Barry Brook at BraveNewClimate.com is beating the drums for the Integral Fast Reactor (IFR). I am ambivalent for a number of reasons, and will at least point to some. The IFR is not the only potential fast neutron reactor, and one fast neutron concept, the Liquid Chloride Fast Reactor belongs to the Molten Salt Reactor class. The offers significant safety, fuel processing and other technological advantages over the IFR, even though it has never been the subject of a serious R&D effort.
I represent the old ORNL tradition about nuclear technology. Oak Ridge scientists quickly rejected the idea of a sodium cooled reactor (1947 to 1950). Indeed Eugene Wigner who was the first post War research director at ORNL and who held the original patent on the Liquid Sodium Cooled Reactor, did not like his own invention. The original Oak Ridge air craft reactor was sodium cooled, but it was developed at K-25 rather than ORNL and the K-25 engineers who were developing the K-25 reactor project, quickly realized that the sodium cooled air craft reactor design had deep safety flaws including a positive coefficient of reactivity, and of course the insidious dangers of a liquid sodium coolant. Ed Bettis and his associates quickly bailed out on the liquid sodium cooled reactor design, and developed the Molten Salt Reactor concept. it was not by accident that the original K-25 MSR concept featured liquid fluoride salts, If K-25 chemists and engineers knew anything, they knew fluoride chemistry. Fluoride salts are, of course, quite safe compared to liquid sodium. The original MSR concept featured a negative coefficient of reactivity. Indeed if American Reactor development policy had been guided by strictly rational considerations from 1950 onward there would have been no more money spent on liquid sodium cooled reactors. As it is over 20 billion 2009 dollars has been spent on Sodium cooled fast breeder research without the development of a single American commercial Fast Breeder prototype.
By the early 1950’s my father, C.J. Barton, Sr., was exploring the chemistry for a Liquid Chloride Fast Breeder that would have been safer, and far more practical than any LMFBR design concept. Had the LCFR rather than the LMFBR been chosen as the major direction for United States Breeder fast breeder research, and been supported at the level that the Liquid Sodium Fast Breeder was to receive, I have little doubt that an American Fast Breeder Reactor would have been developed during the 1960’s. Unfortunately that was not the case, and instead over 20 billion 2009 US dollars were tossed by the United States Government down a rat hole marked Liquid Sodium Fast Breeder Reactors.
In addition to ORNL studies of the LCFR concept, a 1974 British study reached favorable conclusions about the LCFR concept, and a 1978 Swiss report indicated that the LCFR was a promising design.
In his 1982 UCLA dissertation by E. H. Ottewitte, who had participated in the Swiss study stated:
Molten salts compete favorably with liquid metals: they exhibit thermal conductivities intermediate to water and the poorer of the liquid-metal. Their specific heat capacities parallel water’s. Furthermore, an intermediate coolant of molten salt should more closely match the primary salt in physical proper-
ties, thereby reducing freezing and thermal stress problems. They will cost far less then liquid metals.
Fast molten chloride reactors have been cursorily considered before but mainly for the U/Pu fuel cycle. The ORNL MSR program showed the feasibility of fuel salt circulation. The combination of that experience and MCFR research (out-of-pile experiments and theoretical studies, so far) provide a basis for believing the
concept will work.
Chemical stability and corrosion of molten salts are fairly predictable. Low vapor pressure of the salts enhances safety and permits low pressure structural components.
Molten fuel state and cooling out-of-core simplify component design in a radiation environment. They forego complicated refueling mechanism, close tolerances associated with solid fuel, and mechanical control devices. Molten state and low vapor pressure of the salts also offer inherent safety advantages.
Some salient advantages of the MCFR concept are :
1. Simplicity : no control rods, fuel handling mechanisms, fuel elements or associated structures . Very uncluttered: should maximize test space and facilitate access thereto . Fluid fuel can be transferred remotely by pumping through pipes connecting storage and reactor .
2. MSRs don’t refuel or reprocess, just add fuel and process out wastes . Continuous
processing and refueling would minimize reactor downtime . Can usefully consume all fuel forms, simplifying fuel supply while simultaneously solving other people’s
3. MSR is the safest concept of all due to very strong negative temperature coefficient. No gaseous hydrogen can possibly evolve from fuel or primary coolant . Fuel already molten and handled by system . Simple design technique makes boiling impossible. Continuous removal of fission products reduces their heat source by two orders of magnitude: consequently, natural circulation suffices for emergency cooling, thereby greatly reducing the designated evacuation area . Also, under any off-normal conditions, the liquid fuel can be channeled to a continuously cooled drain tank, in a short time.
4. Very fast neutron spectrum in an annular core engenders high neutron fluxes, driving inner and outer thermal neutron flux traps, each variable in size and neutron energy spectrum by means of molten salt composition. Elimination of fuel cladding and structural material significantly improves the neutron economy of the reactor: more neutrons are available for applications.
5 .Elimination of pressurized and pressure-evolving components inside the containment, reducing risk of containment failure.
The American energy establishment, never looked seriously at the LCFR as a viable alternative to the liquid sodium fast breeder. If it had there is a likelihood that the LCFR would fave compared favorably to all LMFBR concepts including the IFR. The question would have been if a fast breeder reactor was needed at all. The LFTR offers sustainable breeding with the advantage of operating in the thermal/epithermal neutron range. The availability of a slow neutron breeding process potentially offers an enormous scalability advantage. A limited nuclear fuel supply would pose a far more serious challenge to the scalability of the IFR or a LCFR than it would to a two-fluid LFTR with or without graphite.
IFR concepts during the 1990’s included the notion of factory constructed modular reactors. But no assessment has been yet offered on possible interaction between IFR size and safety. Safety is a far more critical issue for the IFR than for a MSR for obvious reasons. The NRC has not yet developed safety concepts for either the LFTR or the IFR, but given the implications of major safety problems such as a coolant leak or a core rupture, IFR safety requirements are likely to be far more stringent, and costly to meet. NRC safety requirements will probably include the sort of massive safety related site construction requirements that favor economies of scale.
Compared to both the LFTR and its chloride salt cousin the LCFR, the IFR would pose significant safety hazards, would be larger and probably more expensive to build in a factory setting. It would also po
se significantly more control issues, and a system of defense in depth against sodium related safety concerns is likely to add to reactor complexity and cost. The IFR would require over 10 times as much fissionable materials as a graphite moderated LFTR making the LFTR a far more attractive candidate for the role as a mass produced, widely deployed global warming fighting technology. Indeed, factor produced small LFTRs may offer significant cost advantages over all other post-carbon energy technologies.
Politicians and scientists often feed each other’s insecurities. Since the 1972 firing of Alvin Weinberg for political reasons that included his MSR advocacy and criticism of the safety of LMFBRs the American scientific community has been cowed by the orthodox dogmas of the US Department of Energy. The US government did supply limited support to the concept of a thorium fuel cycle thermal molten salt breeder from the 1950’s to 1970’s, and although that reactor concept received no more than 4% of the money wasted is such a profligate fashion by on the liquid sodium breeder reactor concept, that project proceed in an outstandingly successful fashion, and would have become the crowning success of the United States nuclear program if Washington had been willing to back it with even 25% of the money it wasted on the LMFBR concept.