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Category:NRC Information Notice
MONTHYEARInformation Notice 2008-12, Reactor Trip Due to Off-Site Power Fluctuation2008-07-0707 July 2008 Reactor Trip Due to Off-Site Power Fluctuation Information Notice 2006-13, Ground-Water Contamination Due To Undetected Leakage of Radioactive Water2006-07-10010 July 2006 Ground-Water Contamination Due To Undetected Leakage of Radioactive Water Information Notice 1999-28, Recall of Star Brand Fire Protection Sprinkler Heads1999-09-30030 September 1999 Recall of Star Brand Fire Protection Sprinkler Heads Information Notice 1999-27, Malfunction of Source Retraction Mechanism in Cobalt-60 Teletherapy Treatment Units1999-09-0202 September 1999 Malfunction of Source Retraction Mechanism in Cobalt-60 Teletherapy Treatment Units Information Notice 1999-26, Safety and Economic Consequences of Misleading Marketing Information1999-08-24024 August 1999 Safety and Economic Consequences of Misleading Marketing Information Information Notice 1999-25, Year 2000 Contingency Planning Activities1999-08-10010 August 1999 Year 2000 Contingency Planning Activities Information Notice 1999-24, Broad-Scope Licensees' Responsibilities for Reviewing and Approving Unregistered Sealed Sources and Devices1999-07-12012 July 1999 Broad-Scope Licensees' Responsibilities for Reviewing and Approving Unregistered Sealed Sources and Devices Information Notice 1999-23, Safety Concerns Related to Repeated Control Unit Failures of the Nucletron Classic Model High-Dose-Rate Remote Afterloading Brachytherapy Devices1999-07-0606 July 1999 Safety Concerns Related to Repeated Control Unit Failures of the Nucletron Classic Model High-Dose-Rate Remote Afterloading Brachytherapy Devices Information Notice 1999-22, 10CFR 34.43(a)(1); Effective Date for Radiographer Certification and Plans for Enforcement Discretion1999-06-25025 June 1999 10CFR 34.43(a)(1); Effective Date for Radiographer Certification and Plans for Enforcement Discretion Information Notice 1999-21, Recent Plant Events Caused by Human Performance Errors1999-06-25025 June 1999 Recent Plant Events Caused by Human Performance Errors Information Notice 1999-20, Contingency Planning for the Year 2000 Computer Problem1999-06-25025 June 1999 Contingency Planning for the Year 2000 Computer Problem Information Notice 1999-19, Rupture of the Shell Side of a Feedwater Heater at the Point Beach Nuclear Plant1999-06-23023 June 1999 Rupture of the Shell Side of a Feedwater Heater at the Point Beach Nuclear Plant Information Notice 1999-18, Update on Nrc'S Year 2000 Activities for Material Licensees and Fuel Cycle Licensees and Certificate Holders1999-06-14014 June 1999 Update on Nrc'S Year 2000 Activities for Material Licensees and Fuel Cycle Licensees and Certificate Holders Information Notice 1999-17, Problems Associated with Post-Fire Safe-Shutdown Circuit Analyses1999-06-0303 June 1999 Problems Associated with Post-Fire Safe-Shutdown Circuit Analyses Information Notice 1999-16, Federal Bureau of Investigation'S Nuclear Site Security Program1999-05-28028 May 1999 Federal Bureau of Investigation'S Nuclear Site Security Program Information Notice 1999-15, Misapplication for 10CFR Part 71 Transportation Shipping Cask Licensing Basis to 10CFR Part 50 Design Basis1999-05-27027 May 1999 Misapplication for 10CFR Part 71 Transportation Shipping Cask Licensing Basis to 10CFR Part 50 Design Basis Information Notice 1999-14, Unanticipated Reactor Water Draindown at Quad Cities Unit 2, Arkansas Nuclear One Unit 2, & FitzPatrick1999-05-0505 May 1999 Unanticipated Reactor Water Draindown at Quad Cities Unit 2, Arkansas Nuclear One Unit 2, & FitzPatrick Information Notice 1999-13, Insights from NRC Inspections of Low-and Medium-Voltage Circuit Breaker Maintenance Programs1999-04-29029 April 1999 Insights from NRC Inspections of Low-and Medium-Voltage Circuit Breaker Maintenance Programs Information Notice 1999-12, Year 2000 Computer Systems Readiness Audits1999-04-28028 April 1999 Year 2000 Computer Systems Readiness Audits Information Notice 1999-11, Incidents Involving the Use of Radioactive Iodine-1311999-04-16016 April 1999 Incidents Involving the Use of Radioactive Iodine-131 Information Notice 1999-08, Urine Specimen Adulteration1999-03-26026 March 1999 Urine Specimen Adulteration Information Notice 1999-09, Problems Encountered When Manually Editing Treatment Data on the Nucletron Microselectron-HDR (New) Model 105-9991999-03-24024 March 1999 Problems Encountered When Manually Editing Treatment Data on the Nucletron Microselectron-HDR (New) Model 105-999 Information Notice 1999-07, Failed Fire Protection Deluge Valves & Potential Testing Deficiencies in Preaction Sprinkler Systems1999-03-22022 March 1999 Failed Fire Protection Deluge Valves & Potential Testing Deficiencies in Preaction Sprinkler Systems Information Notice 1999-06, 1998 Enforcement Sanctions as a Result of Deliberate Violations of NRC Employee Protection Requirements1999-03-19019 March 1999 1998 Enforcement Sanctions as a Result of Deliberate Violations of NRC Employee Protection Requirements Information Notice 1999-06, 1998 Enforcement Sanctions As a Result of Deliberate Violations of NRC Employee Protection Requirements1999-03-19019 March 1999 1998 Enforcement Sanctions As a Result of Deliberate Violations of NRC Employee Protection Requirements Information Notice 1999-05, Inadvertent Discharge of Carbon Dioxide Fire Protection System and Gas Migration1999-03-0808 March 1999 Inadvertent Discharge of Carbon Dioxide Fire Protection System and Gas Migration Information Notice 1999-04, Unplanned Radiation Exposures to Radiographers, Resulting from Failures to Follow Proper Radiation Safety Procedures1999-03-0101 March 1999 Unplanned Radiation Exposures to Radiographers, Resulting from Failures to Follow Proper Radiation Safety Procedures Information Notice 1999-03, Exothermic Reactors Involving Dried Uranium Oxide Powder (Yellowcake)1999-01-29029 January 1999 Exothermic Reactors Involving Dried Uranium Oxide Powder (Yellowcake) Information Notice 1999-02, Guidance to Users on the Implementation of a New Single-Source Dose-Calculation Formalism and Revised Air-Kerma Strength Standard for Iodine-125 Sealed Sources1999-01-21021 January 1999 Guidance to Users on the Implementation of a New Single-Source Dose-Calculation Formalism and Revised Air-Kerma Strength Standard for Iodine-125 Sealed Sources Information Notice 1999-01, Deterioration of High-Efficiency Particulate Air Filters in a Pressurized Water Reactor Containment Fan Cooler Unit1999-01-20020 January 1999 Deterioration of High-Efficiency Particulate Air Filters in a Pressurized Water Reactor Containment Fan Cooler Unit Information Notice 1998-45, Cavitation Erosion of Letdown Line Orifices Resulting in Fatigue Cracking of Pipe Welds1998-12-15015 December 1998 Cavitation Erosion of Letdown Line Orifices Resulting in Fatigue Cracking of Pipe Welds Information Notice 1998-44, Ten-Year Inservice Inspection (ISI) Program Update for Licensees That Intend to Implement Risk-Informed ISI of Piping1998-12-10010 December 1998 Ten-Year Inservice Inspection (ISI) Program Update for Licensees That Intend to Implement Risk-Informed ISI of Piping Information Notice 1998-43, Leaks in Emergency Diesel Generator Lubricating Oil & Jacket Cooling Water Piping1998-12-0404 December 1998 Leaks in Emergency Diesel Generator Lubricating Oil & Jacket Cooling Water Piping Information Notice 1998-42, Implementation of 10 CFR 55.55a(g) Inservice Inspection Requirements1998-12-0101 December 1998 Implementation of 10 CFR 55.55a(g) Inservice Inspection Requirements Information Notice 1998-41, Spurious Shutdown of Emergency Diesel Generators from Design Oversight1998-11-20020 November 1998 Spurious Shutdown of Emergency Diesel Generators from Design Oversight Information Notice 1998-41, Spurious Shutdown of Emergency Diesel Generators From Design Oversight1998-11-20020 November 1998 Spurious Shutdown of Emergency Diesel Generators From Design Oversight Information Notice 1998-39, Summary of Fitness-for-Duty Program Performance Reports for Calendar Years 1996 and 19971998-10-30030 October 1998 Summary of Fitness-for-Duty Program Performance Reports for Calendar Years 1996 and 1997 Information Notice 1998-40, Design Deficiencies Can Lead to Reduced ECCS Pump Net Positive Suction Head During Design-Basis Accidents1998-10-26026 October 1998 Design Deficiencies Can Lead to Reduced ECCS Pump Net Positive Suction Head During Design-Basis Accidents Information Notice 1990-66, Incomplete Draining and Drying of Shipping Casks1998-10-25025 October 1998 Incomplete Draining and Drying of Shipping Casks Information Notice 1998-38, Metal-Clad Circuit Breaker Maintenance Issues Identified by NRC Inspections1998-10-15015 October 1998 Metal-Clad Circuit Breaker Maintenance Issues Identified by NRC Inspections Information Notice 1998-37, Eligibility of Operator License Applicants1998-10-0101 October 1998 Eligibility of Operator License Applicants Information Notice 1998-36, Inadequate or Poorly Controlled, Non-Safety-Related Maintenance Activities Unnecessarily Challenged Safety Systems1998-09-18018 September 1998 Inadequate or Poorly Controlled, Non-Safety-Related Maintenance Activities Unnecessarily Challenged Safety Systems Information Notice 1998-33, NRC Regulations Prohibit Agreements That Restrict or Discourage an Employee from Participating in Protected Activities1998-08-28028 August 1998 NRC Regulations Prohibit Agreements That Restrict or Discourage an Employee from Participating in Protected Activities Information Notice 1998-34, Configuration Control Errors1998-08-28028 August 1998 Configuration Control Errors Information Notice 1998-31, Fire Protection System Design Deficiencies and Common-Mode Flooding of Emergency Core Cooling System Rooms at Washington Nuclear Project Unit 21998-08-18018 August 1998 Fire Protection System Design Deficiencies and Common-Mode Flooding of Emergency Core Cooling System Rooms at Washington Nuclear Project Unit 2 Information Notice 1998-30, Effect of Year 2000 Computer Problem on NRC Licensees and Certificate Holders1998-08-12012 August 1998 Effect of Year 2000 Computer Problem on NRC Licensees and Certificate Holders Information Notice 1998-29, Predicted Increase in Fuel Rod Cladding Oxidation1998-08-0303 August 1998 Predicted Increase in Fuel Rod Cladding Oxidation Information Notice 1998-28, Development of Systematic Sample Plan for Operator Licensing Examinations1998-07-31031 July 1998 Development of Systematic Sample Plan for Operator Licensing Examinations Information Notice 1998-26, Settlement Monitoring and Inspection of Plant Structures Affected by Degradation of Porous Concrete Subfoundations1998-07-24024 July 1998 Settlement Monitoring and Inspection of Plant Structures Affected by Degradation of Porous Concrete Subfoundations Information Notice 1998-27, Steam Generator Tube End Cracking1998-07-24024 July 1998 Steam Generator Tube End Cracking 2008-07-07
[Table view] |
UNITED STATES NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, DC 20555-0001
July 7, 2008
NRC INFORMATION NOTICE 2008-12: BRAIDWOOD UNIT 1 REACTOR TRIP DUE TO OFF-SITE POWER FLUCTUATION
ADDRESSEES
All holders of operating licenses for nuclear power reactors, except those who have permanently
ceased operations and have certified that fuel has been permanently removed from the reactor
vessel.
PURPOSE
The U.S. Nuclear Regulatory Commission (NRC) is issuing this information notice (IN) to inform
addressees of the results of a staff evaluation of a recent automatic trip of the Braidwood Unit 1 Nuclear Power Plant due to an offsite power voltage fluctuation coupled with a failed protective
relaying circuit. The NRC expects that recipients will review the information for applicability to their facilities and consi
der actions, as appropriate, to avoid similar
problems. Suggestions contained in this IN are not NRC requirements; therefore, no specific action or written response
is required.
DESCRIPTION OF CIRCUMSTANCES
Braidwood Unit 1 experienced an automatic reactor trip from full power on June 27, 2007. The
reactor trip was triggered by low flow in the 1D Reactor Coolant Loop after the 1D Reactor
Coolant Pump (RCP) tripped (appropriate reactor protection system actuation given loss of flow
due to the RCP trip). The event was initiated by a lighting strike 4.3 miles from the plant that
created a single-phase-to-ground fault on transmission line number 2001, which is a 345kV
transmission line. The ground fault suppressed the B-phase voltage to 48 percent of nominal
until 345kV protective breakers at Braidwood and the East Frankfort Transmission Substation
isolated the line about 3 cycles after fault initiation. The suppressed B-phase voltage created a
momentary phase imbalance on the Braidwood RCPs resulting in elevated current on the
unaffected A- and C-phases. The C-phase current on the 1D RCP exceeded the trip set point of
an instantaneous overcurrent protective relay. Normally (by design), the RCP trip on momentary
overcurrent would have been blocked by an in-series impedance relay; however, at the time of
the event, the impedance relay was in a tripped state due to a failed Bussman type KTN-R fuse
in an impedance monitoring circuit.
The licensee has been working on a generic reliability issue with Bussman KTN and KTN-R style fuses over the last two years (based on Title 10, Part 21, "Reporting of Defects and
Noncompliance," of the Code of Federal Regulations reporting for these fuses). There have been several intermittent or complete fuse failures caused by fuse element cracking
characterized as fatigue failure. After a fuse failure on 6.9kV Bus 157 in January 2007, the licensee made the decision to replace all Bussman fuses installed on the 6.9kV bus
protective relay circuits. However, due to the risk of tripping an RCP during fuse replacement, these fuses were to be replaced during outages. The fuse that failed in the 1D RCP protective
relay circuit was scheduled for replacement in the next refueling outage. The licensee
considered this a small risk, since fuse failures had been self-revealing and promptly replaced to
restore the designed relay scheme. However, the only fuse in the RCP protective relaying circuit
without a loss-of-bus-voltage indication or alarm (not self-revealing), failed in this event. Only
the disturbance in the transmission syst
em and the resulting Unit 1 tr
ip indicated the vulnerability within the RCP protective relaying circuitry.
The corrective action planned by the licensee was to either implement a design change to
eliminate the identified vulnerability from the RCP protective relaying system, or, if design changes were not appropriate, to develop alternate ac
tions to address the vulnerability.
Additional information is available in Braidwood Station, Unit 1, Licensee Event Report 2007-
001-00, dated August 27, 2007 (ADAMS Accession No. ML072400074).
DISCUSSION
The event was initiated by a lightning strike to a 345kV transmission line which caused a
line-to-ground fault. The fault caused the voltage on B-phase to drop to 48 percent of the
nominal voltage until the transmission line breakers opened, appropriately isolating the fault. The
duration of the event from fault initiation until the breakers opened was about 0.051 seconds
(about 3 cycles). With the B-phase voltage low, the plant's RCPs responded by drawing more
current on A- and C-phases to maintain RCP power output. The 1D RCP's supply breaker
tripped on overcurrent in the C-phase. The instantaneous over-current relay set point was
exceeded and it actuated appropriately. Based on the circuit's design, a series impedance relay
should normally block the momentary overcurrent condition; however, at the time of this event, the impedance relay was in a tripped state due to a failed fuse in the impedance relay's voltage
sensing circuit.
The root cause of this event was a design flaw which allowed the RCP protective relay circuit to
be in a degraded state without proper indication to the operators. This degraded relay circuit
state placed the plant in a condition less tolerant to grid voltage excursions without the requisite
knowledge of the operators. A contributing factor was the failure of the fuse used in the relay
voltage sensing circuit. Consequently, as a result of the design flaw coupled with the grid
voltage excursion, a reactor trip occurred from full power. Unplanned reactor trips are identified
in the NRC's Reactor Oversight Process as a performance indicator associated with the
"Initiating Events" cornerstone.
Licensees rely on plant controls, indications, and alarms to inform operators of plant, system, and sub-system conditions such that proper operation of the plant can be conducted during
normal, abnormal, and emergency conditions. More specifically, these controls, indications, and
alarms allow the operation of the plant while avoiding unnecessary transients and automatic
trips. Relaying circuits should provide indication to the operators upon failure or partial failure of
such circuits. In particular, circuits should indicate protective relay actuation within relaying
circuits (such as the fuse opening and the impedance relay operation, in this case).
CONTACT
This IN requires no specific action or written response. Please direct any questions about this
matter to the technical contact listed below.
/RA by TQuay for/
Michael J. Case, Director
Division of Policy and Rulemaking
Office of Nuclear Reactor Regulation
Technical Contact:
Kenneth A Miller, NRR
(301) 415-3152 e-mail: Kenneth.miller2@nrc.gov
Note: NRC generic communications may be found on the NRC public Web site, http://www.nrc.gov. Select Electronic Reading Room and then Document Collections.
CONTACT
This IN requires no specific action or written response. Please direct any questions about this
matter to the technical contact listed below.
/RA by TQuay for/
Michael J. Case, Director
Division of Policy and Rulemaking
Office of Nuclear Reactor Regulation
Technical Contact:
Kenneth A Miller, NRR
301-415-3152 e-mail: Kenneth.miller2@nrc.gov
Note: NRC generic communications may be found on the NRC public Web site, http://www.nrc.gov, under Electronic Reading Room/Document Collections.
Distribution: IN Reading File
ADAMS Accession Number:
ML081830163 OFFICE TECH EDITOR
EEEB:DE BC:EEEB:DE
D:EEEB NAME KAzariah-Kribbs
KMIller GWilson PHiland DATE 06/26/2008
7/2/08 7/2/08 7/3/08 OFFICE LA:PGCB:DPR
PGCB:DPR BC:PGCB:DPR
D:DPR NAME CHawes DBeaulieu
MMurphy TQuay for MCase
DATE 7/3/08 7/03/08 7/07/08 7/07/08 OFFICIAL RECORD COPY
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list | - Information Notice 2008-02, Findings Identified During NRC Component Design Bases Inspections (19 March 2008, Topic: Stroke time, Past operability, Battery sizing)
- Information Notice 2008-04, Counterfeit Parts Supplied to Nuclear Power Plants (7 April 2008, Topic: Time of Discovery)
- Information Notice 2008-04, Recent Counterfeit Valves and Circuit Breakers Supplied to Nuclear Power Plants (7 April 2008, Topic: Time of Discovery)
- Information Notice 2008-05, Fires Involving Emergency Diesel Generators Exhaust Manifolds (12 April 2008, Topic: Temporary Modification)
- Information Notice 2008-06, Instrument Air System Failure Resulting in Manual Reactor Trip (10 April 2008)
- Information Notice 2008-07, Cracking Indications In Thermally Treated Alloy 600 Steam Generator Tubes And Tube-To-Tubesheet Welds (24 April 2008)
- Information Notice 2008-07, Cracking Indications in Thermally Treated Alloy 600 Steam Generator Tubes and Tube-To-Tubesheet Welds (24 April 2008)
- Information Notice 2008-10, Response to Indications of Potential Tampering, Vandalism, or Malicious Mischief (1 May 2008, Topic: Coatings)
- Information Notice 2008-10, Response to Indications of Potential Tampering Vandalism or Malicious Mischief (1 May 2008, Topic: Coatings)
- Information Notice 2008-11, Service Water System Degradation at Brunswicksteam Electric Plant Unit 1 (18 June 2008)
- Information Notice 2008-12, Reactor Trip Due to Off-Site Power Fluctuation (7 July 2008)
- Information Notice 2008-14, Criticality Safety-related Events Resulting from Fissile Material Operations under Procedures Not Reviewed by Criticality Safety Staff (29 July 2008, Topic: Uranium Hexafluoride)
- Information Notice 2008-14, Criticality Safety-related Events Resulting from Fissile Material Operations Under Procedures Not Reviewed by Criticality Safety Staff (29 July 2008)
- Information Notice 2008-16, Summary of Fitness-for-Duty Program Performance Reports for Calendar Year 2007 (2 September 2008, Topic: Fitness for Duty)
- Information Notice 2008-17, Construction Experience with Concrete Placement Process (22 October 2008, Topic: Condition Adverse to Quality)
- Information Notice 2008-18, Loss of Safety-Related Motor Control Center Due to Bus Fault (1 December 2008, Topic: Safe Shutdown)
- Information Notice 2008-20, Failures of Motor Operated Valve Actuator Motors with Magnesium Alloy Rotors (8 December 2008, Topic: Packing leak)
- Information Notice 2008-20, Failures of Motor Operated Valve Actuator Motors With Magnesium Alloy Rotors (8 December 2008)
- Information Notice 2008-21, Impact of Non-Safety Electrical Support System Vulnerabilities on Safety Systems (24 November 2008)
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