IR 05000373/2015010
| ML15308A566 | |
| Person / Time | |
|---|---|
| Site: | LaSalle  |
| Issue date: | 11/04/2015 |
| From: | O'Brien K Division of Reactor Safety III |
| To: | Bryan Hanson Exelon Generation Co, Exelon Nuclear |
| References | |
| EA-15-005 IR 2015010 | |
| Download: ML15308A566 (15) | |
Text
UNITED STATES mber 4, 2015
SUBJECT:
LASALLE COUNTY STATION, UNITS 1 AND 2 - UNRESOLVED ITEM CLOSURE INSPECTION REPORT 05000373/2015010; 05000374/2015010 AND EXERCISE OF ENFORCEMENT DISCRETION
Dear Mr. Hanson:
On September 29, 2015, the U.S. Nuclear Regulatory Commission (NRC) completed their review of Unresolved Item (URI)05000373/2013009-01; 05000374/2013009-01. The URI was issued because of open questions regarding whether the LaSalle switchyards met regulatory requirements. The enclosed inspection report documents the inspection results, which were discussed with Mr. H. Vinyard and other members of your staff on September 29, 2015.
The review examined activities conducted under your license as they relate to safety and compliance with the Commissions rules and regulations and with the conditions of your license.
The inspectors reviewed selected procedures and records, conducted field walkdowns, and interviewed personnel. To address the URI, inspectors reviewed the circumstances surrounding the dual-unit automatic reactor scram and loss of offsite power that occurred on April 17, 2013.
The loss of offsite power occurred when the breakers in the 345-kilovolt switchyard opened shortly following a lightning strike in the adjacent 138-kilovolt switchyard.
Based on the results of the review, the NRC has determined that one self-revealed Severity Level III violation of NRC requirements occurred. The violation was assessed through the traditional enforcement process in accordance with the NRC Enforcement Policy. The current Enforcement Policy is included on the NRC's Web site at http://www.nrc.gov/about-nrc/regulatory/enforcement /enforce-pol.html. The violation involves Exelons failure to meet Title 10 of the Code of Federal Regulations (10 CFR) Part 50, Appendix A, Criterion 17, Electric Power Systems, requirements. Specifically, Exelon failed to properly construct and install the 138 kV switchyard grounding system and the supporting infrastructure of the switchyard to provide an offsite power source that permitted the functioning of structures, systems, and components important to safety. The NRC determined that this violation resulted from matters not reasonably within the licensees control; that is, the failure to meet the requirements could not be readily identified and addressed. Therefore, in accordance with the Enforcement Policy, and after consultation with the Director of the Office of Enforcement, the NRC has decided to exercise enforcement discretion in accordance with Section 3.5 of the NRC Enforcement Policy and to refrain from issuing enforcement action for the violation. In accordance with the NRCs Reactor Oversight Process, this condition will not be considered in the assessment process or the NRCs Action Matrix.
If you contest this violation, you should provide a response within 30 days of the date of this inspection report, with the basis for your denial to the U.S. Nuclear Regulatory Commission, ATTN: Document Control Desk, Washington DC 20555-0001; with copies to the Regional Administrator, Region III; the Director, Office of Enforcement, U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001; and the NRC Resident Inspector at LaSalle County Station.
In accordance with Title 10 of the Code of Federal Regulations (10 CFR) 2.390, Public Inspections, Exemptions, Requests for Withholding, of the NRC's "Rules of Practice," a copy of this letter, its enclosure, and your response (if any) will be available electronically for public inspection in the NRCs Public Document Room or from the Publicly Available Records (PARS)
component of the NRC's Agencywide Documents Access and Management System (ADAMS).
ADAMS is accessible from the NRC Web site at http://www.nrc.gov/reading-rm/adams.html (the Public Electronic Reading Room).
Sincerely,
/RA/
Kenneth G. OBrien, Director Division of Reactor Safety Docket Nos. 50-373; 50-374 License Nos. NPF-11; NPF-18
Enclosure:
Inspection Report 05000373/2015010; 05000374/2015010
REGION III==
Docket Nos: 05000373; 05000374 License Nos: NPF-11; NPF-18 Report No: 05000373/2015010; 05000374/2015010 Licensee: Exelon Generation Company, LLC Facility: LaSalle County Station, Units 1 and 2 Location: Marseilles, IL Dates: June 3, 2013 - September 29, 2015 Inspectors: I. Hafeez, Reactor Inspector M. Jeffers, Reactor Inspector D. Szwarc, Senior Reactor Inspector, Lead Approved by: R. Daley, Chief Engineering Branch 3 Division of Reactor Safety Enclosure
SUMMARY
Inspection Report (IR) 05000373/2015010, 05000374/2015010; 06/03/2013-09/29/2015;
LaSalle County Station, Units 1 and 2; Unresolved Item Closure Inspection.
This report covers offsite inspection activities to resolve URI 05000373/2013009-01 and 05000374/2013009-01. The inspection was conducted by Region III inspectors. The inspectors documented one self-revealing, Severity Level III violation through the traditional enforcement process in accordance with the U.S. Nuclear Regulatory Commissions (NRCs) Enforcement Policy. All violations of NRC requirements are dispositioned in accordance with the NRCs Enforcement Policy dated February 4, 2015. The NRCs program for overseeing the safe operation of commercial nuclear power reactors is described in NUREG-1649, Reactor Oversight Process, Revision 5, dated February 2014.
Cornerstone: Initiating Events
- Severity Level (SL)-III Violation (Enforcement Discretion): A SL-III violation of Title 10 of the Code of Federal Regulations (10 CFR) Part 50, Appendix A, Criterion 17, Electric Power Systems, was self-revealed on April 17, 2013, when a lightning strike and corresponding C phase fault on 138kV line 0112 occurred in the 138kV switchyard and caused a dual unit loss of offsite power (LOOP). Specifically, the lightning strike and corresponding phase to ground fault caused flashovers due to improperly installed ground segments in the 138kV switchyard grounding system installation. The licensee performed a Root Cause Investigation under report number 1503409-04, and identified several deficiencies in the quality of construction of the 138kV switchyard grounding system that allowed a lightning induced fault to flash over onto the DC protective system.
The degradation was due to inadequate workmanship during initial installation of the 138kV ground system in the 138kV switchyard.
In accordance with Inspection Manual Chapter 0612, Power Reactor Inspection Reports, Appendix B, Issue Screening, the inspectors determined that this issue did not meet the definition of a performance deficiency since it was not reasonably within the licensees ability to foresee and correct. However, this issue was a violation of 10 CFR 50, Appendix A, Criterion 17, Electric Power Systems. Therefore, the traditional enforcement process was used in accordance with the NRC Enforcement Policy. The violation was similar to one example in the Enforcement Policy under SL-III violations, Section 6.1(c) (5), Equipment failures caused by inadequate or improper maintenance substantially complicate recovery from a plant transient. Although the improper grounding system was a result of improper installation rather than improper maintenance, the inspectors determined that the violation met the intent of the example.
The NRC determined that this violation resulted from matters not reasonably within the licensees control; that is, the failure to meet the requirements could not be readily identified and addressed. Therefore, in accordance with the Enforcement Policy, and after consultation with the Director of the Office of Enforcement, the NRC has decided to exercise enforcement discretion in accordance with Section 3.5 of the NRC Enforcement Policy and to refrain from issuing enforcement action for the violation. In accordance with the NRCs Reactor Oversight Process, this condition will not be considered in the assessment process or the NRCs Action Matrix. (Section 4OA3)
REPORT DETAILS
OTHER ACTIVITIES
4OA3 Follow-Up of Events and Notices of Enforcement Discretion
(Closed) URI 05000373/2013009-01; 05000374/2013009-01: Review of the Loss of Offsite Power Event Root Cause Evaluation and Switchyard Design Basis
a. Inspection Scope
The inspectors reviewed the licensees preliminary assessment of the cause of the dual-unit loss of offsite power (LOOP) that resulted in the dual-unit reactor scrams at the LaSalle County Station. The inspectors also reviewed the design and licensing bases of the switchyard as described in the Updated Final Safety Analysis Report and interviewed members of the licensees staff.
b. Findings
Introduction:
A Severity Level (SL)-III violation of Title 10 of the Code of Federal Regulations (10 CFR) Part 50, Appendix A, Criterion 17, Electric Power Systems, was self-revealed on April 17, 2013, when a lightning strike and corresponding C phase fault on 138 kilovolt (kV) line 0112 occurred in the 138kV switchyard and caused a dual unit loss of offsite power (LOOP). Specifically, the lightning strike and corresponding phase to ground fault caused flashovers due to improperly installed ground segments in the 138kV switchyard grounding system installation.
Description:
LaSalle is interconnected to the electrical grid via four 345kV transmission lines by way of two separate rights-of-way (i.e., two lines from Braidwood Station and two lines from Plano substation). The function of the offsite power system is to provide sufficient capacity and capability to permit the function of structures, systems, and components important to safety. The 345kV offsite power system is required to be capable of providing adequate voltages to safety-related equipment throughout the anticipated range of voltage variations.
The control power for the 345kV switchyard breakers is supplied by a physically independent 125 Volts Direct Current (VDC) system (nonsafety-related) consisting of two physically separated 125VDC batteries, battery chargers, and distribution systems and is designed to ensure that the loss of either battery will not cause the loss of offsite power sources. Two protective relay systems are used on each transmission line and two trip coils (each supplied by the separate DC systems) are used on each 345kV Oil Circuit Breaker (OCB) to ensure tripping of faulted equipment.
The 345kV switchyard is also connected to the 138kV transmission system at LaSalle through a 345/138kV transformer and shares the 125VDC system for control power.
The 138kV switchyard was originally installed as a temporary source of offsite power during initial construction of LaSalle Unit 1 and Unit2. After the 345kV transmission lines were placed in service, the 138kV transmission system at LaSalle remained connected to the 345kV transmission system through a 345/138kV transformer (TR-81). Because the LaSalle design bases, as described in the Updated Final Safety Analysis Report (UFSAR), still described the 138kV switchyard as an interim offsite source prior to initial plant startup, the licensee performed UFSAR Change # LU2000-035 on February 8, 2001, to document making the 138kV switchyard permanent.
On April 17, 2013, a lightning strike and corresponding C phase fault on 138kV Line 0112 occurred in the LaSalle 138kV switchyard. The fault caused a flashover in the Transformer 81 (TR81) 138kV OCB control cabinet, which affected the DC System and resulted in the unexpected operation of all of the 345kV switchyard circuit breakers.
The 345kV breaker operations resulted in an automatic reactor shutdown of LaSalle Units 1 and 2 and a dual unit LOOP resulting in the stations five emergency diesel generators (EDGs) starting and successfully loading onto their respective safety-related buses. The NRC performed a special inspection as a result of this event and evaluated and documented the plants response in LaSalle County Station, Units 1 and 2 - NRC Special Inspection Team Inspection Report 05000373/2013009; 05000374/2013009.
When the fault occurred in the 138kV switchyard, the energy should have been adequately dispersed via the ground system. Two 400 MCM (400,000 circular mils) lead covered copper wires connect the 138kV grounding system to the 345kV grounding system allowing a fault in the 138kV yard to propagate toward the 345kV switchyard equalizing the potential across the two ground systems. However, due to multiple connection failures in the 138kV ground system installation and ground cable-to-rod connections that were never made (i.e., not installed per design-no exothermic weld made) with the compromised ground segments, the energy did not have a low resistance ground path resulting in an unexpected excessive ground potential rise (GPR)at the TR81 OCB control cabinet. This excessive GPR caused a several thousand volt difference between the grounds in the 138kV TR81OCB control cabinet and 345kV relay control house grounding system. The fault caused the insulation/dielectric to be compromised on the System 2 DC fuse block at the TR81 138kV OCB control cabinet.
This resulted in a flashover thru the System 2 DC fuse block in the TR 81 OCB control cabinet. The GPR effect was propagated (via control cables) from the 138kV switchyard ground system to the 345kV relay control house ground system. The GPR had the effect of causing an actuation of switchyard protective relay internal components, which resulted in the unexpected operation of all of the 345kV switchyard circuit breakers.
The licensee determined in Root Cause Investigation Report 1503409-04 that the 138kV switchyard installation was originally intended as a temporary installation external to the primary plant switchyard, with it not servicing any critical plant functions. The report identified several deficiencies in the quality of its installation/construction of the 138kV switchyard grounding system that allowed a lightning induced fault to flash over onto the DC protective system. The degradation was due to inadequate workmanship during initial installation of the 138kV ground system in the 138kV switchyard. This consisted of a combination of poor exothermic welding and connections that were never made.
Another contributor to the event was also identified as being inadequate lightning shielding of the 138kV switchyard.
The inspectors determined that the nuclear plant licensee had no requirements or standards governing the construction of electrical switchyards. Therefore, there was no requirement for the licensee to verify the construction quality of the ground system during original construction.
As a result of the event, the licensee made an Emergency Notification System notification and issued a Licensee Event Report to report the event. As immediate corrective actions, the licensee inspected and tested the relay house, replaced damaged protective relaying components, and quarantined damaged components for forensics.
The licensee also separated the 138kV and 345kV protective relaying DC System 2 batteries to reduce the probability of fault propagation from the 138kV to 345kV protective systems. The licensee performed ground system testing of the 138kV grounding and identified several deficiencies that were verified by excavation. All ground system weld joints identified to be degraded in the 138kV switchyard were excavated and replaced. Additionally, the licensee installed a separate battery charger and battery for the power supply for the 138kV switchyard control power, installed lightning protection (static line) for the 138kV switchyard, and tested the 345kV ground grid integrity and repaired material condition issues with ground grid connections.
Analysis:
In accordance with Inspection Manual Chapter (IMC) 0612, Power Reactor Inspection Reports, Appendix B, Issue Screening, the inspectors determined that this issue did not meet the definition of a performance deficiency since it was not reasonably within the licensees ability to foresee and correct. However, this issue was a violation of 10 CFR 50, Appendix A, Criterion 17, Electric Power Systems, and, therefore, the traditional enforcement process was used in accordance with the NRC Enforcement Policy. Since this violation did not include a performance deficiency, IMC 0612, Appendix B, defers to the Enforcement Policy for disposition, including the use of Enforcement Discretion, if warranted.
The inspectors used Section 6.1 of the Enforcement Policy to associate example violations that best captured the severity of the violation. The inspectors identified one example under SL-III violations, Section 6.1(c) (5), Equipment failures caused by inadequate or improper maintenance substantially complicate recovery from a plant transient. Although the improper grounding system was a result of improper installation rather than improper maintenance, the inspectors determined that the violation met the intent of the example. Therefore, the inspectors concluded that the violation met the criteria for a SL-III violation. In accordance with the Enforcement Policy, the inspectors did not screen the issue using the significance determination process because they did not identify a performance deficiency with this violation.
The inspectors did not assign a cross-cutting aspect to this issue in accordance with Section 07.04 of IMC 0612 because it was a traditional enforcement violation without a performance deficiency.
Section 3.5 of the Enforcement Policy provided guidance to determine if enforcement discretion was appropriate. Although the installation/construction errors were not discovered as a result of a voluntary initiative, the NRC determined that the issue was related to the original installation/construction. The construction flaws were of a subtle nature, such as ground cable-to-rod connections that were never made (i.e., not installed per design), that only became apparent when a lightning strike occurred to a component of the 138kV electrical system in the switchyard that resulted in the opening of all breakers in the 345kV electrical system ring bus and the loss of offsite power to both LaSalle units. The NRC also determined that the issue was corrected within a reasonable time period and that it was an issue that was unlikely to be identified during routine surveillances or routine quality assurance activities, since installation deficiencies of the ground system were due to poor workmanship during original construction.
Finally, while the violation resulted from matters not reasonably within the licensees control, the failure to meet the requirements could not be readily identified and addressed by the licensee. Specifically, the licensee reasonably expected the 138kV switchyard ground grid connection to have been adequately made during original construction because it had been in use since and did not demonstrate any deficiencies.
Therefore, in accordance with the Enforcement Policy Section 3.5, the NRC has elected to apply and exercise enforcement discretion to not issue a violation and/or civil penalty.
Enforcement:
Title10 CFR Part 50, Appendix A, Criterion 17, Electric Power Systems, requires, in part, that an onsite electric power system and an offsite electric power system shall be provided to permit functioning of structures, systems, and components important to safety.
Contrary to the above, from initial construction until April 17, 2013, the licensee failed to properly construct and install the 138kV switchyard grounding system and the supporting infrastructure of the switchyard to provide an offsite power source that permitted the functioning of structures, systems, and components important to safety. Specifically, the licensee failed to ensure the quality of its installation/construction that when the fault occurred the energy should have been adequately dispersed via the grounding system with no impact to the sites offsite electric power supply. On April 17, 2013, a lightning strike to a component of the 138-kV electrical system in the switchyard resulted in the opening of all breakers in the 345-kV electrical system ring bus and a LOOP to both LaSalle units. This ultimately resulted in a dual unit loss of offsite power which prevented the functioning of components important to safety (e.g., loss of condenser, loss of feedwater).
The NRC determined that this violation resulted from matters not reasonably within the licensees control; that is, the failure to meet the requirements could not be readily identified and addressed. Therefore, in accordance with the Enforcement Policy, and after consultation with the Director of the Office of Enforcement, the NRC has decided to exercise enforcement discretion in accordance with Section 3.5 of the NRC Enforcement Policy and to refrain from issuing enforcement action for the violation. In accordance with the NRCs Reactor Oversight Process, this condition will not be considered in the assessment process or the NRCs Action Matrix.
4OA6 Management Meetings, Including Exit
On September 29, 2015, the inspectors presented the inspection results to Mr. H. Vinyard and other members of the licensees staff. The licensee acknowledged the issues presented. The inspectors confirmed that none of the potential report input discussed was considered proprietary.
ATTACHMENT:
SUPPLEMENTAL INFORMATION
KEY POINTS OF CONTACT
Licensee Personnel
- L. Blunk, Regulatory Assurance
- J. Kowalski, Engineering Manager
- P. Patel, Plant Engineering
- H. Vinyard, Plant Manager
U.S. Nuclear Regulatory Commission Personnel
- R. Daley, Chief, Division of Reactor Safety, Engineering Branch 3
- M. Kunowski, Chief, Division of Reactor Projects, Branch 5
- J. Robbins, Resident Inspector, LaSalle County Station
- R. Ruiz, Senior Resident Inspector, LaSalle County Station
LIST OF ITEMS
OPENED, CLOSED, DISCUSSED
Closed
- 05000373/2013009-01 URI Review of the Loss of Offsite Power Event Root Cause
- 05000374/2013009-01 Evaluation and Switchyard Design Basis (Section 4OA3)