Information Notice 1990-76, Failure of Turbine Overspeed Trip Mechanism Because of Inadequate Spring Tension

Failure of Turbine Overspeed Trip Mechanism Because of Inadequate Spring Tension

ML031130175
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, Fort Saint Vrain, Shoreham, Satsop, Trojan, Atlantic Nuclear Power Plant
Issue date:	12/07/1990
From:	Rossi C Office of Nuclear Reactor Regulation
To:
References
IN-90-076, NUDOCS 9012030076
Download: ML031130175 (9)

UNITED STATES

NUCLEAR REGULATORY COMMISSION

OFFICE OF NUCLEAR REACTOR REGULATION

WASHINGTON, D.C. 20555 December 7, 1990

NRC INFORMATION NOTICE NO. 90-76: FAILURE OF TURBINE OVERSPEED TRIP MECHANISM

BECAUSE OF INADEQUATE SPRING TENSION

Addressees

All holders of operating licenses or construction permits for nuclear power

reactors.

Purpose

This information notice is intended to alert addressees to the potential

failure of the overspeed trip mechanism on turbine-driven pumps as the result

of inadequate tension in the emergency trip spring. 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 require- ments; therefore, no specific action or written response is required.

Description of Circumstances

On March 17, 1990, and on August 14, 1990, during two separate monthly surveil- lance tests of the Terry turbine-driven auxiliary feedwater pump at Arkansas

Nuclear One, actuation of the local manual trip lever on the overspeed trip

mechanism failed to close the turbine trip and throttle valve. If a malfunction

causes the turbine to overspeed, the overspeed trip mechanism (shown in

Figure 1) normally will rapidly close the turbine trip and throttle valve, stopping steam flow to the turbine. Excessive turbine speeds could damage the

turbine and pump and overpressurize the auxiliary feedwater system.

In response to an overspeed, a weight in the turbine shaft is forced outward by

the excessive centrifugal force, striking a tappet, which moves upward, releas- ing the emergency head lever (see Figure 1). This lever normally allows the

emergency trip spring to move a rod connected to the turbine trip and throttle

valve trip mechanism. The movement of the connecting rod should then disengage

a trip hook lever on the trip and throttle valve allowing the valve to close.

However, during the two failed tests, the emergency trip spring failed to move

the connecting rod. During the first of these tests, the plant personnel were

able to actuate the trip mechanism by tapping on the emergency trip spring

holder, which produced an erratic response, indicating that the spring force

and the frictional forces were evenly matched. Arkansas Nuclear One personnel

lubricated the critical mating surfaces and achieved good trip response.

90230076~

IN 90-76 December 7, 1990 However, the second failure clearly indicated that insufficient spring

was the root cause of the problem. The original emergency trip spring, force

which

had been in service approximately nine years, had stretched 1/8 inch beyond its

normal at rest position. This spring was replaced with a new one of identical

design. After this change, plant personnel successfully completed a number of

trip tests.

Discussion:

Inspection of the original emergency trip spring provided neither evidence

manufacturing defect nor that the spring had ever been stretched beyond itsof a

elastic limit. The observed elongation was apparently the result of a long- term relaxation process, which could develop on this or any other

mechanism. The tension in the spring, and thus the force applied similar

to the

trip

connecting rod, can be controlled by adjusting the position of the trip spring

holder on a threaded portion of the connecting rod. This adjustment is made

during turbine installation and normally is not changed or checked thereafter.

The Arkansas Nuclear One staff intends to revise the maintenance procedures to

specify adjustment of the trip spring holder position in the event of any

future problems attributable to insufficient spring force.

The failure of overspeed trip mechanisms could result in severe damage to

turbines and pumps in boiling water reactor high-pressure coolant injection and

reactor core isolation cooling systems and in pressurized water reactor auxil- iary feedwater systems. The resulting overpressurization can also damage other

components. NRC Information Notice 90-45 discussed two overspeed events

involving turbine-driven auxiliary feedwater pumps. One occurred at Rancho

Seco, where the turbine, rated at 3600 rpm, reached 6020 rpm a few seconds

after start. According to calculations, the auxiliary feedwater system

pressure reached 3850 psig, significantly exceeding the system design pressure

of 1325 psig. This overpressurization also affected the motor-driven auxiliary

feedwater train because the two trains were tied together. The other overspeed

event occurred at San Onofre, where the turbine-driven auxiliary feedwater pump

reached 5000 rpm and the auxiliary feedwater system pressure was calculated to

have reached 2420 psig.

The event at Arkansas Nuclear One revealed an additional failure process for

overspeed trip mechanisms. It serves as a reminder that the characteristics of

mechanical components, such as springs, are subject to change. Such

variability highlights the importance of periodic checking and adjustment, inherent to adequate maintenance and testing practices.

Related Generic Communications:

1. NRC Information Notice 90-45, "Overspeed of the Turbine-Driven Auxiliary

Feedwater Pumps and Overpressurization of the Associated Piping Systems',

dated July 6, 1990.

2. NRC Information Notice 88-67, *PWR Auxiliary Feedwater Pump Turbine

Overspeed Trip Failure', dated August 22, 1988.

IN 90-76 December 7, 1990 3. NRC Information Notice 88-09, "Reduced Reliability of Steam-Driven Auxil- iary Feedwater Pumps Caused by Instability of Woodward PG-PL Type

Governors", dated March 18, 1988.

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

Problems", dated March 10, 1986.

5. IE Information Notice 86-14, Supplement 1, "Overspeed Trips of AFW, HPCI,

and RCIC Turbines", dated December 17, 1986.

This information notice requires no specific action or written response. If

you have any questions about the information in this notice, please contact one

of the technical contacts listed below or the appropriate NRR project manager.

arEes oss5, rector

Division of Operational Events Assessment

Office of Nuclear Reactor Regulation

Technical Contacts: Thomas F. Stetka, Region IV

(817) 860-8247 Michael F. Runyan, Region IV

(817) 860-8142 Attachments:

1. Figure 1. Emergency Feedwater Pump Overspeed Trip Mechanism

2. List of Recently Issued NRC Information Notices

Figure I

V-4 EMERGENCY FEEDWATER PUMP

V-1

4.'

a)oLO-

r -1

0

OVERSPEED TRIP MECHANISM

.C S.0 r- uo 5

4.3 U M

4<'.. 4 a a.

SPRING LOADED

EMERG.

OVERSPEED TRIP

TAPPET

' NUT

MANUAL

' TRIP

SPRING

STEAM

INLET

TO TURBINE -WEIGHT

SPRING ADJ. SCREW

I.i

Attachment 2 IN 90-76 December 7, 1990. LIST OF RECENTLY ISSUED

NRC INFORMATION NOTICES

Information Date of

Notice No. Subject Issuance Issued to

90-75 Denial of Access to Current 12/5/90 All Michigan holders

Low-Level Radioactive Waste of NRC licenses.

Disposal Facilities

90-74 Information on Precursors to 12/4/90 All holders of OLs or

Severe Accidents CPs for nuclear power

reactors.

90-73 Corrosion Of Valve-To- 11/29/90 All holders of OLs or

Torque Tube Keys In CPs for nuclear power

Spray Pond Cross Connect reactors.

Valves

90-72 Testing of Parallel Disc 11/28/90 All holders of OLs or

Gate Valves In Europe CPs for nuclear power

reactors.

90-71 Effective Use of Radi- 11/6/90 All NRC licensees

ation Safety Committees authorized to use by- to Exercise Control Over product material for

Medical Use Programs medical purposes.

90-70 Pump Explosions Involving 11/6/90 All uranium fuel

Ammonium Nitrate fabrication and

conversion facilities.

90-38, License and Fee Require- 11/6/90 All fuel facility and

Supp. 1 ments for Processing Fin- materials licensees.

ancial Assurance Submittals

for Decommissioning

89-30, High Temperature Environ- 11/1/90 All holders of OLs

Supp. 1 ments At Nuclear Power or CPs for nuclear

Plants power reactors.

90-69 Adequacy of Emergency and 10/31/90 All holders of OLs

Essential Lighting or CPs for nuclear

power reactors.

90-68 Stress Corrosion Cracking 10/30/90 All holders of OLs

of Reactor Coolant Pump Bolts or CPs for pres- surized water

reactors (PWRs).

OL - Operating License

CP = Construction Permit

IN 90-76 December 7, 1990 3. NRC Information Notice 88-09, "Reduced Reliability of Steam-Driven Auxil- iary Feedwater Pumps Caused by Instability of Woodward PG-PL Type

Governors", dated March 18, 1988.

4. IE Information Notice 86-14, SPWR Auxiliary Feedwater Pump Turbine Control

Problems", dated March 10, 1986.

5. IE Information Notice 86-14, Supplement 1, "Overspeed Trips of AFW, HPCI,

and RCIC Turbines", dated December 17, 1986.

This information notice requires no specific action or written response. If

you have any questions about the information in this notice, please contact one

of the technical contacts listed below or the appropriate NRR project manager.

Charles E. Rossi, Director

Division of Operational Events Assessment

Office of Nuclear Reactor Regulation

Technical Contacts: Thomas F. Stetka, Region IV

(817) 860-8247 Michael F. Runyan, Region IV

(817) 860-8142 Attachments:

1. Figure 1. Emergency Feedwater Pump Overspeed Trip Mechanism

2. List of Recently Issued NRC Information Notices

• SEE PREVIOUS CONCURRENCES

• OGCB:DOEA:NRR AiIV NIV *RPB:ADM jv*C/OGCB:DOEA:NRR

DCKirkpatrick TStetka MRunyan TechEd CHBerlinger

09/15/90 11/ /90 11/ /90 10/05/90 11/29/90

DOCUMENT NAME: IN 90-76

1;

IN 90 X1Ž.0

m-I SoYkmbkr220,

~7~g59,A~ -Page 3 of 1990

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

Problems."

5. IE Information Notice 86-14, Supplement 1, "Overspeed Trips of AFW, HPCI,

and RCIC Turbines."

If

This information notice requires no specific action or written response. one

you have any questions about the information in this notice, please contact

of the technical contacts listed below or the appropriate NRR project manager.

Charles E. Rossi, Director

Division of Operational Events Assessment

Office of Nuclear Reactor Regulation

Technical Contacts: Thomas F. Stetka, Region IV

(817) 860-8247 Michael F. Runyan, Region IV

(817) 860-8142 Attachments:

1. Figure 1. Emergency Feedwater Pump Overspeed Trip Mechanism

2. List of Recently Issued NRC Information Notices

Document Name: OSTRIPIN

• SEE PREVIOUS CONCURRENCES

D/DOEA:NRR

CERossi

11/ /90

• OGCB:DOEA:NRR RIV RIV *RPB:ADM C/OGCB:DOEA:NRR

CHBerlinger

A'1 AYr

DCKirkpatrick TStetka MRunyan TechEd

09/15/90 11/:41/90 10/05/90 11/li/90

1 X/ ;l9 4? 4so

7JW

IN 90-XX

September xx, 1990 5. IE Information Notice 86-14, Supplement 1, "Overspeed Trips of AFW, HPCI,

and RCIC Turbines."

This information notice requires no specific action or written response. If

you have any questions about the information in this notice, please contact one

of the technical contacts listed below or the appropriate NRR project manager.

Charles E. Rossi, Director

Division of Operational Events Assessment

Office of Nuclear Reactor Regulation

Technical Contacts: Thomas F. Stetka, Region IV

(817) 860-8247 Michael F. Runyan, Region IV

(817) 860-8142 Attachments:

1. Figure 1

2. List of Recently Issued NRC Information Notices

Document Name: IN ON TURBINE OS TRIP FAILURE

D/DOEA:NRR

CERossi

09/ /90

OGCB:DOEA:NRR RIV RIV RPB:ADM C/OGCB:DOEA:NRR

DCKirkpatrick TStetka MRunyan TechEd J-Aqi" CHBerlinger

09/i5790 CW 09/ /90 09/ /90 103/5 /90 9> 09/ /90