IR 05000414/2018040
| ML18143B537 | |
| Person / Time | |
|---|---|
| Site: | Catawba  |
| Issue date: | 05/23/2018 |
| From: | Frank Ehrhardt NRC/RGN-II/DRP/RPB1 |
| To: | Simril T Duke Energy Corp |
| References | |
| IR 2018040 | |
| Download: ML18143B537 (11) | |
Text
UNITED STATES NUCLEAR REGULATORY COMMISSION May 23, 2018
SUBJECT:
CATAWBA NUCLEAR STATION - NRC SUPPLEMENTAL INSPECTION REPORT 05000414/2018040 AND ASSESSMENT FOLLOW-UP LETTER
Dear Mr. Simril:
On May 10, 2018, the U.S. Nuclear Regulatory Commission (NRC) completed a supplemental inspection using Inspection Procedure (IP) 95001, Supplemental Inspection Response to Action Matrix Column 2 Inputs. The NRC inspection team discussed the results of this inspection and the implementation of your corrective actions with you and other members of your staff. The results of this inspection are documented in the enclosed report.
The NRC performed this inspection to review your stations actions in response to a White finding in the mitigating systems cornerstone which was documented and finalized in NRC Inspection Report 05000414/2017013 (ADAMS Accession No. ML17289A300). On April 6, 2018, your staff informed the NRC that your station was ready for the supplemental inspection.
The NRC determined that your staffs evaluation identified that the primary root causes of the White finding were: 1) the Portec voltage regulator design is resulting in bridge rectifier diode damage, 2) root cause C-05-1926 (Condition Report 01435421) did not apply adequate analysis techniques, and 3) less than adequate performance of operating experience (OE) evaluations.
The corrective actions to preclude repetition were to: 1) modify the emergency diesel generator (EDG) voltage regulator to address design weaknesses for all four Catawba Nuclear Station EDGs based on detailed simulation of the voltage regulator to prevent diode damage, 2)
implement a diode and silicon-controlled rectifier (SCR) replacement preventive maintenance (PM) activity at a frequency of no greater than 18 months, and 3) issue a procedure revision to AD-PI-ALL-0400, Operating Experience Program, that addressed crediting previously completed actions for OE insight, crediting future engineering changes, and reviewing historical performance trends to ensure PM strategy changes are identified. During this supplemental inspection, the inspectors determined that the licensee performed a comprehensive evaluation of the issue. The NRC inspectors did not identify any finding or violation of more than minor significance. After reviewing Catawba Nuclear Station, Unit 2, performance in addressing the White finding subject of IP 95001, Supplemental Inspection Response to Action Matrix Column 2 Inputs, the NRC concluded that your actions met the objectives of IP 95001. Therefore, in accordance with the guidance in Inspection Manual Chapter 0305, Operating Reactor Assessment Program, the White finding will only be considered in assessing plant performance for a total of four quarters. As a result, the NRC determined the performance at Catawba Nuclear Station, Unit 2, to be in the Licensee Response Column of the Reactor Oversight Process Action Matrix as of July 1, 2018.
This letter, its enclosure, and your response (if any) will be made available for public inspection and copying at http://www.nrc.gov/reading-rm/adams.html and at the NRC Public Document Room in accordance with 10 CFR 2.390, Public Inspections, Exemptions, Requests for Withholding.
Sincerely,
/RA/
Frank Ehrhardt, Chief Reactor Projects Branch 1 Division of Reactor Projects Docket No.: 50-414 License No.: NPF-52
Enclosure:
Inspection Report
Docket Number(s): 50-414 License Number(s): NPF-52 Report Number(s): 05000414/2018040 Enterprise Identifier: I-2018-040-0001 Licensee: Duke Energy Carolinas, LLC Facility: Catawba Nuclear Station, Unit 2 Location: York, SC 29745 Inspection Dates: May 7, 2018, through May 10, 2018 Inspectors: D. Hardage, Senior Resident Inspector (Sequoyah Nuclear Station)
M. Toth, Project Engineer Approved By: Frank Ehrhardt, Chief Reactor Projects Branch 1 Division of Reactor Projects Enclosure
SUMMARY
The NRC continued monitoring licensee performance by conducting a supplemental inspection at
Catawba Unit 2 in accordance with the Reactor Oversight Process. The Reactor Oversight Process is the NRCs program for overseeing the safe operation of commercial nuclear power reactors. Refer to http://www.nrc.gov/NRR/OVERSIGHT/ASSESS/index.html for more information.
List of Findings and Violations No findings were identified.
Additional Tracking Items Type Issue number Title Report Status Section NOV 05000414/2017011-01 Failure to adequately 95001 Closed establish and adjust preventive maintenance for emergency diesel generator excitation system diodes.
INSPECTION SCOPES
Inspections were conducted using the appropriate portions of the inspection procedures (IPs) in effect at the beginning of the inspection unless otherwise noted. Currently approved IPs with their attached revision histories are located on the public website at http://www.nrc.gov/reading-rm/doc-collections/insp-manual/inspection-procedure/index.html. Samples were declared complete when the IP requirements most appropriate to the inspection activity were met consistent with Inspection Manual Chapter (IMC) 2515, Light-Water Reactor Inspection Program - Operations Phase. The inspectors reviewed selected procedures and records, observed activities, and interviewed personnel to assess licensee performance and compliance with Commission rules and regulations, license conditions, site procedures, and standards.
DESCRIPTION OF THE ISSUE On April 11, 2017, during monthly surveillance testing of the 2A EDG, in accordance with PT/2/A/4350/002A, Diesel Generator 2A Operability Test, the EDG output breaker unexpectedly tripped open on an overcurrent relay actuation. The breaker opened approximately three minutes after reaching full load (5750 kW). The diesel was subsequently secured and declared inoperable. During troubleshooting, the licensee discovered that diode CR4 in the EDG excitation circuit shorted, causing the diesel output breaker to trip open on overcurrent. The 2A EDG was returned to service on April 14, 2017, following replacement of the excitation system diodes. Condition Report 2116069 was initiated to investigate the diode failure.
The licensee failed to develop PM strategies which considered OE for the EDG excitation system. Specifically, the licensee did not effectively incorporate OE documented in their corrective action program into the preventive maintenance activities for EDG excitation system diodes. As a result, a condition adverse to quality associated with the elevated diode temperatures was uncorrected. The NRC issued a White inspection finding in the mitigating systems cornerstone for this issue on October 16,
OTHER ACTIVITIES
- TEMPORARY INSTRUCTIONS, INFREQUENT AND ABNORMAL 95001 - Supplemental Inspection Response to Action Matrix Column 2 Inputs Inspectors reviewed the licensees root causes, contributing causes, extent of condition, and extent of cause determinations. Inspectors assessed whether the licenses corrective actions to address the root and contributing causes were sufficient to prevent recurrence. The highlights of the performance review and NRCs assessment are documented below:
- (1) Problem Identification: The finding involved a failure to adequately develop and adjust preventive maintenance activities in accordance with procedure AD-EG-ALL-1202, Preventive Maintenance and Surveillance Testing Administration, thus allowing a condition adverse to quality to remain uncorrected.
a) The issue was NRC-identified after inspectors reviewed the 2A EG output breaker trip that occurred on April 11, 2017, during monthly surveillance testing.
b) The licensees Root Cause Evaluation (RCE) 02116069 documented that there was an opportunity to identify the cause in 2005, however, root cause C-05-1926 (CR 01435421) did not apply adequate analysis techniques. Additionally, the RCE documented that the licensee missed opportunities to address the failure of the diode, by initiating diode replacement preventive maintenance activities or by completion of a voltage regulator engineering change (EC).
c) The NRC determined this issue was White, a finding of low to moderate safety significance, as documented in inspection report 05000414/2017013. In addition, RCE 02116069 documented the consequences of the issue, which included the following:
- Station entered a technical specification 72 hour8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> action statement
- 2A EDG accrued unplanned unavailability hours
- (2) Root Cause, Extent-of-Condition, and Extent-of-Cause Evaluation a) The licensee used the following investigative techniques to complete RCE 02116069:
- equipment reliability form
- fault tree analysis
- events and causal factors chart
- industry comparison
- hazard barrier target analysis
- support/refute matrix
- vendor failure analysis
- performance analysis
- safety culture evaluation The inspectors determined that the licensee evaluated the issue using systematic methodologies to identify root and contributing causes.
b) The licensees RCE included an event narrative, a description of involved equipment, equipment historical information, an OE review, and investigative techniques listed in the previous section. The licensees RCE documented the root causes of the White finding were:
- the Portec voltage regulator design is resulting in bridge rectifier diode damage
- root cause C-05-1926 did not apply adequate analysis techniques, and
- less than adequate performance of operating experience evaluations Based on the documented work performed for this root cause evaluation, the inspectors concluded that the root cause evaluation was conducted to a level of detail commensurate with the significance of the problem.
c) The licensees RCE included an evaluation of internal and external operating experience. The licensee also considered previous occurrences. Based upon the considerations described in the analysis, the inspectors concluded that the analysis appropriately considered prior occurrences of the issue and knowledge of prior operating experience.
d) The licensees RCE considered the extent of condition associated with the White finding.
The RCE documented the results of the same-similar methodology used in the evaluation, which included: 1) all six of the exciter bridge rectifier diodes for all four EDG control panels have been replaced (EOC-CA1), 2) a 40 year replacement PM was established for the 125 VDC auctioneering diode assemblies (EOC-CA2), and 3)procedure IP/0/B/4974/051, SSF Generator Inspection and Maintenance, has been revised to include reverse bias testing on voltage regulator diodes at rated voltage conditions (EOC-CA3). The inspectors concluded that the licensees RCE adequately addressed the extent of condition for the issue.
The licensees RCE considered the extent of cause associated with the White finding.
The licensee concluded several performance improvement areas were necessary, including a technical adequacy review of historical RCEs and previous OE evaluations for risk-significant component related Level 3 and Level 4 INPO Event Reports. The licensee also reviewed a statistically significant sample of OE items that showed design or PM weaknesses to determine if the concerns were properly addressed. Additionally, the licensee completed an assessment of Catawbas operating history for PRA risk-significant and MSPI system components to determine if any Catawba Nuclear Station component was an outlier compared to industry operating experience. Issues stemming from these reviews were entered into the corrective action program and assigned corrective actions. The inspectors concluded that the licensees RCE adequately addressed the extent of cause for the issue.
e) The licensee performed a safety culture analysis and associated the root causes with weaknesses in the following safety culture aspects: Design Margin (H.6), Conservative Bias (H.14), Evaluation (P.2), and Operating Experience (P.5). The inspectors determined that the RCE included an appropriate consideration of whether a weakness in any safety culture component was a root cause or significant contributing cause of the issue.
- (3) Corrective Actions a) The inspectors determined that appropriate corrective actions were specified for each root cause and contributing cause. The inspectors also determined that corrective actions were prioritized with consideration of significance and regulatory compliance.
The licensee has taken the following corrective actions to preclude repetition (CAPR): 1)implemented a diode and SCR replacement PM activity at a frequency of no greater than 18 months, and 2) issued a procedure revision to AD-PI-ALL-0400, Operating Experience Program, that addressed crediting previously completed actions for OE insight, crediting future engineering changes, and reviewing historical performance trends to ensure PM strategy changes are identified. The inspectors determined that the licensee specified appropriate CAPRs for each root cause.
b) The inspectors concluded that the corrective actions had been prioritized with consideration to risk significance and regulatory compliance. Inspectors also determined the licensee assigned appropriate performance improvement actions for the RCE extent of cause review.
c) The inspectors determined that the licensee adequately established a schedule for implementing and completing the corrective actions. The corrective actions that were associated with the root causes were completed in a timely manner. At the time of the inspection, only the voltage regulator EC implementation CAPR (RC1-CA1) was still open, and is scheduled for completion in May 2021. The inspectors noted the first new voltage regulator system is scheduled to be installed in 2A EDG during the fall outage of 2019. Subsequent installations for the remaining EDGs are scheduled afterward. As mentioned previously, until the new voltage regulator is installed, existing voltage regulator diode and SCR replacement will be performed at a frequency of no greater than 18 months.
d) As documented in RCE 02116069, the licensee had established measures for determining the effectiveness of assigned corrective actions. The effectiveness reviews are scheduled but had not been completed at the time of the inspection. The assigned actions include the following:
- perform diode testing and vendor destructive component analysis 18 and 72 months after completion of the voltage regulator design change and installation
- review a sample of completed OE evaluations since the issuance of the newly revised AD-PI-ALL-0400, Operating Experience Program, Rev. 7
- review the Plant Health Committee OE Oversight board governance activities The inspectors reviewed the effectiveness review plans and assigned management actions, and determined that appropriate quantitative or qualitative measures of success had been developed.
e) The inspectors determined that appropriate corrective actions were assigned by the licensees root cause. The NRC inspectors determined that NOV 05000414/2017011-01 related to this supplemental inspection has been adequately addressed in both corrective actions taken and planned.
- (4) Evaluation of IMC 0305 Criteria for Treatment of Old Design Issues The licensee did not request credit for self-identification of an old design issue; therefore, the risk-significant issue was not evaluated against the IMC 0305 criteria for treatment of an old design issue.
- (5) Assessment of licensees evaluation and corrective actions The inspectors determined that the licensee performed a comprehensive evaluation of the issue. The inspectors concluded that the licensees actions met all of the inspection objectives of IP 95001. Therefore, in accordance with the guidance in Inspection Manual Chapter 0305, Operating Reactor Assessment Program, the White finding will only be considered in assessing plant performance for a total of four quarters. As a result, the NRC determined the performance at Catawba Nuclear Station, Unit 2, to be in the Licensee Response Column of the Reactor Oversight Process Action Matrix as of July 1,
EXIT MEETINGS AND DEBRIEFS
No proprietary information was retained by the inspectors or documented in this report.
On May 10, 2018, the inspectors presented the supplemental inspection results to Mr. T. Simril, Site Vice President, and other members of the licensee staff.
Following the supplemental inspection exit meeting, Mr. F. Ehrhardt conducted a regulatory performance meeting with Mr. T. Simril and other members of the licensee staff.
DOCUMENTS REVIEWED
95001 - Supplemental Inspection Response to Action Matrix Column 2 Inputs
Condition Reports
Designation Description
2116069 Root Cause Evaluation for 2A EDG Overcurrent Trip
2183163 Common Mode failure evaluation
01463709 Assignment 31 RCE
C-06-8777 Root Cause Evaluation for Unit 1 Reactor Coolant Leakage
01569949 IER L4-12-82, Emergency Diesel Generator Leaks
2085136 IER L3-16-24, Emergency Diesel Generator Bearing Failure
2197218 Thermography WO task instructions
Condition Reports Generated as a Result of Inspection
Designation Description Date
204696 Potential closure issue w NCR 2116069 RC3CA3 5/8/18
204698 Potential imprv. in ST3825, Equipment WO Hi 5/8/18
204714 AD-EG-ALL-1207 PRR 5/8/18
204932 AD-EG-ALL-1207 PRR 5/9/18
Miscellaneous
Designation Description
WO Query Table of outstanding NCRs and WOs for EDG support
systems
RCE Closure RCE Closure Packages for RCE 02116069
Packages
Meeting Minutes OE Review Subcommittee Meeting Minutes for 3/6/18,
4/18/18, and 5/3/18.
Historical Spreadsheet for 1A, 1B, 2A, and 2B EDG diode temperatures
Thermography from 2005 - present
Data
Committee Charts Organization Charts for the PHC, PHS, and OE Review
Subcommittee
2183898 NCS 95001 Mock Inspection Assessment Report
2181758-06 Flex Cause Evaluation - OE Program Escalation
Miscellaneous
Designation Description
Diode Inspection Completed WOs for temperature dots inspections after EDG
run for 1B EDG (3/9/18) and 2A EDG (2/8/18)
NC State Final Review of Information and Discussion of EDG Excitation
Report to Duke System Diode CR4 Failure, September 12, 2017
Energy
DFR Solutions Power Diode Analysis for Catawba Nuclear Station 1A
Report Emergency Diesel Generator, May 26, 2017 (failure analysis)
DFR Solutions Power Diode and SCR Analysis for Catawba Nuclear Station
Report 2A Emergency Diesel Generator, May 16, 2017
Altran Report Evaluation of Diodes from 1B EDG, 17-0201-TR-000, June
2017, Rev. 0
MPR Report MPR Design Review of EDG Excitation System Diode
Failures, Recommended Actions to Resolve In-Service Diode
Failures, 2079-0047-RPT-001, Rev. 0
CNS Report 2A EDG Test Results for 6/14/17
CNS Report 1B EDG Test Results completed by the Root Cause
Evaluation Team during OP/1/A/6350/002, 6/8/17
Procedures
Designation Description Revision
AD-EG-ALL-1202 Preventive Maintenance and Surveillance Testing 6
Administration
AD-PI-ALL-0105 Effectiveness Reviews 1
AD-PI-ALL-0400 Operating Experience Program 6, 7
AD-EG-ALL-1207 Plant Health Process 5
AD-LS-ALL-0002 Regulatory Correspondence 5
AD-PI-ALL-0100 Corrective Action Program 16
AD-PI-ALL-0101 Root Cause Evaluation 5
AD-WC-ALL-0210 Work Request Initiation, Screening, Prioritization and 9
Classification
AD-EG-ALL-1211 System Performance Monitoring and Trending 6
Work Orders
Designation Description
246273 Inspect Voltage Regulator Diode temperature labels (1A EDG)
246272 Inspect Voltage Regulator Diode temperature labels (1B EDG)
246274 Inspect Voltage Regulator Diode temperature labels (2A EDG)
246277 Inspect Voltage Regulator Diode temperature labels (2B EDG)
243168-01 1 EQC VR A, Install Heat Sensitive Labels on Diodes
238765-01 1 EQC VR B, Replace diodes with old diodes
240512-02 2 EQC VR B, Install Heat Sensitive Labels
20092269-01 1 EQC VR A: D/G Voltage Reg Thermography (old revision)
01724280-01 2 EQC VR A: D/G Voltage Reg Thermography (new revision)