IR 05000461/2021013

Temporary Instruction Report 05000461/2021013

ML21244A258
Person / Time
Site:	Clinton
Issue date:	09/03/2021
From:	Richard Skokowski Engineering Branch 3
To:	Rhoades D Exelon Generation Co, Exelon Nuclear
References
IR 2021013
Download: ML21244A258 (10)

Text

SUBJECT:

CLINTON POWER STATION - 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 05000461/2021013

Dear Mr. Rhoades:

On July 16, 2021, the U.S. Nuclear Regulatory Commission (NRC) completed an inspection at Clinton Power Station. On July 21, 2021, the NRC inspectors discussed the results of this inspection with Mr. T. Chalmers, Site Vice President 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, Richard A. Skokowski, Chief Engineering Branch 3 Division of Reactor Safety Docket No. 05000461 License No. NPF-62

Enclosure:

As stated

Inspection Report

Docket Number: 05000461

License Number: NPF-62

Report Number: 05000461/2021013

Licensee: Exelon Generation Company, LLC

Facility: Clinton Power Station

Location: Clinton, IL

Inspection Dates: May 24, 2021 to May 28, 2021

Inspectors: I. Hafeez, Reactor Inspector L. Kozak, Senior Reactor Analyst

Approved By: Richard A. Skokowski, Chief Engineering Branch 3 Division of Reactor Safety

Enclosure

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 Clinton Power Station, 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.

Starting on March 20, 2020, in response to the National Emergency declared by the President of the United States on the public health risks of the coronavirus (COVID-19), inspectors were directed to begin telework. In addition, regional baseline inspections were evaluated to determine if all or a portion of the objectives and requirements stated in the IP could be performed remotely. If the inspections could be performed remotely, they were conducted per the applicable IP. In some cases, portions of an IP were completed remotely and on site. The inspections documented below met the objectives and requirements for completion of the IP.

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)

This inspection was conducted using Temporary Instruction 2515/194 (ADAMS Accession No. ML20230A328), dated August 18, 2020. The inspectors reviewed the licensees implementation of Nuclear Energy Institute voluntary industry initiative in compliance with Commission guidance. The inspectors discussed the impacts of open phase conditions on the licensees electrical system design, the ability to detect and alarm open phase conditions 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 local and in the control room, and analyzed potential impacts associated with the design implementation on the current licensing basis. The inspectors also reviewed licensee analysis and calculations, and performed distribution system and switchyard equipment walkdowns.

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. ML19163A176), dated June 6, 2019, including updating their licensing basis to reflect the need to protect against open phase conditions. For sites that are implementing the risk-informed evaluation method to demonstrate that operator manual actions will be sufficient to mitigate the impact of an OPC, in lieu of TI Section 03.01.b (automatic protective actions),

TI Section 03.01.c will be performed.

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) Clinton Power Station has Installed Schweitzer Engineering Laboratories (SEL) 451-5 microprocessor based relays for the Open Phase Condition (OPC) Relays which are located on the high voltage side (345kV) of Reserve Auxiliary Transformers (RAT)and (138kV) Emergency Reserve Auxiliary Transformer (ERAT) to the appropriate 4 kV safety related buses that are maintained in a split bus configuration lineup. The relay schemes monitor and compare the positive, negative and zero sequence current input from existing Current Transformers (CTs). The OPC relays monitors/detect an open phase condition, which is defined as one or two phases, with or without a ground for the OPC 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.

If an open or loss of phase is detected the relays actuate contacts which, in turn, provides an alarm in the Main Control Room (MCR).

In lieu of automatic open phase protective actions, Exelon implemented an alarm only strategy that relies on proper operator actions to diagnose and respond to an open phase condition. At the end of this inspection the SEL relays were monitoring the associated power sources and would provide main control room annunciation if a loss of one-or two-phase conditions was detected or if a relay was non-functional.

INSPECTION RESULTS

Observation: Temporary Instruction 2515/194-03.01 Voluntary Industry Initiative 2515/194 Based on discussions with Clinton staff, review of design and testing documentation, and walkdowns of installed equipment, the inspectors had reasonable assurance that Clinton is appropriately implementing, with a noted exceptions discussed below, the voluntary industry initiative at Clinton Power Station. The inspectors verified the following criteria:

(1) [03.01(a)(1)] Open phase conditions are detected and will be alarmed in the Main Control Room (MCR) common annunciator panel.

(2) [03.01(a)(2)] Detection circuits are sensitive enough to identify an OPC for credited loading conditions (i.e., high and low loading). See next section for inspector identified exceptions.

(3) [03.01(a)(3)] The open phase condition design and protective schemes minimize misoperation or spurious action in the range of voltage unbalance normally expected in the transmission system that could cause separation from an operable off-site power source. Additionally, Exelon has demonstrated that the actuation circuit design does not result in lower overall plant operation reliability.

(4) [03.01(a)(4)] No Class-1E circuits were replaced with non-Class-1E circuits in this design.

(5) [03.01(a)(5)] The Updated Final Safety Analysis Report was updated to discuss the design features and analyses related to the effects of any OPC design vulnerability.

(6) [03.01(a)(6)] Identify if Open Phase Isolation System (OPIS) detection and alarm components are maintained in accordance with station procedures or maintenance program, and that periodic tests, calibrations, setpoint verifications, or inspections (as applicable) have been established. See next section for inspector identified exceptions.

Use of Risk-Informed Evaluation Method

(1) [03.01(c)(1)] Review licensees evaluation of NEI 19-02 and Attachment 1 of VII, Revision 3 stated above. Verify that the plant configuration matches the changes made to the PRA model used to evaluate an OPC, and that the logic of the PRA model changes is sound. Consult with regional Senior Reactor Analyst (SRA) if inspectors have any questions or concerns regarding the PRA model. See next section for inspector identified exceptions.

(2) [03.01(c)(2)] Review the procedure(s) and operator actions required to respond to an OPC alarm and potential equipment trip, with an operator walkthrough and simulator demonstration if possible (during the walkthrough, verify that the procedure which validates that the OPC alarm is legitimate would identify the proper indication to validate the OPCs at all possible locations). See next section for inspector identified exceptions.

(3) [03.01(c)(3)] Observations associated with procedures and operator actions required to respond to an OPC alarm and potential equipment trip match the Human Reliability Analysis (HRA).

(4) [03.01(c)(4)] Sensitivity analyses used in the Clinton PRA analysis for using Operator Manual Actions (OMAs) in leu of OPC automatic protective relay actuation, did not exceed the thresholds defined in the NEI 19-02 guidance document for delta Core Damage Frequency (CDF) or delta Large Early Release Frequency (LERF).

(5) [03.01(c)(5)] Assumptions, procedures, and operator actions specified in the Clinton NEI 19-02 analysis are consistent with the plant-specific design and licensing basis, including:

(a) Initiating events considered in the analysis.

(b) Boundary conditions specified in Attachment 1 of the NEI Voluntary Industry Initiative, Revision 3.

(c) Operating procedures for steps taken to recover equipment assumed tripped, locked out, or damaged due to an OPC.

(d) Where recovery was assumed in the PRA analysis for tripped electric equipment, restoration of the equipment was based on analyses that demonstrate that automatic isolation trips did not result in equipment damage.

Observation: Use of Risk-Informed Evaluation Method Exceptions 2515/194

[03.01(a)(2)] - Detection circuits are sensitive enough to identify an OPC for credited loading conditions (i.e., high and low loading).

Exception - Based on review of the licensees calculation for the relay setting limits used in the Open Phase Condition algorithms in some scenarios where automatic detection may not be possible due to very low or no load conditions, or when transformers are in a standby mode. Specifically, an OPC is detected as long as the primary positive sequence current in the RAT and ERAT is greater than the MINLOAD (low load) based on relay sensitivity. The RATs are normally loaded above the MINLOAD threshold and automatic detection will occur as soon as loads are transferred to the standby source. Additionally, where automatic detection is not reliable, Exelon has established monitoring requirements on a per shift basis, to look for evidence of an open phase condition. During low loading of the RATs or open phase detection (OPD) relay trouble alarms, manual actions may be required to address the existence of an OPC condition.

[03.01(a)(6)] - Identify if Open Phase Isolation System (OPIS) detection and alarm components are maintained in accordance with station procedures or maintenance program, and that periodic tests, calibrations, setpoint verifications, or inspections (as applicable) have been established.

Exception - Clinton has not developed any maintenance PMs for the OPC relays. At the time of this inspection, the licensee had not established a functional test schedule, which includes testing the relay metering function (sensing circuit is continuous) 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.

[03.01(c)(1)] - Review licensees evaluation of NEI 19-02 and Attachment 1 of VII, Revision 3 stated above. Verify that the plant configuration matches the changes made to the PRA model used to evaluate an OPC, and that the logic of the PRA model changes is sound.

Consult with regional Senior Reactor Analyst (SRA) if inspectors have any questions or concerns regarding the PRA model.

Exception - The plant configuration did not match the Probabilistic Risk Assessment (PRA)model. The PRA model used an alarm associated with the static var compensator (SVC) and not the OPIS to detect an OPC and prompt operator action. However, the SVC and its associated alarm were being removed from service. The SVC alarm was more distinct than the OPIS alarm, which was a common computer point with multiple inputs. In addition, the SVC alarm was large, red in color, and had an associated hard card that was well trained on. The differences between the SVC alarm and the OPIS computer alarm as the cue for operator action would lead to some differences in the PRA model and associated human reliability analysis. However, the NRC concluded the difference was not likely to impact the overall outcome of the evaluation. The licensee intended to update the risk evaluation to match the plant configuration for OPC detection in the future.

[03.01(c)(2)] - Review the procedure(s) and operator actions required to respond to an OPC alarm and potential equipment trip, with an operator walkthrough and simulator demonstration if possible (during the walkthrough, verify that the procedure which validates that the OPC alarm is legitimate would identify the proper indication to validate the OPCs at all possible locations).

Exception - The procedures which validate that an OPC alarm would identify the proper voltage indication to validate the OPC at all ESF buses. The inspectors discussed this potential outcome with the licensee and the licensee agreed that the current design analysis did not specifically address ESF bus voltage with and without SVC on. Additionally, the licensee initiated IR 04425627, Action Tracking for 2021 NRC Open Phase Inspection, to address weaknesses identified in alarm response procedures. The inspector noted that various alarm response procedures did not provide Operations personnel instructions for the cases where the OPC condition might exist in conjunction with low loading of the RATs or open phase detection (OPD) relay trouble alarms.

EXIT MEETINGS AND DEBRIEFS

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

On July 21, 2021, 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 Mr. T. Chalmers, Site Vice President and other members of the licensee staff.

DOCUMENTS REVIEWED

Inspection Type Designation Description or Title Revision or

Procedure Date

2515/194 Calculations CL-MISC-029 PRA Application Notebook Clinton Power Station Open 0

Phase Condition Evaluation

Drawings E02-1AP01 Single Line Diagram Part 1 Clinton Power Station Unit 1 AE

Clinton, Illinois

E02-1AP03 Electric Loading Diagram Clinton Power Station Unit 1 AD

Clinton, Illinois

E02-1AP12 Relaying & Metering Diagram Reserve Auxiliary Transf. B T

Clinton Power Station Unit 1 Clinton, Illinois

E02-1AP99 Reserve Aux Transformer B Auxiliary Protective Relay B

Clinton Power Station Unit 1 Clinton, Illinois

Engineering EC-ERAT and RATB Open Phase Detection LOCA Analysis 0

Changes 394754/394755

Miscellaneous 11335-293,349 Clinton Power Station Loss of Phase Detection Relay 05/24/2021

Monitoring Final Report for October 2017 - September 2018

Procedures CPS3501.01H001 Loss of RAT SVC Actions Hard Card 0c

CPS3503.01C006 ERAT Open Phase Checklist 03/24/2016

CPS3505.01C007 RAT B Open Phase Checklist 04/13/2017

CPS5009.03 Alarm Panel 5009 Annunciators - ROW 3 04/09/2020

CPS5010.04 Alarm Panel 5010 Annunciators - ROW 4 12/10/2017

CPS5011.08 Alarm Panel 5011 Annunciators - ROW 8 04/09/2020

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