ML25114A194
| ML25114A194 | |
| Person / Time | |
|---|---|
| Site: | Diablo Canyon  |
| Issue date: | 05/07/2025 |
| From: | Patricia Vossmar NRC/RGN-IV/DORS/PBA |
| To: | Gerfen P Pacific Gas & Electric Co |
| Bywater R | |
| References | |
| IR 2025001 | |
| Download: ML25114A194 (1) | |
Text
May 06, 2025 Paula A. Gerfen, Senior Vice President Generation and Chief Nuclear Officer Pacific Gas and Electric Company P.O. Box 56 Mail Code 104/6 Avila Beach, CA 93424
SUBJECT:
DIABLO CANYON POWER PLANT, UNITS 1 AND 2 - INTEGRATED INSPECTION REPORT 05000275/2025001 AND 05000323/2025001
Dear Paula A. Gerfen:
On March 31, 2025, the U.S. Nuclear Regulatory Commission (NRC) completed an inspection at Diablo Canyon Power Plant, Units 1 and 2. On April 10, 2025, 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.
One finding of very low safety significance (Green) is documented in this report. This finding did not involve a violation of NRC requirements.
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.
P. Gerfen 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 and 05000323 License Nos. DPR-80 and DPR-82
Enclosure:
As stated cc w/ encl: Distribution via LISTSERV Signed by Vossmar, Patricia on 05/06/25
SUNSI Review By: RLB
Non-Sensitive
Sensitive
Publicly Available
Non-Publicly Available OFFICE SRI:DORS/PBA RI:DORS/PBA SPE:DORS/PBA BC:DORS/PBA NAME MHayes EGarcia RBywater PVossmar SIGNATURE
/RA/
/RA/
/RA/
/RA/
DATE 04/28/25 05/06/25 04/24/25 05/06/25
Enclosure U.S. NUCLEAR REGULATORY COMMISSION Inspection Report Docket Numbers:
05000275 and 05000323 License Numbers:
DPR-80 and DPR-82 Report Numbers:
05000275/2025001 and 05000323/2025001 Enterprise Identifier:
I-2025-001-0015 Licensee:
Pacific Gas and Electric Company Facility:
Diablo Canyon Power Plant, Units 1 and 2 Location:
Avila Beach, CA Inspection Dates:
January 1, 2025, to March 31, 2025 Inspectors:
E. Garcia, Resident Inspector M. Hayes, Senior Resident Inspector Approved By:
Patricia J. Vossmar, Chief Reactor Projects Branch A Division of Operating Reactor Safety
2
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 Multiple Examples of Failure to Follow Procedures and Work Instructions Cornerstone Significance Cross-Cutting Aspect Report Section Initiating Events Green FIN 05000275,05000323/2025001-01 Open/Closed
[H.12] - Avoid Complacency 71111.15 The inspectors reviewed two examples of a self-revealed Green finding for the failure to follow procedures and work instructions. Specifically, a security officer failed to follow procedures inside of a radio exclusion zone in the Unit 1 pipe rack area, and maintenance personnel failed to follow work instructions when removing a sprinkler head in the Unit 2 turbine building.
Additional Tracking Items None.
3 PLANT STATUS Unit 1 operated at or near rated thermal power for the entire inspection period.
Unit 2 began the inspection period at rated thermal power. On March 10, 2025, the unit reduced power to 50 percent to support condenser cleaning. The unit returned to full power on March 15, 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 71111.01 - Adverse Weather Protection Impending Severe Weather Sample (IP Section 03.02) (1 Sample)
(1)
The inspectors evaluated the adequacy of the overall preparations to protect risk significant systems from impending severe weather with forecasted rain and high winds during an atmospheric river weather event on February 11, 2025.
71111.04 - Equipment Alignment Partial Walkdown Sample (IP Section 03.01) (3 Samples)
The inspectors evaluated system configurations during partial walkdowns of the following systems/trains:
(1)
Unit 2 control room ventilation system on January 27, 2025 (2)
Unit 1 spent fuel pool cooling on January 28, 2025 (3)
Unit 1 auxiliary saltwater pump 1-2 during planned maintenance on auxiliary saltwater pump 1-1 on March 25, 2025
4 71111.05 - Fire Protection Fire Area Walkdown and Inspection Sample (IP Section 03.01) (5 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 1 and Unit 2 Cardox system on February 4, 2025 (2)
Unit 1 and Unit 2 intake structure high-pressure CO2 fire system on February 5, 2025 (3)
Unit 1 and Unit 2 125 Vdc battery rooms on March 24, 2025 (4)
Unit 1 turbine building 119-foot elevation on March 26, 2025 (5)
Unit 1 auxiliary building ventilation fan area 115-foot elevation on March 28, 2025 Fire Brigade Drill Performance Sample (IP Section 03.02) (1 Sample)
(1)
The inspectors evaluated the onsite fire brigade training and performance during an unannounced fire drill on January 25, 2025.
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 Unit 2 licensed operator performance in the control room during an unexpected plant protection system alarm resulting in operators closing and isolating pressurizer power-operated relief valve 8000B on February 26, 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 January 28, 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 remain capable of performing their intended function:
(1) maintenance rule optimization review on January 7, 2025 (2) maintenance review of 480 V breaker contactors on March 20, 2025 71111.13 - Maintenance Risk Assessments and Emergent Work Control Risk Assessment and Management Sample (IP Section 03.01) (5 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:
5 (1)
Unit 2 risk management actions with battery charger 2-2 out of service for maintenance on January 6, 2025 (2)
Unit 1 emergency diesel generator 1-1 major outage window on January 13, 2025 (3)
Unit 1 emergent replacement of emergency diesel generator 1-1 turbocharger on January 21, 2025 (4)
Unit 1 review of risk management during planned work on multiple single point vulnerabilities on January 27, 2025 (5)
Unit 1 emergency diesel generator 1-2 major outage window on February 18, 2025 71111.15 - Operability Determinations and Functionality Assessments Operability Determination or Functionality Assessment (IP Section 03.01) (8 Samples)
The inspectors evaluated the licensee's justifications and actions associated with the following operability determinations and functionality assessments:
(1)
Unit 1 damper M-20 failure to open during weekly auxiliary building fan swaps on January 6, 2025 (2)
Unit 2 centrifugal charging pump 2-2 hot shutdown relay not responding on January 8, 2025 (3)
Unit 1 diesel generator 1-3 missing locknut on fuel rack linkage on February 18, 2025 (4)
Unit 1 momentary low steam line pressure bistable trip on February 20, 2025 (5)
Unit 2 auxiliary building ventilation fan E-1 high thermography reading on February 26, 2025 (6)
Unit 2 letdown heat exchanger room temperature switch failed on March 4, 2025 (7)
Unit 1 battery charger 132 operability determination on March 19, 2025 (8)
Unit 1 refueling water storage tank level transmitter 921 out-of-tolerance on March 25, 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 centrifugal charging pump 2-2 following planned maintenance on January 7, 2025 (2)
Unit 2 auxiliary saltwater pump 2-2 and component cooling water heat exchanger 2-2 return to service following maintenance on January 22, 2025 (3)
Unit 1 diesel generator 1-1 following major outage window on January 23, 2025 (4)
Unit 1 diesel generator 1-2 following major outage window on February 22, 2025 (5)
Unit 2 auxiliary building ventilation fan E-1 return to service after line starter replacement on February 28, 2025 Surveillance Testing (IP Section 03.01) (3 Samples)
(1)
Unit 2 routine surveillance test of containment spray pump 2-2 on February 10, 2025 (2)
Unit 1 safety injection pump 1-2 and Unit 2 auxiliary feedwater pump 2-2 testing on February 14, 2025 (3)
Unit 1 diesel generator 1-1 24-hour load test and hot restart on March 6, 2025
6 Inservice Testing (IST) (IP Section 03.01) (1 Sample)
(1)
Unit 2 auxiliary feedwater pump 2-1 on January 6, 2025 71114.06 - Drill Evaluation Required Emergency Preparedness Drill (1 Sample)
(1)
The inspectors evaluated a tabletop emergency preparedness drill on January 30, 2025.
OTHER ACTIVITIES - BASELINE 71151 - Performance Indicator Verification The inspectors verified licensee performance indicators submittals listed below:
IE01: Unplanned Scrams per 7000 Critical Hours Sample (IP Section 02.01) (2 Samples)
(1)
Unit 1 (January 1 through December 31, 2024)
(2)
Unit 2 (January 1 through December 31, 2024)
IE03: Unplanned Power Changes per 7000 Critical Hours Sample (IP Section 02.02)
(2 Samples)
(1)
Unit 1 (January 1 through December 31, 2024)
(2)
Unit 2 (January 1 through December 31, 2024)
IE04: Unplanned Scrams with Complications (USwC) Sample (IP Section 02.03) (2 Samples)
(1)
Unit 1 (January 1 through December 31, 2024)
(2)
Unit 2 (January 1 through December 31, 2024)
INSPECTION RESULTS Multiple Examples of Failure to Follow Procedures and Work Instructions Cornerstone Significance Cross-Cutting Aspect Report Section Initiating Events Green FIN 05000275,05000323/2025001-01 Open/Closed
[H.12] - Avoid Complacency 71111.15 The inspectors reviewed two examples of a self-revealed Green finding for the failure to follow procedures and work instructions. Specifically, a security officer failed to follow procedures inside of a radio exclusion zone in the Unit 1 pipe rack area, and maintenance personnel failed to follow work instructions when removing a sprinkler head in the Unit 2 turbine building.
==
Description:==
(1) On February 20, 2025, a security officer was assisting instrumentation and controls (I&C) technicians with electrical panel alarm testing located on the 85-foot elevation in the Unit 1 pipe rack area. This area is clearly posted as a radio exclusion zone and signage is present directing individuals not to transmit within the area. The pipe rack area contains transmitters that are sensitive to electromagnetic interference and are used in the engineered safety feature actuation system (ESFAS). Specifically, these transmitters, PT-525 and
7 PT-526, are used to sense the steam pressure in the main steam line for steam generator number two. In assisting the I&C technicians, the security officer was using their radio to communicate to another officer that the security alarm station would receive alarms associated with the activity. The security officer and technicians completed their testing and exited the pipe rack area several minutes later.
During the time that the testing was being performed, the Unit 1 main control room received alarms for low steam pressure on the No. 2 main steam line coincident with high steam flow in the same line and a steam line isolation bistable was tripped. This condition is indicative of a steam line pipe break and if ESFAS logic conditions are met, main steam line isolation valves would automatically close, a safety injection would be initiated, and a reactor trip would all occur. Steam generator pressure was normal and stable, and the alarms and bistable trip cleared shortly after being received. The plant processing computer data showed that pressure transmitter PT-526 had sensed steam pressure to drop below the trip setpoint of 600 psig momentarily. Pressure transmitter PT-525 also showed a pressure drop at about the same time but it did not lower to below the trip setpoint.
The station investigated the event and determined that the pressure drops seen by the plant process computer occurred at the same time the security officer was present in the pipe rack area. The station used badge keycard information, personnel statements, and plant processing computer data to verify the pressure drops seen occurred when the officer was using their radio in the vicinity of the transmitters.
Licensee Procedure OM3.ID7, Portable Radio and Cellular Phone Use, revision 9, implements the restrictions of portable radio use in radio exclusion areas. Section 5.2.1, step b. states, Portable radios shall not be used in the following areas: Outside Containment
- Pipe Rack Area - 85' through 115' Elevation (during MODES 1-4). The security officer failed to adhere to the procedure as well as the signs posted at the entrance to the pipe rack area that directed not to transmit. The officer keyed their radio while near the pressure transmitters resulting in an ESFAS bistable trip and a near reactor trip.
(2) On March 12, 2025, while Unit 2 was operating at 50 percent power, maintenance personnel were performing sprinkler head replacements in the Unit 2 turbine building. The work was scheduled to be completed on the 119-foot elevation on sprinklers associated with the south loop of the fire water system. Operations staff had hung a clearance on the south loop of the fire water system which isolated and drained the loop. Maintenance personnel inadvertently proceeded to the north loop of the fire water system and began removing a sprinkler head. During removal, personnel observed water leakage from the sprinkler head but proceeded on due to previously observing minor water seepage on previous sprinkler head removals. After fully disconnecting the fire sprinkler, water began pouring from the sprinkler head location down to the 70-foot elevation which contained the running heater drain pump for Unit 2. Operations received multiple alarms and indications of water intrusion into the heater drain pump motor. Operations shut down the pump due to the potential for water damaging the heater drain pump. To shut down the fire header leakage, operations isolated the fire water header to the north loop. Had the unit been operating at full power this event would have resulted in an approximately 30 percent power reduction.
Work Order 60157213, step 5.3.1, required personnel to locate and inspect sprinkler head locations on a marked-up version of Drawing 520257, revision 3. Work Order 60157213, step 5.3.6, required personnel to remove only the sprinkler heads designated on marked-up Drawing 520257, revision 3. Also to assist maintenance, personnel had placed correct
8 component verification (CCV) flags to indicate which sprinkler heads were to be removed.
The marked-up drawing did not have any sprinklers associated with the north loop and the sprinkler head that was removed did not have a CCV indicator flag attached to it.
The inspectors reviewed Procedure AD2.ID1, Procedure and Work Plan Use and Adherence, revision 32, step 5.1.2.b, which states, Do NOT deviate from procedures or work plans except when specifically allowed by this procedure or the document in use. The inspectors reviewed Procedure OM3.ID7, Work Order 60157213, and Procedure AD2.ID1 and did not note any allowances for deviations that were applicable to the events referenced above.
Corrective Actions: (1) The licensee updated signage in the various radio exclusion zones for both units to reinforce that transmitting in these areas is prohibited. Plant personnel were also required to check in with the work control shift foreman for a brief prior to entering any radio exclusion zone on site. (2) The licensee inspected the heater drain pump motor for damage and replaced the oil in the motor due to water intrusion into the oil. The licensee also performed a maintenance standdown with the crews involved in replacing the fire sprinklers and developed a return-to-work plan that included a full walk down of the fire sprinkler system to identify the correct sprinklers to be replaced.
Corrective Action References: Notifications 51272647, 51272742, 51273257, 51275416, 51275437, and 51275470 Performance Assessment:
Performance Deficiency: Each deviation from a procedure or work plan when not specifically allowed by Procedure AD2.ID1, Procedure and Work Plan Use and Adherence, was a performance deficiency. First, a security officer failed to follow radio exclusion procedures in a radio exclusion zone when the officer keyed their radio. Second, a maintenance worker failed to follow work instructions when they removed a sprinkler head in the north loop of the turbine building instead of the south loop.
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. First, the keying of the security radio inside the radio exclusion zone caused the trip of an ESFAS bistable and caused a second ESFAS bistable signal to lower but stay above the trip setpoint. Had both bistables tripped a main steam line isolation, safety injection, and reactor trip would have occurred. Second, the removal of the incorrect fire water sprinkler head caused the shutdown of the heater drain pump, which would have caused a 30 percent downpower had the unit been operating at full power.
Significance: The inspectors assessed the significance of the finding using IMC 0609 Appendix A, The Significance Determination Process (SDP) for Findings At-Power, Exhibit 1, Initiating Events Screening Questions, dated November 30, 2020. In each example, the finding was determined to be of very low safety significance (Green) because the finding did not cause a reactor trip and the loss of mitigation equipment relied upon to transition the plant from the onset of the trip to a stable shutdown condition.
Cross-Cutting Aspect: H.12 - Avoid Complacency: Individuals recognize and plan for the possibility of mistakes, latent issues, and inherent risk, even while expecting successful
9 outcomes. Individuals implement appropriate error reduction tools. First, the failure to follow appropriate signage was a failure to recognize the inherent risk associated with radio transmission in an exclusion zone. Second, the licensee failed to complete appropriate component verification, an error reduction tool, prior to performing work on the fire water system. The licensee also failed to stop when water began leaking from the fire water sprinkler because staff had become conditioned to observing seepage from other fire water sprinklers.
Enforcement: Inspectors did not identify a violation of regulatory requirements associated with this finding.
EXIT MEETINGS AND DEBRIEFS The inspectors verified no proprietary information was retained or documented in this report.
On April 10, 2025, 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.
THIRD PARTY REVIEWS The inspectors reviewed World Association of Nuclear Operators reports that were issued during the inspection period.
10 DOCUMENTS REVIEWED Inspection Procedure Type Designation Description or Title Revision or Date 71111.01 Procedures CP M-16 Severe Weather 24 106713-2 Spent Fuel Pool Cooling System 46 106717-7A Intake Structure for Unit 2 216 107723-16 Control Room HVAC (South) 105 Drawings 107723-18 TSC HVAC 108 OP AP-10 Loss of Auxiliary Salt Water 16 71111.04 Procedures OP E-5:I-A Unit 2, Auxiliary Saltwater - Alignment Verification Instruction Sheet 2
Corrective Action Documents Notifications 51270629 106718-11 Carbon Dioxide Fire Protection System 177 111805-14 Radiological Control Area (RCA) & H Bloc Elev 115' 4
111805-72 Intake Structure 5
111906-21 Auxiliary Building Elev 115' 17 111906-32 Fire Protection Intake Structure Elev 18' 9
Drawings 11805-54 Turbine Building Elev 119' 4
CP M-6 Site Fire Response 45 OP AP-34 Fire Response Initial Activities 2
OP E-5:I-A Unit 2, Auxiliary Saltwater - Alignment Verification Instruction Sheet 2
OP K-2B:II Low Pressure Cardox - Manual Use of the Cardox System 13 71111.05 Procedures TQ1.DC12 Fire Brigade and Emergency Response Training 16 Corrective Action Documents Notifications 51273404 TQ2.DC15 Licensed Operator Annual/Biennial Exam Development and Administration 16 71111.11Q Procedures TQ2.DC3 Licensed Operator Continuing Training Program 36 Corrective Action Documents Notifications 51272137, 51169202 Procedures MA1.ID17 Maintenance Rule Monitoring Program 36 71111.12 Work Orders WO 61071556, 64311401, 60148731, 64102662 71111.13 Corrective Action Notifications 51268927, 51269759
11 Inspection Procedure Type Designation Description or Title Revision or Date Documents AD7.ID14 Assessment of Integrated Risk 32, 36, 37 AD7.ID4 On-Line Maintenance Scheduling 36 OP AP-15 Loss of Feedwater Flow 29 Procedures OP O-36 Protected Equipment Postings 33A Work Orders WO 60135504, 60168902, 64185824, 64284159, 64284621, 64291060, 64291156 Corrective Action Documents Notifications 51267553, 51267748, 51272442, 51272647, 51272725, 51272742, 51273257, 51273285, 51276803, 51191228 OM3.ID7 Portable Radio and Cellular Phone Use 9
OP AP-17 Loss of Charging 39 OP AP-18 Letdown Line Failure 12 OP B-1A:IV CVCS - Excess Letdown - Place in Service and Remove from Service 18 71111.15 Procedures STP I-9-L921 Refueling Water Storage Tank Level Channel LT-921 Calibration 6
MP M-17-PMP.3 Auxiliary Salt Water Pump Packing 0
OP J-6A:IV-G 4160 Volt Bus G Breaker Code Orders 12 OP J-6B:V Diesel Generators - Manual Operation of DG 1-2 38 STP M-21-RTS.1 Return Diesel Engine to Service Following Outage Maintenance 28 STP M-26 ASW System Flow Monitoring 34 STP M-9A2 Diesel Engine Generator 1-2 Routine Surveillance Test 15 STP M-9B Overspeed Trip Test of Diesel Generators 32 STP M-9G Diesel Generator 24 Hour Load Test and Hot Restart Test 60 STP M-9I Diesel Generator Start and Load Tracking 30A STP M-9L Diesel Generator Shutdown Lockout Relay Test 33 STP P-AFW-21 Routine Surveillance Test of Turbine-Driven Auxiliary Feedwater Pump 2-1 33 STP P-AFW-22 Routine Surveillance Test of Motor-Driven Auxiliary Feedwater Pump 2-2 18A STP P-CSP-22 Routine Surveillance Test of Containment Spray Pump 2-2 20 71111.24 Procedures STP P-SIP-12 Routine Surveillance Test of Safety Injection Pump 1-2 32
12 Inspection Procedure Type Designation Description or Title Revision or Date STP V-2J6 Outside Containment Safety Injection and Charging Injection Isolation Valves 13 STP V-3I3B Full Stroke Exercise of Containment Spray Valve CS-9001B 9
STP V-3L10B Exercising Valve SI-8923B, Safety Injection Pump 2 Suction Valve 7A STP V-3L2B Exercising Valve SI-1-8821B, Safety Injection Pump Discharge to RCS Cold Legs 4
STP V-3P5 Exercising Valves LCV-106, 107, 108, 109 Auxiliary Feedwater Pump Discharge 22 STP V-3P6A Exercising Valves LCV-110 and LCV-111 Auxiliary Feedwater Pump Discharge 29 Work Orders WO 60170887, 64062926, 64226241, 64289575, 64289586, 64295181, 64305400 71151 Miscellaneous Plant Logs