198 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1955 



that have been in the EBR and in the submarine thermal reactor. 

 These, too, have been valuable. We have a great variety of alloys 

 and have tested various fuel elements. In particular, the submarine 

 thermal reactor has shown that fuel elements sheathed in zirconium 

 will resist corrosion and radiation effects over considerable lengths of 

 time and represent a great improvement over the aluminum-sheathed 

 fuel elements in the Hanford reactors. Radiation effects have also 

 been studied in a variety of coolants including sodium and heavy 

 water. 



In the matter of heat transfer we have found we can remove the heat 

 from a reactor by circulating molten sodium-potassium alloy through 

 it. This is the system of heat removal used in the EBR. We have 

 also done a great deal of work on pure sodium as a possible coolant 

 and are using it in the second type of submarine reactor now under 

 construction. We have also found that we can use a cooling system 

 of pressurized water. This is the system used in the submarine 

 thermal reactor. We have run reactors at much higher temperatures 

 than we were ever able to run them at Hanford, and, therefore, we 

 have moved in the direction of efficient use of the energy from nuclear 

 fission. 



As to control and instrumentation, the most striking results have 

 been those already mentioned where we have found that certain types 

 of reactors are in fact self -regulating as a result of boiling or near 

 boiling as the temperature rises. The only other result I will mention 

 is the use of hafnium as a material for control rods. Hafnium is 

 present as an impurity in zirconium and has to be removed before 

 zirconium cladding can be used for fuel elements because it absorbs 

 neutrons. For the same reason it is very useful as a control material. 

 In the matter of chemical processing, perhaps it is fair to say that 

 most of the work has been accomplished in the laboratory, although 

 we have had experience with actual processing of the various types of 

 fuel elements in the new reactors, none of which is exactly like those 

 at Hanford. We have also proved that the homogeneous reactor will 

 work, at least on a small scale, and we therefore know that that is 

 one direction in which to hope for improvement. 



In the matter of costs, we still have much work to do. None of the 

 reactors we have actually put up is cheap, either to build or to operate. 

 The submarine thermal reactor probably costs somewhere around 

 $1,500 or $2,000 per kilowatt to build, which is to be compared with 

 the cost of a modern steam plant — somewhere around $180 per 

 kilowatt. But the submarine thermal reactor does prove one over-all 

 major result, namely, that it is possible to build a reactor for the 

 production of power that will run continuously and efficiently for at 

 least reasonably long times. 



