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Risk-Informed In-Service Inspection (RI-ISI) Using @RISK

Risk-Informed In-Service Inspection (RI-ISI) Using @RISK. Ching Guey. RI-ISI at Turkey Point. Turkey Point’s application of RI-ISI is limited to Class 1 piping inside containment.

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Risk-Informed In-Service Inspection (RI-ISI) Using @RISK

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  1. Risk-Informed In-ServiceInspection (RI-ISI)Using @RISK Ching Guey

  2. RI-ISI at Turkey Point • Turkey Point’s application of RI-ISI is limited to Class 1 piping inside containment. • The purpose of in-service inspection is to identify conditions, such as flaw indications, that are precursors to leaks and ruptures which violate pressure boundary integrity principles. • In-service inspection (ISI) activities include ultrasonic testing, surface testing, and liquid penetrant testing.

  3. Objectives • More Effective and Efficient Use of @Risk to Streamlize the Analysis Work • Prioritize Turkey Point’s ISI Activities by Risk • Decrease cost of outage inspections, and • Decrease personnel radiation exposure during outage inspections, while • increasing or maintaining personnel safety • increasing or maintaining unit reliability

  4. Risk-Informed ISIProcess Overview Expert Panel Categorization Consequence Evaluation Element/ NDE Selection Scope and Segment Definition Risk- Evaluation Implement Program Structural Element Failure Probability Assessment Feedback Loop @RISK

  5. Turkey Point PRA LOCA Events and Nominal Pipe Sizes • Small-Small LOCA 3/8”< X  2” • Small LOCA 2” < X  6” • Medium LOCA 6” < X  13.5” • Large LOCA 13.5” < X • Any piping with a nominal diameter less than or equal to 3/8” is assumed not to result in a LOCA event, which could lead to core damage.

  6. Failure ProbabilityAssessment Process PLANT INFORMATION (LAYOUT, MATERIALS, OPERATING CONDITIONS, PLANT OPERATING EXPERIENCE) IDENTIFICATION OF POTENTIAL FAILURE MODES AND CAUSES INDUSTRY EXPERIENCE ENGINEERING TEAM SRRA TOOL • Engineering Team • ISI/NDE Engineering • Materials Engineering • Design Stress Engineering • (Engineering Mechanics) • -Plant System Engineer ESTIMATED LEAK AND BREAK PROBABILITIES

  7. Piping Segment Definition • Segment • Section of pipe for which a failure at any point has the same consequences • Over 200 individual segments for each unit

  8. Piping Failure Probability • SRRA Code used to predict piping failure probability • Factors used in SRRA Piping Failure Probability Calculation • Pipe Segment Dimensions • Material Stresses • Pressure, Temperature

  9. Consequences Evaluation • Calculated using the Turkey Point Probabilistic Safety Assessment (PSA). • Postulated different size breaks in each segment. • Calculated Conditional Core Damage Probability (CCDP) and Conditional Large Early Release Probability (CLERP) for each segment and break size.

  10. Risk Evaluation • SRRA Code used to predict piping failure frequency. • Calculated Conditional Core Damage Probability (CCDP) and Conditional Large Early Release Probability (CLERP) for each segment and break size using the PTN PSA model. • Multiplied the segment piping failure frequencies from SRRA by their CCDPs and CLERPs to obtain the CDFs and LERFs for each segment. • Calculated risk importance measures for each segment Using @RISK . • Assigned a preliminary risk category to each segment based on the RRW.

  11. Expert Panel • Convened a panel of experts from ISI/NDE, Plant Engineering, Risk Assessment, Operations, Maintenance, etc. • Provided each Expert Panel member with all of the risk-related and other information calculated and/or collected for each pipe segment. • Reviewed, discussed, and eventually assigned a final risk category to each pipe segment. • Documented the basis of the determination.

  12. Results • Weld Inspection Reduction 84% • Radiation Dose Reduction 20man-rem • Role of @RISK: Methodology approved by the NRC requires doing Monte-Carlo Simulation and use mean values for the ranking of each segment • A sensitivity study to compare Point Estimate and Monte-Carlo Generated Mean provides useful insights for the sensitivity of changes in the input parameters • A function: =RiskMean() used saved many hours of manual work

  13. Other Benefits • Avoidance of potential personnel injury by reduction of: • Scaffold Construction • Asbestos Removal • Insulation Removal • Weld Grinding and Buffing

  14. Expert Panel • Scope limited to changes in program: new segments, modified segments, and segments whose risk ranking changed from Low to High or Medium to High. • Risk ranking change due to changes in SRRA analysis of pipe segment failure frequency, changes in consequence assumptions, and/or changes in PTN PSA model. • Expert Panel members will be provided with all of the risk-related and other information calculated or collected for the relevant pipe segments. • Expert Panel will review, discuss, and eventually assign a final risk category to each pipe segment.

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