Information Notice 2010-03, Failures of Motor-Operated Valves Due to Degraded Stem Lubricant: Difference between revisions

Failures of Motor-Operated Valves Due to Degraded Stem Lubricant
	ML092930025
Person / Time
Issue date:	02/03/2010
From:	Dan Dorman, Mcginty T; NRC/NMSS/FCSS, Division of Policy and Rulemaking
To:	;
	Beaulieu, D P, NRR/DPR, 415-3243
References
	IN-10-003
	Download: ML092930025 (5)
	v • d • e

Latest revision as of 02:23, 14 November 2019

UNITED STATES

NUCLEAR REGULATORY COMMISSION

OFFICE OF NUCLEAR REACTOR REGULATION

OFFICE OF NUCLEAR MATERIAL SAFETY AND SAFEGUARDS

WASHINGTON, DC 20555-0001 February 3, 2010

NRC INFORMATION NOTICE 2010-03: FAILURES OF MOTOR-OPERATED VALVES

DUE TO DEGRADED STEM LUBRICANT

ADDRESSEES

All holders of an operating license or construction permit for a nuclear power reactor issued

under Title 10 of the Code of Federal Regulations (10 CFR) Part 50, Domestic Licensing of

Production and Utilization Facilities, except those who have permanently ceased operations

and have certified that fuel has been permanently removed from the reactor vessel.

All certificate holders for gaseous diffusion plants certified under 10 CFR Part 76, Certification

of Gaseous Diffusion Plants.

PURPOSE

The U.S. Nuclear Regulatory Commission (NRC) is issuing this information notice (IN) to inform

addressees of recent failures and corrective actions for motor-operated valves (MOVs) because

of degraded lubricant on the valve stem and actuator stem nut threaded area. Recipients are

expected to review the information for applicability to their facilities and consider actions to avoid

similar problems. The suggestions contained in this IN are not NRC requirements and no

specific action or written response is required.

DESCRIPTION OF CIRCUMSTANCES

Peach Bottom Atomic Power Station

On March 12, 2009, while the licensee was aligning the condensate storage tank to torus

suction for high-pressure coolant injection (HPCI) testing at Peach Bottom Unit 2, the inboard

torus suction MOV failed to fully open and the HPCI was declared inoperable. The licensee

found dried and hardened grease on the valve stem and stem nut of this Unit 2 HPCI MOV.

On March 21, 2009, while the licensee was conducting a surveillance at Peach Bottom Unit 3, the HPCI outboard torus suction MOV failed to fully open, and HPCI was declared inoperable.

The licensee found dried and hardened grease on the valve stem and stem nut, as well as stem

nut wear, in this Unit 3 HPCI MOV.

Both MOV failures occurred because the valve stem grease had hardened, increasing the

coefficient of friction of the valve stem so that higher torque was required to open the valves.

The required torque was beyond the open torque switch set point, resulting in the open torque

switches activating to trip the MOVs and stop valve movement prior to attaining the full open

position. The root cause was that the Peach Bottom preventive maintenance (PM) program for

MOVs had not appropriately evaluated actuator stem lubricant performance when establishing

PM frequencies and actions. A significant contributing cause was that the grease used for stem

lubrication was beyond its manufacturer recommended shelf life and degraded in service at a

more rapid rate.

Licensee corrective actions for these MOV failures included identifying other valves that could

be susceptible to this type failure mode and performing a visual inspection, grease evaluation, diagnostic testing, and/or corrective maintenance. The licensee also initiated corrective action

to review the stem lubrication and periodic verification testing intervals for all MOV Program

valves. The use of the grease was discontinued at Peach Bottom and replaced with MOV Long

Life grease for all future stem lubrication PMs. Additional information is available in NRC

Inspection Report 05000277/2009003 and 05000278/2009003 dated August 10, 2009, which

can be found on the NRCs public website in the Agency Documents Access and Management

System (ADAMS) under Accession No. ML092220599.

Vogtle Electric Generating Plant

On March 29, 2009, at Vogtle Unit 2, the 2B core spray pump containment suction MOV was

stroked to the open position satisfactorily during its quarterly inservice test (IST) but when the

plant staff attempted to stroke the valve closed, the valve failed after moving only 5 percent of

the stroke length. The licensee concluded that chattering of the MOV actuator was sufficient to

cause the close torque switch contact finger to rotate in its holder and break the circuit which

prevented the valve from going full closed. The chattering was due to hardening of the valve

stem lubricant, Felpro N 5000. The Felpro N 5000 lubricant had likely prematurely aged and

hardened because of cross contamination with actuator internal grease, Nebula EP-0.

Licensee corrective actions included replacing the torque switch, rebuilding the actuator, and

cleaning and lubricating the valve stem. In addition, the licensee performed an extent of

condition analysis, inspected, and stroked suspect MOVs. During extent of condition

inspections, the licensee identified another MOV with hardened lubricant that had likely

prematurely aged and hardened, but no cross-contamination was found.

On August 5, 2009, at Vogtle Unit 1, during the routine 54 month PM and additional extent of

condition diagnostic testing, the core spray pump train A containment suction MOV failed its

as-found diagnostic test in the closed direction due to apparent stem lubrication degradation.

Licensee corrective actions included reviewing the adequacy of the 54 month PM frequency, performing as-found diagnostic testing for long stroke MOVs approaching their 54 month PM

due date and re-lubricating all long-stroke safety-related MOVs during the refueling outages

1R15 and 2R14, whose last stem lubrication is approaching or has exceeded 36 months.

Callaway Plant

On May 25, 2009, the turbine driven auxiliary feedwater pump (TDAFP) failed to start during

surveillance testing. The failure occurred due to excessive frictional loading from the cumulative effects of a lack of lubrication effectiveness coupled with an incorrectly installed thrust washer

for the TDAFP trip & throttle valve (TTV).

The licensee determined that the TTV PM lubrication frequency was inadequate for the

operating conditions. In addition, the licensee found that the last scheduled TTV lubrication had

not been performed, and that an error occurred during TTV assembly. Licensee corrective

actions included revising the trip/throttle MOV installation procedure to incorporate valve

lubrication requirements as a critical step. The TTV was lubricated and a new thrust washer

was installed correctly. Additional information is available in Callaway Licensee Event Report

50-483/2009-002-00 dated November 11, 2009 (ADAMS Accession No. ML093100103).

BACKGROUND

Related NRC Communications

Generic Letter (GL) 89-10, Safety-Related Motor-Operated Valve Testing and Surveillance, dated June 28, 1989, ADAMS Accession No. ML031150300.

Generic Letter 96-05, Periodic Verification of Design-Basis Capability of Safety-Related

Power-Operated Valves, dated September 18, 1996, ADAMS Accession No.

ML031110010.

IN 97-07, Problems Identified during Generic Letter 89-10 Closeout Inspections, dated

March 6, 1997, ADAMS Accession No. ML031050376.

IN 2006-29, Potential Common Cause Failure of Motor-Operated Valves as a Result of

Stem Nut Wear, dated December 14, 2006, ADAMS Accession No. ML062890437.

NUREG/CR-6750, Performance of MOV Stem Lubricants at Elevated Temperatures, dated

October 2001, ADAMS Accession Nos. ML020150273 and ML020150277.

DISCUSSION

At operating nuclear power plants, safety-related MOVs perform a wide range of functions in

controlling fluid flow in plant systems. For example, licensees rely on the operability of MOVs to

satisfy many technical specification requirements. MOVs are also used in systems credited in

accident analyses. Since licensees often use MOVs of the same type and by the same

manufacturers in redundant trains of various fluid systems, the potential for MOV actuator

failures raises the possibility of a common-mode failure of plant safety systems. Safety-related

MOVs are within the scope of 10 CFR Part 50, Appendix B, Quality Assurance Criteria for

Nuclear Power Plants and Fuel Reprocessing Plants. The NRC regulations in 10 CFR

50.55a(b)(3)(ii) require licensees implementing the American Society of Mechanical Engineers

Code for Operation and Maintenance of Nuclear Power Plant as part of their IST program to

ensure that MOVs continue to be capable of performing their design-basis safety functions.

Further, the NRC regulations in 10 CFR 50.65, Maintenance Rule, require licensees to monitor

the performance or condition of structures, systems, and components (SSCs) in a manner sufficient to provide reasonable assurance that these SSCs are capable of fulfilling their

intended functions.

In an MOV, the stem nut converts the rotational motion of the drive sleeve in the motor actuator

to the lateral motion of the stem to open and close the valve. Lubricant must be applied to the

stem in an effective manner at appropriate intervals to ensure that the coefficient of friction

between the stem and stem nut remains within the design assumptions for the MOV. Improper

or inadequate stem lubrication can result in excessively high friction that can cause the torque

switch in the MOV to trip the motor actuator and stop the valve operation. Inadequate

lubrication can also cause excessive wear and degradation of the MOV stem nut such that the

actuator cannot move or control the valve stem.

Degradation of the lubricant or stem and stem nut interface, or both, can affect the efficiency of

the torque conversion thereby reducing the design margin for ensuring the performance of an

MOV. This is of particular concern for MOVs with small design margins. Lubricant type, lubrication frequency, environmental conditions, and manufacturing tolerances of the stem and

stem nut can affect the coefficient of friction of the stem and stem nut interface. This was

verified during GL 89-10 testing. Problems identified during GL 89-10 testing were distributed to

the industry via IN 97-07. An important observation noted in IN 97-07 was that it is difficult to

apply information on stem friction coefficient and rate-of-loading effects from sources other than

the licensees testing program. Therefore, it is important to assess lubricant performance in

MOV applications as it relates to PM intervals, PM practices, environmental conditions, safety

margins, and surveillance testing.

CONTACT

This IN requires no specific action or written response. Please direct any questions about this

matter to the technical contact listed below or the appropriate Office of Nuclear Reactor

Regulation (NRR) project manager.

/RA/ /RA/

Timothy J. McGinty, Director Daniel H. Dorman, Director

Division of Policy and Rulemaking Division of Fuel Cycle Safety and Safeguards

Office of Nuclear Reactor Regulation Office of Nuclear Material Safety and Safeguards

Technical Contact:

Michael F. Farnan, NRR

301-415-1486 E-mail: Michael.Farnan@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. sufficient to provide reasonable assurance that these SSCs are capable of fulfilling their