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Category:NRC Information Notice
MONTHYEARInformation Notice 2006-29, Potential Common Cause Failure of Motor-operated Valves As a Result of Stem Nut Wear2006-12-14014 December 2006
Potential Common Cause Failure of Motor-operated Valves As a Result of Stem Nut Wear
Information Notice 2006-29, Potential Common Cause Failure of Motor-operated Valves as a Result of Stem Nut Wear2006-12-14014 December 2006
Potential Common Cause Failure of Motor-operated Valves as a Result of Stem Nut Wear
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
2006-12-14
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December 14, 2006
INFORMATION NOTICE 2006-29:POTENTIAL COMMON CAUSE FAILURE OFMOTOR-OPERATED VALVES AS A RESULT OF STEM NUT WEAR
ADDRESSEES
All holders of operating licenses for nuclear power reactors except those who have permanentlyceased operation and have certified that fuel has been permanently removed from the vessel.
PURPOSE
The U.S. Nuclear Regulatory Commission (NRC) is issuing this information notice (IN) to alertaddressees of potential common cause failure of motor-operated valves (MOVs) at nuclear power plants as a result of stem nut wea The agency expects that recipients will review the information for applicability to their facilities and consider actions, as appropriate, to avoid similar problem However, the suggestions contained in this IN are not NRC requirements; therefore, no specific action or written response is required.
DESCRIPTION OF CIRCUMSTANCES
On March 27, 2006, during the spring refueling outage for the Susquehanna Nuclear PowerPlant, Unit 1, the suppression pool suction valve for the "D" residual heat removal (RHR) pump failed to close during system functional testin On April 6, 2006, the suppression pool suction valve for the "C" RHR pump failed to stroke during system alignmen The licensee identified the cause of these MOV failures to be excessive wear of the internal threads of the stem nut that converts the rotational motion of the motor actuator to the lateral motion of the stem to open and close the valve.In the MOV Preventive Maintenance (PM) program at Susquehanna, the licensee had relied onthe observation of stem nut thread shavings below the actuator to identify stem nut wear and the need for stem nut inspectio The licensee had not directly inspected the stem nuts for the two failed MOVs for 20 years because no stem nut thread shavings had been found below the actuato The licensee did not have a periodic overhaul program for safety-related MOVs, nor procedures to review stem nut thread clearance when conducting diagnostic testing of safety-related MOV In response to these MOV failures, the licensee evaluated diagnostic traces of rising stem MOVs at Susquehanna, Units 1 and 2 that were within the scope of Generic Letter 89-10,
"Safety-Related Motor-Operated Valve Testing and Surveillance." The licensee studied the time span required for the rotating stem nut to take-up the clearance between the valve stem threads and the stem nut threads to assist in identifying potential stem nut wea The licenseeevaluated previous diagnostic traces to determine changes in thread clearance to estimate the stem nut wear rate and to determine whether sufficient thread would remain through the next operating cycl Based on this information, the licensee inspected 31 safety-related MOVs at Susquehanna and replaced the stem nuts in 18 MOVs with wear exceeding 50% of the original thread thicknes The licensee plans to conduct additional MOV stem nut inspections in the future.The RHR suppression pool suction valves at Susquehanna, Unit 1 are normally open and donot automatically change position to perform their safety function of allowing emergency core cooling water to be taken from the suppression poo These valves also serve a containment isolation function in that they would be remotely closed if there was a break in the RHR syste The RHR suppression pool suction valves are interlocked with the RHR shutdown cooling suction valves to prevent these valves from being open at the same time and inadvertently draining the reactor vesse Therefore, the failure of the RHR suppression pool suction valves might have impacted the emergency core cooling function of the RHR system, or affected the primary containment isolation function, depending on valve position at the time of failur At the time of the event, primary containment integrity was not require With the plant shut down for refueling, the safety significance of having two inoperable RHR suppression pool suction valves was considered lo Although the RHR pumps associated with the failed valves were not being relied upon to fulfill emergency injection requirements, valve failures associated with systems being relied upon for shutdown cooling or emergency core cooling (either shutdown or at power) might have either prevented or unexpectedly altered system function, thus, complicating operator actions and necessitating further response.The licensee submitted Licensee Event Report (LER) 50-387/2006-003-00 on July 26, 2006, inresponse to the MOV stem nut failures at Susquehanna (see Agencywide Documents Access and Management System Accession No. ML062190207). In the LER, the licensee listed the following as root causes for the event: (1) valve stem visual inspections for evidence of stem nut thread wear were an ineffective means for monitoring long-term stem nut thread wear; (2) routine PM activities for periodically inspecting stem nuts did not exist; and (3) procedural guidance for inspection and acceptance of stem nut thread wear was inadequat The licensee reported that immediate corrective actions had been completed to evaluate safety-related MOVs at Susquehanna using previous diagnostic indications of stem nut thread wear and inspection of selected stem nuts to assess stem nut conditio Additional long-term corrective actions planned at Susquehanna include: (1)performing additional MOV inspections and replacing stem nuts, when needed; (2)revising the current 2-year PM activity bases, and to clarify the intent andlimitations of stem inspections in response to the ineffectiveness of visual inspections to detect long-term stem nut wear; (3)developing a new PM activity that periodically inspects selected MOV stem nuts; (4)establishing a methodology and acceptance criteria for measurement of stem nutwear; (5)incorporating detailed instructions for performing stem nut inspections intoexisting procedures; (6)preparing procedural direction for monitoring and trending stem nut wear usingMOV diagnostic data; and (7)modifying stem lubrication PM activities to include valve stroking.
DISCUSSION
In an MOV, the stem nut converts the rotational motion of the drive sleeve in the motor actuatorto the lateral motion of the stem to open and close the valv Stem nut failure can prevent the operation of the MOV from either the motor actuator or manual handwhee Stem nut failure can also cause valve position for the MOV to be incorrectly displayed in the control roo The failure of a stem nut for an individual MOV can interfere with the operation of other plant equipment when its valve position signal is supplied to interlock logic system Further, if the stem nut threads are destroyed, a valve could potentially drift open or closed should the valve packing be unable to hold the valve stem in position.The stem nut of an MOV is typically made of bronze materia Over a period of time and use,the stem nut will undergo wear when rotating to move the steel valve stem to open or close the valv Stem nut wear can be influenced by several factors, including the following: (1) stem nut material; (2) normal operating loads and maximum loads; (3) stem nut rotations during a valve stroke; (4) number and frequency of valve strokes; (5) stem nut manufacture and threaded length; (6) stem and stem nut fit; (7) valve stem thread condition; and (8) stem lubricant, lubrication method and frequency, and environmental conditions for the lubricant.The unexpected failures and significant degradation of stem nuts in MOVs at Susquehannaemphasizes the importance of PM activities in identifying MOV stem nut wear in a timely manne For example, the absence of significant changes in diagnostic performance for monitored MOV parameters (such as stem factor, thrust, or torque), or stem nut thread shavings below the actuator, might not be sufficient to confirm that the stem nut remains in good conditio Additional PM activities, such as periodic overhaul of safety-related MOVs orevaluation of MOV diagnostic test data for stem nut thread clearance, might be needed to identify stem nut wea Further, it is important for the PM program to ensure that new lubricant is applied to the stem nut area, such as by stroking the valve, when lubricating safety-related MOV valve stems.Excessive stem nut wear represents a potential common cause failure mode that could impactmultiple MOVs at nuclear power plant It is typically a long-term issue that is addressed as part of PM programs at nuclear power plant Industry guidance includes stem nut inspection as part of MOV technical repair guideline Vendors of MOV diagnostic equipment include stem nut thread take-up clearance as a specific parameter for monitoring stem nut wea Appropriate PM activities, such as those to be implemented at Susquehanna, can assist in identifying significant stem nut wear prior to MOV failur IN 2006-29
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| list | - Information Notice 2006-02, Use of Galvanized Supports and Cable Trays with Meggitt Si 2400 Stainless Steel Jacketed Electrical Cables (19 January 2006, Topic: Safe Shutdown, Fire Barrier)
- Information Notice 2006-03, Motor Starter Failures Due to Mechanical Interlock Binding (25 January 2006, Topic: Stroke time)
- Information Notice 2006-04, Design Deficiency in Pressurizer Heaters for Pwrs (13 February 2006)
- Information Notice 2006-04, Design Deficiency in Pressurizer Heaters for PWRs (13 February 2006)
- Information Notice 2006-05, Possible Defect in Bussman KWN-R and KTN-R Fuses (3 March 2006)
- Information Notice 2006-07, Inappropriate Use of a Single Parameter Limit as a Nuclear Criticality Safety Limit at Fuel Cycle Facilities (31 March 2006)
- Information Notice 2006-07, Inappropriate Use of a Single Parameter Limit As a Nuclear Criticality Safety Limit at Fuel Cycle Facilities (31 March 2006)
- Information Notice 2006-07, Inappropriate Use of a Single Parameter Limit as a Nuclear Criticality Safety limit at Fuel Cycle Facilities (31 March 2006)
- Information Notice 2006-08, Secondary Piping Rupture at Mihama Power Station in Japan (16 March 2006, Topic: Safe Shutdown)
- Information Notice 2006-08, Secondary Piping Rupture At Mihama Power Station in Japan (16 March 2006, Topic: Safe Shutdown)
- Information Notice 2006-09, Performance of NRC-Licensed Individuals While on Duty With Respect to Control Room Attentiveness (11 April 2006)
- Information Notice 2006-09, Performance of NRC-Licensed Individuals While on Duty with Respect to Control Room Attentiveness (11 April 2006)
- Information Notice 2006-10, Use of Concentration Control For Criticality Safety (23 April 2006)
- Information Notice 2006-10, Use of Concentration Control for Criticality Safety (23 April 2006)
- Information Notice 2006-11, Applicability of Patient Intervention in Determining Medical Events for Gamma Stereotactic Radiosurgery and Other Therapy Procedures (12 June 2006, Topic: Brachytherapy)
- Information Notice 2006-13, Ground-Water Contamination Due To Undetected Leakage of Radioactive Water (10 July 2006, Topic: Time of Discovery)
- Information Notice 2006-13, E-mail from M. Mclaughlin on NRC, Regarding NRC Information Notice 2006-13: Groundwater Contamination (13 July 2006, Topic: Boric Acid, Time of Discovery)
- Information Notice 2006-14, Potentially Defective External Lead-Wire Connections in Barton Pressure Transmitters (25 September 2006, Topic: Functionality Assessment)
- Information Notice 2006-17, Recent Operating Experience of Service Water Systems Due to External Conditions (31 July 2006, Topic: Significance Determination Process, Frazil ice, Biofouling)
- Information Notice 2006-22, New Ultra-Low-Sulfur Diesel Fuel Oil Could Adversely Impact Diesel Engine Performance (12 October 2006)
- Information Notice 2006-29, Potential Common Cause Failure of Motor-operated Valves as a Result of Stem Nut Wear (14 December 2006)
- Information Notice 2006-29, Potential Common Cause Failure of Motor-operated Valves As a Result of Stem Nut Wear (14 December 2006)
- Information Notice 2006-30, Summary of Fitness-for-Duty Program Performance Reports for Calendar Year 2004 and 2005 (21 December 2006, Topic: Time of Discovery, Fitness for Duty)
- Information Notice 2006-31, Inadequate Fault Interrupting Rating of Breakers (26 December 2006)
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