IFR FaD 11 – sodium coolant and pool design

This is the second of a four-part series of extracts from the book Plentiful Energy — The story of the Integral Fast Reactor by Chuck Till and Yoon Chang.

Reproduced with permission of the authors, these sections describe and justify some of the key design choices that went into the making the IFR a different — and highly successful — approach to fast neutron reactor technology and its associated fuel recycling.

These excerpts not only provide a fascinating insight into a truly sustainable form nuclear power; they also provide excellent reference material for refuting many of the spurious claims on the internet about IFR by people who don’t understand (or choose to wilfully misrepresent) this critically important technology. Click here for part 1 (metal fuels and plutonium).

The second extract, on coolant choice and reactor configuration, comes from pages 108-111 of Plentiful Energy. To buy the book ($18 US) and get the full story, go to Amazon or CreateSpace. (Note that the images below do not come from the book).

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The Coolant Choice

Liquid sodium was the choice of coolant from the beginnings of fast reactor development, because the neutron energies must remain high for good breeding and sodium doesn’t slow the neutrons significantly. (Water does, and so nullifies breeding.) But sodium has other highly desirable properties too—it transfers heat easily and removes heat from the fuel quickly; it has a high heat capacity which allows it to absorb significant heat without excessive temperature rise; its boiling point is far too high for it to boil at operating temperatures, and importantly, even to boil at temperatures well above operating; and finally, although a solid at room temperature, it has a low enough melting point to stay liquid at temperatures not too far above that. In addition, there is no chemical reaction at all between the sodium and the structural materials making up the core (such as steel and zirconium). It is chemically stable, stable at high temperatures, stable under irradiation, cheap, and commonly available.

Further, as a metal, sodium does not react at all with metal fuel either, so there is no fuel/coolant interaction as there is for oxide fuel exposed to sodium. In oxide fuel, if the cladding develops a breach such reactions can form reaction products which are larger in volume than the original oxide. They can continue to open the breach, expel reacted product, and could possibly block the coolant channel and lead to further problems. Metal fuel eliminates this concern.

For ease of reactor operation, sodium coolant has one supreme advantage. Liquid at room pressures, it allows the reactor to operate at atmospheric pressure. This has many advantages. Water as a coolant needs very high pressures to keep it liquid at operating temperatures. A thousand- to two-thousand-psi pressure must be maintained, depending on the reactor design. Thick-walled reactor vessels are needed to contain the reactor core with coolant at these pressures.

The diameter of the vessel must be kept as small as possible, as the wall thickness necessary increases directly with diameter. With the room-pressure operation of sodium coolant, the reactor vessel, or reactor tank as it is called, can be any diameter at all; there is no pressure to contain. And leaks of sodium, if they happen, have no pressure behind them, they drip out into the atmosphere, where generally they are noticed as a wisp of smoke. The important thing is that there is no explosive flashing to steam as there is when water at high pressure and temperature finds a leakage path.

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IFR FaD 10 – metal fuel and plutonium

Over the next month or two, I will publish four extracts from the book Plentiful Energy — The story of the Integral Fast Reactor by Chuck Till and Yoon Chang.

Reproduced with permission of the authors, these sections describe and justify some of the key design choices that went into the making the IFR a different — and highly successful — approach to fast neutron reactor technology and its associated fuel recycling.

These excerpts not only provide a fascinating insight into a truly sustainable form nuclear power; they also provide excellent reference material for refuting many of the spurious claims on the internet about IFR by people who don’t understand (or choose to wilfully misrepresent) this critically important technology.

The first extract, on Fuel Choice, comes from pages 104-108 of Plentiful Energy. To buy the book ($18 US) and get the full story, go to Amazon or CreateSpace.

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Metal Fuel

The IFR metal alloy fuel was the single most important development decision. More flows from this than from any other of the choices. It was a controversial choice, as metal fuel had been discarded worldwide in the early sixties and forgotten. Long irradiation times in the reactor are essential, particularly if reprocessing of the fuel is expensive, yet the metal fuel of the 1960s would not withstand any more than moderate irradiation. Ceramic fuel, on the other hand, would. Oxide, a ceramic fuel developed for commercial water-cooled reactors, had been adopted for breeder reactors in every breeder program in the world. It is fully developed and it remains today the de facto reference fuel type for fast reactors elsewhere in the world. It is known. Its advantages and disadvantages in a sodium-cooled fast reactor are well established. Why then was metallic fuel the choice for the IFR?

The Integral Fast Reactor (IFR) system

In reactor operation, reactor safety, fuel recycling, and waste product—indeed, in every important element of a complete fast reactor system—it seemed to us that metallic fuel allowed tangible improvement. Such improvements would lead to cost reduction and to improved economics. Apprehension that the fast reactor and its associated fuel cycle would not be economic had always clouded fast reactor development. Sharp improvements in the economics might be possible if a metal fuel could be made to behave under the temperature and radiation conditions in a fast reactor. Not just any metal fuel, but one that contained the amounts of plutonium needed for reactor operation on recycled fuel. Discoveries at Argonne suggested it might be possible.

Metal fuel allows the highest breeding of any possible fuel. High breeding means fuel supplies can be expanded easily, maintained at a constant level, or decreased at will. Metal fuel and liquid sodium, the coolant, also a metal, do not react at all. Breaches or holes in the fuel cladding, important in oxide, don’t matter greatly with metal fuel; operation can in fact continue with impunity. The mechanisms for fuel cladding failure were now understood too, and very long irradiations had become possible. Heat transfers easily too. Very little heat is stored in the fuel. (Stored heat exacerbates accidents.) Metal couldn’t be easier to fabricate: it’s simple to cast and it’s cheap. The care that must be taken and the many steps needed in oxide fuel fabrication are replaced by a very few simple steps, all amenable to robotic equipment. And spent metal fuel can be processed with much cheaper techniques. Finally, the product fuel remains highly radioactive, a poor choice for weapons in any case, and dangerous to handle except remotely.

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The nuclear fission ‘Flyer’

Below is the foreword I wrote, on invitation of Chuck Till and Yoon Chang, for the book “Plentiful Energy” (I included a shorter version in my review of the book on Amazon).

In this short essay, I draw an analogy between the IFR and the Wright brothers’ 1903 ‘ ‘Flyer’. The idea is that successful technology — especially a revolutionary design — is built on the back of many learning-by-doing failures. Yet, once the initial problems have been solved, the remaining pathway for the technology’s development is one of incremental (but often rapid) evolutionary improvements.

I suspect that with just a few more years of serious investment in RD&D, the LFTR ‘Flyer’ could also launch. The molten-salt thorium reactor concept is extremely appealing, and the ORNL prototype, which ran in the mid- to late-1960s, showed real promise. In my view the Th232-U233 fuel cycle would make an excellent complement to the U238-Pu239 fuel cycle offered by the IFR, and both reactor types hold the promise of safe and inexhaustible energy.

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Foreword to: Plentiful Energy – The book that tells the story of the Integral Fast Reactor

On a breezy December day in 1903 at Kitty Hawk, N.C., a great leap forward in the history of technology was achieved. The Wright brothers had at last overcome the troubling problems of ‘inherent instability’ and ‘wing warping’ to achieve the first powered and controlled heavier-than-air flight in human history. The Flyer was not complicated by today’s standards – little more than a flimsy glider – yet its success proved to be a landmark achievement that led to the exponential surge of innovation, development and deployment in military and commercial aviation over the 20th century and beyond.

Nonetheless, the Flyer did not suddenly and miraculously assemble from the theoretical or speculative genius of Orville and Wilbur Wright. Quite the contrary – it was built on the back of many decades of physical, engineering and even biological science, hard-won experience with balloons, gliders and models, plenty of real-world trial-and-error, and a lot of blind alleys. Bear in mind that every single serious attempt at powered flight prior to 1903 had failed. Getting it right was tough!

Yet just over a decade after the triumphant 1903 demonstration, fighter aces were circling high above the battlefields of Europe in superbly maneuverable aerial machines, and in another decade, passengers from many nations were making long-haul international journeys in days, rather than months.

What has this got to do with the topic of advanced nuclear power systems, I hear you say? Plenty. The subtitle of Till and Chang’s book “Plentiful Energy” is “The complex history of a simple reactor technology, with emphasis on its scientific bases for non-specialists”. The key here is that, akin to powered flight, the technology for fully and safely recycling nuclear fuel turns out to be rather simple and elegant, in hindsight, but it was hard to establish this fact – hence the complex history. Like with aviation, there have been many prototype ‘fast reactors’ of various flavors, and all have had problems.

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Plentiful Energy – The book that tells the story of the Integral Fast Reactor

Yesterday the hard copy of the book “Plentiful Energy — The story of the Integral Fast Reactor” (CreateSpace, Dec 2011, 404 pages) arrived in the post. It is wonderful to see it in print, and now available for all to enjoy and absorb. I was honoured to play a small part in its realisation.

The subtitle of the book is “The complex history of a simple reactor technology, with emphasis on its scientific basis for non-specialists”. Written by the two leading engineers and Argonne National Laboratory Associate Directors behind the integral fast reactor, Dr. Charles E. Till and Dr. Yoon Il Chang, it is a landmark in the sustainable energy literature.

The first paragraph of the Acknowledgements explain the authors’ motivation for writing the book:

In beginning this book we were thinking of a volume on fast reactor technology in general to be done in a manner suited to the more technically inclined of the general public. There had been advances in this technology that had not been adequately covered in the literature of the time, we didn’t think, and we felt that a book on this area of nuclear technology could play a useful role. However, at about this time the enthusiastic advocacy of the IFR in the writings of Tom Blees, Steve Kirsch, Terry Robinson, Joe Shuster, Barry Brook and Jim Hansen began to appear.

In books and articles they outlined the merits of the Integral Fast Reactor and advocated its urgent deployment. Written by these highly technically literate non-specialists in the technology, they provided a general understanding of the IFR and what its implications for energy supplies would be for the future. And they did this admirably, describing accurately and vividly the capabilities of the IFR and the reasons for urgency in its deployment. They could only touch on the technology underlying it, however, and the why and how of the technology that caused it to work as it did, and the influence of the history of its development on the development itself, were obvious to us as being very important too. These things then became the focus of our efforts in this book…

After visiting Chicago and Idaho Falls in 2009/2010, talking to Yoon and Chuck, visiting the EBR-II site, and really getting immersed in the background to the technology, I was delighted to assist in the production of this book by reading and doing a technical edit on the entire draft manuscript — and so I think I can claim to be the first person to have read it all, other than the authors!

More about the book is given at its CreateSpace publishing page, and you can purchase it at Amazon.com (currently for $US 18). Obviously, I thoroughly recommend that all BNC readers get a copy.

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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.

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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.

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