We haven't either, but this could explain some of low level dose rate alarms that we seen without being able to verify it with a survey meter. We use Thermo EPD's, mostly Mk 2.3
John Geyster RP Support Supv Entergy Vermont Yankee [email protected] ________________________________ From: [email protected] [mailto:[email protected]] On Behalf Of Earls, Leonard Sent: Monday, June 18, 2012 3:55 PM To: '[email protected]' Subject: Powernet: RE: Dose rate threshold Make and model does make some difference. The Thermo EPD Mk2.3 or Mk2.5 uses a longer time constant at low dose rates to collect a "statistically valid" number of counts. Some makes/models use the same time interval to determine rate irrespective of the dose rate. Even with that feature, it is not unusual to see a peak dose rate at 125% of what can be found with a survey instrument. I don't think you'd ever have a situation where the peak rate would be more than a factor of two higher than "true"; I've never seen it in 10+ years dealing with the EPD. Regards, Leonard Earls Consulting Engineer 361-972-7759 [email protected] ________________________________ From: [email protected] [mailto:[email protected]] On Behalf Of Geyster, John J Sent: Monday, June 18, 2012 14:17 To: [email protected] Subject: Powernet: RE: Dose rate threshold What make and model was the testing done on? Not that it makes that much of a difference as they all use a similar method. ________________________________ From: [email protected] [mailto:[email protected]] On Behalf Of [email protected] Sent: Thursday, June 14, 2012 6:18 PM To: [email protected] Subject: Powernet: RE: Dose rate threshold Yes. since the primary function of most electronic dosimeters is to integrate dose, an algorithm is used to approximate a dose rate by dividing incurred dose over a short sample time (generally around three seconds). While this works fairly well in moderate to high dose rate fields, in low dose rate situations the short sample time coupled with the random nature of decay introduces significant low background counting statistical errors which result in erroneous (false) alarms. We did extensive empirical testing of this and found that dose rate setpoints < 50 mR/hr are of little to no value due to high false alarm rates. To ensure low to no false alarms, minimum setpoint values for rate alarms at or above 75 mR/hr work very well. ********************************************************************** Seth J. Kanter, CHP, RRPT Sr. Health Physicist Palo Verde Nuclear Generating Station Mail Sta. 7397 5801 S. Wintersburg Rd. Tonopah, AZ 85354 Phone (623) 393-3130 Fax (623) 393-1853 Unless otherwise noted, all opinions are my own Liviu Librescu ********************************************************************** From: [email protected] [mailto:[email protected]] On Behalf Of THOMPSON, THEODORE W Sent: Thursday, May 31, 2012 8:55 AM To: [email protected] Subject: Powernet: Dose rate threshold I would like to know if anyone has established or proceduralized a minimum threshold to set the dose rate on the electronic dosimeters at in low dose rate areas (i.e. 5 mrem/hour general area). If not, are you using INPOs guidance of 150% for dose rates up to 100 mrem/hr general area and 125% above 100 mrem/hr general area. Ted Thompson Health Physicist Ft. Calhoun Nuclear Station OPPD Email: [email protected]<mailto:[email protected]> Phone: 402-533-7152 ________________________________ This e-mail contains Omaha Public Power District's confidential and proprietary information and is for use only by the intended recipient. Unless explicitly stated otherwise, this e-mail is not a contract offer, amendment, or acceptance. If you are not the intended recipient you are notified that disclosing, copying, distributing or taking any action in reliance on the contents of this information is strictly prohibited. --- NOTICE --- This message is for the designated recipient only and may contain confidential, privileged or proprietary information. If you have received it in error, please notify the sender immediately and delete the original and any copy or printout. Unintended recipients are prohibited from making any other use of this e-mail. Although we have taken reasonable precautions to ensure no viruses are present in this e-mail, we accept no liability for any loss or damage arising from the use of this e-mail or attachments, or for any delay or errors or omissions in the contents which result from e-mail transmission.
