Risk-Informed Revision of the NRC’s Rules Regulating ...web.mit.edu/ans/www/documents/seminar/S09/kirk_slides.pdf · Risk-Informed Revision of the NRC’s Rules Regulating Pressurized

Risk-Informed Revision of the Risk-Informed Revision of the NRC’s Rules Regulating

Pressurized Thermal Shock (PTS)Pressurized Thermal Shock (PTS)

Mark EricksonKirkMark EricksonKirkRES/DE/CIB

[email protected] i k ki k@ i [email protected]

American Nuclear Society Meeting – MIT Section6th April 2009Massachusetts Institute of TechnologyCambridge, MA

Presentation Outline

• What is PTS• Current (circa-1984) PTS regulations• Why revise? Why risk-informed?

PTS U i d li & j h• PTS – Uncertainty modeling & project approach• PTS – Major outcomes

L l d & ff t i f d• Lessons learned & efforts moving forward





What is PTS?Primary Side Break• Inventory (water &

steam) lost through the

Primary Water in

Downcomer EmbrittledEmbrittledsteam) lost through the break is replaced by colder (40-70F) water held in external tanks

(212oF to 40oF)

Embrittled 8-inch

thick RPV Steel Wall

t 550F

Embrittled 8-inch


t 550FSecondary Side Break• Loss of pressurization in

the secondary leaves t b ili (212F) t

ID OD

at 550F

Thermal

at 550F

water boiling (212F) at atmospheric pressure

• Primary side inventory just across the heat

ThermalShock

jexchanger also approaches 212F

• Natural circulation in primary draws colderprimary draws colder water into downcomer

What is PTS?

1. Rapid cooling high thermal stresses

Primary Water instresses

2. Pressure may add to stresses3 Years of operation

Water in Downcomer

(212oF to 40oF)

Embrittled 8-inch


Embrittled 8-inch

thick RPV Steel Wall3. Years of operation

embrittled vessel

• Combination of 1&2&3 may ID OD

Steel Wall at 550F

Steel Wall at 550F

• Combination of 1&2&3 may challenge vessel integrity

b Th l l t i t

ID ODThermalShock

• n.b.: Thermal-only transients excluded a priori in 1980s … should not have been





10CFR50.61 Provisions• Vessel condition monitored using

an estimate of the steel’s fracture toughness transition temperature f i di i (RT ) b i d

Primary Break T = 35oFafter irradiation (RTNDT) obtained

through a 10CFR50 App. H surveillance program. Secondary Break

TMIN = 212oF

TMIN = 35 F

hnes

s

• If RTNDT exceeds 300ºF (for circ. welds) or 270ºF (for all other materials) before end of license (EOL), the licensee must re

Tou

gh( )

– Do something to keep RTNDT below 300ºF or 270ºF

• Reduce Flux: Reduce embrittlement rateA l b i l h i l

Frac

tur

• Anneal: De-embrittle the material (see RG 1.162)

– Show that RTNDT above 300ºF or 270ºF is safe

• Analyze: Plant specific analysis T t

RTNDTRTNDTRTNDTRTNDT RTNDTRTNDTRTNDT@LIMIT

• Analyze: Plant specific analysis per RG 1.154

TOPERATING = 550oF

Temperature





Technical Motivations PRA

• Use of latest PRA/HRA d t

Developments since the 1980s suggested the overalldata

• More refined binning• Operator action

credited PFM

1980s suggested the overall conservatism of the rule.

• Acts of commission considered

• External events considered

• Significant conservative bias in toughness model removed

• Spatial variation in fluence recognized

• Medium and large-break LOCAs considered

TH

• Most flaws now embedded rather than on the surface, also smaller

• Material region dependent embrittlement props• Many more TH

sequences modeled• TH code improved

embrittlement props.• Non-conservatisms in arrest

and embrittlement models removed

Regulatory Motivations

• Produces unnecessary burdenTechnical improvements suggest strongly that current RT limits of 300ºFTechnical improvements suggest strongly that current RTNDT limits of 300 F and 270ºF are more conservative than needed to maintain safety.

• Does not necessarily increase overall plant safetyFocus on unnecessarily conservative RTNDT limits can divert resources from other more risk-significant matters.

• Creates an artificial impediment to license renewalpUnnecessarily conservative RTNDT limits alter perception of the safe operational life of a nuclear power plant.

• Causes work that produces no real benefit• Causes work that produces no real benefit

Why Risk Informed / Probabilistic?Probabilistic?

• Consistent with Commission policy guidance

• Provides a logical and systematic way to address uncertainties in a complex physical systemuncertainties in a complex physical system

• EnablesEnables– Engineers to do engineering– Decision makers to make decisions





PTS ProjectParticipantsParticipants

PEAI

PNLSandiaNational

SARTREX

NationalLaboratories

PTS ProjectTimelineTimeline

1-1998

2001

2001

2002

2005 6-2009

2004

Planning &Model Building

3½ years

Computing / Thinking/ Defending

4 years

Deciding & Approving4 years

6- 12-

12- 6-12-

3½ years 4 years

PTS ProjectUncertainty Modeling a Central Feature

Good engineering practiceOur approach features

• Explicit treatment of Good engineering practice

Ensures that themathematical model

t t i ti

• Explicit treatment of uncertainties

• Uncertainty classification & separation represents uncertainties as

they are physicallyunderstood (or believed)

to exist.

separation Aleatory Epistemic

• Uncertainty

Epistemic Uncertainty (per Scott Adams)Irreducible

yquantification

Following a systematic (per Scott Adams)

Knowable(in principal)

Irreducibleprocess makes uncertainties “visible” and, thereby, improves

comprehensiveness

Uncertainty TreatmentJanus Approach Janus Approach

• Examine / characterize uncertainties duringuncertainties during model development

• Examine / characterize uncertainties after

l i i lanalysis is complete

Uncertainty TreatmentDuring Model DevelopmentDuring Model Development

#1: Establish a credible model

Quantify Uncertainties Address Uncertainties

#1: Establish a credible model

Relative to data

Relative to physical understanding

Intentionally conservative models / parameters / judgmentsunderstanding

(independent metric of truth) & data

judgments

Ignore (uncertainty very small)

Ignore (uncertainty very small relative to other factors included in model)

Uncertainty TreatmentFollowing AnalysisFollowing Analysis

#1: Perform sensitivity studies on credible perturbations to baseline model.perturbations to baseline model.

#2: Assess “balance” of residual uncertainties.

ResidualConservatisms

ResidualNon-Conservatisms

Scope of Analysis• Detailed analysis of 3 PWRs

– All PWR manufacturers

Beaver ValleyBeaver ValleyPalisadesPalisades

• 1 Westinghouse (W)• 1 Combustion Engineering (CE)• 1 Babcock & Wilcox (B&W)

1 l t f i i l (1980 )– 1 plant from original (1980s) PTS study

– 2 plants very close to the current PTS screening criteriaPTS screening criteria

• Generality to all PWRs assessed– Characteristics of dominantCharacteristics of dominant

transients– Examination of 5 more high

embrittlement plantsOconeeOconee

Overall Model

PRA E tTh lP b bili ti

Probabilistic Estimation of Through-Wall Cracking FrequencyAcceptance Criterion for TWC Frequency

PRA EventSequenceAnalysis

(SAPPHIRE)

ThermalHydraulicAnalysis(RELAP)

ProbabilisticFractureAnalysis(FAVOR)

SequenceDefinitions

P(t), T(t), &HTC(t)

Established consistent with• 1986 Commission safety goal

policy statement• June 1990 SRM• RG1.174

ConditionalProbability of

Thru-WallCracking, CPTWC

YearlyF f [CPTWC]

Screening Limit Development

SequenceFrequencies

freq

Frequency ofThru-WallCracking

[CPTWC]x

[freq]

Freq

uenc

y of

Wal

l Cra

ckin

g

freq

Vessel damage, age,

Year

ly F

Thru

-W Screening Limit

Generalizationto all U.S.

PWRs

20

or operational metric

Risk-Informed PTS Limits Follow from Policy DecisionsFollow from Policy Decisions

51 FR 28044, Safety Goal Policy Statement (1986)

SECY-00-0077, Modifications to Safety Goal Policy Statement

QHOs < 0.1% of the total public risk

(prompt & latent)

Mean Mean

Regulatory Guide 1.174 CDF < 1x10-4/ryCDF & QHO limits for

generic decisions10 CFR 50.61aV l Al i P i d Th l Sh k R l Mean -Mean

CDF 10-4/ry 10-5/ryLERF 10-5/ry 10-6/ry

Voluntary Alternative Pressurized Thermal Shock Rule

• Accident sequence progression study shows that through-wall cracking rarely leads to LERFwall cracking rarely leads to LERF

• Conservatively assumes equivalence of LERF and the yearly through-wall cracking frequency (TWCF) of the reactor pressure vessel

• Tolerable limit on TWCF established as 10-6/ry

Model for TWCF EstimationManagement ViewManagement View

PRA EventSequence

ThermalHydraulic

ProbabilisticFracture SP(t) T(t) & Sequence

Analysis(SAPPHIRE)

HydraulicAnalysis(RELAP)

FractureAnalysis(FAVOR)

SequenceDefinitions

P(t), T(t), &HTC(t)

ConditionalProbability of

Thru-WallCracking, CPTWCg, TWC

YearlyFrequency of

Thru-Wall[CPTWC]

xf

SequenceFrequencies

Cracking [freq]

Frequenciesfreq

Pressurevs. time in

Downcomer

Temperaturevs. time in

Downcomer

Vapor• Viscosity• Density• Enthalpy• Conductivity

STOP

NO LookupTablesPlant State

att + t

ProductForm

Weld% SMAW

Plate & Forging Cladding-

% Repair

TWCF Model – Some Details

Physical Plant

Fluid StaticEquilibrium

Model

Fluid• Viscosity• Density• Enthalpy• ConductivitySequence

Definition

Conditions ateach node_____• Pressure• Temperature• Fluid velocity• Gas velocity• Void fraction

FlowRegime

Correlations

HeatTransfer

Coefficients

YES

IsTMIN < 400F

ANDdT/dt > 100F/hr? Increment

Time

t = t+t

time = 0Initial

ConditionGuess

Equilibrium Conditions ateach node_____• Pressure• Temperature• Fluid velocity• Gas velocity• Void fraction

SequenceComplete?

YES

NO

T vs. tto PFM Metal

• Thermal conductivity• Metal surface

roughness• Metal area

ShorehamWeld Flaw

DensityModel

Sh. & PVRFlaw Size

Model

Sh. & PVRAspectRatioModel

E.J.Truncation

Model(=2-in)

Weld Dir.Orientation

Model(Phys + Obs)

Distribution of EmbeddedWeld Flaws x

WeldFusionArea

Sh. WeldFlaw Density

Model(/10 lg.,/40 sm.)

(E.J.)

Sh. & PVRWeld

Flaw SizeModel

Sh. & PVRWeld

AspectRatio Model

E.J.Truncation

Model(0.43-in.)

Coin TossOrient. Model

(Obser. & Phys.)

Distribution of EmbeddedPlate Flaws x Plate

Volume

Obs. BuriedClad FlawDensity

in PVRUF/ 10(E.J.)

E.J. FlawDepthModel

(a = tCLADALWAYS)

PVR & HCAspectRatioModel

E.J.Truncation

Model (tCLAD)

Circ. Orient.Model(Obs.)

Distribution of Surface Flawsin Plates& Welds x Clad

Area

Flaw Locationin Vessel Wall, x’

# ofLayers?

NoSurf.Flaws

1

>1

Bead Size

Groove Design

Weld LengthPlate Area

Vessel Thickness

Vessel Inner Rad.

Vessel Length

Clad Bead Width

% SAW

Vessel Thickness

P&T vs. tto PFM

Best-EstimateID Fluence

(Reg-Guide Calcs.)

GlobalFluence

THModel

1

Layout “inside” the • SG steam outlet• SG feed line• ECCS input

THNodalization(1D Model)

MathematicalIdealization

of Plant

Control System

Geometric LossCoefficients

(e.g., for elbows)

Clad Thickness

CTEPLATE

Flaw Depth, a

Flaw AspectRatio, 2c/a

Flaw Density,

STOP

NO

YESIs

Location > 3/8T from ID?

Weld residual

CTE Mismatchresidual

CTEWELD

CharpyIrradiation

ShiftCharpy

TemperatureShift (T30)

Cu(RVID)

Thru-WallAttenuation

Model

Ni(RVID)

P

FluenceUncertainty

SampledID Fluence

LocalFluence

Uncertainty

FluenceAt Flaw

CuUncertainty

SampledCu

NiUncertainty

SampledNi

PSampled

Flaw Model

CrackInitiationM d l Applied

KI

Elastic Modulus

Vessel Diameter

IrradiatedInitiation

ToughnessIndex

Temperature(RTTOUGH(I))

ResistanceKIc

dKI/dt > 0AND

A-KI > R-KIc

InitiationToughnessTransition

Curve

CPI>0

OperatingProcedures

SelectionCriteria

SingleSequence ofEvents that

Represent Bin

BinFrequencyHistogram

StressIntensity

FactorModeldKI/dt

RTNDT(u)Method

YES

Generic?

YES

NO(u) = 0

C i

IrradiatedToughness Shift

(RTTOUGH)

+

CPI=0

NO

Vessel Thickness

Poisson’s Ratio

CoarseBinningLogic

Coarse Binned

Sequences(50 - 150)

RiskDominantSequencesPRA

JudgmentsOK?

TWCFSEQUENCE>

1% TWCFTOTAL?

ANALYSISCOMPLETE

RefinePRA

P&T vs. t

T vs. t

WeldFlaw?

NO

YES

YESNO

YES

INDEX TEMPERATURE SHIFT MODEL

UNIRRADIATED INDEXTEMPERATURE MODEL

FRACTURE DRIVINGFORCE MODEL

SampledFluence At Flaw

ModelShift (T30)

Oper.Temp.

P(RVID)

Oper.Time

ProductForm

VesselMfg.

Conversionto Toughness

Shift

PUncertainty

SampledP

PRAModel

Completion CheckModel

Un-IrradiatedIndex

Temperature(RTNDT(u)*)

EventTree

Analysis(SAPPHIRE)

Simulator Info.

Plant Equipment

Plant Design

Training

Sequence &Cut Set

Definitions(1E5)

FineBinningLogic

(SAPPHIRE)

Fine Binned

Sequences(300)

ExpertJudgments

HistoricalIncidence

of Plant Upsets

RTNDT(u)(RVID)

YES

(u) = S()+Conversion

to ToughnessTransition

TemperatureUn-Irradiated

Toughness IndexTemperature(RTTOUGH(U))

NUREG/CR-5750

g(50 50)COMPLETE YES

RTTOUGH(I) =MAXIMUM OF RTTOUGH(I)

WELD, & RTTOUGH(I)

ADJACENT PLATE

Initiation-ArrestTransition Curve

SeparationModel

RTARREST

ArrestToughnessTransition

Fluenceat Flaw


Model+Irradiated

ArrestToughness

IndexTemperatureResistance

KIa*

Pf 1=S{ RAND[0,1] }

MAT=Weld&

ResistanceKIa@T

NoInitiation-Arrest

Interaction Model ONKIa(MAX) = KIc

a’>¼T

NO

ResistanceKIa* @T

ld

YES

MAT=Weld&

a’ in Next ¼ TMatrix

Multiply

Yearly VesselFailure

Frequency(TWCF)

Curve

NO

YES

AppliedKI

A-KI>

R-KI

CPF=CPI*FAIL/COUNT

YES

1Irradiated

Toughness Shift(RTTOUGH)

NO

Extend flaw to Infinite Length

Increment Flaw Deptha’ = a + a

Re-Sample

Cu

Ni

P

T vs. t

&a’ in Next ¼ T

Pf xT/4=S{ RAND[0,1] }

Yes

a >¼T?

YES

MINResistance

KI @T

CRACK ARREST MODEL

PROPERTYGRADIENT

MODEL

Initiation-ArrestInteraction Model OFF

Unrestricted KIa(MAX)

Weld?

NO

ResistanceKIa@T

A

FAIL = 0

COUNT = 0

FAIL=FAIL+1

COUNT=COUNT+1

COUNT=100?

YES

Initiation-ArrestInteraction Model ON

KIa(MAX) = KIc

StressIntensity

FactorModel

TUSModelTUS

Upper ShelfToughness

Vs.Temperature

Curve

T vs. t

ResistanceK{J-R}@T

Elastic Modulus

Vessel Diameter

Vessel Thickness

Clad Thickness

CTEPLATE

Poisson’s Ratio

P&T vs. t

Weld residual


CTEWELD


DUCTILE TEARING MODEL

A

NO

Thru-WallCrackingModel

Irradiated InitiationToughness Index


(from initiation model)

ProductForm

Weld% SMAW

Plate & Forging Cladding-

% Repair

Focus on the PFM Models

ShorehamWeld Flaw

DensityModel

Sh. & PVRFlaw Size

Model

Sh. & PVRAspectRatioModel

E.J.Truncation

Model(=2-in)

Weld Dir.Orientation

Model(Phys + Obs)

Distribution of EmbeddedWeld Flaws x

WeldFusionArea

Sh. WeldFlaw Density

Model(/10 lg.,/40 sm.)

(E.J.)

Sh. & PVRWeld

Flaw SizeModel

Sh. & PVRWeld

AspectRatio Model

E.J.Truncation

Model(0.43-in.)

Coin TossOrient. Model

(Obser. & Phys.)

Distribution of EmbeddedPlate Flaws x Plate

Volume

Obs. BuriedClad FlawDensity

in PVRUF/ 10(E.J.)

E.J. FlawDepthModel

(a = tCLADALWAYS)

PVR & HCAspectRatioModel

E.J.Truncation

Model (tCLAD)

Circ. Orient.Model(Obs.)

Distribution of Surface Flawsin Plates& Welds x Clad

Area


# ofLayers?

NoSurf.Flaws

1

>1

Bead Size

Groove Design

Weld LengthPlate Area

Vessel Thickness

Vessel Inner Rad.

Vessel Length

Clad Bead Width

% SAW

Vessel Thickness


(Reg-Guide Calcs.)

GlobalFluence

1Clad Thickness

CTEPLATE

Flaw Depth, a


Flaw Density,

STOP

NO

YESIs

Location > 3/8T from ID?

Weld residual


CTEWELD

CharpyIrradiation

ShiftCharpy

Temperaturehif ( )

Cu(RVID)


Model

Ni(RVID)

FluenceUncertainty

SampledID Fluence

LocalFluence

Uncertainty

FluenceAt Flaw

CuUncertainty

SampledCu

NiUncertainty

SampledNi

Flaw Model

CrackInitiation

AppliedKI

Elastic Modulus

Vessel Diameter


ToughnessIndex


ResistanceKIc

dKI/dt > 0AND

A-KI > R-KIc


Curve

CPI>0

StressIntensity

FactorModeldKI/dt

RTNDT(u)Method

YES

Generic?

NO (u) = 0


(RTTOUGH)

+

CPI=0

NO

Vessel Thickness

Poisson’s Ratio

P&T vs. t

T vs. t

WeldFlaw?

NO





ShiftModelShift (T30)

Oper.Temp.

P(RVID)

Oper.Time

ProductForm

VesselMfg.


Shift

PUncertainty

SampledPModel

Un-IrradiatedIndex


(RTTOUGH(I))

RTNDT(u)(RVID)

YES





YES


WELD, & RTTOUGH(I)

ADJACENT PLATE

Initiation-ArrestTransition Curve

SeparationModel

RTARREST

ArrestToughness

Fluenceat Flaw


Model+Irradiated

ArrestToughness

IndexTemperatureResistance

KIa*

Pf 1=S{ RAND[0,1] }

MAT=WeldResistance

NoInitiation-Arrest

Interaction Model ONKIa(MAX) = KIc

NO

Resistance*

YES

MAT=Weld&

a’ in Next ¼ TMatrix

Multiply

Yearly VesselFailure

Frequency(TWCF)

TransitionCurve

NO

YES

AppliedK

A-KI>

R-KI

CPF=CPI*FAIL/COUNT

YES

1Irradiated

Toughness Shift(RTTOUGH)

NO

Extend flaw to Infinite Length

Increment Flaw Deptha’ = a + a

Re-Sample

Cu

Ni

P

Ia

T vs. t

MAT=Weld&

a’ in Next ¼ T

KIa@T

Pf xT/4=S{ RAND[0,1] }

Yes

a’>¼T?

YES

KIa* @T

MINResistance

KI @T

CRACK ARREST MODEL

PROPERTYGRADIENT

MODEL

Initiation-ArrestInteraction Model OFF

Unrestricted KIa(MAX)

Weld?

NO

ResistanceKIa@T

A

FAIL = 0

COUNT = 0

FAIL=FAIL+1

COUNT=COUNT+1

COUNT

YES

Initiation-ArrestInteraction Model ON

KIa(MAX) = KIc

BinFrequencyHistogram

KI

StressIntensity

FactorModel

TUSModelTUS

Upper ShelfToughness

Vs.Temperature

Curve

T vs. t

ResistanceK{J-R}@T

Elastic Modulus

Vessel Diameter

Vessel Thickness

Clad Thickness

CTEPLATE

Poisson’s Ratio

P&T vs. t

Weld residual


CTEWELD


DUCTILE TEARING MODEL

=100?

A

NO

Thru-WallCrackingModel

Irradiated InitiationToughness Index


(from initiation model)

Focus on the Crack Initiation ModelsOverall Diagram


(Reg-Guide Calcs.)

GlobalFluence

Uncertainty


Flaw Depth, a

Flaw Aspect

Flaw Density,


Model

Uncertainty

SampledID Fluence

Vessel Diameter

1Clad Thickness

CTEPLATE


Weld residual


CTEWELD

CharpyIrradiation

ShiftModel

CharpyTemperatureShift (T30)

Cu(RVID)

Ni(RVID)

P

LocalFluence

Uncertainty

FluenceAt Flaw

CuUncertainty

SampledCu

NiUncertainty

SampledNi

PSampled

AppliedKI

Elastic Modulus

Vessel Diameter

StressIntensity

FactorModeldKI/dt

CPI=0

NO

Vessel Thickness

Poisson’s Ratio

P&T vs. t




Model

Oper.Temp.

(RVID)

Oper.Time

ProductForm

VesselMfg.


Shift

UncertaintyP

Un Irradiated


ToughnessIndex


ResistanceKIc

ResistanceKIc

dKI/dt > 0AND

A-KI > R-KIc


Curve

CPI>0

RTNDT(u)Method

YES

Generic?

YES

NO(u) = 0

Conversion


(RTTOUGH)

+

T vs. t

WeldFlaw?

NO

YES



Un-IrradiatedIndex


RTNDT(u)(RVID)





YES


WELD, & RTTOUGH(I)

ADJACENT PLATE

Crack Initiation ModelsCoded for Accuracy


(Reg-Guide Calcs.)

GlobalFluence

Uncertainty

Accurate

Unknown

Accurate

Unknown

y


Model

Uncertainty

SampledID Fluence


Flaw Depth, a

Flaw Aspect

Flaw Density,

Other ModelsAvailable

Conservative

Accurate, ConservativeJ d t h U k

Other ModelsAvailable

Conservative

Accurate, ConservativeJ d t h U k

Vessel Diameter

1Clad Thickness

CTEPLATE

Weld residual


CTEWELD

CharpyIrradiation

ShiftModel


Cu(RVID)

Ni(RVID)

P

LocalFluence

Uncertainty

FluenceAt Flaw

CuUncertainty

SampledCu

NiUncertainty

SampledNi

PSampled

Flaw AspectRatio, 2c/a Judgments when UnknownJudgments when Unknown

AppliedKI

Elastic Modulus

Vessel Diameter

StressIntensity

FactorModeldKI/dt

CPI=0

NO

Vessel Thickness

Poisson’s Ratio

P&T vs. t




Model

Oper.Temp.

(RVID)

Oper.Time

ProductForm

VesselMfg.


Shift

UncertaintyP

Un Irradiated


ToughnessIndex


ResistanceKIc

ResistanceKIc

dKI/dt > 0AND

A-KI > R-KIc


Curve

CPI>0

RTNDT(u)Method

YES

Generic?

YES

NO(u) = 0

Conversion


(RTTOUGH)

+

T vs. t

WeldFlaw?

NO

YES



Un-IrradiatedIndex


RTNDT(u)(RVID)





YES


WELD, & RTTOUGH(I)

ADJACENT PLATE

Crack Initiation ModelsCoded for Probabilistic


(Reg-Guide Calcs.)

GlobalFluence

Uncertainty

Probabilistic – Aleatory

Probabilistic – Epistemic

Probabilistic – Aleatory

Probabilistic – Epistemic


Model

Uncertainty

SampledID Fluence


Flaw Depth, a

Flaw Aspect

Flaw Density,

Deterministic – Accurate

Deterministic – Conservative

Deterministic – Accurate

Deterministic – Conservative

Vessel Diameter

1Clad Thickness

CTEPLATE

Weld residual


CTEWELD

CharpyIrradiation

ShiftModel


Cu(RVID)

Ni(RVID)

P

LocalFluence

Uncertainty

FluenceAt Flaw

CuUncertainty

SampledCu

NiUncertainty

SampledNi

PSampled


AppliedKI

Elastic Modulus

Vessel Diameter

StressIntensity

FactorModeldKI/dt

CPI=0

NO

Vessel Thickness

Poisson’s Ratio

P&T vs. t




Model

Oper.Temp.

(RVID)

Oper.Time

ProductForm

VesselMfg.


Shift

UncertaintyP

Un Irradiated


ToughnessIndex


ResistanceKIc

ResistanceKIc

dKI/dt > 0AND

A-KI > R-KIc


Curve

CPI>0

RTNDT(u)Method

YES

Generic?

YES

NO(u) = 0

Conversion


(RTTOUGH)

+

T vs. t

WeldFlaw?

NO

YES



Un-IrradiatedIndex


RTNDT(u)(RVID)





YES


WELD, & RTTOUGH(I)

ADJACENT PLATE

Initiation Fracture ToughnessFracture Toughness

400 E1921 Valid E399 Valid

ASME KIC Curve

Parameters of the Initiation 200

300

MPa

*m0.

5 ]

KIc

Model

RT100

KJc

[M

RTNDT0-150 -100 -50 0 50

T-RT NDT [oC]

Mixed Epistemic (RTNDT) & Aleatory (KI ) UncertaintiesAleatory (KIc) Uncertainties

• Need to be separated for accuracyI th t K tt• Increase the apparent KIc scatter

RTNDT too high

Need to quantifythe epistemicuncertainty in

ness

g

A t

uncertainty inRTNDT so that wecan get the KIcscatter correct

re T

ough

n

Correct RTNDT

Apparent KIc scatter too large

scatter correct

Frac

tur

Correct KIc Scatter

T - RTNDT

Separation of Uncertainties Using T

400E1921 V lid

Uncertainties Using To• Fracture toughness models

based on the RT index

300

5 ]

E1921 Valid E399 Valid

ASME KIC Curve

based on the RTNDT index temperature contain both epistemic & aleatory uncertainties

E1921 Valid

E399 Valid

1% LB

Median

99% UB

200

[MPa

*m0.

5uncertainties• Use of the best-estimate

Master Curve index temperature (T ) effectively

99% UB

100

KJc

[temperature (To) effectively removes epistemic uncertainty, leaving only the aleatory uncertainties

0-150 -100 -50 0 50

T RT [oC]

aleatory uncertainties produced by material variability

T T [oC]T-RT NDT [ C]T-To [oC]





Major Outcomes

• What operational transients most influence PTS risk?

• What material features most influence PTS risk?

• Are these dominant material features / transients common across the fleet?common across the fleet?

• New limits on embrittlement based on RI calculationsNew limits on embrittlement based on RI calculations

Technical BasisTransient Classes ModeledTransient Classes Modeled

Primary System Faults Secondary System Faultsi li b k• Pipe breaks

– LargeMedium

• Main steam line break• Stuck open valves• Steam generator tube– Medium

– Small• Stuck open valves that

• Steam generator tube rupture

• Pure overfeedplater re-close

• Feed and bleed

33

Important Transient ClassesClasses

1.E-05

1.E-04

5

4

5

4Medium & Large

Pipe

Main Steam Line

Stuck-Open

Primary

1.E-07

1.E-06

7

6

7

6

TWC

F

Pipe Breaks

Line Breaks

Primary Valves

1 E 10

1.E-09

1.E-08

August 2006 0

9

8

August 2006 0

9

8

August 2006rcen

tile

T

1.E-12

1.E-11

1.E-10 August 2006FAVOR 06.1

Beaver 2

0 August 2006FAVOR 06.1

Beaver 2

1

0 August 2006FAVOR 06.1

Beaver

95th

Pe

1.E-14

1.E-13

550 650 750 850

Oconee

Palisades

Fit4

3

550 650 750 850

Oconee

Palisades

Fit4

3

550 650 750 850

Oconee

Palisades

Fit

34

550 650 750 850Max RT [R]

550 650 750 850Max RT [R]

550 650 750 850Max RT [R]

Important Transient ClassesClasses

100%

WC

F

60%

80%

Tota

l TW

40%

60%

tion

to T Medium and Large Diameter Pipe Breaks (LOCAs)

Stuck Open Valves, Primary SystemMain Steam Line Breaks

20%

ontr

ibut

0%200 250 300 350 400 450

Co

Max RT [oF]

35

Max RT [ F]

Summary of FindingsImportant Transient ClassesImportant Transient Classes

• Primary side faults dominate riskl i id (3 )– Due to low temperature on primary side (35oF)

• Very severe secondary faults (MSLB) make a minor contributioncontribution– Primary side temperature cannot fall below 212oF, so

material still tough even at high embrittlement• All other transient classes produce no significant risk

– Challenge is low even if transient occurs

36

Important Material FeaturesFeatures

1.E-04

1.E-03August 2006FAVOR 06.1

August 2006FAVOR 06.1 August 2006

FAVOR 06.1

TWC

F

1 E-07

1.E-06

1.E-05

7 7

Circumferential Weld Flaws

Plate Flaws

erce

ntile

T

1.E-09

1.E-08

1.E-07 7 7

Axial Weld

95th

Pe

1.E-12

1.E-11

1.E-10

Beaver

Oconee

Beaver

Oconee

Beaver

Oconee

Flaws

1.E-14

1.E-13

550 650 750 850

Oconee

Palisades

Fit

550 650 750 850

Palisades

Fit

550 650 750 850

Palisades

Fit

37

Max. RTAW [R] Max. RTPL [R] Max RTCW [R]

Important Material FeaturesFeatures

100%

WC

F

60%

80%

Tota

l TW

40%

60%

tion

to T Axial Weld Flaws

Flaws in Plates (remote from welds)Circumferential Weld Flaws

20%

ontr

ibut

0%200 250 300 350 400 450

C

Max RT [oF]

38

[ ]

Summary of FindingsImportant Material FeaturesImportant Material Features

• Axial cracks dominate risk, circumferential cracks do not– Circ cracks arrest due to vessel geometry– Axial cracks are much less likely to arrest

• Thus the properties of materials associable with axial flaws• Thus, the properties of materials associable with axial flaws dominate– Axial weld properties

Pl i– Plate properties• 3-parameter characterization of RPV embrittlement unifies results

across all study plants– Failures are blamed on the responsible material/flaw features

39

10 CFR 50.61a RT LimitsImplementation for Plate PlantsImplementation for Plate Plants

350

4001x10-6/ry TWCF limit 300

1x10-6/ry TWCF limit

250

300

o F]

Simplified ImplementationRTMAX-AW ≤ 269F, andRTMAX-PL ≤ 356F, andRTMAX-AW + RTMAX-PL ≤ 538F.

200

250

AX-

PL [

o F] Simplified ImplementationRTMAX-AW ≤ 222F, andRTMAX-PL ≤ 293F, andRTMAX-AW + RTMAX-PL ≤ 445F.

Plate Welded Plants at 48 EFPY (EOLE)

150

200

250

T MA

X-PL

[o

Palo Verde 1, 2, and 3at 48 EFPY (EOLE)

100

150RT M

50

100

150RT

0

50

0 50 100 150 200 250

tWALL = 10½- to 11½-in.

0

50

0 50 100 150 200 250 300

0 50 100 150 200 250

RTMAX-AW [oF]tWALL < 9½-in.

40

RTMAX-AW [oF]

10 CFR 50.61aSummarySummary

• Limits apply to all currently operating U S PWRs 12

14 Plate Welded Plants at 48 EFPYRing Forged Plants at 48 EFPY

PYPY

ng

operating U.S. PWRs• All plants assessable based

only on available materials and fluence information

8

10

12

Rea

ctor

s

o 4E

-7

of O

pera

tinW

Rs

fluence information• All PWRs conform to limits,

even through 60 years of operation 2

4

6

Pow

er R

2E-7

to

Num

ber o PW

operation• To use less restrictive limits of

10CFR50.61a, plant specific aspects must be checked

0

Below E-13

13 to

E-1212

to E-11

11 to

E-10E-10

to E-9

E-9 to

E-8E-8

to E-7

E-7 to

E-6

Naspects must be checked (defense in depth)– Flaw distribution

Embrittlement

BelE-13 E-12 E-11 E-1 E E E

95th Percentile TWCF

– Embrittlement





Lessons Learned

1. Conservatisms are not an absolute goodConservatisms create the perception of plant specificity which– Conservatisms create the perception of plant specificity, which may not exist

– Converse: Realistic models can reveal general trends, if they exist

2. An important point for our European colleagues– Deterministic and probabilistic analyses are not as different as

they may initially seemy y y3. Human perception challenges associated with small

numbers4 The PTS project has taken a very long time to complete4. The PTS project has taken a very long time to complete

– Need it have been so?– Is there a better way?

Deterministic / ProbabilisticOverviewOverview

• A PTS Analysis is just a structural integrity assessmentassessment

• To perform the analysis, you calculate– Structural driving force (DF) to fractureStructural driving force (DF) to fracture– Materials’ resistance (R) to fracture

and you comparey p• DF and R are inherently distributed quantities• Deterministic and probabilistic analyses both provide

a mathematical representation these distributed quantities

Deterministic / ProbabilisticDF & R are Distributed QuantitiesDF & R are Distributed Quantities

PFAILURE Distributions DeterministicRepresentation of Distributions

ProbabilisticActual Situation

DF RZero

DF R DF RDF R DF R DF REstimate: No Failure Estimate: PFAIL=0

DF RSmall

DF R DF REstimate: Failure Estimate: PFAIL= Very Small

DF RLarge

DF R DF RDF R DF R DF REstimate: Failure Estimate: PFAIL= Large

Note: The actual DF and R distributions are also shown, lightly, in the deterministic and probabilistic columns.

Deterministic / ProbabilisticMathematical RepresentationMathematical Representation

PFAILURE Distributions DeterministicRepresentation of Distributions

ProbabilisticActual Situation

DF RZero

DF R DF RDF R DF R DF REstimate: No Failure Estimate: PFAIL=0

DF RSmall

DF R DF REstimate: Failure Estimate: PFAIL= Very Small

DF RLarge

DF R DF RDF R DF R DF REstimate: Failure Estimate: PFAIL= Large

Note: The actual DF and R distributions are also shown, lightly, in the deterministic and probabilistic columns.

Deterministic / ProbabilisticSimilarities and DifferencesSimilarities and Differences

• Similaritiesh i

• Differencesl i d– Both treat uncertainty

• Deterministic models bound uncertaintyP b bili i d l

– How result is expressed• Deterministic: “Failed” or “Not

Failed”P b bili i A f il b bili• Probabilistic models

quantify uncertainty– Probabilistic models

t i

• Probabilistic: A failure probability– Who the decisionmaker is

• Deterministic: Only the may contain many deterministic aspects

engineering analyst (because “failure” is unacceptable)

• Probabilistic: Many people (because some failure probability(because some failure probability can be tolerable)

Human Perceptions of Small NumbersSmall Numbers

• 1.14E-5 / year

?y

– My probability of dating a supermodel

• Basis: Baer, G., “Life, The Odds”?&

• 3.4E-8 / year– Probability of PTS failing a US

334x more likely

Probability of PTS failing a US vessel after 60 years of operation (worst case)

• Basis: NUREG-1806153x less

lik l

• 2.2E-10 / year– Probability of an extinction

level meteor impact on Earth

likely

level meteor impact on Earth• Basis: 1 event in 4.5 billion years

Regulatory Resolution of a Complex Issue Takes a LONG TiLONG Time

1-1998

2001

2001

2002

2005 6-2009

2004

Planning &Model Building

3½ years

Computing / Thinking/ Defending

4 years

Deciding & Approving4 years

6- 12-

12- 6-12-

3½ years 4 years

ObservationThe Same Features Define Every St t l I t it P bl

E

Structural Integrity Problem

Environment• Feature Summary

TAT

E

Loading

Environment– Environment, Loading, Geometry, and

Material,

ND

ST

Geometry• The temporal variation (or not) of these• A definition of the end state or states

EN

Material

A definition of the end state, or states, we care about

time

Proposed 4 Components of A Generic Approach to Probabilistic A t f St t l I t itAssessment of Structural Integrity

• A general template onto which any structural integrity problem can be mappedintegrity problem can be mapped

• A questionnaire designed to comprehensively identify and define the models and parameters thatidentify and define the models and parameters that populate the template– This becomes the programming specification

• A modular computer code that mirrors the structure of the template

• A standard documentation and review process that• A standard documentation and review process that mirrors the structure of the template

General Template for …A Generic Approach to Probabilistic A t f St t l I t itAssessment of Structural Integrity

Define Initial Conditions

(t 0)

Define Temporal Variations

(t>0)

Define End StateWhat does end(t=0)

Geometry

Material

(t>0)# of timescales that

define problem?

What (of geometry,

What does end state (or states)

matter?

Max tolerable failure frequency

for reg latorLoading

Environment

What (of geometry, material, loading, &

environment) change in each

timescale?

C l

for regulatory review?

Max tolerable failure frequency for mitigation?

In each case:• Define models and

parameters (M&P)• Define relationships

between M&P• Decide if each M&P is

Can progress along the timescale be

altered?

for mitigation?

Decide if each M&P is modeled as• Certain or uncertain• If uncertain,

epistemic or aleatory• Characterize M&P

quality

• For each M&P, answer the same questions as for the initial condition

• Define interdependenciesquality

• Pretty good• Conservative

interdependencies between models and parameters

Application of Lessons LearnedLearned

• We are trying the general template and questionnaire out in a new projectout in a new project

• Risk informed revision of leak before break guidance• Risk-informed revision of leak before break guidance

• Too soon to say how well it has workedToo soon to say how well it has worked

• Check back again later (hopefully in less than aCheck back again later (hopefully in less than a decade!!)

Thank You for Your AttentionAttention

• Questions?????

Documents

Risk-Informed Revision of the NRC’s Rules Regulating ...web.mit.edu/ans/www/documents/seminar/S09/kirk_slides.pdf · Risk-Informed Revision of the NRC’s Rules Regulating Pressurized