Second License Amendment Request for the Unit 3

Train B Diesel Generator

Palo Verde Nuclear Generating StationDecember 29, 2016

Agenda• Background• Regulatory Commitments• Event Investigation• Risk Assessment• Second License Amendment Request• Conclusions

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First License Amendment Request (LAR)

• One-time Technical Specification (TS) Change to Allow a 21 day Completion Time In Response to Failure of Unit 3 B Train DG on December 15, 2016– Extension of 11 days needed to collect/analyze data and

continue repair – Deterministic justification based upon BTP 8-8– Risk insights provided to support change – NRC commitments made in LAR– NRC Amendment 199 issued on December 23, 2016

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Regulatory Commitments• Commitments documented in NRC

Amendment #199 include but are not limited to:– Three, 2 MW portable DGs staged, tested and

hooked-up to Unit 3 FLEX 4.16KV connections– Diesel driven FLEX Steam Generator make-up

pump staged in Unit 3– Suspension of discretionary maintenance on

SBOGs, Switchyard, Safety Systems– Establish protected equipment controls for Train A

equipment, SBOGs, portable equipment– Commitments monitored and tracked by OPS– Dedicated personnel

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Palo Verde AC Power System

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Palo Verde AC Power System

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Event Investigation

• Partnerships established with MPR, Goltens, Structural Integrity, EPRI, and the Cooper-Bessemer Owners Group

• Evidence of high cycle fatigue on master connecting rod

• Second major failure of 3B DG (9R)• 1986 event created localized misalignment

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Operating Experience (OE)

• Cooper-Bessemer KSV-20 OE – 1986 – Palo Verde 3B DG connecting rod (9R)

failure during unit startup testing program– 1989 – South Texas Project DG 22 connecting rod

failure during a surveillance test – 2003 – South Texas Project DG 22 connecting rod

failure during a surveillance test (one-time LAR using a two-phased approach to extend allowable outage time to 113 days)

– 2016 – Palo Verde 3B DG connecting rod (9R) failure during a surveillance test

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DIRECT CAUSE OF FAILURE

• High cycle fatigue failure of the master connecting rod ligament which surrounds the lower part of the articulating rod pin.

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Event Investigation

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Master Rod Fracture Surface

ROOT CAUSE OF FAILURE

FLAW + STRESS = FATIGUE

POTENTIAL FLAWS STRESS

1. Residual tensile within master connecting rod bore due to machining process change

Mis-Alignment2. Fretting

3. “Undersized” Oversized Bearing following 1987 repair.

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3A/3B COMPARITIVE EVALUATION

• Evaluating Wide Array of Data• Relevant Data– Vibration – Engine Analysis– Line Bore Data–Work History– Event History

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3A/3B COMPARITIVE EVALUATION• Unit 3 “B” Emergency Diesel Generator

experienced a catastrophic failure that induced crankshaft mis-alignment which increased the stress profile within the engine

• Unit 3 “A” engine has not had a catastrophic failure

• Unit 3 “A” engine vibration displacement data is consistently less and has significantly less variability

• Unit 3 “A” Master connecting rods are original equipment (i.e. Pre machining change)

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Engineering Conclusion

There is no common cause mode of failure to Unit 3 “A” Emergency Diesel Generator due to the unique aspects of the Unit 3 “B” Diesel Generator root cause.

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Risk Assessment

• PRA models for– Internal Events– Internal Flood– Internal Fire– Seismic

• Other hazards screened out

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PRA Model and Risk-Informed Application Model History

Pre-2010 2010 2011 2012 2013 2014 2015 2016

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Internal Events CEOG peer review & numerous risk-informed TS changes

TSTF-425 Surveillance Frequency Control Program approved

2nd fire PRA peer review

TSTF-505 submitted

Internal Flood peer review

Risk-informed 7-day inverter TS approved

Seismic PRA peer review1st fire PRA peer review

Internal Events self-assessment per RG 1.200 App B

All Unit 3Mods Comp & all ASMEPRA Std SRs Met to CC II

External Hazards Screening peer review

Risk Assessment• Palo Verde PRA Aspects

– Six 100% capacity SG makeup pumps all supplied by onsite power sources

– Only one of these powered by B DG if loss of offsite power– RCP seal LOCAs negligible – ECCS significance minimal in

loss of offsite power events– No Pressurizer power-operated relief valves– Very low internal events CDF and LERF - consistent with STP

and Millstone 3– Only shared systems in PRA are SBOGs and firewater– Dedicated fire department staff and equipment– Risk significant FLEX connections outside of unit– Did not need to implement NFPA-805 to address multiple

spurious operations

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PRA Model Credited Changes • Revised emergency operating procedures and night order

to direct timely use of firewater to auxiliary feedwatercross-tie in total loss of feedwater event – validated in simulator– Additional dedicated auxiliary operator added to each shift to

implement cross-tie• Post continuous fire watch in fire zone FCCOR2 (120’

Corridor Building)• Establish new transient combustible and hot work exclusion

zones and conduct shiftly inspections– Fire zones FCCOR2 (120’ Corridor Building) and FCCOR2A (120’

Corridor Riser Shaft)– Fire zones FCTB04 (upper level only, non-class DC Equipment,

[FCTB04-TRAN1])– Fire zone FC86A (train A Seismic Gap, make part of train A Electrical

Protected Equipment)– Fire zone FCTB100 zone ZT1G (SW corner, south half of 100’ Turbine

between columns TA and TC)

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Risk Assessment• Defense-in-Depth Evaluation

– Unavailability does not reduce the amount of available equipment to a level below that necessary to mitigate a design basis accident

• Safety Margin Evaluation– No significant reduction in margin of safety

• Regulatory Guide 1.200, Revision 2 compliant• Regulatory Guide 1.177, Revision 1 compliant• Regulatory Guide 1.174, Revision 2 compliant

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Second License Amendment Request

• Requesting a extension of TS 3.8.1 Condition B.4 Completion Time to complete the DG Repairs

• Request on Emergency Basis• Risk-informed LAR• Carrying forward the Commitments made in

Deterministic LAR• To be submitted Friday, December 30• Request approval by early Thursday morning

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Conclusions

• Direct cause of the 3B DG failure has been determined

• No common mode failure applicability to 3A DG

• Continue to have diverse and redundant sources of AC power and steam generator makeup

• PRA risk acceptable in accordance with Regulatory Guides 1.174 and 1.177

• No significant hazards consideration criteria satisfied

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Questions?