On June 23, 2017, at 10:18 PM CDT, an unanticipated reactor scram occurred during scheduled testing of the main turbine generator. The plant was operating at 100 percent power at the time, and no safety-related equipment was out of service. A reactor recirculation system flow control valve runback occurred as designed, and the recirculation pumps properly downshifted to slow speed. The main feedwater system responded properly to control reactor water level. The scram signal was initiated by the closure of the main turbine control valves, which was an automatic response to a trip of the main generator. The associated steam pressure increase following turbine valve closure resulted in the actuation of 12 main steam safety-relief valves. A reactor water level 3 signal was received, as expected, following the turbine trip and reactor scram and was promptly restored to the normal reactor water level band. The non-safety related turbine building chillers tripped as a result of the electrical transient caused by the generator trip. One area served by that cooling system is the reactor water cleanup ( RWCU) system heat exchanger room. Approximately 20 minutes after the scram, the temperature in that room exceeded the trip setpoint of the area temperature monitors, resulting in the automatic closure of the primary containment isolation valves for the RWCU system. |
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Category:Letter
MONTHYEARML24214A2752024-08-0202 August 2024 Acknowledgement of Readiness for Supplemental Inspection RBG-48308, Notification of Readiness for Supplemental Inspection2024-07-31031 July 2024 Notification of Readiness for Supplemental Inspection IR 05000458/20240022024-07-30030 July 2024 Integrated Inspection Report 05000458/2024002 and Notice of Violation ML24164A0862024-06-12012 June 2024 Notification of Commercial Grade Dedication Inspection (05000458/2024010) and Request for Information ML24060A2192024-05-30030 May 2024 Authorization of Alternative to Use EN-RR-01 Concerning Proposed Alternative to Adopt Code Case N-752 ML24081A0072024-05-16016 May 2024 Issuance of Amendment No. 213 Revision to Technical Specifications to Adopt TSTF 505, Revision 2, Provide Risk-Informed Extended Completion Times – RITSTF Initiative 4b ML24093A0892024-05-16016 May 2024 Issuance of Amendment No. 214 Adoption of 10 CFR 50.69, Risk-Informed Categorization and Treatment of Structures, Systems, and Components for Nuclear Power Reactors IR 05000458/20240012024-05-14014 May 2024 Integrated Inspection Report 05000458/2024001 ML24102A2842024-05-0707 May 2024 Summary of Regulatory Audit in Support of LARs to Revise Technical Specifications to Adopt Risk-Informed Completion Times and Implement the Provisions of 10 CFR 50.69 ML24128A0422024-05-0707 May 2024 License Amendment Request to Remove Obsolete License Conditions RBG-48276, 2023 Annual Radioactive Effluent Release Report2024-04-23023 April 2024 2023 Annual Radioactive Effluent Release Report IR 05000458/20244022024-04-15015 April 2024 Security Baseline Inspection Report 05000458/2024402 (Full Report) RBG-48288, Louisiana Pollutant Discharge Elimination System Permit Renewal2024-04-15015 April 2024 Louisiana Pollutant Discharge Elimination System Permit Renewal ML24106A0432024-04-11011 April 2024 June 2024 Emergency Preparedness Exercise Inspection Request for Information RBG-48277, 2023 Annual Radiological Environmental Operating Report2024-04-10010 April 2024 2023 Annual Radiological Environmental Operating Report ML24101A3882024-04-10010 April 2024 Response to Request for Confirmation of Information by the Office of Nuclear Reactor Regulation Proposed Alternative Request EN-RR-22-001 “Risk-Informed Categorization and Treatment for Repair IR 05000458/20243012024-04-0202 April 2024 Notification of NRC Initial Operator Licensing Examination 05000458/2024301 ML24089A2262024-03-29029 March 2024 Entergy Response to Regulatory Issue Summary 2024-01, Preparation and Scheduling of Operator Licensing Exams IR 05000458/20240402024-03-15015 March 2024 – 95001 Supplemental Inspection Report 05000458/2024040 and Follow-Up Assessment ML24075A1712024-03-15015 March 2024 Nuclear Onsite Property Damage Insurance (10 CFR 50.54(w)(3)) ML24074A2892024-03-14014 March 2024 Proof of Financial Protection (10 CFR 140.15) ML24066A1802024-03-0707 March 2024 Notification of NRC Follow-Up Inspection for Any Severity Level I or II Traditional Enforcement Violation IR 05000458/20230062024-02-28028 February 2024 Annual Assessment Letter for River Bend Station - Report 05000458/2023006 RBG-48278, 2023 Spent Fuel Storage Radioactive Effluent Release Report2024-02-27027 February 2024 2023 Spent Fuel Storage Radioactive Effluent Release Report RBG-48286, Revision to Owners Activity Report Form (OAR) for Cycle 222024-02-27027 February 2024 Revision to Owners Activity Report Form (OAR) for Cycle 22 ML24031A0042024-02-21021 February 2024 Exemption from Select Requirements of 10 CFR Part 73 (EPID L-2023-LLE-0052 (Security Notifications, Reports, and Recordkeeping and Suspicious Activity Reporting)) RBG-48274, Notification of Readiness for Supplemental Inspection2024-02-0505 February 2024 Notification of Readiness for Supplemental Inspection IR 05000458/20230042024-01-30030 January 2024 Integrated Inspection Report 05000458/2023004 IR 05000458/20230402024-01-18018 January 2024 95001 Supplemental Inspection Supplemental Report 05000458/2023040 and Follow-Up Assessment Letter ML24012A1962024-01-12012 January 2024 Response to 2nd Round Request for Additional Information Concerning Relief Request Number EN-RR-22-001 Proposed Alternative to Use ASME Code Case N-752, Risk-Informed Categorization and RBG-48271, Supplement to License Amendment Request to Adopt Risk Informed Completion Times TSTF-505, Revision 2, Provide Risk-Informed Extended Completion Times RITSTF Initiative 4b and Application to Adopt 10 CFR 50.69, Risk2024-01-12012 January 2024 Supplement to License Amendment Request to Adopt Risk Informed Completion Times TSTF-505, Revision 2, Provide Risk-Informed Extended Completion Times RITSTF Initiative 4b and Application to Adopt 10 CFR 50.69, Risk ML24011A1742024-01-11011 January 2024 Security Baseline Inspection Report (Cover Letter) ML23349A1672023-12-21021 December 2023 Request for Withholding Information from Public Disclosure ML23348A3572023-12-14014 December 2023 Application to Revise Technical Specifications to Use Online Monitoring Methodology Slides and Affidavit for Pre-Submittal Meeting ML23340A1592023-12-13013 December 2023 Entergy Operations, Inc. - Entergy Fleet Project Manager Assignment ML23352A0292023-12-13013 December 2023 Entergy - 2024 Nuclear Energy Liability Evidence of Financial Protection IR 05000458/20230102023-12-12012 December 2023 Biennial Problem Identification and Resolution Inspection Report 05000458/2023010 RBG-48267, Reply to a Notice of Violation, NRC Inspection Report 05000458/20230032023-12-0707 December 2023 Reply to a Notice of Violation, NRC Inspection Report 05000458/2023003 ML23333A1362023-11-29029 November 2023 Supplement to Request for Exemption from Enhanced Weapons, Firearms Background Checks, and Security Event Notifications Implementation ML23325A1432023-11-21021 November 2023 Request for Exemption from Enhanced Weapons, Firearms Background Checks, and Security Event Notifications Implementation IR 05000458/20230032023-11-13013 November 2023 Integrated Inspection Report 05000458/2023003 ML23310A0322023-11-13013 November 2023 Integrated Inspection Report 05000458/2023003 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 ML23311A4322023-11-0909 November 2023 Notification of NRC Supplemental Inspection (95001) and Request for Information RBG-48264, Core Operating Limits Report (COLR) - Cycle 23, Revision 12023-11-0606 November 2023 Core Operating Limits Report (COLR) - Cycle 23, Revision 1 RBG-48260, Notification of Readiness for Supplemental Inspection2023-10-12012 October 2023 Notification of Readiness for Supplemental Inspection ML23278A2402023-10-0606 October 2023 Regulatory Audit Plan in Support of License Amendment Requests to Revise TSs to Adopt Risk-Informed Completion Times and Implement the Provisions of 10 CFR 50.69 RBG-48258, Notification of Readiness for Supplemental Inspection2023-10-0505 October 2023 Notification of Readiness for Supplemental Inspection RBG-48259, Revision to Reply to Notice of Violation; EA-23-0552023-10-0303 October 2023 Revision to Reply to Notice of Violation; EA-23-055 ML23270B9932023-09-29029 September 2023 Request to Update ASME Boiler & Pressure Vessel Code Relief Request SE with NRC-Approved Revision of Bwrip Guidelines (GG-ISI-020 & RBS-ISI-019) (EPID L-2022-LLR-0090) - Non-Proprietary 2024-08-02
[Table view] Category:Licensee Event Report (LER)
MONTHYEAR05000458/LER-2017-0092017-11-13013 November 2017 Potential Loss of Safety Function of Secondary Containment due to Unsecured Personnel Door, LER 17-009-00 for River Bend, Unit 1 Regarding Potential Loss of Safety Function of Secondary Containment due to Unsecured Personnel Door 05000458/LER-2017-0072017-08-21021 August 2017 Automatic Reactor Scram due to Failure of Main Generator Voltage Regulator Mode Transfer Relay, LER 17-007-00 for River Bend Station - Unit 1 Regarding Automatic Reactor Scram due to Failure of Main Generator Voltage Regulator Mode Transfer Relay 05000458/LER-2017-0062017-07-13013 July 2017 Potential Loss of Safety Function of Onsite Power Sources due to Inadvertent Inoperability of Control Building Chiller, LER 17-006-00 for River Bend, Unit 1 re Potential Loss of Safety Function of Onsite Power Sources due to Inoperability of Control Building Chiller 05000458/LER-2016-0032017-06-0808 June 2017 Operations Prohibited by Technical Specifications Due to Reactor Control Rod Drift During Core Alterations, LER 16-003-01 for River Bend Station, Unit 1, Regarding Operations Prohibited by Technical Specifications Due to Control Blade Drift During Core Alterations 05000458/LER-2017-0052017-06-0505 June 2017 1 OF 3, LER 17-005-00 for River Bend Station, Unit 1, Regarding Operations Prohibited by Technical Specifications Due to Inoperable Main Control Room Filter Train 05000458/LER-2017-0042017-05-22022 May 2017 Loss of High Pressure Core Spray Safety Function During Surveillance Due to Malfunction of Test Return Valve, LER 17-004-00 for River Bend Station, Unit 1, Regarding Loss of High Pressure Core Spray Safety Function During Surveillance Due to Malfunction of Test Return Valve 05000458/LER-2017-0032017-05-0909 May 2017 Manual Reactor Scram Initiated in Response to Increase in Steam Pressure During Steam Leak Troubleshooting, LER 17-003-00 for River Bend Station, Unit 1, Regarding Manual Reactor Scram Initiated in Response to Increase in Steam Pressure During Steam Leak Troubleshooting 05000458/LER-2017-0022017-04-18018 April 2017 Loss of Safety Function of Onsite Electrical Distribution Due to Malfunction of Control Building HVAC System, LER 17-002-00 for River Bend Station, Unit 1, Regarding Loss of Safety Function of Onsite Electrical Distribution Due to Malfunction of Control Building HVAC System 05000458/LER-2017-0012017-04-0303 April 2017 Operations Prohibited by Technical Specifications (Conduct of Operations With a Potential to Drain the Reactor Vessel With Primary Containment Open), LER 17-001-00 for River Bend Station, Unit 1, Regarding Operations Prohibited by Technical Specifications (Conduct of Operations With a Potential to Drain the Reactor Vessel With Primary Containment Open) 05000458/LER-2016-0072016-07-25025 July 2016 1 Operations Prohibited by Technical Specifications Due to Failure to Implement Required Actions Within Completion Time, LER 16-007-00 for River Bend Station, Unit 1, Regarding Operations Prohibited by Technical Specifications Due to Failure to Implement Required Actions Within Completion Time 05000458/LER-2016-0062016-07-12012 July 2016 Potential Loss of Safety Function of Multiple Systems Due to Design Deficiency in 480-volt Circuit Breakers, LER 16-006-00 for River Bend Station re: Potential Loss of Safety Function of Multiple Systems Due to Design Deficiency in 480-volt Circuit Breakers 05000458/LER-2016-0042016-03-29029 March 2016 Actuation of the Division 1 Emergency Diesel Generator and Primary Containment Isolation Logic Due to Partial Loss of Offsite Power, LER 16-004-00 for River Bend, Unit 1, Regarding Actuation of the Division 1 Emergency Diesel Generator and Primary Containment Isolation Logic Due to Partial Loss of Offsite Power 05000458/LER-2016-0022016-03-0707 March 2016 Automatic Reactor Scram and Division 2 Primary Containment Isolation Due to Offsite Grid Electrical Transient, LER 16-002-00 for River Bend, Unit 1, Regarding Automatic Reactor Scram and Division 2 Primary Containment Isolation Due to Offsite Grid Electrical Transient 05000458/LER-2016-0012016-03-0707 March 2016 Potential Loss of Secondary Containment Safety Function Due to Failure of Auxiliary Building Ventilation System, LER 16-001-00 for River Bend, Unit 1, Regarding Potential Loss of Secondary Containment Safety Function Due to Failure of Auxiliary Building Ventilation System 05000458/LER-2015-0102016-02-0808 February 2016 Potential Loss of Safety Function of High Pressure Core Spray Due to Failure of Main Control Building Ventilation Chiller, LER 15-010-00 for River Bend Station, Unit 1, Regarding Potential Loss of Safety Function of High Pressure Core Spray Due to Failure of Main Control Building Ventilation Chiller 05000458/LER-2015-0092016-01-26026 January 2016 1 OF 3, LER 15-009-00 for River Bend Station, Unit 1 Regarding Automatic Reactor Scram Due to Partial Loss of Offsite Power Caused by Fault in Local 230K Switchyard 05000458/LER-2015-0082016-01-18018 January 2016 Potential Loss of Safety Function of High Pressure Core Spray Due to Failure of Main Control Building Ventilation Chiller, LER 15-008-00 of River Bend Station, Unit 1, Regarding Loss of Safety Function of High Pressure Core Spray Due to Failure of Main Control Building Ventilation Chiller 05000458/LER-2015-0072016-01-18018 January 2016 Potential Loss of Safety Function of High Pressure Core Spray Due to Failure of Main Control Building Ventilation Chiller, LER 15-007-00 for River Bend Station - Unit 1 Regarding Potential Loss of Safety Function of High Pressure Core Spray Due to Failure of Main Control Building Ventilation Chiller RBG-47473, Special Report for NEI 07-07 Notification2014-06-0404 June 2014 Special Report for NEI 07-07 Notification ML0627100382006-05-16016 May 2006 Final Precursor Analysis - River Bend Station, LER-458/04-005-01, Automatic Reactor Trip Due to Loss of Non-Vital 120V Instrument Bus 2017-08-21
[Table view] |
comments regarding burden estimate to the Information Services Branch tT-2 F43). U S. Nuclear Regulatory Commission Washington. DC 20555-0001, or by e-mail to Infocollects.Resourceenrc.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 :s trot required to ,espond to the information collection the River Bend Station — Unit 1 05000-458 1-REM
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REPORTED CONDITION
On June 23, 2017, at 10:18 PM CDT, an unanticipated reactor scram occurred during scheduled testing of the main turbine generator. The plant was operating at 100 percent power at the time, and no safety-related equipment was out of service. A reactor recirculation system flow control valve runback occurred as designed, and the recirculation pumps properly downshifted to slow speed. The main feedwater system responded properly to control reactor water level.
The scram signal was initiated by the closure of the main turbine control valves, which was an automatic response to a trip of the main generator. The associated steam pressure increase following turbine valve closure resulted in the actuation of 12 main steam safety-relief valves. A reactor water level 3 signal was received, as expected, following the turbine trip and reactor scram and was promptly restored to the normal reactor water level band.
The non-safety related turbine building chillers tripped as a result of the electrical transient caused by the generator trip.
One area served by that cooling system is the reactor water cleanup (RWCU) system heat exchanger room.
Approximately 20 minutes after the scram, the temperature in that room exceeded the trip setpoint of the area temperature monitors, resulting in the automatic closure of the primary containment isolation valves for the RWCU system.
This event is being reported in accordance with 10 CFR 50.73(a)(2)(iv)(A) as an unplanned actuation of the reactor protection system.
INVESTIGATION
At the time of the event, the operators were performing scheduled quarterly testing of the voltage regulator for the main generator [EL]. It has both a manual and automatic mode of operation.
Generator excitation is controlled by varying field current to the exciter, and field excitation is controlled by a static voltage regulator. The regulator includes both automatic and manual functions to regulate generator terminal voltage or generator field voltage, respectively.
When operating in manual control, the DC regulator holds the main generator field voltage constant. When operating in automatic control, the AC regulator holds the main generator output voltage constant. A transfer voltmeter is used for matching signals to provide a smooth transfer between the two regulators. A tracking circuit is provided to automatically match the two regulators. The regulator mode transfer relay (**RLY**) is energized by the automatic mode pushbutton to place the excitation system in automatic control. It is de-energized by the auto mode pushbutton, over excitation limit circuit, or high exciter field current.
The voltage regulator test is performed on a quarterly basis. At a specific point in the test, the "Voltage Regulator Mode Select MAN" pushbutton is depressed. The expected response would be a swap of the voltage regulator control to the manual mode from the automatic mode. This test had been successfully performed in March 2017, following the used to impose an information collection does not display a currently valid OMB control numoer. the NRC may not conduct or sponsor. and a person is riot required to respond to. the information collection.
replacement of the mode transfer relay. During the test performed on June 23rd, the main generator tripped when that procedure step was performed.
CAUSAL ANALYSIS
The main generator trip and subsequent turbine trip and reactor scram was caused by a failed relay in the transfer circuit between the automatic and manual voltage regulation modes. The regulator mode transfer relay was changed in the March 2017 refueling outage as a scheduled 10-year preventive maintenance task. The failed relay has been shipped to a vendor for failure analysis. Possible signs of arcing were seen on several contact pins, but no definitive failure cause was found. The postulated failure mode could not be replicated. Since the relay had been in service for only 4 months, this is considered an "infant mortality" type of failure.
Based on the failure analysis, it was determined that the generator voltage regulator mode transfer relay failed to perform its function when the operator attempted to switch from the automatic mode to the manual mode. High electrical resistance measured across some of the contact pins exceeded the troubleshooting acceptance criteria. It is postulated that the relay contacts did not effectively change state during the test, and thus failed to provide continuous excitation to the voltage regulator, which led to the automatic generator trip.
CORRECTIVE ACTION TO PREVENT RECURRENCE
The voltage regulator mode transfer relay was replaced with an updated model that has demonstrated no vulnerability to the failure mode postulated to have caused this event.
PREVIOUS OCCURRENCE EVALUATION
No similar occurrence has been reported by River Bend Station in the last three years.
SAFETY SIGNIFICANCE
The plant response to this event was bounded by the Updated Safety Analysis Report analysis of a main generator load reject with steam bypass / pressure regulation in service. Thus, this event was of minimal significance to the health and safety of the public.
(NOTE: Energy Industry Identification System component function identifier and system name of each component or system referred to in the LER are annotated as (**XX**) and [XXI, respectively.)