Thursday, June 20, 2013

MIT Students Propose Fast Molten Salt Reactor

MIT Technology Review recently published an article about an ambitious MSR project being undertaken by two MIT PhD candidates.  The project includes the development of a plutonium burning molten salt reactor.

 Mark Massie and Leslie Dewan, PhD candidates at MIT, have formed Transatomic to develop their reactor design concept.  According to the MIT report, they have raised $1 million in seed money so far. In addition to the MIT project, money is being raised or has already been raised for MSR projects in Alabama and in Canada. The Chinese have raised far more money for their MSR project.  

The Massie-Dewan project appears to be influenced by French thinking on MSR design.  French Reactor scientists at the University of Grenoble believe that graphite is an undesirable material for MSR cores.  Graphite shrinks and swells when exposed to neutrons.  On the other hand graphite is an excellent neutron moderator, and graphite moderated LFTRS can be excellent thermal breeders with thorium.  Fast reactors, without graphite, can be excellent uranium-plutonium cycle breeders, as well as plutonium burners.  Massie and Dewan may intend to build a breeder or a burner, but they do intend to make highly efficient use of their nuclear fuel to create virtually no dangerous and long term nuclear waste and very little short term nuclear waste.  There is one major flaw to such a reactor, namely there are limits to its scalability.  A graphite moderated, thermal breeder reactor does not require a lot of fissionable fuel to start.  In contrast a fast reactor will require an enormous amount of fuel to start a chain reaction.  This problem has been at the heart of my debate with Berry Brooks and the IFR crowd. Mind you, these are very intelligent scientists and engineers, but they have not been able to demonstrate from peer reviewed papers that I am wrong.  

My readers may wonder what is the big deal here?  The big deal has to do with scalability.  In particular, the answer to the question, is it possible to build and bring to operation enough rectors to meet human society energy needs by 2050?  The answer is yes, provided that we we take advantage of graphite moderated molten salt reactor technology.  With Fast Molten Salt Reactor technology, as with the IFR, the answer is no, because to much fuel is needed.

This does not mean that Fast Molten Salt Reactors should not be built. FMSRs can serve useful purposes.  FMSRs can serve as TRU burners, and as thorium breeders.  This would solve the problem of nuclear wast while also providing a potentially useful source of LFTR fuel.   The fast MSR provides a method of long term disposal of almost all nuclear waste that is likely to be acceptable to the public.  Like other forms of MSR technology, the FMSR is extremely safe and can be made absurdly safe at a low cost.  

The MIT Technology Review claims that a 500 Mw FMSR can be built for as little as $1.7 billion.  It makes a major issue of the small FMSR core size and the savings on material costs, as if graphite is an expensive material.  What the MIT Review article also fails to  note is that ordinary steel can be used in MSR core structure.  In addition, the cost of a startup charge for a 500 Mw fast reactor might run to $500 million, making the start charge a significant addition to the FMSR cost.

The future of nuclear power rests with three types of Thermal Molten Salt Reactors, the Uranium MSR, the Denatured MSR and the Thorium MSR (the LFTR).  Of the three, the DMSR is a sort of mixture or hybrid of the other two.  The LFTR probably poses the most developmental challenges, while the UMSR relies mostly on existing technology.  It may turn out that these technologies represent a sort of evolutionary path to the future of nuclear power.

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