diablo canyon npp risk-informed in-service inspection

IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making

Diablo Canyon NPPDiablo Canyon NPPRisk-Informed In-service InspectionRisk-Informed In-service Inspection

Workshop InformationWorkshop InformationIAEA WorkshopIAEA Workshop City , Country

XX - XX Month, Year

LecturerLesson IV 3_11.3


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Purpose of In-service InspectionPurpose of In-service Inspection

To identify conditions, such as flaw indications, that are To identify conditions, such as flaw indications, that are precursors to leaks and rupture, which violate pressure precursors to leaks and rupture, which violate pressure boundary integrity principles.boundary integrity principles.


3

RI-ISI benefitsRI-ISI benefits

Enhance or maintained plant safety (CDF/LERF) Enhanced component reliability for high safety significance

components (HSSCs) Reduce nondestructive exams (NDE) Reduced man-rem exposure Other unquantifiable benefits

Reduced costs of engineering analysis (flaw evaluations, etc.) Reduced outage time Reduced chance of complicating plant operations

(scaffolding, leakage, etc.)


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ASME Section XI Enhanced by Risk-ASME Section XI Enhanced by Risk-Informed ISIInformed ISI

Calculating pipe failure Calculating pipe failure prob. by considering prob. by considering design, experience and design, experience and operationsoperations

High design stress and High design stress and fatigue locations fatigue locations augmented by random augmented by random selectionselection

Failure ProbabilityFailure Probability

Exercising of PSA Exercising of PSA Model (CDF, LERF, Model (CDF, LERF, others)others)

Class 1, 2, and 3Class 1, 2, and 3ConsequenceConsequence

Risk-Informed ISIRisk-Informed ISIASME Section XI ASME Section XI ProcessProcess


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Overall Risk-Informed ISI ProcessOverall Risk-Informed ISI Process

Scope and Segment Definition

ConsequenceEvaluation

Structural ElementFailure ProbabilityAssessment

ImplementProgram

Expert PanelCategorization

Element/NDESelection

Risk-Evaluation

Feedback

Loop


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Segment DefinitionSegment Definition

Full Scope Definition All Class 1, 2, and 3 piping systems in ASME Section XI Piping fluid systems modeled in PSA Various balance of plant (non-nuclear code class) fluid systems

of importance Systems included under scope of Maintenance Rule determined

to be risk-significant Systems included in program are reviewed by expert panel for

concurrence

Partial Scope Definition Subset of piping classes such as ASME Class 1 piping only

(includes piping exempt from current requirements)


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Segment DefinitionSegment Definition Segment defined based on:

Piping which have same consequence (loss of train A of RHR, loss of RWST, inside or outside containment consequences)

Where flow splits or joins (traditional PSA modeling points) Includes piping to a point in which a pipe failure could be

isolated (e.g., check valve, MOV, AOV, no credit for manual valves)

Pipe size changes Failure probability expected to be markedly different due to

material properties

Iterative process with Consequence Evaluation


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Subdivided system into piping segments

Assigned numerical identifier Based upon similar consequence Marked P&Ids & field isometrics

Determined failure modes effects analysis (FMEA)

Without operator action With operator action


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Consequence EvaluationConsequence Evaluation

Both direct and indirect (spatial) effects are considered PSA is used to quantify impact

Consistent with EPRI PSA Applications Guide Calculations for CDF and LERF Conditional probability/frequency given piping failure

Considers multiple impacts Initiating event impact Single/multiple component/train/system impacts Combinations of impacts


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Direct Effects EvaluationDirect Effects Evaluation

Failure effect based on disabling segment function leak PRA and system information used to determine if piping

failure causes:

An initiating event (e.g. LOCA, Reactor Trip) Loss of train or system Loss of multiple trains or systems Combination of the above


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Overview Of Indirect Effects EvaluationOverview Of Indirect Effects Evaluation

Purpose of Evaluation

• To review any issues in identifying potential indirect effects/consequences from piping failures

• Identify indirect effects that would differentiate piping segments from each other


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Indirect EffectsIndirect Effects

Considerations

• Flooding, spraying, dripping – should be primarily addressed by the PSA internal flooding analyses for all plant areas

• Pipe Whip, jet impingement – concern is primarily for high-energy fluid system piping


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Indirect Effects ProcessIndirect Effects Process

Prewalkdown• Review existing documents which examine the local effects of pipe

breaks for the systems in the risk-informed ISI program• Identify other systems/trains affected by a failure in each area• Identify plant areas for plant walkdown• Document evaluation• Develop walkdown sheets for key areas

Walkdown• Perform walkdown and document results, actions, issues

Post Walkdown• Evaluate results• Resolve actions


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Failure Probability Assessment ProcessFailure Probability Assessment Process

Industry failure experience Identification of potential failure modes and causes Specific-plant information – layout, materials, operating

conditions and experience Use of tools or data to calculate failure probability Estimation of leak and break probabilities by engineering

team


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Failure Probability Assessment ProcessFailure Probability Assessment Process

INDUSTRY EXPERIENCE

ENGINEERINGTEAM CALC. TOOL

PLANT INFORMATION(LAYOUT, MATERIALS,

OPERATING CONDITIONSPLANT OPERATING

EXPERIENCE)

IDENTIFICATION OFPOTENTIAL FAILUREMODES AND CAUSES

ESTIMATEDLEAK AND BREAK

PROBABILITIES

Engineering Team-ISI/NDE Engineering

-Materials Engineering

-Design Stress Engineering

(Engineering Mechanics)

-Plant System Engineer


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RI-ISI Expert Panel ProcessRI-ISI Expert Panel Process

- IMPACT- RRW- RAW- INDIRECT EFFECTS

RISK EVALUATION

- MECHANISM- PROBABILITY- BASIS

PRESSURE BOUNDARYFAILURE PROBABILITY

-CONTAINMENT PERFORMANCE-EXTERNAL EVENTS-SHUTDOWN RISK-OTHER SCENARIOS-MAINTENANCE/OPERATION INSIGHTS-DESIGN BASIS/DEFENSE-IN-DEPTH-OTHER DETERMINISTIC INSIGHTS

OTHER CONSIDERATIONS

EXPERT PANEL

HIGH AND LOWSAFETY – SIGNIFICANT

PIPING SEGMENTS


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Mapping of Surry Segments on Structural Mapping of Surry Segments on Structural Element Selection MatrixElement Selection Matrix

HIGH

FAILURE

IMPORTANCE

SEGMENT

LOW

FAILURE

IMPORTANCE

SEGMENT

OWNER

DEFINED

PROGRAM

3

(a) SUSCEPTIBLE

LOCATIONS (100%)

(b) INSPECTION

LOCATION

SELECTION PROCESS1

ONLY

SYSTEM PRESSURE

TEST & VISUAL

EXAMINATION

4

INSPECTION

LOCATION

SELECTION

PROCESS

2

LOW

SAFETY

SIGNIFICANT

SEGMENT

HIGH

SAFETY

SIGNIFICANT

SEGMENT


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Presentation FormatPresentation Format

• Overview of RI-ISI approach• Detailed comparison

Scope and segment definition Consequence evaluation Failure probability assessment process Risk evaluation Selection of elements and NDE methods (expert

panel) Change in Risk calculations RI-ISI implementation (not addressed here)


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EPRI-RI-ISI ProcessEPRI-RI-ISI Process

Determine Scope

Perform SegmentConsequence Analysis

Perform Segment DamageMechanism Analysis

Perform Service Review

Finalize Program

Perform Risk Impact Assessment

Select Elements for Inspection andElement Inspection Methods

Determine Segment Risk Category

AdjustElementSelection Performance

Monitoring


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Segment definition guidelines (similar in both methodologies)

Piping which have same consequences Where flow splits or joins Pipe size changes Change in piping material Isolation capability

EPRI uses the above plus same failure mechanism criterion


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Consequence EvaluationConsequence Evaluation Deterministic evaluation of piping failure-induced impact

(both methodologies)

Direct impact (e.g. loss of a train) Indirect impact (e.g. damage caused by flooding, jet

impingement) Multiple impacts (e.g. initiating events + Accident

mitigation) Probabilistic evaluation

EPRI uses a bounding worst case evaluation (using matrix or calculation)

WOG uses surrogate(s) to quantify condition CDF (CDP) and LERF (LERP) for spectrum of failure modes (leak, disabling leak, double ended break) utilizing internal events PSA model


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Structural Reliability AssessmentStructural Reliability Assessment Both methodologies evaluate potential for pipe failure EPRI qualitatively classifies potential for pipe rupture

as “High”, “Medium”, or “Low” based on degradation mechanisms, in-service data, expert knowledge (no code).

WOG uses SRRA code (stays with the user) to quantify leak/rupture frequency/probability based on in-service data, potential failure mechanisms, and plant specific information (e.g. layout, materials, operating and conditions, etc.)


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Risk EvaluationRisk Evaluation EPRI uses risk matrix to separately categorize piping

segments in the high, medium, or low classifications using prescriptive criteria for the consequence and rupture potential elements (risk is not calculated). It uses plant staff to review the results and concur with the risk ranking results

WOG methodology uses standard approaches for CDF/LERF calculation (ie. Frequency * CCDP) and risk ranking process (RAW and RRW). Additionally, expert panel discussions are held to review PSA results and include other potential risk contributors (e.g. shutdown risk, external events, etc.) WOG methodology allows credit for aumented

programs


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Element SelectionElement Selection

Both methodologies inspect for cause EPRI methodology uses prescriptive rules (fixed

percentages) to determine the population of elements to be inspected

WOG methodology uses a combination of prescriptive and statistical rules to determine the population of elements to be inspected.


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WOG MatrixWOG Matrix

HIGH

FAILURE

IMPORTANCE

SEGMENT

LOW

FAILURE

IMPORTANCE

SEGMENT

OWNER

DEFINED

PROGRAM

3

(a) SUSCEPTIBLE

LOCATIONS (100%)

(b) INSPECTION

LOCATION

SELECTION PROCESS1

ONLY

SYSTEM PRESSURE

TEST & VISUAL

EXAMINATION

4

INSPECTION

LOCATION

SELECTION

PROCESS

2

LOW

SAFETY

SIGNIFICANT

SEGMENT

HIGH

SAFETY

SIGNIFICANT

SEGMENT


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EPRI Risk MatrixEPRI Risk Matrix

MEDIUMMEDIUM(Cat. 4)(Cat. 4)LOWLOW

(Cat. 6)(Cat. 6)LOWLOW(Cat. 7) (Cat. 7)

LOWLOW(Cat. 7)(Cat. 7)LOWLOW

HIGHHIGH(Cat. 2)(Cat. 2)

MEDIUMMEDIUM(Cat. 5)(Cat. 5)

LOWLOW(Cat. 6)(Cat. 6)

LOWLOW(Cat. 7) (Cat. 7) MEDIUMMEDIUM



MEDIUMMEDIUM(Cat. 5)(Cat. 5)

LOWLOW(Cat. 7)(Cat. 7)HIGHHIGH

HIGHHIGHMEDIUMMEDIUMLOWLOWNONENONE

CONSEQUENCE CATEGORY CONSEQUENCE CATEGORY CCDP and CLERP PotentialCCDP and CLERP Potential

DE

GR

AD

AT

ION

CA

TE

GO

RY

Pipe

Rup

ture

Pot

entia

l

Failure Potential

Assessment

Consequence Assessment


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Change in Risk CalculationsChange in Risk Calculations EPRI methodology uses a progressively more

quantitative evaluation to assess the changes in Risk Qualitative Bounding Simplified Complex

WOG methodology calculates the change in Risk based on the change in pipe failure frequency (probability) due to the proposed change in the Inspection program. The calculations are consistent with those performed to calculate the Risk.

diablo canyon npp risk-informed in-service inspection

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