194 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1955 



THE HANFORD REACTORS 



I have been speaking of the general technical problems of reactor 

 design. To be more concrete, let me recall briefly in specific terms how 

 these problems are met in the Hanf ord reactors. 



For neutron economy, the reactor is large. It uses graphite as a 

 moderator, and the natural uranium fuel elements are arranged in 

 a lattice. Both graphite and uranium are very highly purified. Cool- 

 ing channels and protecting coatings of the uranium fuel elements are 

 aluminum of minimum dimensions. 



To shield operating personnel, the reactor is surrounded by heavy 

 composite walls and all control and operations are from outside the 

 shields. To reduce corrosion of the aluminum, the cooling water is 

 purified and the temperatures held relatively low. To avoid corro- 

 sion or distortion of the uranium, it is canned in aluminum and not 

 left in the reactor very long. 



Heat is removed by large volumes of Columbia River water with 

 relatively low exit temperature. The water is then held in retention 

 basins before returning to the river. 



Control is by neutron-absorbing rods that move in and out of the 

 reactor. The position of the rods is recorded at the control desk and 

 varied by the operators or automatically in response to instruments. 



Chemical processing by a solvent extraction process is done in a 

 separate plant to which the fuel elements are transported in shielded 

 railroad cars, with all operations remotely controlled. 



Fundamentally, it is the low exit temperature of the cooling water 

 and the short life of the fuel elements that make this plant imprac- 

 ticable as a power source. 



BREEDING 



Uranium 235 is the isotope of uranium in which fission occurs most 

 readily. Unfortunately, it is present in natural uranium only 1 part 

 to 140. Natural uranium is none too plentiful, and to be able to 

 use only seven-tenths of a percent of it is frustrating. Neutrons 

 absorbed in the other uranium isotope, uranium 238, lead to the produc- 

 tion of plutonium and plutonium is readily fissionable. This fact 

 early suggested the possibility that a reactor could simultaneously 

 produce heat energy from the uranium 235 in natural uranium, and 

 produce plutonimn from the uranium 238, and that then the plu- 

 tonium could be used as fuel for further production of energy. It 

 was even suggested that the plutonium produced might be greater in 

 quantity than the uranium 235 burned up. Such a process is called 

 a breeding process, since more fuel can be produced than would 

 be burned. 



