1. CAC Meeting May 20, 2008 Computer Modeling of Impacts

2. Presentation Plan Issue raised by Community Working Group Conventional Emission Models Radiological Emission Models Empirical Emission Factors Issue resolution

3. Issue #103 Review of effectiveness of current OHN quantitative computer models of impacts and effects on the environment including humans To what extent does OPG use mathematical models to predict potential environmental impacts caused by routine operation of PNGS? What models does it use? Are they reliable for predicting impacts to the environment, including humans? How often does OPG review/update them What does OPG mean when it uses the term empirical dilution factors? Explain how they are quantified.

4. Conventional Emission Impact Models All installations that will result in conventional emissions must be approved by the Ontario Ministry of the Environment (MOE). For installations that will emit to air that includes emission modeling using models specified by the MOE. Any changes to the models required to be used are dictated by the MOE. The same models are used for all Ontario industries. Currently the MOE allows the use of Regulation 346 model programs. These models are being phased out and replaced with new air dispersion models developed by the US EPA (i.e. AERMOD, ASHRAE, ISCPRIME, SCREEN 3).

5. IMPACT Radiological Emission Model The IMPACT model is used to assess the impact of radiological emissions. IMPACT Background OPG commissioned BEAK international to develop a Guidance Document with respect to the calculation of Derived Release Limits (DRLs) for OPGN sites using the most recent International Commission on Radiation Protection guidance This Guidance Document was reviewed and approved by the CNSC for use. It is also being turned into a CSA Standard (288.1) and will be applicable to the nuclear industry as a whole

6. IMPACT Radiological Emission Model IMPACT was then developed by the external consultants, for the DRL Calculation, and also to be used for the Public Dose Calculation. It considers all the pathways by which an emission can reach a member of the public. Compliant with CSA N286.7 Quality Assurance of Analytical, Scientific and Design Computer Programs for Nuclear Power Plants IMPACT is updated as required based on user need and revisions to CSA N288.1.

7. IMPACT as an Emission Limit Setting Tool Used to determine the maximum emission limits to be set for the station. (DRLs) A DRL is a radionculide release rate that would expose a member of the public to the public dose limit OPG facilities are required to operate with radionuclide release rates well below their DRLs

8. IMPACT for Public Dose Calculation Normally, we calculate radiological dose to the public, resulting from station operation, based on measurements directly in the environment (tritium, carbon-14, noble gas). However, some of the materials we emit are at levels that cannot be measured in the environment. Instead of simply assuming they are insignificant, we model them based on emissions measured at the station. The IMPACT program is used to calculate dose to the public from environmental measurements and from station emissions using prevailing weather conditions, and adjusted ingestion/inhalation parameters.

9. IMPACT Program Summary Converts radionuclide emissions or concentrations in the environment (measured or calculated) into doses. Developed for OPG by Beak International and supported by Ecometrix Inc. IMPACT is updated as required based on user need and revisions to CSA N288.1. In terms of quality assurance the IMPACT software was verified and validated in accordance with the CSA N286.7 software quality assurance standard, and the CNSC Guideline G-149. Basically this program is state of the art.

10. Empirical Dilution Factors Empirical dilution factors are used to quickly determine the significance of unplanned releases of radioactivity into the lake They are based on long term observations of the stations routine emissions, and the factor by which they are diluted before reaching the nearest water supply plants PNGS to Horgan Water Supply Plant dilution factor = 10 PNGS to Ajax Water Supply Plant dilution factor = 7

11. Empirical Dilution Factors (cont) They are used as input into whether to trigger the Provincial liquid emission notification process Once the Province is notified, their staff are responsible for the modeling of the potential impact of the event using tools that they apply to other spill events to Lake Ontario. This responsibility is set out in the Provincial document Coordination of the Response to a Liquid Emission Drills are routinely conducted where the Provincial staff model liquid emission events

12. Issue #103 Review of effectiveness of current OHN quantitative computer models of impacts and effects on the environment including humans To what extent does OPG use mathematical models to predict potential environmental impacts caused by routine operation of PNGS? What models does it use? Are they reliable for predicting impacts to the environment, including humans? How often does OPG review/update them What does OPG mean when it uses the term empirical dilution factors? Explain how they are quantified.

13. Suggested Disposition Category 1 No further action required, the issue has been dealt with to the extent required or the extent possible. or The issue is being managed satisfactorily and would be brought back to the CAC only if an unusual result or event arose calling into question the managed process for the issue.