IR 05000275/2021012

Temporary Instruction 2515/194 Report 05000275/2021012 and 05000323/2021012

ML21207A199
Person / Time
Site:	Diablo Canyon
Issue date:	07/28/2021
From:	Nick Taylor NRC/RGN-IV/DRS/EB-2
To:	Welsch J Pacific Gas & Electric Co
References
IR 2021012
Download: ML21207A199 (9)

Text

July 28, 2021

SUBJECT:

DIABLO CANYON POWER PLANT, UNITS 1 AND 2 - TEMPORARY INSTRUCTION 2515/194 REPORT 05000275/2021012 AND 05000323/2021012

Dear Mr. Welsch:

On June 15, 2021, the U.S. Nuclear Regulatory Commission (NRC) completed an inspection at Diablo Canyon Power Plant, Units 1 and 2 and discussed the results of this inspection with Ms.

Paula Gerfen 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, Nicholas H. Taylor, Chief Engineering Branch 2 Division of Reactor Safety

Docket Nos. 05000275 and 05000323 License Nos. DPR-80 and DPR-82

Enclosure:

As stated

Inspection Report

Docket Numbers:

05000275 and 05000323

License Numbers:

DPR-80 and DPR-82

Report Numbers:

05000275/2021012 and 05000323/2021012

Licensee:

Pacific Gas and Electric Company

Facility:

Diablo Canyon Power Plant, Units 1 and 2

Location:

Avila Beach, CA

Inspection Dates:

June 07, 2021 to June 11, 2021

Inspectors:

S. Graves, Senior Reactor Inspector

D. Loveless, Senior Reactor Analyst

Approved By:

Nicholas H. Taylor, Chief

Engineering Branch 2

Division of Reactor Safety

Enclosure

SUMMARY

The U.S. Nuclear Regulatory Commission (NRC) continued monitoring the licensees performance by conducting a Temporary Instruction 2515/194 at Diablo Canyon Power Plant,

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 Temporary Instruction (TI) in effect at the beginning of the inspection unless otherwise noted. Currently approved Inspection Procedures (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 TI 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 this TI.

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 inspectors reviewed the licensees implementation of Revision 3 to the Nuclear Energy Institute Industry Initiative on Open Phase Condition, (ADAMS Accession No. ML19163A176)dated June 6, 2019. This review included the licensee's application of risk screening techniques to determine that the risk associated with an open phase condition (OPC) event is significantly reduced through the implementation of detection circuits and the use of operator manual actions in lieu of automatic trip functions. The inspectors also reviewed the updates to the DCPP 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) 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)

Pacific Gas and Electric Company (PG&E) had selected the open phase detection system designed and manufactured by Power System Sentinel Technologies, LLC, (PSSTech) as the design vendor for Diablo Canyon Power Plant (DCPP). The licensee had installed dual-channel open phase detection systems on the 500-kV main transformer banks for both Unit 1 and 2, as well as on the Standby Startup 230-kV transformers for both units. In total, the licensee installed eight PSSTech open phase detection systems on four transformers.

During normal operation each unit generates and delivers power to the 500-kV transmission system via the main transformer banks. Each transformer bank has three single-phase transformers connected in a grounded-Wye primary and Delta secondary configuration. Each units main generator also provides power to the unit auxiliary loads through two auxiliary transformers (Delta configured primary windings). During periods in which the main generator is offline, such as outages, the unit main transformers can be manually realigned in a backfeed configuration. This configuration can also be used to provide offsite power to the unit if the preferred offsite source is unavailable. The licensee identified that this backfeed configuration was susceptible to open phase conditions and installed open phase detection using the common neutral connection to mitigate this condition.

The licensee also installed open phase detection systems on each units Standby Startup transformers. Each unit has a 230-kV/12-kV transformer (SUT11, SUT21) connected in a grounded-Wye/Delta configuration. These transformers are part of the preferred offsite power supply and during off-normal conditions supply offsite power to the units startup and vital loads.

As part of the licensee's implementation of Revision 3 to the open phase initiative, the licensee used contractor services to model and evaluate the effects of open phase conditions (OPCs) on the DCPP electrical distribution system and ESF/PRA-credited loads. The inspectors reviewed the contractor's report and assumptions, and discussed the distribution system behavior under various open-phase scenarios with licensee staff, including the use of existing 51N neutral overcurrent relaying and pilot wire differential protection relaying as protective elements in the licensee's OPC mitigating strategy. The inspectors noted that the 4.16-kV ESF motor circuit breaker protective relays did not use a seal-in function for overcurrent trips, allowing the motors to be reset and restarted from both the local control and the control room. The circuit breakers have an anti-pump feature which prevents the circuit breakers from immediately reclosing onto a fault.

INSPECTION RESULTS

Observation: Temporary Instruction 2515/194-03.01 - Voluntary Industry Initiative 2515/194 Based on discussions with DCPP staff, review of design and testing documentation, and walkdowns of installed equipment, the inspectors had reasonable assurance that PG&E is appropriately implementing the voluntary industry initiative at DCPP. The inspectors verified the following criteria:

Detection, Alarms and General Criteria

2. [03.01(a)(2)] In scenarios where automatic detection may not be possible due to very

low or no load conditions, or when transformers are in a standby mode, automatic detection will occur as soon as loads are transferred to the standby source.

Additionally, where automatic detection is not reliable, PG&E has established monitoring requirements on a per shift basis, to look for evidence of an open phase condition.

3. [03.01(a)(4)] No Class 1E circuits were being replaced with non-Class 1E circuits in

this design.

4. [03.01(a)(5)] The Final Safety Analysis Report was updated to discuss the design

features and analyses related to the effects of any open phase condition design vulnerability.

5. [03.01(a)(6)] The open phase condition detection and alarm components are

maintained in accordance with PG&E procedures or maintenance program, and periodic tests, calibrations setpoint verifications or inspections (as applicable) have been established. The open phase equipment is covered under the licensees maintenance rule requirements.

Use of Risk-Informed Evaluation Method

1. [03.01(c)(1)] The plant configuration matched the changes made to the probabilistic

risk assessment model to address an open phase condition, and the logic of the probabilistic risk assessment model changes is sound.

2. [03.01(c)(2)] The procedures which validate that the open phase condition alarm would

identify the proper indication to validate the open phase conditions at all possible locations.

3. [03.01(c)(3)] Observations associated with procedure(s) and operator actions required

to respond to an open phase condition alarm and potential equipment trip match the Human Reliability

4. [03.01(c)(4)] Assumptions listed in the NEI 19-02 Appendix A evaluation and the

sensitivity analyses listed in Section 5 of the evaluation were verified.

5. [03.01(c)(5)] Assumptions, procedures, operator actions, and PG&E analyses specified

above 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 from the effects of open phase conditions (or use of alternate equipment) was appropriate.

d. Where recovery was assumed in the probabilistic risk assessment 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

No findings or exceptions were identified.

EXIT MEETINGS AND DEBRIEFS

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

• On June 15, 2021, the inspectors presented the Exit Meeting inspection results to Ms.

Paula Gerfen, Site Vice President, and other members of the licensee staff.

DOCUMENTS REVIEWED

Inspection

Procedure

Type

Designation

Description or Title

Revision or

Date

2515/194

Calculations20-064

Diablo Canyon Power Plant Open Phase Analysis (Zachry)

PRA 19-07

Risk Impacts of the Open Phase Condition at DCPP

PRA 19-07

Risk Impacts of the Open Phase Condition at DCPP

Corrective Action

Documents

SAPN

50304396, 51073848, 51080145, 51091117, 51091286,

51094821, 51102249, 51110258, 51118174, 51118204,

51122198, 51122347

Corrective Action

Documents

Resulting from

Inspection

SAPN

51122198

Drawings

437530, Sheet 1

Electrical Single Line Meter & Relay Diagram 12KV Start-Up

System

437531, Sheet 1

Electrical Single Line Meter and Relay Diagram 12KV

System

437532, Sheet 1

Unit 1 Electrical Single Line Meter & Relay Diagram 4160

Volt System

437595, Sheet 1

Electrical Schematic Diagram Charging Pumps No. 11 & 12

437618, Sheet 1

Electrical Schematic Diagram Stand By Start-Up Transformer

No. 11 And Associated Circuit Breakers

437619, Sheet 1

Electrical Schematic Diagram StandBy Start-Up Transformer

No. 11 And Associated Circuit Breakers

500790, Sheet 1

Electrical Schematic Diagram Main Annunciator Windows

PK2013 - PK2025

500808, sheet 1

Electrical Arrangement of Main Annunciator Window

501140, Sheet 1

Electrical Schematic Diagram Main Annunciator Windows

PK2013 - PK2025

2110, Sheet 1

Electrical Single Line Diagram 500/230/25/12/4.16KV

Systems

57554, Sheet 1

Electrical Cable Tray and Conduit Layout Plan Below Elev.

140' - 0" Area "A"

57568, Sheet 1

Electrical Cable Tray and Conduit Layout Plan Below Elev.

107' - 0" Area "A"

Inspection

Procedure

Type

Designation

Description or Title

Revision or

Date

Miscellaneous

230kV Open Phase Simulator Scenario

NA

DCP 1000025547

REV 0

ATTACHMENT 8

UFSAR Change Request - Section 8. 2. 3. 2. 2. 4, Operation

During Severe Grid Disturbances Analysis

Procedures

AR PK20-19

Unit 1 Annunciator Response 230 KV Open Phase

AR PK20-19

Unit 2 Annunciator Response 230 KV Open Phase

AR PK20-24

Unit 1 Annunciator Response 230 KV SWYD

AR PK20-24

Unit 2 Annunciator Response 230 KV SWYD

EOP ECA-0.3

Unit 1 Restore 4kV Buses

MP E-50.46ST

SUT Open Phase Detection Relay Maintenance and Testing

MP E-50.46ST.1

SUT Open Phase Detection Relay Data Acquisition

MP E-

50.46TGM.2

Main Bank Transformer (MBT) Open Phase Detection Relay

Channel Reference

OP J-2:XII

Unit 2 230kV Open Phase Protection System Operation

OP J-2:XII

Unit 1 230kV Open Phase Protection System Operation

Self-Assessments

Temporary Instruction (TI) 2515/194 Open Phase Condition

Design Vulnerabilities in Electric Power Systems Inspection

Date June 8, 2021 SAPN 51105830