IFR FaD Nuclear

The IFR vs the LFTR: An Exchange of Emails

With regards to Generation IV nuclear fission technology, most of the attention on BNC has been on the Integral Fast Reactor (IFR), for reasons explained in this post, which I quote:

The focus of this series (IFR FaD) is aimed squarely at the Integral Fast Reactor (IFR) rather than other Gen IV designs, such as the Liquid Fluoride Thorium Reactor (LFTR) or Advanced High Temperature Reactor (AHTR). The reason for this is two fold: (i) I’m more familiar with the IFR technology (and I am in regular email exchange with the world experts on this technology, via SCGI and other links), and (ii) LFTR has a strong and welcoming advocacy group elsewhere, and I’d encourage people to go there to ask more questions about that technology … However, I should make it quite clear that I’m not “for IFR and against LFTR” — both 4th generation nuclear designs hold great appeal to me, and I will sometimes consider IFR vs LFTR comparisons in the IFR FaD series, as a point of comparison or contrast.

I think we need to be pursuing the final stages of research, development and commercial-scale deployment of all of these next-generation fission technologies, since it would require such a trivial input compared to the huge investment that will be required anyway in energy infrastructure over the next few decades (>$26 trillion globally by 2030). However, it is nevertheless useful to consider the relative merits of the individual technologies, and I hope to look at this from a number of angles in blog posts during 2012.

For some initial ideas and to initiate discussion, below I reproduce an email exchange on this matter, including aspects of commercial readiness,  that was recently posted on the Science Council for Global Initiatives website. The conversation is from three highly experienced nuclear physicists/engineers, Dr George Stanford, Dr Dan Meneley, and Prof. Per Peterson. I’m sure this will stir some debate! (And, as I said, I will have more to post on this in the new year).

I have also added a few hyperlinks to clarify terms that may be unfamiliar to the general reader; please note that the links and pictures were added by me (Barry Brook), not the original correspondents.


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 plutonium (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:


Your assessment on the relative technical maturity of LFTR versus IFR is correct.

But there are other substantive technical differences besides the lower fissile start up requirement for thorium reactors.

Thorium reactors operate in with a thermal spectrum, which allows them to use graphite as the primary structural material in the reactor core.  Graphite can be heated to very high temperatures without losing structural integrity. Combined with the very high boiling temperature of the fluoride-salt coolant (> 1400°C), thorium reactors can deliver heat at substantially higher temperature (between 600 and 700°C with current primary pressure boundary structural materials) than IFR (between 370 and 510°C with current fuel cladding materials).  This is a sufficiently higher temperature that several options exist for gas-Brayton power conversion, while at the IFR temperatures steam Rankine is likely to remain the most practical option.

There are a number of substantive theoretical advantages to gas Brayton power conversion (this is the reason Brayton cycles are now used universally with natural gas), but essentially all of the existing turbine and compressor technologies optimized to open combustion cycles and thus substantive development is needed to adapt it to nuclear power conversion.  Once successfully developed, though, one would expect substantial commercial pressure to move from steam Rankine to gas Brayton cycles as the dominant approach for nuclear power conversion (as has already happened with natural gas).

The other major differences arise from the different thermophysical properties of the two coolants.  The fluoride salts have volumetric heat capacity slightly larger than water and about 4.5 time larger than sodium.  So the primary systems for thorium reactors are physically much smaller than for IFRs, or alternatively, a primary system of the same physical size can produce substantially more power (factor of a 2 to 4).  Thorium reactors have no sources of stored energy that can pressurize containment, so they also can use a compact, low-pressure containment structure and thus a correspondingly smaller reactor building.

These are substantive technical differences that are likely to affect the relative levelized cost of electricity (LCOE) produced by the two systems.   But one of the major issues with LFTR is that one must overcome multiple, substantive technology development problems simultaneously (gas-Brayton power conversion, qualification of materials for corrosion resistance, on-line fuel processing, licensing for fluid-fuel reactors). This creates a significant activation energy problem, even if the final LFTR technology would have desirable LCOE and sustainability characteristics.    One of the reasons that we’ve been working on solid-fuel variants at UC Berkeley is to see if one can reduce the activation energy barrier by capturing most of the LCOE benefits (which come primarily from improved power conversion efficiency and reduced capital cost relative to advanced light water reactors [ALWRs]) while keeping the licensing approach much closer to that used for passive ALWRs and not taking on the technical issues for fluid fuel.

In the end, LCOE will be a dominant consideration in commercial decisions to deploy nuclear power. In the near term the best opportunities involve further improvement to ALWR technology and construction methods (with AP-1000 providing the best role model to date).  In the longer term some mix of uranium fast spectrum and thorium thermal spectrum reactors is likely to emerge as optimal.

-Per F. Peterson 11/29/10

G. Stanford wrote:


Thanks much for the additional information, clarifying the technical challenges and strengthening the case that thorium power is worth pursuing and might well have an important role down the line.

While the LCOE will undoubtedly be an important consideration, it seems to me that breeding potential also is destined to be important if we are to have abundant clean energy.  It also seems likely that thermal efficiency per se will not ba a major issue, in view of the very low cost of fuel for breeders (or “isobreeders” like the LFTR) — but you point out that the Brayton cycle potentially offers significant additional advantages.

I gather that you do not take issue with the proposition that it would behoove us now to complete the development of what is currently closest to commercial readiness with the characteristics needed for an assured indigenous energy supply — namely LMFBRs with metallic fuel and pyroprocessing.  At present, that appears to be a U.S.-developed technology that we have abandoned, bequeathing it to other countries for exploitation.


—  George S. Stanford 11-29-10

P. Peterson wrote:


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 next-generation nuclear plant (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

George Stanford wrote:


Thanks for the further elucidation.

To get quantitative about LFTRs, suppose the world were to want 50,000 GWe of isobreeding LFTRs by 2100, primed with 10% EU at 1 tonne of U-235 per GWe.  That U-235 would be contained in 10 tonnes of EU, which would come from ~200 tonnes of Unat.  Thus the amount of uranium to be mined would be ~ 50,000 x 200 = 10 million tonnes of Unat — which is well within the realm of the possible.

However, a downside would be the perpetuation and global expansion of uranium enrichment infrastructure, with its proliferation implications.  Also, left over would be some 9.5 million tonnes of orphaned depleted uranium containing 9.5 million GWe-years of unavailable (and unwanted) energy.

—  George S. Stanford 11/30/10

CANDU reactors in Qinshan, China

D. Meneley wrote:

George, Per:

You guys seem to be intent to ignore the only fully developed, in service, economically competitive, high conversion ratio, and safe medium size reactor system on earth [namely, the CANDU-type heavy-water reactor]. Perhaps you could explain why.

Dan Meneley 11/30/10

G. Stanford wrote:


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

By Barry Brook

Barry Brook is an ARC Laureate Fellow and Chair of Environmental Sustainability at the University of Tasmania. He researches global change, ecology and energy.

137 replies on “The IFR vs the LFTR: An Exchange of Emails”

Yes Alex, safety is a state of mind. Apparently, objective evaluation of relative risk of optional technologies does not operate in the same world as does the “gut feel” of the people who vote.

In this world of political correctness some words are said to be inherently “bad” and are, therefore, to be avoided along with the engineering options that are described by them. You show a partial list, in your latest message. But who chooses these bad words? As the famous Humpty Dumpty advised Alice (in Wonderland), “The question is, “Who is to be master?”

By all means, we should proceed “post haste” to develop these new nuclear generation technologies. But it is also true that this is not happening in the so-called Western Democracies. Even the fundamental, life-saving task is faltering. We are not building a few hundred power plants to replace the fading fossil-fuelled supplies, and must face the consequences.

But this does not matter much. Korea, China, India and Russia are carrying on. Even Japan might get back in the race after they finish (unnecessarily) digging up a broad swath of topsoil and burying it somewhere else. Some day Westerners just might notice the real progress of those countries, and run to catch up.


Reposted from Open thread 19:

I’ve just returned from the Thorium Symposium held at Parliament House yesterday and today. There was a lot of material covered, and i’ll get to work soon writing up an article putting my perspective on the event. For now, a few points which may be of interest to people here:

When Martin Ferguson introduced the symposium, a couple of things he said stuck in my mind. First, there was a strong indication that Labor’s anti-nuclear stance was not exactly etched in stone, but he made a firm statement that nuclear power is not competitive with La Trobe coal. I suspect there could be more than one opinion on this, but he certainly presented that view as being solidly held.

Martin Hoffman (Deputy Secretary at the Dept. of Resources, energy and Tourism, Martin Ferguson’s dept.) affirmed the government line, but gave plenty of hints that trhere were some inconsistencies here and there. He also was quite careful to point out that residential electricity consumption only accounted for 7% of energy consumed in Australia not long before explaining some things about residential demand management and the potential of smart grids. His talk was quite wide ranging and deserving of close attention.

Dr. Adrian (Adi) Patterson, CEO of ANSTO, offered a great and insightful summary of the current state of play of thorium, MSRs, various other nuclear technologies, and ANSTO’s involvement with them. I had the opportunity to ask him if consideration had been given to the application of synrock technology to the storage of the high-level fission products produced by thorium breeder MSRs. I’m pleased to report that some consideration has been given to this issue by ANSTO, and there do not appear to be any obvious show stoppers.

For some reason, many attendees are enamoured of the potential of subcritical ADS systems.

There was much more, of course. I shall look at my notes over the weekend. We are also told that the presentations will be made available on their website in about a week.


This forum of comments regarding IFR vs LFTR has been most enjoyable, and I thank all of the participants for their thoughtful contributions.

Back in the United States, I am trying to raise awareness about our energy challenge and some of the most promising solutions. I am particularly looking at what is possible to accomplish using past projects like the Space Race and the Manhattan Project as inspiration for the Thorium Race. The pessimism regarding our situation is as well-founded as the optimism, and it will take a considerable social effort to bring about the change of thought necessary to transition to a sustainable existence.

I am emphasizing several points above all others as priorities for an effective solution:

– Inherent safety features: the safer the plant, the easier it will be to sell to the communities and businesses that will buy them- lower insurance and public resistance. This is critical for a high-deployment technology. The issue isn’t whether current technologies can be made safe- remember, we are trying to expand applicability and public acceptance while lowering costs.
– Small, automated and affordable plants- plant cost is a primary contributor to the expense of its products.
– High operating temperatures to allow for more efficient chemical synthesis and air cooling. Improving cogeneration significantly reduces the number of plants necessary to serve any particular industry, like NH3 synthesis for transportation. Air cooling reduces the dependence upon scarce water supplies, removing one source of costs and conflicts with local communities.
– The right technology for long-term development, diversification, standardization, and mass production. The technology is better if it can have multiple uses which improves rapidly with time. We want these things to end up in cement factories as well as container ships.
– Scalability- we need to be able to build many of these machines quickly. Small fissile requirements for startup is essential.
– The lack of significant emissions. (Of course!)
– A superior waste profile with a simpler fuel cycle.

I am not deterred by bureaucratic or industry inertia. We have very particular technical needs, and if the public has to be roused to put the country on a sane course of action, so be it. Economic competitiveness with China is also a factor here, so having an efficient carbon-free infrastructure is a national security imperative.

A rich nuclear economy will have a variety of needs from electricity generation, waste processing, breeding, etc. and I am not stuck on only one approach or technology, but I do need to have something to sell to garner public support, and LFTR is easy to sell as Green Nuclear, the key to a sustainable future.


[…] I would argue not, because in its environmentalist (not fundamentalist) form, a nuclear-friendly advocacy does not seem to meet any of the criteria Martin outlines above for religiosity. In this ‘doctrine’, no energy source is demonised — the argument is instead that all energy sources ought to be weighed fairly on their merits and demerits, on the basis of irreligious laws of nature (and market forces!). Gurus are lacking, at least those dedicated to the creed. Nor are there obvious counterpart advocacy institutions (or perhaps we count the WNA and or bibles (see Loftus et al. 2014 for a review of such global decarbonisation scenarios). But we do definitely have our denominations and bellum sacrum – witness the fast reactor vs thorium schism! […]


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