196 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1955 



The second reactor built at Idaho was the so-called experimental 

 breeder reactor, EBE. As the name implies, it was specifically aimed 

 at demonstrating whether or not breeding was possible. It has dem- 

 onstrated that breeding is possible and has had a number of other 

 incidental interesting results. 



The third reactor was a special-purpose one aimed at providing 

 power for a submarine. You have heard a great deal about that one 

 and about the submarine in which a similar reactor is now being 

 installed. 



In all three of these reactors, the neutron economy problem was 

 solved by using uranium from which much of the uranium 238 isotope 

 has been extracted. Whether or not, in the long run, this is the kind 

 of reactor we will build for power purposes will be largely a question 

 of economics. Personally, I doubt it, but I do not doubt the wisdom 

 of having built these three reactors and the value of the results we 

 have obtained from them. 



A more modest undertaking initiated later is the homogeneous- 

 reactor experiment at Oak Ridge. From the atomic point of view, 

 the homogeneous reactor is misnamed. In reality, one can think of it 

 as a lattice where the spacing is very small and the size of the fuel 

 elements is of atomic dimension. To put it more simply, and in more 

 f amilar terms, the homogeneous reactor is a solution of uranyl sulphate 

 in water. The water serves as the moderator, and the uranyl-sulphate 

 molecules serve as the fuel elements in which the chain reaction 

 is set up. 



The immediate and obvious advantage of the homogeneous reactor is 

 that fuel fabrication and processing is enormously simplified. The 

 solution is pumped continuously through the reactor chamber and then 

 cooled in outside heat exchangers, and some of it can be continually 

 bled off for purification and then reintroduced into the circulating 

 stream of combined fuel and moderator. One of the interesting fea- 

 tures of the homogeneous reactor is that it turns out to be self -regulat- 

 ing. As the temperature of the reactor rises, its reactivity decreases 

 and therefore it controls itself. One difficulty that was anticipated in 

 the homogeneous reactor was that the water itself would be dissociated 

 by the radiation. This does occur, but it has been found possible to re- 

 combine the hydrogen and oxygen formed without too great difficulty. 



In addition to the results obtained with the three reactors I have 

 been discussing, and the homogeneous-reactor experiment, there has, of 

 course, been an extensive program of study of the various associated 

 problems in the laboratory. These range from fundamental studies of 

 what causes radiation damage, or of the absorption probabilities of 

 various materials for neutrons of various energies, to component testing 

 in heat loops, and experimental fabrication of fuel elements. Some of 



