Information Notice 1988-67, PWR Auxiliary Feedwater Pump Turbine Overspeed Trip Failure

PWR Auxiliary Feedwater Pump Turbine Overspeed Trip Failure

ML031150167
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:	08/22/1988
From:	Rossi C Office of Nuclear Reactor Regulation
To:
References
IN-88-067, NUDOCS 8808160414
Download: ML031150167 (7)

UNITED STATES

NUCLEAR REGULATORY COMMISSION

OFFICE OF NUCLEAR REACTOR REGULATiON

WASHINGTON, D.C. 20555 August 22, 1988 NRC INFORMATION NOTICE NO. 88-67: PWR AUXILIARY FEEDWATER PUMP TURBINE

OVERSPEED TRIP FAILURE

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 affecting the reliability of turbine-driven auxiliary feedwater (AFW)

pumps to trip during overspeed events. Similar overspeed trip mechanisms are

employed on turbine-driven high-pressure coolant injection (HPCI) and reactor

core isolation cooling (RCIC) pumps. 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

The steam-driven AFW pumps at San Onofre Units 2 and 3 are powered by Terry

steam turbines, which are provided with a mechanical overspeed trip assembly.

Actuation of the trip assembly causes the steam inlet valve to the turbine to

close by releasing the stop valve closure spring.

On July 3, 1988, personnel at San Onofre Unit 2 were performing low-voltage

testing of the steam inlet valve to the AFW turbine. During the test, the steam

inlet valve failed to close within the required period of time. In accordance

with procedures, the valve technician in the pump room removed power fron the

steam inlet valve, which also removed power from the governor valve to the AFW

turbine (fails open). Loss of power to the governor resulted in the turbine

reaching an overspeed cornition. Control room indication showed the pump

discharge pressure to be at full scale (2000 psig), and maximum rotational speed

was approximately 5000 rpm (the overspeed trip setpoint is 3500 rpm). An attempt

8808160414

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IN 88-67 August 22, 1988 Page " of 3 was made to close the steam inlet valve from the control room, but this was

unsuccessful since power had been removed. The control room operator then

closed the turbine inlet isolation valve, terminating the event.

Discussion:

The licensee's investigation into this event identified the root cause to be

failure of the mechanical overspeed trip device because of damage to the

tappet ball located in the mechanical trip linkage. The licensee made visual

inspections for damage from overpressurization of piping, valves, and

instrumentation. There was no evidence of cracks, leaks, or deformation of

the overpressurized piping. Analysis performed after the event revealed that

piping code stresses were not exceeded.

The mechanical overspeed trip linkage consists of an emergency governor weight

(located in the shaft of the turbine), an emergency tappet (see attachment 1),

and linkage (not shown in attachment 1) to the trip (steam inlet) valve.

During an overspeed condition, centrifugal force causes the emergency governor

weight to overcome a restraining spring located in the shaft. The weight then

strikes the emergency tappet, which, in turn, rises against a spring allowing

the trip linkage to release the stop valve spring closure mechanism closing

the steam inlet valve. Initial inspection and test results failed to duplicate

the overspeed event. Upon disassembly of the mechanical trip device, visual

inspection showed excessive wear on the polyurethane tappet ball. The tappet

ball fits into the emergency tappet as shown in attachment 1, with the ball

free to rotate. Approximately half the polyurethane was missing from the

tappet ball so that the emergency governor weight could not contact the tappet

ball with sufficient force to actuate the trip mechanism. The ball was also

covered with a gummy substance of unknown origin.

The licensee implemented several corrective actions and plans to upgrade

the mechanical trip linkage to the current vendor design (the new design has

no tappet ball arrangement). The vendor recommended overspeed testing every

refueling outage. Licensees may wish to consider a visual examination of the

tappet ball arrangement during the refueling outage.

Information Notice 86-14, "PWR Auxiliary Feedwater Pump Turbine Control

Problems," Supplement 1 to Information Notice 86-14, "Overspeed Trips of AFV1, HPCI, and RCIC Turbines," and Information Notice 88-09, "Reduced Reliability

of Steam-Driven Auxiliary Feedwater Pumps Caused by Instability of Woodward

PG-PL Type Governors," discuss problems related to the Terry turbine overspeed

trip systems.

. '..

IN 88-67 August 22, 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: J. Thompson, NRR

(301) 492-1175 T. Silko, NRR

(301) 492-9059 Attachments:

1. Terry Turbine Mechanical Trip Device Tappet and Ball Linkage

L. List of Recently Issued NRC Information Notices

Attachment I

IN 88-67 August 22, 1988 TERRY TURBINE MECHANICAL TRIP DEVICE

TAPPET AND BALL LINKAGE

DIRECTION OF

TAPPET MOVEMENT

TAPPET

BALL

EMERG.

SPRING

ADJ. SCREW

- SET SCREW

EMERG.

GOV.

WEIGHT-

RESTRAINING

SPRING

EMERG.

GOV. DISC.-

TURB. SHAFT EMERO. WEIGHT

ADJ. SCREW

SET SCREW

Attachment 2 IN 88-67 August 22, 1988 Paae l of 1 LIST OF RECENTLY ISSUED

NRC INFORMATION NOTICES

Information Date of

Notice No. Subject Issuance Issued to

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 Nucledr 8/18/88 All holders of OLs

Process Systems at Nuclear or CPs for nuclear

Power Plants power reactors.

88-63 High Radiation Hazards 8/15/88 All holders of OLs

from Irradiated Incore or CPs for nuclear

Detectors and Cables power reactors, research reactors

and test reactors.

88-62 Recent Findings Concerning 8/12/88 All holders of NRC

Implementation of Quality quality assurance

Assurance Programs by program approval

Suppliers of Transport for radioactive

Pdckages material packages.

88-61 Control Room Habitability - 8/11/88 All holders of OLt

Recent Reviews of Operating or CPs for nuclear

Experience power reactors.

88-60 Inadequate Design and 8/11/88 All holders of OLs

Installation of Watertight or CPs for nuclear

Penetration Seals power reactors.

88-04, Inadequate Qualification 8/9/88 All holders of OLs

Supplement 1 and Documentation of Fire or CPs for nuclear

Barrier Penetration Seals power reactors.

88-59 Main Steam Isolation Valve 8/9/88 All holders of OLs

Guide Rail Failure at or CPs for nuclear

Waterford Unit 3 power reactors.

88-58 Potential Problems with 8/8/88 All holders of OLs

ASEA Brown Boveri ITE-51L or CPs for nuclear

Time-Overcurrent Relays power reactors.

OL'= Operating License

CP = Construction Permit

IN 88-67 August 22, 1988 information notice.

No specific action or written response is required by this one of the

If you have any questions about this matter, please contact

of the

technical contacts listed below or the Regional Administrator

appropriate regional office.

Charles E. Rossi, Director

Division of Operational Events Assessment

Office of Nuclear Reactor Regulation

Technical Contacts: J. Thompson, NRR

(301) 492-1175 T. Silko, NRR

(301) 492-9059 Attachments:

1. Terry Turbine Mechanical Trip Device Tappet and Ball Linkage

2. List of Recently Issued NRC Information Notices

• SEE PREVIOUS CONCURRENCES *C:OGCB:NRR

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IN 88- August , 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: J. Thompson

(301) 492-1175 T. Silko

(301) 492-9059 Attachment: 1. Terry Turbine Mechanical Trip Device Tappet and Ball Linkage

2. List of Recently Issued NRC Information Notices

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