IR 05000275/2025004
| ML26021A192 | |
| Person / Time | |
|---|---|
| Site: | Diablo Canyon  |
| Issue date: | 01/28/2026 |
| From: | Ami Agrawal NRC/RGN-IV/DORS/PBB |
| To: | Gerfen P Pacific Gas & Electric Co |
| References | |
| IR 2025004 | |
| Download: ML26021A192 (0) | |
Text
January 28, 2026
SUBJECT:
DIABLO CANYON POWER PLANT, UNITS 1 AND 2 - INTEGRATED INSPECTION REPORT 05000275/2025004 AND 05000323/2025004
Dear Paula A. Gerfen:
On December 31, 2025, the U.S. Nuclear Regulatory Commission (NRC) completed an inspection at Diablo Canyon Power Plant, Units 1 and 2. On January 15, 2026, the NRC inspectors discussed the results of this inspection with Adam Peck, Site Vice President, and other members of your staff. The results of this inspection are documented in the enclosed report.
One finding of very low safety significance (Green) is documented in this report. This finding 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.
If you contest the violation or the significance of the violation 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 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, Ami N. Agrawal, Chief Reactor Projects Branch B Division of Operating 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:
Report Numbers:
05000275/2025004 and 05000323/2025004
Enterprise Identifier:
I-2025-004-0011
Licensee:
Pacific Gas and Electric Company
Facility:
Diablo Canyon Power Plant, Units 1 and 2
Location:
Avila Beach, CA
Inspection Dates:
October 1, 2025, to December 31, 2025
Inspectors:
J. Drake, Senior Reactor Inspector
E. Garcia, Resident Inspector
M. Hayes, Senior Resident Inspector
E. Lantz, Senior Resident Inspector
Approved By:
Ami N. Agrawal, Chief
Reactor Projects Branch B
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.
List of Findings and Violations
Failure to Correctly Plan Work to Avoid Unnecessary Emergency Diesel Generator Inoperability Cornerstone Significance Cross-Cutting Aspect Report Section Mitigating Systems Green NCV 05000323/2025004-01 Open/Closed
[H.1] -
Resources 71111.24 The inspectors reviewed a self-revealed Green finding and associated non-cited violation of Technical Specification 5.4.1.a associated with the licensees failure to follow the work planning guidance contained in Procedure AD7.DC8, Work Planning, Revision 61.
Specifically, the licensee failed to isolate an electrical circuit which resulted in unexpectedly declaring diesel generator 2-3 inoperable during maintenance.
Additional Tracking Items
None.
PLANT STATUS
Unit 1 operated at or near rated thermal power for the entire inspection period, except for shutting down the unit to repair a feedwater heater tube leak from December 16 through 19, 2025.
Unit 2 began the inspection period at rated thermal power. On October 5, 2025, the unit was shut down to enter refueling outage 25. On November 4, 2025, the unit began a controlled power ascension to rated power after completing refueling outage 25. The unit reached full power on November 7, 2025. The unit remained at or near rated thermal power for the remainder of the 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) (2 Samples)
The inspectors evaluated system configurations during partial walkdowns of the following systems/trains:
- (1) Unit 2 spent fuel pool gravity makeup from refueling water storage tank during core offload on October 14, 2025
- (2) Unit 1 component cooling water pump 1-3 on December 11, 2025
Complete Walkdown Sample (IP Section 03.02) (1 Sample)
- (1) The inspectors evaluated system configurations during a complete walkdown of the Unit 2 high head safety injection system on October 30, 2025.
71111.05 - Fire Protection
Fire Area Walkdown and Inspection Sample (IP Section 03.01) (3 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) Unit 2 containment 117-foot elevation on October 16, 2025
- (2) Unit 2 containment 91-foot elevation on October 16, 2025
- (3) Unit 2 containment 140-foot elevation on October 31, 2025
71111.07A - Heat Exchanger/Sink Performance
Annual Review (IP Section 03.01) (1 Sample)
The inspectors evaluated readiness and performance of:
- (1) Units 1 and 2 component cooling water testing on November 17, 2025 71111.08P - Inservice Inspection Activities (PWR)
Due to the government shutdown, this inspection was completed remotely via in office document review from December 5 to 12, 2025. The inspectors verified that the reactor coolant system boundary, reactor vessel internals, risk-significant piping system boundaries, and containment boundary are appropriately monitored for degradation and that repairs and replacements were appropriately fabricated, examined and accepted by reviewing documents associated with the following activities in Unit 2 during refueling outage 2R25.
PWR Inservice Inspection Activities Sample - Nondestructive Examination and Welding
Activities (IP Section 03.01) (1 Sample)
The inspectors verified that the following nondestructive examination and welding activities were performed appropriately:
- (1) Ultrasonic Examination
- pressurizer, weld girth 1
- charging, WIB-858K, socket weld
- component cooling water, 25-VI, 25-IV, lug welds and baseplate
- reactor coolant, WIB-435, Line 16-14 SPL, pipe to elbow Dye Penetrant Examination
- charging, WIB-858K, socket weld Visual 1 Examination
- reactor coolant, reactor coolant pump seal house bolts, 12
- component cooling water, 25-VI, 25-IV, lug welds PWR Inservice Inspection Activities Sample - Vessel Upper Head Penetration Inspection Activities (IP Section 03.02)
No ASME Code inspection of vessel upper head penetration was required this outage.
PWR Inservice Inspection Activities Sample - Boric Acid Corrosion Control Inspection Activities (IP Section 03.03) (1 Sample)
The inspectors verified the licensee is managing the boric acid corrosion control program through a review of the following evaluations:
(1)
- 51262879, chemical and volume control, CVCS-2-195 body-to-bonnet
- 51272594, chemical and volume control, welded joint above CVCS-2-8514
- 51276814, spent fuel, SFS-2-75 Bonnet Bolts
- 51262410, chemical and volume control, CVCS-2-273 pipe cap
- 51277473, safety injection, accumulator 2-3 outlet weld PWR Inservice Inspection Activities Sample - Steam Generator Tube Inspection Activities (Section 03.04)
No ASME Code inspection of the steam generator tubes was required this outage.
71111.11Q - Licensed Operator Requalification Program and Licensed Operator Performance
Licensed Operator Performance in the Actual Plant/Main Control Room (IP Section 03.01) (1 Sample)
- (1) The inspectors observed and evaluated licensed operator performance in the control room during Unit 2 shutdown activities during the start of refueling outage 2R25 on October 4, 2025.
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 November 19, 2025.
71111.12 - Maintenance Effectiveness
Maintenance Effectiveness (IP Section 03.01) (2 Samples)
The inspectors evaluated the effectiveness of maintenance to ensure the following structures, systems, and components (SSCs) remain capable of performing their intended function:
- (1) Emergency diesel generator governors on October 29, 2025
- (2) Unit 2 chemical and volume control system check valves on December 1, 2025
71111.13 - Maintenance Risk Assessments and Emergent Work Control
Risk Assessment and Management Sample (IP Section 03.01) (2 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 Yellow shutdown outage risk during lowered inventory with a single source of offsite power available on October 8, 2025
- (2) Unit 1 feedwater heater 1-5C emergent tube leak repair on December 17, 2025
71111.15 - Operability Determinations and Functionality Assessments
Operability Determination or Functionality Assessment (IP Section 03.01) (1 Sample)
The inspectors evaluated the licensee's justifications and actions associated with the following operability determinations and functionality assessments:
- (1) Unit 2 blown fuse during component cooling water pump 2-1 recirculation valve relay replacement causing emergency diesel generator 2-3 inoperability on November 13, 2025
71111.20 - Refueling and Other Outage Activities
Refueling/Other Outage Sample (IP Section 03.01) (1 Sample)
- (1) The inspectors evaluated Unit 2 refueling outage 2R25 activities from October 5, 2025, to November 5, 2025.
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) (5 Samples)
- (1) Unit 2 source range detector replacements on October 6, 2025
- (2) Unit 2 component cooling water pump 2-1 recirculation valve relay replacement on November 12, 2025
- (3) Unit 1 auxiliary building 480 V switchgear supply fan S-44 maintenance on November 17, 2025
- (4) Unit 2 battery charger 221 two-year periodic maintenance on November 18, 2025
- (5) Unit 1 safety injection pump 1-1 following 8-year coupling maintenance on December 3, 2025
Surveillance Testing (IP Section 03.01) (2 Samples)
- (1) Unit 2 emergency diesel generator outage testing on October 5, 2025
- (2) Unit 2 auxiliary saltwater pump 2-2 testing on December 8, 2025
Containment Isolation Valve (CIV) Testing (IP Section 03.01) (2 Samples)
- (1) Unit 2 containment isolation valve testing on October 16, 2025
- (2) Unit 1 containment isolation valve testing on December 16, 2025
OTHER ACTIVITIES - BASELINE
71151 - Performance Indicator Verification The inspectors verified licensee performance indicators submittals listed below:
BI01: Reactor Coolant System (RCS) Specific Activity Sample (IP Section 02.10) (2 Samples)
- (1) Unit 1 (October 1, 2024, through September 30, 2025)
- (2) Unit 2 (October 1, 2024, through September 30, 2025)
BI02: RCS Leak Rate Sample (IP Section 02.11) (2 Samples)
- (1) Unit 1 (October 1, 2024, through September 30, 2025)
- (2) Unit 2 (October 1, 2024, through September 30, 2025)71152A - Annual Follow-up Problem Identification and Resolution
Annual Follow-up of Selected Issues (Section 03.03) (2 Samples)
The inspectors reviewed the licensees implementation of its corrective action program related to the following issues:
- (1) Emergency diesel generator 2-2 jacket water pump replacement frequency overdue on November 7, 2025
- (2) Unit 1 feedwater heater 1-5C high level causing a shutdown for repairs on December 15, 2025
71152S - Semiannual Trend Problem Identification and Resolution Semiannual Trend Review (Section 03.02) (1 Sample)
- (1) The inspectors reviewed the licensees corrective action program to identify potential trends in water intrusion during heavy rains that might be indicative of a more significant safety issue.
INSPECTION RESULTS
Failure to Correctly Plan Work to Avoid Unnecessary Emergency Diesel Generator Inoperability Cornerstone Significance Cross-Cutting Aspect Report Section Mitigating Systems Green NCV 05000323/2025004-01 Open/Closed
[H.1] -
Resources 71111.24 The inspectors reviewed a self-revealed Green finding and associated non-cited violation of Technical Specification 5.4.1.a associated with the licensees failure to follow the work planning guidance contained in Procedure AD7.DC8, Work Planning, Revision 61.
Specifically, the licensee failed to isolate an electrical circuit which resulted in unexpectedly declaring diesel generator 2-3 inoperable during maintenance.
Description:
On September 29, 2025, Unit 2 experienced a spurious opening of component cooling water pump 2-1 recirculation valve FCV-606. FCV-606 provides pump protection to component cooling water (CCW) pump 2-1 during low flow conditions. At the time of the valve opening CCW pump 2-1 was operating normally. Operations personnel were dispatched to attempt to close FCV-606 from its local control handswitch. Personnel were able to get FCV-606 closed while holding the control switch in the closed position, but the valve would reopen sometime after releasing the handswitch. The valve remained open until October 24, 2025, when the valve was shut by operations. After investigation, plant personnel made the decision to calibrate relay 37HF12.
On November 11, 2025, maintenance personnel removed and attempted to calibrate relay 37HF12. During the calibration personnel had trouble getting the relay into tolerance and a decision was made to reinstall the removed relay and attempt to recalibrate the relay the next day. During reinstallation plant personnel inadvertently contacted an incorrect termination point and blew two fuses, UY-01 and UA, in the circuit. The termination points were partially taped for electrical isolation, but this was not sufficient to isolate the circuit during inadvertent contact between two wires. When the fuses blew operations lost white potential light indication for all components associated with electrical bus F. Operations still had open/close light indication for bus F and did not receive any undervoltage component starts on bus F. Operations performed an operability assessment and determined overall safety function was not affected because they believed undervoltage bus protection was still maintained. During the operability assessment operators referred to a similar failure in a prior notification on bus G.
On November 12, 2025, the residents reviewed the notification associated with the blown fuse, SAPN 51311497, and the previous occurrence of blown fuses in a similar circuit on safety bus G. This notification, SAPN 50543217, initially stated diesel generator operation was not impacted with this condition, but in a later task stated the diesel generator would not auto sequence emergency loads onto the bus during a loss of power from the normal source.
This was due to the failure keeping a load shed signal in on all motor loads associated with bus G. The inspectors presented the results of SAPN 50543217 to operations and engineering management for evaluation. After investigation operations declared diesel generator 2-3 inoperable.
Corrective Actions: Maintenance replaced the blown fuses and replaced relay 37HF12 and returned FCV-606 to service.
Corrective Action References: Notifications 51311497, 51311564, and 50543217
Performance Assessment:
Performance Deficiency: The failure to isolate electrical circuits while performing relay calibration to prevent unintended equipment actuations was a performance deficiency.
Screening: The inspectors determined the performance deficiency was more than minor because it was associated with the Equipment Performance attribute of the Mitigating Systems cornerstone and adversely affected the cornerstone objective to ensure the availability, reliability, and capability of systems that respond to initiating events to prevent undesirable consequences. Specifically, the failure to isolate the circuit electrically caused an unanticipated inoperability of emergency diesel generator 2-3 when maintenance workers landed a wire associated with maintenance on relay 37HF12.
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 2, Mitigating Systems Screening Questions, the finding screened as having very low safety significance (Green) because the finding did not affect the design or qualification of a mitigating SSC, did not represent a loss of the probabilistic risk assessment (PRA) function of a single train technical specification system for greater than its technical specification allowed outage time, did not represent a loss of the PRA function of one train of a multi-train technical specification system for greater than its technical specification allowed outage time, did not represent a loss of the PRA function of two separate technical specification systems for greater than 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />, did not represent a loss of a PRA system or function as defined in the plant risk information book (PRIB) or the licensees PRA for greater than 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />, and did not represent a loss of the PRA function of one or more non-technical specification trains of equipment designated as risk-significant in accordance with the licensees maintenance rule program for greater than 3 days.
Cross-Cutting Aspect: H.1 - Resources: Leaders ensure that personnel, equipment, procedures, and other resources are available and adequate to support nuclear safety.
Specifically, the licensee failed to adequately update the clearance package to electrically isolate the system prior to performing maintenance.
Enforcement:
Violation: Technical Specification 5.4.1.a, requires, in part, written procedures shall be maintained covering the applicable procedures recommended in Regulatory Guide 1.33, Revision 2, Appendix A, February 1978. Regulatory Guide 1.33, Revision 2, Appendix A, Section 9, states, in part, maintenance that can affect the performance of safety-related equipment should be properly pre-planned and performed in accordance with written procedures, documented instructions, or drawings appropriate to the circumstances.
AD7.DC8, Work Planning, Revision 61, step 8.8.1.a, states in part, when performing maintenance on electrical equipment, the equipment shall be isolated to prevent any unintended equipment actuations.
Contrary to the above, on November 11, 2025, the licensee failed to properly perform maintenance on safety-related electrical equipment. Specifically, the licensee failed to isolate the circuit associated with relay 37HF12, while performing relay calibrations, to prevent the unintended fuse clearing of fuses UY-01 and UA when landing electrical wires which resulted in the inoperability of diesel generator 2-3.
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 December 22, 2025, the inspectors presented the Unit 2 inservice inspection results to Blair Jones, Vice President Business and Technical Services, and other members of the licensee staff.
- On January 15, 2026, the inspectors presented the integrated inspection results to Adam Peck, Site Vice President, and other members of the licensee staff.
DOCUMENTS REVIEWED
Inspection
Procedure
Type
Designation
Description or Title
Revision or
Date
106714-2
Component Cooling Water
106718-10
Units 1 & 2 Inside Auxiliary Building
203
107707-2
107708-2
Chemical Volume and Control System
27
107708-5
Chemical Volume and Control System
135
107709-2
Safety Injection
Drawings
107709-3
Safety Injection
AD8.DC55
SFP Gravity Makeup Valve Reference List
OP AP-22
Spent Fuel Pool Abnormalities
Procedures
OP B-3A:II
Safety Injection System Alignment Verification for Plant
Startup
111805-42
Containment Building Elev. 117'
111906-29
Containment Building Elev. 91'
111906-30
Containment Building Elev. 117'
Drawings
111906-31
Containment Building Elev. 140'
Corrective Action
Documents
Notifications
51109260, 51144943, 51201059, 51225507
MA1.ID20
Testing/Inspections for Aux Saltwater System NRC Generic Letter 89-13 Compliance
PEP M-234
CCW Heat Exchanger Performance Test
20, 21, 22
Procedures
STP M-26A
FCV-601, ASW Unit 1 and 2 Cross-Tie Dividing Valve, Flow
Test
50601807
Quick HIT Self-Assessment for Reactor Coolant System
Materials Degradation Management Program (RCS MDMP)
and Steam Generator Management Program (SGMP)
11/06/2013
51057867
ASMP SAQH Weld Program QHSA
07/20/2021
Miscellaneous
51067384
DCPP Inservice Inspection Program 2020 Formal Self-
Assessment
06/25/ 2020
AD4.ID2
Plant Leakage Evaluation
ER1.ID2
Boric Acid Corrosion Control Program
Procedures
ISI X 2
Visual Inspection of Reactor Upper Internals and Fuel
Assembly Guide Pins
2A
Inspection
Procedure
Type
Designation
Description or Title
Revision or
Date
ISI X-101
Reactor Coolant System Pressure Boundary Pressure Test
(Portions of ASME Class 1 and 2 Requiring Operator
Assistance)
MA3
Special Processes
3A
Visual Examination During Section XI System Pressure Test
STP R-8C
Containment Walkdown for Evidence of Boric Acid Leakage
13A
WDI-STD-088
Underwater Remote Visual Examination of Reactor Vessel
Internals
WDI-STD-1 013
(PDI-ISI-254-SE-
NB)
Remote In Service Inspection of Reactor Vessel Nozzle to
Safe End, Nozzle to Pipe and Safe End to Pipe Welds Using
the Nozzle Scanner
WDI-STD-146
ET Examination of Reactor Vessel Pipe Welds Inside
Surface
Procedures
OP L-4
Unit 2, Normal Operation at Power
Corrective Action
Documents
Notifications
51307931, 51308323
MP M-21.8
Diesel Engine Governor Actuator Maintenance
Procedures
STP M-21-SCH
Diesel Engine Inspections - General Procedure
Corrective Action
Documents
Notifications
51156419, 51315323
Miscellaneous
2R25 Outage Safety Plan
AD8.DC51
Outage Safety Management Control of Off-Site Power
Supplies to Vital Buses
AR PK10-16
FDWTR HTRS LEVEL HI
OP C-7:IV
Condensate System - Feedwater Heaters Remove from
Service
Procedures
OP O-36
Protected Equipment Postings
33A
Corrective Action
Documents
Notifications
50543217, 51311497
Miscellaneous
2R25 Outage Safety Plan
OP L-0
Mode Transition Checklists
OP L-1
Unit 2, Plant Heatup from Hot Shutdown to Hot Standby
OP L-2
Hot Standby to Startup Mode
Procedures
OP L-3
Secondary Plant Startup
Inspection
Procedure
Type
Designation
Description or Title
Revision or
Date
OP L-5
Plant Cooldown from Minimum Load to Cold Shutdown
100
OP L-6
Cold Shutdown/Refueling
Corrective Action
Documents
Notifications
287579, 51287740, 51287754, 51311497, 51311564
MP I-2.32-1
Source/Intermediate Range Detector Replacement
STP I-37-N31.A
Source Range N31 Channel Operational Test
STP I-37-N31.B
Source Range N31 Channel Calibration
STP I-37-N32.A
Source Range N32 Channel Operational Test
STP I-37-N32.B
Source Range N32 Channel Calibration
STP I-4B4
Determination of Source Range Detector Characteristic
Curves
STP M-13F
4kV Bus F Non-SI Auto-Transfer Test
STP M-13G
4kV Bus G Non-SI Auto-Transfer Test
64A
STP M-13H
4kV Bus H Non-SI Auto-Transfer Test
STP M-15
Integrated Test of Engineered Safeguards and Diesel
Generators
STP M-8D
Combined Type B and C Leakage Evaluation
Procedures
STP V-600
Valve and Penetration Leakage Summary
Work Orders
WO 60174540, 60174543, 60177645, 64158439, 64198967,
246354, 64258830, 64258831, 64262446, 64306434
Corrective Action
Documents
Notifications
51133450, 51300035, 51315323
MP M-21.5
Diesel Engine Water Pump Replacement
STP M-21-ENG.4
Diesel Engine Generator Inspection (Every Fourth Refueling
Outage)
Procedures
STP M-21-ENG.8
Diesel Engine Generator Inspection (Every Eighth Refueling
Outage)
5A
Corrective Action
Documents
Notifications
50573202
Work Orders