Tuesday, January 1, 2008

The Molten Salt Reactor

I am not going to post an extensive discussion of the Molten Salt Reactor (MSR) right now. Kirk Sorensen has everything you ever want to know and a great deal more about Molten Salt Reactors at Energy from Thorium.

From the AEC's point of view in the 1960's, the Molten Salt Reactor had little to commend it. As far as the AEC was concerned the Light Water Reactor worked. There was plenty of uranium available to fuel them; manufacturers knew how to build them. Thus LWRs were the AEC's candidate for the reactor to power America. 40 years later, our actions on nuclear power are still largely controlled by the AEC vision. 40 years later the latest commercial reactor designs still look like the reactor power plant in a 1950's nuclear submarine.

Alvin Weinberg, who held the patent on the LWR, knew what its weaknesses were. The LWR certainly could be made safer, but making it safer costs money, and makes the light water reactor very expensive to build. The LWR probably unfairly carries the taint of Three Mile Island, but that was a consequence of the AEC's choice.

The commercial LWR is also a resource hog, as will be discovered if we try to build them in large numbers, although perhaps not a greater resource hog that ST, PV or Wind farming.

In the 1960's the AEC thought that the Liquid Metal Fast Breeder reactor insure that plenty of fissionable fuel could be produced for future reactor power needs. The coolant of choice for LMFB reactors is sodium. Anyone who contemplates building a reactor cooled by sodium should know that the very idea is the work of the devil. Be prepared to abandon all hope if you enter that gate. The Molten Salt Reactor had the sort of neutron economy needed to successfully breed fissionable materials. In fact the Molten Salt Experiment at ORNL showed that MSR could produce Pu239 from U238, and U233 from Th232. Several things made Thorium breeding more attractive than U238 breeding.

The AEC was not impressed with these and other MSR advantages. What impressed them was the LMFB had a far superior theoretical breeding ratio. In theory the LMFB could produce 1.8 Pu239 atoms for every Pu239 atom that split. The MSB in contrast would chug along producing 1.08 U233 atoms for every U233 atom that split. As a breeder the MSR did not look like a good deal to the AEC. The AEC listened to the Devil's song, and bought into the LMFB myth.

What the AEC forgot was no theoretical breeding ratio advantage can compensate for the failure of a reactor to work. No one has yet to build a successful sodium cooled reactor.
The MSR was a beautiful idea, and idea whose time had not come in 1967. It is not clear if its time has come today, but given its strong advantages and the desperate need of human societies for long term energy sources that are safe and do not hog resources, the time for the MSR should come soon.

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