esbwr plant performance - nrc

GE Nuclear Energy

ESBWR Plant Performance

Y.K. Cheung

NRC Staff - GE MeetingJune 20 and 21, 2002Rockville, Maryland

Performance PS0206-1

Outline

• Normal Operation• Transients• LOCA and Containment• Comparison to operating plants and ABWR• Summary


ESBWR Normal Operation

• No recirculation pumps – total reliance on natural circulation

• Significant natural circulation flow exists in all BWR’s

• For a given core power, there is a corresponding natural circulation flow

• ESBWR uses enhanced design features to increase the flow compared to standard BWR’s


Performance and Core Flow

• Parametric studies show that– Minimum Critical Power Ratio (MCPR) and Stability Ratio are

strong functions of core flow

• Design was enhanced to increase core flow for improved plant performance


Key Design Parameters Affecting Natural Circulation• Core flow depends on

– driving head– losses through the loop

• Driving head– proportion to chimney height

• Void Fraction• Loop losses

– downcomer • Single-phase pressure drop, handbook

loss coefficient– core (fuel bundle)

• Two-phase pressure drop, data/correlation

– chimney ~ very small– Separator

• Two-phase pressure drop, data/correlation

3

Chimney /upper plenum

Core

Standpipe &Separator

Steam LIne

Feedwater LIne

Driving Head

Separator ∆P

Chimney ∆P

Core ∆P

Downcomerloss

Schematic of Flow and Pressure Drops in a Reactor


Downcomer Losses Depend on the Plant Design

• Jet pump plant– Large loss at the jet pump suction (~ 0.034 sq.m. per jet pump)

• Internal pump plant– Very large loss at the internal pump minimum flow area

• Natural circulation plant (ESBWR)– insignificant loss


Comparison of ESBWR and ABWR

• Key parameters that increase core flow in ESBWR– Shorter fuel– Tall chimney– Un-restricted downcomer

• Key parameters that increase core flow in ESBWR– Shorter fuel– Tall chimney– Un-restricted downcomer

ESBWR ABWR

Fuel Length 3.05 m 3.66 m

Chimney/upper plenum

tall short

Downcomer flow area

open restricted

Steam flow out

Feedwater flow in(mixes with separatorreturn)

ESBWR Reactor System Internal Flow Path

ABWR RPV System AssemblyESBWR

ABWR


Effect of Downcomer Flow Area on Total Core Flow

(3613 M W th, ESBW R reference RPV)

0.0

10.0

20.0

30.0

40.0

50.0

60.0

70.0

80.0

90.0

100.0

0.00 1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00

Downcom er Flow Area at Restricted Location (sq. m .)

Frac

tion

of E

SBW

R C

ore

Flow

(%)

Typical BW R Flow Area with 20 jet pum ps

ESBW R Reference Geometry


Effects of ESBWR Design Features on Natural Circulation Flow

0.0

0.5

1.0

1.5

2.0

2.5

3.0

1 2 3 4

Nat

ural

Circ

ulat

ion

Flow

Improved Separator

Improved InternalsTaller chimney

Shorter Fuel

Ele. Down. RestrictionTypical BWR

Typical BWR

Eliminating downcomer restriction

Taller vessel, shorter fuel

Improved internals/separator

DESIGN FEATURES


0.00

0.50

1.00

1.50

2.00

2.50

3.00

3.50

4.00

4.50

5.00

0.00 2.00 4.00 6.00 8.00 10.00 12.00 14.00 16.00 18.00 20.00

Average Flow per Bundle (kg/s)

ABWR

ESBWR

BWR/5

POWFLO-2.xls chart 9(3)

Jet Pump Plant Nat. Circulation

Internal Pump Plant Nat. Circulation

Comparison of Natural Circulation Flow for BWRs

ESBWR has 2 to 3 times more natural circulation flow;power/flow ratio same as pumped plants at rated conditionESBWR has 2 to 3 times more natural circulation flow;power/flow ratio same as pumped plants at rated condition


Minimum Critical Power Ratio (MCPR)• Assures no boiling transition will occur during normal plant

operational transients• MCPR is the ratio of the critical bundle power, at which

boiling transition is calculated to occur, to the operating bundle power

• Operating limit MCPR = Safety limiting MCPR + ∆CPR

Design target MCPR

Plant designed to operateabove this line

∆CPR for limitingtransient

Operating limit MCPR

Safety limit MCPR = 1.0999.9% fuel rods no boiling transition

Margin

MCPR

Cycle Exposure


ESBWR ∆CPR

• ESBWR Transient Analyses -- ∆CPR

• For 33% Bypass capacity, limiting ∆CPR is 0.1

Case Event and condition ∆CPR

1 Generator load rejection with failure of all bypass valves (Stop valve position scram, similar to ABWR – K6/7)

0.095

2 Feedwater controller failure, (maximum demand at 150%)

0.101


Margins to Operating Limit MCPR

ESBWR Design Target 1.38

Bypass Capacity 33%

Scram signal Valve Position

Safety Limit MCPR for GE12 1.09

Target ∆CPR 0.1

Operating Limit MCPR 1.19

Margin to Operating Limit 16%


LOCA and Containment Responses• TRACG used to perform both the LOCA and

containment analyses• For LOCA (0 to 1 hours)

– Fine nodalization in RPV, coarse nodalization in containment to provide system responses to the RPV

– Key output: mixture level inside shroud and Peak Cladding Temperature (PCT)

• For containment (0 to 72 hours)– Fine nodalization in containment, coarse nodalization in

RPV to provide system responses to the containment– Key output: Long term containment pressure


Main Steam Line Break – Largest Pipe Break• Objective

– To demonstrate the LOCA and Containment responses after a postulated pipe break

– To show the design margins in the ESBWR

• Key assumptions– 4 PCCs with a total capacity of 54 MW– No credit for the ICs– For long term containment calculation, leakage flow

between DW and WW included as

21.0cmk

A=


Main Steam Line Break – LOCAIC PCC

Dryer

Steam Dome

GDCS Pool

Suppression Pool

Upper Drywell

LowerDrywell

BDL

SDCL

GDCS

DPV

To DW

MSL

SRV

DPV

ICL V.B.

-10.0

0.0

4.65

17.50

24.600

29.853

To VSSL

Tank

10.10

16.75

L0 0.0000

L21 27.560

3.55

ESBWR TRACG LOCA MODEL

FW

ESBWR1-a.CNV

• Nodalization– Fine nodalization in RPV, coarse

nodalization in containment

• Key design objectives– Core covered by mixture at all times– No core heatup


Mixture Levels Inside Shroud and Downcomer

0

5

10

15

20

25

0 500 1000 1500 2000 2500 3000 3500 4000

Tiime (sec)

Top of Upper Plenum

Top of Active Fuel

Downcomer Mixture LevelMixture Level inside Shroud


MSL Break LOCA – Downcomer and GDCS Pool Levels

0

5

10

15

20

25

0 500 1000 1500 2000 2500 3000 3500 4000

Tiime (sec)

Top of Active Fuel

Downcomer Mixture Level

Downcomer Collapse Level

GDCS Pool Level

Level 1

GDCS Flow


RPV, DW and WW Pressures

0

10

20

30

40

50

60

70

80

90

100

0 500 1000 1500 2000 2500 3000 3500 4000

Time (Sec)

RPV Pressure

Drywell Pressure

Wetwell Pressure

Design Pressure

Note 1Note 2

Note 1: Bounding estimate, DW Press = all air in WW + PCC vent submergence, before GDCS drainNote 2: Bounding estimate, DW Press = all air in WW + PCC vent submergence, after GDCS drain

DW pressure shows > 20% Margin to the design pressureDW pressure shows > 20% Margin to the design pressure


Differential Pressure (DW – WW)

-2

0

2

4

6

8

10

12

0 500 1000 1500 2000 2500 3000 3500 4000

Time (Sec)

Differential Pressure (Drywell - Wetwell)

DW/WW pressure difference drives the flow through the PCC heat exchangersDW/WW pressure difference drives the flow through the PCC heat exchangers


Reactor Decay Heat and PCCS Heat Removal

0

10

20

30

40

50

60

70

80

0 500 1000 1500 2000 2500 3000 3500 4000

Time (Sec)

Decay Heat

PCCS Condensation Power

PCCS removes heat during the blowdown phase, limiting suppression pool heatupPCCS removes heat during the blowdown phase, limiting suppression pool heatup


PCC Tube Total and Partial Air Pressures

0

10

20

30

40

50

60

0 500 1000 1500 2000 2500 3000 3500 4000

Time (Sec)

Pres

sure

(Psi

a) Total PCC Tube Pressure

Partial Air Pressure at Bottom of PCC Tube

at Middle of PCC Tube

at Top of PCC Tube


0

100

200

300

400

500

600

0 500 1000 1500 2000 2500 3000 3500 4000

Time (Sec)

Mas

s Fl

ow R

ate

(kg/

s)

Total GDCS Flow

~ 8200 gpm

GDCS - Low pressure and low flow rate makeup system

GDCS Flow


Main Steam Line Break – Containment

• Nodalization– Fine nodalization in

containment, coarsenodalization in RPV

• Key design objectives– Long term DW pressure

below design value with margin

IC1 PCC

BREK41

VLVE 47VLVE 51PIPE 46

24.6

17.50

4.65

0.00m

VLVE 10, 18, 42

VLVE 07

SUPPRESSIONPOOL

CHIMNEY

RPV

STEAMDOME

W ETWELL

TEE 09

1GDCSPOOL

CORE

CHAN 08

LOWERPLENUM

TEE 35(LOWER DRYW ELL)

PIPE 11

VSSL 01

VLVE24, 28

TEE 02

TEE 03

TEE 04

3 PCC

PIPE 52

PIPE 86PIPE 91PIPE 92

TEE 88TEE 25TEE 26

VLVE12, 1319

TEE 62

To Drywell

To RPV

TEE 63

To Drywell

To RPV

16.75


MSL Break Containment – RPV, DW and WW Press.

0

10

20

30

40

50

60

70

80

90

100

0 12 24 36 48 60 72

TIME (HR)

RPV

DRYWELL

WETWELL

Design Pressure

Note 1Note 2

RPV

DWWW

DW pressure shows > 20% margin to the design pressureDW pressure shows > 20% margin to the design pressure


WW Airspace Temperatures

40

60

80

100

120

140

160

180

200

220

0 12 24 36 48 60 72

TIME (HR)

WetwellAirspace Tv

Tsat


Reactor Decay Heat and PCCS Condensation Power

0.0E+00

1.0E+07

2.0E+07

3.0E+07

4.0E+07

5.0E+07

6.0E+07

7.0E+07

8.0E+07

0 12 24 36 48 60 72

TIME (HR)

DECAY HEAT

Total PCC PR

3-PCC PR

1-PCC PR

Decay Heat

Total PCC PR

3-PCC

1-PCC


Total PCCS Drain Flow to RPV

0

10

20

30

40

50

60

70

80

90

100

0 12 24 36 48 60 72

TIME (HR)

MA

SS F

LO

W (L

BM

/S)

Total Drain Flow

~ 150 gpm


-1

-0.5

0

0.5

1

1.5

2

2.5

3

0 12 24 36 48 60 72

TIME (HR)

Pdw-Pww

Differential Pressure (DW – WW)


Leakage Flow (DW to WW)

DW-WW LEAKAGE FLOW

-0.03

-0.02

-0.01

0

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0 12 24 36 48 60 72

TIME (HR)

LEAK


Summary of Main Steam Line Break (largest break) Analyses

• ESBWR has large margin (> 3m) to core uncovery and heatup

• Calculated DW pressure shows > 20% Margin to the design pressure

• Total PCCS heat removal capacity greater than decay heat (after 2 hours)

• Overall pressure and level (inventory) responses are mild in nature, NO requirements for fast action

Other breaks expected to have similar responsesOther breaks expected to have similar responses


Design Features Affecting LOCA Response

Steam flow out

Feedwater flow in(mixes with separatorreturn)

ESBWR Reactor System Internal Flow Path

ABWR RPV System Assembly

ESBWR has much more water inventory!ESBWR has much more water inventory!

ESBWR

ABWR

ShortShortShortLongSeparator standpipes

~21.8~21.921.127.7Vessel height, m

929488222Water volume outside shroud (above TAF), m3

~1/2~1/2~ 1/2~ 1/4TAF above RPV bottom

~3.66~3.663.663.05Core height, m

YesYesNoNoLarge pipes below core

BWR4BWR5ABWRESBWR


Comparison of Mixture Levels Inside Shroud Following a Pipe Break

-4

-3

-2

-1

0

1

2

3

4

5

6

7

8

9

10

11

0 100 200 300 400 500 600 700 800 900 1000 1100 1200

TIME AFTER PIPE BREAK (sec)

TOP OF ACTIVE FUEL (TAF)

ESBWR

ABWRBWR4BWR5

SBWR

Mixture Level Inside Shroud

LPCS LPCI

ADS LPFL

ESBWR has large margin to core uncovery and heatup– other breaks expected to have similar responses

ESBWR has large margin to core uncovery and heatup– other breaks expected to have similar responses


ESBWR Features That Improve Transient Pressure Response

• Taller reactor vessel• Large steam volume in the chimney region• Higher safety valve setpoint to prevent valve opening

and inventory loss


Reactor Pressure Response to Isolation Events

ESBWR has slower pressurization - no relief valves openESBWR has slower pressurization - no relief valves open

6

7

8

9

0 10 20 30 40 50 60TIME (sec.)

RPV

PR

ESSU

RE

(MPa

)

SRV Setpoint (ABWR)

SRV Setpoint (ESBWR)

ABWR SRV Open

ESBWRABWR

Initial Pressurization Rate: (ABWR) ~ 2x(ESBWR)

Load Rejection Without Bypass


ESBWR Design Features That Improve Containment Response

• Wetwell gas space volume increased– GDCS pool gas space connected to wetwell– 10 to 25% increase in wetwell volume after GDCS pool drains

• PCCS capacity increased– Total PCCS heat removal capacity greater than decay heat (after 2

hours)

• Containment overpressure relief system added


Containment Pressure Following a Pipe Break

0.0

0.2

0.4

0.6

0.8

1.0

10 100 1000 10000 100000TIME AFTER PIPE BREAK (SEC)

(DR

YWEL

L PR

ESS.

/DES

IGN

PR

ESS.

)

ABWR

SBWR

1 hr 24 hrs

ESBWR

ESBWR has > 20% margin to design pressureESBWR has > 20% margin to design pressure


Summary

• Natural circulation flow increased– Un-restricted downcomer, tall chimney, shorter fuel & taller vessel– Power/flow ratio same as pump plants at rated condition

• LOCA response improved– Taller vessel and larger initial inventory in the vessel downcomer – No need for fast acting, high pressure and large flow rate inventory

makeup– Large margin to core uncovery and heatup

• Containment response improved– Wetwell volume increased by moving GDCS pool– Containment overpressure relief system added– ESBWR containment has > 20% margin to design pressure even with

lower containment design pressure than ABWR/SBWR

ESBWR design features improve plant performanceESBWR design features improve plant performance

esbwr plant performance - nrc

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