussion of how much uranium might slip out to waste in either system (U238 is of no concern, U233, U234 and U236 more so). In order to recycle all those uranium isotopes in a DMSR we might have to send the used uranium off to be re-enriched to throw out some of the harmless U238 (in order to get it more reactive again). This is only a tiny bit of SWU work so you just make sure the U238 tails are a very low percentage (i.e. almost pure U238) so virtually no U233 or U234 goes with it. I know you mentioned that with any U232 present, enrichment plants might not like it but in discussions with Per Peterson and Jess Gehin they didn't think it would be too much an issue (it goes through the centrifuges so quickly that nasty daughter products don't really have time to form).

Anyhow, most of this has been discussed on your website as well. My main focus is just trying to show that any molten salt reactor can be great for reducing long lived wastes and not to assume that just because U238 is present that this somehow automatically means more transuranics to worry about in the wastes.

David LeBlanc

Anonymous said...

I just gave a long response for Kirk that might have been lost as I seemed to get an error message for length. If I don't see it appear, I'll rewrite it (arrggg). If it does appear, ignore this message Charles.

David LeBlanc

Charles Barton said...

David, Nuclear Green will always be open for a guest post from you whether or not our views agree. If you are interested, I can set it up.

Anonymous said...

Thanks Charles, that is probably a good idea.

I'll try to answer Kirk's question more briefly. The modeling I use is Oak Ridge's original DMSR study and often the extensive recent work of the French group.

Again, I am just trying to say that a DSMR design can be also amazing at having almost no long lived waste, just like a pure Th-U233 cycle. When the DMSR was designed, they had little concern of sending some transuranics to waste so didn't consider recovering it when the batch of salt was finished after 30 years. The salt would have a little under 1000 kg of TRUs (Transuranics=Np,Pu,Am,Cm). If one assumes a traditional 0.1% loss this is only 1 kg for 30 years operation or a few tens of grams per GWe year.

For systems that try to break even on the Th-U233 chain and also not throw out TRUs then they also build up to appreciable levels. From the Ph.d of L. Mathieu (table 7.3) when they were still looking into a variety of spectrums with graphite, the TRUs build up to between 89 and 427 kg for a GWe plant (very thermal to hard epithermal). To break even you'd need to process this salt at least every 6 months. So the best case is 0.1% of 89x2kg is under a couple hundred grams per GWe year.

More in a next post...

David LeBlanc

Anonymous said...

Just to continue, the other actinide that needs to be recycled is the uranium content. U238 is no worry but the lower isotopes U233, U234, U236 and U235 (in that order of importance) should be recycled.

This step is the easiest as uranium is the easiest to remove. It can then be recycled in the next batch of salt (or next reactor) like the TRUs. There is some debate whether it would be a little weak (not enough fissile) to just put back into the DMSR core. If so, there are numerous solutions. The basic idea is to send it to be re-enriched which basically is like throwing away U238. It would take very little enrichment work (SWU) to do this so we can run the tails very low (i.e. almost pure U238). Some might say that any U232 present might make that very hard. From the people I've asked this (Per Peterson and Jess Gehin) they thought it wouldn't be a major problem since it goes through the centrifuges so quickly. I have another plan but to be brief (and a little secretive for a change) I'll keep it to myself for now.

So again, I love both the pure Th-U233 approach and the DMSR typically mostly burns thorium but with the help of uranium. I am just trying to help dispel some of the misconceptions of this approach.

David LeBlanc

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