Information Notice 1988-72, Inadequacies in the Design of DC Motor-Operated Valves

Inadequacies in the Design of DC Motor-Operated Valves

ML031150133
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
Issue date:	09/02/1988
From:	Rossi C Office of Nuclear Reactor Regulation
To:
References
IN-88-072, NUDOCS 8808300018
Download: ML031150133 (9)

UNITED STATES

NUCLEAR REGULATORY COMMISSION

OFFICE OF NUCLEAR REACTOR REGULATION

WASHINGTON, D.C. 20555 September 2, 1988 NRC INFORMATION NOTICE NO. 88-72: INADEQUACIES IN THE DESIGN OF DC MOTOR-

OPERATED VALVES

Addressees

All holders of operating licenses or construction permits for nuclear power

reactors.

Purpose

This information notice is being provided to alert addressees to potential

problems in the design specifications of dc motor-operated valves, especially

for conditions that may involve reduced or degraded dc voltage and/or elevated

temperatures. 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 do not constitute NRC requirements; therefore, no specific action or

written response is required.

Description of Circumstances

On July 1, 1988, a high pressure coolant injection (HPCI) steam admission valve

failed to open during a post-maintenance test at the Brunswick nuclear power

plant, Unit 1. The same valve had failed in December 1987 and on May 28, 1988.

The licensee, Carolina Power and Light Company, established a team to investi- gate the cause of failure, and the team identified the most probable cause as

a dc motor failure due to a shunt-winding to series-winding short circuit. The

team believed that this condition was precipitated by thermal binding of the

valve internals. The previous failure in May was also diagnosed as having been

caused by thermal binding. As a result of these failures, the licensee reviewed

the design of the dc motor-operated valves for both the HPCI and the reactor

core isolation cooling (RCIC) systems. This review identified a number of

significant design deficiencies going well beyond the problems with thermal

binding. The deficiencies constitute a potential common cause failure mechanism

for safety-system valves. Unit 1 was shut down on July 14, 1988 to replace the

failed HPCI valve motor and to implement design modifications to other motor- operated valves.

Discussion:

Pressure locking and thermal binding of gate valves were identified as poten- tially important valve failure mechanisms within the nuclear industry several

880830018t

A"Py-

. I

IN 88-72 September 2, 1988 years ago. Pressure locking occurs when a gate valve is closed under full

system pressure and fluid is trapped in either the bonnet cavity or between

the disks of a double disk valve. When the valve is subsequently heated, the

trapped fluid expands or flashes to steam and causes pressure to increase in

the valve bonnet area and between the wedges of the valve disk. The pressure

increase inhibits opening of the valve by causing the wedges to press tightly

against the valve seats, resulting In binding of the valve. This phenomenon

contributed to the May 1988 HPCI valve failure. To prevent recurrence-of this

failure, the licensee drilled a small drain hole in the upstream disk to provide

a pressure relief path. This remedy was only partially successful because the

valve also underwent thermal binding, which was not recognized at that time.

Thermal binding occurs when a valve is seated in a hot condition and, during

subsequent temperature changes, the valve body contracts a proportionally

greater amount than the valve internals because of the different expansion

and contraction characteristics of the valve body and the disk. This is

particularly true for valves with internals which have reduced clearances

due to improper maintenance or alterations. Several potential remedies have

been suggested to alleviate this situation, including slightly opening and

reclosing a valve during cooldown, limiting valve actuator closing forces, and using compensating spring packs to reduce valve inertial closing forces.

In general, neither ac nor dc valve motor operator sizing analyses account

for the extra torque needed to unseat a valve when it is thermally bound.

It should be noted that certain valves may become functionally inoperable

when conditions induce thermal binding.

The dc motor operator design problems discovered at Brunswick as a result of

the review following the July 1 HPCI valve failure were attributed by the

licensee to a lack of design coordination and inadequate consideration of

the valves' functional operability requirements by the architect engineering

firm, United Engineers and Constructors. The licensee found that inadequate

torque was available to open the valves, particularly under reduced dc bus

voltage conditions, and when MOVs were installed in locations that are-normally

at elevated ambient temperatures. Reduced or degraded dc bus voltage conditions

could occur during accidents in which battery charging capability is lost (for

example, during a station blackout or failure of the chargers). Four design

flaws were identified in the licensee's review.

(1) The specified motor operator torque was found to be deficient. Also, the design temperatures-used for sizing the motors were found to be

below the actual ambient temperature in which some valves were oper- ating. Thus, the motors were unable to develop the torque required

to unseat (open) the valves under reduced dc voltage conditions. Ad- ditionally, the operability of some of the valves during accident

conditions, such as high-energy line breaks, was questionable.

IN 88-72 September 2, 1988 (2) The presence of starting resistors and their impact on starting

torque were not considered in motor sizing. The resistors were

installed to limit the dc current until the motor starts and ac- celerates toward rated speed. However, they were found to reduce

the "hammer blow" effect needed to ensure valve opening. They also

increased the potential for motor stalling against a seated valve.

(3) Cable resistance contributed to reduced motor terminal voltage and

starting current. As a result, actual torque supplied by the motor

was further reduced.

(4) High-voltage transients were induced in the dc motor's shunt windings

whenever the motor's power supply circuit breaker was opened. (In

some cases, high voltage transients may also result when motor starter

contacts are opened in installations in which the shunt field is set

up for intermittent service; i.e. energized only when the armature is

energized.) This process led to degradation of the insulation on the

shunt and field windings.

These dc motor-related design flaws were not uncovered during routine surveil- lance testing nor during post-maintenance testing. In part, this was because

dc voltage was normally maintained at or above nominal values by battery chargers

operating "in float" with the batteries when the tests were conducted. Thus, design flaws related to reduced dc voltage performance would not be readily

detected.

Additionally, Motor Actuator Characterizer (MAC) traces were made from valve

tests performed during certain maintenance testing activities. These-MAC

traces indicated anomalies in valve performance. However, the deviations

from expected performance were subtle. Careful engineering review was neces- sary to properly interpret these traces.

The corrective actions taken by the licensee included removal of starting re- sistors, replacement of certain motors and cable, and the addition of metal

oxide varistors to dissipate induced voltage transients during power supply

interruptions. (Discussions with Limitorque have revealed that, for the past

five years, the company has recognized the need to control voltage transients

in their motor operators. Therefore, they have included depictions of voltage

surge suppression devices in their electrical drawings for their motor-operated

valves.)

It is important to note that the removal of dc motor operator starting resistors

may cause a significant increase in the 1-minute load on the station's batteries.

A battery performance assessment was conducted by the Brunswick licensee to

ensure that the dc power system continued to meet plant safety analysis require- ments following removal of the resistors.

IN 88-72 September 2, 1988 No specific action or written response is required by this information notice.

If you have any questions about this matter, please contact one of the technical

contacts listed below or the Regional Administrator of the appropriate regional

office.

Charles E. Rossi, Director

Division of Operational Events Assessment

Office of Nuclear Reactor Regulation

Technical Contacts: P. W. Baranowsky, NRR

(301) 492-1157 E. N. Fields, NRR

(301) 492-1173 Attachment: List of Recently Issued NRC Information Notices

Attachment

IN 88-72 September 2, 1988 LIST OF RECENTLY ISSUED

NRC INFORMATION NOTICES

Information Date of

Notice No. Subject Issuance Issued to

88-71 Possible Environmental 9/1/88 All holders of OLs

Effect of the Reentry or CPs for nuclear

of COSMOS 1900 and power reactors, fuel

Request for Collection cycle licensees, and

of Licensee Radioactivity Priority 1 material

Measurements Attributed licensees. -

to That Event

88-70 Check Valve Inservice 8/29/88 All holders of OLs

Testing Program or CPs for nuclear

Deficiencies power reactors.

88-69 Movable Contact Finger 8/19/88 All holders of OLs

Binding in HFA Relays or CPs for nuclear

Manufactured by General power reactors.

Electric (GE)

88-48, Licensee Report of Defective 8/24/88 All holders of OLs

Supplement 1 Refurbished Valves or CPs for nuclear

power reactors.

88-68 Setpolnt Testing of Pres- 8/22/88 All holders of OLs

surizer Safety Valves with or CPs for nuclear

Filled Loop Seals Using power reactors. -

Hydraulic Assist Devices

88-67 PWR Auxiliary Feedwater Pump 8/22/88 All holders of OLs

Turbine Overspeed Trip or CPs for nuclear

Failure power reactors.

88-66 Industrial Radiography 8/22/88 All NRC industrial

Inspection and Enforcement radiography licensees.

88-65 Inadvertent Drainages of 8/18/88 All holders of OLs

Spent Fuel Pools or CPs for nuclear

power reactors and

fuel storage facilities.

88-64 Reporting Fires in Nuclear 8/18/88 All holders of OLs

Process Systems at Nuclear or CPs for nuclear

Power Plants power reactors.

OL = Operating License

CP = Construction Permit

IN 88-72 September 2, 1988 No specific action or written response is required by this information notice.

If you have any questions about this matter, please contact one of the technical

contacts listed below or the Regional Administrator of the appropriate regional

office.

Charles E. Rossi, Director

Division of Operational Events Assessment

Office of Nuclear Reactor Regulation

Technical Contacts: P. W. Baranowsky, NRR

(301) 492-1157 E. N. Fields, NRR

(301) 492-1173 Attachment: List of Recently Issued NRC Information Notices

• see previous concurrence

• OEAB:NRR *OEAB:NRR *RPB:ARM *C:OEAB:NRR *D:DEST:NRR *C: OGCB: NRR&!~VC

PBaranowsky NFields TechEd WLanning LShao CHBerlinger CERossi

8/12/88 8/12/88 8/04/88 8/12/88 8/17/88 8/25/88 8/3//88

IN 88- August , 1988 ( some cases, high voltage transients may also result when motor

sta er contacts are opened in installations in which the shunt

field is set up for intermittent service, i.e. energized only when

the arm ture is energized.) This process led to degradation of the

insulati on the shunt and field windings.

These dc motor-relate design flaws were not uncovered during routine

surveillance testing no0during post-maintenance testing. In part this was

because dc voltage was no ally maintained at or above nominal values by

battery chargers operating 'infloat" with the batteries when the tests were

conducted. Thus, design fla related to reduced dc voltage performance would

not be readily detected.

Additionally, Motor Actuator Cha terizer (MAC) traces were made from valve

tests performed during certain main enance testing activities. These MAC

traces indicated anomalies in valve rformance. However, the deviations from

expected performance were subtle. Car ful engineering review was necessary to

properly interpret these traces.

The corrective actions taken by the licens included removal of starting

resistors, replacement of certain motors and able, and the addition of metal

oxide varistors to dissipate induced voltage t ansients during power supply

interruptions. (Discussions with Limitorque ha revealed that, for the past

five years, the company has recognized the need t control voltage transients in

their motor operators. Therefore they have include depictions of voltage

surge suppression devices in their electrical drawin for their motor

operated valves.

It is important to note that the removal of dc motor oper tor starting resistors

may cause a significant increase in the 1-minute load on t station's

batteries. A battery performance assessment was conducted t ensure that the

dc power system continued to meet plant safety analysis requi ments following

removal of the resistors.

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

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

contact listed below or the Regional Administrator of the appropriate egional

office.

Charles E. Rossi, Director

Division of Operational Events Assessment

Office of Nuclear Reactor Regulation

P.W. Baranowsky

(301) 492-1157 E.N. Fields

(301) 492-1173 p

Attachment: List of Recently Issued NRC Information Notices

• see previous concurrence M145

• OEAB:NRR *OEAB:NRR *RPB:ARM C:OEAB:NRR D:DEST:NRR C:OGCB:NRR D:DOEA:NRR

PBaranowsky NFields TechEd WLanning LShao CHBerlinger CERossi

/ /88 / /88 / /88 / /88 / /88 J'/,S88 / /88

IN 88- August , 1988 (In me cases, high voltage transients may also result when motor

starte contacts are opened in installations in which the shunt

field i set up for intermittent service, i.e. energized only when

the armat e is energized.) This process led to degradation of the

insulation the shunt and field windings.

These dc motor-related d ign flaws were not uncovered during routine

surveillance testing nor ing post-maintenance testing. In part this was

because dc voltage was norma ly maintained at or above nominal values by

battery chargers operating in oat with the batteries when the tests were

conducted. Thus, design flaws elated to reduced dc voltage performance would

not be readily detected.

Additionally, Motor actuator charac rizer (MAC) traces were made from valve

tests performed during certain mainte nce testing activities. These MAC

traces indicated anomalies in valve pe ormance. However, the deviations from

to

expected performance were subtle. Caref 1 engineering review was necessary

properly detect and interpret these trace The corrective actions taken by

the licensee included removal of starting r sistors, replacement of certain

motors and cable, and the addition of metal ide varistors to dissipate

induced voltage transients during power supply interruptions. (Discussions

with Limitorque have revealed that for the past five years the company has

recognized the need to control voltage transients in their MOVs. Therefore

they have included depictions of voltage surge sup ression devices in their

electrical drawings for their MOVs.)

It is important to note that the removal of dc motor o erator starting resistors

may cause a significant increase in the 1-minute load batteries. A battery

performance assessment was required to ensure that the d power system

continued to meet plant safety analysis requirements folbo ing removal of the

resistors.

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

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

contact listed below or the Regional Administrator of the appropr ate regional

office.

Charles E. Rossi, Director

Division of Operational Events Assessm t

Office of Nuclear Reactor Regulation

P.W. Baranowsky

(301) 492-1157 E.N. Fields

(301) 492-1173 Attachment: List of Recently Issued NRC Information Notices

• See previous concurrence

• OEAB:NRR *RPB:ARM C:; P NRR D:D W R C:OGCB:NRR D:DOEA:NRR

IB ranowsky NFields Tech.Ed. WLanning I, o CHBerlinger CERossi

M 17/88 g.//i8/ /8/8 88 //(V

/17/88 / /88 / /88

+ W4 YOU IN 88-

<AX August , 1988 Motor act tor characterizer (MAC) traces were made f om valve tests performed

during certa maintenance testing activities. These traces indicated anomalies

in valve perfo ance. However, the deviations from expected performance were

subtle. Careful gineering review was necessary to properly detect and

interpret these tra s. The corrective actions taken by the licensee included

removal of starting re istors, replacement of certain motors and cable, and the

addition of metal oxides ristors to dissipate induced voltage transients during

power supply interruptions I

It is important to note that t removal of dc motor operator starting resistors

may cause a significant increase n the 1-minute load on batteries. A battery

performance assessment was require to ensure that the dc power system

continued to meet plant safety analy s requirements following removal of the

resistors.

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

If you have any questions about this matter please contact the technical

contact listed below or the regional/dminist tor of the appropriate regional

office.

Charles E. Rossi, rector

Division of Operatio _ Event

Office of Nuclear Reac r Re(

P.W. Baranowsky

(301) 492-1157 E.N. Fields

(301) 492-1173 A1"^,o+: *u5+- , 9t .CAOY TES& LtA MAJ 1o fNorhcSt

• 0EAB:NRR 10EAB:NRR TV)OEs C:4 EAB:NRR D:DEST:NRR C:OGCB:NRR D:DOEA:NRR

PBaranowsky 8 Fields Wianning LShao CHBerlinger CERossi

/o5/88 £/of/88 'i/O9I/88 / /88 / /88 / /88 / /88