ML20011D469

LER 89-015-02:on 890825,presssurizer Safety Valve Body Inlet Temp Increased to Greater than 450 F & Acoustic Leak Monitor Alarmed,Causing RCS to Depressurize & Reactor Trip. Caused by Loss of Loop Seal.Valve replaced.W/891220 Ltr

ML20011D469
Person / Time
Site:	Summer
Issue date:	12/20/1989
From:	Bradham O, Higgins W SOUTH CAROLINA ELECTRIC & GAS CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-89-015, LER-89-15, NUDOCS 8912270294
Download: ML20011D469 (5)

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December 20, 1989 l

t Document Control Desk U. S. Nuclear Regulatory Commission ,

Washington, DC -20555 .

SUBJECT:

Virgil C. Summer Nuclear Station Docket No. 50/395 Operating License No. NPFil2, LER 89-015. Revision 2  !

Gentlemen:

• As promulgated in Licensee Event Report No,89-015 for the' Virgil.C. Summer Nuclear Station. attached is Revision 2 to Licensee Event Report No.89-015.

Specifically, this revision provides the'cause of event-for the August 25, 1989, incident and supplements the " Additional' Corrective Action" section. Two-i typographical changes are also made in this revision.- Specifically, the suffix-

' "ed" was added to " alarm" in the " Abstract" section and the date cf LER 89-011 wac corrected from June 7, 1989, to June 27, 1989, in the " Prior Occurrences" .

l section. This report is submitted pursuant to the requirements of 10CFR50.73 l (a)(2)(iv). '

Should there be any questions, please call-us at:your, convenience.

Very truly yours, O..S. Bradham EWR/OSB:1bs Attachment c:. D. A. Nauman/0. W. Dixon, Jr./T. C. Nichols, Jr.

E. C. Roberts W. A. Williams, Jr. J. C. Snelson 1

S. D. Ebneter R. L. Prevatte.

J. J. Hayes, Jr. J. B. Knotts, Jr.

General Managers INP0 Records Center C. A. Price ANI Library G. J.. Taylor Marsh & McLennan J. R.: Proper NPCF -

R. B. Clary NSRC F. H. lander RTS (0N0-890082)

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$UPPLEMENT AL REPont tatlCTIO nel s kPECTED vis est ,.e compiere Sk9fCTIO SUSM'S$tCh DA til k0 l l l A , Ae, av.,,,, ,. , a .-e, , e . e .- n, e., e -e -,H. .. > n si At 1000 hours0.0116 days <br />0.278 hours <br />0.00165 weeks <br />3.805e-4 months <br /> on August 25, 1989, the "A" pressurizer safety valve body inlet temperature increased to greater than 450 F and a plant shutdown was initiated.

Shortly af ter the load reduction was started, the "A" pressurizer safety valve opened at a system pressure of approximately 2260 psig. At 1003 hours0.0116 days <br />0.279 hours <br />0.00166 weeks <br />3.816415e-4 months <br />, the acoustic leak monitor alarmed, the Reactor Coolant System (RCS) began to rapidly depressurize and at approximately 1004 hours0.0116 days <br />0.279 hours <br />0.00166 weeks <br />3.82022e-4 months <br /> the Shift Supervisor directed a manual reacter trip. The pressurizer safety valve reseated prior to reaching the Safety Injection setpoint of 1850 psig. All plant parameters recovered to their expected post trip values except RCS pressure which was controlled around 2000 psig to avoid lifting the safety valve again. The plant was taken to cold shutdown, the "A" pressurizer safety valve replaced, and the reactor was restarted at 0635 hours0.00735 days <br />0.176 hours <br />0.00105 weeks <br />2.416175e-4 months <br /> on September 1, 1989. Further investigation by the Licensee has shown that a loss of loop seal on the "A" pressurizer safety valve was the cause of the valve's misoperation.

LER 89-011, dated June 27, 1989, documents a similar event involving the "C" pressurizer safety valve. The Licensee has determined that a loss of loop seal was a contributing factor in the event'and will submit this finding in a supplemental report. The expected submission date of this report is January 3, 1990.

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Westinghouse o Pressurized Water Reactor ~I EQUIPMENT IDENTIFICATION:

Pressurizer Safety Valve - EIIS - None IDENTIFICATION OF EVENT:

Pressurizer Safety Valve "A" body inlet temperature exceeded a preestablished limit, a controlled shutdown commenced, "A" safety valve lifted resulting in a rapid depressurization of RCS and a manual reactor trip was initiated.

EVENT DATE:

August 25, 1989 REPORT DATE: No later than September 24, 1989.

This report was initiated by Off-Normal Occurrence Report 89-082.

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CONDITION PRIOR TO EVENT:

Mode 1 - Reactor Power 100% ,

DESCRIPTION OF EVENT:

Licensee Event Report 89-011 dated June 27, 1989, documents a manual reactor trip following the unseating of "C" pressurizer safety valve. One of the actions taken as the resdit of the event was the installation of thermocouples to facilitate the .

monitoring of the pressurizer safety valve body inlet temperature. A rapid.

,_ increase in the valve body inlet temperature is indicative of the-loss of loop 4 I seal. A special instruction was issued detailing the monitoring'of the temperature  ;

and the initiation of a shutdown should the valve body inlet temperature reach  !

450 F. At 0945 hours0.0109 days <br />0.263 hours <br />0.00156 weeks <br />3.595725e-4 months <br /> on August 25, 1989, a temperature of'403 F was indicated on.  ;

"A" safety valve. This temperature was in an alert range which required Operations to continuously monitor the temperature. At approximately 1000 hours0.0116 days <br />0.278 hours <br />0.00165 weeks <br />3.805e-4 months <br />.-the i

" Pressurizer Safety Valve Temperature Limit Exceeded" alarm annunciated and a normal shutdown was commenced at .5%/ minute and later increased to 3%/ minute. At l 1003 hours0.0116 days <br />0.279 hours <br />0.00166 weeks <br />3.816415e-4 months <br />, the acoustic leak monitor alarmed and the Reactor Coolant System (RCS) began to rapidly depressurize and at approximately 1004 hours0.0116 days <br />0.279 hours <br />0.00166 weeks <br />3.82022e-4 months <br />, the Shift Supervisor directed a manual reactor trip be inserted. The RCS pressure was monitored ~by the operators and the lowest system pressure observed was 1950 psig. All plant ,

parameters recovered to their expected post trip values except RCS pressure which was controlled at 2000 psig to avoid the possibility of lifting the safety valve l ~again, y,y "" "" _ , __

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CAUSE OF EVENT:

P The Licensee has determined that a loss of loop seal on the "A" pressurizer safety valve caused the valve's misoperation. The valve was initially leaking, which-caused the high loop seal temperature (403"F at 0945 hours0.0109 days <br />0.263 hours <br />0.00156 weeks <br />3.595725e-4 months <br /> on August'25, 1989). As the loop seal temperature exceeded 450"F, the leakage increased-rapidly, leading to a loss of the loop seal. With the loop seal gone, the setpoint was dramatically reduced. When the " Pressurizer Safety Valve Temperature Limit Exceeded" alarm .

L annunciated, shutdown was initiated causing the system pressure to increase. When the system pressure reached 2260 psig, the "A" pressurizer safety valve, which was -'

set at the low end of the tolerance band, momentarily lifted.

ANALYSIS OF EVENT:

The safety significance of this event was moderate in that'if the safety valve had not seated following the Reactor Trip, a Safety Injection would have been challenged.

IMMEDIATE CORRECTIVE ACTION:

Immediate corrective action was taken with the initiation of the manual Reactor ,

Trip. The operators monitored RCS pressure to ensure that the pressurizer safety valve reseated and were prepared to initiate Safety Injection. Plant parameters were monitored and the plant was stabilized in Mode 3 at a reduced operating pressure of.2000 psig. The plant was subsequently taken.to Mode 5.for replacement i of the safety valve. ~

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ADDITIONAL CORRECTIVE ACTION:

The pressurizer safety valve body inlet temperature shutdown criterion remains at-390*F, however at 350 F action will be taken.to develop a plan ~for plant shutdown taking into account, among other variables, the rate of change of temperature.

I -SCE&G management and the Resident NRC Inspector will be notified when the safety valve temperature reaches 350 F. '

The event has been discussed with all Operations personnel. The discussion--

included the rapid response of the valve upon the loss of loop seal.

SCE&G intends to:- 1) modify the pressurizer' safety valves' internals for, steam a application, and 2) eliminate loop seal capability on the pressurizer. safety-valves. . This modification is scheduled for the fifth refueling outage (currently scheduled to begin March 23,1990) and is contingent upon receiving-the required materials in time for implementation.

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