05000423/LER-1993-004, :on 930331,turbine Valve Closure Resulted in Reactor Trip Followed by Turbine Trip.Caused by Faulty Power Supply in electro-hydraulic Control Sys Mfg by Crosby Valve & Gauge Co.Also Reported Per Part 21

:on 930331,turbine Valve Closure Resulted in Reactor Trip Followed by Turbine Trip.Caused by Faulty Power Supply in electro-hydraulic Control Sys Mfg by Crosby Valve & Gauge Co.Also Reported Per Part 21

ML20035H685
Person / Time
Site:	Millstone
Issue date:	04/30/1993
From:	Scace S, Young J NORTHEAST NUCLEAR ENERGY CO., NORTHEAST UTILITIES
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
REF-PT21-93 LER-93-004, LER-93-4, MP-93-349, NUDOCS 9305060219
Download: ML20035H685 (5)

LER-1993-004, on 930331,turbine Valve Closure Resulted in Reactor Trip Followed by Turbine Trip.Caused by Faulty Power Supply in electro-hydraulic Control Sys Mfg by Crosby Valve & Gauge Co.Also Reported Per Part 21

Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2)(iv), System Actuation
4231993004R00 - NRC Website

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' fW1heast Naciea Energy Company (203)S65-5000 April 30, 1993 MP-93-349 Re: 10CFR50.73(a)(2)(iv)

U.S. Nuclear Regulatory Commission Document Control Desk Washington, D.C. 20555 i

Reference:

Facility Operating License No. NPF-49 Docket No. 50-423 Licensee Event Report 93-004-00 l

Gentlemen:

This letter forwards Licensee Event Report 93-004-00 required to be submitted within thirty (30) days pursuant to 10CFR50.73(a)(2)(iv) any event or condition that resulted in manual or automauc actuation of any Encineered Safetv Feature (ESF) including the Reactor Protection System (RPS).

ll Very truly yours, NORTHEAST NUCLEAR ENERGY COMPANY

'h Stephen}E r mcv cace Vice President - Millstone Station i

i SES!JSY:ljs Attachment: LER 93-004-00 cc:

T. T. Martin, Region 1 Administrator P. D. Swetland, Senior Resident Inspector, Millstone Unit Nos.1, 2 and 3 V. L. Rooney, NRC Project Manager, Millstone Unit No. 3 050032 (2nd fff 9305060219 930430 I

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ASSTR/ CT tum u 400 scates ie anoco mtet 1 **eer s ngte-s;. ace typewrtt:en imes) os 1 At 0103 on March 31, 1993. with the plant in Mode 1 at 100cc power, a turbine valve closure resulted in a reactor inp followed by a turbine inp.

Turbme rahe closure was the resuh of a faulty power supply in the Electro-Hydraulic Control (EHC) system.

With the exception of a steam generator code safety valve not completely reseaung, the plant responded normally to the transte,t.

Extensive trouble shooting determmed that a power supply m the EHC system was faulty and caused the turbine valves to close. The faulty power supply was replaced. As action to present recurrence, the power supphes in the EHC system will be replaced or refurbished on a 10 year perio.l.

Subsequent msesugation determmed that the steam generator safet z vahe which did not completely rescat had an incorrect lower adjustment rmg settmg. Additional inspection r.tvealed that 7 other safety valves also had inconect settings. Three of these valves mdicated that they hfied ; nd reseated during the transient. The other 4 vahes did not open.

The root cause of the improper settings has not been dm%ed Crosby Valve and Gage Company, who perfonned maintenance on the safeties, documented Troper settmgs and sne records do not show any work performed on the safenes after dehvery to the site.

NRC Form 306 (6-82)

NRC For'n a66 A U S. NUCLE AR REGULATORY CoMM:SSON APPROVED OMB NO 3150-0 44 T-SD)

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Descrmnon of Es en' On March 31,1993, at 0103 wnh the plant m Mode 1 at 1009 power (566 degrees Fahrenheit and 2250 psia) a turbme load rejecuon alarm was recened as the turbine control vahes began to close. A normal response to tu bme vah'e closure occurred. This consisted of all steam dumps opening, atmosphene dumps on 3 steam generators opening, and 1 Pressunzer Power Operated Relief Valve (PORV) cychng open for 6 seconds. In addmon, mdicauon was received that several code safety valves on 2 steam generators hfted. Smeteen seconds after the turbine vahes began to clote, steam generator lesels shrank to the loa low seipoim which resulted m a reactor trip followed by a turbme trip. After the reactor and turbme trip, the atmospheric dumps on the fourth steam generator opened and indication was received that code safet es on a third steam generator htted. As steam pressure decreased, all atmosphen steam dumps and safeties reseated with the exception of I safety on the "D' steam generator.

At the time of the inp, operators venfied that the Reactor Tnp and Bypass Breakers were open, that all control rods were fully mserted, and that neutron flux was decreasmg. An automatic start of the Auxihary Feedwater System occurred due to the 20w low water level in one steam generator and the turbme drnen Auxihary Feedwater Pump staned on low low water level m two steam generators. A Feedwater Isolation occurred due to the low average Reactor Coolant System temperature (564 degrees Fahrenheit) comeident with the reactor trip. Subsequently, the plant stabihzed at the no load temperature of 557 degrees Fahrenheit, These were expected system responses. No additional Engineered Safety Feature (ESF) actuations uere required or initiated.

Aher the plant had stabihzed, the safety was gagged but still did not close completely. A normal plant cooldown was performed and the safety reseated at approximately 1000 psig steam generator pressure.

Subsequent mvestiganon revealed that the lower adjustment ring of the malfunctioning safety valve was 4

inconect. When set properly. the lower nng insures a clean, forceful popping action when the safety lifts and a cushioned reseatmg when the safety c!oses. If this ring is set too high, steam cannot escape as rapidly when the vahe begms to close. As a resuh the blowdown is increased. The settings of the lower

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adjustment rings on 11 other safeties which h9 oeen worked on by Crosby Valve were checked. All 7 of the vahes which were installed were found to be set improperly. Of these, 3 indicated that they had hfted and reseated dunnp the transient and 4 did not open because their setpoints were not reached.

II.

Cause of Es ent The root cause of the turbine sahe closure was equipment failure. A capacitor failure m one of the EHC power supplies caused noise to EHC solenoids resulting in a slow closure of all turbine vahes with i

sersos The root cause of the safety vahe fathng to completely reseat has not been determmed. When the contractor performed malmenance on 4 safeties in 1957 and 1988, NNECO Ouahty Control performed I

an inspection of the work on 2 that required ring adjustment. No discrepancies uere noted and the rmg settings of these safeties were correct. Work on another group of 8 safeties was performed between 1989 and 1991. During this period, the ring settings were documented and a certification statement was inued; howeser, NNECO mspection was not requ red as the work was performed under Crosby Valve and Gage Company's Appendix B program. Since plant records indicate that no adjustments were made onsite, a dehmte cause for the improper adjustment has not been determined. NNECO will continue to work with the contractor to determine when and how the improper adjustments may have occurred.

III.

Apah* nf Es ent This esent is being reported in accordance with 10CFR50.73(a)(2)(iv) as any event or condition that resulted in automatic actuation of an ESF including the Reactor Protection System. An immediate nouhcation was made in accordance with 10CFR50.72(b)f 2)(ii).

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All safety systems funcuaned as de.igned as a result of the reactor inp. The Auxihary Feeduater System started automancally due to the lov lou steam generator water les el. A Feeduater isolation occurred due to the lou Reactor Coolant Sysam aserage temperature coincident with the reactor inp. No other ESF signah were 1ruuated and the es ant posed no sigmficant hazard to the heahh and safety of the pabltc. Secondary plant equipment wa3 returned to normal operanon. and the unit was returned to power The :mproper 3etung of the louer adjustnient rmp or the safety vahes did not place the plant out side of the de-ign ba(n for a stuck open safet) ahe. i ne pLmt is analyzed for a flou of C~,200 lbm/hr for ihn accidem Each safety vahe o designed to pass 5G (970.000 lbm/hr) of total steam flow. Hou erer, parameter mdicauons showed that the af fected safety salve had not completely reseated but was not i

stuck full > open. The parually open safety did not resuh m an uncontrolled cooldown and the plant 5

operators were aHe to mamtam normal shutdou n plant temperature and pressure. Indicated proper operanon of ^ other safenes uhich had improper nng adjustment durmg the transient showed that improper setung of the louer adjustment nng doe ( not necessarily mean that a safety will not reseat.

While actual operanon and subsequent tesung of the malfuncuan:ng safety (see below) shoved that it reseated at lower Pressures, these pressures are normally reached seseral hours after plant shutdown.

Therefore, any other vahe which did not fully resea would esentually close by itself.

Test Number Ghe Reseated Reseat Pressure Dunny Test (PSIG) 1 No

< 1055 2

Yes 10M 3

Yes 1062 4

No

< 1065 Therefore, the 4 sahes that did not open may have reseated properly if they had opened. In addition, they would not hate stuck fulh open if they had failed to receat and would have closed completely by themsehes after a controlled plant cooldoun to approximately 530 degrees Fahrenheit.

Because there is no mea urable onmary to secondary leakage in the "D" steam generator, there was no release of radioacute matenal as a resuh of the parually open safety valve.

The imphtations of the improperly set safety vahes on other postulated accidents base not been determmed A review of these impbcations will be completed and reported in a supplement to this report.

IV.

Correcme Action As immediate correcthe action for the inp, the faulty power supply was replaced. As action to prevent recurrence, the power supph will be replaced or refurbished on a 10 year period. Due to replacement unavailabihty, the other power supphes in the EHC system will be replaced during the upcoming refuelmg i

outage.

As immediate corrective action for the improper ring settings, the 11 other safety vahes which had been refurbished, repaired or set by Crosby Whe were examined for proper ring settings. The 7 (excluding the malfunctioning one) which were improperly set were adjusted as necessary to their proper ring settmgs. All Fpare safeties currentl3 out for mamtenance at any comractor will be venfied before return to the site.

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Additional Information

No other Licensee Esent Reports (LERs) have been submined for reactor trips resulung from a failed power suppl 3 in the EHC system _

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This LER also satisfies NNECO's ecaluauon, nonficanon and reporting obligation to repon defects under 10CFR21. In addition, a copy of this LER will be sent to Crosby Valve and Gage Company.

No simibt power supply malfuncuens were found in a renew of NPRDS.

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