4 Nonuse time . Experience indicates that electron machines generally require 

 considerable downtime for maintenance;, This should be considered when appraising 

 the relative advantages of cobalt 60 and X=ray machines as sources of radiation,, 

 In this study, the cobalt 60 facilities are assumed to have a use factor of 95 percent 

 and the X-ray machine facilities to have a use factor of 80 percent, 4/ 



Table 4 shows the number of pounds of food that can be irradiated per hour per 

 kilowatt of radiation source capacity at selected dosage levels and net source uti- 

 lization efficiencies,. Hourly facility output can be computed from the data in this 

 table by using the number of kilowatts of facility capacity as an expansion factor. 

 For example, assume a 3-kilowatt cobalt 60 facility, an applied dosage level of 

 220 kilorads and a 30°percent net source utilization efficiency, and proceed as follows: 

 (1) Enter table 4 to find the relevant output for 1 kilowatt of operation per hour, 

 which is 1,120 pounds; (2) reduce this poundage 5 percent, to 1,064 pounds, to adjust 

 for estimated nonuse time during facility operating periods; and (3) multiply 1,064 

 by the expansion factor 3 to obtain the answer, which is 3,192 pounds of facility 

 output per hour. 



Accordingly, the output would be 6,384,000 pounds for 2,000 hours of annual 

 operation. 



Table 4. — Number of pounds of food that can be treated per hour per kilowatt of ra- 

 diation facility capacity by selected dosage level and net utilization efficiency 



Net utilization efficiency 



Ra 



iiation dosage in ki 



lorads 



200 



: 220 : 



240 





Pounds 





2,000 



1,867 



1,734 



1,800 



1,681 



1,460 



1,600 



1,494 



1,387 



1,400 



1,307 



1,213 



1,200 



1,120 



1,040 



1,000 



934 



867 

 694 



800 



747 



50 

 45 



40 

 35 

 30 



25 



20 



Source: The Handbook of High Voltage Electron-Beam Processing (7). 



4/ Boehm (3) cites experience by one firm in sterilizing medical sutures and other 

 products with electrons from Van de Graaff accelerators. These machines had 

 occasional breakdowns, and operated 70 to 80 percent of the time. This firm has 

 also operated linear accelerators for several years. 



Other estimates of downtime range from 10 to over 30 percent, depending on the 

 electron machine considered. Because no industrial experience base has been 



established for the 3-Mev„, 60-kilowatt insulating core transformer (ICT-3000), 

 it is assumed for this analysis that it would be out of service for maintenance 15 

 percent of the time. This seems to be consistent with a facility use factor of about 

 80 percent, because additional time would be required for maintaining ancillary 

 equipment. 



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