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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