ML20045F589

LER 93-013-00:on 930603,noted That Main Turbine Generator EHC Sys Caused an Increase in Pressurizer Pressure,Resulting in Reactor Trip,Due to Closing of Intercept & Cv.Operators Performed EOP & Sys Performed as expected.W/930702 Ltr

ML20045F589
Person / Time
Site:	Millstone
Issue date:	07/02/1993
From:	Perry R, Scace S NORTHEAST NUCLEAR ENERGY CO., NORTHEAST UTILITIES
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-93-013, LER-93-13, MP-93-522, NUDOCS 9307080096
Download: ML20045F589 (4)

Text

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,1 NORTHEAST UTILITIES amere mas seeen sueet Berna connecucm 1 de'steUla$5I nS5NE ec$ c"Co n P.O. BOX 270

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Y[o E[astYtIe$~se $*o)pany Nyt*ieast Nuctear Ener;;y ComLB9y H ARTFORD, CONNECTiouT D6141-0270 (2031665-5000 i

July 2, 1993 MP-93-522 i Re: 10CFR50.73(a)(2)(iv) l U.S. Nuclear Reculatorv Commission Document Contr'ol Dess Washington, D.C. 20555

Reference:

Facility Operatine License No. DPR-65 Docket No. 50-336 Licensee Event Report 93-013-00 Gentlemen:

This letter forwards Licensee Event Report 93-013-00 required to be submitted within thirty (30) days pursuant to 10CFR50.73(a)(2)(iv).

Very truly yours, NORTHEAST NUCLEAR ENERGY COMPANY of./m - . pg Stephen E. cace Vice President - Millstone Station SES/RB:ljs

Attachment:

LER 93-013-00 cc: T. T. Martin, Region I Administrator P. D. Swetland, Senior Resident Inspector, Millstone Unit Nos.1, 2 and 3 G. S. Vissing, NRC Project Manacer, Millstone Unit No. 2 1

I 070068 9307080096 930702 l PDR ADOCK 05000336 h[h*

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Reactor Tnp on High Pressunzer Pressure E VE NT D ATE (5 t do NuvsEm rE) AEDOCT OATE I7i OTHED F ACitmES INv0 SED @

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TELEDHONE NUVBEA NAME A9EA 0005 Richard A. Perry, Engineer, Ext. 6067 2l0l3 4l 4l 7l-l 1l 7) 9l 1  !

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On June 3.1993, at 1624 hours0.0188 days <br />0.451 hours <br />0.00269 weeks <br />6.17932e-4 months <br />, with the plant in mode 1 at 100"c power, the mam turbine generator Electro-Hydraulic Control (EHC) system truuated a signal that caused the mam turbine to rapidly decrease load.

The sudden load drop caused an increase in pressunzer pressure, resultmg m a reactor inp. The EHC signal has been attributed to spunous relay actuations as a result of operations within the EHC cabmet.

Operators performed Emergency Operatinc Procedure EOP 2525, " Standard Post Tnp Actions" and aIf safety related equipment performed as expected.

This is bemg reponed pursuant to requirements of Paragraph 50.73(a)(2)(iv), reporting any event or condition that resuhed m manual or automauc actuauon of any Engmeered Safety Feature system, mcludmg the Reactor Protection System (RPS).

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On June 3.1943. at 1624 hours0.0188 days <br />0.451 hours <br />0.00269 weeks <br />6.17932e-4 months <br />, wnh the plant m Mode 1 at 100cc power. the EHC monnor panel trouble alarm along wnh several other alarms were annunciated on the control room mam boards.

Approumateh ten seconds later, the reactor tnpped. Seconds before the EHC monnor panel uouble hcht came on, a plant equ:pment operator had opened and closed the EHC cabmet doors The mam turbme generator Electro-Hy drauhc Control (EHC) system minated a signal that caused the

mam turbine miercept vahes and control vahes to close. The mam turbme rapidh decreased load. The resulung load imbalance between the reactor plam and the steam piam caused an increase m reactor l temperature and pressure, opening both Power Operated Rehef Yahes (PORVs) and seseral steam l penerator safety vah es. The reactor inpped on lugh pressurizer pressure. The pressunzer PORVs and steam generator safety vahes properly reseated. The main turbme automaucally inpped as a result of the reactor inp. Elecincal power output at the ume of the turbme inp was approximatelt 166 Megawatts.

I Operators performed Emergency Operating Procedure EOP 2525, " Standard Post Trip Actions.' Both the secondary and pnmary p!arn response was as expected for a reactor,turbme inp on high pressurizer pressure. All safety related eqmpment performed as expected. There were no ESF system actuauons.

11. Cauce of Esent The root cause of the automauc reactor /turbme inp on lugh pressunzer pressure was the closmg of the main turbine miercept and conuol valves m response to signals from the EHC cabmet. The cause of the EHC signals that closed the vahes has not been determined.

A plant equ:pment operator opened the doors of the EHC cabmet to check the temperature, as part of his normal rounds. The opening and closing of the EHC cabinet doors was determmed to be essentiahy comadent wnh an EHC trouble alarm and mdication of miercept valve closure. Potennal causes ara Electro-Magneuc Field (EMF) inducuan while the doors were open or vibrauon from the door operung or Closing Ill. Anah m of Event These condmons are being reported pursuant to requirements of Paragraph 50.73(a r(21hv). reporting any l esent or condinon that resulted m manual or automanc actuauon of any Engineered Safety Feature ,

system. mciudmg the Reactor Protecuon System (RPSL All safet) 9 stems funcuoned as designed i Therefore, there are no safety consequences as a result of this event  !

IV. Correcuve Acuen  ;

Extensne troubleshooting of the EHC system was conducted. All relevant EHC mstrument loops and power supphe> were checked. An attempt was made to reproduce a current path to the relays that could base tesuhed in the mtercept vab es closmg. but the EHC signal that caused the intercept and control vahes to close was not able to be reproduced. Repeated door opening and closmg dunng low load turbme operauons did not reproduce any abnonnal operauons.

To minirmze the probabihty of reoccurrence, caution tags are now hung on the EHC cabmet dnors.

These tags require control room notificanon before opening the cabinet doors uc e mm as

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V. Ad6nonn1 Informanon Similar LERs:

01-001 Ells Codes for referenced components-Niam Turbine - TA-TRB-G054 EHC Cabmet - TG-C AB-G054 Power Operated Rehef Valves - AB-RV-D243 Steam Generator Safety Valves - SB-RV-D243 l

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