08-15-2017 | On June 16, 2017, with the plant in Mode 1 and 100% reactor power, the 'A' Ultimate Heat Sink ( UHS) Cooling Tower Fan was operating in fast-speed to cool the UHS retention pond. The fan spuriously tripped after 44 minutes of operation. The most probable cause of the spurious trip was a defective fast-speed thermal overload relay that had been installed as a replacement during recent preventative maintenance activities.
In Mode 1, Technical Specifications require each of two redundant UHS cooling tower trains to be capable of dissipating the heat contained in the Essential Service Water (ESW) system. An inoperable UHS cooling tower fan renders its UHS cooling tower train inoperable. Review determined that the fan was inoperable from the start of the preventative maintenance task, and existed for a duration of 96 hours0.00111 days <br />0.0267 hours <br />1.587302e-4 weeks <br />3.6528e-5 months <br /> and 23 minutes while the plant was in Mode 1. Consequently, it was concluded that the 'A' UHS Cooling Tower Train had been inoperable for a period of time longer than allowed by the plant's Technical Specifications.
Failure analysis is being performed by a vendor which will provide insight into the nature of the defective fast speed thermal overload relay. Maintenance procedures will be revised to include additional pre-installation testing of similar thermal overload relays to ensure that defects similar to the one that caused the reported failure are detected prior to installation in the plant. |
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LER-2017-001, Violation of Technical Specification 3.7.9 Due to Ultimate Heat Sink (UHS) Cooling Tower Train InoperabilityDocket Number |
Event date: |
06-16-2017 |
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Report date: |
08-15-2017 |
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Reporting criterion: |
10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
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4832017001R00 - NRC Website |
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Category:Letter
MONTHYEARULNRC-06853, Submittal of 2023 Fitness for Duty Performance Data Per Per 10 CFR 26.7172024-01-29029 January 2024 Submittal of 2023 Fitness for Duty Performance Data Per Per 10 CFR 26.717 ML24008A0552024-01-19019 January 2024 Acceptance of Requested Licensing Action - Proposed Alternative to the Requirements of the ASME Code (EPID L-2023-LLR- 0061) IR 05000483/20230042024-01-19019 January 2024 Integrated Inspection Report 05000483/2023004 ML23353A1712024-01-18018 January 2024 Issuance of Amendment No. 237 to Clarify Support System Requirements for the Residual Heat Removal System and Control Room Air Conditioning System Under Technical Specifications 3.4.8, 3.7.11, and 3.9.6 ML23317A0012024-01-12012 January 2024 Audit Summary Regarding LAR to Clarify Support System Requirements for the Residual Heat Removal and Control Room Air Conditioning System Under Technical Specifications 3.4.8, 3.7.11, and 3.9.6 ML23347A1212024-01-11011 January 2024 Issuance of Amendment No. 236 to Adopt TSTF-501, Revision 1, Relocate Stored Fuel Oil and Lube Volume Values to Licensee Control EPID L-2023-LLA-0046) ML24011A1492024-01-11011 January 2024 Notification of Post-Approval Site Inspection for License Renewal and Request for Information (05000483/2024011) ULNRC-06847, Supplement to Relief Request from Requirements of ASME BPV Code, Section XI, Subsection Iwl Regarding Examination and Testing of the Unbonded Post-Tensioning System (Relief Request C3R-01)2023-12-21021 December 2023 Supplement to Relief Request from Requirements of ASME BPV Code, Section XI, Subsection Iwl Regarding Examination and Testing of the Unbonded Post-Tensioning System (Relief Request C3R-01) ULNRC-06849, License Renewal Resolution for Commitments 34 and 35 Perform Evaluation of Crack Initiation and Propagation in Steam Generator Divider Plate and Tube-To-Tubesheet Welds2023-12-20020 December 2023 License Renewal Resolution for Commitments 34 and 35 Perform Evaluation of Crack Initiation and Propagation in Steam Generator Divider Plate and Tube-To-Tubesheet Welds ML23346A0392023-12-14014 December 2023 Supplemental Information Needed for Acceptance of Requested Licensing Action Request for Relief from Requirements of ASME Code, Section Xl, Examination and Testing Unbonded Post-Tensioning System ULNRC-06844, Request for Exemption from Specific Requirements in 2023 Security Rule, Enhanced Weapons, Firearms Background Checks, and Security Event Notification2023-12-0707 December 2023 Request for Exemption from Specific Requirements in 2023 Security Rule, Enhanced Weapons, Firearms Background Checks, and Security Event Notification 05000483/LER-2023-001, Submittal of LER 2023-001-00 for Callaway, Unit 1, Inoperable Instrument Tunnel Sump Level Indication Resulted in Condition Prohibited by Technical Specifications2023-11-29029 November 2023 Submittal of LER 2023-001-00 for Callaway, Unit 1, Inoperable Instrument Tunnel Sump Level Indication Resulted in Condition Prohibited by Technical Specifications ULNRC-06827, Supplement to License Amendment Request Regarding Support System Requirements for Residual Heat Removal and Control Room Air Conditioning Systems Under Technical Specifications 3.4.8, 3.7.11, and 3.9.6 (LDCN 22-0029)2023-11-20020 November 2023 Supplement to License Amendment Request Regarding Support System Requirements for Residual Heat Removal and Control Room Air Conditioning Systems Under Technical Specifications 3.4.8, 3.7.11, and 3.9.6 (LDCN 22-0029) IR 05000483/20230102023-11-15015 November 2023 NRC License Renewal Phase 1 Inspection Report 05000483 2023010 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 IR 05000483/20233012023-11-0909 November 2023 NRC Examination Report 05000483-2023301 ML23297A2502023-11-0606 November 2023 Individual Notice of Consideration of Issuance of Amendment to Renewed Facility Operating License, Proposed No Significant Hazards Consideration Determination and Opportunity for a Hearing (EPID L-2022-LLA-0176) - Letter IR 05000483/20240122023-10-24024 October 2023 Information Request for the Cybersecurity Baseline Inspection, Notification to Perform Inspection (05000483/2024012) ML23293A2652023-10-24024 October 2023 3rd Quarter 2023 Integrated Inspection Report ML23234A1522023-10-0505 October 2023 Exemption from the Requirements of 10 CFR Part 50, Section 50.46, and Appendix K Regarding Use of M5 Cladding Material (EPID L-2022-LLE-0030) (Letter) ML23240A3692023-10-0505 October 2023 Issuance of Amendment No. 235 to Revise Technical Specifications to Use of Framatome Gaia Fuel (EPID L-2022-LLA-0150) (Non-Proprietary) ML23305A0942023-10-0202 October 2023 10-CW-2023-09 Post-Exam Submittal ML23270B9662023-09-27027 September 2023 10 CFR 50.55a(z)(I) Request for Relief from ASME OM Code Pump and Valve Testing Requirements for Fifth 120-Month Inservice Testing Interval ML23228A0252023-09-25025 September 2023 Issuance of Amendment No. 234 to Revise Technical Specification 5.5.16, Containment Leakage Rate Testing Program, for Permanent Extension of Type a and Type C Leak Rate Test Frequencies ML23261C3852023-09-25025 September 2023 Safety Evaluation for Operating Quality Assurance Manual Revision 36A ML23166B0882023-09-20020 September 2023 Issuance of Amendment No. 233 for Adoption of Alternative Source Term and Revision of Technical Specifications ML23206A1992023-09-15015 September 2023 Regulatory Audit Summary Regarding License Amendment and Regulatory Exemptions Request for Fuel Transition to Framatome Gaia Fuel (Epids L-2022-LLA-0150 and L-2022-LLE-0030) IR 05000483/20234012023-09-13013 September 2023 NRC Security Baseline Inspection Report 05000483/2023401 ML23240A7572023-08-31031 August 2023 NRC Initial Operator Licensing Examination Approval 05000483/2023301 IR 05000483/20230052023-08-23023 August 2023 Updated Inspection Plan for Callaway Nuclear Power Plant, Unit 1 (Report 05000483/2023005) - Mid Cycle Letter 2023 ULNRC-06824, Response to Request for Additional Information Regarding Operating Quality Assurance Manual (Oqam) Revision 36A2023-08-17017 August 2023 Response to Request for Additional Information Regarding Operating Quality Assurance Manual (Oqam) Revision 36A ML23219A1392023-08-15015 August 2023 Request for Withholding Information from Public Disclosure ULNRC-06830, Transmittal of Updated Technical Specification Markup and Clean Pages for License Amendment Request to Revise Technical Specification 5.5.16, Containment Leakage Rate Testing Program, for Permanent Extension of Type a and Type C Leak2023-08-15015 August 2023 Transmittal of Updated Technical Specification Markup and Clean Pages for License Amendment Request to Revise Technical Specification 5.5.16, Containment Leakage Rate Testing Program, for Permanent Extension of Type a and Type C Leak ML23215A1972023-08-0303 August 2023 Supplement to License Amendment and Exemption Request Regarding Use of Framatome Gaia Fuel (LDCN 22-0002) ULNRC-06223, Minor Correction to License Amendment Request to Revise Technical Specification 5.5.16, Containment Leakage Rate Testing Program, for Permanent Extension of Type a and Type C Leak Rate Test Frequencies (LDCN 2020-0004)2023-07-25025 July 2023 Minor Correction to License Amendment Request to Revise Technical Specification 5.5.16, Containment Leakage Rate Testing Program, for Permanent Extension of Type a and Type C Leak Rate Test Frequencies (LDCN 2020-0004) ULNRC-06799, Submittal of Licensee Event Report 2022-003-01, Class 1E Electrical Air Conditioning System Thermal Expansion Valve Failure Resulted in Condition Prohibited by Technical Specifications2023-07-13013 July 2023 Submittal of Licensee Event Report 2022-003-01, Class 1E Electrical Air Conditioning System Thermal Expansion Valve Failure Resulted in Condition Prohibited by Technical Specifications IR 05000483/20230022023-07-10010 July 2023 Integrated Inspection Report 05000483/2023002 ML23174A1272023-06-23023 June 2023 Cw FFD Document Request List 2023 ML23171A9942023-06-22022 June 2023 Acceptance of Request for Approval of Operating Quality Assurance Manual Revision 36a ULNRC-06821, Post-Audit Follow-Up Information in Support of Callaway'S License Amendment Request and Proposed Exemption to Allow Use of Framatome Gaia Fuel (LDCN 22-0002) (EPID L-2022-LLA-0150 and EPID L-2022-LLE-00301)2023-06-21021 June 2023 Post-Audit Follow-Up Information in Support of Callaway'S License Amendment Request and Proposed Exemption to Allow Use of Framatome Gaia Fuel (LDCN 22-0002) (EPID L-2022-LLA-0150 and EPID L-2022-LLE-00301) IR 05000483/20230112023-06-15015 June 2023 Comprehensive Engineering Team Inspection (CETI) Inspection Report 05000483/2023011 ULNRC-06822, Additional Information Regarding Request for NRC Approval of Operating Quality Assurance Manual (Oqam) Revision 36a2023-06-14014 June 2023 Additional Information Regarding Request for NRC Approval of Operating Quality Assurance Manual (Oqam) Revision 36a ML23158A1462023-06-13013 June 2023 Notification of Post-Approval Site Inspection for License Renewal and Request for Information Inspection (05000483/2023010) ULNRC-06818, Response to Request for Additional Information Regarding License Amendment Request to Revise Technical Specification 5.5.16, Containment Leakage Rate Testing Program, for Permanent Extension of Type a and Type C Leak Rate .2023-06-0505 June 2023 Response to Request for Additional Information Regarding License Amendment Request to Revise Technical Specification 5.5.16, Containment Leakage Rate Testing Program, for Permanent Extension of Type a and Type C Leak Rate . ULNRC-06815, Request for NRC Approval of Operating Quality Assurance Manual, Revision 36a2023-06-0505 June 2023 Request for NRC Approval of Operating Quality Assurance Manual, Revision 36a ML23093A0952023-05-10010 May 2023 Issuance of Amendment No. 232 Regarding Technical Specification Changes for Spent Fuel Storage ULNRC-06816, Withdrawal of Previously Submitted Enclosures Regarding License Amendment Request for Adoption of Alternative Source Term and Revision of Technical Specifications (LDCN 21-0015)2023-05-0909 May 2023 Withdrawal of Previously Submitted Enclosures Regarding License Amendment Request for Adoption of Alternative Source Term and Revision of Technical Specifications (LDCN 21-0015) ML23129A7942023-05-0909 May 2023 Post-Audit Supplement to License Amendment Request and Exemption to Allow Use of Framatome Gaia Fuel (LDCN 22-0002) (Iepid L-2022-LLA-0150 and EPID L-2022-LLE-0030) ML23118A3492023-05-0808 May 2023 Request for Withholding Information from Public Disclosure ML23122A3172023-05-0808 May 2023 Review of the Spring 2022 Steam Generator Tube Inservice Inspections 2024-01-29
[Table view] Category:Licensee Event Report (LER)
MONTHYEAR05000483/LER-2023-001, Submittal of LER 2023-001-00 for Callaway, Unit 1, Inoperable Instrument Tunnel Sump Level Indication Resulted in Condition Prohibited by Technical Specifications2023-11-29029 November 2023 Submittal of LER 2023-001-00 for Callaway, Unit 1, Inoperable Instrument Tunnel Sump Level Indication Resulted in Condition Prohibited by Technical Specifications 05000458/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 ULNRC-06398, Special Report 2017-02: Non-Functional Seismic Instrument for Greater than 30 Days2017-11-0808 November 2017 Special Report 2017-02: Non-Functional Seismic Instrument for Greater than 30 Days 05000483/LER-2017-0022017-10-13013 October 2017 Inadequate Protection from Tornado Missiles Identified Due to Nonconforming Design, LER 17-002-00 for Callaway Plant, Unit 1, Regarding Inadequate Protection from Tornado Missiles Identified Due to Nonconforming Design 05000483/LER-2017-0012017-08-15015 August 2017 Violation of Technical Specification 3.7.9 Due to Ultimate Heat Sink (UHS) Cooling Tower Train Inoperability, LER 17-001-00 for Callaway, Unit 1, Regarding Violation of Technical Specification 3.7.9 Due to Ultimate Heat Sink (UHS) Cooling Tower Train Inoperability 05000286/LER-2017-0022017-08-0909 August 2017 Manual Isolation of Chemical and Volume Control System Normal Letdown to Stop a Valve Leak Resulted in an Exceedance of Technical Specification 3.4.9 Condition A Limit for Pressurizer Level, LER 17-002-00 for Indian Point, Unit 3 re Manual Isolation of Chemical and Volume Control System Normal letdown to Stop a Valve Leak Resulted in an Exceedance of Technical Specification 3.4.9 Condition A Limit for Pressurizer Level 05000483/LER-2015-0012016-12-0202 December 2016 Completion of a Shutdown Required by the Technical Specifications - TS 3.4.13, LER 15-001-01 for Callaway Plant, Unit 1, Regarding Completion of a Shutdown Required by the Technical Specifications - TS 3.4.13 05000483/LER-2015-0022016-09-0707 September 2016 Manual Auxiliary Feedwater System Actuation, LER 15-002-00 for Callaway, Unit 1, Regarding Manual Auxiliary Feedwater System Actuation 05000336/LER-2016-0012016-06-27027 June 2016 Turbine Driven Auxiliary Feedwater Putnp Room HELB Door Left Open, LER 16-001-00 for Millstone Power Station Unit 2 RE: Turbine Driven Auxiliary Feedwater Pump Room HELB Door Left Open 05000483/LER-2016-0012016-06-20020 June 2016 Control Room Air Conditioning Inoperability Due To Essential Service Water Pressure Transient, LER 16-001-00 for Callaway, Unit 1, Regarding Control Room Air Conditioning Inoperability Due to Essential Service Water Pressure Transient 05000423/LER-2016-0032016-06-0808 June 2016 Loss of Safety Function- Supplementary Leak Collection and Release System, LER 16-003-00 for Millstone Power Station, Unit 3, Regarding Loss of Safety Function-Supplementary Leak Collection and Release System 05000483/LER-2015-0032016-01-21021 January 2016 Reactor Trip Caused by Transmission Line Fault, LER 15-003-01 for Callaway, Unit 1, Regarding Reactor Trip Caused by Transmission Line Fault ULNRC-06162, Special Report 2014-05 Inoperability of Loose Parts Monitoring Instrument for Greater than 30 Day2014-12-11011 December 2014 Special Report 2014-05 Inoperability of Loose Parts Monitoring Instrument for Greater than 30 Day ULNRC-06142, SR-14-002 Callaway, Unit 1 - Special Report 2014-02-PAM Report Inoperability of Post Accident Monitoring (PAM) Instrument2014-09-16016 September 2014 SR-14-002 Callaway, Unit 1 - Special Report 2014-02-PAM Report Inoperability of Post Accident Monitoring (PAM) Instrument ULNRC-05991, Special Report 13-001-00 for Callaway, Unit 1, Inoperability of a Seismic Instrument for Greater than 30 Days2013-05-13013 May 2013 Special Report 13-001-00 for Callaway, Unit 1, Inoperability of a Seismic Instrument for Greater than 30 Days ULNRC-05932, Special Report 2012-02 - Pam Report: Inoperability of a Post Accident Monitoring (PAM) Instrument for Greater than 30 Days2012-11-14014 November 2012 Special Report 2012-02 - Pam Report: Inoperability of a Post Accident Monitoring (PAM) Instrument for Greater than 30 Days ULNRC-05824, Special Report 2011-01 for Callway, Unit 1 Regarding Inoperability of a Seismic Instrument for Greater than 30 Days2011-11-10010 November 2011 Special Report 2011-01 for Callway, Unit 1 Regarding Inoperability of a Seismic Instrument for Greater than 30 Days ULNRC-05721, Special Report, Inoperable Channel 8 of the Loose Parts Monitoring System (Lpms)2010-07-22022 July 2010 Special Report, Inoperable Channel 8 of the Loose Parts Monitoring System (Lpms) ULNRC-05374, Special Report 07-001 Re Historical Inoperability of Seismic Instrument SGAR00082007-03-0808 March 2007 Special Report 07-001 Re Historical Inoperability of Seismic Instrument SGAR0008 ML0413203792004-05-0303 May 2004 Special Report for Callaway Plant Unit 1 Regarding Inoperability of 60 Meter Meteorological Monitoring Instrumentation on the Primary Meteorological Tower 2023-11-29
[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 Infocollects.Resource@nrc gov, and to the Desk Officer, Office of Information and Regulatory Affairs.
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cm.) 05000-483 2017 - 001 - 00
1. DESCRIPTION OF STRUCTURE(S), SYSTEM(S) AND COMPONENT(S):
Ultimate Heat Sink (UHS) System Description:
The UHS [EIIS system: BS] consists of a seismic Category I mechanical draft cooling tower and a seismic Category I source of makeup water (retention pond) for the tower. The UHS cooling tower provides heat dissipation from the Essential Service Water (ESW) system [EIIS system: BI] for safe shutdown of the plant following an accident. The UHS cooling tower is divided into two trains each with two cells having one fan assembly (fan, gear reducer, and motor) per cell. A single train with two cells is required for safe shutdown. Supply headers and spray pipes for each train are separated by interior walls.
Per Technical Specification 3.7.9, "Ultimate Heat Sink," two UHS cooling tower trains are required to dissipate the heat contained in the ESW system during Modes 1, 2, 3, and 4. An inoperable UHS cooling tower fan renders its UHS cooling tower train inoperable. If one cooling tower train is inoperable, action must be taken to restore the inoperable cooling tower train to Operable status within 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />. If the cooling tower train cannot be restored to Operable status within the associated Completion Time, the plant must be placed in Mode 3 within 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> and in Mode 5 within 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br />.
Thermal Overload Relay:
Thermal overload relays function to protect motors, motor control apparatus and motor-branch circuit conductors against excessive heating due to motor overloads and failure to start.
2. INITIAL PLANT CONDITIONS:
The plant was in Mode 1, Power Operation, at 100% reactor power at the time of this event. Besides the noted defective fast-speed thermal overload relay, there were no structures, systems, or components inoperable that contributed to the event.
3. EVENT DESCRIPTION:
On June 13, 2017, at approximately 0730, the 'A' Train of the UHS Cooling Tower was rendered inoperable when a maintenance activity to clean and inspect starter NGO7SAF1 was authorized to start. During this maintenance activity, the fast-speed thermal overload relay was replaced. The 'A' train of the UHS Cooling Tower was declared operable upon completion of the maintenance activity and the associated post-maintenance testing on June 14, 2017 at 1340.
On June 16, 2017 at 0732, an unexpected ESW Engineered Safety Feature Actuation Signal (ESFAS) alarm was received in the Control Room. At the time, the 'A' Train of the UHS Cooling Tower (Fans 'A' and 'C') was operating in fast speed to cool the UHS retention pond. Upon investigation, it was determined that the 'A' fan was not running and that the fast-speed thermal overload relay (on starter NGO7SAF1) was tripped. The 'A' Train of the UHS Cooling Tower was declared inoperable as a result of the failure to run the 'A' UHS Cooling Tower Fan, CEFO1A. Operability was restored when post maintenance testing was satisfactorily completed on June 17, 2017 at 0753.
The duration of the 'A' UHS Cooling Tower Fan (CEFO1A) inoperability was 96 hours0.00111 days <br />0.0267 hours <br />1.587302e-4 weeks <br />3.6528e-5 months <br /> and 23 minutes, beginning with the maintenance activity (and associated thermal overload relay replacement). The inoperability existed while the plant was in Mode 1.
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NO
- 00 The UHS provides a source of water for use by the ESW system. The UHS retention pond and cooling tower are designed to work together to meet temperature and inventory requirements for up to a 30-day (post-accident) mission time. The inoperable condition associated with the 'A' UHS Cooling Tower Fan (CEFO1A) would have prevented the 'A' UHS Cooling Tower Train from performing its specified safety functions. The protected 'B' UHS Cooling Tower Train remained Operable during this event. Due to established procedural guidance to secure the inoperable train, a loss of UHS safety function would not have occurred. The 'B' Train of the UHS Cooling Tower would have been able to maintain UHS retention pond temperature limits and adequate UHS retention pond inventory for the required 30-day UHS mission time.
Partial train failures of the UHS cooling tower are specifically analyzed in the licensing basis analyses of record for Callaway. Sensitivities using the GOTHIC model developed for the licensing basis UHS thermal hydraulic analysis of record show that an unmitigated failure of the 'A' UHS Cooling Tower Fan, CEFO1A, would have resulted in no adverse impact on water inventory in the UHS retention pond, but would have resulted in post-Design Basis Accident (DBA) UHS retention pond temperatures in excess of the analyzed limit discussed in the Callaway FSAR. However, specific procedural guidance exists for the Operators to diagnose and mitigate failure of a UHS Cooling Tower fan during post- accident conditions. This guidance is incorporated into the Callaway Emergency Operating Procedure (EOP) network.
Licensed operators receive training on EOPs.
The specific operator actions required to diagnose and mitigate a partial train failure in the UHS cooling tower are included in Callaway's Significant Operator Response Timing program. This provides assurance of the ongoing validity of the operator response times credited in the Callaway analysis of record. Crediting manual operator actions to diagnose and mitigate partial train failures or failure of an entire train of the UHS Cooling Tower was submitted for and received NRC approval as a part of License Amendment 208. Based on the Operability of the 'B' UHS Cooling Tower Train, and the ability of Callaway operators to diagnose and mitigate a partial failure of the 'A' UHS Cooling Tower Train, it can be concluded that the event described in this LER did not prevent the fulfillment of any safety function or significantly degrade plant safety.
5. REPORTING REQUIREMENTS:
This LER is submitted pursuant to 10 CFR 50.73(a)(2)(i)(B) to report an operation or condition prohibited by Technical Specifications.
Technical Specification 3.7.9 requires the UHS to be Operable in Modes 1, 2, 3, and 4. With one UHS Cooling Tower train inoperable, Condition A applies such that Required Action A.1 must be entered. Required Action A.1 requires the inoperable train to be restored within a specified Completion Time of 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />. With Required Action A.1 and its associated Completion Time not met, Condition B applies such that Required Action B.1 and B.2 must be entered. These actions direct the plant to be in Mode 3 in 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> and in Mode 5 within 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br />, respectively.
The 'A' Train of the UHS Cooling Tower was inoperable for a duration of approximately 96 hours0.00111 days <br />0.0267 hours <br />1.587302e-4 weeks <br />3.6528e-5 months <br /> and 23 minutes, with the plant operating in Mode 1. This was a violation of TS 3.7.9, and consequently, this event is required to be reported as a condition or operation prohibited by the plant's Technical Specifications, pursuant to 10 CFR 50.73(a)(2)(i)(B).
comments regarding burden estimate to the Information Services Branch (T-2 F43), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001.
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Callaway Plant Unit 1 05000-483 NUMBER NO
6. CAUSE OF THE EVENT:
The most probable root cause was determined to be a defective fast-speed thermal overload relay (Cutler-Hammer Freedom Series C306) based on additional bench testing of the relay. The failure of the relay resulted in a trip of the 'A' UHS Cooling Tower Fan. Pre-installation testing and setup of the relay was performed in accordance with Callaway procedures and work instructions. The pre-installation testing and setup confirmed that the relay would provide fan motor protection by tripping under overload conditions. However, the testing did not confirm that the relay would not spuriously trip during extended operation in elevated ambient temperatures representative of the installed location.
Failure analysis is being performed by an offsite vendor which will provide better insight into the nature of the defective thermal overload relay and establish if a potential manufacturing defect exists.
Once vendor testing results are received, a supplemental report will be submitted to clarify root cause and/or corrective actions.
7. CORRECTIVE ACTIONS:
Maintenance procedures will be revised to include an elevated temperature hold-in test prior to installation of Cutler- Hammer Freedom Series C306 thermal overload relays in the plant. This will prevent installation of relays that are defective in the manner that caused this event. Subjecting the overload relays to temperatures that are likely to occur in the plant rather than just room temperature will indicate which relays are defective in regards to ambient temperature compensation.
8. PREVIOUS SIMILAR EVENTS:
A review of Callaway LERs for the past three years did not identify any other examples of defective thermal overload relays that caused a component to fail to run in a manner that resulted in a condition or operation prohibited by Technical Specifications. Two corrective action documents were identified in which thermal overloads were involved with UHS Cooling Tower Fan start failures. Those two documents, i.e. CAR 200704421 and CAR 201703163 (written in 2007 and 2017, respectively) are included as internal Operating Experience in the Root Cause Analysis for the current event.
These two events document start failures, not failures of the fan to run subsequent to a successful start.