ML17003A033
| ML17003A033 | |
| Person / Time | |
|---|---|
| Site: | Palo Verde  |
| Issue date: | 12/29/2016 |
| From: | Arizona Public Service Co |
| To: | Office of Nuclear Reactor Regulation |
| Watford M | |
| References | |
| CAC MF9019 | |
| Download: ML17003A033 (23) | |
Text
Second License Amendment Request for the Unit 3 Train B Diesel Generator Palo Verde Nuclear Generating Station December 29, 2016
Agenda
Background
Regulatory Commitments Event Investigation Risk Assessment Second License Amendment Request Conclusions 2
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 3
- 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 4
Palo Verde AC Power System 5
Palo Verde AC Power System 6
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 7
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 8
DIRECT CAUSE OF FAILURE
- High cycle fatigue failure of the master connecting rod ligament which surrounds the lower part of the articulating rod pin.
9
Event Investigation 10 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-Alignment
- 2. Fretting
- 3. Undersized Oversized Bearing following 1987 repair.
11
12
3A/3B COMPARITIVE EVALUATION
- Evaluating Wide Array of Data
- Relevant Data
- Vibration
- Engine Analysis
- Line Bore Data
- Work History
- Event History 13
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) 14
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.
15
Risk Assessment
- PRA models for
- Internal Events
- Internal Flood
- Internal Fire
- Seismic
- Other hazards screened out 16
PRA Model and Risk-Informed Application Model History Pre-2010 2010 2011 2012 2013 2014 2015 2016 17 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 review 1st fire PRA peer review Internal Events self-assessment per RG 1.200 App B All Unit 3 Mods Comp
& all ASME PRA 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 18
PRA Model Credited Changes Revised emergency operating procedures and night order to direct timely use of firewater to auxiliary feedwater cross-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) 19
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 20
Second License Amendment Request
- 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 21
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 22
Questions?