Re[2]: Electronic Dosimetry

[WERNER.K.PAULHARDT@bge.com]

     Bob,
     
     You make some good points and all have been addressed.  I am not 
     recommending abandoning the secondary dosimeter.  In fact, I am 
     planning on using the TLD as a back-up (I also spoke with ANI when 
     they were here for an inspection).  Some benefit can be derived from 
     this.  One could set up a program where the TLD is not processed 
     unless it is necessary (e.g., ED failure, or ED dose >= to 100 mrem or 
     some other dose setpoint), or the TLD processing frequency could be 
     extended to say once per 6 months.  The ratio (TLD/EPD) could continue 
     to be monitored for problems (performance indicator).  
     
     As far as investigation of a failed ED, with the back-up TLD, you have 
     an alternative, also with the Siemens EPD and associated software, we 
     have the ability to identify (with a couple of computer keystrokes) 
     every user of the particular EPD in question since it was issued from 
     Dosimetry.  Not really a problem!  Consider this:  TLDs are issued to 
     different workers also.  If the worker's dose is typically low each 
     processing period (20-30 or anything <100 mrem for that matter), an 
     under-responding TLD may be hard to detect.  At the end of the 1 or 
     two year period when it comes time to generate ECFs, and a particular 
     TLD(s) ECF changes by, oh say 25%, what do you do then?  We have to go 
     back and look at all of the personnel dose associated with that or 
     those particular TLDs and make adjustments as necessary.  If you are 
     reading TLDs monthly or quarterly or whatever, chances are you are not 
     issuing the worker the same TLD you took from him/her to process.  So 
     you see, you have the same problem as with a failed ED ("could be 
     man-years of work per failed dosimeter!"). 
     
     Data Loss.  With the Siemens EPD (I hope with the others also) the 
     data is written to an EEPROM every 15 minutes.  If the EEPROM were 
     totally obliterated, then the dose would be lost.  Anything short of 
     obliteration, dose can be retrieved from the EEPROM.
     
     Calibration.  With two irradiators, EPDs can be calibration verified 
     at a rate of 1 per minute with one person.  Considering lunch break 
     and a few other breaks, you could realistically calibrate between 
     300-400 in a 8 hour day.  That is about how many we use during normal 
     non-outage conditions.  Also, this verification is only done once per 
     6 months.  The TLD/EPD lab here is currently run with 1 work leader, 2 
     Techs and a Dosimetry Clerk.  That is for both EPDs and TLDs.  We have 
     approximately 1800 people badged and process quarterly.
     
     Finally, we could spend all day/week debating on TLDs and EDs.  There 
     is no such thing as a perfect dosimeter (not even the TLD)!  If you 
     want to pursue Electronic Dosimeter Dose of Record, you need to have 
     at least the following (in my opinion):
     
     An ED that performs like a TLD.  
     A back-up Dosimeter.
     NVLAP Accreditation, including proficiency testing in all categories 
     except 3A and Neutrons.
     A sound Calibration or Calibration Verification program.
     A well documented basis to support ED as dose of record.
     Regulator (NRC etc.) concurrence.
     Plant Management concurrence.
     
     A major problem that we have in this industry is that there is no 
     REALISTIC Standard for us to measure against as far as EPD 
     performance.  Some that have been issued previously are based on dated 
     information.  
     
     As with you Bob, unless otherwise noted, all opinions are mine alone.
     
     Werner K. Paulhardt
     S-D
     CCNPP 
     
     
     
______________________________ Reply Separator _________________________________
Subject: Re: Electronic Dosimetry
Author:  radsafe@romulus.ehs.uiuc.edu at Internet 
Date:    3/7/97 2:54 PM
     
     
At 01:38 PM 3/7/97 -0600, you wrote: 
>     The EPD has passed 
>     "mock" NVLAP Proficiency testing in all categories with the exception 
>     of 3A shallow and Neutrons.
     
Neither of these is critical for using an ED in a nuclear power plant 
environment. A supplemental neutron dosimeter can be used for those few 
situations where neutron dose is expected. Dose from low energy photons at 
nuclear plants arises mainly from noble gas submersion, and this dose can
be calculated from air sample data (and generally is throughout the industry).
     
Reliability of EDs has been generally good - the self-diagnostic features 
that can be built into such devices make an undetected failure a low 
frequency event. However...
     
Electronic dosimeters make sense only if they are used as shared 
dosimeters, i.e., the user takes one to enter a controlled area and returns 
upon exiting (otherwise, you've just replaced a $20 TLD with a $300 ED). 
The user rarely gets the same dosimeter in succession, and a given ED will 
be used by a large number of people, especially during an outage. My 
greatest concern about EDs as the sole dosimeter for dose of record is the 
QC failure where the device reads too low. An infrequent event, to be sure, 
but such a failed dosimeter could have an impact on potenially thousands of 
people's dose totals. Identifying every user, obtaining coworker data from 
same or similar jobs, evaluating the data and deciding which to use and 
which to exclude in the dose investigation on each case, plus management 
reviews, data entry to correct dose totals, and documentation of it all 
could be man-years of work per failed dosimeter! 
     
The other concern I have is about abandoning the use of secondary 
dosimetry. It isn't needed for everyone, but there are a lot of jobs where 
there's a real risk of data loss if an ED is damaged or destroyed. The last 
time I discussed this with someone from ANI (a few years ago), they were 
opposed to using an unaccredited dosimeter when an accredited one is 
available, and they, too, didn't like the lack of secondary dosimetry.
     
Nevertheless, EDs can provide very good measurements. I just suggest that 
you discuss it with your company lawyers and your insurer before making a 
final decision.
     
Another note: Not all EDs are easy to calibrate or test in quantity. If you 
have a system that is not automated, you may need more manpower to operate 
a stand-alone ED system than it would take to operate an automated TLD with 
pocket chamber system. Something to consider.
     
     
Bob Flood
Stanford Linear Accelerator Center
(415) 926-3793     bflood@slac.stanford.edu
Unless otherwise noted, all opinions are mine alone.