An Analytical Screening Technique to Estimate the Effect of Cooling Ponds on Meteorological Measurements

1
An Analytical Screening Technique to Estimate the
Effect of Cooling Ponds on Meteorological
Measurements A Case Study

• Stephen A. Vigeant, CCM and Carl A. Mazzola, CCM
• Shaw Environmental Infrastructure

PAMS Mini-Conference, Columbia, SC April 3, 2009
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Outline

• Introduction
• Study Objective
• Technical Approach
• Sensible heat and moisture flux source terms
• Atmospheric transport and diffusion
• Results
• Conclusions

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Introduction

• Situation Overseas nuclear power station
  meteorological monitoring program with 2
  instrumented towers (58-meter 10-meter)
• Cooling system Includes two 12 m x 12 m cooling
  ponds with elevated water temperatures
• Ponds Located 62 meters from 10-meter tower
  instrumentation
• Issue Nuclear regulatory agency concerned about
  possible effects of cooling ponds on 10-meter
  tower measurements

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Study Objective

• Develop analytical technique to estimate
  potential impact of cooling ponds on 10-meter
  tower temperature and RH measurements
• Source Terms Estimate sensible heat and moisture
  fluxes from cooling ponds
• Atmospheric Transport and Diffusion Determine
  impacts of fluxes on 10-meter tower measurements
  using appropriate model
• Use 1-year of onsite data to estimate source term
  and atmospheric transport and diffusion
• Calculate temperature and moisture impacts to
  10-meter tower instrumentation

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Technical ApproachSensible Heat and Moisture
Fluxes

• Bulk aerodynamic formulae of Friehe and Schmitt
  (1976) selected to estimate sensible heat and
  moisture fluxes from cooling ponds
• Fluxes primarily driven by
• Water and air temperature differences
• Wind speed above ponds

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Sensible Heat and Moisture Fluxes
Wind
Sensible Heat Moisture Fluxes
Ta
Discharge Pond Ts
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Technical ApproachSensible Heat and Moisture
Fluxes

• Sensible Heat Flux Hs rCpCHU(Ts Ta)
• where
• Hs sensible heat flux (cal m-2 sec-1)
• r air density (g m-3)
• Cp heat capacity of air (cal g-1 K-1)
• CH sensible heat transfer coefficient
  (dimensionless)
• U mean wind speed (m sec-1) at reference
  height (10 meters)
• Ts mean water temperature (K)
• Ta mean air temperature at reference height
  (10 meters) (K)

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Technical ApproachSensible Heat and Moisture
Fluxes

• Moisture Flux E CeU(Qs Qa)
• where
• E moisture flux (g m-2 sec-1)
• Ce moisture transfer coefficient
  (dimensionless)
• U mean wind speed (m sec-1) at reference
  height (10 meters)
• Qs mean water vapor density (g/m3) near the
  water surface
• (assume saturation)
• Qa mean water vapor density (g/m3) at reference
  height
• (10 meters)

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Technical ApproachSensible Heat and Moisture
Fluxes

• Water vapor densities (Qs and Qa)
• Qs and Qa r?(RH x Ws) / (1 RH x Ws)
• where
• r air density (g m-3)
• Ws saturation mixing ratio (dimensionless)
• RH relative humidity (dimensionless)
• Qs (based on water temperature)
• Qa (based on air temperature)

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Technical ApproachSensible Heat and Moisture
Flux Source Terms

• Calculate hourly sensible heat and moisture
  fluxes using one year of onsite measurements
• Base sensible heat transfer coefficients (CH) on
  seasonal values obtained from site-specific study
  
• Base moisture transfer coefficient (Ce) on Friehe
  Schmitt
• Use seasonal intake water temperature
  measurements
• Assume pond temperature is 7C higher
• Assume flux homogeneity over entire pond surface
• Multiply calculated fluxes (cal m-2 sec-1 g m-2
  sec-1) by pond surface area
• Obtain sensible heat and moisture source terms
  (cal sec-1 g sec-1)

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Technical ApproachAtmospheric Transport and
Diffusion

• Determine transport and diffusion of sensible
  heat and moisture source terms
• Calculate normalized concentrations (C/Qs) at
  10-meter tower located 62 meters from cooling
  ponds
• Use NRC ARCON96 code due to close proximity of
  source and receptor
• Horizontal and vertical diffusion coefficients
  adjusted for plume meander and aerodynamic
  building wake
• Empirical adjustments based on many wind tunnel
  and atmospheric tracer studies
• NUREG/CR-6331 Revision 1
• Use hourly onsite data from 10-m tower ARCON96
  input

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Technical ApproachAtmospheric Transport and
Diffusion

• ARCON96 Code Description
• Straight-line Eulerian Gaussian plume
• Ground-level, vent, and elevated releases
• Incorporates low wind speed plume meander
• Incorporates aerodynamic building wake effects
• Valid at source-receptor distances as close as 10
  meters
• Recommended by NRC for use in control room
  habitability analyses in Regulatory Guide 1.194

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Technical ApproachAtmospheric Transport and
Diffusion

• ARCON96 Code Input Options
• Area source (virtual point) option used for
  cooling ponds
• Sector averaging constant (4.3)
• Wind direction sector width (90 degrees azimuth)
• Surface roughness length (0.2 m)
• One year of hourly onsite meteorological data

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Technical Approach Sensible Heat and Moisture
Concentrations

• Multiply sensible heat (cal sec-1) and moisture
  (g sec-1) fluxes by calculated ARCON96 C/Q values
  (sec m-3)
• Obtain hourly values of sensible heat (XH) (cal
  m-3) and moisture concentration (Xw) (g m-3) at
  10-m tower instruments
• XH Hs (C/Q) Sensible Heat Concentration
• XW E (C/Q) Water Vapor Concentration

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Technical ApproachPond Sensible Heat and
Moisture Impact Calculations

• Calculate increase in temperature (DTa) at
  10-meter tower
• DTa XH/Cpr
• Calculate increase in RH (DRH) at 10-meter tower
• DRH 100 x XW (g m-3) / rW (g m-3)

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Results

• Temperature Impact
• Largest hourly temperature impact 0.2C
• Increase between 0.10C - 0.19C (0.3 of time)
• Increase between 0.01C - 0.09C (24 of time)
• Increase of lt 0.01C (14 of time)
• No impact when wind direction outside of
  90-degree azimuth ARCON96 window (62 of time)
• RH Impact
• Largest hourly RH impact 0.7
• ANSI/ANS-3.11 (2005) and NRC Regulatory Guide
  1.23 Revision 1 accuracy requirements
• Air temperature 0.5 C
• RH 4

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Conclusions

• Temperature and moisture increases due to
  presence of discharge ponds at 10-meter tower not
  significant
• Slight increases
• Much smaller than ANSI/ANS-3.11 accuracy standard
  for each parameter
• Have no meaningful effect on meteorological data
  used to evaluate environmental impacts of nuclear
  power plant
• No effect of discharge pond on wind speed and
  wind direction is expected