05000530/LER-1916-002-01, Regarding Emergency Diesel Generator Failure Resulting in a Condition Prohibited by Technical Specifications

Regarding Emergency Diesel Generator Failure Resulting in a Condition Prohibited by Technical Specifications

ML17178A383
Person / Time
Site:	Palo Verde
Issue date:	06/27/2017
From:	Lacal M Arizona Public Service Co
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
102-07536-MLL/RAC LER 16-002-01
Download: ML17178A383 (7)

LER-1916-002, Regarding Emergency Diesel Generator Failure Resulting in a Condition Prohibited by Technical Specifications

Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2)(i)(A), Completion of TS Shutdown 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(i) 10 CFR 50.73(a)(2)(ii)(A), Seriously Degraded 10 CFR 50.73(a)(2)(ii)(B), Unanalyzed Condition 10 CFR 50.73(a)(2)(iii) 10 CFR 50.73(a)(2)(iv)(A), System Actuation 10 CFR 50.73(a)(2)(v)(A), Loss of Safety Function - Shutdown the Reactor 10 CFR 50.73(a)(2)(v)(B), Loss of Safety Function - Remove Residual Heat 10 CFR 50.73(a)(2)(v), Loss of Safety Function 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability 10 CFR 50.73(a)(2)(viii)(A) 10 CFR 50.73(a)(2)(viii)(B) 10 CFR 50.73(a)(2)(ix)(A) 10 CFR 50.73(a)(2)(x)
5301916002R01 - NRC Website

text

Oaps 102-07536-MLL/RAC June 27, 2017 ATTN; Document Control Desk U.S. Nuclear Regulatory Commission Washington, DC 20555-0001

Dear Sirs:

10 CFR 50.73 MARIA L. LACAL Senior Vice President Nuciear Reguiatory and Oversight Palo Verde Nuclear Generating Station P.O. Box 52034 Phoenix, AZ 85072 Mail station 7605 Tel 623 393 6491

Subject:

Palo Verde Nuclear Generating Station (PVNGS) Unit 3 Docket No. STN 50-530 / License No. NPF 74 Licensee Event Report 2016-002-01 Enclosed please find Licensee Event Report (LER) supplement 50-530/2016-002-01 that has been prepared and submitted pursuant to 10 CFR 50.73. This LER supplement provides the causes and corrective actions determined for the previously reported event in which the Unit 3 train B diesel generator failed during the performance of a surveillance test. This failure resulted In a condition prohibited by Technical Specification (TS) Limiting Condition for Operation (LCO) 3.8.1, AC Sources -

Operating, and a condition that could have prevented the fulfillment of a safety function.

In accordance with 10 CFR 50.4, copies of this LER are being forwarded to the Nuclear Regulatory Commission (NRC) Regional Office, NRC Region IV, and the Senior Resident Inspector.

Arizona Public Service Company makes no commitments in this letter. If you have questions regarding this submittal, please contact Matthew Kura, Department Leader -

Nuclear Regulatory Affairs, at (623) 393-5379.

Sincerely, Lacal, Maria UZ06149)

MLL7RAC Enclosure ON: cnsLacal, Maria L(Z06149)

Date: 2017.06.27 09:41:48

- 07'00 cc:

K. M. Kennedy S. P. LIngam C. A. Peabody NRC Region IV Regional Administrator NRC NRR Project Manager for PVNGS NRC Senior Resident Inspector PVNGS A member of the STARS Alliance LLC Callaway

• Diablo Canyon

• Palo Verde

• Wolf Creek

NRC FORM 366 (06-2016)

U.S. NUCLEAR REGULATORY COMMISSION LICENSEE EVENT REPORT (LER)

(See Page 2 for required number of digits/ctiaracters for each block)

(See NUREG-1022, R.3 for instruction and guidance for completing this form httDy/www.nrc.Qov/readina-rm/doc-collections/nureas/gtaff/grinpp/rfV)

APPROVED BY 0MB: NO. 3150-0104 EXPIRES: 10/31/2018 Estimated burden per response to comply with this mandatory collection request: 80 hours9.259259e-4 days <br />0.0222 hours <br />1.322751e-4 weeks <br />3.044e-5 months <br />.

Reported lessons learned are incorporated into the licensing process and fed back to industry.

Send comments regarding burden estimate to the FOiA, Privacy and information Coliections Branch (T-5 F53), U.S. Nuciear Reguiatory Commission, Washington, DC 20555-0001, or by e-mail to lnlocollects.Resource0nrc.gov, and to the Desk Officer, Office of Information and Reguiatory Affairs, NEOB-10202, (3150-0104), Office of Management and Budget, Washington, (X! 20503. If a means used to impose an information coliecSon does not display a currently valid 0MB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection._______________________

1. FACILITY NAME Palo Verde Nuclear Generating Station (PVNGS) Unit 3

2. DOCKET NUMBER 05000530

3. PAGE 1 Of 6

4. TITLE Emergency Diesel Generator Failure Resulting in a Condition Prohibited by Technical Specifications

5. EVENT DATE MONTH DAY YEAR 2016

6. LER NUMBER YEAR SEQUENTIAL NUMBER REV NO.

2016 - 002 - 01

7. REPORT DATE MONTH DAY YEAR 2017

8. OTHER FACILITIES INVOLVED FACILITY NAME FACILITY NAME DOCKET NUMBER DOCKET NUMBER

9. OPERATING MODE 11.THS REPORT IS SUBMmED PURSUANT TO THE REQUIREMENTS OF 10CFR§:

20.2201(b) 20.2201(d) 20.2203(a)(1) 20.2203(a)(2)(i)

10. POWER LEVEL 100 20.2203(a)(2)(ii) 20.2203(a)(2)(iii) 20.2203(a)(2)(iv) 20.2203(a)(2)(v) 20.2203(a)(2)(vi) 20.2203(a)(3)(i) 20.2203(a)(3)(ii) 20.2203(a)(4) 50.36(c)(1)(i)(A) 50.36(c)(1)(ii)(A) 50.36(c)(2) 50.46(a)(3)(ii) 50.73(a)(2)(i)(A) la 50.73(a)(2)(i)(B) 50.73(a)(2)(i)(C) 50.73(a)(2)(ii)(A) 50.73(a)(2)(ii)(B) 50.73(a)(2)(iii) 50.73(a)(2)(iv)(A) 50.73(a)(2)(v)(A) 50.73(a)(2)(v)(B) 50.73(a)(2)(v)(C) 50.73(a)(2)(v)(D) 50.73(a)(2)(vii)

'Check all that apply) 50.73(a)(2)(viii)(A) 50.73(a)(2)(viii)(B) 50.73(a)(2)(ix)(A) 50.73(a)(2)(x) 73.71(a)(4) 73.71(a)(5) 73.77(a)(1) 73.77(a)(2)(i) 73.77(a)(2)(ii)

OTH ER Speeily in Abstract below or in NRC Form 366A

12. LICENSEE CONTACT FOR THIS LER LICENSEE CONTACT Matthew Kura, Department Leader, Nuclear Regulatory Affairs TELEPHONE NUMBER (Include Area Code) 623-393-5379 ia COMPLETE ONE UNE FOR EACH COMPONENT FAILURE DESCRIBED IN THS REPORT

CAUSE

SYSTEM COMPONENT MANU FACTURER REPORTABLE TO EPIX

CAUSE

SYSTEM COMPONENT MANU FACTURER REPORTABLE TO EPIX C628

14. SUPPLEMENTAL REPORT EXPECTED YES (ttyes, complete 15. EXPECTED SUBMISSION DATE)

S NO

15. EXPECTED SUBMISSION DATE MONTH DAY YEAR ABSTRACT (Limit to 1400 spaces, i.e., approximately 15 single-spaced typewritten lines)

On December 15, 2016, the Unit 3 train B (3B) diesel generator (DG) experienced a failure during the performance of a monthly surveillance test. At 0356 Mountain Standard Time, a master connecting rod mechanically failed and caused significant damage to the 3B DG. Unit 3 control room staff declared the 3B DG inoperable and entered Technical Specification Limiting Condition for Operation (LCO) 3.8.1, AC Sources - Operating, Condition B. To support repairs, Palo Verde Nuclear Generating Station (PVNGS) received two license amendments to extend the LCO 3.8.1, Condition B required action completion time for the 3B DG from 10 days to 62 days.

The root cause analysis determined the 3B DG master connecting rod failed due to high cycle fatigue caused by misalignment of the crankshaft bore introduced by a previous failure that occurred in 1986. The failure mechanisms that caused the 1986 and 2016 3B DG failures are not present in any other PVNGS DG. As a corrective action, the crankshaft was removed from the 3B DG and alignment was restored to within manufacturer specifications. All damaged components were replaced or repaired, testing was completed, and the 3B DG was declared operable on February 10, 2017. As an additional corrective action, PVNGS will perform more frequent testing on DG master rods to ensure effective identification of fatigue cracks prior to failure. PVNGS will also perform master rod bearing clearance and master rod stud preload ihecks.

All times are Mountain Standard Time and approximate unless otherwise indicated.

1. REPORTING REQUIREMENT(S)

This Licensee Event Report (LER) is being submitted pursuant to 10 CFR 50.73(a)(2)(i)(B) to report a condition prohibited by Technical Specification (TS) Limiting Condition for Operation (LCO) 3.8.1, AC Sources - Operating and 10 CFR 50.73(a)(2)(v)(D) for a condition that could have prevented the fulfillment of a safety function of a system needed to mitigate the consequences of an accident. On December 15, 2016, the Unit 3 train B (3B) diesel generator (DG) (EIIS Code: EK) experienced a significant mechanical failure during the performance of a monthly surveillance test. To support the repairs, Palo Verde Nuclear Generating Station (PVNGS) received two license amendments to extend the LCO 3.8.1, Condition B required action completion time for the 3B DG from 10 days to 62 days. PVNGS Unit 3 entered the extended required action completion time for LCO 3.8.1, Condition B on December 25, 2016. Repairs were completed, and the 3B DG was declared operable on February 10, 2017.

Based upon the results of the cause investigation, the 3B DG was likely not capable of performing the specified safety function for the entire 7-day mission time within the required action completion time specified in TS LCO 3.8.1, Condition B. Also, on October 4, 2016, and September 7, 2016, the 3B DG was likely not capable of performing the specified safety function for the entire 7-day mission time when the Unit 3 train A (3A) DG was inoperable for planned maintenance.

Therefore, during time periods when the 3A DG was inoperable, the degraded condition of the 3B DG could have prevented the fulfillment of the safety function of a system needed to mitigate the consequences of an accident.

The failure of the 3B DG resulted in the declaration of an alert emergency classification on December 15, 2016, at 0410 in accordance with Emergency Action Level HA2.1 based on an explosion resulting in visible damage to a safety system required for safe shutdown. This alert was reported in Event Number 52435 pursuant to 10 CFR 50.72(a)(1)(i). The alert was terminated on December 15, 2016, at 0636.

2. DESCRIPTION OF STRUCTURE(S), SYSTEM(S), AND COMPONENT(S)

In each PVNGS unit, the class 1E electrical distribution system AC sources consist of the preferred offsite power sources (normal and alternates) and the onsite standby power sources (3A and 3B DGs). Offsite power is supplied from startup transformers (EIIS Code; EA) through two engineered safety features (ESF) (EIIS Code: JE) service transformers to the two class 1E 4.16 kV buses. The design of the AC electrical distribution system provides independence and redundancy to ensure an available source of power to the ESF systems.

The onsite class 1E AC distribution system in each unit is divided into redundant load groups (A and B trains). Either of the load groups is capable of providing power for safe plant shutdown and event mitigation so that the loss of any one group does not prevent the safety functions from being performed. Each train has connections to two preferred offsite power sources (normal and alternate) and the related train DG.

The PVNGS DGs are Cooper-Bessemer Model KSV-20-T diesel engines designed in a v-type configuration. The DGs are 20-cylinder engines that incorporate 10 pairs of right and left bank power cylinders. Each power cylinder includes a cylinder liner, head assembly, piston, connecting rod, and associated crankshaft throw and bearings. The connecting rods for each pair of power cylinders include one master rod and one articulating rod, each made of forged steel and configured as shown in Attachment 1, Figure of the Connecting Rod Configuration.

Each DG attains full load speed of 600 rpm and is ready to accept sequenced load within 10 seconds following an emergency start signal. The DG is designed to operate during and after a safe shutdown earthquake. The DG operates L:Page 2 of 6U.S. NUCLEAR REGULATORY COMMISSION (06-2016)

LICENSEE EVENT REPORT (LER)

CONTINUATION SHEET (See NUREG-1022, R.3 for instruction and guidance for completing this form httD://www.nrc.aov/readina-rm/doc-collections/nurecis/staff/srin?P/r3/t APPROVED BY OUB: NO. 3150-0104 EXPIRES: 10/31/2018 Estimated burden per response to comply with this mandatory collection request: 80 hours9.259259e-4 days <br />0.0222 hours <br />1.322751e-4 weeks <br />3.044e-5 months <br />.

Reported lessons learned are incorporated into the licensing process and fed back to industry.

Send comments regarding burden estimate to the FOIA, Privacy and Information Collections Branch (T-5 F53), U S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by e-mail to lnfocollects.Resource@nrc.gov, and to the Desk Officer, Office of Infomnation and Ftegulatory Affairs, NEOB-10202, (3150-0104), Office of Management and Budget, Washington, DC 20503, If a means used to impose an information collection does not display a currently valid 0MB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.

1. FACIUTYNAME Z DOCKETNUMBER a LER NUMBER YEAR SEQUENTIAL REV NUMBER NO.

2016 002

- 01 Palo Verde Nuclear Generating Station (PVNGS) Unit 3 05000-530 at a frequency of 60 Hz +!-1.2 Hz when operating under any load and is rated for 5500 kW continuous output and 6050 kW output for 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> out of 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />. Each DG unit has its own independent and redundant auxiliary support systems.

3. INITIAL PLANT CONDITIONS

On December 15, 2016, PVNGS Unit 3 was in Mode 1 (Power Operation) at 100 percent power, normal operating temperature, and normal operating pressure. There were no other structures, systems, or components out of service that contributed to this event.

4. EVENT DESCRIPTION

On December 15, 2016, the 3B DG experienced a significant mechanicai failure during the performance of a regularly scheduled monthly surveillance test. At 0356, the 3B DG was operating at approximately 2700 kW when a low lube oil pressure trip occurred. Operators responded to alarms and identified physical damage to the 3B DG based on oil and metal debris on the 3B DG room floor near the 9-right cylinder. The 3B DG trip functioned satisfactorily, and the DG shutdown immediately following the lube oil pressure trip without operator actions. The Unit 3 control room staff immediately declared the 3B DG inoperable and entered TS LCO 3.8.1, Condition B. The failure of the 3B DG resulted in the declaration of an alert emergency classification on December 15, 2016, at 0410 in accordance with Emergency Action Level HA2.1 based on an explosion resulting in visible damage to a safety system required for safe shutdown.

The alert was terminated on December 15, 2016, at 0636. The plant continued to operate at 100% power. There were no automatic or manual safety system responses initiated as a result of the failure. No other systems were impacted.

An investigation was initiated to determine the cause and corrective actions for the failure. As part of the investigation, a damage assessment was performed which identified the following engine internal components had evidence of mechanical overload, plastic deformation, or impact marks:

• Power assemblies #9 right (9R) and #9 left (9L) (includes pistons, cylinder liners, crankshaft counterweights, master and articulating rods, and associated rod bearings and bushings)

• Power assemblies #8 right (8R) and #8 left (8L) (includes pistons, cylinder liners, crankshaft counterweights, master and articulating rods, and associated rod bearings and bushings)

• Cylinder block and liner in the 9R location

• Centerframe in the 9R and 9L locations

• Crankcase floor under the #9 and #8 crankshaft throw locations

• Lube oil headers and hoses in the #9 and #8 crankshaft throw locations PVNGS initiated a comprehensive disassembly, repair, and reassembly process to restore the DG to manufacturer specifications. Due to the extensive nature of the repair effort, PVNGS submitted two emergency license amendment requests (LARs) to request additional time to allow for completion of the repairs and testing. The NRC staff approved the two LARs that granted one-time extensions of the 10-day LCO 3.8.1, Condition B required action completion time.

1. License Amendment 199 (Agencywide Documents Access and Management System (ADAMS) Accession Number ML16358A676), which extended the required action completion time to 21 days using a deterministic approach

2. License Amendment 200 (ADAMS Accession Number ML17004A020), which extended the required action completion time to 62 days using a risk-informed approach PVNGS has completed the comprehensive disassembly, repair, and reassembly process. The disassembly efforts included removal of the generator, flywheel, engine rotating parts (crankshaft, connecting rods, and pistons), main bearings, cylinder liners, centerframe, head assemblies, turbocharger, intercoolers, and attendant enginePage 3 of 6U.S. NUCLEAR REGULATORY COMMISSION (06-2016)

LICENSEE EVENT REPORT (LER)

CONTINUATION SHEET (See NUREG-1022, R.3 for instruction and guidance for completing this form httD7/www.nrc.aov/readina-im/doc-collections/nureas/staft/sr1022/r3/f APPROVED BY OMB: NO. 3150-0104 EXPIRES: 10/31/2018 Estimated burden per response to comply with this mandatory collection request: 80 hours9.259259e-4 days <br />0.0222 hours <br />1.322751e-4 weeks <br />3.044e-5 months <br />.

Reported lessons learned are incorporated into the licensing process and led back to industry.

Send comments regarding burden esbmate to the FOIA, Privacy and Information Collections Branch (T-5 F53), U.S. Nuclear Regulatory Commission, Washington, DC 20655-0001, or by e-mail to lnfocollects.Resource@nrc.gov, and to the Desk Officer, Office of Informabon and Regulatory Affairs, NEOB-10202, (3160-0104), Office of Management and Budget, Washington, DC 20503. If a means used to impose an information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collecbon.

1. FACIUTYNAME Z DOCKETNUMBER a LERNUMBER YEAR SEQUENTIAL REV NUMBER NO.

2016 002

- 01 Palo Verde Nuclear Generating Station (PVNGS) Unit 3 05000-530 main bore alignment checks. Repair activities included centerframe metal repairs, machining of some centerframe and block mating surfaces, a centerframe precision line bore, and a base check after line bore. Line boring is an engine machining process to establish alignment of the crankshaft main bearing bores. This re-established crankshaft alignment within the centerframe in accordance with manufacturer specifications. Reassembly activities included replacement or refurbishment of damaged parts including the crankshaft, all master and articulating rods, and bearings. Pistons and cylinder liners were replaced as necessary. Although not damaged, the generator was also refurbished.

The damage assessment activities included non-destructive examination of critical parts, visual inspections, parts recovery, and analysis. A review of past engine analysis data and predictive maintenance histories for all six PVNGS DGs has been performed along with a detailed review of the maintenance history for both Unit 3 DGs. An extensive internal and external operating experience review has also been performed. A metallurgical analysis was conducted to determine the direct cause of the #9 master connecting rod failure. Industry experts were enlisted to assess the condition of the engine bearings. Engineering finite element analyses were performed to generate a static and dynamic model of the engine and a flaw versus stress sensitivity analysis to aid in characterization of the failure. An engineering analysis was also performed to evaluate the vibrational data and enhance future vibration monitoring capabilities for the 3B DG.

A detailed retest plan, including post-maintenance and surveillance tests, was developed considering manufacturer recommendations, regulatory guidance, industry expertise, and operating experience. Testing was completed, and the 3B DG was declared operable on February 10, 2017.

5. ASSESSMENT OF SAFETY CONSEQUENCES

This event did not result in a challenge to the fission product barriers or result in the release of radioactive materials. The event did not result in a potential transient more severe than those analyzed in the Updated Final Safety Analysis Report.

This event did not result in any personnel injuries or any damage to other safety-related equipment.

The DG is designed to provide a redundant, standby source of AC power for safe plant shutdown in the event of loss of preferred power and for post-accident operation of ESF loads. The direct cause of the 3B DG failure was high cycle fatigue, which suggests that prior to the failure, the 3B DG was likely not capable of performing the specified safety function for the entire 7-day mission time. Although PVNGS does not have firm evidence of when the fatigue failure mechanism progressed to the point where the mission time couid not be satisfied, it is reasonable to assume that, on October 4, 2016, and September 7, 2016, the 3B DG was likely not capable of performing the specified safety function for the entire 7-day mission time when the 3A DG was inoperable for planned maintenance. Therefore, during time periods when 3A DG was inoperable, the degraded condition of 3B DG could have prevented the fulfillment of the safety function of a system needed to mitigate the consequences of an accident. These periods represent a safety system functional failure. The station blackout generators were available to provide an alternate source of AC power during the periods when both DGs were impacted.

During the repair process, PVNGS implemented significant compensatory measures in accordance with the two LARs to manage the risk associated with the 3B DG being unavailable.

Because 3B DG has been repaired and restored to operable status, there are no additional nuclear safety impacts.

6. CAUSE OF THE EVENT

The direct cause of this event was high cycle fatigue of the #9 master rod ligament. The root cause analysis determined the 3B DG had a misaligned crankshaft bore that resulted from a previous failure of the 3B DG that occurred in 1986.

The misalignment of the crankshaft bore resulted in sufficient cyclic stresses at the #9 master rod ligament to initiate andPage 4 of 6(0^2016)

U.S. NUCLEAR REGULATORY COMMISSION LICENSEE EVENT REPORT (LER)

CONTINUATION SHEET (See NUREG-1022, R.3 for instruction and guidance for compieting this form httDy/www.nrc.aov/readinQ-rm/doc-coiiections/nureQs/staff/sr1022/r3/)

APPROVED BY OMB; NO. 3150-0104 EXPIRES: 10/31/2018 Estimated txjrden per response to compiy with this mandatory collection request: 80 hours9.259259e-4 days <br />0.0222 hours <br />1.322751e-4 weeks <br />3.044e-5 months <br />.

Reported lessons learned are incorporated into the licensing process and fed back to industry.

Send comments regarding burden estimate to the FOIA, Privacy and Infonnation Collections Branch (T-5 F53), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by e-mail to lnfocollects.Resourcenrc.gov, and to the Desk Officer, Office of Infonnation and Regulatory Affairs, NEOB-10202, (3160-0104), Office of Management and Budget, Washington, DC 20503. If a means used to impose an information collection does not dsplay a cunently valid OMB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information coiiection.

1. FACIUTYNAME Z DOCKETNUMBER a LER NUMBER Palo Verde Nuclear Generating Station (PVNGS) Unit 3 05000-530 YEAH SEQUENTIAL NUMBER REV NO.

2016 002 propagate a fatigue crack. Refer to Attachment 1 for a figure of the master rod configuration and the location of the ligament crack. Evidence indicates the 3B DG crankshaft bore misalignment was due to the previous 1986 connecting rod failure and subsequent repair, which did not include a check of the crankshaft main bore alignment. The other five DGs at PVNGS have not had a connecting rod failure or any other mechanical event that could have introduced such misalignment.

Therefore, the failure mechanisms that caused the 1986 and 2016 3B DG failures are not present in the 3A DG or any other PVNGS DG. The 1986 event is discussed further in the previous occurrences section of this report.

7. CORRECTIVE ACTIONS

As an initial response, PVNGS rigorously pursued disassembly, inspection, and repair of the damaged 3B DG since initial failure on December 15, 2016. PVNGS established an outage control center to schedule, manage, and oversee the work activities needed for the repairs. Multi-discipline teams were formed to assess the extent of damage, inspect and recover parts, and determine the cause of failure.

To address the direct cause of the failure, the misalignment of the crankshaft bore has been corrected by precision line boring, which restored the crankshaft bearing alignment to within manufacturer specifications. All damaged equipment has been repaired or replaced. To ensure misalignment is appropriately addressed in the future, PVNGS has revised vendor documentation to ensure that main bore misalignment following a significant engine failure Is not verified solely through crankshaft web deflection measurements.

A detailed post-maintenance and surveillance test plan was performed prior to returning the 3B DG to service. The retest plan received input from industry experts and a third-party independent review. Upon successful completion of the retest plan, the 3B DG was declared operable on February 10, 2017.

As an additional corrective action, PVNGS will perform more frequent testing on DG master rods to ensure effective identification of fatigue cracks prior to failure. PVNGS will also perform master rod bearing clearance and master rod stud preload checks to provide a leading indication of conditions that could contribute to high cycle fatigue cracks.

8. PREVIOUS OCCURRENCES

In 1986, the 3B DG experienced a significant mechanical failure of the #9 master rod during pre-operational testing. A manufacturing process flaw was identified as the root cause of the PVNGS 1986 master rod failure. The articulated rod pin bore on the #9 master rod was initially oversized during manufacturer machining and repaired by the manufacturer using an iron-plating process. The electroplated iron was more brittle than the base material and was found dis-bonded in some locations during the root cause investigation. A fatigue crack originated near the center oil hole of the articulated rod pin bore and propagated through the ligament into the crank pin bore of the master connecting rod precipitating the master connecting rod failure. This high cycle fatigue failure occurred after approximately 100 hours0.00116 days <br />0.0278 hours <br />1.653439e-4 weeks <br />3.805e-5 months <br /> of engine runtime.

There was engine centerframe and block damage which was repaired in situ, and damaged parts were replaced, as necessary. However, the engine repairs did not include crankshaft main bore alignment checks.

As a corrective action and in addition to replacement of the failed #9 master rod, the 3B DG #2 master rod was also replaced during the engine repair as it had received an iron-plating repair. A 10 CFR Part 21 report was issued to the NRC documented under letter ANPP-40058, dated February 9,1987, for the manufacturer connecting rod iron-plating repair process. Subsequent inspection of the other five PVNGS DGs identified that the #9 master rod in the Unit 2 train A DG also had an Iron-plating repair, which was replaced in 1987. This issue of iron-plating repairs performed during connecting rod manufacturing was addressed for all PVNGS DGs and did not contribute to the 3B DG 2016 failure.Page 5 of 6(06-2016)

U.S. NUCLEAR REGULATORY COMMISSION LICENSEE EVENT REPORT (LER)

CONTINUATION SHEET (See NUREG-1022, R.3 for instruction and guidance for completing this form httDyA)vww.nrc.aov/readinQ-rm/doc-collections/nureQs/staff/sr1022/r3/l APPROVED BY 0MB: NO. 3150-0104 EXPIRES: 10/31/2018 Estimated burden per response to comply with this mandatory coilection request: 80 hours9.259259e-4 days <br />0.0222 hours <br />1.322751e-4 weeks <br />3.044e-5 months <br />.

Reported lessons learned are incorporated into the licensing process and fed back to industry.

Send comments regarding burden estimate to the FOIA, Privacy and Information Collections Branch (T-5 F53), U.S. Nuclear Regulatory (iimmission, Washington, DC 20555-0001, or by e-mail to lnfocollects.Resource@nrc.gov, and to the Desk Officer, Office of infomnation and Regulatory Affairs, NEOB-10202, (3150-0104), Office of Management and Budget, Washington, DC 20503. If a means used to impose an information colleotion does not display a currently valid 0MB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.

1. FACIUTYNAME Z DOCKETNUMBER a LERNUMBER Palo Verde Nuclear Generating Station (PVNGS) Unit 3 05000-530 YEAH SEQUENTIAL NUMBER REV NO.

2016 002 Figure of the Connecting Rod Configuration Ligament where crack originated

1. Piston Pin

2. Washer

3. Piston Pin Bolt

4. Articulatel Rod

5. Articulated Rod Pin Bolt

6. Washer

7. Dowel

8. Oil Passage

9. Articulated Rod Pin

10. Bushing Dowel Pin

11. Bushing

12. Dowel

13. Connecting Rod Cap

14. Locknut

15. Stud

16. Bearing Shell

17. Master Rod

18. Nut Tightening Sequence 6S-76APage 6 of 6