IR 05000275/2023002
| 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, 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:
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
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 Aspect Report Section Initiating Events Green FIN 05000323,05000275/2023002-01 Open/Closed
[H.1] -
Resources 71152A 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 Aspect Report Section Initiating Events Green NCV 05000323/2023002-02 Open/Closed None (NPP)71153 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 System Pressure Boundary Degradation 71153 Closed
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.
REACTOR SAFETY
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) (6 Samples)
- (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 Aspect Report Section Initiating Events Green FIN 05000323,05000275/2023002-01 Open/Closed
[H.1] -
Resources 71152A 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 Aspect Report Section Initiating Events Green NCV 05000323/2023002-02 Open/Closed None (NPP)71153 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
Procedure
Type
Designation
Description or Title
Revision or
Date
Corrective Action
Documents
Notifications
51133201, 51145231
Drawings
107709-3
Safety Injection System
Drawings
107709-4
Safety Injection System
Drawings
107723-12
Auxiliary Building: Condenser Unit Room, Cable Spreading
Room, 480V Switchgear Room Supply and Exhaust
110
Drawings
107723-13
Auxiliary Building: 480V AC Switchgear, Battery, Inverter, and
Reactor Rod Drive Control Rooms
Procedures
OP H-10:I
Auxiliary Building General Ventilation - Make Available and
Place in Service
Procedures
OP H-10:II
Auxiliary Building General Ventilation - Normal Operation
Procedures
OP H-10:III
Auxiliary Building General Ventilation - Shutdown and Clearing
Procedures
OP J-6B:II
Diesel Generator 1-2 Make Available
45A
Procedures
OP J-6B:II-A
Diesel Generator 1-2 - Alignment Checklist
1A
Procedures
OP K-10
Systems Requiring Sealed Component Checklists
Procedures
OP K-10A12
Sealed Component Checklist for Safety Injection Pump 2-1
Procedures
OP K-10A13
Sealed Component Checklist for Safety Injection Pump 2-2
Procedures
OP K-10K
Sealed Valve Checklist for Emergency Diesel Generators
Procedures
OP O-35
Bumped Component Protection Program
Procedures
OP1.DC20
Sealed Components
Procedures
STP M-11A
Station Battery and Pilot Cell Condition Monitoring
Drawings
111805-72
Intake Structure
Drawings
111805-8
Radiological Control Area (RCA) Elev. 73'
Drawings
111906-16
Auxiliary Building Elev. 73'
Drawings
111906-32
Intake Structure 18'
Drawings
11805-49
Fire Preplan Turbine Building Elevation 85'
Procedures
CP M-6
Site Fire Response
Procedures
OP AP-34.2.7
Fire Response - Turbine Deck and Main Condenser Area
Procedures
TQ1.DC12
Fire Brigade and Emergency Response Training
Work Orders
Inspection
Procedure
Type
Designation
Description or Title
Revision or
Date
Corrective Action
Documents
Notifications
51139208, 51145773, 51168633
04/26/2023
Miscellaneous
PI/RIE/Procedure Revisions
Miscellaneous
PI/RIE/Procedure Revisions
Miscellaneous
Emergency Preparedness Lesson Plan
1A
Miscellaneous
OPS Human Performance DLA Lesson
Miscellaneous
23 NRC Biennial Exam Schedule
Miscellaneous
NRC Biennial Examination Results - Week 1
Miscellaneous
23 NRC Written Exam Package
Miscellaneous
23 NRC Operating Test Package
Miscellaneous
Simulator Security Checklist
Miscellaneous
Simulator JPM Reset Checklist
Miscellaneous
Simulator Setup Checklist
Miscellaneous
Licensed Operator Reactivation Package 2022-2023
05/17/2023
Miscellaneous
23 NRC Exam Overlap Tool
Miscellaneous
Simulator Inspection Report
04/24/2023
Miscellaneous
SRT Sub-committee Meeting Minutes
07/07/2021
Miscellaneous
SRT Meeting Minutes
07/12/2021
Miscellaneous
SRT Sub-committee Meeting Minutes
05/04/2022
Miscellaneous
SRT Meeting Minutes
06/01/2022
Miscellaneous
SRT Meeting Minutes
10/06/2021
Miscellaneous
SRT Sub-committee Meeting Minutes
09/22/2022
Miscellaneous
SRT Meeting Minutes
09/21/2022
Miscellaneous
SRT Sub-committee Meeting Minutes
01/05/2022
Miscellaneous
SRT Meeting Minutes
01/06/2022
Miscellaneous
SRT Sub-committee Meeting Minutes
2/27/2022
Miscellaneous
SRT Meeting Minutes
2/28/2022
Miscellaneous
Curriculum Review Committee Meeting Minutes Package
21-2023
05/17/2023
Miscellaneous
Open Modification Report
04/24/2023
Miscellaneous
Closed Modification Report
04/24/2023
Miscellaneous
Diablo Canyon 2022 Operating Tests
Miscellaneous
Licensed Watch Report (1/1/23 to 6/7/23)
06/07/2023
Inspection
Procedure
Type
Designation
Description or Title
Revision or
Date
Miscellaneous
NDR
1C24 Core Physics Testing
07/26/2022
Miscellaneous
NDR
Rod Worth Test
03/29/2022
Miscellaneous
51106561
Licensed Operator Continuing Training Self-Assessment
09/14/2021
Miscellaneous
51181059
Pre-Inspection Self-Assessment Report for NRC 71111.11
2/28/2023
Miscellaneous
SAPN-
51157434
TQ2.DC Procedural Non-compliance
06/29/2022
Miscellaneous
SAPN-51134539
Training Gaps on Polisher Alarm
01/28/2022
Miscellaneous
SAPN-51157468
SRO Biennial Exam Grading Error
09/01/2022
Miscellaneous
SAPN-51157469
TQ-2 Non-compliance
09/01/20222
Miscellaneous
SAPN-51158988
LOCT Lesson Guide References
06/29/2022
Miscellaneous
STP R-30
Reload Cycle Initial Criticality
04/21/2022
Miscellaneous
STP R-6
Low Power Reload Physics Tests
03/29/2021
Miscellaneous
STP R-7A
Determination of Moderator Temperature Coefficient at HZP,
BOL
04/18/2022
Miscellaneous
TQ2.ID4
Training Program Implementation
Procedures
CF2.DC1
Configuration Management Plan for the Operator Training
Simulator
Procedures
OM14.ID2
Medical Examinations
Procedures
OP1.DC10
Conduct of Operations
Procedures
TQ1.DC28
Simulator Testing
5A
Procedures
TQ2.DC15
Licensed Operator Annual/Biennial Exam Development and
Administration
Procedures
TQ2.DC3
Licensed Operator Continuing Training Program
Procedures
TQ2.ID4
Training Program Implementation
Procedures
TQ2.ID9
Conduct of Training
Corrective Action
Documents
Notifications
50041375, 51190387
Procedures
OP C-3:III
Main Unit Turbine - At-Power Operations
Procedures
OP J-6B:IX
Diesel Generator Extended On-Line Maintenance
Procedures
STP M-9G
Diesel Generator 24 Hour Load Test and Hot Restart Test
59B
Radiation Work
Permits (RWPs)
STP M-21D
Main Turbine/Generator Lube Oil Functional Tests
Work Orders
Inspection
Procedure
Type
Designation
Description or Title
Revision or
Date
Corrective Action
Documents
Notifications
50798440, 51177676, 51186721, 51186966, 51189476,
51189483, 51189562, 51189631, 51192903, 50333862
Drawings
437666-1
Unit 1 Electrical Schematic Diagram 4KV Diesel Generators
and Associated Circuit Breakers
Drawings
438203-1
Containment Structure
Drawings
498050-1
Solid State Protection System Power Range Trip Logic Train A
& B
Procedures
AR PK18-11
Diesel Gen 13 Neg Seq
6A
Procedures
MP E-60.1DEG13
Circuit Function Test - Emergency Diesel Generator 13
Protection Scheme
Procedures
OM7.ID12
Procedures
STP I-37-N42.B
Power Range N42 Channel Calibration
Procedures
STP I-38-B.1
SSPS Train B Actuation Logic Test in Modes 1, 2, 3, or 4
Corrective Action
Documents
Notifications
51118041, 51193684
Procedures
MP E-57.10C
Generic 4kV Motor Preventive Maintenance
Procedures
MP E-57.14A
PI and Hipot Testing
Procedures
MP M-17.9
Auxiliary Salt Water Pump Maintenance
Procedures
NUCON
Procedure 12-101
Airflow Capacity and Distribution Test
Procedures
NUCON
Procedure 12-366
Envelope Leakage Testing and Characterization using the
Constant Injection Test Method
Procedures
OP H-10:II
Auxiliary Building General Ventilation - Normal Operation
Procedures
OP J-6A:IV-F
4160 Volt Bus F Breaker Code Orders
Procedures
STP M-39A2
Routine Test of Diesel Generator 1-2 or 2-2 Room CO2 Fire
System Operation
26A
Procedures
STP M-57
Control Room Ventilation System Tracer Gas Test
Procedures
STP P-AFW-13
Routine Surveillance Test of Motor-Driven Auxiliary Feedwater
Pump 1-3
Procedures
STP P-ASW-12
Routine Surveillance Test of Auxiliary Saltwater Pump 1-2
31A
Procedures
STP P-ASW-A11
Comprehensive Test of Auxiliary Saltwater Pump 1-1
13B
Procedures
STP V-2U3D
Exercising SG 1-3 AFW Supply Valves LCV-108 and LVC-115
Procedures
STP V-2U4D
Exercising SG 1-4 AFW Supply Valves LCV-109 and LCV-113
Inspection
Procedure
Type
Designation
Description or Title
Revision or
Date
Procedures
STP V-3R1
Exercising 10% Atmospheric Dump Valves PCV-19, 20, 21, 22
and Isolation Valves
Work Orders
WO 64194665, 64247074, 64261387, 64270307, 64270510,
283396, 64286621
71151
Corrective Action
Documents
Notifications
51152921, 51152923, 51152924, 51154349, 51154402,
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
Unavailability Index (UAI)
04/24/2023
71151
Miscellaneous
MSPI Derivation Report: Unit 1 Emergency AC Power System
Unreliability Index (URI)
04/24/2023
71151
Miscellaneous
MSPI Derivation Report: Unit 2 Emergency AC Power System
Unavailability Index (UAI)
04/24/2023
71151
Miscellaneous
MSPI Derivation Report: Unit 2 Emergency AC Power System
Unreliability Index (URI)
04/24/2023
71151
Miscellaneous
MSPI Derivation Report: Unit 1 High Pressure Injection
System Unavailability Index (UAI)
04/24/2023
71151
Miscellaneous
MSPI Derivation Report: Unit 1 High Pressure Injection
System Unreliability Index (URI)
04/24/2023
71151
Miscellaneous
MSPI Derivation Report: Unit 2 High Pressure Injection
System Unavailability Index (UAI)
04/24/2023
71151
Miscellaneous
MSPI Derivation Report: Unit 2 High Pressure Injection
System Unreliability Index (URI)
04/24/2023
Corrective Action
Documents
Notifications
51154402, 51154489
Miscellaneous
22-0041-RPT-
001
Estimation of Minimum Installation Torque for DEG Fuel Pump
Inlet to Fuel Header Cap Screws
Miscellaneous
22-0052-RPT-
001
Evaluation of DCPP DEG Fuel Header Special Cap Screw
Loss of Preload
Miscellaneous
8000004815
Replacement Part Evaluation (RPE)
08/07/2014
Inspection
Procedure
Type
Designation
Description or Title
Revision or
Date
Procedures
CF3.ID17
Design and Analysis Documents Prepared by External
Contractors
Procedures
CF7.ID4
Processing of Documents Received from Suppliers
16A
Procedures
EOP E-0
Reactor Trip or Safety Injection
45D
Procedures
OP O-19
Nuclear Operator Actions Following a Reactor Trip
Work Orders
Corrective Action
Documents
Notifications
51193375, 51178249, 51184859, 51187810, 51193424,
51194324
Corrective Action
Documents
Notifications
51167081, 51168277
Miscellaneous
Root Cause Evaluation Report - Through-wall Weld Defect on
Unit 2 Line 1140
Miscellaneous
LER 2022-001-00
Unit 2 Reactor Coolant System Pressure Boundary
Degradation
0