OPG

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

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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

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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.