Friday, April 30, 2010

The Case for the LFTR

Fast reactors can either be designed to be actinide burners, or they can be designed to be breeders, if breeding is required to produce nuclear fuel. With breeding, the continued manufacture of LWRs will no longer be required, if fast reactors can be manufactured more cheaply. Also, Fast Breeder Reactors produce produce plutonium and plutonium is not particularly compatible with Light Water Reactors. Only about two thirds of Pu-239 gets burned in a Light Water Reactor, in addition the reactor grade plutonium produced by FBRs includes a significant percentage of non-fissionable plutonium isotopes. In Light Water Reactors this means a very poor neutron economy. So the excess plutonium produced in FBRs makes excellent nuclear fuel for fast breeders but relatively poor fuel for LWRs. If Fast Breeders can be built more cheaply than LWRs, then LWRs will be obsolete.

The fast breeder is not the only Generation IV reactor design that could compete with the LWR. Molten Salt Reactors are characterized a simplified design was well as an extremely compact core. Molten Salt Reactors could be mass produced in factories, have significant inherent safety features, and could dramatically lower reactor construction costs. A number of attractive breeding options are available with molten salt technology, including Liquid Chloride Fast Reactor a reactor that would combine fast breeding with the superior safety of the molten salt reactor. Liquid-fluoride reactors can operate as thorium fuel cycle breeders in the thermal neutron spectrum. The Liquid Fluoride Thorium Reactor (LFTR) would be simple, easy to operate, compact, and could eliminate the safety problems of LWRs and Liquid Sodium Fast Breeders, and would be in expensive to operate. in addition they would almost completely eliminate the problem of nuclear waste. LFTRs potentially can convert 98% of the Thorium used in breeding into fission products. Most of the fission products have short half lives, and many of the long half lived Fission products are relatively benign. The fission product mass would be no more radioactive than unprocessed uranium metal after only 300 years. Although safe sequestration of the fission product mass is possible after 300 years, the fission product mass would includes significant amounts of valuable and rare minerals, and mineral recovery is quite possible.

LFTRs could be started with plutonium from nuclear waste, and in fact the LFTR like the fast reactor have been proposed for use as actinide burners. LFTRs can be built rapidly, at low cost and with a lot of actinides around in the form of LWR waste, LFTRs capable of producing hundreds of GWs of electricity can be brought online almost as quickly as they roll off assembly lines.

LFTRs have some interesting properties. The Molten Salt Reactor was originally designed to provide energy to jet engines, and MSRs can automatically respond to throttle driven energy demands. Thus LFTRs can operate in a load balancing capacities, something that is currently being done on the grid by carbon emitting natural gas turbines. Because they are expected to be inexpensive to build and operate LFTRs could be used as peak and back up reserve power units. LFTRs have a negative temperature coefficient of reactivity, and designed to shut down at a predetermined peak temperature. This means that a LFTR using closed cycle helium or carbon dioxide turbines can be brought on line to peak power as fast as its turbines can be spun up.

In addition, with materials development, LFTRs are potentially capable of producing up to 1200 C heat safely. That means that LFtTRs could be used to produce industrial process heat, something that neither fast reactors nor renewables can be expected to do,

If the use of fossil fuels is to be limited during the next 40 years, due to supply and climate concerns, then their most likely energy replacement will take the form nuclear power. Arguably Light Water Reactors would not be the best option for a nuclear transformation of the energy economy. They are relatively expensive to build. They pose significant construction challenges, and arguably may lack scalability required to quickly transform the energy economy. The global energy economy could not be powered by uranium from conventional sources, and new uranium production technologies would have to be developed quickly. Running the global energy economy with once through LWRs would create an enormous amount of nuclear waste. They are too expensive to operate in an electrical backup, and lack the rapid spin up capacity of natural gas powered reserve turbines. They cannot provide industrial process heat.

Finally, Molten Salt Nuclear technology, and thorium breeding have both been successfully tested. Developmental challenges still remain, but there is no reason to anticipate that such challenges cannot be overcome with sufficient commitment. The Manhattan Project demonstrated that dramatic technological breakthroughs are possible in a short period of time with enough commitment. The development of the LFTR would be a far less significant challenge than that faced by American Scientists between 1942 and 1945. Indeed the development of the LFTR might cost less than the appropriations now budgeted to NASA for a single year.

1 comment:

SteveK9 said...

Might have better luck convincing the Indians to look at LFTR, although they have their own approach and LFTR would be NIH. Any contact between Indian physicists and the 'thorium' community here in the US?


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