PP640.1

North Anna Unit 3 Hybrid Cooling

John D. Waddill, P.E.Dominion Resources, Inc.

EPRI Workshop on Advanced Cooling Technologies

Acknowledgement: Douglas A. Kemp, P.E.

Bechtel Power Corporation

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Why the North Anna Site?

SpaceEnvironmentallyacceptableNo superior alternativeOriginally planned for 4 units

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Available Water Supply

Net Inflow

369 cfsPre-Operational Evaporation

93 cfs

Minimum Dam Release

40 cfsAvailable Water Supply

236 cfs

Unit 3 Water NeedsOnce Through System

28 cfs

Storage Volume: 25,400 acre-ft (250 ft to 248 ft, msl)

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Overview of North Anna Project

ESP application submitted to NRC in 2003 –

2 units at 1520 MWe each

Unit 3 cooling system changed in 2005 from open to closed cycle due to agency and public concerns–

Thermal Discharge–

Lake level and downstream flow impacts

COL application submitted in Nov 2007ESP received in Nov 2007

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Cooling Technologies Considered

Closed Cycle Conventional Cooling TowerThermal Issue: SolvedWater Use Issue: Potentially Worse

Combination Wet-Dry Cooling (Hybrid)Thermal Issue: SolvedWater Use Issue: Significantly Reduced

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Available Cooling Technologies

*Data from filed ESP and COL Applications

0.00

5.00

10.00

15.00

1 2 3 4 5 6 7 8 9 10

GPM

/ G

ross

MW

Out

put

Reservoir Mechanical Draft Natural DraftNA3

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Wet / Dry Cooling Concept – How does it work?

Closed cycle cooling system design

–

Dry Tower and water-conserving Hybrid Tower in series

–

Unit 3’s Circulating Water cooled initially in Dry Towers

–

Circulating Water then passed through Hybrid Towers•

Dry section of Hybrid tower cools incoming Circulating Water and provides warm air for limiting visible plume.

•

Wet section completes the heat rejection using evaporation

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Wet / Dry Cooling Concept – How does it work?

Two conceptual operating modes

–

Energy Conservation (EC) –

Dry cooling will be reduced with reliance on hybrid tower for heat removal.

–

Water Conservation (WC) –

Minimum 1/3 heat removal by Dry Tower, balance of heat removal by Hybrid.

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Conceptual Flow Path & Cycles

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Projected Plant Consumptive Water Use

System Average Water Use (CFS)

28 27.4

19.4

8.4

05

1015202530

Closed CycleReservoir

Hybrid Tower Hybrid Tower& Dry Tower

(EC/WC)

Hybrid Tower& Dry Tower

(WC Only)

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Hybrid Cooling

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Hybrid Cooling

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Look to the Future

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Concept Design – How much dry cooling?

Land UseCostPower RequiredPotential impact on turbine performance

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Concept Design – How much dry cooling?

Comparison of Dry Cooling Percentages

Percent Dry Cooling Capacity

Approx. Number of

Tower Cells Required

Percent increased land use

(over 33% design)

Approx. Dry Tower Cost, 2005 dollars

Approx. Electrical

Power Required,

MWe33 100 - 51M 15

67 240 350 137M 36

83 336 500 171M 50

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Resulting Performance

Bad News –

The system performs best when normally not needed → Cool weather.

Approach temperature has significant impact on dry tower performance/duty.Resulting higher circulating water temperature has consequence of higher turbine backpressure → lower turbine efficiency → lower power output.Remedy?–

More tower cells–

Results in higher hotel loads, land use, cost

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Resulting Performance Effect of Ambient Air Temperature on Dry Tower CWT

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Resulting Performance

Good News –

When you really need it, the system can perform → Long droughts.

Projected annual average evaporation reduced by more than 30% using EC/WC operation.

Projected annual average evaporation reduced by 70% using WC only.

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Resulting Performance

Percent Decrease (Increase) in Average Water Consumption Vs. Once Through Cooling Design

Energy Conservation

Only (EC)

Water Conservation

Only (WC)

Proposed Operating Plan –

EC and WC Dependent on Lake Level

Annual 2 70 30

Winter (9) 90 22

Spring 3 73 11

Summer 5 51 31

Fall 5 71 55Preliminary Data

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Resulting Performance

Existing Units

Existing UnitsPlus

Unit 3 with Once Through Design

Existing UnitsPlus

Unit 3 with Hybrid Cooling

5.2% 11.6% 7.0%

Model Prediction for Time Below Lake Low Level Elevation

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Lake Level Hydrograph

Open Cycle Cooling

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Lake Level Hydrograph

Closed Cycle Cooling

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Summary

The North Anna Unit 3 hybrid cooling system:Eliminates thermal impacts to the lakeSignificantly reduces water use from a once through or conventional wet cooling tower system.Minimizes impact on period of time lake is below low levelProvides a balance between environmental stewardship and cost (capital and lost revenue due to reduced plant efficiency/power production)

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Questions?