ML18044A983

Meeting Slides for February 15, 2018, Public Meeting Regarding Industry Response to Flowserve Part 21 on Anchor Darling Double Disk Gate Valves and NRC Staff Next Steps

ML18044A983
Person / Time
Issue date:	02/15/2018
From:	Bailey S N NRC/NRR/DE/EMIB
To:
Bailey S N
References
Download: ML18044A983 (21)

Text

Industry Response to Flowserve Part 21 onAnchor Darling Double Disk Gate Valves and NRC Staff Next StepsPublic MeetingFebruary 15, 2018 1

Overview*Operating Experience has identified failures of Anchor/Darling (A/D) Double Disk Gate Valves (DDGVs)*Significant progress has been made-Industry has developed guidance and is correcting the issue-All licensees have submitted information on the affected valves, including commitments for valve repairs*The NRC staff and Industry continue to discuss the issue*The NRC staff is preparing to inspect licensees' corrective actions*The NRC staff continues to assess the need for a Generic Communication 2

Background*Failure of Anchor/Darling (A/D) Double Disk Gate Valve (DDGV) at Browns Ferry in 2013 revealed that threaded stem-to-wedge connection had not been properly torqued*Flowserve Part 21 notification February 25, 2013-Recommended assessing wedge pin susceptibility to shear and rework the valve if needed*BWROG developed guidance to address Part 21 to include:-Prioritization and Screening Criteria-Evaluation Methods

-Inspection and Diagnostics

-Repair Methods 3

Background (cont.)*NRC staff evaluated the Part 21 and determined the issue would be monitored with no generic communication*Additional failures occurred at LaSalle Unit 2 and Columbia

• LaSalle event elevated to NRC special inspection

• Information Notice (June 2017)

• Flowserve updated Part 21 (July 2017)

• BWROG updated guidance to Rev. 4 (August 2017)

• NRC staff considered the need for generic communication due to larger population of failures and limited information readily available to the staff 4

Progress to Date*NRC staff held public meetings on guidance and licensee corrective actions-Staff requested clarification of guidance (October 2017)-NEI provided clarification (November 2017)*All licensees submitted information (December 2017)-Valve population

-Valve characteristics (susceptible, non susceptible, risk category)

-Rework status

-Commitments for future repairs 5

NRC Observations on BWROG Guidance 6

Summary*Allowance to use engineering judgement for key assumptions that determine whether a valve is

"susceptible"-Credit for thread friction-Maximum actuator torque*Limited effectiveness of testing and diagnostics 7

Engineering JudgementonCredit for Thread Friction*Rev. 4 guidance implies that friction should only be used for borderline cases (small negative margin) and low levels of friction should be

assumed*Stem-to-Wedge thread friction has a wide range of possible values that could change over time and system conditions (.02 to .78 steel on steel)*Staff questions crediting of stem-to-wedge thread friction to declare a valve "non susceptible." Thread friction is acceptable for short term operability until the valve can be reworked to Flowserve Part 21 recommendations. A reasonable thread friction value to use for interim

evaluations is 0.10

1.1 Staff

letter dated October 31, 2017 8

Engineering Judgement on Maximum Applied Torque*Rev. 4 guidance provides little direction on actuator torque*Many plants are using as-tested values instead of full actuator capability*Other licensees are using limiting value of the spring pack capability or maximum torque from the valve/actuator weak

link analysis. *Staff questions use of less-than-maximum actuator torque, which is stall torque and stall efficiency as appropriate, to

bound potential over-torque events 9

Hidden Over-Torque Events and Reliance on Spring Pack*Licensees have experienced motor stall events caused by a sticky contactors, such as those in the motor control center *Excessive force may be been applied in the early test years, such as when addressing GL 89-10*Valve may have been subjected to a pressure locking event

• Test equipment in early test years was not as accurate as current test equipment (GL 89-10 Supplement 5)*Spring pack does not limit torque on stem during over torque event, it prevents over travel of torque switch assembly 10 Diagnostics for Evaluating Stem-to-Wedge Connection*NRC SIT team for LaSalle Unit 2 MOV failure concluded that diagnostic testing and stem rotation checks are inconclusive in determining active stem-to-disc connection

degradation 1*Diagnostics can be useful to help plan the schedule for rework*Diagnostic testing and stem rotation checks will identify gross failure of the stem-to-wedge connection 2 1Staff inspection report dated August 31, 2017 2 Staff letter dated October 31, 2017 11 Example of Diagnostic Test Inability to Conclusively Determine Degradation of Stem-to-Wedge Connection 12 LaSalle Unit 2 Anomaly 2015 -Example used in BWROG Guide as Active Stem-to-Wedge Connection Degradation 13 LaSalle Unit 2 As Left Thrust/Torque Trace After Rework 14 Recent MOV Rework As-Found-Left Thrust Trace 15 LaSalle Unit 2 Anomaly Compared to Recent MOV Post Rework Trace Unit 2 AnomalyRecent MOV Post Rework As Left Torque & Thrust Trace 16 Summary of A/D DDGV Population from Licensee Submittals*584 -Total # of valves reported*119 -Total # of valves repaired

• 425 -Total # of valves not repaired

• 40 -Total # of valves N/A (T-Head design, not always reported)

• 106 -Total # of high risk valves

• 163 -Total # of medium risk valves

• 305 -Total # of low risk valves

• 182 -Total # of valves that use thread friction > 0.10

• 59 -Total # of valves that use thread friction < or = 0.10

• 38 -Total # of valves that are non-safety

• 225 -Total # of valves that require further NRC review 17 A/D DDGVs Requiring Further Review*113 -Total # of valves considered not susceptible using thread friction > 0.10 with no plans to repair*51 -Total # of valves considered not susceptible using thread friction < or = 0.10 with no plans to repair*39 -# of High Risk valves using thread friction with no plans to repair*14 -# of High Risk valves with no plans to repair and provided data not clear*13 -# of valves that have been repaired and using thread friction to justify final repair*35 -# of non-safety related valves. Need to verify failure does not affect other systems.

18 NRC Inspection Plans*NRC staff is developing an inspection sample *NRC draft Temporary Instruction is in internal review

• Focus of inspection:-Verify licensee properly identified valves population-Evaluate thrust for impact on valve integrity

-Evaluate torque/shear pin to determine whether valve is susceptible

-Evaluate history of over torque events and plans for identifying future over torque events if licensee does not use maximum torque-Review risk categorization

-Evaluate planned corrective actions 19 NRC Next Steps*Public Meeting (April 2018)*Finalize TI (May 2018)

• TI inspections (2018 into 2019)

• Continue to assess need for generic communication 20 QUESTIONS?

Future Questions Stewart.Bailey@nrc.gov 301-415-1321 Michael.Farnan@nrc.gov 301-415-1486 21