During an investigation of a nitrogen leak inside the Unit 2 containment, Nitrogen Accumulator Relief Valve (RV) RV-355 was found to be leaking. The leak caused the pressure in the back up nitrogen accumulator supply to Power Operated Relief Valve ( PORV) PCV-455C to decrease to a level that made the PORV inoperable. Based on a review of the ti-end data for nitrogen usage in the containment, it is conservatively assumed that RV-355 had been degraded since December 1, 2016, rendering the PORV inoperable for longer than permitted by Technical Specifications.
The presumptive cause was inadequate instructions provided in plant procedures for placing a new nitrogen bottle in service. These instructions did not provide a sequence that assures system pressure transients are mitigated. This may have caused excessive pressure excursions resulting in multiple lifts of RV-355 which resulted in damage to the RV 0-ring seat and a nitrogen leak path.
Corrective actions include replacing RV-355 and revising procedures to provide instructions on placing nitrogen supply bottles in service to maintain back pressure and minimize pressure transients on the nitrogen system.
This event did not affect the health and safety of the public. |
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Category:Letter
MONTHYEARIR 05000275/20230042024-02-0909 February 2024 Integrated Inspection Report 05000275/2023004 and 05000323/2023004 ML24002B1802024-01-29029 January 2024 LRA Audit Plan DCL-24-010, Nuclear Material Transaction Report for New Fuel2024-01-29029 January 2024 Nuclear Material Transaction Report for New Fuel ML24018A0152024-01-29029 January 2024 License Renewal Application Review Schedule Letter ML24017A2492024-01-24024 January 2024 Letter to Neil Peyron, Chairman, Tule River Tribe, Re. Diablo Canyon ML24024A1752024-01-24024 January 2024 Letter to Tribal Council San Luis Obispo County Chumash Indians on Section 106 Consultation and Scoping Process for the Environmental Review of Diablo Canyon Nuclear Plant, Unit 1 and 2 License Renewal Application ML24003A8902024-01-24024 January 2024 Letter to P. Gerfen - Diablo Canyon Notice of Intent to Conduct Scoping and Prepare an Environmental Impact Statement ML24012A1582024-01-24024 January 2024 Letter to Hon. Violet Sage Walker, Chairwoman Northern Chumash Tribal Council on Section 106 Consultation and Scoping Process for the Environmental Review of Diablo Canyon Nuclear Plant, Unit 1 and 2 License Renewal Application ML24012A0062024-01-24024 January 2024 Achp Scoping Letter for Diablo Canyon License Renewal ML24012A0552024-01-24024 January 2024 Letter to J. Polanco, Shpo, on Request to Initiate Section 106 Consultation and Scooping Process for the Environmental Review of Diablo Canyon Nuclear Plant, Unit 1 and 2 License Renewal Application ML24024A1562024-01-24024 January 2024 Letter to Hon. Gabe Frausto, Coastal Band of Chumash Indians on Section 106 Consultation and Scoping Process for the Environmental Review of Diablo Canyon Nuclear Plant, Unit 1 and 2 License Renewal Application ML24024A1652024-01-24024 January 2024 Letter to Hon. Mona Olivas Tucker, Yak Tityu Tityu Yak Tilhini Northern Chumas Indians on Section 106 Consultation and Scoping Process for the Environmental Review of Diablo Canyon Nuclear Plant, Unit 1 and 2 License Renewal Application ML24024A1612024-01-24024 January 2024 Letter Hon. Gary Pierce, Salian Tribe of Monterey and San Luis Obispo Counties on Section 106 Consultation and Scoping Process for the Environmental Review of Diablo Canyon Nuclear Plant, Unit 1 and 2 License Renewal Application ML24012A0362024-01-24024 January 2024 Request to Initiate Section 106 Consultation and Scoping Process for the Environmental Review License Renewal Application DCL-24-009, Nuclear Material Transaction Report for New Fuel2024-01-17017 January 2024 Nuclear Material Transaction Report for New Fuel DCL-24-008, Schedule Considerations for Review of the DCPP License Renewal Application2024-01-17017 January 2024 Schedule Considerations for Review of the DCPP License Renewal Application DCL-24-004, Supplement to License Amendment Request 23-01 Revision to Technical Specifications to Adopt Risk-Informed Completion Times TSTF-505, Revision 2, Provide Risk-Informed Extended Completion Times - RITSTF Initiative 4b2024-01-15015 January 2024 Supplement to License Amendment Request 23-01 Revision to Technical Specifications to Adopt Risk-Informed Completion Times TSTF-505, Revision 2, Provide Risk-Informed Extended Completion Times - RITSTF Initiative 4b IR 05000275/20230112024-01-12012 January 2024 NRC License Renewal Phase 1 Inspection Report 05000275/2023011 DCL-23-129, Nuclear Material Transaction Report for New Fuel2023-12-27027 December 2023 Nuclear Material Transaction Report for New Fuel ML23326A0122023-12-21021 December 2023 12-21-23 Letter to the Honorable Byron Donalds from Chair Hanson Responds to Letter Regarding 2.206 Petition to Close Diablo Canyon Nuclear Power Plant, Unit 1 ML23341A0042023-12-19019 December 2023 LRA Acceptance Letter ML23352A2342023-12-18018 December 2023 Notification of Age-Related Degradation Inspection (05000275/2024014 and 05000323/2024014) and Request for Information DCL-23-122, Request for Exemption from Enhanced Weapons, Firearms Background Checks, and Security Event Notifications Implementation2023-12-14014 December 2023 Request for Exemption from Enhanced Weapons, Firearms Background Checks, and Security Event Notifications Implementation DCL-23-128, Emergency Plan Update2023-12-13013 December 2023 Emergency Plan Update ML23355A0952023-12-0808 December 2023 License Renewal Application Online Reference Portal DCL-23-125, Core Operating Limits Report for Unit 1 Cycle 252023-12-0606 December 2023 Core Operating Limits Report for Unit 1 Cycle 25 ML23291A2702023-11-28028 November 2023 Letter to Nakia Zavalla, Shpo, the Santa Ynez Band of Chumash Indians; Re., Diablo Canyon ISFSI Initiating Section 106 Consultation ML23320A2442023-11-28028 November 2023 Letter to Kerri Vera, Director of Department of Environmental Protection, Tule River Tribe; Re., Diablo Canyon ISFSI Initiating Section 106 Consultation ML23325A1382023-11-27027 November 2023 ISFSI Tribal Letter to San Luis Obispo County Chumash Indians ML23325A1322023-11-27027 November 2023 ISFSI Tribal Letter to Salian Tribe of Montgomery, San Luis Obispo ML23325A1332023-11-27027 November 2023 ISFSI Tribal Letter to Yak Tityu Tityu Northern Chumash Indians ML23307A0062023-11-27027 November 2023 ISFSI Tribal Letter to Northern Chumash Tribal Council ML24003A7242023-11-27027 November 2023 Independent Safety Committee; Diab Lo Canyon Nuclear Power Plant Operations, Thirty-Third Annual Report on the Safety ML23325A1292023-11-27027 November 2023 ISFSI Tribal Letter to Coastal Band of Chumash ML23320A1502023-11-17017 November 2023 Individual Notice of Consideration of Issuance of Amendment to Facility Operating License, Proposed No Significant Hazards Consideration Determination, & Opportunity for Hearing (Exigent Circumstances) (EPID L-2023-LLA-0155) - LTR DCL-23-121, Supplement to License Amendment Request 23-03, Revision to Technical Specification3.7.8, Auxiliary Saltwater System2023-11-16016 November 2023 Supplement to License Amendment Request 23-03, Revision to Technical Specification3.7.8, Auxiliary Saltwater System ML23296A0982023-11-15015 November 2023 Notification and Request for Consultation Regarding Pacific Gas and Electric Diablo Canyon Independent Spent Fuel Storage Installation Material License Renewal Request (Docket Number: 72-26) DCL-23-120, License Amendment Request 23-03 Revision to Technical Specification 3.7.8, Auxiliary Saltwater (Asw) System2023-11-14014 November 2023 License Amendment Request 23-03 Revision to Technical Specification 3.7.8, Auxiliary Saltwater (Asw) System ML23293A1052023-11-14014 November 2023 Receipt and Availability of License Renewal Application IR 05000275/20230032023-11-13013 November 2023 Integrated Inspection Report 05000275/2023003 and 05000323/2023003 ML23311A2082023-11-0909 November 2023 Reassignment of U.S. Nuclear Regulatory Commission Branch Chief in the Division of Operating Reactor Licensing for Plant Licensing Branch IV DCL-23-118, License Renewal Application2023-11-0707 November 2023 License Renewal Application ML23318A2102023-10-31031 October 2023 Independent Safety Committee; Thirty-Third Annual Report on the Safety of Diablo Canyon Nuclear Power Plant Operations DCL-2023-520, Discharge Self-Monitoring at Diablo Canyon Power Plant (DCPP)2023-10-19019 October 2023 Discharge Self-Monitoring at Diablo Canyon Power Plant (DCPP) DCL-23-103, Independent Spent Fuel Storage Installation - Withdrawal of License Amendment Request 22-01, Request for Approval of Alternative Security Measures for Early Warning System2023-10-13013 October 2023 Independent Spent Fuel Storage Installation - Withdrawal of License Amendment Request 22-01, Request for Approval of Alternative Security Measures for Early Warning System IR 05000275/20240152023-10-10010 October 2023 Information Request for the Cybersecurity Baseline Inspection, Notification to Perform Inspection (050002752024015 and 050003232024015) 2024-02-09
[Table view] Category:Licensee Event Report (LER)
MONTHYEAR05000323/LER-2017-0012017-10-0303 October 2017 Relief Valve Leakage Resulting in Inoperable Pressurizer Power Operated Relief Valve, LER 17-001-00 for Diablo Canyon, Unit 2, Regarding Relief Valve Leakage Resulting in Inoperable Pressurizer Power Operated Relief Valve 05000323/LER-2016-0012016-07-28028 July 2016 Reactor Trip Breakers Manually Opened During Shutdown Due to a Control Rod Movable Gripper Fuse Failure, LER 16-001-00 for Diablo Canyon, Unit 2, Regarding Reactor Trip Breakers Manually Opened During Shutdown Due to a Control Rod Movable Gripper Fuse Failure 05000275/LER-2015-0012016-02-11011 February 2016 Both Trains of Residual Heat Removal Inoperable Due to Circumferential Crack on a Socket Weld, LER 15-001-01 for Diablo Canyon, Unit 1, Regarding Both Trains of Residual Heat Removal Inoperable Due to Circumferential Crack on a Socket Weld DCL-15-042, Supplemental Licensee Event Report 1-2014-004-01 for Diablo Canyon, Units 1 and 2 Regarding Actuation of Six Emergency Diesel Generators Due to Loss of Offsite Power2015-03-30030 March 2015 Supplemental Licensee Event Report 1-2014-004-01 for Diablo Canyon, Units 1 and 2 Regarding Actuation of Six Emergency Diesel Generators Due to Loss of Offsite Power DCL-15-041, Supplemental LER 2-13-004-01 for Diablo Canyon, Unit 2 Regarding Technical Specification 3.8.1 Not Met Due to Failed Wire Lug on Emergency Diesel Generator 2-32015-03-30030 March 2015 Supplemental LER 2-13-004-01 for Diablo Canyon, Unit 2 Regarding Technical Specification 3.8.1 Not Met Due to Failed Wire Lug on Emergency Diesel Generator 2-3 DCL-13-034, Licensee Event Report 12-005-00 for Diablo Canyon Regarding Expected Submittal Date2013-04-0101 April 2013 Licensee Event Report 12-005-00 for Diablo Canyon Regarding Expected Submittal Date DCL-11-118, LER 11-05-001 for Diablo Canyon Unit 1, Emergency Diesel Generator Actuations Upon Loss of 230 Kv Startup Due to Electrical Maintenance Testing Activities2011-11-0808 November 2011 LER 11-05-001 for Diablo Canyon Unit 1, Emergency Diesel Generator Actuations Upon Loss of 230 Kv Startup Due to Electrical Maintenance Testing Activities DCL-11-119, LER 11-04-001 for Diablo, Unit 1, Regarding Emergency Diesel Generator Actuated Upon 230 Kv Isolation Due to Maintenance Activities on Relay Panel2011-11-0808 November 2011 LER 11-04-001 for Diablo, Unit 1, Regarding Emergency Diesel Generator Actuated Upon 230 Kv Isolation Due to Maintenance Activities on Relay Panel 2017-10-03
[Table view] |
comments regarding burden estimate to the Information Services Branch (T-2 F43), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by e-mail to NE08-10202, (3150-0104), Office of Management and Budget, Washington, DC 20503. If a means used to impose an information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.
2017 001 Diablo Canyon Power Plant, Unit 2 05000323 00
I. Reportable Event Classification
This event is reportable pursuant to the following criteria:
- 10 CFR 50.73(a)(2)(v)(A & D), Any event or condition that could have prevented the fulfillment of the safety function of structures or systems that are needed to shut down the reactor and maintain it in a safe shutdown condition, and mitigate the consequences of an accident.
II. Plant Conditions
At the time of the event, Diablo Canyon Power Plant (DCPP) Unit 2 was in Mode 1 (Power Operation), operating at 100 percent power.
III. Probkyrn Description
A. Background
The DCPP Unit 2 pressurizer is equipped with three Power Operated Relief Valves (PORVs), two safety-related (PCV-455C and PCV-456) and one non safety-related (PCV-474). The pressurizer maintains Reactor Coolant System (RCS) pressure and volume through the surge line during operation, and limits pressure changes during transients. During plant load reduction or increase, reactor coolant volume changes arc accommodated in the pressurizer via the surge line, pressurizer sprays and/or heaters, and the PORVs. The PORVs are normally operated by instrument air. When instrument air is isolated, the backup nitrogen supply provides the motive force to operate the PORVs. The safety-related PORVs and associated backup nitrogen accumulators are credited to mitigate the Feedwater Line Break (FLB) event, the Spurious Safety Injection (SSI) event, the Steam Generator Tube Rupture (SGTR) event and the Low Temperature Overpressure Protection (LTOP) event.
An FLB event generates a Safety Injection (SI) signal and Phase A containment isolation signal, which isolates instrument air and nitrogen supply to the containment. The backup Nitrogen accumulator is therefore credited to provide an adequate capacity to cycle the PORV at least 300 times following a FLB event. This provides adequate time for the operators to take action to terminate the Emergency Core Cooling System (ECCS) injection now and re-establish a bubble in the pressurizer.
The safety-related PORVs and operator actions are credited to mitigate the SSI event for pressurizer overfilling.
If the pressurizer overfills, the pressurizer PORVs are available to relieve water inventory from the RCS, as comments regarding burden estimate to the Information Services Branch (T-2 F43), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by e-mail to used to impose an information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.
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2017 SEOUENI1AL 001 00 long as nitrogen is available from the DCPP Design Class I backup nitrogen accumulators (instrument air is not available).
The safety-related PORVs are credited to open and depressurize the RCS as part of the SGTR event.
When an LTOP transient occurs, a pressurizer PORV opens until the pressure returns to acceptable limits.
B. Event Description
On July 28, 2017, at 1206 PDT, with DCPP Unit 2 operating at 100 percent power, an Alert notification was declared due to low oxygen levels inside the containment. The cause of the low oxygen level was a nitrogen leak inside the containment. The nitrogen source was isolated and the containment atmosphere was restored to ormal conditions. The Alert notification was terminated on July 28, 2017, at 1819 PDT. During an investigation of the nitrogen leak inside the containment, RV-355 was found to be leaking. The leak caused the le ressure in the back up nitrogen accumulator supply to PORV PCV-455C to decrease to a level that made the ORV inoperable.
ased on a review of trend data for nitrogen usage in the containment, it is conservatively assumed that RV-355 I ad been degraded since December 1, 2016, rendering the PORV inoperable for longer than permitted by Technical Specifications. Technical Specification 3.4.11.B requires an inoperable PORV to be restored to operable within 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />. Therefore, the event is reportable as an event or condition prohibited by Technical Specifications. In addition, because the other safety-related PORV PCV-456 had been declared inoperable for esting multiple times since December 1, 2016, this event is reportable as an event or condition that could have .revented the fulfillment of a safety function.
C. Status of Inoperable Structure, Systems or Components That Contributed to the Event one.
1). Other Systems or Secondary Functions Affected None.
E. Method of Discovery
During an investigation of the nitrogen leak inside the containment, RV-355 was found to be leaking. The leak caused the pressure in the back up nitrogen accumulator supply to PORV PCV-455C to decrease to a level that made the PORV inoperable.
comments regarding burden estimate to the Information Services Branch (T-2 F43), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by e-mail to Infocallects.Resource@nrc.gov, and to the Desk Officer, Office of Information and Regulatory Affairs, used to impose an information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a person is not required to respond to. the information collection.
Diablo Canyon Power Plant, Unit 2 YEAR 05000323 2017 001 00
F. Operator Actions
Operators declared PCV-455C inoperable and entered Technical Specification 3.4.11.E on July 29, 2017, at 0457 PDT. RV-355 was replaced and Technical Specification 3.4.11.6 was exited on July 30, 2017, at 1533 PDT.
U. Safety System Responses
None.
IV. Cause of the Problem
The presumptive cause was inadequate instructions provided in plant procedures for placing a new nitrogen supply bottle in service. These instructions did not provide a sequence that assures system pressure transients are mitigated. This may have caused excessive pressure excursions resulting in multiple lifts of RV-355 which resulted in damage to the RV 0-ring seat and a nitrogen leak path.
V. Assessment of Safety Consequences
DCPP assessed the Unit 2 risk significance of the inoperability of PCV-455C using Probabilistic Risk Assessment and the Significance Determination Process. The assessment concluded that the PORV would be available for the most risk significant functions. An incremental conditional core damage probability associated with this event was estimated to be less than 1.0E-06.
VI. Corrective Actions
A. Immediate Actions
1. Relief Valve RV-355 was replaced on July 29. 2017.
B. Other Corrective Actions
1. Plant procedures will be revised to provide instructions for placing nitrogen supply bottles in service to minimize pressure transients on the nitrogen system.
comments regarding burden estimate to the Information Services Branch (T-2 F43), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by e-mail to NEOB-10202, (3150-0104). Office of Management and Budget, Washington, DC 20503. If a means used to impose an information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.
3. LER NUMBER
L 00 2017 001
VII. Additional Information
A. Failed Components
Component: Relief Valve Model: 951282ME Manufacturer: Anderson Greenwood Crosby
B. Previous Similar Events
Internal Operating Experience A similar event occurred on January 5, 2000, while DCPP Unit 2 was at 100 percent power. A failure of RV-355 caused nitrogen pressure to decrease rapidly, resulting in PORV PCV-455C being inoperable.
RV-355 was replaced and PCV-455C was returned to service.