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

ML032480905
IN 2003-15

Page 2 of 4

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.
IN 2003-15

Page 3 of 4

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.” 
IN 2003-15

Page 4 of 4

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. O’Keefe, 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