ML20042E162

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LER 90-009-00:on 900309,automatic Turbine Trip W/Subsequent Reactor Trip Occurred Due to High Stator Cooling Water Temp. Caused by Failure of Mechanical Linkage on Fisher & Portor Controller.Controller Replaced w/spare.W/900409 Ltr
ML20042E162
Person / Time
Site: Millstone Dominion icon.png
Issue date: 04/09/1990
From: Scace S, Matthew Smith
NORTHEAST NUCLEAR ENERGY CO., NORTHEAST UTILITIES
To:
NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-90-009, LER-90-9, MP-90-352, NUDOCS 9004200305
Download: ML20042E162 (5)
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Nor yD'd.ny' Northeast Nucear Ener0y Company HARTFORD. CONNECTICUT 06414-0270'

, (203)665-6000 April'9, 1990 ll 'MP-90-352' Re: 10CFR50.73(a)(2)(iv). .

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L U.S. Nuclear Regulatory Commission

' Document Control Desk- i

. Washington, D.C. 20555

Reference:

Facility Operating License No. NPF--49 j,

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Docket No. 50-423 Licensee Event Report 90-009-00 Gentlemen: ,

This letter forwards Licensee Event Report 90-009-00 required to be submitted within

l. thirty (30) days pursuant to 10CFR50.73(a)(2)(iv), any event or condition that resulted L in manual or automatic actuation of any Engineered Safety Feature (ESF), including the = ,

I Reactor Protection System (RPS)

L. Very truly. yours,. c NORTHEAST NUCLEAR ~ ENERGY COMPANY l.

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Step n E. Scace ;

Director, Millstone Station >

SES/ MAS:ljs

Attachment:

LER 90-009-00 cc: T. Tl 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 '

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HRC Form 366 U.S. NUCLEAR REGULATORY COMM4SSION APPROVED OMB NO. 3160-0104 (6-80)e EXPIRE S: 4/30/92 Estimated buroen por response to comply with tnes information conection reouest: 60 0 hrt. Fo warc LICENSEE EVENT REPORT (LER) Ine U M 'a Q e Ulnt E '.' E s s'$0'"' ***Tffeios, t -

Regulatory Commesuon. Wasnmoto1. DO 20555. anc to the Paperwork Recuction Project (3160-0104). Office of Management and Budget. Washington. DO 20503.

F ACILITY NAME (1) DOCNE T NUMMR (2) PAM

  • Millstone Nuclear Power Station Unit 3 ol 5I of ol of 4 l2 l3 1lOFl 0l 4 TITLE (4)

Reactor Trip Due to Turbine Trip Due to Hich Stator Coolant Temperature EVENT DATE ISt LE A NUMBE A #6)

AEPORT DATE (76 OTHF A F ACUTIE S INVotvED (8)

MONTF DAY YEAR YEAR *- MONTH DAY YEAR F ACLUTY NAMES of si of of of I I

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O 3 0l9 9 0 9 l0 OJ 0 l 9 0l 0 ol4 0l 9 9l 0 olSlofolof I l OPERATING THlS REPORT IS BEING SUBMITTED PURSUANT TO THE REQUIREMENTS Or to CF3 l- ICneck one or more of the fobowingif11) 20 402(c) _

20 402(c) 1 60.73(al'2)(w) _

73.71(D)

PO R 20 40$la)(1)(i) 60.36(c)(1) 60.73(a)(2)(vl _

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oTHER (Specify in Abstract beeow and m

4 20 405(a)(1)(hl) 60.73(a)(2)(1) 50. 73(a)(2)(vih)( A) Text. NRC Form 366A) gry

. 20 405(a)(1)(w) 60,73(a)(2)(ii) 50.73(a)(2)(viii)(B) 20 405talfiltwi 60.73(a)(2 Hiii) 50.73(alf2)(x)

UCENSEE CONTACT FOR THis LER (12)

NAME TELEPHONE NUMBER AREA COQt -

Mark A. Smith, Engineer, Ext. 4614 2]0j3 4l4l7l-l1l7l9l1 COMPLETE ONE UNE FOR E ACH COMDONENT FAILURE DESCR8EO IN THl$ REPORT (131 CAUSE SYSTEU COMPONENT p* ,

yh CAUSE SYSTEV COMPONENT h s s B Tl J l Tl C l O Fl1l2l0 Y x b l l l l l l l' sRBdb X N Y 'M Tl B l Rl L l Y Dl1l4l1 Y l l l l l l l SUPDLEMENTAL REPOAT EXPECTED tidi MONTH DAY YEAR SUBMAS$10N YES (H yes comoiste EXPECTE0 SUBM!SSION DATE) NO l l l ABSTRACT (Limit to 1400 spaces. l.e.. approximately fifteen singie-soace typewritten knes) (16)

On March 9,1990, at 1653 hours0.0191 days <br />0.459 hours <br />0.00273 weeks <br />6.289665e-4 months <br />, while operating in Mode 1 at 100cc power, 2250 psia and SS7 degrees Fahrenheit, an automatic turbine trip with subsequent reactor trip occurred due to high Stator Cooling Water temperature, l

The cause of the event was the failure of the mechanical linkape on the Fischer & Porter controller for the Stator Cooling Water temperature control valve due to wear at the linkage connections, The root cause of the event was inadequate design, in that the temperature controller is mounted directly on the temperature control valve. The wear found on the mechanical linkage of the controller was induced from vibration of the temperature control valve.

As short term corrective action, the failed controller was replaced with a spare of the same model. The l actions to prevent recurrence include replacing the original model controller with a more reliable controller with manual over-ride capabilities, and relocating the new controller to an area of low vibration.

l NRC Form 366 (6-80)

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    • Rc Form 366A - U.S. NUCLEAR REGULATORY CoMMISSloN - APPROVED oMB No. 31s0-o1o4 g, -(6-69) . EXPIRE S: 4/3o192 -

, Estimat.d bureen per response to compty with this LICENSEE EVENT' REPORT (LER) n, g

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FAcWTY NAME (t) DOCKET NUMBER (2) L F A NUMBF A is t PAGE(31 YEAR s Millstone Nuclear Power Station Unit 3 0l 5l 0l 0l 0l4j2 [3 9l0 OF 0l 1

.0l 0l 9 0l0 0l 2

.;. Text in more wae. is reautred. us. dditional NRO Form 366A's) (17)

1. Descrintinn of Event On March 9,1990, at-1653 hours, while operating in Mode 1 at 100re power, 2250 psia and 587 degrees Fahrenheit, an automatic turbine trip with subsequent reactor trip occurred due to high -

Stator Cooling Water temperature, At 1647 hours0.0191 days <br />0.458 hours <br />0.00272 weeks <br />6.266835e-4 months <br /> on March 9,1990, the operators received a Stator Coolant outlet high temperature -

alarm. A Second Stator coolant pump, 3GMC-P',B, was started and a non-licensed operator (PEO) was dispatched to investigate both the Staior Cooling system and the heat exchanger secondary supply water system temperature. At 1650 hours0.0191 days <br />0.458 hours <br />0.00273 weeks <br />6.27825e-4 months <br />, the operators received a Stator Coolant inlet high temperature annunciator alarm. The PEO noted that the Stator Cooling

  • temperature controller, 3GMC-TIC 36, had failed to the low temperature direction, which resulted in a full bypass of the heat exchangers. He attempted to manually manipulate the failed linkage, but was unsuccessful. The Stator Coolant pumps were switched from the A to the B pump at this time. At 1651 hours0.0191 days <br />0.459 hours <br />0.00273 weeks <br />6.282055e-4 months <br />, the operators received a Stator Coolant protective circuit energized alarm, and the A Stator Coolant pump was restarted. At 1653 hours0.0191 days <br />0.459 hours <br />0.00273 weeks <br />6.289665e-4 months <br />, the turbine tripped, without a.

turbine runback occurring. With the plant greater than 50rc power,' an automatic reactor trip signal resulted upon receipt of the turbine trip signal. At the time of the reactor trip, operators verified that both reactor trip breakers opened, that all rods were at the bottom and that neutron flux was decreasing. A Feedwater Isolation occurred, which is a normal plant response following a reactor ,

inp. No other safety signals were expected or received, There were no operational, maintenance, or construction activities in progress at the time _ of the event that affected the event. No safety systems were out of service or in off-normal status at the time of the event and there were no failures of any safety-related equipment, Plant stability, based on average Reactor Coolant temperature, was achieved at 1713 hours0.0198 days <br />0.476 hours <br />0.00283 weeks <br />6.517965e-4 months <br /> on March-9,1990.

11. Cauce of Event I The cause of the temperature controller malfunction.was equipment failure due to induced vibration wear. The root cause of the event was inadequate design, in that the location of the temperature l- controller is not conducive to reliable operation-of the temperature controller for the Stator Cooling ,

l: Water system.

The mechanical linkage on the controller, 3GMC-TIC 36, for the Stator Cooling Water temperature control valve, 3GMC-TV36, failed due to wear at the linkage connections; The temperature ,

l controller is mounted directly on the temperature control valve. The wear found on the mechanical linkage of the controller was induced from vibration of the temperature control valve. The linkage failure caused the temperature indicator to fail low, indicating low Stator Cooling Water temperature. This caused the temperature control valve to a shift to full bypass position, allowing the Stator Cooling Water to bypass the Stator Cooling Water heat exchangers, 3GMC-E1A and ,

3GMC-ElB. As a result, Stator Cooling Water temperature rose above its setpoint of 79 degrees Centigrade, initiating the turbine load set runback circuit. The two-minute timer was started in the -

turbine load set runback circuit, and with stator current above the 25,783 ampere limit, the turbine generator tripped.

The purpose of the two-minute timer in the turbine load set runback circuit is to allow a reduction below 25,783 amperes in two minutes from the onset of a high temperature indicator in the Stator Cooling Water system. For this event, the high temperature indication did initiate the two-minute

  • timer. However, the turbine load set runback did not occur and load was not reduced from full load. A relay in the turbine load set runback circuit was identified as being defective,' preventing a turbine runback.

NRC Form 366A (6-M) :

o orm a66A .. U,6, NucLEt.R REGULATORY.coMMI5 don APPROV oBN $0-01D4

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Estimated buroen per response to comply with this m

LICENSEE EVENT REPORT (LER).' g f,f',*g ,f,"n*,7l,,,

- (", 7n n* g n, g y "J,',a,1 5h ,50 TEXT CONTINUATION ano Report, Management aranen tp-saci. u.s. Nuciear t a Re in Pro e (3 60 104 Off c o

' Management and Budget. Washinoton. Oc 20503 FActuTY NAME (1) DOCKET NUMBER (2) tro N@APEm @ PAGE (3)

YEAR Pd Millstone Nuclear Power Station - ~ ~

- Unit 3, ol 5[ ol ol ol4 l2 l3 9l0 ~ 0 l 0l9 0l0 0l 3 OF 0 l .1 q TEXT (11 more space is reovired. use accitional NAc Form 366A's) (17) .

111. Anahe of Event This event is rt. portable pursuant to 10CFR50.73(a)(2)(iv), any event or condition that resulted in manual or automatic actuation of any Engineered Safety Feature, including the Reactor Protection =

System, immediate notifications were made in accordance with 10CFR50.72(b)(2)ii).  ;

. There were no significant safety consequences due to this event. The components that failed, Stator Cooling temperature-controller, 3GMC-TIC 36, and the turbine load set runback circuit are not ,

required to perform any safety function, nor did their failure prevent any of the plant's safety

-systems from performing their intended safety funcuons.

The turbine runback circuitry is intended to provide a pre-emptive means to preclude generator -

stator winding damage. To accomplish this, the runback circuit automatically reduces armature.

current (i.e., to decrease the load) without causing a turbine trip-reactor trip conditfor.. With the ~

runback circuit failure, generator protection was provided by the Stator Coolant high tempeiature .

turbine trip. Whenever the plant is above 507e power, a turbine trip will cause a reactor trip ..

(because the instantaneous load rejection capability of the turbine bypass valves - steam dumps and the rod control system would be exceeded). : The turbine trip-reactor trip protection circuitry is not a safety grade feature. It is designed to. occur prior to the initiation of safety grade reactor trips on -

either overtemperature. delta temperature (OTAT) or overpower delta temperature (OPAT). The (OTAT) trip limit prevents an excessive mismatch between turbine load and reactor power to minimize undesirable reactor coolant thermal excursions. The OPAT reactor trip provides assurance of fuel integrity from core overpower conditions.

IV. Corrective Action Once the plant had been stabilized in Hot Standby (Mode 3),.the Stator Cooling Water -

temperature controller, 3GMC-TIC 36, was replaced with an exact replacement. ,

in order to increase the reliability of the Stator Cooling Water temperature controller and to prevent recurrence, the following actions will be taken:

1. Relocate the temperature controller to an area of low vibration.
2. Replace the existing temperature controller with a new (Fisher Model 43AP) type controller of improved design, which will allow for manual temperature control valve, 3GMC-TV36, operation.

The defective relay in the turbine load set runback circuit has been replaced with an exact replacement, and the entire load set runback circuit was tested, with acceptable results. The generator manufacturer (General Electric) has been contacted to evaluate whether any damage has been incurred as a result of this event.

NRc Form 366A-(6-89)

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/4RC Form 366A U.6,. NUCLEAR REouLATORY COMMISSION - QPPROVED OMS NO. 3150-0104 i

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EXPIRES: 4/30/92 '

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LICENSEE EVENT REPORT (LER)<

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' in. utatory Commission, Paperwork Was.h6ngton.

R.ouction DC 20555.

Pro; ct (3160-0104L ano of Office to Manap.m.nt ano Buopet. Washington DO 20503 FA0tLITY NAME -(1) DOOKET . NUMBER (2) . L E A MIMBF A @ ' PAGE (3)

' Millstone Nuclear Power Station ~

Unit 3 ~

ol 6l ol ol ol4 l2 l3 9l0 0l0l9 0l0 0l 4 OF 0l4 TEXT of more .s .c. is e.auir.o. us. aooitmi NRC Form 366A's) (17) ,

_E Additional information There have been no similar events with the same root cause and sequence of events.- ,

Routine turbine runback 'c'. cuit surveillances are performed every refueling outage to verify .

O satisfactoir_ performance. . Based on the previous satisfactory surveillances and the fact that the -

aforementioned relay failure is the. first identified in the plant's operating history, the relay failure is considered .or dom and isolated.

The Stator avling Water temperature indicating controller was manufactured by Fischer & Porter Company and is a Model 1451. The failed runback circuit relay is a Deutsch model E210-1173; EIIS Codes System Main Generator Stator Cooling System - TJ Comnonent Temperature Controller - TC Relay - RLY Temperature Control Valve - TCV

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t 4 NRC Form 366A (6-801'

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