09-20-2017 | On July 23, 2017, the Emergency Diesel Generator ( EDG) lube oil cooler immersion heater temperature switch failed (in the on position) which together with residual heat from 12 EDG operation actuated the EDG engine temperature switch resulting in a valid start signal to the 12 EDG Emergency Service Water ( ESW) System pump and transfer of pump control to the Alternate Shutdown System panel. In accordance with 10 CFR 50.73(a)(2)(iv)(A) an automatic actuation of the ESW System is reportable. The apparent cause of the 12 EDG hot engine condition was a failed temperature switch for the immersion heater in concert with operating the 12 EDG. From the time of the problem identification through the 12 EDG surveillance test, lube oil temperature was monitored by Operations and never exceeded the normal operating band when the EDG was in the shutdown ready-to-start configuration and during the EDG monthly surveillance run. Therefore, the 12 EDG remained operable. The immediate corrective action was replacement of the failed temperature switch. A long-term corrective action is to evaluate the immersion heater and associated control circuit to determine if the temperature switch design and preventative maintenance frequency are appropriate. Corrective action will be taken based on the results of this evaluation. |
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Category:Letter
MONTHYEARML24025A9362024-01-31031 January 2024 Exemption from Select Requirements of 10 CFR Part 73 (EPID L-2023-LLE-0055 (Security Notifications, Reports, and Recordkeeping and Suspicious Activity Reporting)) IR 05000263/20230042024-01-31031 January 2024 Integrated Inspection Report 05000263/2023004 ML24024A0722024-01-24024 January 2024 Independent Spent Fuel Storage Installation, Onticello, Supplement to Request for Exemption from Enhanced Weapons, Firearms Background Checks, and Security Event Notifications Implementation IR 05000263/20244012024-01-22022 January 2024 Information Request for the Cyber-Security Baseline Inspection, Notification to Perform Inspection 05000263/2024401 L-MT-23-054, Subsequent License Renewal Application Supplement 82024-01-11011 January 2024 Subsequent License Renewal Application Supplement 8 L-MT-23-047, License Amendment Request: Revision to the MNGP Pressure Temperature Limits Report to Change the Neutron Fluence Methodology and Incorporate New Surveillance Capsule Data2023-12-29029 December 2023 License Amendment Request: Revision to the MNGP Pressure Temperature Limits Report to Change the Neutron Fluence Methodology and Incorporate New Surveillance Capsule Data L-MT-23-056, Subsequent License Renewal Application Response to Request for Additional Information and Request for Confirmation of Information - Set 1 Part 22023-12-18018 December 2023 Subsequent License Renewal Application Response to Request for Additional Information and Request for Confirmation of Information - Set 1 Part 2 ML23349A0572023-12-15015 December 2023 and Independent Spent Fuel Storage Installation, Revision to Correspondence Service List for Northern States Power - Minnesota IR 05000263/20234022023-12-13013 December 2023 Security Baseline Inspection Report 05000263/2023402 L-MT-23-042, 2023 Annual Report of Changes in Emergency Core Cooling System Evaluation Models Pursuant to 10 CFR 50.462023-12-11011 December 2023 2023 Annual Report of Changes in Emergency Core Cooling System Evaluation Models Pursuant to 10 CFR 50.46 L-MT-23-052, Subsequent License Renewal Application Supplement 72023-11-30030 November 2023 Subsequent License Renewal Application Supplement 7 L-MT-23-051, Update to the Technical Specification Bases2023-11-28028 November 2023 Update to the Technical Specification Bases L-MT-23-049, Subsequent License Renewal Application Response to Request for Additional Information and Request for Confirmation of Information - Set 12023-11-21021 November 2023 Subsequent License Renewal Application Response to Request for Additional Information and Request for Confirmation of Information - Set 1 ML23319A3182023-11-15015 November 2023 Request for Exemption from Enhanced Weapons, Firearms Background Checks, and Security Event Notifications Implementation IR 05000263/20230032023-11-13013 November 2023 Integrated Inspection Report 05000263/2023003 and 07200058/2023001 L-MT-23-043, 10 CFR 50.55a(z)(1) Request Regarding OMN-17, Revision 1. VR-092023-11-13013 November 2023 10 CFR 50.55a(z)(1) Request Regarding OMN-17, Revision 1. VR-09 L-MT-23-038, License Amendment Request to Revise Monticello Technical Specification Surveillance Requirement 3.8.6.62023-11-10010 November 2023 License Amendment Request to Revise Monticello Technical Specification Surveillance Requirement 3.8.6.6 L-MT-23-046, Subsequent License Renewal Application Response to Request for Additional Information Round 2 - Set 12023-11-0909 November 2023 Subsequent License Renewal Application Response to Request for Additional Information Round 2 - Set 1 ML23291A1102023-10-23023 October 2023 Environmental Audit Summary and RCIs and RAIs ML23285A3062023-10-12012 October 2023 Implementation of the Fleet Standard Emergency Plan for the Monticello Nuclear Generating Plant and the Prairie Island Nuclear Generating Plant L-MT-23-041, Subsequent License Renewal Application Response to Request for Confirmation of Information Set 22023-10-0303 October 2023 Subsequent License Renewal Application Response to Request for Confirmation of Information Set 2 L-MT-23-037, Subsequent License Renewal Application Response to Request for Additional Information Set 32023-09-22022 September 2023 Subsequent License Renewal Application Response to Request for Additional Information Set 3 ML23262B0372023-09-19019 September 2023 Response to NRC Request for Additional Information Regarding the 2023 Monticello and Prairie Island Plant Decommissioning Funding Status Reports ML23248A2092023-09-18018 September 2023 Proposed Alternative VR-11 to the Requirements of the ASME OM Code Associated with Periodic Verification Testing of MO-2397, Reactor Water Cleanup Inboard Isolation Valve ML23256A1682023-09-13013 September 2023 Independent Spent Fuel Storage Installation and Monticello Nuclear Generating Plant - Voluntary Security Clearance Program 2023 Insider Threat Program Self-Inspection IR 05000263/20230102023-09-0707 September 2023 Commercial Grade Dedication Inspection Report 05000263/2023010 L-MT-23-036, Subsequent License Renewal Application Response to Request for Additional Information Set 2 and Supplement 62023-09-0505 September 2023 Subsequent License Renewal Application Response to Request for Additional Information Set 2 and Supplement 6 ML23214A2412023-08-31031 August 2023 Letter: Aging Management Audit - Monticello Unit 1 - Subsequent License Renewal Application IR 05000263/20230052023-08-30030 August 2023 Updated Inspection Plan for Monticello Nuclear Generating Plant (Report 05000263/2023005) L-MT-23-035, Subsequent License Renewal Application Supplement 52023-08-28028 August 2023 Subsequent License Renewal Application Supplement 5 ML23241A9732023-08-21021 August 2023 Request for Scoping Comments Concerning the Environmental Review of Monticello Nuclear Generating Plant, Unit 1, Subsequent License Renewal Application (Docket No. 50-263) L-MT-23-034, Subsequent License Renewal Application Response to Request for Additional Information Set 12023-08-15015 August 2023 Subsequent License Renewal Application Response to Request for Additional Information Set 1 ML23222A0122023-08-10010 August 2023 Independent Spent Fuel Storage Installation and Monticello Nuclear Generating Plant - Changes in Foreign Ownership, Control or Influence ML23215A1312023-08-0909 August 2023 License Renewal Regulatory Audit Regarding the Environmental Review of the Subsequent License Renewal Application IR 05000263/20230022023-08-0707 August 2023 Plantintegrated Inspection Report 05000263/2023002 L-MT-23-028, 2023 Refueling Outage 90-Day Inservice Inspection (ISI) Summary Report2023-07-31031 July 2023 2023 Refueling Outage 90-Day Inservice Inspection (ISI) Summary Report L-MT-23-032, 10 CFR 50.55a(z)(2) Request Regarding MO-2397, VR-112023-07-31031 July 2023 10 CFR 50.55a(z)(2) Request Regarding MO-2397, VR-11 ML23198A0412023-07-28028 July 2023 LRA Availability Letter ML23206A2342023-07-25025 July 2023 Independent Spent Fuel Storage Installation, and Monticello Nuclear Generating Plant, Changes in Foreign Ownership, Control or Influence ML23201A0352023-07-24024 July 2023 Notification of an NRC Biennial Licensed Operator Requalification Program Inspection and Request for Information ML23202A0032023-07-21021 July 2023 Independent Spent Fuel and Independent Spent Fuel Storage Installation, Monticello Nuclear Generating Plant, Submittal of Quality Assurance Topical Report (NSPM-1) L-MT-23-031, Subsequent License Renewal Application Supplement 4 and Responses to Request for Confirmation of Information - Set 12023-07-18018 July 2023 Subsequent License Renewal Application Supplement 4 and Responses to Request for Confirmation of Information - Set 1 ML23195A1732023-07-14014 July 2023 Revision of Standard Practice Procedures Plan IR 05000263/20235012023-07-13013 July 2023 Emergency Preparedness Inspection Report 05000263/2023501 2024-01-31
[Table view] Category:Licensee Event Report (LER)
MONTHYEAR05000263/LER-2017-0062018-01-12012 January 2018 Loss of Reactor Protection System Scram Function During Main Steam Isolation Valve and Turbine Stop Valve Channel Functional Tests due to Use of a Test Fixture, LER 17-006-00 for Monticello Regarding Loss of Reactor Protection System Scram Function During Main Steam Isolation Valve and Turbine Stop Valve Channel Functional Tests Due to Use of a Test Fixture 05000263/LER-2017-0052017-09-20020 September 2017 Diesel Generator Emergency Service Water System Automatic Transfer to Alternate Shutdown Panel, LER 17-005-00 for Monticello Nuclear Generating Plant Regarding Diesel Generator Emergency Service Water System Automatic Transfer to Alternate Shutdown Panel 05000263/LER-2015-0042017-08-22022 August 2017 Past Inoperability of Turbine Stop Valve Scram Function Exceeded Technical Specification Requirements, LER 15-004-01 for Monticello Regarding Past Inoperability of Turbine Stop Valve Scram Function Exceeded Technical Specification Requirements 05000263/LER-2017-0042017-08-16016 August 2017 High Pressure Coolant Injection Steam Stop Valve Failed to Open During Test, LER 17-004-00 for Monticello Regarding High Pressure Coolant Injection Steam Stop Valve Failed to Open During Test 05000263/LER-2017-0032017-06-14014 June 2017 Main Steam Isolation Valve Leakage Exceeds Technical Specification Limits, LER 17-003-00 for Monticello Regarding Main Steam Isolation Valve Leakage Exceeds Technical Specification Limits 05000263/LER-2017-0012017-06-13013 June 2017 Reactor Scram and Group II Isolation Due to 11 Reactor Feed Pump (RFP) Removal from Service with 12 RFP Isolated, LER 17-001-00 for Monticello Regarding Reactor Scram and Group II Isolation Due to 11 Reactor Feed Pump (RFP) Removal from Service with 12 RFP Isolated 05000263/LER-2017-0022017-06-13013 June 2017 Main Steam Isolation Valve Closure Time Outside of Technical Specification Requirements, LER 17-002-00 for Monticello Nuclear Generating Plant Regarding Main Steam Isolation Valve Closure Time Outside of Technical Specification Requirements 05000263/LER-2016-0032017-05-25025 May 2017 HPCI Declared Inoperable Due to Excessive Water Level in Turbine, LER 16-003-01 for Monticello Regarding HPCI Declared Inoperable Due to Excessive Water Level in Turbine 05000263/LER-2016-0012017-05-25025 May 2017 High Pressure Coolant Injection System Cracked Pipe Nipple Caused Oil Leak, LER 16-001-02 for Monticello Regarding High Pressure Coolant Injection System Cracked Pipe Nipple Caused Oil Leak 05000263/LER-2016-0022016-09-30030 September 2016 Inadequate Appendix R Fire Barrier Impacts Safe Shutdown Capability, LER 16-002-00 for Monticello Regarding Inadequate Appendix R Fire Barrier Impacts Safe Shutdown Capability 05000263/LER-2014-0032016-07-13013 July 2016 Torus to Drywell Vacuum Breaker Dual Indication During Testing, LER 14-003-01 for Monticello Nuclear Generating Plant RE: Torus to Drywell Vacuum Breaker Dual Indication During Testing 05000263/LER-2014-0022016-07-13013 July 2016 Torus to Drywell Vacuum Breaker Did Not Indicate Closed During Testing, LER 14-002-01 for Monticello Regarding Torus to Drywell Vacuum Breaker Did Not Indicate Closed During Testing 05000263/LER-2015-0072016-01-21021 January 2016 Loss of Residual Heat Removal Capability, LER 15-007-00 for Monticello Regarding Loss of Residual Heat Removal Capability 05000263/LER-2015-0062016-01-21021 January 2016 - Reactor Scram due to Group 1 Isolation from Foreign Material in the Main Steam Flow Instrument Line, LER 15-006-00 for Monticello Regarding Reactor Scram due to Group 1 Isolation from Foreign Material in the Main Steam Flow Instrument Line ML1015505712009-09-12012 September 2009 Event Notification for Monticello on State Offsite Notification Due to Not Meeting Permit Requirements L-MT-05-035, LER 50-004-00 for Monticello Nuclear Generating Plant Regarding Voluntary LER for Control Rod Drive Insert Line Leakage2005-05-12012 May 2005 LER 50-004-00 for Monticello Nuclear Generating Plant Regarding Voluntary LER for Control Rod Drive Insert Line Leakage ML0216100952002-05-15015 May 2002 LERs 02-001-01 & 02-002-01 for Monticello Nuclear Generating Plant Re Mechanical Pressure Regulator Failure Causes Reactor Scram & Application of Instrument Deviation Acceptance Criteria Allowed As-Found Settings to Be Outside Tech Spec Val 2018-01-12
[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 Infccollects.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.
EVENT DESCRIPTION
On July 19, 2017, at 1149 hours0.0133 days <br />0.319 hours <br />0.0019 weeks <br />4.371945e-4 months <br />, it was identified that lube oil temperature for the 12 Emergency Diesel Generator (EDG) [EllS: DG] had made a step change stabilizing at approximately 150°F.
The step change indicated that the immersion heater was either not operating properly or was cycling abnormally. On July 20, 2017, at 1634 hours0.0189 days <br />0.454 hours <br />0.0027 weeks <br />6.21737e-4 months <br />, after troubleshooting, it was identified that the temperature switch controlling the 12 EDG immersion heater had failed, causing it to be continuously on. It was determined that since this condition did not result in temperatures outside the normal operating band, no compensatory measures were required but additional monitoring by Operations was implemented.
On July 23, 2017, with the unit in Mode 1, at 100 percent rated thermal power, surveillance procedure 0187-02, "12 Emergency Diesel Generator / 12 ESW [Emergency Service Water System] Quarterly Pump and Valve Test," was performed. After shutting down the 12 EDG in accordance with the surveillance procedure, at 1332 hours0.0154 days <br />0.37 hours <br />0.0022 weeks <br />5.06826e-4 months <br />, Annunciator 8-C-21 (NO. 12 DIESEL ENG TROUBLE) was logged in the Control Room. An in-plant operator reported that Annunciator C94-A- 13 (HOT ENGINE) was in alarm and could not be reset. This condition resulted in a valid start signal to the 12 EDG Emergency Service Water System [BI] (EDG-ESW) pump (which was already running) and an automatic transfer of the pump control to the Alternate Shutdown System (ASDS) panel.
EDG cooling water flows from the heat exchangers to a EDG lube oil system [LA] lube oil cooler.
At the inlet to the lube oil cooler is a manifold containing an engine temperature switch and an immersion heater [EHTR] temperature switch (TS-7195) [TS]. If EDG engine water temperature reaches 190°F the engine temperature switch actuates the hot engine relay, which starts and transfers control of the 12 EDG-ESW pump to the ASDS panel. During EDG engine shutdown, water heated by a 15 KW immersion heater (controlled by TS-7195) circulates through the lube oil cooler by natural circulation to maintain oil temperature between 135°F and 165°F; 85°F is the required minimum temperature to ensure EDG fast start capability.
Investigation identified that the switch contacts for the immersion heater temperature switch (Manufacturer: Square D, Model No. GZW2-5102, Serial No. 40036996) had failed in the closed position, causing the immersion heater to be continuously on when the 12 EDG was shutdown in a standby state. While this condition did not raise temperature out of specification prior to EDG engine operation, it did add enough local heat to bring in the alarm after the engine was shutdown following a run due to the residual heat.
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.
This condition activated the engine temperature switch, in turn actuating the hot engine relay, which resulted in an auto start signal to the already running 12 EDG-ESW pump, and an automatic transfer of pump control to the ASDS panel. The immersion heater temperature switch was replaced on July 25, 2017.
EVENT ANALYSIS
This condition is being reported in accordance with 10 CFR 50.73(a)(2)(iv)(A), "Any event or condition that resulted in manual or automatic actuation of any of the systems listed in paragraph 10 CFR 50.73(a)(2)(iv)(B)". Specifically, criteria 10 CFR 50.73(a)(2)(iv)(B)(9) for ESW "systems that do not normally run and that serve as ultimate heat sinks" applies. This event is not classified as a safety system functional failure.
CAUSE
The apparent cause of the 12 EDG hot engine condition was a failed temperature switch for the immersion heater in concert with operating the 12 EDG. Following completion of the surveillance test, the 12 EDG was shutdown and returned to the automatic standby mode. When the EDG is shutdown the immersion heater automatically cycles back on and controls lube oil temperature to between 135°F and 165°F. With the immersion heater failed in the on position along with the residual heat from engine operation a localized hot spot occurred that was sufficient to actuate the transfer of control of the 12 EDG-ESW pump to the ASDS panel.
SAFETY SIGNIFICANCE
The immersion heater (and control) is required to maintain EDG engine operability while in the standby state by maintaining EDG lube oil temperature greater than 85°F to ensure fast start capability. With the immersion heater continuously on, the 12 EDG lube oil temperature stabilized at 154°F, well above the minimum and within the required band. Prior to the monthly surveillance test, engine temperatures recorded on operator rounds were within the normal acceptance band.
During the 12 EDG engine run, the coolant temperature was maintained at approximately 175°F, which is within the normal operating range, and below the hot engine alarm setpoint. From the time of problem identification through the 12 EDG surveillance test, lube oil temperature was monitored by operations and never exceeded the normal operating band. This includes when the EDG was in the shutdown ready-to-start configuration and during the EDG monthly surveillance run. Therefore, the 12 EDG remained operable.
Monticello Nuclear Generating Plant 05000-263 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 Infocollects.Resource@nrc.gov, arid to the Desk Officer. Office of Information arid 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.
There was no safety significance to transmittal of the valid start signal to the 12 EDG-ESW pump.
The start of the 12 EDG-ESW pump and transfer of control to the ASDS panel does not prevent the cooling of the 12 EDG or impact the ability of the 12 EDG to perform its safety function. This condition did not impact EDG, EDG-ESW System, or ASDS System operability since the lube oil temperatures never exceeded the normal EDG operating band, and the system logic operated as designed and engine cooling was always available.
CORRECTIVE ACTIONS
The immediate corrective action was to replace the failed immersion heater temperature switch, TS-7195.
The long-term corrective actions are:
1. Evaluate the immersion heater and associated control circuit to determine if the temperature switch design and preventative maintenance frequency are appropriate. Based on the results, take action to address identified deficiencies.
2. Revise plant procedures to include discussion of component(s) not operating correctly or in configurations that are abnormal, so that the impact of the condition is properly understood and controlled.
PREVIOUS SIMILAR EVENTS
On April 29, 2014, it was identified that a similar issue occurred following shutdown from performance of the surveillance. The engine temperature switch and the immersion heater temperature switch setpoint bands were found to be out of adjustment resulting in the 12 EDG engine residual heat actuating the hot engine temperature switch. This resulted in an automatic start signal to the 12 EDG-ESW pump and transfer of pump control to the ASDS panel. Note, the immersion heater temperature switch did not fail during this occurrence. The condition was corrected by installation of new temperature switches with the proper operating parameters.