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Atmospheric Dispersion Factors: What Are They and Why Do We Use Them? R. Brad Harvey, C.C.M.

Atmospheric Dispersion Factors: What Are They and Why Do We Use Them? R. Brad Harvey, C.C.M. Theodore A Messier Marlboro, MA 978-568-2727 rbharvey@framatech.com. Atmospheric Dispersion Factors. Outline Components of an Atmospheric Dispersion Model Gaussian Plume Model

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Atmospheric Dispersion Factors: What Are They and Why Do We Use Them? R. Brad Harvey, C.C.M.

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  1. Atmospheric Dispersion Factors: What Are They and Why Do We Use Them? R. Brad Harvey, C.C.M. Theodore A Messier Marlboro, MA 978-568-2727 rbharvey@framatech.com

  2. Atmospheric Dispersion Factors Outline • Components of an Atmospheric Dispersion Model • Gaussian Plume Model • Applications in the Nuclear Power Industry • Atmospheric Dispersion Factors (CHI/Q Values) as a Function of Averaging Time and Probability Level • References

  3. Atmospheric Dispersion Factors Components of an Atmospheric Dispersion Model • Emissions • Source location • Source effective release height • Stack height plus plume rise • Source Emission Rate • Meteorology • Wind speed • Wind direction • Delta-temperature (stability class) • Receptor • Receptor location • Receptor height • Receptor pathways

  4. Atmospheric Dispersion Factors Gaussian Plume Modeling Assumptions • Conservation of Mass • Dry Deposition • Decay in transit • Crosswind and Vertical Gaussian (Normal) Concentration Distributions • Hourly Dispersion Factors • Steady-State Meteorological Conditions • Continuous Emission Rate

  5. Atmospheric Dispersion Factors Coordinate System Receptor coordinates: (x,y,z) Source coordinates: (0,0,H)

  6. Emission and Downwind Factors Atmospheric Dispersion Factors Low Wind Speed High Wind Speed

  7. Atmospheric Dispersion Factors Crosswind Factor

  8. Atmospheric Dispersion Factors Vertical Factor

  9. Atmospheric Dispersion Factors Resulting Basic Equation Concentration = emissions factor x downwind factor x crosswind factor x vertical factor • Simplifying assumptions: • Receptors at ground level (z=0) • Receptor beneath plume centerline (y=0)

  10. Atmospheric Dispersion Factors Applications in the Nuclear Power Industry • Routine Releases (ODCM) • Design Basis Accident • Emergency Response

  11. Atmospheric Dispersion Factors Applications in the Nuclear Power Industry

  12. Atmospheric Dispersion Factors CHI/Q Values as a Function of Averaging Time and Probability Level

  13. Atmospheric Dispersion Factors Potential Causes for Predicting Year-to-Year Variations in CHI/Q Values • Changes in Local Topography • Ground Cover, Nearby Buildings • Changes in Met Monitoring Program • Sensors, Calibration Procedures, Data Processing • Calibration Accuracy • WS ± 0.5 mph; WD ± 5 deg; Delta-T ± 0.1 deg C • Climatic Variability

  14. Atmospheric Dispersion Factors How Often Should Meteorological Data be Updated? • Whenever there are changes to the met monitoring program or its nearby topography How Many Years of Met Data Should be Used in Dispersion Calculations? • RG 1.70 (1978): Two consecutive cycles, and preferably three or more whole years • ANSI/ANS-3.11 (2000): At least three to five years • DG-1111 (2001): Five years (minimum: one complete year)

  15. Atmospheric Dispersion Factors References • Routine Releases (ODCM) • RG 1.111 • NUREG/CR-2919 (XOQDOQ) • Design Basis Accident • RG 1.145 • NUREG/CR-2858 (PAVAN) • Emergency Response • NUREG/CR-5247 (RASCAL 2.0) • RASCAL 3.0 (to be published)

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