IR 05000456/2019011
| ML19353B470 | |
| Person / Time | |
|---|---|
| Site: | Braidwood  |
| Issue date: | 12/19/2019 |
| From: | Robert Daley Engineering Branch 3 |
| To: | Bryan Hanson Exelon Generation Co, Exelon Nuclear |
| References | |
| IR 2019011 | |
| Download: ML19353B470 (10) | |
Text
December 19, 2019 Mr. Bryan Senior VP, Exelon Generation Company, LLC President and CNO, Exelon Nuclear Exelon Generation Company, LLC 4300 Winfield Road Warrenville, IL 60555 SUBJECT: BRAIDWOOD STATION UNITS 1 AND 2 - NRC INSPECTION OF TEMPORARY INSTRUCTION 2515/194, INSPECTION OF THE LICENSEE'S IMPLEMENTATION OF INDUSTRY INITIATIVE ASSOCIATED WITH THE OPEN PHASE CONDITION DESIGN VULNERABILITIES IN ELECTRIC POWER SYSTEMS (NRC BULLETIN 2012-01) REPORT 05000456/2019011 AND 05000457/2019011
Dear Mr. Hanson:
On November 22, 2019, the U.S. Nuclear Regulatory Commission (NRC) completed an inspection at Braidwood Station, Units 1 and 2 and discussed the results of this inspection with John Keenan and other members of your staff. The results of this inspection are documented in the enclosed report.
No findings or violations of more than minor significance were identified during this inspection.
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 Title 10 of the Code of Federal Regulations 2.390, Public Inspections, Exemptions, Requests for Withholding.
Sincerely,
/RA/
Robert C. Daley, Chief Engineering Branch 3 Division of Reactor Safety Docket Nos. 05000456 and 05000457 License Nos. NPF-72 and NPF-77
Enclosure:
As stated
Inspection Report
Docket Numbers: 05000456 and 05000457 License Numbers: NPF-72 and NPF-77 Report Numbers: 05000456/2019011 and 05000457/2019011 Enterprise Identifier: I-2019-011-0049 Licensee: Exelon Generation Company, LLC Facility: Braidwood Station Units 1 and 2 Location: Braceville, IL Inspection Dates: November 18, 2019 to November 22, 2019 Inspector: I. Hafeez, Reactor Inspector Approved By: Robert C. Daley, Chief Engineering Branch 3 Division of Reactor Safety Enclosure
SUMMARY
The U.S. Nuclear Regulatory Commission (NRC) continued monitoring the licensees performance by conducting a NRC Inspection of Temporary Instruction 2515/194, Inspection of the Licensee's Implementation of Industry Initiative Associated with the Open Phase Condition Design Vulnerabilities in Electric Power Systems (NRC Bulletin 2012-01) at Braidwood Station Units 1 and 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 https://www.nrc.gov/reactors/operating/oversight.html for more information.
List of Findings and Violations No findings or violations of more than minor significance were identified.
Additional Tracking Items None.
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 inspector 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.
OTHER ACTIVITIES
- TEMPORARY INSTRUCTIONS, INFREQUENT AND ABNORMAL 2515/194 - Inspection of the Licensees Implementation of Industry Initiative Associated With the Open Phase Condition Design Vulnerabilities In Electric Power Systems (NRC Bulletin 2012-01)
The inspector reviewed the licensees implementation of the Nuclear Energy Institute Voluntary Industry Initiative, (ADAMS Accession No. ML15075A454) dated March 16, 2015.
The objective of Temporary Instruction 2515/194 is to verify that licensees have appropriately implemented the Nuclear Energy Institute voluntary industry initiative (ADAMS Accession No. ML15075A454), dated March 16, 2015, including updating their licensing basis to reflect the need to protect against open phase conditions (OPCs). The inspector discussed the impacts of OPCs on the licensees electrical system design, the ability to detect and alarm OPCs on station transformers, and ongoing implementation of training and updates to operating procedures with plant staff. The inspector reviewed licensee and vendor documentation, and performed system walkdowns to verify that the installed equipment was supported by the design documentation. The inspector verified that the licensee had completed the installation and testing of equipment (with the exception of the tripping functions), installed and tested alarming circuits both locally and in the control room, and analyzed potential impacts associated with the design implementation on the current licensing basis. The inspector also reviewed licensee analysis and calculations, and performed distribution system equipment walkdowns.
The inspector performed Section 03.01 of the Temporary Instruction in order to determination whether the licensee appropriately implemented the voluntary industry initiative, dated March 6, 2015 (ADAMS Accession No. ML15075A454). This included reviewing how the licensee updated their licensing basis to reflect the need to protect against open phase conditions.
Inspection of the Licensees Implementation of Industry Initiative Associated With the Open Phase Condition Design Vulnerabilities In Electric Power Systems (NRC Bulletin 2012-01)
(1 Sample)
- (1) The Braidwood Station selected Schweitzer Engineering Laboratories (SEL) 451-5 microprocessor based relays for the open phase detection system. The relay schemes monitor and compare the positive, negative and zero sequence current input from existing Current Transformers on the high side of System Auxiliary Transformers (SATs) 142-1, 142-2, 242-1 and 242-2 to detect loss of phase or low load conditions. The relay algorithm/scheme and associated setpoint calculations were developed by the licensee to detect the loss of phase on the preferred offsite source for the engineered safety feature buses and initiate actions to separate that source from the onsite distribution system. The relay schemes also used a time delay to ride out a short duration transient but allow sufficient time to detect a valid phase failure condition. The licensee completed the monitoring mode of operation of open phase system and enabled the tripping function for full implementation in December
INSPECTION RESULTS
Observation: Detection, Alarms, and General Criteria 2515/194
- (1) The inspector determined by walkdowns and observation that open phase conditions will be detected and alarmed in the Main Control Room (MCR).
- (2) See Item 2 in table titled Detection, Alarms, and General Criteria Exceptions for inspector identified exceptions.
- (3) The licensees design document, test results and analysis showed that the short time delay (a time delay of 0.5 seconds was selected for the OPC relays to coordinate with the fault clearing time of 345kV switchyard primary and zone 2 relays and the downstream RCP Bus Undervoltage reactor trip) used in the open phase condition design/protective scheme is expected to minimize misoperation or spurious trips in the range of voltage unbalances normally expected in the transmission system. The analysis also showed that the time delay may properly coordinated with switchyard fault assumptions. Based on this, the inspector had reasonable assurance that the actuation circuit design would not result in lower overall plant operation reliability. Additionally, the open phase condition scheme was activated or placed in-service in December of 2015. Since that time, there have not been any inadvertent actuations of this system that resulted in a trip signal or spurious actions.
- (4) No Class-1E circuits were replaced with non-Class 1E circuits in the design.
- (5) See Item 5 in table titled Detection, Alarms, and General Criteria Exceptions for inspector identified exceptions.
Observation: Protective Actions Criteria 2515/194
- (1) The Braidwood Station has determined that OPCs are credible events and have implemented design changes to mitigate the effects. The EC 390213 and EC 390214 have installed an open phase relay scheme to detect, alarm and protect from open phase conditions.
- (2) The inspector determined that with an open phase condition present and no accident condition signal, the OPC protection relay system would not adversely affect the function of important-to-safety systems, structures and components when the trip function is active.
As per the design description, the OPC relays will trip the System Auxiliary Transformer (SAT) lockout relays after a 0.5 second time delay. The SAT lockout relays would isolate the SAT by opening both primary and secondary side breakers.
After the SAT isolates, this will result in the bus loss of voltage relays dropping out and transferring the safety related busses to their respective emergency diesel generators. The licensees analysis verified that the OPC relays can detect and isolate an OPC prior to any motor damage. The algorithm time delay limits the motors exposure to negative sequence current which helps prevent excessive motor heating.
See Item 2 in table titled Protective Actions Criteria Exceptions for inspector identified exceptions.
- (3) See Item 3 in table titled Protective Actions Criteria Exceptions for inspector identified exceptions.
- (4) No surveillance requirements for the SEL 451-5 were added to the plant Technical Specifications.
See Item 4 in table titled Protective Actions Criteria Exceptions for inspector identified exceptions.
Observation: Detection, Alarms, and General Criteria Exceptions 2515/194
- (2) Based on review of the licensees calculation for the relay settings used in the Open Phase Condition (OPC) algorithms, the inspector determined that the OPC relay detection does not function under all loading conditions. The design is sensitive enough to identify an OPC when SAT transformer loading is above the MINLOAD threshold. To insure detection of an OPC, the design/implementation of OPC detection at Braidwood Station has a minimum loading requirement for the SAT transformers. Specifically, an OPC will be detected as long as the primary positive sequence current in the SAT is greater than the MINLOAD (low load) alarm setting (approximately 1.4MVA (BRW-12-0159E, Rev. 0)). During normal operations, the SATs are routinely loaded above the MINLOAD threshold. At other times, e.g.
refueling or maintenance outages, SAT loading may not be above the MINLOAD setpoint.
Also, the OPC relay trips are routinely disabled during SAT isolation and restoration. Guidance to operations staff regarding expected alarms, during open phase conditions were identified in alarm response procedures The procedures indicate that alarms associated with the open phase condition would be expected during SAT isolation and restoration activities. The guidance did not explicitly address the potential for an actual open phase condition to exist during SAT isolation and restoration activities. The inspector discussed this issue with the licensee and they captured this issue in Condition Record AR04299258, NRC Open Phase INSP - Identified OPS Proc Enhancement.
- (5) Licensee revised Braidwood Station Updated Final Safety Analysis Report (UFSAR),
Section 8.3.1.1.2.1, Offsite Power Sources (SATs) was revised to add SATs feed breakers Automatic trips will occur on a bus undervoltage load shed condition, a SAT fault, a bus fault condition, or upon a loss of phase on the feed to the SAT.
The change was incorporated into UFSAR, Revision 16. The revision did not discuss the design features and analysis in detail. However, the licensee concluded that the level of detail provided for the open phase condition protection was consistent with the level of detail provided for the other conditions that could trip the SAT feed breakers to the engineered safety feature buses. After discussions with the inspector, the licensee generated Condition Record AR04299289 to evaluate additional updates to the UFSAR to include the design features and analyses related to the effects of ability to detect open phase conditions on the high side of the main transformers.
Observation: Protective Actions Criteria Exceptions 2515/194
- (2) During low loading of the SAT or open phase detection (OPD) relay trouble alarms, manual actions may be required to address the existence of an OPC condition.
The inspector discussed the potential need for manual actions with the licensee and the licensee agreed that the current procedures did not specifically address implementation of protective actions if manual actions were required. The lack of guidance for system response when manual actions are needed, and weaknesses identified in alarm response procedures was captured in AR 04299258, NRC Open Phase Insp-Identified Procedure Enhancement.
- (3) The following information was aggregated from engineering analyses, training materials and conversations with licensee staff as a detailed description of the system operation and performance was not located within the UFSAR.
The following description presumes that the SAT transformer is loaded above the low load alarm point. For the case where an OPC occurs and an accident condition (LOCA) signal are present simultaneously, the accident signal causes the diesel generators to start. Additionally, the accident signal will start the Engineered Safety Feature (ESF) loads. The fist start attempt will place the ESF loads onto the transformer with the missing phase. The ESF load start attempt is initiated because the OPD to SAT lockout actuation takes 0.65 seconds to execute. The SAT lockout relays would isolate the SAT by opening both primary and secondary side breakers. After the SAT isolates, with an accident signal present, the analysis showed the safety-related undervoltage relaying scheme would separate the engineered safety feature busses from the SAT. Subsequently, the Emergency Diesel Generator (EDG) associated with each ESF bus would automatically connect to the ESF bus and allow the ESF loads to be powered from the EDG.
- (4) At the time of this inspection, the licensee had established a functional test schedule which includes testing the relay metering function and verifying relay settings against calculated values. The licensee had not established a periodic setpoint calibrations testing schedule to verify relay performance is within tolerances assumed within supporting analyses. These activities were captured in Condition Record AR04299358 to identify Fleet Procedure Enhancements related to testing relay setpoints.
EXIT MEETINGS AND DEBRIEFS
The inspector verified no proprietary information was retained or documented in this report.
- On November 22, 2019, the inspector presented the NRC Inspection of Temporary Instruction 2515/194, Inspection of the Licensee's Implementation of Industry Initiative Associated with the Open Phase Condition Design Vulnerabilities in Electric Power Systems (NRC Bulletin 2012-01) results to John Keenan and other members of the licensee staff.
DOCUMENTS REVIEWED
Inspection Type Designation Description or Title Revision or
Procedure Date
2515/194 Calculations BRW-12-0159E Unit 1 and Unit 2 Loss of Phase Detection Relay Settings 02
BRW-12-0267E Loss of Phase Detection EMTP Analysis 00
BRW-13-0107E Open Phase Detection LOCA Analysis 01
EC 390213 U1-SAT Loss of Phase Detection Scheme Phase Unbalance 02
Relay Installation
EC 390214 U2-SAT Loss of Phase Detection Scheme Phase Unbalance 02
Relay Installation
EC 392220 Potential Design Vulnerability in Switchyard Single Open 02
Phase Detection
Corrective Action AR 01333607 U1 LOOP 04/14/2012
Documents AR 01333629 Unit 1 Stats De- Energized Due to a Phase Opening/Shorting 04/27/2012
Corrective Action AR 04299258 NRC Open Phase Insp - Identified OPS Proc Enhancements 11/22/2019
Documents AR 04299289 2019 NRC Open Phase Inspection - UFSAR Update 11/22/2019
Resulting from AR 04299358 NRC Open Phase Insp - Fleet Procedure Enhancement 11/22/2019
Inspection
Drawings 20E-1-4001A Station One Line Diagram T
20E-1-4002B Single Line Diagram System Auxiliary Transformer And L
6.9KV Switchgear
20E-1-4016C Relaying & Metering Diagram System Auxiliary Transformers L
2-1 & 142-2
20E-1- Schematic Diagram Annunciator Window Engraving 1UL- P
4030AN002 AN023 & 1UL-AN024 AT 1PM01J
20E-1-4030AP01 Schematic Diagram System Auxiliary Transformer 142-1 O
Tripping Relays
20E-1-4030AP02 Schematic Diagram System Auxiliary Transformer 142-2 P
Tripping Relays
20E-1-4697A Internal/External Wiring Diagram SAT 142-1 & 142-2 Loss of A
Phase Detection Panel 1PA55J
6E-0-4000B One Line Relay & Instrument Diagram of 345KV Bus-4, 5, 6 Q
&7
Procedures 1BwOS AP1a AAR Unit 1 SAT Low Load Condition Loss of Phase 1
Monitoring
Inspection Type Designation Description or Title Revision or
Procedure Date
BwAR 1-20-A3 SAT 142-1 Lockout Relay Trip Alarm 12
BwAR 1-20-E5 SAT 142-1 Loss of Phase Alarm 3
BwAR 1-20-E7 SAT 142-1 Low Load/Trouble Alarm 3
BwOP AP-15 Isolating System Auxiliary Transformer (SAT) 142-1 with Unit 27
Energized
BwOP AP-17 Restoring System Auxiliary Transformer (SAT) 142-1 with 21
Unit 1 UAT Energized
MA-BR-773-232 Braidwood Station Unit 2 System Auxiliary Transformer 6
Control Circuit Checks
MA-MW-772-712 Calibration of Microprocessor Based Relays 2
Work Orders 01570215 SAT Loss of Phase Relay Installation-1AP02E 01/12/2013
01570216 SAT Loss of Phase Relay Installation-2AP02E 11/14/2012
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