The IFR vs the LFTR: An Exchange of Emails

George S. Stanford, Per F. Peterson and Dan Meneley

G. Stanford wrote (11-29-10):

We'll see what others on this list have to say, but in my opinion, Carlsen's enthusiasm for thorium is premature, to say the least.  The ONLY significant advantage a thorium cycle would have over fast reactors with metallic fuel (IFR/PRISM) is its lower requirement for start up fissile.  That advantage is offset by the fact that the thorium reactor is at a stage of development roughly equivalent to where the IFR was in 1975 -- a promising idea with a lot of R&D needed to before it's ready for a commercial demonstration -- which puts its deployment about 20 years behind what could be the IFR's schedule.  The thorium community has not yet even agreed on what will be the optimum thorium technology to pursue.

I think that thorium should indeed be investigated as a possible future competitor for the IFR.   But what would be gained by putting off demonstrating the IFR/PRISM technology while waiting to see if thorium really lives up to its promise?  Nothing would be lost by getting a fleet of IFRs up and running.  They could be breeding fissile for decades while a possible thorium fleet gets up and running, and the IFR-bred fissile -- several times more than was started with -- could be used for expanding the hypothetical thorium fleet at the end of the IFRs' lifetimes.

If the current perceived urgency is to sequester plutonium to put it out of the reach of proliferators, that can be done much faster with early deployment of IFRs rather than by later deployment of thorium reactors -- and each IFR will sequester 8 - 10 times as much Pu per GWe as a thorium reactor.

-- George S. Stanford 11-29-10

 D. Meneley wrote:

On the matter of thorium, George and others have repeated a . . . realistic picture.

[Boosting thorium] will do no good. This is another idealist's dream, like large scale wind energy. They only want to save the world and are not interested in practical details.

If you've tried to do control, fuel cycle, and safety system design on a thorium reactor you'll not be so enthusiastic. The flux shape is a strong function of the past flux shape -- because of the protactinium. After you shut the thing down you must account for the later reactivity increase. And then there's the detail of not having any fissile isotope to start up in the first place.

If you're using thoria fuel, how are you going to extract the U233 economically?

And so on.

Thorium if absolutely necessary, but absolutely no thorium if not necessary.

--Dan Meneley 11/27/10

P. Peterson wrote:

George,

For LFTRs, the breeding potential may not be particularly important, as long as they can achieve isobreeding.  Uranium from seawater provides a backstop technology that sets the maximum cost of fissile material, much as coal-to-liquids provides a backstop for the cost of oil (absent a price on carbon dioxide emissions).  The startup of an isobreeding LFTR requires about 1/4 to 1/2 the fissile needed to start up an LWR, and uranium from seawater will have a cost around 4 times greater than current uranium prices.  Thus the capital cost for the fissile to start up isobreeding LFTRs will be comparable to the current cost for the initial core loading for LWRs, which constitutes a modest fraction of the total capital cost of current LWRs.

Our experience to date is that "backstop" energy technologies never emerge to be economically competitive, because lower cost alternatives tend to be developed instead (at the scale that we use energy, the economic incentives are very large).

So I would be very surprised that the cost of fissile will ever rise to the point where one would actually begin commercial efforts to recover uranium from seawater (although there is always some slim probability that the government might in the future enact a "seawater uranium portfolio standard," to create an assured market for seawater uranium, so the technology will be brought to commercial readiness regardless of cost).  Absent such government intervention, the cost of fissile to start up LFTRs will likely remain lower than the cost of fissile to start up current LWRs, in perpetuity.

My expectation is that the LCOE for electricity from ALWRs will drop well below the LCOE for new pulverized coal plants before the end of this decade, as Westinghouse's costs to build AP-1000's and enhancements to the AP-1000 drop and as competing LWR technologies for the AP-1000 emerge, and as construction methods improve further. Financing nuclear construction will likely remain a challenge, although SMRs may prove to be helpful in this respect.

But we need an aggressive effort to develop multiple technologies that can improve upon and ultimately replace ALWRs.  Fast-spectrum reactors clearly have advantages, along with thorium cycles, from the perspective of fuel cycle.  IFR metal fuels are vastly better than conventional oxide fuels from the perspective of affordable and secure fuel recycle. LFTR is also a potentially attractive technology, but clearly has substantial technology risk.  So yes, I strongly support demonstration of IFR technology.  The key issue is that IFR needs to remain a part of a portfolio of technologies the federal government invests in, and that IFR demonstration needs to sustain discipline to assure that federal investment is likely to result in commercial success

A simple type of evidence, which Congress has required for the NGNP project, would be 50% cost sharing by commercial interests.    I think that this approach is too simplistic, since it does not recognize how risk changes during design, licensing, and construction of a demonstration reactor.  The best approach is to require very small or zero commercial investment at the stage of conceptual design and NRC pre-application review, moderate commercial investment during detailed engineering and NRC licensing, and substantive commercial investment for the construction of a prototype unit (where the intellectual property and up-side commercial potential ends up being owned by the commercial entities who invest).

This sort of decision framework is also easier to implement in statute, since one can authorize the needed expenditures, but the actual appropriations can depend upon progress being made and commercial investment materializing.

What commercial interests will tell you is that it is much easier to make a decision to make a substantial investment if they have an NRC construction license to build a reactor, while it is almost impossible if the reactor is just a concept that needs a lot of detailed engineering work.  But in the end, the commercial entities that perform this reactor development work are also in the best position to assess its commercial potential--so a lack of willingness to place some commercial money at risk (less earlier and more later) should be viewed as evidence that the concept needs more R&D, not accelerated demonstration.

For IFR, though, the availability of affordable fuel is a big issue.  It requires the capacity to recycle used LWR and IFR fuel, as well as to test and qualify recycled fuels for use in IFRs.  This is a problem that the commercial sector is not going to be willing to take on, and thus it requires purely federal effort.

-Per F. Peterson 11/29/10

G. Stanford wrote:

Dan:

Sorry if I slighted the CANDU. It’s a fine reactor design, struggling to acquire a bigger share of the international market. To believers (like you and me) in the importance of conserving fissile material, its high conversion ratio is an important asset. But – apart from the fact that it doesn’t need enriched uranium -- to a first approximation it’s just another thermal reactor. Since most of the generalities about LWRs apply also to CANDUs, much of the time it’s convenient to use the term “LWR” as shorthand for “uranium-based thermal reactor.”

While I can’t speak for Per, of course, I suspect that he would ascribe less importance to a high conversion ratio than I do.

George S. Stanford 12/01/10