Information Notice 1985-20, Motor-Operated Valve Failures Due to Hampering Effect

Motor-Operated Valve Failures Due to Hampering Effect

ML031180428
Person / Time
Site:	Beaver Valley, Millstone, Hatch, Monticello, Calvert Cliffs, Dresden, Davis Besse, Peach Bottom, Browns Ferry, Salem, Oconee, Mcguire, Nine Mile Point, Palisades, Palo Verde, Perry, Indian Point, Fermi, Kewaunee, Catawba, Harris, Wolf Creek, Saint Lucie, Point Beach, Oyster Creek, Watts Bar, Hope Creek, Grand Gulf, Cooper, Sequoyah, Byron, Pilgrim, Arkansas Nuclear, Three Mile Island, Braidwood, Susquehanna, Summer, Prairie Island, Columbia, Seabrook, Brunswick, Surry, Limerick, North Anna, Turkey Point, River Bend, Vermont Yankee, Crystal River, Haddam Neck, Ginna, Diablo Canyon, Callaway, Vogtle, Waterford, Duane Arnold, Farley, Robinson, Clinton, South Texas, San Onofre, Cook, Comanche Peak, Yankee Rowe, Maine Yankee, Quad Cities, Humboldt Bay, La Crosse, Big Rock Point, Rancho Seco, Zion, Midland, Bellefonte, Fort Calhoun, FitzPatrick, McGuire, LaSalle, 05000000, Zimmer, Fort Saint Vrain, Shoreham, Satsop, Trojan, Atlantic Nuclear Power Plant, Skagit, Marble Hill
Issue date:	03/12/1985
From:	Jordan E NRC/IE
To:
References
IN-85-020, NUDOCS 8503070477
Download: ML031180428 (4)

SSINS No.: 6835 IN 85-20

UNITED STATES

NUCLEAR REGULATORY COMMISSION

OFFICE OF INSPECTION AND ENFORCEMENT

WASHINGTON, D.C. 20555 March 12, 1985 IE INFORMATION NOTICE NO. 85-20: MOTOR-OPERATED VALVE FAILURES DUE TO

HAMMERING EFFECT

Addressees

All nuclear power reactor facilities holding an operating license (OL) or con- struction permit (CP).

Purpose

This information notice is provided to alert recipients of a potentially

significant problem pertaining to motor-operated valve failures due to the

hamrnering that may result when a fully closed (opened) valve continues to

receive a close (open) signal at the valve operator. It is expected that

recipients will review the information for applicability to their facilities

and consider actions, if appropriate, to preclude a similar problem occurring

at their facilities. However, suggestions contained in this notice do not

constitute NRC requirements, therefore, no specific action or written response

is required.

Description of Circumstances

On March 19, 1984, and September 25, 1984, Commonwealth Edison reported

[licensee event report (LER) 84-003] the failure of a core spray valve to

operate from the control room at the Dresden Nuclear Power Station Unit 2. The

immediate cause of failure was a mechanical failure of the gear housing of the

valve, probably caused by mechanical overloading during operation.

The same LER identified the failure of a second core spray valve. In this

case, the immediate cause of failure was a cracked bearing race and gear

housing. Metallurgical analysis by the licensee indicated that the valve gear

housing had failed as a result of a mechanical overload. In addition, the

valve thermal overload breaker had tripped.

Further investigation by the licensee showed that these mechanical overloads

were the result of the valve being repeatedly hammered closed by the valve

operator. This hampering would continue as long as the valve operator contin- ued to receive a close demand signal.

8503070477

IN 85-20

March 12, 1985 In general, the sequence of events would be:

1. On receiving a close signal, power would be applied to the valve motor

and the valve would begin closing.

2. Once closed, torque would build up and the torque switch would open

removing power from the valve motor.

3. With the power removed, the valve motor would stop and the torque on

the valve would relax.

4. With torque removed, the torque switch would reset.

5. Once the torque switch reset, if a close signal was still present at the

valve motor operator, power would be re-applied to the valve motor and

the valve would be driven further closed.

6. Since the valve was already closed, torque would immediately begin

to build up and the torque switch would open removing power from the

valve motor.

The last four steps would then repeat over and over. However, the torque

switch would not stop the motor instantaneously. Thus, the loads would gradu- ally build up in the valve until either something failed or the close signal

was removed-ffom the vaTvei-iotor -oiffroller. The potential for "valve-hammer- ing" exists if the automatic or manual valve-close demand signal continues

after the torque switch has been activated open. That is, if the valve full

close limit switch is out of calibration. A similar condition could occur on

valve opening, if backseating loads are limited by a torque switch.

Recognizing this condition as a possible common mode failure mechanism for all

valves with this particular valve motor controller logic, the NRC's Office of

Analysis and Evaluation of Operational Data (AEOD) performed a search of LERs

on the Sequence Coding and Search System for the 1983 through 1984 tire period

(AEOD Engineering Evaluation Report No. AECC/E501). Although they did riot find

any events attributed to hammering, they did find 47 events which had symptoms

indicative of the hamnering problem. Among these were failure and damage due

to mechanical overloading, overheating of the valve operator motor, repeated

cycling and failure of the starter contactors, thermal overloading, circuit

breaker trips, ard valve seat Janning. From this, AEOD concluded that

licensees have not consistently identified the root cause of motor-operated

valve failures, but rather have only identified the symptomatic ones. (This

concept has been previously addressed in IE Information Notice No. 82-10,

"Following up Symptomatic Repairs to Assure Resolution of Problem.")

As a part of their corrective action for the valve failures at Dresden, the

licensee plans on modifying the control circuitry of the valves to prevent this

hammering effect. This action will be taken on the valves ir both units. Tr, the interim, caution cards have been put on the valves to warn the operators

not to hold on to the control switch when closing the valves.

IN 85-20

March 12, 1985 It is important that any modifications made to the valve's motor controller

logic not adversely affect the valve's safety-related functioning. For in- stance, simply locking out a close signal once the torque switch opens will

result in improper valve operation if the valve should experience momentarily

high friction loads from either tight packing or high pressure differential

across the valve.

LER 84-014 submitted by Commonwealth Edison on August 14, 1984, described the

failure of both low pressure coolant injection valves to open at Quad Cities

Nuclear Power Station Unit 1. In 1980 the motor control logic for these valves

was modified to prevent hammering. However, some time later, when the brakes

on the valve motors were removed, it became apparent that the modification had

not eliminated the problem. This is indicative of the difficulty involved in

performing this type of modification.

No specific action or written response is required by this information notice.

If you have any questions about this matter, please contact the Regional

Administrator of the appropriate NRC regional office or this office.

42or an, Divisio of Emergency Preparedness

and Engineering Response

Office of Inspection and Enforcement

Richard J. Kiessel, IE

(301) 492-8119 Attachment: List of Recently Issued IE Information Notices

Attachment 1 IN 85-20

March 12, 1985 LIST OF RECENTLY ISSUED

IE INFORMATION NOTICES

Information.Date of--- ----- -------

Notice No. Subject Issue Issued to

85-19 Alleged Falsification Of 3/11/85 All power reactor

Certifications And Alteraticn facilities holding

Of Markings On Piping, Valves an OL or CP

And Fittings

84-18 Failures Of Undervoltage 3/7/85 All power reactor

Output Circuit Boards In The facilities holding

Westinghouse-Designed Solid an CL or CP

State Protection System

83-70 Vibration-Induced Valve 3/4/85 All power reactor

Sup. I Failures facilities holding

an OL or CP

85-17 Possible Sticking Of ASCO 3/lE/5 All power reactor

Solenoid Valves facilities holding

an OL or CP

85-16 Time/Current Trip Curve _ 2/27/85 All power reactor

Discrepancy Of ITE/Siemens- facilities holding

Allis Molded Case Circuit an OL or CP

Breaker

Nonconforming Structural 2/22/85 All power reactor

Steel For Safety-Related facilities holding

Use an OL or CP

8E-14 Failure Of A Heavy Control 2/22/85 All power reactor

Rod (B4C) Drive Assembly facilities holding

To Insert On A Trip Signal an OL or CP

85-13 Consequences Of Using 2/21/85 All BWR ard PWiR

Soluble Dars facilities holding

an OL or CP

Recent Fuel Handling Everts 2/11/85 All power reactor

facilities holding

an OL or CP

Licensee Programs For 2/11/85 All power reactor

Inspection Of Electrical facilities holding

Raceway And Cable Installation a CP

, ~~~. . . .. .

CRp+aetinig License

El

= . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .......

CP = Constructior Permit