Fermi - same as Glen's response, and same reasoning Benjy Bertossi Fermi2 - RP Supervisor 734-586-4935 [email protected]
From: "Vickers, Glen:(GenCo-Nuc)" <[email protected]> To: "[email protected]" <[email protected]> Date: 01/09/2014 03:04 PM Subject: Powernet: RE: Quick Benchmarking Question - Dosimetry Location in PCs Sent by: [email protected] We wear the ED in the PC pocket and TLD on the lanyard, so we’re within 4-6”. I’ve looked at ED/TLD ratios for workers on different types of RWPs where geometry might be diff. I’ve looked at the ratios for BWR undervessel workers with a top down gradient, BWR Drywell RR Pump replacement workers in every conceivable geometry, BWR Rx disassembly/reassembly, and BWR IVVI workers with inspection poles in the water. We don’t use any special geometry device, but the ED and TLD are probably within 6” on the chest. The ED/TLD ratios for all the RWPs except the water workers have about the same amount of variance and bias. The water workers have a greater ED/TLD bias. I think it is because the water has a lot of mfps of scatter and probably reduces the average energy a bit so the ED is more likely to catch a count. You can see the same phenomena with an increased divergence of underwater ion chamber vs gm meters. They respond the same in the Cs-137 calibrator in air, but the response begins to diverge in water. The response can be quite noticeable when you take the bias way out to high dose rates. Not seeing a difference in variance and bias in the different RWPs with different geometries empirically told me that geometry was not a significant variable. I’d scatter plot your total ED and TLD dose for an outage for each worker before and after you started using the card to see if you can see differences in the entire population distribution… Look for changes in distribution with the couple thousand data points… We all know the ED/TLD bias for an outage is a distribution from high, medium and low dose workers and in general we find much less variance as dose increases. This is to be expected and we also desire that our variance get smaller as the worker dose get’s higher. When we do our >100 mrem and >25% bias review we always find the ED>TLD which is key. I can’t solve all of the variance when you plot all of the outage workers, but my distribution is consistent, overall bias has the ED higher, my high dose workers have little variance, and the bias is predictable based upon the total amount of population exposure. I’m doing okay on the key attributes and haven’t found a strong driver to have everyone use an ED/TLD geometry card. I’ve seen such a thing, but didn’t have a strong driver to use it. Glen Vickers Exelon Corp RP Technical Lead, CHP 815-216-2723 (work/cell) From: [email protected] [mailto:[email protected]] On Behalf Of Sewell, Linda Sent: Thursday, January 09, 2014 10:27 AM To: [email protected] Subject: Powernet: Quick Benchmarking Question - Dosimetry Location in PCs Hi All, Diablo Canyon began using TLDs supplied by a vendor on 1/1/14. The new TLD has been integrated into the keycard lanyard. For work in CAs we have used an ED/TLD orientation card that fit into the PC pocket. Our new TLDs do not easily integrate into our existing cards. 1) Where do your workers typically place the TLD/DLR and ED when working in PCs? 2) If both are placed in the PC pocket, how do you keep the ED separate from the TLD/DLR? 3) If they are not both placed in the PC pocket, have you had any issues with ED/TLD discrepancies attributed to this possible positioning difference? Please provide a contact for follow-up questions. Thanks!!! Linda Linda M. Sewell, CHP Principal Health Physicist Pacific Gas & Electric Company Diablo Canyon Power Plant MS 119/1/117 PO Box 56 Avila Beach, CA 93424 P: 805.545.4315 | F: 805.545.2618| [email protected] PG&E is committed to protecting our customers' privacy. To learn more, please visit http://www.pge.com/about/company/privacy/customer/ This e-mail and any attachments are confidential, may contain legal, professional or other privileged information, and are intended solely for the addressee. If you are not the intended recipient, do not use the information in this e-mail in any way, delete this e-mail and notify the sender. -EXCIP
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