Source term reduction due to chemistry changes/controls should not be confused with the composition of the source term. The net effect of these efforts is to address the surface crud layers. Having done extensive in-situ gamma spectroscopy inside S/G bowls and RCS piping, I can tell you that the long-term crud layer is mostly Co-60. However, the surface layer of the crud is predominately Co-58 and other shorter lived isotopes. Chemistry control changes predominately affect this surface layer, chemical cleaning, electro-polishing and component replacement are needed to address the based crud layer.
What we have seen in twenty-five years of operation is typically and simply described as high-energy photons. Even with the addition of zinc (Zn-65 emits two photons at .511 and 1.12 MeV), these energies would be well within the expected energy range that we deal with routinely. Operating unit RCS piping include a significant quantity of 511 keV photons from several short-lived isotopes, but they irradiate EDs and TLDs (short-lived does not matter to an operating unit). I would be surprised if many stations have average photon energies outside of 0.600 to 1.0 MeV composed mostly of scattered Co-58/60 and Cs-134/137. From what I have seen in the industry, there is a great deal of effort needed to correlate EDs and TLDs well. I'm not sure that crud layer average photon energy variations is first and foremost, but if some people think that their photon energies might be a component, include it in your analysis. Certainly, the concern noted about isotope component changes is an issue to be aware of at decommissioning. However, this is due to decay not chemistry. Seth. ********************************************************************** Seth J. Kanter, CHP, RPT Sr. Health Physicist Palo Verde Nuclear Generating Station Mail Sta. 7397 5801 S. Wintersburg Rd. Tonopah, AZ 85354 Phone (623) 393-3130 Fax (623) 393-2487 Unless otherwise noted, all opinions are my own Liviu Librescu ********************************************************************** From: [email protected] [mailto:[email protected]] On Behalf Of Armstrong, Joel L Sent: Thursday, January 13, 2011 5:54 PM To: [email protected] Subject: RE: Powernet: RE: Electronic Dosimeter Bias Just returned from the EPRI symposium in warm Ft Lauderdale. One of the papers discussed the need to evaluate the ED bias due to our source term reduction efforts particularly chemistry changes/controls. The programs we're pushing to reduce the source term may well be changing the component isotopes in the crud layers and as such changing the average gamma energy. TVA like most utilities still calibrates EDs with Cs-137 but the average energy assumptions may no longer be true which may cause the EDs to under respond. None of us want to get our TLD reads and find our outage dose is higher than what we though. Joel Armstrong From: [email protected] [mailto:[email protected]] On Behalf Of [email protected] Sent: Tuesday, January 11, 2011 4:11 PM To: [email protected] Subject: Powernet: RE: Electronic Dosimeter Bias Palo Verde provides the following response: Palo Verde uses the DMC-2000S electronic dosimeters and they are biased by 1.07 (+7%). Our ED to TLD comparison by total dose is routinely +/- 2%. Management is fully aware of how close the dose is by both systems and that the only dose we get back during outages is in multi-pack incremental recording. Over the years, we have performed numerous TLD/ED studies of all of the individual results and have very stringent criteria for their comparisons. With these reviews, we have refined the ED bias to where it is today. As of yet, we have not seen any changes in ED to TLD data based on Steam Generator and Rx Head replacements, or from the power up-rate. One of our "advantages" is that, with an outage every six months, and six-month monitoring cycles, we never have a low total dose personnel cycle. Each read cycle contains outage man-rem exposure totals. So with our TLD LLD of only 5 mrem, and minimal doses incurred by personnel in the PA when EDs are not worn but TLDs are, the TLDs and EDs do match very well. And we are very pleased with the accuracy, rather than any extra conservatisms. Seth. ********************************************************************** Seth J. Kanter, CHP, RPT Sr. Health Physicist Palo Verde Nuclear Generating Station Mail Sta. 7397 5801 S. Wintersburg Rd. Tonopah, AZ 85354 Phone (623) 393-3130 Fax (623) 393-2487 Unless otherwise noted, all opinions are my own Liviu Librescu ********************************************************************** From: [email protected] [mailto:[email protected]] On Behalf Of Courtenay, Christopher C Sent: Tuesday, December 14, 2010 12:37 PM To: [email protected] Subject: Powernet: Electronic Dosimeter Bias Duke Energy would like to know the following: 1. Do you bias your EDs to over-respond in the field? 2. What bias do you apply if you do? (5%, 10%, etc) 3. Have you noticed a change in ED response due to changing plant conditions (Co58/Co60 ratio changes due to Zinc injection, etc) or specific jobs (weld overlay, alloy 600, etc)? Point of reference - Duke uses the DMC2000S from Mirion. Chris Courtenay Engineer, Duke Energy 980-875-5005 "To the optimist, the glass is half full. To the pessimist, the glass is half empty. To the engineer, the glass is twice as big as it needs to be." --- 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.
