135 



The natural uranium reactors offered the advantage that a country 

 possessing uranium deposits could have nuclear power without having 

 to build its own enrichment facilities or obtain enrichment from 

 abroad. On the other hand, for technical reasons, this type of reactor 

 is larger and more expensive than reactors of other types. To get the 

 same power out of smaller, less expensive reactors it is necessary to 

 process the uranium fuel to increase the relative proportion of U-235 

 atoms from the 0.7 percent in nature to perhaps 3 percent. This de- 

 sired "enrichment" can be obtained by several processes. The process 

 in general use is the gaseous diffusion process in which a gaseous form 

 of uranium — uranium hexaHuoride — is diffused through a porous 

 ceramic barrier. Each time the gas passes through such a barrier, there 

 is a slight separation of the lighter U-235 atoms from the heavier 

 U-238 atoms. Many hundreds of diffusion stages, even a thousand or 

 more for a large plant, are needed to manufacture material sufficiently 

 enriched in U-235 for use in weapons. Another enrichment process 

 that has strong proponents today is the gas centrifuge process. Here 

 the uranium hexaHuoride is whirled rapidly about with the heavier 

 atoms being forced outward by centrifugal force. As with gaseous dif- 

 fusion, a series or cascade of centrifuges is required, for the separa- 

 tion at each stage is slight. Of the two processes, the gaseous diffusion 

 process requires a large industrial facility and a large supply of elec- 

 tricity. In principle, centrifugal separation, if it is demonstrated to be 

 economically feasible, should permit building of smaller plants at less 

 capital investment and with less demand for electricity. 



Because enriched uranium has been available in the United States 

 from the three plants that were built to make materials for weapons 

 and for naval propulsion, and because of advantages of enriched 

 uranium as fuel, it was natural for the infant nuclear industry to 

 apply its military experience with enriched uranium to commercial 

 nuclear power plants. As a result, the principal path of evolution for 

 U.S. nuclear power technology has been the use of slightly enriched 

 fuels. Now, at the outset of the 1970's, this technology has become 

 dominant for much of commercial nuclear power in the United States, 

 in the Soviet bloc nations, and in Europe. Even in the United Kingdom 

 and France it appeal's that many future nuclear power plants are 

 likely to use enriched fuels. 



Plutonium : a Manmade Nuclear Fuel 



Nuclear power reactors fueled with natural or slightly enriched 

 uranium also produce plutonium as a byproduct. 6 While some of the 

 plutonium atoms are fissioned, enough remain in the used fuel when it 

 is removed from a reactor to make recovery of this byproduct nuclear 

 fuel economically feasible. The recovered plutonium can be used for 

 weapons or as fuel for other nuclear reactors. This dual utility of plu- 

 tonium is troublesome for world peace : As nuclear power grows, so 

 will the stocks of plutonium, which some observers fear may increase 

 the risk of theft or undetected diversion of this material to clandestine 

 manufacture of nuclear weapons. Fortunately, the operation of a nu- 

 clear reactor for power produces a mixture of plutonium isotopes, 

 plutonium-239 and plutonium-240. The longer uranium fuel is ex- 



U-238 atoms capture neutrons emitted by the fissioning U-235 atoms and are trans- 

 formed into plutonium. 



