Information Notice 2003-15, Importance of Followup Activities in Resolving Maintenance Issues
| ML032480905 | |
| Person / Time | |
|---|---|
| Issue date: | 09/05/2003 |
| From: | Beckner W NRC/NRR/DIPM |
| To: | |
| Hodge, CV, NRR/DIPM/IROB, 415-1861 | |
| References | |
| IN-03-015 | |
| Download: ML032480905 (8) | |
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, D.C. 20555-0001 September 5, 2003 NRC INFORMATION NOTICE 2003-15: IMPORTANCE OF FOLLOWUP ACTIVITIES IN
RESOLVING MAINTENANCE ISSUES
Addressees
All holders of operating licenses for nuclear power reactors except those who have permanently
ceased operation 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 to alert
addressees to recent experience that emphasizes the importance of followup activities in
resolving maintenance issues in nuclear power plants. It is expected that recipients will review
the information for applicability to their facilities and consider actions, as appropriate, to avoid
similar problems. However, suggestions contained in this information notice are not NRC
requirements; therefore, no specific action or written response is required.
Background
Nuclear power plant licensees establish and implement programs to maintain the capability of
a wide range of components to perform their safety functions and provide assurance of safe
plant operation. In addition to prescribing planned work activities based on industry standards
or vendor recommendations, these maintenance programs address component performance
issues that are identified through plant-specific and industry-wide operating experience, and
through NRC and industry research activities. As illustrated by the example described herein
regarding motor-operated valves (MOVs), followup activities to verify implementation of
corrective actions are an important part of a successful plan to resolve maintenance issues for
safety-related components at nuclear power plants.
For the purposes of the example in this information notice, an MOV can be described as a valve
operated by an actuator gear train driven by an electric motor. In an MOV, motor torque is
transmitted through a motor pinion gear on the motor shaft to the worm shaft clutch gear in the
actuator, which uses additional gearing to open or close the valve. The motor pinion gear and
the motor shaft are connected through a key placed in a recessed keyway in the pinion gear
and motor shaft. The key is staked to prevent it slipping from the keyway. A set screw in the
motor pinion gear is located at a recess mark on the motor shaft to prevent axial movement of
the gear. A lockwire is wrapped around the motor shaft to help the set screw remain in place.
For many years, MOVs used in nuclear power plants experienced deficiencies in the connection
of the motor pinion gear to the motor shaft. In some instances, failure to secure the motor
pinion gear to the motor shaft in an adequate manner has prevented MOVs from opening or
closing. In response to this operating experience, the NRC issued several information notices.
In addition, the nuclear industry has updated MOV maintenance guidance for securing the
motor pinion gear to the motor shaft. For example, in 1989 Limitorque Corporation issued
Maintenance Update 89-1 to provide improved guidance for the installation of the motor pinion
gear in its MOV actuators.
Description of Circumstances
On January 25, 2003, at South Texas Unit 2, an MOV in the residual heat removal (RHR)
system failed to open upon demand. The licensee determined that the MOV failed because the
motor pinion gear had moved along the motor shaft until it contacted the MOV declutch
mechanism. The resulting increased friction loading on the motor shaft caused the motor to
stall and its electric circuit breaker to trip. The licensee found that the motor pinion set screw
was not properly installed in the drilled recess on the motor shaft. Although not the cause of
this MOV failure, the licensee also found that the motor pinion key for the RHR MOV had not
been adequately staked so that the key had become partially disengaged from its keyway
(Licensee Event Report [LER] 50-499/2003-01, dated April 18, 2003, ADAMS Accession
No. ML031150024).
In determining the cause of the MOV failure, the licensee discovered that the most recent work
activity on the failed RHR MOV that involved the motor pinion gear was in 1993. The licensee
corrected an identical deficiency but did not enter it into the corrective action program. The
licensee stated that the previous work activity involving the motor pinion gear for this MOV
occurred in 1987 during the Unit 2 construction phase. The 1987 work activity did not ensure
that maintenance instructions for spot-drilling the motor shaft and properly installing the set
screw were accomplished.
The licensee inspected 327 other MOVs installed in South Texas Units 1 and 2 and identified
deficiencies in the connection of the motor pinion gear to the motor shaft in many of them.
Deficiencies in 24 of the MOVs required operability evaluations. The licensee determined that
these deficiencies had not progressed to an extent that rendered the MOVs inoperable.
However, these deficiencies might have eventually caused some MOVs to be incapable of
performing their intended functions. For example, one of those MOVs, a flow control valve in
the auxiliary feedwater (AFW) system, had lost its motor pinion key and was depending solely
on the set screw to secure the motor pinion gear to the motor shaft. Because the set screw is
not designed to transfer torque from the motor shaft to the motor pinion gear, the AFW MOV
might have failed to operate under its design-basis hydrodynamic loading conditions.
Discussion
Appendix B, Quality Assurance Criteria for Nuclear Power Plants and Fuel Reprocessing
Plants, to Part 50 in Title 10 of the Code of Federal Regulations (10 CFR Part 50) specifies
requirements applicable to the assessment of operating experience that can reflect the inability
of safety-related MOVs to perform their design-basis functions. For example, Criterion V,
Instructions, Procedures, and Drawings, in 10 CFR Part 50, Appendix B, states, in part, that
activities affecting quality shall be prescribed by documented procedures of a type appropriate
to the circumstances and shall be accomplished with these procedures. Criterion XVI,
Corrective Action, states, in part, that measures shall be established to assure that conditions
adverse to quality, such as failures, malfunctions, deficiencies, deviations, defective material
and equipment, and nonconformances, are promptly identified and corrected. During inspections at nuclear power plants, the NRC identified instances where licensees failed
to satisfy the criteria in Appendix B to 10 CFR Part 50 with respect to their responses to MOV
operating experience and other performance information. For example, in reviewing the recent
RHR MOV failure at South Texas Unit 2, the NRC identified a 10 CFR Part 50, Appendix B,
Criterion V, issue in that the licensee failed to track implementation of corrective actions
recommended in Limitorque Maintenance Update 89-1 on applicable MOV actuators (NRC
Inspection Report 05000498/2003002 and 05000499/2003002, dated August 5, 2003, ADAMS
Accession No. ML032170569). Similarly, the NRC found that the Comanche Peak licensee had
not satisfied Criterion V of 10 CFR Part 50, Appendix B, by failing to properly identify the
applicability of Limitorque Maintenance Update 92-02 and, as a result, failing to evaluate the
applicability of a change to the criterion for determining the acceptable tolerance for actuator
torque switch repeatability (NRC Inspection Report 05000445/9310 and 05000446/9310, dated
May 3, 1993, NUDOCS Accession No. 9305070163).
When responding to operating experience and other component performance information, it is
important for licensees to have a clear plan of action to identify specific potentially affected
components and to address and track to completion those components in a reasonable amount
of time based on their safety significance. For example, the identification of deficiencies
associated with the connection of the motor pinion gear to the motor shaft in safety-related
MOVs at South Texas after the issuance of NRC information notices and vendor guidance over
a long time period emphasizes the importance of followup activities to verify the implementation
of revised maintenance procedures. The revision of maintenance procedures will only resolve a
generic issue if the revised procedures are implemented during work activities associated with
the applicable components. In particular, if MOV maintenance procedures are revised to
improve the connection of the motor pinion gear to the motor shaft, the procedures need to
ensure the removal of the motor from the MOV during the maintenance activity so the motor
pinion gear connection can be inspected and appropriate corrective action taken. Where
revised procedures are not implemented in a manner that fully resolves a maintenance issue, the potential for common cause failure can continue to exist for affected components in multiple
plant systems. The importance of a plan when responding to operating experience issues and
other component performance information is applicable to all components that perform a safety
function at a nuclear power plant, not just MOVs.
Addressees
are reminded of the quality assurance requirements in 10 CFR Part 50,
Appendix B, to address operating experience issues and component performance information
and the maintenance requirements in 10 CFR 50.65 to consider industry-wide operating
experience and component performance information (including issues described in NRC
information notices), where practical, when setting goals and performing periodic evaluations.
Related Generic Communications
NRC Information Notice 85-67, Valve-Shaft-to-Actuator Key May Fall Out of Place When
Mounted Below Horizontal Axis.
NRC Information Notice 88-84, Defective Motor Shaft Keys in Limitorque Motor Actuators.
NRC Information Notice 90-37, Sheared Pinion Gear-to-Shaft Keys in Limitorque Motor
Actuators. NRC Information Notice 94-10, Failure of Electric Power Train Due to Sheared or Dislodged
Motor Pinion Gear Key.
NRC Information Notice 96-48, Motor-Operated Valve Performance Issues.
This information notice requires no specific action or written response. If you have any
questions about this notice, contact one of the persons listed below or the appropriate Office of
Nuclear Reactor Regulation (NRR) project manager.
/RA/
William D. Beckner, Chief
Reactor Operations Branch
Division of Inspection Program Management
Office of Nuclear Reactor Regulation
Technical contacts: Thomas G. Scarbrough, NRR Dr. C. Vernon Hodge, NRR
301-415-2794 301-415-1861 Email: tgs@nrc.gov Email: cvh@nrc.gov
Cornelius F. OKeefe, Region IV Michael F. Runyan, Region IV
361-972-2507 817-860-8142 Email: nfo@nrc.gov Email: mfr@nrc.gov
Attachment: List of Recently Issued NRC Information Notices
- See previous concurrence
DOCUMENT NAME: C:\ORPCheckout\FileNET\ML032480905.wpd
OFFICE IROB:DIPM Tech Editor RGN-IV RGN-IV RGN-IV
NAME CVHodge* PKleene* AHowell* OKeefe MRunyan*
DATE 08 /21/2003 08/04/2003 08/22/2003 / /2003 08/22/2003 OFFICE EMEB:DE EMEB:DE EMEB:DE SC:IROB:DIPM BC:IROB:DIPM
NAME TScarborough* DTerao* GImbro* TReis WDBeckner
DATE 08/22/2003 08/22/2003 08/22/2003 09/05/2003 09/05/2003
Attachment LIST OF RECENTLY ISSUED
NRC INFORMATION NOTICES
_____________________________________________________________________________________
Information Date of
Notice No. Subject Issuance Issued to
_____________________________________________________________________________________
2003-14 Potential Vulnerability of Plant 08/29/2003 All holders of operating licenses
Computer Network to Worm for nuclear power reactors, Infection except those who have
permanently ceased operations
and have certified that fuel has
been permanently removed from
the reactor vessel.
2003-13 Steam Generator Tube 08/28/2003 All holders of operating licenses
Degradation at Diablo Canyon for pressurized-water reactors
(PWRs), except those who have
permanently ceased operations
and have certified that fuel has
been permanently removed from
the reactor.
89-69, Sup 1 Shadow Corrosion Resulting in 08/25/2003 All holders of operating licenses
Fuel Channel Bowing for boiling water reactors (BWRs),
except those who have
permanently ceased operations
and have certified that fuel has
been permanently removed from
the reactor vessel.
2003-12 Problems Involved in 08/22/2003 All holders of 10 CFR Parts 32, Monitoring Dose to the Hands 33, and 35 licenses.
Resulting from the Handling of
Radiopharmaceuticals
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