Information Notice 1988-09, Reduced Reliability of Steam-Driven Auxiliary Feedwater Pumps Caused by Instability of Woodward PG-PL Type Governors

Reduced Reliability of Steam-Driven Auxiliary Feedwater Pumps Caused by Instability of Woodward PG-PL Type Governors
	ML031150561
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:	03/18/1988
From:	Rossi C; Office of Nuclear Reactor Regulation
To:	;
References
	IN-88-009, NUDOCS 8803140284
	Download: ML031150561 (7)
	v • d • e

UNITED STATES

NUCLEAR REGULATORY COMMISSION

OFFICE OF NUCLEAR REACTOR REGULATION

WASHINGTON, D.C. 20555 March 18, 1988 NRC INFORMATION NOTICE NO. 88-09: REDUCED RELIABILITY OF STEAM-DRIVEN

AUXILIARY FEEDWATER PUMPS CAUSED BY

INSTABILITY OF WOODWARD PG-PL TYPE

GOVERNORS

Addressees

All holders of operating licenses or construction permits for nuclear power

reactors.

Purpose

This information notice is provided to alert addressees to continuing problems

affecting the reliability of steam-driven auxiliary feedwater pumps caused

by instability problems with Woodward governors. It is expected that recipi- ents will review the information for applicability to their facilities and

consider actions, if appropriate, to avoid similar problems. However, sugges- tions 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 auxiliary feedwater pumps at Calvert Cliffs are powered by

Terry steam turbines (GS-2N) with Woodward PG-PL type governors. Before

July 23, 1987, periodic surveillance testing of the steam-driven auxiliary

feedwater pumps (AFWPs) was preceded by a warmup of the turbines before

initiation of the quick startup tests. On July 23, 1987, during a loss- of-offsite-power event, the number 11 AFWP on Unit 1 tripped on its initial

demand as a result of turbine overspeed. To ensure that future periodic

(monthly) surveillance testing of the turbine-driven AFWPs would be con- ducted under more realistic conditions, the test procedures were modified

to require quick starts from cold conditions. During subsequent tests in

July through October 1987, a number of trips of the steam-driven AFWPs oc- curred at Calvert Cliffs. On July 30, 1987, during rapid cold startup testing, both of the Unit 2 steam-driven pumps tripped. On September 26, 1987, the

number 11 AFWP on Unit 1 began oscillating after the initial startup attempt

and subsequently tripped on overspeed. On October 23, 1987, the number 12 AFWP on Unit I tripped on overspeed.

The licensee conducted an intensive testing and troubleshooting program to

determine the causes of the failures. During these tests, a number of test

3140284

IN 88-09 March 18, 1988 failures were experienced because of turbine governor oscillation and overspeed.

The most frequent failure sequences were either rapid initial acceleration of

the turbine to the overspeed trip point, or large undamped speed oscillations

that increased in magnitude to the overspeed trip point. Less frequently, trips

occurred when the mechanical latch mechanism holding the trip valve open (which

appeared to be overly sensitive) tripped. Subsequent attempts to test the pumps

immediately after initial steam-driven AFWP failures were normally successful.

Discussion:

Several factors were identified which appear to have contributed to the reduced

reliability of the AFWPs. These include:

1. Use of governor buffer springs of less than optimal stiffness, resulting

in the inability of the governor to dampen out upset conditions. One of

the installed governors and all three of the spare governors had buffer

springs of a lower stiffness than that listed in the procurement specifi- cation on file at the Woodward company.

2. Excessive condensate trapped in the steam supply lines, resulting in

governor valve damage, governor linkage damage, and throttle control

instabilities as slugs of water hit the governor valve and turbine wheel.

3. Improperly adjusted and degraded governor linkage, resulting in excessive

linkage-play. _

4. Governor valve binding, resulting in governor actuator over-reaction to

small feedback signals.

5. A failed governor on the Unit 2, number 22 AFWP.

6. Damaged and misaligned overspeed trip mechanisms, resulting in

oversensitivity to vibration, Jarring, and waterhammer.

The licensee implemented several corrective actions and plans additional upgrades.

These are described below.

1. Stiffer buffer springs were installed in the governors of all AFWPs to

increase control system dampening at the expense of increased control

system response time.

2. Upgrading of both the procedures and the systems was initiated, which

included more thorough drain procedures and drain lineup verification.

The interval for manually draining the steamlines and turbine casings

was decreased from every 8 to every 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br />. Additional manual drains

were Installed in the system low points to eliminate water from the

steamlines.

3. Various parts of the governor valves, governor linkages, and trip linkages

were overhauled, adjusted, and replaced. Trip linkages associated with

IN 88-09 March 18, 1988 the overspeed mechanisms and the trip throttle valves were adjusted to

Increase trip latch engagement and thereby reduce sensitivity to physical

shock. For some parts, such as linkage plates (cams), it was necessary

for the utility to obtain the special materials involved and fabricate

replacement parts in house.

4. Further steamline drain improvements are being evaluated.

The Calvert Cliffs problems highlight the importance of optimally sizing buffer

springs, since the single, most effective short-term corrective action appeared

to be installation of the stiffer buffer springs. However, changes in spring

stiffness for the purpose of improving stability can adversely affect other

governor response characteristics. Therefore, the selection of optimal spring

stiffness should be carefully considered. In addition, it is important to

ensure maintenance of proper spring stiffness following initial determination

of optimal stiffness. In the case of Calvert Cliffs, the addition of stiffer

springs appeared to provide an extra margin of stability. This temporarily

compensated for other auxiliary feedwater system deficiencies that also re- quired correction.

Reliability problems were much more evident when the auxiliary feedwater pumps

were periodically tested using quick starts from cold conditions. This demon- strates the importance of surveillance testing which, in so far as practical, duplicates the service conditions that would exist if the equipment were called

on tooperate.

Information Notice 86-14, "PWR Auxiliary Feedwater Pump Turbine Control Prob- lems,' and 86-14, Supplement 1, "Overspeed Trips of AFW, HPCI, and RCIC Tur- bines," discuss problems closely related to those discussed in this information

notice.

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

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

contact listed below or the Regional Administrator of the appropriate NRC

regional office.

mAs . os*torV

Division of Operational Events Assessment

Office of Nuclear Reactor Regulation

Technical Contact:

D. Limroth, RI

(215) 337-5121 Attachment: List of Recently Issued NRC Information Notices

Attamelnt

March aI 1988 ,_^

Po I1 ; I

LIST Of RE2CVLY ISSUEM

NRCINFOIATIOX 11MCES

Infornation Dt.* -0

btice No. Subject v ,

Issuance Issued to

88-0 cinical Reactione with 3/2418 All NRClicsees

Radioactive Watt generating or pro.

Solidification Age"t ceasing lo level

radioactive waste.

88407 Inadvertnt Transfer of 3/718 All IRCbroad lcenses

Licensed Material te and liceses authoried

Uncontrolled Locations to possess byproduct

mterial as sealed

sources In telutherepy

usits or *self-conteior

Irradiator,.

83-06 Foreiga Objects in Stem 2198 All holders of CLs

Genrntors or CPs for PM .

Fire In Aununciator Contrel 2/11188 All holders of Ols

Cabinets or CPs for nualear

poewr reactors.

Inadequate Qualification 2W/83 All holders of Ms

and Documentation of Firs or CPs for nuclear

Berrier Penetration Seals powr reator.

n-OS Cracks In Shroud SuPICort 2/2/ All holders of Mls

Access Hole Cover Wods or CPSfor Dies.

88-02 Lost or Stela rauge 2/J8 All NuClic ees

authorized to posse

gauges under a

specttie or geea

licesm.

a8401 Safety Injection Pip& 1/M/3 All holders of OLs

Failure or CU for nuclear

pwe reactors.

U-J1, Drokn External Clo 2/11E13 All hulder, of

Supp. 1 Springs os Atwbod

Merrill d s

or CPs for nuclear

Main Steam Isolation Valve powr reactor.

Ct

Opet1n icnse

Cf

Conucti Permit

UNITED STATES FIRST CLASS MAIL

NUCLEAR REGULATORY COMMISSION POSTAGE a FEES PAID

WASHINGTON, D.C. 20555 USNRC

PERMIT No. 0-67 OFFICIAL BUSINESS

PENALTY FOR PRIVATE USE. $300

IN 88-09 March 18, 1988 the overspeed mechanisms and the trip throttle valves were adjusted to

increase trip latch engagement and thereby reduce sensitivity to physical