Ralph Moir and Edward Teller. Nuclear Technology Vol. 151 Sep. 2005 If the molten salt reactor appears to meet our criteria so well, why has it not already been developed since the molten salt reactor experiment operated over 30 yr ago? The competition came down to a liquid metal fast breeder reactor ~LMFBR! on the uranium-plutonium cycle and a thermal reactor on the thorium-233U cycle, the molten salt breeder reactor. The LMFBR had a larger breeding rate, a property of fast reactors having more neutrons per fission and less loss of neutrons by parasitic capture, and won the competition. This fact and the plan to reduce the number of candidate reactors being developed were used as arguments to stop the development of the molten salt reactor rather than keep an effort going as a backup option. In our opinion, this was an excusable mistake.