ML20043F826

LER 90-006-00:on 900508,reactor Manually Tripped When Decreasing Levels Noted in Steam Generator 1 & Feedwater Regulating Valve Indicated Full Open.Caused by Valve Stem Separating from Plug.Feedwater Flow restored.W/900607 Ltr

ML20043F826
Person / Time
Site:	Millstone
Issue date:	06/07/1990
From:	Bonner R, Scace S NORTHEAST NUCLEAR ENERGY CO., NORTHEAST UTILITIES
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-90-006-02, MP-90-558, NUDOCS 9006180193
Download: ML20043F826 (5)

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' T ' IEE**$YlE' ar EnerDy Company 6*'vD*Eaany .

P.O. box 270 HARTFORD. CONNECTICUT 06414 0270 Northeast Nuce (203)665-6000 June 7,-1990 ,

'MP-90-558 ,

Re: 10CFR50.73(a)(2)(iv)

U.S. Nuclear Regulatory Commission Document Control Desk >

Washington, D.C. 20555 ,

Reference; . Facility Operating License No. DPR-65

! Docket No. 50-336 -

Licensee Event Report 90-006-00 Gentlemen:  ;

This letter forwards Licensee Event Report 90-006-00 required to be submitted within .

thirty (30) days pursuant to paragraph 50.73(a)(2)(iv).

Very truly yours, NORTHEAST NUCLEAR ENERGY COMPANY e

to Step en . cace Director, Millstone Station i

SES/RCB:mo  ;

Attachment:

LER 90-006-00 cc: ' T. T. Martin, Region I Administrator W. J. Raymond, Senior Resident inspector, Millstone Unit Nos.1, 2 and 3 L G. S. Vissinc, NRC Project Manager, Millstone Unit No. 2 y'

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NHO Form 366 U.S. NUCLE AR REoJLATORY COMMISSION APPROVf D OMB NO. 3160-01D4 l (6dt) EXP!AES: 4/30/92 e* Istimateo buroen por esponse to comply with this -

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LICENSEE EVENT REPORT (LER) comments reparoing purpen es,timate to the Recorpsano Roooris M us Regulatory Commission. Washington. DC 20666 anc to l F

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, Management anc Buccet Washington. DC 20603.- y FACluTY NAME (1) DOW1 NVMbEh (21 WM Millstone Nuclear Power Station Unit 2 ol sl ol ol ol3 l3 ls 1 l opl 0l 3 -

mEm l Manual Reactor Trip on Steam Generator ! Low Level i EVENT DATE (61 LE A NUMBE A f 6 RFPOAT DATE #7 otHEs1 F ADitTIE6 INVOLVED f Bi .

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NAME TELEPHONE NUMBE A ARE A COQt Richard C. Bonner, Engineerms Supervisor, Ext, 5230 2l0l3 4l4l7l-llj7l9l1 COMPLETE ONE LINE FOR E ACH COMPONENT F AILURE DE SCRIBED IN TH18 AEPOAT (13)

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M NO { g g ABSTRACT (Lemit to 1400 spaces, t.o., aproximately fifteen single-space typewritten lines) (16)

On May 6,1990 at 00:49 hours with the Unit in MODE I at 100cc power, plant operators manually tripped the reactor due to decreasing levels in th: #1 steam generator. The secondary plant operator observed a rapidly decreasing level in the #1 steam generator, .vith the feedwater regulating valve, 2-FW-51 A, indicating full-open.

With control of main feed flow to #1 steam aenerator apparently lost and since steam generator level was decreasing, the unit was manua ly tripped. Cperators then performed EOP 2525, " Standard Post Trip Actions" and EOP 2526. " Reactor Trip .tecovery". All equipment responded as expected and the unit was placed in a stable condition. Main feed flow to the #1 steam generator was restored and controlled with the feedwater-regulating bypass valve, 2-FW-41A. The 91 feedwater regulating valve, 2-FW-51 A, was disassembled and inspected. During the disassembly it was discovered that the stem had separated from the plug. This event is being reported pursuant to the requirements of paragraph 50.73(a)(2)(iv) due to the manual reactor trip on decreasing steam generator level.

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F ACILITY NAME (0 - DOCKET NUMBER (2) trA HUMDFA #6) PAGE(31 YEAR N hillistone Nuclear power Station Unit 2 0l 5l 0l 0l 0l3 l3 l 6 9l0 0l0l6 0l0 0l 2 OF 0l3 ]

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1. Descrintion of Event On hlay 8,1990 at 00:49 hours with the Unit in N10DE I at 1004 power, plant operetors manually tripped the reactor due to decreasing levels in the #1 steam generator. The secondary plant operator observed a rapidly decreasing level in the #1 steam generator, with the feedwater regulating salve, 2-FW-51 A, indicating full open. With control of main feed flow to #1 r. team generator apparently lost and since steam generator level was decreasing, the unit was manually tripped. Operators then performed EOP 2525, " Standard Post Trip Actions" and EOP 2526, " Reactor Trip Recovery". All equipment responded as expected and the unit was placed in a stable condition. hialn feed Flow to the

1. 1 steam generator was restored and controlled with the feedwater regulating bypass valve, 2-FW-41 A.

No other systems were affected.

Prior tn the trip, feed flow to the #2 steam generator was controlled by manual operation of the #2 feedwater regulating valve, 2-FW-510, and feedwater regulating bypass valve, 2-FW-41B, because automatic operation of 2-FW-51D had become erratic. The #1 feedwater regulating valve remained in automatic operation.

The unit was subsequently taken to Cold Shutdown and remains in Cold Shutdown for maintenance and inspection unrelated to the feedwater regulating valve failure.

II. Cause of Event The #1 feedwater regulating vahe was disassembled and inspected. During the disassembly it was discovered that the valve plug had separated from the stem and had been forced by feedwater flow into the shut position. The valve stem is threaded into the plug and secured with a roll pin. Upon disassembly,-the stem threads were found stripped and the roll pin sheared. No loose parts were released to the feedwater system. Based on the results of a visual and dimensional inspection, the root cause of the fallure has been determined to be a machining error associated with the stem and plug tapered fit. - As a result of a poor fit, insufficient preload was applied to the connection which then subjected the stem threads and roll pin to excessive vibration, fatigue and eventual failure.

The #2 feedwater regulating valve was also disassembled and inspected. The stem / plug roll pin was found intact, however the threaded connection was found to be loose.

A similar failure of a feedwater regulating valve stem and plug connection caused an automatic reactor trip on September 2.1987. In that event reported in t.ER 87-009, the stem / plug roll pin was noted to be missing from the connection allowing the stem to unthread from the plug. The root cause of the event was determined to be the loss of the roll pin during operation or lack of the pin at assembly. The valve overhau! procedure was revised at that time to require that the roll pin be staked to prevent it from becoming dislodged. Also, a preventive maintenance program was initiated to overhaul the valves every refueling. This proved to be an effective method of preventing loose parts in this event.

111. Analysis of Event This event is being reported pursuant to the requirements of paragraph 50.73(a)(2)(lv) due to the manual reactor trip on decreasing steam generator level.

There were no safety consequences from this reactor trip since all safety systems functioned to restore the unit to a stable condition. All equipment responded as expected ar'd plant operators executed applicable Emergency Operating Procedures accordingly.

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F ACILfTY NAME (t) DOcVIT NUMBEH (2) (E n M IMgEn (e) PAGE (3) vi:An ' Emmet m -

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0l 5l ol ol oja l3 ls 9l0 0l 0l 6 0l0 0l 3 OF 0l3 text in more space is required, use addlilonai NRO Form 306A's) (trl IV. Currective Action immediate action was taken to restore feedwater flow to the #1 steam generator via the feedwater regulating bypass valve and to assure tliat all plant equipment functioned properly and the plant was in a safe condition.

As an action to prevent recurrence of the event, the feedwater regulating valve overhaul prwjure was revised to add dimensional checks of the stem and plug connection prior to assembly. Also ,he stem installation torque was increased and the connection secured with a high temperature retaining compound, in addition, a design change to both feedwater regulating valves was implemented, replacing the hollow Mem!phig roll pin with a solid taper pin. i V, Additional Information

Attachment:

Feedwater Regulating Valve Drawing Feedwater Regulating Valve hlanufacturer - Copes - Vulcan hlodel: p-200-12 Angle i

Size : 12 inch 900#

Ells Code : SJ-LCV-C635 Similar Events :

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Page 1 of 1 At'achment to LER 90-006 Rev. O Docket Number 05000336 i

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FEEDWATER REOULATING VALVE