ML20044A135

LER 90-017-00:on 900527,main Feedwater Flow Control Valve Failed Closed,Resulting in Reduced Feedwater Flow & Decreasing Steam Generator Water Level.Caused by Failure of Solenoid Valve Coil.Solenoid Coil replaced.W/900626 Ltr

ML20044A135
Person / Time
Site:	Comanche Peak
Issue date:	06/26/1990
From:	William Cahill, Mcgee G TEXAS UTILITIES ELECTRIC CO. (TU ELECTRIC)
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-90-017, LER-90-17, TXX-90213, NUDOCS 9006280113
Download: ML20044A135 (8)

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E ifNe e,nu,,,, June 26, 1990

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U. S. Nuclear Regulatory Commission i Attn:

Document Control Desk Washington, D.,C. 20555

SUBJECT:

COMAN'CHE PEAK STEAM ELECTRIC STATION  !

DOCKET N0..50-445

. ENGINEERED SAFETY FEATURE ACTUATION LICENSEE EVENT REPORT 90-017-00 Gentlemen: . t Enclosed is Licensee Event Report 90-017-00 for Comanche Peak Steam Electric

' Station Unit 1, " Reactor Trip Due to Feedwater Control Valve Solenoid failure."

Sincerely, l_ '

William J. Cahill, Jr.

FSP/dai Enclosure c - Mr.-R. D. Martin, Region IV

' Resident Inspectors, CPSES (3) i i

. 9006280113 900626

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PDR- ADOCK 03000445 S~ PDC SX) North Ohve Street LB81 Dallas. Texas 75201

1 Enclosure to TXX 90213 j NRC FORM 306 - , U.S. NUCLE AR REGULATORY COMMIS$ON APPROVED OMB NO. 31640104

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On May 27,1990, at 0126 while performing Steam Generator Atmospheric Relief Valve (ARV) l capacity testing, a Main Feedwater Flow Control Valve (FCV) failed closed. This resulted in 3 reduced feedwater flow and decreasing Steam Generator (SG) No. 3 water level. The Operator closed the ARV, which was open for test purposes, and started to manually ramp down the main turbine to reduce reactor power. The Operator then opened the bypass flow L control valve around the failed closed FCV, but the SG water level continued to decrease. At L 0128, when No. 3 SG water level reached approximately 30 percent (automatic reactor trip is at L 28 percent GG water level), the operator manually tripped the reactor. All other plant systems operated properly.

The cause of the event was the failure of a solenoid valve coli, associated with No. 3 SG FCV, l due to rain water intrusion (FCV's are located outside). A temporarily removed covar allowed water to enter a junction box then drain via conduit to the solenoid coil housing.

C_orrective action included the replacement of the failed solenoid coil and inspection of the other solenoids for water / moisture intrusion. An evaluation will determine if additional critical components exist in a similar configuration. Guidance for the conduct of outdoor maintenance activities will be addressed programatically.

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1. DESCRIPTION OF THE REPORTABLE EVENT A. PLANT OPERATING CONDITIONS BEFORE THE EVENT On May 27,1990 at 0126, Comanche Peak Steam Electric Station (CPSES) Unit 1

" was in Mode 1, Power Operation, with reactor power at 43 percent.  ;

I B. REPORTABLE EVENT CLASSIFICATION  !

An event or condition that resulted in the manual or automatic actuation of any b

- Engineered Safety Feature (ESF), including the Reactor Protection System (RPS),

C. STATUS OF STRUCTURES. SYSTEMS. OR COMPONENTS s THAT WERE INOPERABLE AT THE START OF THE EVENT -;

Atip THAT CONTRIBUTED TO THE EVENT Not applicable - no structures, systems, or components were inoperable at the start '

of the event that contributed to the event.

D. NARRATIVE

SUMMARY

OF THE EVENT. INCLUDING DATES AND APPROXIMATE TIMES At 0126 on May 27,1990, the Steam Generator Atmospheric Relief Valve (ARV) 1 (Ells:(RV)(SB)) capacity testing was in progress on Steam Generator (SG)

(Ells:(SG)(AB)) No. 4 when the SG No. 3 Feedwater Flow / Steam Fbw Mismatch -

Alarm (Ells:(ALM)(IB)) annunciated. The Reactor Operator (utility-licensed) observed the Main Feedwater Flow Control Valve (FCV)(Ells:(FCV)(SJ)) to SG No. 3 i indicated fully closed with a 100 percent open demand on the controller. A few seconds later, a SG No. 3 Low Level Alarm (Ells:(ALM)(IB)) annunciated. The Unit Supervisor (utility licensed) ordered the SG No. 4 ARV closed and the Main Feedwater Flow Control Bypass Valve (Ells:(FCV)(SJ)) to SG No. 3 opened. The Flow Control Bypass Valve was opened fully to increase feedwater flow to SG No. 3.

At this time SG No. 3 level was at approximately 35 percent. ihe Balance of Plant Operator (utility licensed) reduced load on the main turbine (Ells:(TRB)(TA)) to attempt to reduce steam flow to less than feedwater flow on SG No. 3. A discussion between the Unit Supervisor and the Reactor Operator followed and a decision was made to trip the reactor (Ells:(RCT)(AB)) if SG level could not be stabilized above 30

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percent on narrow range indication. At 0128, when SG level decreased to approximately 30 percent narrow range the Unit Supervisor ordered the Reactor Operator to manually trip the reactor. The reactor was tripped, all rods (Ells:(ROD)(AA)) fully inserted into the core. Steam dumps (Ells:(RV)(SB)) operated-normally. An Auxiliary Feedwater System (Ells:(BA)) actuatloa occurred as a result of Low Low SG Level Signal, and all components functioned as designed. All other plant systems operated properly. The plant was stabilized in Mode 3, Hot Standby.

An intermittent ground on Direct Current (DC) Bus 1 ED2 (Ells:(JA)(EJ)) was noticed the day before the event. This intermittent ground was never indicated for more than 10 seconds. Control Room personnel had reviewed the drawings for DC Bus 1ED2 before the event; however, the ground could not be located since the alarm was intermittent. Also, the loads of DC Bus 1ED2 are not conducive to isolation as they 4 feed protection / control related equipment and to isolate them in Mode 1 would cause a reactor trip. On May 27,1990, after the reactor trip, the ground indication was constant, j An event or condition that results in a manual or automatic actuation of any ESF, including the RPS is reportable within 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> under 10CFR50.72(b)(2)(li). At i approximately 0201 on May 27,1990, the' Nuclear Regulatory Commission 1

Operations Center was notified of the event via the Emergency Notification System. 1 E. THE METHOD OF DISCOVERY OF EACH COMPONENT OR SYSTEM i FAILURE OR PROCEDURAL OR PERSONNEL ERROR The closure of SG No. 3 FCV was initially discovered as a result of a Feedwater Flow / Steam Flow Mismatch Alarm annunciation in the control room. Additionally, y intermittent ground alarms were received on DC Bus 1ED2. A Work Order was subsequently initiated to troubleshoot the ground on DC Bus 1ED2, which disclosed v water in the solenoid coil housing and associated conduit.

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010 014 OF 017 ll. COMPONENT OR. SYSTEM FAILUPES A. FAILURE MODE. MECHANISM AND EFFECT OF EACH FAILED COMPONENT The FCV closed because its position controlling solenoid had failed due to electrical grounding caused by water latrusion, resulting in loss of feedwater flow to SG No. 3.

B. CAUSE OF EACH COMPONENT OR SYSTEM FAILURE Water intrusion at the junction box (Ells:(JBX)(SJ)), creating partial submergence of r

the solenoid coll, has been determined to be the cause of the failure. When the i

solenold was disassembled the coil (Ells:(CL)(SJ)) was discovered to be sitting in~ '

cpproximately one inch of water.

C, SYSTEMS OR SECONDARY FUNCTIONS THAT WERE AFFECTED BY FAILURE OF COMPONENTS WITH MULTIPLE FUNCTIONS Not appicette no failures of components with multiple functions have been identified.  !

D. EALLFACOMEONDLTMEORMATION 1 FCV 0530 SV1 Solenold Valve Manufacturer: ASCO Valver, Automatic Switch Co.

Model Number: 208 4921W (Solenoid Valve Coll)

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-lll. ANALYSIS OF THE EVENT A. SAEEI_Y_S.YSIBUigSPONSES TH AT OCCURRED. <

The following eLfety system actuations occurred as a result of the event:

Reactor Protection System (Ells:(JC))

Auxiliary Feedwater System (Ells:(BA))

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. =.i1 .m n B. DURATION OF SAFETY SYSTEM TRAIN INOPERABILITY Not applicable - there were no safety systems which were rendered inoperable due to a failure.

C. SAFETY CONSEQUENCES AND IMPLICATICNS OF THE EVENT The Main Feedwater System is designed to provide feedwater to the SGs. The Main Feedwater FCV's regulate feedwater flow to the SGs. Failure of the solenoid coil causes the FCV to close (Fall Safe Position), restricting / isolating feedwater flow to the SGs.

If the event had occurred at full power an automatic reactor trip would have occurred.

However, since the plant was operating at reduced power for testing, the operator was able to shutdown the reactor manually.

i This event is bounded by the Final Safety Analysis Report Accident Analysis (Section 15.2.7) regarding a Loss of Normal Feedwater, which assumes the worst single failure in the Auxillary Feedwater System. However,in this event, an Auxillary Feedwater System actuation occurred and all components functioned as designed.

Therefore, this event did not adversely affect the safe operation of CPSES Unit 1 or the health and safety of the public.

IV. CAUSE OF THE EVENT BOOT _CAUSE Water intrusion into SG No. 3 Main Feedwater Flow Control Valve 1 FCV 0530 Train "B" solenoid assembly (Ells:(SOL)(SJ)) and associated conduit caused the solenold coll to ground. Conduit from the solenoid assembly (approximately six feet long), connects to the bottom of the junction box. The configuration is installed with the junction box slightly elevated with respect to the solenold assembly. Water entering the junction box drained via the conduit into the ,

solenoid assembly, leading to the failure of the coll. It is concluded that the water intrusion resulted from maintenance activities which left the junction box cover I

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temporarily removed during a period of heavy rainfall. This in turn failed the Flow Control Valve closed and restricted / shutoff feedwater flow to SO No. 3, V. CORRECTIVE ACTIONS A. IMMEDIATE The junction box, conduit and solenoid valve housing were cleaned and dried. A new solenoid coil was installed.

B. CORRECTIVE ACTIONS TO PREVENT RECURRENCE ._

Root Cause Failure of SG No. 3 Main Feedwater FCV Train 'B' solenoid coil was caused by water intrusion resulting from outdoor maintenance activities during a period of heavy rainfall.

Corrective Action

1. All work organizations will review the event with personnel to stress the need to adequately protect equipment from external environmental conditions during ongoing work activities.

2. All work organizations will evaluate their programs to ensure that appropriate guidance is provided prior to performing work on outdoor equipment.

C. CORRECTIVE ACTION TAKEN ON GENERIC CONCERNS IDENTIFIED AS A DIRECT RESULT OF THE EVENT Generic Considerations i

Other solenold assemblies on the FCVs may have had moisture / water intrusion.

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010 017 OF 017 3.c u . . . . . a..e Nw.n mA.m n Corrective Action The Work Order v' . Msed to inspect all the solenoid assemblies on the other Main Feedwater FCV' . a toth i seven. All the solenoid coils were found dry with no signs of previou wator .nrusion. The Work Order also inspected for any other possible metns t v .er intrusion into the solenoid assemblies. No additional  ;

intrusion paths we ' ,dentified. Based on the inspection of the other solenoid i assemblies this incident was determined to be an isolated case.

Generic Considerations Additional critical components may exist which have the potential for a similar ,

occurrence.

Corrective Action i The Single Point Failure Analysis identifies critical components whose failure can initiate a sequence of events, resulting in a reactor trip. This analysis will be reviewed to identify outdoor components which have the potential for a similar occurrence as the FCV solenold valve co:1. Inspections will be performed on any identified components.

VI. PREVIOUS SIMILAR EVENTS There have been no previous similar events .eported pursuant to 10CFR50.73.

Vll. AQDlIlRNALINEQBblAIl0B The times listed in the report are approximate ano ae, tral Day Ight Savings Time (CDT).

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