Claire, Duke validates the effectiveness of our passive monitoring program by measuring the sensitivity of the passive monitors. We think that our method for characterizing the sensitivity of passive monitors described below is solid and we don't think anything would be gained by performing random WBCs. Considering how little internal exposure we get, we would have to count the entire workforce to approach meaningful statistics. We certainly do perform WBC for a variety of reasons like facial contamination or a monitor alarm.
We use Co-57, Ba-133. Cs-137 and Co-60. For each radionuclide we have a set of sources of 1.00, 2.00, 4.00, 8.00 etc. nCi (for Co-57 50.0, 100, 200 etc. nCi) Combinations of these sources can be used to give any desired total activity in steps of 1 nCi (50 nCi for Co-57). For each radionuclide, we place a phantom in the monitor and try an activity. If we get 10 out of 10 alarms, we consider that a success and try a lower activity. If that is successful, we try a still lower activity. If we get one or more failures to alarm, we move to an activity between the tested activity and the most recent success. This quickly converges. We consider the sensitivity of the monitor for the radionuclide being tested to be the lowest activity tested that gave 10 out of 10 alarms. We repeat for the other three radionuclides. Note that the activities are in integer values for the reference date. We then decay correct each sensitivity for the actual activity on the date of testing. We convert these sensitivities to sensitivities normalized to an imaginary radionuclide of the actual energy but a single 100% abundant photon. We plot these normalized sensitivities versus energy. We then look at our station radionuclide distribution, including alpha and other difficult to detect. We compute the number of nCi of that distribution that would be required for an alarm (10 out of 10) using the normalized sensitivity versus energy plot every line of every radionuclide with appropriate weightings applied. (much easier than it sounds using a spreadsheet) Finally, we calculate the internal dose corresponding to this total activity of our station mix, again considering alpha and other difficult to detect. We consider the GEM-5s at our protected area exits to be our final monitors and so characterize every one of them. We have found by experience that monitors that are calibrated to perform identically at Co-60 or Cs-137 can have very different sensitivities for lower energy radionuclides like I-131. Per ANI, we also characterize one each of all the other types of fixed monitors that could be of any use as passive monitors. Bob Sorber Corporate Radiation Protection 704-382-7259 [email protected]<mailto:[email protected]> From: Claire C Fage [mailto:[email protected]] Sent: Thursday, December 29, 2016 8:06 AM To: '[email protected]' Subject: [powernet] Passive Monitoring Program *** Exercise caution. This is an EXTERNAL email. DO NOT open attachments or click links from unknown senders or unexpected email. *** Recently at Cook we have instituted the practice of exclusively passive monitoring every worker in and out processing. My question is, what does your plant do to validate the effectiveness of your passive monitoring program? Do you perform random whole body counts? If so, with what frequency? Does your frequency increase during outages? Thanks for your time, Claire Fage Associate Health Physicist Donald C. Cook Nuclear Power Plant (269) 465-5901 x1117
