Presentation on theme: "Carbon 14 Gaseous Effluent Dose The importance of Human Performance Ron Chrzanowski Corporate Chemistry Manager Exelon Nuclear June 27, 2011."— Presentation transcript:
Carbon 14 Gaseous Effluent Dose The importance of Human Performance Ron Chrzanowski Corporate Chemistry Manager Exelon Nuclear June 27, 2011
2 Carbon 14 Effluent Dose Impact Carbon 14 has not been reported in our annual effluent reports in the past because it was not considered a principle radionuclide that required reporting NRC recently determined that Carbon 14 either needs to be reported or plants need to prove that it is not a principle radionuclide Initial preliminary estimates using current & conservative methodology at Limerick determined that Carbon 14 dose impact could be significant (22 mrem)
3 Regulatory Background Reg Guide 1.21 rev. 1 does not discuss Carbon 14 effluent dose Only Indian Point in US reports C-14 in annual effluent report and has since mid 1980’s Reg Guide 1.21 rev 2 issued in June 2009 specifically states “Licensees should evaluate whether C-14 is a principal radionuclide for gaseous releases from their facilities” We are not committed to Reg Guide 1.21 rev. 2 However, 10CFR50.36a(2) requires that principle radionuclides must be reported, therefore we are required to report C-14 if it is a principle radionuclide and the backfit argument will not work The principal radionuclides may be determined based on their relative contribution to (1) the public dose compared to the 10 CFR 50 Appendix design objectives or (2) the amount of activity discharged compared to other site radionuclides (NEI has provided guidance that if C-14 is 1% of the dose contribution or 1% of the activity discharged then it is a principal radionuclide)
4 Issue Management For the 2010 annual effluent report (submitted in May 2011) plants must report the C-14 dose contribution to off site dose EPRI recently completed an emergent project to determine a standard methodology for utilities to use to calculate the C-14 generation rate for their units
5 Background C-14 is a weak beta emitter (156.5 keV) therefore it only poses an ingestion hazard C-14 has half life of 5,730 years and will build-up in the environment over time C-14 is predominantly produced at nuclear power plants via activation of water and nitrogen impurities in the reactor, moderator and fuel materials In BWRs C-14 will be predominantly released in form of CO2. Then CO2 is available in environment for photosynthesis. The pathway is from vegetation to animals to humans through ingestion In PWRs C-14 will be predominantly released as a mix of organic carbon and carbon dioxide from the waste gas system. The pathway will be the same as the BWRs. C-14 does not impact liquid effluents or REMP Direct Measurement has been performed in Canada for years, but has not been performed in US, except for Indian Point. CANDU (heavy water) designs produce significantly more C-14
6 Calculation The Carbon 14 Calculation consists of the following factors: Generation rate Dispersion from the release point to the receptor Dose Conversion factors Generation Rate (EPRI) This has recently been determined to be 18 curies per yr per Unit for a BWR and 11 curies per yr per Unit for a PWR
7 Calculation Dispersion from release point This is determined in accordance with the site ODCM It is site specific depending on the release point, the weather factors and the distance to the site boundary or receptor Most plants have conservative default Χ/Q values that are used in the calculation Dose Conversion factors The standard method used in US plants dates back to 1960’s
8 Actions in Progress Revising the Calculation Methodology to Remove Overly Conservative Assumptions Generation rate EPRI completed this emergent project at the end of Dispersion from release point Limerick obtained plant specific weather information from Met Tower vendor and used actual distances to the receptor (nearest farm/cow). This methodology reduced dose number to 0.2 mrem from 22 mrem Exelon performed the same estimate as Limerick at the other sites The more realistic dispersion model was in place for the 2010 annual effluent report (submitted in May 2011) Dose Conversion factors NEI has the lead to work with the NRC to get the methodology updated to ICRP 72. Potential factor of 2 reduction.
9 Going forward actions In the industry, there will be measurements for generation in stacks to validate the EPRI generation estimate. There will be work with REMP vendors to measure C-14 impact from Sites in milk and vegetation (validation of calculation). This in my opinion has a lot of margin based on the Canadian data. Effluent Reports will include the C-14 component for the first time in May 2011 for 2010 data and going forward.
10 Human Performance Exelon like many Nuclear utilities outsource work where it make sense from a cost basis and risk basis Cost is self explanatory The Risk side includes assumptions that the work will be performed by our vendors error free This error free performance is a very important aspect of all work performed at a Nuclear Plant, but may be very different for some of our vendors
11 Error Free Work The work you do for us is used in many ways Carbon 14 calculations for X/Q Emergency Preparedness recommendations to the States for the protection of the public Entering abnormal procedures based on real time weather conditions, wind speed & weather advisories Offsite dose calculations for all gaseous effluents NPDES flow rates for liquid effluent releases As you can see much of this work is regulatory driven and impacts what the Utilities report to our regulators
12 Human Performance Nuclear Utilities are very process and procedurally driven and have a series of reviews that are performed on the reporting documents that are submitted to ensure accuracy But, the data can be corrupted or missing due a variety of reasons, including mechanical and electrical issues with collection devices In addition, the data can be corrupted by mishandling on the part of our vendors This is where human performance tools are essential to ensure that the data remains accurate and that timely communications are made when issues arise
13 Example At our Clinton plant last year, there was liquid effluent flow data from one of our outfalls that is collected by our vendor This is performed each month No issues identified or reported to us during the year This year (2011), during the preparation of the yearly report to the State of Illinois, it was identified that there were instances of missing monthly flow data for the outfall Since the report is compiled in 2011, there was no time to recover or collect additional flow data from this outfall Exelon made a report to the state that we did not have the data for that time period and could not ensure that the NPDES permit was always met
14 Human Perforance Tools In hind sight, it would have been more appropriate for our vendor to verify that indeed there was data that was being collected each month It would have been more appropriate to have an established expectation that Exelon require periodic reporting of the data before the preparation of the final report Neither of these actions were performed and an NPDES violation occurred
15 HU Lessons Learned I expect that our vendors have verification practices in place to ensure that the data being collected is indeed present and accurate We have since established expectations that periodic reports are now required back to the sites that prove the data was collected Documented oversight of our vendors is a priority while the vendor is performing their work on site so that Exelon can ensure the proper work is performed using your approved procedures