IR 05000373/2019013

County Station: NRC Inspection of Ti 2515/194, Inspection of the Licensees Implementation of Industry Initiative Associated with the Open Phase Condition Design Vulnerabilities in Electric Power Systems Report50-373/19013 and 50-374/19013

ML19325D947
Person / Time
Site:	LaSalle
Issue date:	11/21/2019
From:	Robert Daley Engineering Branch 3
To:	Bryan Hanson Exelon Generation Co, Exelon Nuclear
References
IR 2019013
Download: ML19325D947 (9)

Text

November 21, 2019

Mr. Bryan Senior VP, Exelon Generation Company, LLC President and CNO, Exelon Nuclear 4300 Winfield Road Warrenville, IL 60555

SUBJECT:

LASALLE COUNTY STATION, UNITS 1 AND 2 - NRC INSPECTION OF TEMPORARY INSTRUCTION 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) REPORT 05000373/2019013 AND 05000374/2019013

Dear Mr. Hanson:

On October 4, 2019, the U.S. Nuclear Regulatory Commission (NRC) completed an inspection at Lasalle County Station, Units 1 And 2. On October 4, 2019, the NRC inspectors discussed the results of this inspection with Phil Hansett and other members of your staff. The results of this inspection are documented in the enclosed report.

The NRC inspectors did not identify any finding or violation of more than minor significance.

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 Karla Stoedter for/

Robert C. Daley, Chief Engineering Branch 3 Division of Reactor Safety

Docket Nos. 05000373 and 05000374 License Nos. NPF-11 and NPF-18

Enclosure:

As stated

Inspection Report

Docket Numbers:

05000373 and 05000374

License Numbers:

NPF-11 and NPF-18

Report Numbers:

05000373/2019013 and 05000374/2019013

Licensee:

Exelon Generation Company, LLC

Facility:

LaSalle County Station, Units 1 and 2

Location:

Marseilles, IL

Inspection Dates:

September 30, 2019 - October 4, 2019

Inspectors:

Ijaz Hafeez, Reactor Inspector

Approved By:

Robert C. Daley, Chief

Engineering Branch 3

Division of Reactor Safety

SUMMARY

The U.S. Nuclear Regulatory Commission (NRC) continued monitoring the licensees performance by conducting an NRC Inspection of Temporary Instruction 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) at LaSalle County 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 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.

INSPECTION RESULTS

Observation: Detection, Alarms, and General Criteria 2515/194

(1) Open Phase Conditions (OPCs) that are detected will be alarmed in the Main Control Room (MCR) common annunciator panel.

(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 0.65 seconds was selected for the OPC relays to coordinate with the fault clearing time of 345kV switchyard primary and zone 2 relays) 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 OPC scheme was activated or placed in-service in October of 2017. 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 being replaced with non-Class 1E circuits in the design.

(5) The licensee revised Lasalle Updated Final Safety Analysis Report (UFSAR), Section 8.3.1.1.2. Offsite Power Sources (SATs), and added the loss of phase protection to Table 8.3-2. The change was incorporated into the UFSAR Report.

See item 5 in table titled Detection, Alarms, and General Criteria Exceptions for inspector identified exceptions.

Observation: Protective Actions Criteria 2515/194

(1) LaSalle County Station has determined that OPCs are credible events and have implemented design changes to mitigate the effects. EC 387695 and EC 387696 have installed an open phase relay scheme to detect, alarm and protect from open phase conditions.

(2) The inspectors 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 0.65 second time delay. The SAT lockout relays would isolate the SAT by opening both primary and secondary side breakers. After the SAT isolates, an automatic fast transfer connects the safety-related buses fed by the SAT to the Unit Auxiliary Transformer (UAT). 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.

The Lasalle UFSAR states that during a power loss to the M-G set, the high-inertia flywheel is designed to maintain generator output within 5% of rated values for at least one second to keep the Reactor Protection System (RPS) bus energized. The fast bus transfer from the SAT to UAT recovers the bus voltage allowing RPS operation to be sustained throughout the transient. Analyses completed by the licensee support the ability of this arrangement to be completed within associated time constraints.

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 OPC algorithms, the inspectors 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 LaSalle 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 3.6MVA (L-003786, Revision 0)). During normal operations, the SATs are routinely loaded above the MINLOAD threshold.

(5) While the change was incorporated into UFSAR table as a trip to the SAT lockout relays, the revision did not reference any design analysis, discuss design features, discuss theory of operation for the OPC system, or list major components associated with the open phase condition equipment in detail. However, the licensee maintained that the level of detail provided in the UFSAR for the open phase condition protection was consistent with the level of detail provided for other non-safety conditions that provide an input to the associated transformer lockout relay trips.

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 inspectors 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 IR 04284977, NRC IDD 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 inspectors noted that, for the case where an OPC occurs and an accident condition (LOCA) signal are present simultaneously, safety-related equipment would receive a start request and would attempt to start while the OPC exists on the safety-related buses. This first start attempt occurs due to the time delay associated with 1) OPC coordination with other protective features and 2) the time delay associated with detection and actuation of the OPC equipment.

Once the SAT lockout relays isolate the SAT by opening both primary and secondary side breakers, the analysis showed the safety-related undervoltage relaying scheme would automatically separate the engineered safety feature (ESF) 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 calibration testing schedule to verify relay performance is within the tolerances assumed within the supporting analyses. The licensees relay testing procedure for microprocessor-based relays does not require calibration or setpoint verification.

EXIT MEETINGS AND DEBRIEFS

The inspectors verified no proprietary information was retained or documented in this report.

• On October 4, 2019, the inspectors presented the NRC Inspection of Temporary Instruction 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) results to Phil Hansett and other members of the licensee staff.

DOCUMENTS REVIEWED

Inspection

Procedure

Type

Designation

Description or Title

Revision or

Date

2515/194

Calculations

L-003750

LaSalle Offsite Power System Open Phase EMPT Evaluation

001

L-003786

Unit 1 and Unit 2 Loss of Phase Detection Relay Settings

003

L-003885

Open Phase Detection LOCA Analysis

Corrective Action

Documents

Resulting from

Inspection

284977

NRC IDD Procedure Enhancement

10/04/2019

Drawings

1E-1-4000FC

Key Diagram Essential Div. 2 125V DC Distribution Panel

2X (1DC12E) and Panel 112Y (1DC13E)

P

1E-1-4004AG

Schematic Diagram Main Power System MP Part 7

K

1E-1-4005DQ

Schematic Diagram Auxiliary Power System AP Part 87

M

1E-2-4000A

Single Line Diagram Generator, Transformers & 6900V

Buses Part 1

V

1E-2-4000NF

Relaying & Metering Diagram System Auxiliary

Transforme242 (2AP91E)

G

Engineering

Changes

387695

Single Phase Fault Mitigation

000

Procedures

LOA-AP-101

Unit 1, AC Power System Abnormal

LOR-1PM01J-

A117

Sat 142(242) System 1 Prot Relay Trip

LOR-1PM01J-

A405

Sat 142 Low Load

LOR-242 Loss of

Phase Relay

Trouble

Sat 242 Loss of Phase Relay Trouble

LOR-2PM01J-

A217

SAT 242 System 2 Prot Relay Trip

LST-2013-040

Single Phase Fault Mitigation Relay (EC 387695)

LST-2015-009

Open Phase Condition Concurrent with a LOCA Bus Transfer

Logic Change (EC 400355)

MA-LA-773-231

Unit 1, System Aux Transformer Relay and Meter

Calibrations By OAD

Inspection

Procedure

Type

Designation

Description or Title

Revision or

Date

Work Orders

01513170

OAD Perform Bench Testing of Relay SEL-451 Per

EC387696

2