07-28-2016 | On May 30, 2016, at 0930 PDT, with Unit 2 in Mode 4, "Hot Shutdown," licensed operators responding to a difference greater than 12 steps between digital rod position indication (DRPI) and demand position indication in the control room, manually opened the Reactor Trip Breakers in accordance with plant procedures. The plant operators stabilized the plant and technicians identified a failure of a control rod moveable gripper fuse. At 1611 PDT, plant operators made an 8-hour, nonemergency notification in accordance with 10 CFR 50.72(b)(3)(iv)(A). Plant technicians replaced the fuse and plant operators confirmed proper operation by performance of surveillance testing.
The cause was attributed to Surveillance Test Procedure (STP) R-1C, "Digital Rod Position Indicator Functional Test," which did not explicitly specify actions to identify improper DRPI indications prior to exceeding a 12-step difference between rod demand and rod position indication.
Corrective actions to prevent recurrence include revision of STP R-1C to include guidance regarding verification of rod motion prior to exceeding 12 steps and operator training of the changes to the procedure.
This event did not adversely affect the health and safety of the public.
APPROVED BY OMB: NO. 3150-0104 EXPIRES: 10/31 hours. Reported lessons learned are incorporated into the licensing process and fed back to industry. Send comments regarding burden estimate to the FOIA, Privacy and Information Collections Branch (T-5 F53), U.S. Nuclear Regulatory Commission, Washington, DC 205550001, or by e-mail to Infocollects.Resource@nrc.gov, and to the Desk Officer, Office of Information and Regulatory Affairs, 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. |
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Category:Letter
MONTHYEARDCL-24-075, Response to Request for Additional Information for License Amendment Request 23-02, Application to Adopt 10 CFR 50.69, “Risk-Informed Categorization and Treatment of Structures, Systems and Components for Nuclear Power React2024-08-0808 August 2024 Response to Request for Additional Information for License Amendment Request 23-02, Application to Adopt 10 CFR 50.69, “Risk-Informed Categorization and Treatment of Structures, Systems and Components for Nuclear Power React IR 05000275/20240022024-08-0606 August 2024 Integrated Inspection Report 05000275/2024002 and 05000323/2024002 DCL-24-070, License Amendment Request 24-03 Revision to Technical Specification 5.5.16 for Permanent Extension of Type a and Type C Leak Rate Test Frequencies2024-07-31031 July 2024 License Amendment Request 24-03 Revision to Technical Specification 5.5.16 for Permanent Extension of Type a and Type C Leak Rate Test Frequencies DCL-24-071, Core Operating Limits Report for Unit 2 Cycle 252024-07-22022 July 2024 Core Operating Limits Report for Unit 2 Cycle 25 DCL-2024-523, Submittal of Report on Discharge Self-Monitoring2024-07-18018 July 2024 Submittal of Report on Discharge Self-Monitoring ML24187A1352024-07-16016 July 2024 Letter to Paula Gerfen - Diablo Canyon Units 1 and 2 - Summary of June 2024 Audit Related to the License Renewal Application Severe Accident Mitigation Alternatives Review IR 05000275/20240142024-07-11011 July 2024 Age-Related Degradation Inspection Report 05000275/2024014 and 05000323/2024014 IR 05000275/20243012024-07-10010 July 2024 NRC Initial Operator Licensing Examination Approval 05000275/2024301; 05000323/2024301 IR 05000275/20244012024-07-0808 July 2024 Security Baseline Inspection Report 05000275/2024401 and 05000323/2024401 (Full Report) IR 05000323/20240112024-07-0303 July 2024 License Renewal Phase Report 05000323/2024011 DCL-2024-527, Sea Turtle Stranding Report (Loggerhead Sea Turtle) Diablo Canyon Power Plant2024-07-0101 July 2024 Sea Turtle Stranding Report (Loggerhead Sea Turtle) Diablo Canyon Power Plant DCL-24-066, Request to Extend the Nrg Approval of Alternative for Use of Full Structural Weld Overlay, REP-RHR-SWOL2024-06-27027 June 2024 Request to Extend the Nrg Approval of Alternative for Use of Full Structural Weld Overlay, REP-RHR-SWOL ML24155A2182024-06-18018 June 2024 OEDO-23-00350-NRR - (LTR-23-0228-1) - Closure Letter - 10 CFR 2.206 Petition from Mothers for Peace and Friends of the Earth Regarding Diablo Canyon ML24129A1762024-06-14014 June 2024 National Historic Preservation Act Section 106 Consultation – Results of Identification and Evaluation (Docket Number: 72-026) ML24200A2052024-06-0707 June 2024 Fws to NRC, List of Threatened and Endangered Species That May Occur in Your Proposed Project Location or May Be Affected by Your Proposed Project for Diablo Canyon License Renewal ML24099A2192024-05-29029 May 2024 Plants, Units 1 and 2 Issuance of Amendment Nos. 245 and 247 Revision to TSs to Adopt TSTF-505, Revision 2, Provide Risk-Informed Extended Completion Times - RITSTF Initiative 4b ML24117A0132024-05-20020 May 2024 Letter to Paula Gerfen-Diablo Canyon Units 1 and 2-Regulatory Audit Regarding Severe Accident Mitigation Alternatives for the License Renewal Application DCL-24-052, Responses to NRC Requests for Additional Information on the Diablo Canyon Power Plant License Renewal Application Environmental Report2024-05-16016 May 2024 Responses to NRC Requests for Additional Information on the Diablo Canyon Power Plant License Renewal Application Environmental Report DCL-24-051, One Hundred Eighty Day Steam Generator Report for Twenty-Fourth Refueling Outage2024-05-0808 May 2024 One Hundred Eighty Day Steam Generator Report for Twenty-Fourth Refueling Outage ML24127A2042024-05-0202 May 2024 02May2024 Ltr - California Coastal Commission to Pg&E, Coastal Development Permit Needed for Pg&E’S Proposed Relicensing of Diablo Canyon Nuclear Power Plant DCL-24-049, 2023 Annual Radiological Environmental Operating Report2024-05-0101 May 2024 2023 Annual Radiological Environmental Operating Report DCL-24-047, 2023 Annual Non-radiological Environmental Operating Report2024-05-0101 May 2024 2023 Annual Non-radiological Environmental Operating Report DCL-24-048, O CFR 50.59 and 1 O CFR 72.48 Summary Report for the Period of January 1, 2022, Through December 31, 20232024-04-30030 April 2024 O CFR 50.59 and 1 O CFR 72.48 Summary Report for the Period of January 1, 2022, Through December 31, 2023 L-24-004, Independent Spent Fuel Storage Installation - Responses to NRC Requests for Additional Information on the Diablo Canyon Independent Spent Fuel Storage Installation License Renewal Application (Cac/Epid 001028/L-2022-RNW-0007)2024-04-30030 April 2024 Independent Spent Fuel Storage Installation - Responses to NRC Requests for Additional Information on the Diablo Canyon Independent Spent Fuel Storage Installation License Renewal Application (Cac/Epid 001028/L-2022-RNW-0007) DCL-24-027, 2023 Annual Radioactive Effluent Release Report2024-04-28028 April 2024 2023 Annual Radioactive Effluent Release Report DCL-24-045, Annual Report of Occupational Radiation Exposure for 20232024-04-24024 April 2024 Annual Report of Occupational Radiation Exposure for 2023 IR 05000275/20240012024-04-23023 April 2024 Integrated Inspection Report 05000275/2024001 and 05000323/2024001 ML24114A2032024-04-22022 April 2024 Request for Information for EP Program and Performance Indicator Verification Inspection (Wolf Creek Nuclear Generating Station) Inspection Report 05000482/2024003 ML24106A2882024-04-18018 April 2024 License Renewal Application Environmental Review RCIs and RAIs ML24106A2892024-04-18018 April 2024 Letter to Paula Gerfen - Diablo Canyon Units 1 and 2 - Summary of March 2024 Audit Regarding the Environmental Review of the License Renewal Application DCL-24-042, Response to NRC Regulatory Issue Summary 2024-01, Preparation and Scheduling of Operator Licensing Examinations2024-04-17017 April 2024 Response to NRC Regulatory Issue Summary 2024-01, Preparation and Scheduling of Operator Licensing Examinations ML24108A1122024-04-15015 April 2024 License Amendment Request 24-02 Request for Approval of DCPP Early Warning System to Meet 10 CFR 73.55(i)(2) and 10 CFR 73.55(e)(9)(vi)(A) DCL-24-023, Revised Certification of Permanent Cessation of Power Operations2024-04-0202 April 2024 Revised Certification of Permanent Cessation of Power Operations DCL-24-022, Notification of Changes to Decommissioning Schedule2024-04-0202 April 2024 Notification of Changes to Decommissioning Schedule DCL-24-032, 2024 Annual Statement of Insurance for Pacific Gas and Electric Company’S Diablo Canyon Power Plant2024-03-27027 March 2024 2024 Annual Statement of Insurance for Pacific Gas and Electric Company’S Diablo Canyon Power Plant DCL-24-031, Decommissioning Funding Report2024-03-27027 March 2024 Decommissioning Funding Report ML24082A2592024-03-25025 March 2024 Notice of Enforcement Discretion for Diablo Canyon Power Plant, Unit 2 (EPID L-2024-LLD-0002) - March 25, 2024 ML24081A0462024-03-22022 March 2024 Audit Summary in Support of the License Amendment Request to Adopt TSTF-505, Revision 2, Provide Risk-Informed Extended Completion Times - RITSTF Initiative 4b ML24081A4052024-03-21021 March 2024 Request for Enforcement Discretion Regarding Compliance with Technical Specification 3.0.3, Limiting Condition for Operation Applicability DCL-24-028, Request for Enforcement Discretion Regarding Compliance with Technical Specification 3.0.3, Limiting Condition for Operation Applicability2024-03-21021 March 2024 Request for Enforcement Discretion Regarding Compliance with Technical Specification 3.0.3, Limiting Condition for Operation Applicability ML24065A1312024-03-20020 March 2024 ISFSI Renewal RAI Transmittal Letter IR 05000275/20244032024-03-12012 March 2024 Cyber Security Inspection Report 05000275/2024403 and 05000323/2024403 (Cover Letter) ML24071A1742024-03-0404 March 2024 Email - (External_Sender) Shutdown Petition to NRC Commissioners ML24065A3662024-03-0404 March 2024 Notification of Site Inspection for License Renewal and Request for Information Inspection (05000323/2024011) IR 05000275/20230062024-02-28028 February 2024 Annual Assessment Letter for Diablo Canyon Power Plant, Units 1 and 2 (Report 05000275/2023006 and 05000323/2023006) DCL-24-018, License Amendment Request 24-01 Revision to Technical Specification 5.6.6, Reactor Coolant System (RCS) Pressure and Temperature Limits Report (PTLR)2024-02-28028 February 2024 License Amendment Request 24-01 Revision to Technical Specification 5.6.6, Reactor Coolant System (RCS) Pressure and Temperature Limits Report (PTLR) DCL-2024-507, 2023 Annual Report on Discharge Self-Monitoring2024-02-27027 February 2024 2023 Annual Report on Discharge Self-Monitoring ML24056A0022024-02-27027 February 2024 – License Renewal Regulatory Audit Regarding the Environmental Review of the License Renewal Application ML24058A2552024-02-22022 February 2024 Formal Acceptance from Sy Chumash Re Regarding Consultation on the DC NPP ML24058A2562024-02-22022 February 2024 Santa Ynez Band or Chumash Tribe - 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[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] |
L Reportable Event Classification This event is reportable pursuant to 10 CFR 50.73(a)(2)(iv)(A), System Actuation.
II. Plant Conditions
Unit 2 was in Mode 4, Hot Shutdown, preparing for restart following the nineteenth refueling outage (2R19).
Ill. Description of Problem
A. Background
The rod control system [AA] is a Design Class II system for positioning the reactor control rods for reactor power modulation by manual or automatic control of control rod banks. The rod control system is provided motive power through the redundant Design Class I Reactor Trip breakers that open to perform the safety-related function of rod insertion by removing all motive power to the control rod drive mechanism. The rod group demand position indication is located in the control room on the control board and indicates the individual rod position demands made for rod motion.
The digital rod position indication (DRPI) system measures the position of the control rod drive mechanism shafts within the control rod drive housings so that the positions of the control rods within the core are verified.
Equipment Control Guideline (ECG) 41.2, "Special Test Exceptions - Position Indication System — Shutdown", requires that position indication systems be operable when the reactor trip breakers are closed. With less than the above required position indication systems operable, the reactor trip breakers are required to be immediately opened. Surveillance Requirement (SR) 41.2.1 requires verification "that the demand position indication system and the DRPI system agree within 12 steps when rods are stationary.
Surveillance Test Procedure (STP) R-1C, "Digital Rod Position Indicator Functional Test," verifies the OPERABILITY of the DRPI System. The rod banks are individually withdrawn in 24 step increments while a comparison is made between the DRPI indication and the demand step counter for each rod. When the bank is fully withdrawn, it is then inserted to the rod bottom light emitting diode (LED) point and the position at which each rod bottom LED was actuated is recorded.
B. Event Description
During plant restart following 2R19, plant operators initiated DRPI operability testing of Shutdown Bank A in accordance with STP R-1C.
On May 30, 2016, at 0930 PDT with Unit 2 in Mode 4, licensed operators responded to an indicated difference between the Rod B4 demand position indication and DRPI indication greater than 12 steps and initiated manual opening of the reactor trip breakers in accordance with plant procedures.
On May 30, 2016, at 1611 PDT, operations made an 8-hour, nonemergency notification in accordance with 10 CFR 50.72(b)(3)(iv)(A).
C. Status of Inoperable Structures, Systems, or Components that Contributed to the Event Control rod moveable gripper fuse (FU49) for Rod B4 was open.
D. Other Systems or Secondary Functions Affected
None.
E. Method of Discovery
The condition was discovered during the performance of STP R-1C as required by plant ECG 41.2.
F. Operator Actions
Licensed operators initiated manual opening of the reactor trip breakers removing motive power from the rod control system in accordance with plant procedures.
G. Safety System Responses
Unit 2 rod control system was deactivated by opening the reactor trip breakers, which deenergized the gripper circuits and control rods that were withdrawn then reinserted into the core as designed.
III. Cause of the Problem
A. Immediate Cause
The rod control demand position indication and DRPI had an observed difference of 14 steps, requiring the immediate opening of the reactor trip breakers.
B. Cause
A failure of the Rod B4 moveable gripper fuse (FU49) prevented Rod B4 from movement upon demand. This caused the Rod B4 to remain at the core bottom as indicated by the DRPI system while the demand counter counted up to 14 steps.
Gripper coil fuses are replaced every refueling outage to prevent failure due to cyclic fatigue. Handling and installation stress can weaken fuses and cause them to fail when first energized. These issues are detected when post maintenance testing is performed.
STP R-1C, Revision 21, did not explicitly specify actions to identify improper DRPI indications prior to exceeding a 12 step difference between rod demand and rod position indication. STP R-1C, Revision 17, dated March 19, 2009, had steps to withdraw the rod bank to 10 steps and then check rod control fuse integrity. These steps were added to STP R-1C, as a corrective action to a previous Licensee Event Report (LER) 2-2003-004-00.
Subsequently, this step was removed in Revision 18 of the procedure dated July 14, 2009. If this step had been in STP R-1C at the time of the event, the faulted fuse would have been detected prior to exceeding the 12-step limit and a manual opening of the reactor trip breakers would not have been required.
IV. Assessment of Safety Consequences
Procedure controlled pre-operation testing discovered the inoperable system prior to pulling more than one shutdown bank. A control rod moveable gripper fuse (FU49) was identified as failed open preventing Rod B4 from being moved, thus, no unanticipated positive reactivity change was possible. At the time of this event, the boron concentration in the reactor coolant system was approximately 2100 ppm; therefore, compliance with shutdown margin requirements was maintained. This event was not safety significant and it did not adversely affect the health and safety of the public.
V. Corrective Actions
A. Immediate Corrective Actions 1. Unit 2 rod control system was deactivated by opening the reactor trip breakers, which deenergized the gripper circuits and control rods that were withdrawn then reinserted into the core as designed.
2. Plant staff identified a failed moveable gripper coil fuse (FU49) for Rod B4 and replaced the failed fuse.
B. Corrective Actions to Prevent Recurrence 1. STP R-1C has been revised to provide adequate guidance regarding confirmation of rod motion prior to exceeding 12 steps demand indication.
2. Plant operators will receive training on the changes to STP R-1C.
VI. Additional Information
A. Failed Components:
Component: Fuse, 10A 250V ceramic cartridge Manufacturer: BUSSMANN # 2432659
B. Previous Similar Events
of a Control Rod F2 moveable coil power supply fuse which caused Rod F2 to remain on the core bottom, as indicated by the DRPI system. Corrective actions included revising STP R-1C to provide adequate guidance regarding confirmation of rod motion prior to exceeding 12 steps demand indication.
However, as noted above, these steps were inadvertently deleted in a subsequent revision to the procedure.
Diablo Canyon Power Plant, Unit 2 05000323