Re: Nuclear Power Plant Conversion Factors

[russelmj@songs.sce.com]

     Dan Strom asked:
     
     
     Power reactor folks,  I have a couple of questions on power reactor 
     outage operations.
     
     1.  NRC Info notice 97-36, June 20, 1997 describes an incident in the 
     fuel transfer canal at Haddam Neck.  Removable beta-gamma 
     contamination is given as "80 mrad/hr."  I need an estimate of the 
     conversion from mrad/hr to dpm/100 cm^2, and the variability in or 
     range of this estimate (i.e., "1 mrad/hr is within a factor of 2 of 
     5E6 dpm/100 cm^2 95% of the time."  I'd also like to learn about what 
     affect this conversion, e.g., age of fission products, whether
     it's fission or activation, etc.
     
     2.  In the same notice, the airborne radioactivity levels were quoted 
     as "0.8 DAC beta and 24 DAC alpha."  What would these DACs be?  
     Probably a plant-specific value for the kind of stuff they usually 
     find, but I'd like to know the isotope mix, the assumptions (D, W, Y 
     mix, particle size), etc., that are used for this kind of DAC.  How do 
     you calculate results in DACs?  X dpm beta-gamma per m^3 is Y DAC, and 
     Z dpm alpha per m^3 is W DAC?
     
     ----------------------------------------------------------------------
     
     Since these questions refer to measurements and events at CY, you'd 
     have to get a response from them.
     
     But a general response can be given with the precaution that not all 
     nuclear plants do it the same way:
     
     CONTAMINATION MEASURMENTS AND CONVERSION FACTORS
     
     Contamination levels that exceed the range of a frisker/scaler are 
     expressed in terms of survey instrument response.  
     
     The older frisker/scaler combination of an Eberline HP-210/RM-14 has a 
     range of 50,000 cpm (500,000 dpm).  The up-to-date Eberline ASP-1 scaler 
     can go up to 10E+6 cpm.  At this count rate, dead time (even with the 
     built in dead-time correction) causes considerable uncertainty. 
     
     When using a survey instrument to measure contamination, levels are 
     expressed in terms of instrument response rather than dose rate per 
     se.  No energy or geometry correction factors are applied.
     
     For example, the expression "mR/hr o/w" on a contamination survey 
     using a ion chamber survey instrument such as the Eberline RO-2 is 
     interpreted as an open window instrument response measurement.  
     Usually, these are measurements of smears taken over 100 cm2.
     
     Our "rule of thumb" is 1 mR/hr OW is equivalent to 10,000 cpm for our 
     isotopic mixture.  This "factor of 2 approximation" is derived 
     empirically.  
     
     AIRBORNE RADIOACTIVITY
     
     Airborne radioactivity expressed in "DAC beta" normally refers to a 
     gross count using a GM or proportional counter.  The gross activity is 
     converted to DAC using an "effective DAC" derived from more detailed 
     analysis (often based on "Part 61 analysis" of plant smears").
     
     Air samples are more often analyzed by gamma spec and the resulting 
     "particulate beta/gamma DAC" is based on the nuclide specific activities 
     measured.  Note that scaling factors are sometimes applied to the gamma 
     spec measurement to estimate the DAC from non-gamma emitters.
     
     Alpha DAC refers to a gross alpha counts performed after a sufficient 
     delay to allow the radon daughters to decay (8-24hours).  The longer 
     lived thoron daughters which require about a 6 day decay time are not 
     normally an interference problem at least not here in Southern 
     California.
     
     The gross alpha activity is converted to DAC using an "effective DAC" 
     derived from a detailed analysis.  Transuranic analysis involves 
     radiochemical separation.  The most abundant nuclides are 
     curium-242,244, americium-241, and plutonium-238/239.  John Frazier's 
     PEP at the 1988 Boston HPS Annual Meeting entitled "Alpha Emitters an 
     Nuclear Plants" is a good reference.
     
     Mike Russell 
     San Onofre
     
     
     
     

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