Streamlined RI-ISI. Patrick O Regan EPRI

Transcription

1 Streamlined RI-ISI Patrick O Regan EPRI poregan@epri.com

2 Introduction Background Streamlined RI-ISI Methodology Results Discussion, Lessons Learned, Improvements Summary

3 Background GOAL: Based upon the lessons learned from 50+ RI-ISI applications, develop a streamlined process for implementing and maintaining a RI-ISI program But why?

4 Background Number of high safety significant (HSS) locations added by plant review VY = zero BWR-N560 ANO-1 = zero B&W-N560 ANO-2 = zero CE N578 (fullscope) Fitzpatrick = zero BWR N578 (fullscope) South Texas 1 & 2 = zero West N560 Number of HSS locations added by NRC review VY = zero ANO-1 = zero ANO-2 = zero Fitzpatrick = zero South Texas 1 & 2 = zero

5 Background RI- Break Exclusion Requirements (HELB) EPRI TR Approved June 2002 NRC Review Inspection population < 10 percent Implementation via procedure WCAP-14572, Addendum 1 Approved March 2004 NRC Review Inspection population < 10 percent Implementation via procedure

6 Background Code Case N663 Alternative Surface Examination Requirements Incorporates lessons learned from EPRI RI-ISI methodology and applications Eliminates many unnecessary examinations Reduces worker exposures Minimal analysis cost (as compared to typical RI-ISI applications) A number of plants approved to date

7 Background Recent Experiences (RI-ISI Submittals) Results of Regulatory Reviews* Plant A 70 locations added Plant B 40 locations added Plant C 40 locations added Plant D 17 locations added Plant E 13 locations added * Reference -NEI 04-05

8 Background Recent Experiences (cont.) RI-ISI Program Updates Plant A PRA model updates Physical plant changes (e.g. power uprate, S/G replacement) No change in HSS No change in inspection program Plant B PRA model updates Minor physical plant changes ~ 80 segments moved from Low to High/Medium ~ 30 segments moved from High to Low

9 Background Recent Experiences (cont.) NEI Update Review Four Plants Updated with: No changes to the RI-ISI selections / inspections Four Plants Updated with: Six exams eliminated and one added Twenty exams eliminated and five added Twenty eight exams eliminated and seven added Nineteen exams eliminated

10 Summary -1 Background Some applications approved with no changes required Some applications appear to be pushing the envelope (i.e. riskbased versus risk-informed) Some applications experienced difficulty in gaining regulatory approval (e.g. numerous RAIs, re-analysis, changes to program) Costs associated with program updates Updates may challenge initial program validity

11 Summary -2 GOAL: Background Develop a consistent and streamlined process for implementing and maintaining a RI-ISI program RESULT: Code Case N716; Risk-Informed / Safety Based ISI (RIS_B)

12 Methodology ASME Whitepaper Reviewed over fifty plant-specific RI-ISI applications, Thirty, of which, were Class 1 & 2 or fullscope applications Reviewed a number of industry and USNRC risk assessments Delta risk assessment conducted for eight plants N716 (RIS_B) provides a risk reduction or at worst, risk neutrality Looked at BWRs and PWRs, Looked at plants that used the EPRI and West RI-ISI methods Does not credit the positive impact of 2(a)(5) (i.e. CDF > 1E-06)

13 Methodology High Safety Significant (HSS) Reactor Coolant Pressure Boundary (e.g. Class 1) Shutdown Decay Heat Removal (out to containment / isolation) Break Exclusion Region (BER) Main Feedwater from S/Gs to BER Segments with > 1E-6 CDF (from internal flooding study) Low Safety Significant (LSS) Remaining items (i.e. other Class 2, all Class 3, all NNS

14 Methodology Treatment Criteria (PSI/ISI) HSS population equal to 10%, plus augmented programs HSS welds selected as follows: 25 percent of the population identified as susceptible to each degradation mechanism and degradation mechanism combination For the RCPB, at least two thirds of the examinations shall be located between the first isolation valve (i.e., isolation valve closest to the RPV) and the reactor pressure vessel. A minimum of ten percent of the welds in that portion of the RCPB that lies outside containment (e.g., portions of the main feedwater system in BWRs) shall be selected. A minimum of ten percent of the welds within the break exclusion region shall be selected.

15 Methodology Additional Requirements Risk assessment of internal flooding events (flooding, pipe whip, spray, etc.) Augmented inspection programs for FAC, IGSCC- BWRs and localized corrosion (HSS & LSS Systems) Delta risk per EPRI TR

16 BWR -1 System Safety Significance Break Failure Potential Code Weld Section XI Selections Case N-716 Selections High Low Location DMs Rank Category Count Vol/Sur Sur Only RIS_B Other RPV LOCA TASCS, TT, (IGSCC) Medium (Medium) B-F RPV LOCA TT, (IGSCC) Medium (Medium) B-F B-J RPV LOCA None (IGSCC) Low (Medium) B-F B-J RPV LOCA None Low B-F B-J FW LOCA TASCS, TT Medium B-J FW ILOCA TASCS, TT Medium B-J FW BER TASCS, TT Medium C-F FW ILOCA TASCS Medium B-J FW LOCA TT Medium B-J FW ILOCA None Low B-J FW BER None Low C-F MS LOCA None Low B-J MS ILOCA None Low B-J MS PLOCA None Low B-J MS BER None Low C-F SD LOCA None Low B-J SD ILOCA None Low B-J SP LOCA None Low B-J RCR LOCA None (IGSCC) Low (Medium) B-J RCR LOCA None Low B-J RCR PLOCA None Low B-J CRD Class 2 N/A Assume Medium C-F SLC LOCA None Low B-J SLC PLOCA None Low B-J

17 BWR -2 System Safety Significance Break Failure Potential Code Weld Section XI Selections Case N-716 Selections Location Category Count High Low DMs Rank Vol/Sur Sur Only RIS_B Other RHR BER TT, CC Medium C-F RHR BER TT Medium C-F RHR LOCA None Low B-J RHR PLOCA None Low B-J RHR BER None Low C-F RHR Class 2 N/A Assume Medium C-F LPCS LOCA None Low B-J LPCS PLOCA None Low B-J LPCS Class 2 N/A Assume Medium C-F HPCS LOCA TT Medium B-J HPCS LOCA None Low B-J HPCS PLOCA None Low B-J HPCS Class 2 N/A Assume Medium C-F MSLC ILOCA None Low B-J FWLC PLOCA None Low B-J RCIC LOCA None Low B-J RCIC PLOCA None Low B-J RCIC BER None Low C-F RCIC Class 2 N/A Assume Medium C-F CGC Class 2 N/A Assume Medium C-F C-F RWCU LOCA None Low B-J RWCU ILOCA None Low B-J B-J RWCU BER None Low C-F Class Other RWCU Class 2 None Low B-J RWCU Class 2 N/A Assume Medium C-F

18 System Safety Significance Failure Potential Code Section XI Selections Case N-716 Selections Break Location Weld Count High Low DMs Rank Category Vol/Sur Sur Only RIS_B Other RC LOCA TASCS, TT Medium B-J RC LOCA TT, PWSCC Medium B-F RC LOCA TASCS Medium B-J RC LOCA TT Medium B-J RC LOCA PWSCC Medium B-F RC LOCA None Low B-F B-J RC PLOCA None Low B-J CS LOCA TT Medium B-J CS ILOCA TT Medium B-J CS PLOCA TT Medium B-J CS LOCA None Low B-J CS PLOCA None Low B-J CS Class 2 LSS N/A Assume Medium C-F RH LOCA None Low B-J RH PLOCA None Low B-J RH Class 2 SDC IC None Low C-F RH Class 2 LSS N/A Assume Medium C-F SI PLOCA IGSCC Medium B-J SI LOCA None Low B-J SI PLOCA None Low B-J SI PILOCA OC None Low B-J SI PILOCA IC None Low B-J SI Class 2 LSS N/A Assume Medium C-F FW Class 2 FWU IC TASCS Medium C-F FW Class 2 FWU OC None Low C-F FW Class 2 FWU - IC None Low C-F FW Class 2 FWI OC None Low C-F MS Class 2 LSS N/A Assume Medium C-F CTS Class 2 LSS N/A Assume Medium C-F

19 Lessons Learned Pilot plants Application of approved RI-BER process results in inspection populations below 10 percent [RIS_B sets floor at 10 percent] Application of approved RI-ISI for the RCPB results in inspection populations below 10 percent [RIS_B sets floor at 10 percent] 2(a)(5) Requirement: Plant 1 internal flooding study did not identify piping > 1E-06 Plant 2 plant made procedural/ hardware changes to reduce CDF to < 1E-06 Plant 3 -updated analysis to remove excessive conservatism to reduce CDF contribution to < 1 E-06 Added criterion for LERF > 1 E-07

20 Lessons Learned Industry Application 40 Units have applied the streamlined RI-ISI methodology and fall into four categories Plants that do not identify any safety significant (HSS) piping outside the pre-defined scope Plants that initially identify Class 3 or non safety related piping as HSS but conduct additional / more realistic analyses Plants that identify HSS piping in Class 3 or non safety related system and plant modification to eliminate to issue Plants that identify HSS piping in Class 3 or non safety related piping that conduct NDE on subject piping

21 Considerations for application Materials and operating conditions are factors in determining applicable degradation mechanism and susceptibility criteria Current inspection program/philosophy Periodic based ISI (e.g. deterministic rules) Operating experience based ISI (e.g. local corrosion, flow accelerated corrosion) Risk assessment of internal flooding events important in identify plant specific HSS piping, if any Systems that support multiple units may require additional thought System failures that could impact multiple units may require additional thought

22 Summary Founded upon previously conducted Risk-informed work: Deterministic approaches Qualitative risk approaches Quantitative risk approaches (e.g. WCAP-14572, EPRI TR , EPRI TR , N663, international experience) Uses generic insights to: Reduce cost of implementation and maintenance Assure defense in depth is maintained (e.g. high consequence sites) Uses plant-specific insights to: Assure important plant specific inspections are conducted Maintain or improve pressure boundary reliability (e.g. degradation mechanisms) Requirement for augmented programs for PWSCC, IGSCC, FAC, LC Requires and cost-effectively performs a full plant evaluation (safety related and non safety related systems)