AREMThe B&W

1% IN Owners Group I

Revision to BAW-23741 0 CFR 50.46 Long-Term Core

Cooling following a Hot LegU-bend LBLOCA

John Klingenfus - AREVAFebruary 24, 2005

Rockville, MD

Topics for Discussion

*m Thermal-Hydraulic BackgroundE Challenges to Demonstrating Post-LOCA

Long-Term Core Cooling and Key ParametersNeeded to Demonstrate Long-TIerm CoreCooling

* Inputs needed to perform the dose evaluation

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ThermalmHydrauaic Background

m The greatest challenge to the first four 1 0 CFR 50.46 criteria(POT, local oxidation, whole-rcore hydro'gen generation,- andcoolable geometry) are produced by LOCAs in the CLPDp'iping for the B&W-designel plants. This is due primarily tothe bypass of ECCS flow to the break without passingthrough the core and providing heat removal.

E Other break locations are less limiting for these four criteria,however, they can produce unique challenges to the fifthcriterion of demonstrating lorng-term core cooling.

II The hot leg U-bend LOCA presents a unique challenge tolong-term core cooling because it has the potential toproduce large SG tube stresses that could result in primary-to-secondary leakage and loss of liquid needed for adequateNPSH for continuous sump recirculation.

....... .BAW2374-_ARE VA o

HL UBEND

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m ot Leg U-Bend Transient

m The ECCS refill following a LOCA in the upper portions ofhot leg piping will cool the thinner SG tubes faster than the

* thicker shell, resulting in a large temperature differentialbetween the SG shell and SG tubes.

E This temperature differential results in large tensile loadson the tubes that could lead to failure of SG tubes that havesubstantial circumferential cracks or volumetric flaws.'

i- This break location does not produce limiting PCTs, peaklocal oxidation, and hydrogen generation predictions,however, it produces a different type of challenge for long-term cooling if SG tubes rupture after the RCS is refilled.

E If the primary-to-secondary leakage from broken tubes is3 not stopped, it could deplete the sump liquid inventory andpotentially compromise ECCS pump NPSH during thesump recirculation phase of the event.

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HL UBEND

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NM BAW-2374 AREVAThe S&WOwners Group

TTS AT Background

E Maximum SG tube loads are calculated for the largesttemperature differential between the SG shell and tubes (TTSAT)

a SG tube loads are dependent on the radial location of the tubes.o Tubes on the periphery have the highest loads.o The loads on the interior tubes are lower due to the deflection of the tube

sheets.

* Many parameters have some bearing on the. SG tube and SGshell temperatures.

a Keys to establishing the maximum. TTS AT includeo SG tube temperatures during the transient* Initial SG shell temperature plus the transient cooling

Pes B 374 R E VA O era Group

SG Tube Temperatures-

a The transient SG tube temperatures are dependent on break sizeand locationo Lower and middle hot leg breaks limit SG tube refill level

+ Tubes approaches RCS saturation temperature based primarily onECCS flow, break area, and containment pressure

e Upper hot leg break* Ultimately approaches ECCS liquid temperature plus temperature rise

from core decay heat contribution* Break size determines the ECCS flow rates, which determines the time

for the RCS refill and time required for the tube to asymptoticallyapproach its quasi-steady long-term temperature

* Number of ECCS trains in operations defines the refill time and time ofmaximum TTS AT

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SG Shell Temperatures

E SG shell average temperatureo A function of initial operating conditions

* SG pressure - DC saturation temperature* ThOt-core power level, RCS flow, Taveo SG superheat

- MFW flow, T RCS flow, Fouling, SG tubeo Transient shell cooling

D Conduction-limited slower cooling (no amto Secondary side level

- Initial OTSG water inventory- MFW termination- MFW Line flashing- EFW flow

plugging, etc.

)ient losses)

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FIGURE A-5. 177-FA Raised-Loop 14.4 Sq ft DE Hot Leg BreakBroken Loop Shell and Tube Temperatures

800

700 +

LEGEND

Broken Loop Shell Temperature-Broken Loop Tube TemperatureBroken Loop Shell-Tube Temp Diff

640

600

LL

F-a-

wI--

500

400

300'I

i*13.

560

La

480 ¢

a-

I--400

320

200]

100-

00 400 800 1200 1600

TIME, SECONDS ACBWGPcrgessMeting oBAW2374 AAR EVA

2000

FIGURE A-6. 177-FA Raised-Loop 14.4 Sq ft DE Hot Leg BreakIntact Loop Shell and Tube Temperatures

800

700'

600

I -- -

LEGEND

Intact Loop Shell TemperatureIntact Loop Tube TemperatureIntact Loop Shell-Tube Temp Diff

-640

LL6

w

w0-nS

wl

500'

400

300

N."- - -

560

Iii

.LL

-4800

w

wa_

-400200

100'~I

I 320

)000

0 400 800 1200 1600 2C

TIME, SECONDS

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FIGURE A-7. 177-FA Raised-Loop 14.4 Sq ft DE Hot Leg BreakPrimary and Secondary Pressures

800

700-

600

c 500C)IL

w1= 400Cn(nwa. 300'~

IIn

1\X

A-

id .

LEGEND

Primary System PressureIntact Loop Secondary PressureBroken Loop Secondary Pressure

48

40

ua32 5

Cl)w

24 fnw

0-

16

8

-o02000

200

100-

00 400 800 1200 1600

TIME, SECONI -' ru

JZ)A E

A....:

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FIGURE A-8. 177-FA Raised-Loop 14.4 Sq ft DE Hot LegTube to Shell Temperature & Pressure Differences

Break

800

600 .

LEGEND

Intact Loop Shell-Tube TempBroken Loop Shell-Tube TempIntact Loop Prim-Sec PressureBroken Loop Prim-Sec Pressure400*

LL 200w

M

0 0 -w

F- -200-

I,-,

--1-V=_

… ,--.------

II

Ii

-800

. 600

* 400

-*200 <

LL. cc. OD

CnCn

--200 a.

-400

. -600

- -8002000

II ~

-400*I I- I x

~I

I/

I.-/

-600

-8000 400 800 1200 1600

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TTS AT Vs Break Size and Location

m The SG TTS AT was estimated for all break locationsand sizeso The spreadsheet.technique calculated the SG shell temperature

based on a length weighted average based on the SG secondaryside level with a time-dependent steam and liquid pool metaltemperature.

* The break location determined the SG tube temperature.O Break locations that did not have continuous ECCS liquid flow through the

SG tubes used a time-dependent RCS saturation temperature for thetube temperature.

u* Upper hot leg breaks used the ECCS liquid temperature plus an additivevalue for the core power temperature rise.

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Estimated TTS AT Vs Break Size and Location400

350

I

Ca)

0a)4-

CuL-a)

Ea)F-

300

250

. - - - - - - - - - - - -

._ - - - I ' - - - - -

-:1 ------ -= _ ,--

-Upper HL

I- HL Pzr SL Elev

-I-Lower HL

-." CLPS

200

150

100

*-O Analyzed Pzr SL

0 Analyzed HL U-Bend

O HL Vent Line

50

0

- - - - - - -I- - - - - - - - - - - - -I -I I

i I I

0.01 0.1 1 10 100Break Size, ft2

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Limiting Breakl Size and Location

* DEG break in the HL U-bend (candycane) region is limiting for:o Highest ECCS flows that refill the RCS in the shortest time periodo Quickest cooling of SG tubes via flow of the ECCS through the steam

generators to the breako Largest TTS AT based on BAW-2374 Revision 1 Evaluations

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The B&WOwner� Group

Primary-to-Secondary Leak Flows

m However, if one or more tubes break, the DEG break may limit

primary-to-secondary leak rate.o The number of SG tubes that could break is neededa AP across SG tubes after rupture is controlled by containment

pressure, SG pressure, and RCS elevation heado After the SG secondary fills, the steam line (SL) geometry will

determine the secondary side elevation heado Some plant geometries will limit the liquid loss to SG secondary tube

bundle and SL up to the containment pressure plus RCS elevationhead

* Others may have continuous flow outside of containment if isolationis not established by the operators because the SL routing is belowthe hot leg break location

,l g O BAW-2374 A R E VA

Primary-to-Secondary Leak Flows

a A reduced RCS break area can raise the primary side pressureand increase AP across SG tubes and push liquid over SL spillover (SO) elevation.

E But, a reduction in the RCS break size wouldo Reduce the TTS AT and SG tube loado Potentially reduce the number of SG tubes that fail* Increase the time to maximum tube loado Increase time for operator action

P BAW-2374 -- A R E VA

Sampile SG Tube Leakage Calculation

E General calculation to define times to fill thesecondary side to an approximate SG tubebundle and steam line volume to the isolationvalves of 4700 ft3.

E Used conservatively high containmentpressure of 30 psia (constant).

* Used constant 14.7 psia secondary pressure.E Freespan double-ended SG tube leak in the

broken loop SG.

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Approximate Time to Fill the SGISL (4700 ft3) Vs# Tubes Broken

12 -

10 -

8 -

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\ II Il I I. ' I II .I . I

. I 'I I .I II

I ' I I I II

I I I .II II I I

I I IIII

I I I I

I I I

4 -

2 -

U I ;

0 1 2 3 4 5 6 7Time, (hour)

5 m BAW-2374 . R EVA The B&W ro IOwners Group|

Primary-to-Secondary Leak Flows

a A failure of secondary side isolation has the potential forcontinual loss of RCS liquid after the SG and SL are full whichwill continue to deplete the sump inventory.

o Based on containment pressure

o Plant SL geometry

m Additional operator actions may be needed to isolate. any leakagepathways to preserve the sump liquid inventory

* The dose from the leakage will be a function of:o Leakage rate based on number of failed tubes and EOP actionso Status of the fuel pin cladding during the transient

4 Break size, break location, core power shape, CFT initial conditions mayplay a role

_3RC 0 onBAWT-2374: AREVA O r1 ; rup

Summary Key Meeting Objectives

This background discussion has been provided to set the stagefor the discussion on the methods used to determine the numberof tubes ruptured for the limiting RCS break area and resultantSG tube loads.

* The scope of future 10 CFR 50.46 long-term core coolingcalculations is highly dependent on the number of SG tubes thatbreak as a result of the transient.

* The scope of 10 CFR 100 calculations is highly dependent onfuel pin rupture.

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