6 Thermal Stratificaiton Monitoring Angra2

8/6/2019 6 Thermal Stratificaiton Monitoring Angra2

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Thermal Stratification Monitoring in Angra 2

NPP - Brazil

Miguel CisternasELETRONUCLEAR

Nuclear Plant Fatigue Applications Workshop, January 21-23, 2009, Charlotte, NC


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ELETRONUCLEAR - BRAZIL

PWR

4 LOOPS

1350 MWNSSS VENDOR:SIEMENS/KWUAbout 5,6 EFPY

PWR

2 LOOPS657 MWNSSS VENDOR:WESTINGHOUSEAbout 11 ,5 EFPY

FatigueProThermal StratificationMonitoring System

Angra 1Angra 2

Thermal Stratification Monitoring(RHR, Feedwater, Excess Letdown)


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THERMAL STRATIFICATION

The temperature difference between thehot water(top) andcoldwater(bottom) in a piping is known as thermal stratification.

Hot Water

Cold Water

Pipe

ThermalStratification::Cause increasing in piping displacements

ThermalStratification: Thermal stresses increase (fatigue life is reduced)

THOT

STRATIFIED PIPE

TCOLD


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THERMAL STRATIFICATION IN ANGRA 2 NPP

USNRC Bulletins 88-08/88-11 Ground Zero

- Surge Line was analyzed considering the

phenomenon of thermal stratification.

- Operational experience shows that other pipingcan operate with stratified pipes, who in certainconditions can lead the piping to undergo fatigue.

- AREVA recommended in Angra 2, that a fatigue

monitoring system were implemented.

- Following this recommendation,

ELETRONUCLEAR developed a thermalstratification monitoring system.


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TYPICAL THERMOCOUPLES CONFIGURATION

Two typical configurations are used in Angra 2:

Angular position T1 (270)


Single Configuration Full Configuration

The thermocouples are installed on the externalsurface of the pipe, in several sections of the

piping, and have the function of determine theoperational transients







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FULL CONFIGURATION OF THERMOCOUPLES AT

SURGE LINE OF ANGRA 2

Angra 2 Surge Line


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DATA ACQUISITION UNIT FieldChart NOVUS

The FieldChart software allows to display the Field Logger's datain digital and graphic format, in batches or in real time, and inreal time trend and historic trend views. The Microsoft Windows-compatible software allows to zoom, superimpose and link

graphs, and print or export all data.


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MONITORING LOCATIONS in ANGRA 2 NPP

Temperature measurements locations are listed next

Surgeline:3 sections with 15 thermocouples (tc)

Residual Heat Removal System:8 sections with 19 tc

Hot RCL :2 sections with 7 tc Main Feedwater Line :4 sections with 11 tc

Auxiliary Feedwater Line:4 sections with 8 tc

21 measurements sections with a total of60 thermocouples


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SUMMARY OF RESULTS OF THERMAL

STRATIFICATION IN ANGRA 2 NPP


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THERMAL STRATIFICATION NOT SPECIFIED IN

ANGRA 2 NPP AT MAIN FEEDWATER LINE

The steam generator feedwater nozzle is connectedhorizontally to the steam generator as shown next


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Measured performed during hot standby mode ofoperation for a longer period of time due to repairsplant conditions, captured thermal stratification that

was not specified in the existing thermodynamicloading transients for the SG Nozzles of Angra 2


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MODES OF OPERATION OF ANGRA 2 NPP

Full Power

Hot Standby

Full Power

Cold Leg

Hot Leg


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Transient 1240 C - 115 c(464F - 239F)

Thermal

StratificationT= 115 C(T= 207 F)

Transient 2115 C - 240 c(239F - 464F)


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Summary of Fatigue Analysis at Loop 4of Main Feedwater Line

at section close to the Steam Generator Nozzle


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CONCLUSIONS

Thermal Stratification of the Main Feedwater Lineoccur while the plant is starting up or cooling down,or when the plant is in hot standby mode of operation.

Besides global thermal stratification (unexpectedmovement ), Angra 2 discovered cyclic thermalstratification (pipe cracks ), acting simultaneously at

Main Feedwater Line. This kind of thermalstratification was not specified in the existingthermodynamic loading transients for the MainFeedwater Line.

In order to reduce the effects of the thermalstratification at the Main Feedwater Line, which can

result in a large fatigue and a short load life, Angra 2is now, limiting the hot standby mode of operation.

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6 Thermal Stratificaiton Monitoring Angra2