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3 Today and tomorrow, t h i s technological base which has been developed f o r the MSHE w i l l be explained i n detail. I hope you are a s favorably impressed a s I am, by the broad coverage, yet thoroughness, of the developments t h a t have been conducted here a t O m . I venture t o predict t h a t there w i l l be another information meeting here i n the not too distant future t o introduce the operation of a molten-salt breeder prototype. I hope t o see you a l l here a t t h a t time.



R. B. Briggs Realization of a system t h a t makes full use of the potential energy i n thorium t o produce cheap e l e c t r i c i t y i s the primary mission of reactor development a t the Oak Ridge National Laboratory. That system must be an e f f i c i e n t breeder system. An advanced converter may be a worthwhile step i n the development, but an advanced converter does not reach the goal. No matter how good the conversion r a t i o , i f it i s significantly l e s s than 1, the amount of uranium t h a t must be mined t o make up the defi c i t i n fissionable material i s greater than the amount of thorium t h a t must be mined t o compensate f o r the thorium converted t o 233U and burned. For example, i f the conversion r a t i o i s 0.90, the 235U from 20 tons of natural uranium w i l l be burned with each ton of thorium consumed. Even with a conversion r a t i o of 0.99, the 235U from 2 tons of uranium must be supplied with each ton of thorium. One feature of the Th-233U f’uel system i s t h a t breeding should be possible with thermal and intermediate reactors as well a s with fast reactors. Many technical and economic factors combine t o favor the thermal breeders; so we have chosen t o emphasize them i n our program. Our studies lead us t o believe t h a t molten-salt reactors are the most promising of the several possible thermal breeder reactors f o r achieving a satisfactory breeding gain and producing cheap e l e c t r i c i t y .

Our estimate’ of the breeding performance of a two-fluid, graphitemoderated thermal breeder i 6 shown i n Table 1. The neutron yields and losses are known with l e s s accuracy than the numbers imply, but the table was prepared t o show some of the smaller losses and t o balance. We see t h a t the uranium and thorium concentrations and the r a t i o of uranium t o carbon atoms can be adjusted t o obtain a good balance between the neutron y i e l d and the p a r a s i t i c absorptions i n moderator and i n carr i e r salts. This leaves a net of about 12 neutrons per 100 neutrons absorbed i n f u e l f o r production of excess 233U. The losses t o 233Pa can