ML20042G891

Special Rept:On 900408,pressurizer Spray Valve Failed Open Causing Depressurization of Rcs.Caused by Equipment Malfunction.Feedback Arm Holding Screw on Pressurizer Spray Valves Replaced W/Longer Screws & Secured W/Locknuts

ML20042G891
Person / Time
Site:	Millstone
Issue date:	05/07/1990
From:	Scace S NORTHEAST NUCLEAR ENERGY CO., NORTHEAST UTILITIES
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
MP-90-454, NUDOCS 9005160241
Download: ML20042G891 (2)

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p ,U.S. Nuclear Regulatory Commission Attn: Document Control. Desk Washington, D.C. 20555, Gentlemen:

Millstone Nuclear Power Station, Unit No. 3 y- Failure of Pressurizer Spray Valve

This. event is being submitted-as a Special Report since the event is '

7 . considered-to be of sufficient interest to warrant a report. However, none

, .of'the reporting criteria of 10CFR50.72 or 10CFR50.73 apply.

-On April 8, 1990,:at 1632. hours,;with the plant in. Mode 3, Hot' Standby, 555 _

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degrees Fahrenheit and 2250 psia, the Number 1 Pressurizer Spray Valve (3RCS*PCV455B) failed open, causing a depressurization of the Reactor .

Coolant System ' (RCS) . . Attempts by the control room opcrators to close the valve failed. The Number 1 Reactor Coolant Pump was stopped, significantly

- reducing the: spray. flow through the failed open valve, and thereby reducing ' *

.the rate'of depressurization.. As the RCS depressurized, temperature 1in the

-RCS was reduced to maintain adequate subcooling. . Operations and Instrument 1

& Contro1 (I&C). personnel entered Containment at approximately 2030 hours0.0235 days <br />0.564 hours <br />0.00336 weeks <br />7.72415e-4 months <br /> ,

and. caused the valve to fail closed by isolating the air supply to the  ;

valve.. The plant was then stabilized at 385 degrees Fahrenheit and 450 psia, a

The root cause of this event was equipment malfunction. . Investigation by ,

4 -I&C personnel revealed that the holding screw for the feedback arm of the L -valve positioner had loosened and fallen out of the valve bracket. This i V- Scaused the valve t.o fail open. The Pressurizer spray valves use a model

, AP4 Bailey positioner to control valve position. .A survey of other

. Westinghouse plants revealed two other instancras of Bailey positioner

@ failures causing. valves to fail open. +

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Operator response to this event was guided by plant Operating Procedure  !{

OP 3208,. Plant Cooldown. In addition, Emergency Operating Procedure *

(EOPs) contain-guidance on- responding to a failed open Pressurizer Spray Valve. .Even though the entry conditions were not met for entering any of l 4 -

the EOPs, the guidance; contained in them were used.- .An uncontrolled depressurization-of the RCS from a failed open Pressurizer Spray valve is bounded in the accident analysis.for Millstone 3 by an uncontrolled l depressurization from an inadvertent opening-of.a Pressurizer Safety-Valve. 1 LTherefore, this event did not place the plant in an unanalyzed condition, nor was_the plant outside its design basis, and there' was no.significant L impact to public safety. y To prevent the failure that led to this event from recurring, the feedback f

" arm holding screw on both the Number 1 and Number 2 Pressurizer Spray; O  ; Valves were replaced with longer screws, and secured with locknuts. This-E action-is consistent with corrective action taken at' other plants where'a y similar_ problem has occurred. Since this is the first instance were an uncontrolled depressurization of the RCS has occurred due to a failure of a

- Pressurizer Spray Valve, and since the corrective action should prevent'his

' type of failure from-recurring, no further action'is warranted or deemed

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y, e necessary.

The licensee contact for this Special Report is Jeffry Langan, who may be-reached at (203) 447-1791, Ext. 5544.

Very truly yours,-

l NORTHEAST NUCLEAR ENERGY COMPANY j s

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Step e# E. Scace Director, Millstone Station SES/JAL:bjo t cc: T. T. Martin, Region I Administrator-W. J. Raymond, Senior Resident Inspector, Millstone Unit Nos. 1, 2 and 3 D. H. Jaffe, NRC Project Manager, Millstone Unit No. 3 4

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HARTFORD. CONNECTICUT 06141-0270 L L J "JZ',%fl',,CO'!!"ll. 1203) 665 5000 May 7, 1990 f MP-90-454-  !

Docket No. 50-423 i

U.S. Nuclear Regulatcry Co:w.ission i

' Attn: Document Control. Desk Washington, D.C. 20555 Gentlemen:

Millstone Nuclear Power Station, Unit No. 3 Failure of Pressurizer Spray Valve This event is being' submitted as a Special Report since the event.is considered to be of sufficient interest to warrant a report. However,- none u of the reporting criteria of 10CFR50.72 or 10CFR50.73 apply. .!

On April 8, 1990, at 1632 hours0.0189 days <br />0.453 hours <br />0.0027 weeks <br />6.20976e-4 months <br />, with the plant in Mode 3, Hot Standby, 555 '

. degrees Fahrenheit and 2250Lpsia, the Number 1 Pressurizer Spray Valve

(3RCS*PCV455B) failed open, causing a- depressurization of the Reactor il Coolant System (RCS) . Attempts by the contrcl room operators to close the valve ~ failed. The Number 1 Reactor Coolant Pump was stopped, significantly-reducing the spray flow through the , failed' open valve, and. thereby reducing

-the rate of depressurization. As'the RCS depressurized, temperature in the RCS was reduced to maintain adequate subcooling. Operations and Instrument i

& Control- (I&C) personnel entered Containment 'at approximately 2030 hours0.0235 days <br />0.564 hours <br />0.00336 weeks <br />7.72415e-4 months <br /> .

and caused the valve to fail closed by isolating the air supply to.the  !

valve. The plant was then stabilized at 385. degrees Fahrenheit and 450 '

psia.

The root cause of this event was equipment malfunction. Investigation by I&C personnel revealed that the. holding screw for the feedback arm of the "

' valve positioner had loosened and fallen out of the valve bracket. This

. caused the valve to fail open. .The Pressurizer spray valves use a model  :

AP4 Bailey positioner to control valve position. A survey of other Westinghouse plants revealed two other instances of Bailey positioner I failures causing valves to fail open.

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• 2-r j Operator response to this event was guided by plant Operating Procedure OP 3208, Plant Cooldown. In addition, Emergency Operating Procedure (EOPs) contain guidance on responding to a failed open Pressurizer Spray Valve. Even though the entry conditions were not met for entering any of ,

the EOPs, the guidance contained in them were used. An uncontrolled depressurization of the RCS from a failed open Pressurizer Spray valve is bounded in the accident analysis for Millstone 3 by an uncontrolled depressurization from an inadvertent opening of a Pressurizer Safety Valve.

Therefore, this event did not place the plant in an unanalyzed condition,_

nor was the plant outside its design basis, and there was no significant impact to public safety.

To prevent the failure that led to this event from recurring, the feedback arm holding screw on both the Number 1 and Number 2 Pressurizer Spray Valves were replaced with longer screws, and secured witn locknuts. This action is consistent with corrective action taken at other plants where a similar problem has occurred. Since this.is the first: instance were an.

uncontrolled depressurization of the RCS has occurred due to a failure of a .

Pressurizer Spray Valve, and since the corrective action should prevent his I type of failure from recurring, no further action is warranted or deemed necessary.

The licensee contact for this Special Report is Jeffry Langan, who may be reached at (203) 447-1791, Ext. 5544.

1 Very truly yours, NORTHEAST NUCLEAR ENERGY COMPANY t&

Step e E. Scace Director, Millstone Station SES/JAL:bjo cc: T. T. Martin, Region I AdT.iniht:retor W. J. Raymond, Senior hesibent !cupector, Millstone Unit Nos.1, 2 and 3 D. H. Jaffe, NRC Projbet Manager, Millstone Unit No. 3 I

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