ML20044F254

LER 93-007-00:on 930420,noted That an Isolation of Inboard & Outboard MSIV & Ms Line Drains Occurred.Caused by Lack of Personnel Knowledge of Unique Maint Conditions.Precaution Will Be Added to Sys Operating procedure.W/930520 Ltr

ML20044F254
Person / Time
Site:	River Bend
Issue date:	05/20/1993
From:	Booker J, England L GULF STATES UTILITIES CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-93-007, LER-93-7, RBG-38531, NUDOCS 9305270254
Download: ML20044F254 (7)

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May 20, 1993 i

RBG- 38531 File Nos. G9.5, G9.25.1.3  ;

U.S. Nuclear Regulatory Commission  :

Document Control Desk Washington, D.C. 20555 ,

Gentlemen:

River Bend Station - Unit 1 Docket No. 50-458 1

Please find enclosed Licensee Event Report No.93-007 for River Bend Station -

Unit 1. This report is submitted pursuant to 10CFR50.73.  ;

Sincerely, ,

i kN, Jg2 r 11 6 J. E. Booker Manager - Safety Assessment ,

and Quality Verification  !

River Bend Nuclear Group 171 9 ) CLv LAE/JPS/NRC/ C /RCL/SDB/ktm t t

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P cc: U.S. Nuclear Regulatory Commission '

611 Ryan Plaza Drive, Suite 400 l Arlington, TX 76011 NRC Resident Inspector P.O. Box 1051 1 St. Francisville, LA 70775

• INPO Records Center 700 Galleria Parkway Atlanta, GA 30339-5957 l t

Mr. C.R. Oberg  :

Public Utility Commission of Texas l 7800 Shoal Creek Blvd., Suite 400 Nonh Austin, TX 78757 i

Depanment of Environmental Quality .

Radiation Protection Division P.O. Box 82135 i l Baton Rouge, IA 70884-2135 ATTN: Administrator i

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EXPIRES 5/31/95  !

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" ESTMATED BURDEN PER RESPONSE TO COMPLY WTH TH'S [

- INT ORMATiON COLLEC'lON REQUEST: 53.0 HRS. F ORWAFC  !

LICENSEE EVENT REPORT (LER) COMMEms neaAnDuG BURDEN Es uct ,0 THe monMnON .

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THE PAPERWDFu( REDUCTION PratECT (31504104), OFrtCE or l (See reverse for required number of digrts/ characters fc7 each block) MANAGEMENT AND BUDGET. WASHNGTON. DC 20503.

f ACILITY NAME (1) DOCKET NUMBER (2) PAGE (3) h RIVER BEND STATION 05000 458 1 OF 4 I mm ISOLATION OF MAIN STEAM ISOLATION VALVES DUE TO PERSONNEL LACK OF l UNDERSTANDING WHILE UNIQUE MAINTENANCE CONDITIONS PREVAIL L

EVENT DATE (5) LER NUMBER (61 REPORT NUMBER (7) OTHER FACILITIES INVOLVED (8) j SEQUENTIAL PEVISION MN#"

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, MODE (9) 4 20 402tb) 20 405(c) X $0.73(a)(2)(iv) 73 71(b)

POWER 20 405(a)(110) 50.36(c)(1) 50.73(a)(2)(v) 73.71(c) [

LEVEL (10) 0 20 405(a)(1)(n) 50 36te)(2) 50.73(a)(2)(vn) OTHER  !

20.405(a)(1) tai) 50.73(aH2)(s) 50 73(a)(2)(viei)(A) WV 'n Ab5"ad 2 beion and in Text, NRC 20 405(aH1)0v) 50.73(a)(2)(n) 50.73(a)(2)(vin)(B) rmm asuq ,

20 405taH1)(v) 50 73(a)(2)(in) 50.73(a)(2)(x) ,

LICENSEE CONTACT FOR THIS LER (12)  !

Nm TaEPauNt Nuusta enauo. A ee coom a L.A. England - Director - Nuclear Licensing (504) 381-4145 1 COMPLETE ONE LINE FOR EACH COMPONENT FAILURE DESCRIBED IN THIS REPORT (13)  ;

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SUPPLEfu.NAL REPORT EXPECTED (14) l EXPECTED "WT" W YE'"

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4 e ABSTRACT (Umst to 1400 spaces, i e.. approxima*ely 15 single-spaced typewritten lines) (16) i On April 20,1993 at 0911, with the reactor in Cold Shutdown (Operational Condition 4), an ,

isolation of inboard and outboard main steam isolation valves and main steam line drains occurred.

The isolation signal was low condenser vacuum. GSU is submitting this report pursuant to  ;

10CFR50.73(a)(2)(iv) as an automatic actuation of an engineered safety feature (ESF). ,

The root cause was determined by barrier analysis. The mot cause is that the operating crew did not )

understand the specific details of the turbine control logic for the unique maintenance conditions that l existed at the time of the event. This lack of understanding was also responsible for the absence of j precautions in Operations Department procedures. Therefore, the protection of a procedural barrier i did not exist. Corrective actions include revision of Opemtions policies and procedures. All l systems functioned as designed during this event. i v+cronM 3,s waa

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.l REQUIRED NUMBER OF DIGITS / CHARACTERS .

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2 DOCKET NUMBER 31N ADDITI N O 05000  ;

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6 LER NUMBER 3 FOR SEQUENTIAL NUMBER I 2 FOR REVISION NUMBER .l R ORT DATE 2 PER BLOCK UP TO 18 - FACILITY NAME j 8 OTHER FACluTIES INVOWED e TOTAL - DOCKET NUMBER .l 3 IN ADDITION TO 05000 9 1 OPERATING MODE i 10 3 POWER LEVEL 1

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THE FAPERw3M REDUCTON PRalECT p1SD 01M, OFFCE OF MANAGEMENT ANO BJDGET, WASHINGTON, DO 20503.

FACILITY NAME 0) DOCP ET NUMBER (2) LERNU9ABERtel F AGE (3)

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93 - 007 00 2 4 no m n.c..<. a..,,.. ~ , - .w w ~ s on REPORTED CONDITION On April 20,1993 at 0911, with the reactor in Cold Shutdown (Operational Condition 4), an isolation of the inboard and outboard main steam isolation valves (MSIV) (*ISV*) and main steam line drains occurred. The isolation signal was low condenser vacuum. GSU is submitting this report pursuant to 10CFR50.73(a)(2)(iv) as an automatic actuation of an engineered safety feature (ESF).

INVESTIGATION The initial conditions for this event were as follows:

1. The MSIVs were open with the exception of IB21-F022B, which was undergoing maintenance.

2. The main turbine speed contml setting was " closed valves." Note that them are five speed control settings, " closed valves," slow, medium, fast, and 1800 rpm.

3. The main turbine was reset, in support of electrohydraulic contml (EHC) testing. Note that having the turbine in this condition enables it te provide hydraulic power to the turbine stop valves.

4. Both main generator output breakers were open.

5. Main condenser low vacuum, with bypass switch in the bypass position.

6. Maintenance on generator output breaker 20635 underway at Fancy Point switchyard.

At 09:10:28 main generator output breaker 20635 was closed due to testing by the transmission and distribution (T&D) department. Since the main turbine was reset at this time, closing of the breaker caused two things to occur in the turbine control cabinet. First, the scal-in line (a logic circuit that feeds downstream relays) on the speed control logic card IS2-A001 deenergized, dropping out relay K7. This caused the turbine speed control to select the 1800 rpm speed setting and deselect the

" closed valves" setting. Second, relay K2 on the speed contml card IS3-B002 dropped out. When NRO FDRV 366A @ 9E

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'I this happened, the closing bias input to the #2 stop valve position contml card (IF1-A102) was lost.

This close bias is normally present when the " closed valves" speed contial setting pushbutton is  :

selected. The #2 stop valve began to open and when it reached 93%, the interlocks to open #1, #3, l and #4 stop valves were satisfied and they opened as well. [

The nuclear steam supply shutoff system (NSSSS) senses stop valve position during low condenser  ;

vacuum conditions and initiates MSIV and steamline dmin isolation when the stop valves are greater j than 90% open. When the stop valves opened, the low coudenser bypass interlock was defeated  ;

causing the isolation. The EHC and NSSSS logic functioned as designed.

i It was noted after the isolation that the turbine speed contml setting had changed from " closed  !

valves" to 1800 rpm and that the turbine stop valves had opened. The turbine was then tripped, closing the stop valves. The closing of the stop valves allowed the MSIV and the steamline drains to be opened, thus re-establishing a vent path fmm the reactor vessel to the main condenser.

I ROOT CAUSE i

The root cause was detennined by barrier analysis. The root cause is that the operating cmw did not understand the specific details of the turbine control logic for the unique maintenance conditions that existed at the time of the event. This lack of understanding was also responsible for the abse.nce of precautions in Opemtions Depanment procedures. Therefore, the protection of a procedum! barrier j did not exist. ,

i A review of previous LERs revealed none similar, h CORRECTIVE ACTION TO PREVENT RECURRENCE  !

Corrective actions are as follows: j

1) Opemtions Policy #009 has been revised to state:  ;

i "To prevent the receipt of main steam line and main steam line drain isolation signals when j perfonning work on the main generator output breakers (20635 & 20640), ensure the main turbine is in the tripped condition prior to commencing any work." (completed 4/28/93) 1 N40 FORV 3f4A (5 92,

. L NRC FORM 366A U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB NO. 31504104 l pa EXPIRES 5/31/95 ,

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2) A precaution will be added to system operating procedure (SOP)-0080, " Turbine Genemtor  ;

Operation" to alert the operators of the requirements in the Operations Policy. (estimated completion date - 6/1/93) l

3) Licensed opemtors will be tmined on this event, the revisions to Operations Policy #009, and

. on SOP-0080 during the next requalification module. (estimated completion date - 7/20/93)  ;

4) The interaction between the main generator output breakers (206635 and 20640) and the I turbine control logic will be included in the system training progmm for operator initial hot license training.  ;

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, SAFETY ASSESSMENT

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There were no equipment malfunctions during this event. All systems functioned as designed.

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Note: Energy industry identification codes are indicated in the text as (*XX*).  !

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