IR 05000275/2023002

Quarterly Integrated Inspection Report 05000275/2023002 and 05000323/2023002- August 7, 2023

ML23220A212
Person / Time
Site:	Diablo Canyon
Issue date:	08/14/2023
From:	Patricia Vossmar NRC/RGN-IV/DORS/PBA
To:	Gerfen P Pacific Gas & Electric Co
Vossmar P
References
IR 2023002
Download: ML23220A212 (22)

Text

August 14, 2023

SUBJECT:

DIABLO CANYON POWER PLANT, UNITS 1 AND 2 - INTEGRATED INSPECTION REPORT 05000275/2023002 AND 05000323/2023002

Dear Paula A. Gerfen:

On June 30, 2023, the U.S. Nuclear Regulatory Commission (NRC) completed an inspection at Diablo Canyon Power Plant, Units 1 and 2. On June 29, 2023, the NRC inspectors discussed the results of this inspection with you and other members of your staff. The results of this inspection are documented in the enclosed report.

Two findings of very low safety significance (Green) are documented in this report. One of these findings involved a violation of NRC requirements. We are treating this violation as a non-cited violation (NCV) consistent with section 2.3.2 of the Enforcement Policy.

A licensee-identified violation which was determined to be of very low safety significance is also documented in this report. We are treating this violation as a non-cited violation (NCV)

consistent with section 2.3.2 of the Enforcement Policy.

If you contest the violations or the significance or severity of the violations documented in this inspection report, 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 IV; the Director, Office of Enforcement; and the NRC Resident Inspector at Diablo Canyon Power Plant, Units 1 and 2.

If you disagree with a cross-cutting aspect assignment or a finding not associated with a regulatory requirement in this report, you should provide a response within 30 days of the date of this inspection report, with the basis for your disagreement, to the U.S. Nuclear Regulatory Commission, ATTN: Document Control Desk, Washington, DC 20555-0001; with copies to the Regional Administrator, Region IV; and the NRC Resident Inspector at Diablo Canyon Power Plant, Units 1 and 2. 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, Signed by Vossmar, Patricia on 08/14/23 Patricia J. Vossmar, Chief Reactor Projects Branch A Division of Operating Reactor Safety Docket Nos. 05000275, 05000323 License Nos. DPR-80, DPR-82

Enclosure:

As stated

Inspection Report

Docket Numbers: 05000275 and 05000323 License Numbers: DPR-80 and DPR-82 Report Numbers: 05000275/2023002 and 05000323/2023002 Enterprise Identifier: I-2023-002-0000 Licensee: Pacific Gas and Electric Company Facility: Diablo Canyon Power Plant, Units 1 and 2 Location: Avila Beach, CA Inspection Dates: April 1, 2023, to June 30, 2023 Inspectors: A. Athar, Resident Inspector M. Hayes, Senior Resident Inspector N. Hernandez, Operations Engineer J. Meszaros, Resident Inspector C. Osterholtz, Senior Operations Engineer D. You, Operations Engineer Approved By: Patricia J. Vossmar, Chief Reactor Projects Branch A Division of Operating Reactor Safety Enclosure

SUMMARY

The U.S. Nuclear Regulatory Commission (NRC) continued monitoring the licensees performance by conducting an integrated inspection 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. A licensee-identified non-cited violation is documented in report section: 71152

List of Findings and Violations

Failure to Provide Adequate Written Instructions for Swapping Plant Equipment Cornerstone Significance Cross-Cutting Report Aspect Section Initiating Events Green [H.1] - 71152A FIN 05000323,05000275/2023002-01 Resources Open/Closed The inspectors reviewed a self-revealed, Green finding for the licensees failure to provide adequate written instructions for swapping bio-lab pumps. Specifically, the licensee failed to provide adequate detail in Procedure OP E-2:VII, Saltwater Supply to the Suez Water Seawater Tank, revision 34, while routinely swapping bio-lab pumps, to prevent simultaneous two-pump operation. This issue resulted in a failure of the PVC piping associated with the bio-lab system, subsequent flooding of circulating water pump 2-2, and ultimately resulted in Unit 2 reducing power to approximately 50 percent power.

Failure to Identify a Deficient Weld Resulting in a Degraded Reactor Coolant System Pressure Boundary Cornerstone Significance Cross-Cutting Report Aspect Section Initiating Events Green None (NPP) 71153 NCV 05000323/2023002-02 Open/Closed The inspectors reviewed a self-revealed, Green finding and associated non-cited violation of Title 10 of the Code of Federal Regulations (10 CFR) Part 50, Appendix B, Criterion IX, Control of Special Processes, when the licensee failed to identify a deficient weld in reactor coolant system pressure boundary piping during installation of a vent line in 1994. In October 2022, the licensee identified dry boric acid deposits indicating that this deficient weld had caused reactor coolant system pressure boundary leakage in the vent line connected to the Unit 2, loop 1 cold leg.

Additional Tracking Items

Type Issue Number Title Report Section Status LER 05000323/2022-001-00 Unit 2 Reactor Coolant 71153 Closed System Pressure Boundary Degradation

PLANT STATUS

Unit 1 and Unit 2 operated at or near rated thermal power for the entire inspection period.

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 performed activities described in IMC 2515, Appendix D, Plant Status, observed risk significant activities, and completed on-site portions of IPs. 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.

71111.04 - Equipment Alignment

Partial Walkdown Sample (IP Section 03.01) (4 Samples)

The inspectors evaluated system configurations during partial walkdowns of the following systems/trains:

(1) Units 1 and 2 125 V vital dc system on April 21, 2023

(2) Unit 2 vital switchgear ventilation fans E-46/S-46 while E-45/S-45 were out of service for planned maintenance on May 24, 2023

(3) Unit 2 safety injection system on June 15, 2023

(4) Unit 1 emergency diesel generator 1-2 while emergency diesel generator 1-1 was out of service for planned major maintenance on June 27, 2023

71111.05 - Fire Protection

Fire Area Walkdown and Inspection Sample (IP Section 03.01) (4 Samples)

The inspectors evaluated the implementation of the fire protection program by conducting a walkdown and performing a review to verify program compliance, equipment functionality, material condition, and operational readiness of the following fire areas:

(1) Units 1 and 2 intake structure on May 10, 2023

(2) Unit 2 radiological control area, 73-foot elevation, on May 17, 2023

(3) Unit 2 turbine building, 85-foot elevation, emergency diesel generator 2-1, 2-2, and 2-3 rooms on May 26, 2023

(4) Unit 1 turbine building, 85-foot elevation, emergency diesel generator 1-1, 1-2, and 1-3 rooms on May 30, 2023

Fire Brigade Drill Performance Sample (IP Section 03.02) (1 Sample)

(1) The inspectors evaluated the onsite fire brigade training and performance during an announced fire drill on May 12, 2023.

71111.11A - Licensed Operator Requalification Program and Licensed Operator Performance

Requalification Examination Results (IP Section 03.03) (1 Sample)

(1) The inspectors reviewed and evaluated the licensed operator examination failure rates for the requalification annual operating exam administered from May 23 -

June 24, 2023.

71111.11B - Licensed Operator Requalification Program and Licensed Operator Performance

Licensed Operator Requalification Program (IP Section 03.04) (1 Sample)

(1) Biennial Requalification Written Examinations The inspectors evaluated the quality of the licensed operator biennial requalification written examination administered from May 23 - June 24, 2023.

Annual Requalification Operating Tests The inspectors evaluated the adequacy of the licensees annual requalification operating test.

Administration of an Annual Requalification Operating Test The inspectors evaluated the effectiveness of the licensee in administering requalification operating tests required by 10 CFR 55.59(a)(2) and that the licensee is effectively evaluating their licensed operators for mastery of training objectives.

Requalification Examination Security The inspectors evaluated the ability of the licensee to safeguard examination material, such that the examination is not compromised.

Remedial Training and Re-examinations The inspectors evaluated the effectiveness of remedial training conducted by the licensee, and reviewed the adequacy of re-examinations for licensed operators who did not pass a required requalification examination.

Operator License Conditions The inspectors evaluated the licensees program for ensuring that licensed operators meet the conditions of their licenses.

Control Room Simulator The inspectors evaluated the adequacy of the licensees control room simulator in modeling the actual plant, and for meeting the requirements contained in 10 CFR 55.46.

Problem Identification and Resolution The inspectors evaluated the licensees ability to identify and resolve problems associated with licensed operator performance.

71111.11Q - Licensed Operator Requalification Program and Licensed Operator Performance

Licensed Operator Requalification Training/Examinations (IP Section 03.02) (1 Sample)

(1) The inspectors observed and evaluated a crew of licensed operators during simulator training on April 18, 2023.

71111.12 - Maintenance Effectiveness

Quality Control (IP Section 03.02) (1 Sample)

The inspectors evaluated the effectiveness of maintenance and quality control activities to ensure the following SSC remains capable of performing its intended function:

(1) observation of receipt inspections on June 26, 2023

71111.13 - Maintenance Risk Assessments and Emergent Work Control

Risk Assessment and Management Sample (IP Section 03.01) (3 Samples)

The inspectors evaluated the accuracy and completeness of risk assessments for the following planned and emergent work activities to ensure configuration changes and appropriate work controls were addressed:

(1) Unit 2 replacement of a programmable logic card in solid state protection system train B on April 11, 2023

(2) Unit 1 emergency diesel generator 1-1 24-hour load test maintenance risk assessment on April 15, 2023

(3) Unit 1 electro-hydraulic pump 1-2 failed to run while testing, placing Unit 1 in a single point vulnerability, on May 16, 2023

71111.15 - Operability Determinations and Functionality Assessments

Operability Determination or Functionality Assessment (IP Section 03.01) (4 Samples)

The inspectors evaluated the licensee's justifications and actions associated with the following operability determinations and functionality assessments:

(1) Unit 2 NI-42 power range high flux rate bistable spurious actuation on April 10, 2023

(2) Unit 1 emergency diesel generator 1-3 operability given multiple failed relays on May 4, 2023

(3) Unit 1 auxiliary feedwater pump 1-1 gearbox oil level low on June 13, 2023

(4) Unit 1 containment concrete chunk broken off on June 21, 2023

71111.24 - Testing and Maintenance of Equipment Important to Risk

The inspectors evaluated the following testing and maintenance activities to verify system

operability and/or functionality: Post-Maintenance Testing (PMT) (IP Section 03.01)

(1) Unit 1 electro-hydraulic pump 1-2 return to service testing following pump replacement on May 18, 2023

(2) Unit 1 auxiliary feedwater pump 1-3 following maintenance outage window on May 24, 2023

(3) Unit 2 480 V vital switchgear ventilation following maintenance on June 13, 2023

(4) Unit 1 10 percent atmospheric dump valve PCV-21 following maintenance on June 20, 2023

(5) Unit 2 auxiliary saltwater pump 2-1 following maintenance on June 20, 2023

(6) Unit 1 auxiliary saltwater pump 1-2 following maintenance on June 23, 2023

Surveillance Testing (IP Section 03.01) (2 Samples)

(1) Units 1 and 2 control room ventilation system tracer gas tests on April 5, 2023

(2) Unit 1 emergency diesel generator 1-2 fire suppression system testing on

June 14, 2023 Inservice Testing (IST) (IP Section 03.01) (1 Sample)

(1) Unit 1 auxiliary saltwater 1-1 comprehensive pump test on April 28, 2023

71114.06 - Drill Evaluation

Select Emergency Preparedness Drills and/or Training for Observation (IP Section 03.01)

(1 Sample)

(1) emergency response organization drill simulating a faulted and ruptured steam generator on April 20, 2023

Drill/Training Evolution Observation (IP Section 03.02) (1 Sample)

The inspectors evaluated:

(1) emergency response organization drill on May 11,

OTHER ACTIVITIES - BASELINE

===71151 - Performance Indicator Verification The inspectors verified licensee performance indicators submittals listed below:

MS05: Safety System Functional Failures (SSFFs) Sample (IP Section 02.04) ===

(1) Unit 1 (April 1, 2022, through March 31, 2023)

(2) Unit 2 (April 1, 2022, through March 31, 2023)

MS06: Emergency AC Power Systems (IP Section 02.05) (2 Samples)

(1) Unit 1 (April 1, 2022, through March 31, 2023)

(2) Unit 2 (April 1, 2022, through March 31, 2023)

MS07: High Pressure Injection Systems (IP Section 02.06) (2 Samples)

(1) Unit 1 (April 1, 2022, through March 31, 2023)

(2) Unit 2 (April 1, 2022, through March 31, 2023)

71152A - Annual Follow-up Problem Identification and Resolution Annual Follow-up of Selected Issues (Section 03.03)

The inspectors reviewed the licensees implementation of its corrective action program related to the following issues:

(1) review of down power caused by tripping of circulating water pump 2-2 due to flooding of circulating water pump 2-2 on May 30, 2023

(2) review of cause evaluation for emergency diesel generator 2-3 cap screw issue on June 13, 2023

71152S - Semiannual Trend Problem Identification and Resolution Semiannual Trend Review (Section 03.02)

(1) The inspectors reviewed the licensee's corrective action program for potential adverse trends that might be indicative of a more significant safety issue. The inspectors' review was focused on the Unit 1 480 V switchgear ventilation due to multiple failures to automatically start on low flow during routine ventilation swaps during the period from January 1, 2023, to June 30, 2023.

71153 - Follow Up of Events and Notices of Enforcement Discretion Event Report (IP section 03.02)

The inspectors evaluated the following licensee event reports (LERs):

(1) LER 05000323/2022-001-00, Unit 2 Reactor Coolant System Pressure Boundary Degradation (ML22355A081). The inspection conclusions associated with this LER are documented in this report under the Inspection Results Section [71153]. This LER is Closed.

INSPECTION RESULTS

Failure to Provide Adequate Written Instructions for Swapping Plant Equipment Cornerstone Significance Cross-Cutting Report Aspect Section Initiating Events Green [H.1] - 71152A FIN 05000323,05000275/2023002-01 Resources Open/Closed The inspectors reviewed a self-revealed, Green finding for the licensees failure to provide adequate written instructions for swapping bio-lab pumps. Specifically, the licensee failed to provide adequate detail in Procedure OP E-2:VII, Saltwater Supply to the Suez Water Seawater Tank, revision 34, while routinely swapping bio-lab pumps, to prevent simultaneous two-pump operation. This issue resulted in a failure of the PVC piping associated with the bio-lab system, subsequent flooding of circulating water pump 2-2, and ultimately resulted in Unit 2 reducing power to approximately 50 percent power.

Description:

The bio-lab system was originally installed as a single pump system to supply seawater to the bio-lab facility to sample intake structure seawater for various water board permit requirements. In this single pump configuration, the control switch to start the pump consisted of an OFF position and an ON position. When the saltwater reverse osmosis (SWRO) facility was constructed in 1985, an additional pump, and associated control switch, was added to the single supply line. When the second pump was added, an AUTO position was added to each control switch. The AUTO position also added an interlock so that when a running pump was in AUTO and the other standby pump is started by taking its switch from AUTO to ON, the running pump trips off and the standby pump is started. Each pump control switch position has remained in an OFF-AUTO-ON configuration. In 2008 system modifications were required to add a second line of bio-lab piping to the intake structure to improve reliability of make-up water supplied from the SWRO. The bio-lab facility has been removed, but the naming convention of bio-lab pumps (0-1 and 0-2), lines (0-1 and 0-2), etc.

has been maintained.

On March 10, 2023, while Unit 2 was operating at 100 percent power, bio-lab pump discharge line 0-1 fractured at a PVC flange-to-pipe joint above circulating water pump 2-2 during a routine swap of bio-lab pumps from bio-lab pump 0-1 to bio-lab pump 0-2. This fracture resulted in flooding of circulating water pump 2-2 bearing and the intake structure from the bio-lab system. Operators made the decision to reduce power on Unit 2 to 50 percent power and secure circulating water pump 2-2 to protect it from damage.

The inspectors reviewed the licensees casual evaluation and noted the two direct causes of the event were inadequate cementing of the PVC joint where the flange and pipe transition, and simultaneous two-pump operation during pump swaps. During the causal evaluation the licensee determined the operator assigned to swap the bio-lab pumps on March 10, 2023, using Procedure OP E-2:VII, Saltwater Supply to the Suez Water Seawater Tank, revision 34, dated February 2, 2022, observed the running pump control switch to be in the ON position while the standby pump was in the AUTO position. When the operator started the standby pump, the running pump did not automatically stop causing the system to operate with two pumps simultaneously. The intent of the procedure was to start the pump swap with both control switches in the AUTO position and rely on the interlock previously mentioned to stop the running pump automatically to avoid running the system in two-pump operation.

The inspectors reviewed the procedure in effect at the time of the event, Procedure OP E-2:VII, Saltwater Supply to the Suez Water Seawater Tank, revision 34, dated February 2, 2022. During the review the inspectors noted several inadequacies in the procedure. The procedure did not have a check to ensure both pump control switches were in AUTO before the evolution began to ensure when the standby pump was started the running pump trips. The procedure did not have any precautions, limitations, or notes stating two-pump operation should be avoided during the evolution of swapping pumps.

The inspectors reviewed Procedure AD1.ID1, Nuclear Generation Procedure Writers Manual, revision 32, dated June 16, 2020, and noted step 8.2.6.b provides guidance on how procedure steps should be written. Step 8.2.6.b states, in part, steps should be written with sufficient detail so individuals can perform the task without direct supervision. Also, the level of detail in procedure steps is commensurate with the complexity of the task, frequency of which the task is performed, skill of the craft, and the risk potential to plant equipment. The inspectors determined the steps in procedure OP E-2:VII, revision 34, were not adequate for routine swapping of bio-lab pumps because the procedure did not instruct operators to check that the control switches were in the proper alignment, and there were no precautions for avoiding two-pump operation in the bio-lab system.

Additionally, the licensee uses electronic Shift Operations Management System (eSOMS) for documenting operator rounds using a handheld computer. The electronic rounds template contains a space for each data point required and selected basis information associated with that point. When the operator round is complete the data is uploaded to eSOMS where it is reviewed, approved, and subsequently archived on a network drive. The intake watch operator has regular eSOMS identified points for each of the bio-lab pump control switches (weekly) and the status of each pump (daily) on the handheld computer. At the time of the event, the eSOMS short text instructions for bio-lab control switch weekly rounds read, Check Switch Status. The long text instructions read, Check that only one pump is running with both pump switches in AUTO. Ref. OP E-2:VII. The long text is hidden in eSOMS until actively clicked-on by the watch stander operator if the watch stander determines the short text is unclear. The inspectors determined eSOMS short text instructions for checking proper switch alignment in the bio-lab system were not adequate. The short text instructions did not provide sufficient detail on the alignment of bio-lab pump switches to support the intent of procedure OP E-2:VII to prevent simultaneous two-pump operation.

Corrective Actions: The licensee repaired the broken PVC pipe and revised procedure OP E-2:VII to prevent simultaneous two-pump operation in the bio-lab system.

The licensee also updated eSOMS so if bio-lab pump switches were found in the incorrect position a status message would appear so the operator would be notified to correct the alignment of the pump switches.

Corrective Action References: notifications 51183713 and 51184018

Performance Assessment:

Performance Deficiency: The inspectors determined the failure to provide written instructions with sufficient detail, to account for the potential risk of damage to PVC piping, to prevent simultaneous two-pump operation in the bio-lab system in accordance with Procedure AD1.ID1, Nuclear Generation Procedure Writers Manual, was within the licensee's ability to foresee and correct, and therefore, a performance deficiency.

Screening: The inspectors determined the performance deficiency was more than minor because it was associated with the Procedure Quality attribute of the Initiating Events cornerstone and adversely affected the cornerstone objective to limit the likelihood of events that upset plant stability and challenge critical safety functions during shutdown as well as power operations. Specifically, on February 7, 2022, the licensee failed to provide written instructions with enough detail that the swapping of bio-lab line pumps could be done without placing the system in two-pump operation. Subsequently, on March 10, 2023, bio-lab line 0-1 failed due to the hydraulic loading of the line while in two-pump operation. The failure of bio-lab line 0-1 resulted in the flooding of circulating water pump 2-2, the tripping of circulating water pump 2-2, and reducing plant power to approximately 50 percent power.

Significance: The inspectors assessed the significance of the finding using IMC 0609, Appendix A, The Significance Determination Process (SDP) for Findings At-Power. Using Exhibit 1, Initiating Events Screening Questions, the finding was screened as having very low safety significance (Green) because the finding caused internal flooding that did not result in the loss of mitigation equipment relied upon to transition the plant from the onset of the flooding event to a stable shutdown condition.

Cross-Cutting Aspect: H.1 - Resources: Leaders ensure that personnel, equipment, procedures, and other resources are available and adequate to support nuclear safety.

Specifically, licensee leaders failed to ensure eSOMS rounds guidance alerted operators to bio-lab pump switches being left in a position that could allow for simultaneous two-pump operation on the subsequent pump start.

Enforcement:

Inspectors did not identify a violation of regulatory requirements associated with this finding.

Licensee-Identified Non-Cited Violation 71152A This violation of very low safety significance was identified by the licensee and has been entered into the licensee corrective action program and is being treated as a non-cited violation, consistent with section 2.3.2 of the Enforcement Policy.

Violation: Title 10 of the Code of Federal Regulations Part 50, Appendix B, Criterion V, Instructions, Procedures, and Drawings, requires, in part, activities affecting quality shall be prescribed by documented instructions, procedures, or drawings, of a type appropriate to the circumstances and shall be accomplished in accordance with these instructions, procedures, or drawings. The licensee established Procedure CF3.ID17, "Design and Analysis Documents Prepared by External Contractors," revision 21, as the quality-related implementing procedure for reviewing and accepting third-party analyses and the licensee established Procedure CF7.ID4, "Processing of Documents Received from Suppliers,"

revision 16A, as the quality-related implementing procedure for reviewing documents from suppliers.

Contrary to the above, in 2016, the licensee did not accomplish an activity affecting quality in accordance with procedures of a type appropriate to the circumstances while reviewing a third-party analysis related to emergency diesel generators. Specifically, the licensee used station Procedure CF7.ID4, "Processing of Documents Received from Suppliers,"

revision 16A, to review an analysis prepared by a non-supplier external contractor related to special cap screws on emergency diesel generator 2-3. Using a procedure that was inappropriate to the circumstances led to the failure of station personnel to recognize the significance of consultant recommendations for embedment of special cap screws; consequently, as-found torque on special cap screws on emergency diesel generator 2-3 were found to be below the minimum allowable torque on May 24, 2022.

Significance/Severity: Green. The inspectors assessed the significance of the finding using Inspection Manual Chapter (IMC) 0609, Appendix A, "The Significance Determination Process for Findings At-Power." Using Exhibit 2, "Mitigating Systems Screening Questions,"

the inspectors determined the finding to be of very low safety significance (Green) because the emergency diesel generator maintained its probabilistic risk assessment functionality.

Corrective Action References: notification 51154489 Failure to Identify a Deficient Weld Resulting in a Degraded Reactor Coolant System Pressure Boundary Cornerstone Significance Cross-Cutting Report Aspect Section Initiating Events Green None (NPP) 71153 NCV 05000323/2023002-02 Open/Closed The inspectors reviewed a self-revealed, Green finding and associated non-cited violation of Title 10 of the Code of Federal Regulations (10 CFR) Part 50, Appendix B, Criterion IX, Control of Special Processes, when the licensee failed to identify a deficient weld in reactor coolant system pressure boundary piping during installation of a vent line in 1994. In October 2022, the licensee identified dry boric acid deposits indicating that this deficient weld had caused reactor coolant system pressure boundary leakage in the vent line connected to the Unit 2, loop 1 cold leg.

Description:

On October 23, 2022, Diablo Canyon Power Plant (DCPP) inservice inspection personnel identified evidence of a small through-wall leak on a 2-inch socket weld connecting a coupling to a vent line. The vent line, in turn, is connected to the Unit 2 reactor coolant system (RCS) loop 1 cold leg. The leak path was initially discovered during a routine refueling outage containment walkdown and was evident based on the presence of boric acid crystals located on insulation external to the defective weld. The reactor was in Mode 6 at the time of discovery, and no active leak was present while the RCS was depressurized. The licensee evaluated the as-found defect and concluded that the through-wall leakage was too small to measure.

The vent line, known as line 1140, is classified as American Society of Mechanical Engineers (ASME) Code Class 1 piping, is seismically qualified, and constitutes part of the Unit 2 RCS pressure boundary. It was added to the cold leg piping as a high point vent in 1994, and it was approved for use in post-outage RCS vacuum refill operations in 2000. The location of the leak renders it non-isolable. Upon discovery of the through-wall leak path, the licensee made a notification in accordance with 10 CFR 50.72(b)(3)(ii)(A) for an event or condition that results in the condition of the nuclear power plant, including its principal safety barriers, being seriously degraded.

The licensee noted in a causal report associated with this event that the original weld placed in 1994 should not have passed visual inspection required by ASME Boiler and Pressure Vessel Code (BPVC),Section III, due to poor surface contour and weld lag transition on the process pipe side of the socket weld. The resulting surface defect reduced the life of the associated socket weld and, when exposed to vibrations associated with expected RCS transient vibrations (e.g., RCS heatups and cooldowns), the through-wall condition was propagated.

Corrective Actions: Prior to returning line 1140 to service and Unit 2 to power operation, the licensee performed a weld repair in accordance with ASME BPVC,Section XI, Case N-666-1.

During the next Unit 2 refueling outage, the licensee intends to replace the coupled vent lines with a straight run of piping, thus eliminating the coupling and the repaired weld.

Corrective Action References: notifications 51167081 and 51168277

Performance Assessment:

Performance Deficiency: The inspectors determined that the failure in 1994 to identify a deficient weld, in accordance with qualified procedures required by 10 CFR Part 50, Appendix B, Criterion IX, Control of Special Processes, in RCS pressure boundary piping in accordance with ASME BPVC requirements was within the licensees ability to foresee and correct, and therefore, a performance deficiency.

Screening: The inspectors determined the performance deficiency was more than minor because it was associated with the Human Performance attribute of the Initiating Events cornerstone and adversely affected the cornerstone objective to limit the likelihood of events that upset plant stability and challenge critical safety functions during shutdown as well as power operations. Specifically, the licensees failure to identify the defective weld in 1994 reduced expected design life of the weld and resulted in a non-isolable, through-wall leak path in the vent line connected to the Unit 2, loop 1 cold leg.

Significance: The inspectors assessed the significance of the finding using IMC 0609, Appendix A, The Significance Determination Process (SDP) for Findings At-Power. The inspectors considered using IMC 0609, Appendix G, Shutdown Operations Significance Determination Process, dated January 8, 2020; however, the licensee determined that there was no active, ongoing leak during shutdown conditions. The identified presence of boric acid crystals external to line insulation instead suggests an active leak at operating pressures and temperatures. As such, the inspectors determined that IMC 0609, Appendix A, The Significance Determination Process for Findings At-Power, dated November 30, 2020, was more appropriate. Using the Initiating Events Screening Questions found in Exhibit 1, Section A, Loss of Coolant Accident (LOCA) Initiators, the inspectors determined that the finding screened as Green, or very low safety significance, because the finding does not result in exceeding the RCS leak rate for a small LOCA (leakage in excess of normal makeup), nor could the finding have likely affected other systems used to mitigate a LOCA (e.g., Interfacing System LOCA).

Cross-Cutting Aspect: Not Present Performance. No cross-cutting aspect was assigned to this finding because the inspectors determined the finding did not reflect present licensee performance. Specifically, the licensees failure to identify the defective weld occurred in 1994.

Enforcement:

Violation: 10 CFR Part 50, Appendix B, Criterion IX, Control of Special Processes, requires that measures shall be established to assure that special processes, including welding, heat-treating, and nondestructive testing, are controlled and accomplished by qualified personnel using qualified procedures in accordance with applicable codes, standards, specifications, criteria, and other special requirements.

Contrary to the above, in 1994, the licensee failed to ensure that welding and nondestructive testing requirements were controlled and accomplished by qualified personnel using qualified procedures in accordance with applicable codes when installing a vent line on the Unit 2, loop 1 cold leg. Specifically, the licensee identified evidence (dry boric acid deposits) of RCS pressure boundary leakage on October 23, 2022, that they specifically attributed to their previous failure to identify that an installed socket weld did not meet the applicable ASME BPVC visual acceptance criteria.

Enforcement Action: This violation is being treated as a non-cited violation, consistent with section 2.3.2 of the Enforcement Policy.

EXIT MEETINGS AND DEBRIEFS

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

On June 29, 2023, the inspectors presented the biennial requalification inspection results to Abdul Kadir, Manager, Nuclear Operations Training, and other members of the licensee staff.

On June 29, 2023, the inspectors presented the integrated inspection results to Paula A.

Gerfen, Senior Vice President, Generation and Chief Nuclear Officer, and other members of the licensee staff.

DOCUMENTS REVIEWED

Inspection Type Designation Description or Title Revision or

Procedure Date

71111.04 Corrective Action Notifications 51133201, 51145231

Documents

71111.04 Drawings 107709-3 Safety Injection System 67

71111.04 Drawings 107709-4 Safety Injection System 68

71111.04 Drawings 107723-12 Auxiliary Building: Condenser Unit Room, Cable Spreading 110

Room, 480V Switchgear Room Supply and Exhaust

71111.04 Drawings 107723-13 Auxiliary Building: 480V AC Switchgear, Battery, Inverter, and 94

Reactor Rod Drive Control Rooms

71111.04 Procedures OP H-10:I Auxiliary Building General Ventilation - Make Available and 46

Place in Service

71111.04 Procedures OP H-10:II Auxiliary Building General Ventilation - Normal Operation 10

71111.04 Procedures OP H-10:III Auxiliary Building General Ventilation - Shutdown and Clearing 20

71111.04 Procedures OP J-6B:II Diesel Generator 1-2 Make Available 45A

71111.04 Procedures OP J-6B:II-A Diesel Generator 1-2 - Alignment Checklist 1A

71111.04 Procedures OP K-10 Systems Requiring Sealed Component Checklists 47

71111.04 Procedures OP K-10A12 Sealed Component Checklist for Safety Injection Pump 2-1 4

71111.04 Procedures OP K-10A13 Sealed Component Checklist for Safety Injection Pump 2-2 4

71111.04 Procedures OP K-10K Sealed Valve Checklist for Emergency Diesel Generators 12

71111.04 Procedures OP O-35 Bumped Component Protection Program 20

71111.04 Procedures OP1.DC20 Sealed Components 20

71111.04 Procedures STP M-11A Station Battery and Pilot Cell Condition Monitoring 30

71111.05 Drawings 111805-72 Intake Structure 4

71111.05 Drawings 111805-8 Radiological Control Area (RCA) Elev. 73' 5

71111.05 Drawings 111906-16 Auxiliary Building Elev. 73' 13

71111.05 Drawings 111906-32 Intake Structure 18' 9

71111.05 Drawings 11805-49 Fire Preplan Turbine Building Elevation 85' 3

71111.05 Procedures CP M-6 Site Fire Response 44

71111.05 Procedures OP AP-34.2.7 Fire Response - Turbine Deck and Main Condenser Area 4

71111.05 Procedures TQ1.DC12 Fire Brigade and Emergency Response Training 16

71111.05 Work Orders WO 68065040

Inspection Type Designation Description or Title Revision or

Procedure Date

71111.11B Corrective Action Notifications 51139208, 51145773, 51168633 04/26/2023

Documents

71111.11B Miscellaneous PI/RIE/Procedure Revisions 0

71111.11B Miscellaneous PI/RIE/Procedure Revisions 1

71111.11B Miscellaneous Emergency Preparedness Lesson Plan 1A

71111.11B Miscellaneous OPS Human Performance DLA Lesson 0

71111.11B Miscellaneous 2023 NRC Biennial Exam Schedule 0

71111.11B Miscellaneous NRC Biennial Examination Results - Week 1 0

71111.11B Miscellaneous 2023 NRC Written Exam Package 0

71111.11B Miscellaneous 2023 NRC Operating Test Package 0

71111.11B Miscellaneous Simulator Security Checklist 21

71111.11B Miscellaneous Simulator JPM Reset Checklist 1

71111.11B Miscellaneous Simulator Setup Checklist 2

71111.11B Miscellaneous Licensed Operator Reactivation Package 2022-2023 05/17/2023

71111.11B Miscellaneous 2023 NRC Exam Overlap Tool 0

71111.11B Miscellaneous Simulator Inspection Report 04/24/2023

71111.11B Miscellaneous SRT Sub-committee Meeting Minutes 07/07/2021

71111.11B Miscellaneous SRT Meeting Minutes 07/12/2021

71111.11B Miscellaneous SRT Sub-committee Meeting Minutes 05/04/2022

71111.11B Miscellaneous SRT Meeting Minutes 06/01/2022

71111.11B Miscellaneous SRT Meeting Minutes 10/06/2021

71111.11B Miscellaneous SRT Sub-committee Meeting Minutes 09/22/2022

71111.11B Miscellaneous SRT Meeting Minutes 09/21/2022

71111.11B Miscellaneous SRT Sub-committee Meeting Minutes 01/05/2022

71111.11B Miscellaneous SRT Meeting Minutes 01/06/2022

71111.11B Miscellaneous SRT Sub-committee Meeting Minutes 12/27/2022

71111.11B Miscellaneous SRT Meeting Minutes 12/28/2022

71111.11B Miscellaneous Curriculum Review Committee Meeting Minutes Package 05/17/2023

21-2023

71111.11B Miscellaneous Open Modification Report 04/24/2023

71111.11B Miscellaneous Closed Modification Report 04/24/2023

71111.11B Miscellaneous Diablo Canyon 2022 Operating Tests

71111.11B Miscellaneous Licensed Watch Report (1/1/23 to 6/7/23) 06/07/2023

Inspection Type Designation Description or Title Revision or

Procedure Date

71111.11B Miscellaneous 24 NDR 1C24 Core Physics Testing 07/26/2022

71111.11B Miscellaneous 24 NDR Rod Worth Test 03/29/2022

71111.11B Miscellaneous 51106561 Licensed Operator Continuing Training Self-Assessment 09/14/2021

71111.11B Miscellaneous 51181059 Pre-Inspection Self-Assessment Report for NRC 71111.11 02/28/2023

71111.11B Miscellaneous SAPN- TQ2.DC Procedural Non-compliance 06/29/2022

51157434

71111.11B Miscellaneous SAPN-51134539 Training Gaps on Polisher Alarm 01/28/2022

71111.11B Miscellaneous SAPN-51157468 SRO Biennial Exam Grading Error 09/01/2022

71111.11B Miscellaneous SAPN-51157469 TQ-2 Non-compliance 09/01/20222

71111.11B Miscellaneous SAPN-51158988 LOCT Lesson Guide References 06/29/2022

71111.11B Miscellaneous STP R-30 Reload Cycle Initial Criticality 04/21/2022

71111.11B Miscellaneous STP R-6 Low Power Reload Physics Tests 03/29/2021

71111.11B Miscellaneous STP R-7A Determination of Moderator Temperature Coefficient at HZP, 04/18/2022

BOL

71111.11B Miscellaneous TQ2.ID4 Training Program Implementation 55

71111.11B Procedures CF2.DC1 Configuration Management Plan for the Operator Training 13

Simulator

71111.11B Procedures OM14.ID2 Medical Examinations 12

71111.11B Procedures OP1.DC10 Conduct of Operations 67

71111.11B Procedures TQ1.DC28 Simulator Testing 5A

71111.11B Procedures TQ2.DC15 Licensed Operator Annual/Biennial Exam Development and 15

Administration

71111.11B Procedures TQ2.DC3 Licensed Operator Continuing Training Program 35

71111.11B Procedures TQ2.ID4 Training Program Implementation 55

71111.11B Procedures TQ2.ID9 Conduct of Training 22

71111.13 Corrective Action Notifications 50041375, 51190387

Documents

71111.13 Procedures OP C-3:III Main Unit Turbine - At-Power Operations 45

71111.13 Procedures OP J-6B:IX Diesel Generator Extended On-Line Maintenance 13

71111.13 Procedures STP M-9G Diesel Generator 24 Hour Load Test and Hot Restart Test 59B

71111.13 Radiation Work STP M-21D Main Turbine/Generator Lube Oil Functional Tests 20

Permits (RWPs)

71111.13 Work Orders WO 60152795

Inspection Type Designation Description or Title Revision or

Procedure Date

71111.15 Corrective Action Notifications 50798440, 51177676, 51186721, 51186966, 51189476,

Documents 51189483, 51189562, 51189631, 51192903, 50333862

71111.15 Drawings 437666-1 Unit 1 Electrical Schematic Diagram 4KV Diesel Generators 31

and Associated Circuit Breakers

71111.15 Drawings 438203-1 Containment Structure 8

71111.15 Drawings 498050-1 Solid State Protection System Power Range Trip Logic Train A 5

&B

71111.15 Procedures AR PK18-11 Diesel Gen 13 Neg Seq 6A

71111.15 Procedures MP E-60.1DEG13 Circuit Function Test - Emergency Diesel Generator 13 5

Protection Scheme

71111.15 Procedures OM7.ID12 Operability Determinations 44

71111.15 Procedures STP I-37-N42.B Power Range N42 Channel Calibration 18

71111.15 Procedures STP I-38-B.1 SSPS Train B Actuation Logic Test in Modes 1, 2, 3, or 4 15

71111.24 Corrective Action Notifications 51118041, 51193684

Documents

71111.24 Procedures MP E-57.10C Generic 4kV Motor Preventive Maintenance 9

71111.24 Procedures MP E-57.14A PI and Hipot Testing 32

71111.24 Procedures MP M-17.9 Auxiliary Salt Water Pump Maintenance 37

71111.24 Procedures NUCON Airflow Capacity and Distribution Test 7

Procedure 12-101

71111.24 Procedures NUCON Envelope Leakage Testing and Characterization using the 3

Procedure 12-366 Constant Injection Test Method

71111.24 Procedures OP H-10:II Auxiliary Building General Ventilation - Normal Operation 10

71111.24 Procedures OP J-6A:IV-F 4160 Volt Bus F Breaker Code Orders 9

71111.24 Procedures STP M-39A2 Routine Test of Diesel Generator 1-2 or 2-2 Room CO2 Fire 26A

System Operation

71111.24 Procedures STP M-57 Control Room Ventilation System Tracer Gas Test 12

71111.24 Procedures STP P-AFW-13 Routine Surveillance Test of Motor-Driven Auxiliary Feedwater 18

Pump 1-3

71111.24 Procedures STP P-ASW-12 Routine Surveillance Test of Auxiliary Saltwater Pump 1-2 31A

71111.24 Procedures STP P-ASW-A11 Comprehensive Test of Auxiliary Saltwater Pump 1-1 13B

71111.24 Procedures STP V-2U3D Exercising SG 1-3 AFW Supply Valves LCV-108 and LVC-115 14

71111.24 Procedures STP V-2U4D Exercising SG 1-4 AFW Supply Valves LCV-109 and LCV-113 15

Inspection Type Designation Description or Title Revision or

Procedure Date

71111.24 Procedures STP V-3R1 Exercising 10% Atmospheric Dump Valves PCV-19, 20, 21, 22 58

and Isolation Valves

71111.24 Work Orders WO 64194665, 64247074, 64261387, 64270307, 64270510,

283396, 64286621

71151 Corrective Action Notifications 51152921, 51152923, 51152924, 51154349, 51154402,

Documents 51154663, 51159015, 51160630, 51160767, 51162005,

51162159, 51162350, 51163955, 51164822, 51167184,

51167847, 51177405, 51179159, 51179933, 51181127,

51181314, 51181727, 51182340, 51184281, 51184975,

51185484, 51185836

71151 Miscellaneous MSPI Derivation Report: Unit 1 Emergency AC Power System 04/24/2023

Unavailability Index (UAI)

71151 Miscellaneous MSPI Derivation Report: Unit 1 Emergency AC Power System 04/24/2023

Unreliability Index (URI)

71151 Miscellaneous MSPI Derivation Report: Unit 2 Emergency AC Power System 04/24/2023

Unavailability Index (UAI)

71151 Miscellaneous MSPI Derivation Report: Unit 2 Emergency AC Power System 04/24/2023

Unreliability Index (URI)

71151 Miscellaneous MSPI Derivation Report: Unit 1 High Pressure Injection 04/24/2023

System Unavailability Index (UAI)

71151 Miscellaneous MSPI Derivation Report: Unit 1 High Pressure Injection 04/24/2023

System Unreliability Index (URI)

71151 Miscellaneous MSPI Derivation Report: Unit 2 High Pressure Injection 04/24/2023

System Unavailability Index (UAI)

71151 Miscellaneous MSPI Derivation Report: Unit 2 High Pressure Injection 04/24/2023

System Unreliability Index (URI)

71152A Corrective Action Notifications 51154402, 51154489

Documents

71152A Miscellaneous 0322-0041-RPT- Estimation of Minimum Installation Torque for DEG Fuel Pump 0

001 Inlet to Fuel Header Cap Screws

71152A Miscellaneous 0322-0052-RPT- Evaluation of DCPP DEG Fuel Header Special Cap Screw 0

001 Loss of Preload

71152A Miscellaneous 8000004815 Replacement Part Evaluation (RPE) 08/07/2014

Inspection Type Designation Description or Title Revision or

Procedure Date

71152A Procedures CF3.ID17 Design and Analysis Documents Prepared by External 21

Contractors

71152A Procedures CF7.ID4 Processing of Documents Received from Suppliers 16A

71152A Procedures EOP E-0 Reactor Trip or Safety Injection 45D

71152A Procedures OP O-19 Nuclear Operator Actions Following a Reactor Trip 42

71152A Work Orders WO 60145142

71152S Corrective Action Notifications 51193375, 51178249, 51184859, 51187810, 51193424,

Documents 51194324

71153 Corrective Action Notifications 51167081, 51168277

Documents

71153 Miscellaneous Root Cause Evaluation Report - Through-wall Weld Defect on 0

Unit 2 Line 1140

71153 Miscellaneous LER 2022-001-00 Unit 2 Reactor Coolant System Pressure Boundary 0

Degradation

19