21M062007D The Shaw Group Inc. ® An Analytical Screening Technique to Estimate the Effect of Cooling Ponds on Meteorological Measurements – A Case Study

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The Shaw Group Inc. ®

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

A Case Study

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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OutlineOutline

• Introduction

• Study Objective

• Technical Approach– Sensible heat and moisture flux source terms– Atmospheric transport and diffusion

• Results

• Conclusions

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IntroductionIntroduction

• 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 ObjectiveStudy 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 Approach:Sensible 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 FluxesSensible Heat and Moisture Fluxes

Discharge Pond Ts

Wind

Sensible Heat & Moisture Fluxes

Ta

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Sensible Heat Flux Hs = CpCHU(Ts – Ta)

where:

Hs = sensible heat flux (cal m-2 sec-1)

= 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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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 saturationassume saturation)

Qa = mean water vapor density (g/m3) at reference height

(10 meters)

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Water vapor densities (Qs and Qa)

QQss and Q and Qaa = = [(RH x W[(RH x Wss) / (1 + RH x W) / (1 + RH x Wss)])]

where:

= 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 Approach:Sensible Heat and Moisture Flux Source Terms

Technical Approach:Sensible 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 7°C 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 Approach:Atmospheric Transport and Diffusion


• Determine transport and diffusion of sensible heat and moisture “source terms”

• Calculate normalized concentrations 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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ARCON96 Code DescriptionARCON96 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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ARCON96 Code Input OptionsARCON96 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

Technical Approach: Sensible Heat and Moisture Concentrations

• Multiply sensible heat (cal sec-1) and moisture (g sec-1) fluxes by calculated ARCON96 /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

XXHH = H = Hss ( (/Q)/Q) Sensible Heat ConcentrationSensible Heat Concentration

XXWW = E ( = E (/Q)/Q) Water Vapor ConcentrationWater Vapor Concentration

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Technical Approach:Pond Sensible Heat and Moisture Impact

Calculations

Technical Approach:Pond Sensible Heat and Moisture Impact

Calculations

Calculate increase in temperature (Ta) at 10-meter tower

TTaa = X = XHH/C/Cpp

Calculate increase in RH (RH) at 10-meter tower

RH = 100 x [XRH = 100 x [XWW (g m (g m-3-3) / ) / WW (g m (g m-3-3)])]

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ResultsResults

• Temperature Impact– Largest hourly temperature impact: + 0.2°C– Increase between 0.10°C - 0.19°C (0.3% of time)– Increase between 0.01°C - 0.09°C (24% of time)– Increase of < 0.01°C (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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ConclusionsConclusions

• 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

Documents

21M062007D The Shaw Group Inc. ® An Analytical Screening Technique to Estimate the Effect of Cooling Ponds on Meteorological Measurements – A Case Study