ML16335A439
| ML16335A439 | |
| Person / Time | |
|---|---|
| Site: | Diablo Canyon  |
| Issue date: | 11/30/2016 |
| From: | Jeremy Groom NRC/RGN-IV/DRP/RPB-A |
| To: | |
| Jeremy Groom | |
| References | |
| Download: ML16335A439 (34) | |
Text
NOTE:
The following slides were presented by representatives of Pacific Gas & Electric (PG&E) /Diablo Canyon Power Plant during a Regulatory Conference (a Category 1 Public Meeting) conducted in the NRC Region IV Office on November 15, 2016.
The purpose of the Regulatory Conference was to discuss an apparent violation related to inadequate procedures associated with the installation of external limit switches on motor operated valves as documented in NRC Inspection Report 05000275/2016010 and 05000323/2016010, issued on October 3, 2016.
Slide 19 of the presentation includes an embedded video file which is available to be viewed in this downloaded Adobe Acrobat PDF file. The video was presented at the Regulatory Conference to demonstrate the timeline and actions PG&E staff would have used to prepare and open a chamber in the auxiliary building in attempting to recover valve SI-8982 under certain accident conditions.
The events in the video were notional (i.e., were conducted as a drill) and the emergency events leading to the demonstrated actions did not actually occur at the Diablo Canyon Power Plant.
PUBLIC MEETING CONTACT: Jeremy Groom, Chief Reactor Project Branch A, Division of Reactor Projects, Region IV Phone: (817) 200-1148 ML16335A439
Diablo Canyon Power Plant NRC Regulatory Conference Limit Switch Finding Significance November 15, 2016
Opening Remarks Jim Welsch Vice President Nuclear Generation Introduction Generation 2 of 33
PG&E Representatives Diablo Canyon Power Plant Participants Jim Welsch - Vice President Nuclear Generation Jan Nimick - Senior Director Nuclear Services John Whetsler - Operations Shift Manager Bob Waltos - Assistant Director Engineering Services Nathan Barber - Senior PRA Analyst 3 of 33
Agenda Topic Presenter Preliminary Finding Jan Nimick ECCS Operational Overview John Whetsler Plant Design Bob Waltos Condition Description Bob Waltos ECCS Operation with the Condition John Whetsler Capability to Recover Local Manual John Whetsler Remote Electrical John Whetsler Interlock Jumper Bob Waltos SPAR Risk Significance Nathan Barber Summary and Conclusion Jan Nimick 4 of 33
Preliminary Finding Why are we here today?
Performance deficiency: Failure to provide instructions for limiting the travel of external limit switches installed on safety related motor operated valves.
Violation: of Technical Specification(TS) 5.4.1.a, Procedures Resulted in failure of an external closed limit switch for the Residual Heat Removal (RHR) Pump (PP) 2-2 Suction valve, RHR-2-8700B. This blocked control logic to open RHR PP 2-2 Containment Recirculation Sump Suction Valve SI-2-8982B.
PG&E agrees with the performance deficiency PG&E has identified new information that results in a change to Core Damage Frequency when entered into the plant-specific SPAR Model.
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Preliminary Finding What will you be hearing from PG&E?
New Information not considered in the NRCs Significance Determination Program Evaluation Three primary areas of new information affecting the safety significance:
Contribution of medium break Loss of Coolant Accidents Operational strategies improving time to recover Robust and reliable recovery methods 6 of 33
Emergency Core Cooling System (ECCS)
Operational Overview ECCS Operation and Switchover to Recirculation 8700A 8700B 7 of 33
Plant Design RHR Pump Suction Valve from Containment Recirculation Sump (SI-8982)
Located within the Recirc Chamber beneath the RHR Containment Sump Unobstructed access to valve via 36 manway opening Chamber is opened every refueling outage Valve is operated from the Control Room to initiate Cold Leg Recirculation 8 of 33
Plant Design RHR Pump 2-2 Suction Valve from the Refueling Water Storage Tank (RHR-2-8700B)
Valve is located in an easily accessible uncontaminated area in the Auxiliary Building External position switch performs an interlock function with SI 8982B Access to the position switch, switch contacts, motor, gear box and valve are unobstructed 9 of 33
ECCS Operation with the Condition ECCS Operation and Switchover to Recirculation If BOTH Recirculation Sump Suction Valves (SI-2-8982A & B) fail to open, Operators transition to the Loss of Emergency Coolant Recirculation, procedure and:
Initiate continuous actions to restore ECCS recirculation from the sump Initiate makeup water to the RWST to add inventory Minimize SIP/CCP injection to match the decay heat load and further preserve inventory Depressurize the Steam Generators to cool down and depressurize the RCS 10 of 33
ECCS Operation with the Condition Condition Timeline (MAAP 3.5 LOCA)
NRC Recovery Window 11 of 33
ECCS Operation with the Condition Plant Specific SPAR Model Medium LOCA (MLOCA) Modeling NRC analysis distributed the total MLOCA initiating event frequency linearly based on break size range.
NUREG-1829 shows that the relationship between frequency and break size is logarithmic.
NUREG - 1829 NUREG-1829 Use of NUREG-1829 data results in a break frequency for 3.5 to 6 of ~8E-06 per year, lower than the NRC estimate of
~1E-04.
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ECCS Operation with the Condition Frequency and Break Size Interpolation Use of NUREG-1829 data results in a break frequency for 3.5 to 6 of
~8E-06 per year, lower than the NRC estimate of ~1E-04.
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ECCS Operation with the Condition Effect on CDF LOCA Frequencies Break % of total NRC IR Freq. NUREG-1829 % of total Diameter (NUREG -
(/yr) Freq. (/yr) (NRC IR)
Range 1829)
Initiator Small MLOCA 2"-3.5" 5.6E-05 1.28E-04 37.5% 94%
Large MLOCA 3.5"-6" 9.4E-05 8.09E-06 62.5% 6%
Plant-Specific SPAR Model Model Input Decrease in CDF Internal CDF NRC Baseline Internal CDF 7.10E-06 MLOCA Modeling 2.17E-06 4.93E-06 14 of 33
ECCS Operation with the Condition Plant Specific SPAR Model Common Cause Factor (CCF)
Current NRC SPAR model for DCPP uses alpha factors from the 2010 parameter update Updated alpha factors from 2013 are lower (alpha2 is 1.77E-02 vs. 1.92E-02)
Replaced 2010 MOV alpha factors with 2013 values Reduction in CDF is most pronounced for large MLOCA 15 of 33
ECCS Operation with the Condition Effect on CDF Plant Specific SPAR Model Model Input Decrease in CDF Internal CDF NRC Baseline Internal CDF 7.10E-06 MLOCA Modeling 2.17E-06 4.93E-06 CCF Alpha Factor Update 1.08E-07 4.82E-06 16 of 33
Capability to Recover Recovery a) Work Locations Within the Auxiliary Building Non Local Manual b RCA Operation Recovery b)
Remote c
Electrical Opening a Recovery c)
Interlock Jumper Radiologically Controlled Area (RCA)
The condition would be revealed during implementation of EOPs when transferring to cold leg recirculation The control room would contact the TSC to request assistance in opening valve SI 8982B Three independent recoveries would be available:
a) Manually open the SI-2-8982B valve using the handwheel b) Electrically open the SI-2-8982B valve at the switchgear c) Make-up the failed interlock on valve RHR-2-8700B using a jumper 17 of 33
Capability to Recover Local Manual Operation of the Recirculation Sump Suction Valve (SI-2-8982) 8982 chamber is an uncongested area accessed every refueling outage.
Expected post accident ambient temperatures would be 83 F.
Operating experience substantiates that the chamber will not be contaminated or require a respirator.
Chamber access instructions are readily available to personnel in the Operations Support Center.
Time to start of valve opening was 50 min from start of pre-job brief.
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Capability to Recover Video - Opening SI-8982 Chamber 19 of 33
Capability to Recover Plant Specific SPAR Model Local Manual Recovery The Human Error Probability (HEP) for local manual recovery using SPAR-H was updated based on new information:
Increase in time available for action. Time Available - Extra Time required for action reduced based on actual hatch operation timing test.
Based on new information, ergonomics reassessed. No need for respirator or ladder, and the space is expansive.
Ergonomics - Nominal Operators are trained on manual operation of similar MOVs.
Experience/Training - Nominal A change in these PSFs results in a significant reduction in the human error probability for manual valve operation.
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Capability to Recover Effect on CDF Plant Specific SPAR Model Model Input Decrease in CDF Internal CDF NRC Baseline Internal CDF 7.10E-06 MLOCA Modeling 2.17E-06 4.93E-06 CCF Alpha Factor Update 1.08E-07 4.82E-06 Open 8982 Manually 4.28E-06 5.42E-07 21 of 33
Capability to Recover Opening 8982 MOV at Switchgear Remote Electrical Operation Procedure OP O-22, training, and Task Performance Evaluation ensure operators are familiar with requirements to open or close MOVs by actuating the motor contactor at the 480V breaker.
OP O-22 instructions ensure timely identification and correction LKD Temp Rise of wrong contactor use. In Seconds Motor curve predicts no damage from Locked Rotor Amps, up to 10 seconds 8 Ft-Lb Temp Rise Min Reliance Electric AC Motor Performance Curve M4635 22 of 33
Capability to Recover Plant Specific SPAR Model Remote Electrical Recovery The HEP for remote electrical recovery was updated:
Increase in time available for diagnosis. Time Available -
Expansive A change in the action PSF for procedures is warranted based on the availability of procedures (OP O-22).
OP O-22 contains a diagram of a typical layout. Procedure -
Available, but Poor OP O-22 Diagram 23 of 33
Capability to Recover Effect on CDF Plant Specific SPAR Model Model Input Decrease in CDF Internal CDF NRC Baseline Internal CDF 7.10E-06 MLOCA Modeling 2.17E-06 4.93E-06 CCF Alpha Factor Update 1.08E-07 4.82E-06 Open 8982 Manually 4.28E-06 5.42E-07 Open 8982 from Switchgear 5.64E-08 4.86E-07 24 of 33
Capability to Recover Install Interlock Jumper on 8700B Actuator to allow Opening 8982B from the Control Room Jumper &
Installation Location Maintenance Procedure would be used to jumper the position switch contacts on 8700B.
Installation would be at the valve actuator, removing the actuator housing and jumpering across the switch contacts on the actuator rotors.
Unobstructed Access to RWST Suction Valve (8700B) and Actuator 25 of 33
Capability to Recover Plant Specific SPAR Model Install Interlock Jumper on 8700 MOV and Open 8982 From the Control Room
- MP E-53.10A has instructions on jumpering 8982B interlocks including wire IDs. Procedure provides specific instructions for landing jumper.
Procedure - Available but Poor
- Jumpers would be installed at 8700B -
valve is easily accessible.
Ergonomics - Nominal
- Electrical technicians are trained on how to install jumpers.
Experience - Nominal Typical MOV Limit Switch finger base with Jumper
- Very low ambiguity in execution.
Complexity - Moderately Complex
- Action time available.
Time Available - Nominal 26 of 33
Capability to Recover Plant Specific SPAR Model Recovery of common cause valve SI-2-8982A failure to open Dominant scenarios include common cause failure of 8982A A failure of 8982A due to the same procedure deficiency would allow the same recovery RHR-8700A/B actions to be applied Given the large amount of time available for recovery, SI-8982A/B sufficient time is available to attempt recovery of A train following failure of B train actions.
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Capability to Recover Plant Specific SPAR Model Calculation of Internal and External CDF PG&E used the current NRC SPAR model to assess CDF given the previously discussed new inputs Internal CDF = 4.86E-07.
Reduction in Large MLOCA frequency reduces contribution from breaks >3.5.
CDF for Small LOCAs and Small MLOCAs (3.5) is reduced due to changes in SPAR-H PSFs.
Additional recovery actions are appropriate given substantial increase in the time available.
External CDF values were calculated by applying the updated recovery actions to the CDF from the inspection report. After crediting recovery, external CDF was reduced to 4.56E-08.
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SPAR Risk Significance Effect on CDF Plant Specific SPAR Model Final Results Model Input NRC CDF PG&E CDF Total Internal CDF 7.10E-06 4.86E-07 Total External CDF 5.40E-07 4.56E-08 Total CDF 7.64E-06 5.32E-07 29 of 33
SPAR Risk Significance Plant Specific SPAR Model PRA Conservative Inputs NOT Modeled LOCA must be >4.5 to actuate containment spray. No recovery from breaks >3.5 and <4.5 was credited.
Recovery time for all SLOCAs used the shorter 3.5 LOCA time. No credit for very long recovery times provided by small LOCAs.
Recovery of Train A recirculation sump suction valve common cause failure was not credited.
Credible procedural operator actions in timeline not taken:
Refilling RWST from Liquid Holdup Tanks Normal charging from the Volume Control Tank and Boric Acid Blender makeup after RWST reaches 4% level.
Action to refill the Spent Fuel Pool.
The inputs listed above are currently being evaluated to determine their significance.
Note that different combinations of input values may change their individual contribution to Core Damage Frequency which would warrant inclusion of the above inputs into the final assessment and require further analysis.
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SPAR Risk Significance Effect on CDF Plant Specific SPAR Model Sensitivities MLOCA Frequency Sensitivities Sensitivity Large MLOCA CDF Use of 4.5" LOCA category from NUREG-1829. Large 1.20E-07 MLOCA = 2.88E-06 /Small MLOCA = 1.34E-04 Use of 3" LOCA category from NUREG-1829. Large MLOCA 6.67E-07
= 1.36E-05 /Small MLOCA = 1.23E-04 Recovery Action Sensitivities Sensitivity Internal CDF Electrical and Manual Recovery (1.30E-03) 4.86E-07 Jumper and Electrical Recovery (2.12E-02) 8.50E-07 Manual with Poor Ergonomics plus Electrical (1.82E-03) 4.95E-07 Manual with Poor Ergonomics (1.29E-02) 6.97E-07 31 of 33
Summary and Conclusions
SUMMARY
The preliminary significance documented in IR 2016-010 is a conservative and bounding assessment of condition significance.
The new information presented by PG&E today, using the NRCs SPAR model, provides a robust revision of the assessment of condition significance.
CONCLUSION A robust revision of the assessment of this condition demonstrates a total CDF of 5.32E-07/yr.
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Closing Remarks Jim Welsch Vice President Nuclear Generation 33 of 33