ML19261F225

Environ Incident 76-37/1T:on 761021,blown Fuse in Group 6 Programmer Resulted in Motor Fault Signal Which Tripped Rod Control Sys.Overlap Resulted Between Rod Groups 6 & 7 Exceeding 30% Tech Specs Limit

ML19261F225
Person / Time
Site:	Three Mile Island
Issue date:	11/04/1976
From:	Arnold R METROPOLITAN EDISON CO.
To:
References
GQL-1548, NUDOCS 7910250649
Download: ML19261F225 (4)

Text

. _

m NRC popu 195 U.S. NUCLE AR R EGULAToRY Cs ulSSloN ooCKET NUMBE R (2 76) F 3 ,. _ f O ==1 $ $

NRC DISTRIBUTION Fon PART 50 DOCKET MATERIAL $CIDb" 7 REPORT TO: Mr O'Reilly FROM: Metropolitan Edison Co oATE oF ooCUMENT 6

Reading, Pa

+ R C Arnold oATE RECEIVEo SLETTEa ONoronizEo enon iseurromu NUusEm or copies ascEivEo s oRiciN AL dVNCLASSIFIEo

_ Ocopy one signed oESCRIPTioN ,

ENCLoSU R E Ltr reporting Reportable Event 476-37/lT which occurred on 10-21-76 & concerned overlap between control rod group six & seven exceeding allowable 307......

PIANT NAME. Three Mile Island #1 IOTE: I? PERSONNEL EXPOSURE IS I?NOLVED SENDDIRECTLYTOKREGER/J.. COLLINS FOR ACTION /INFORMATION 11-20-76 chf ERANCII CHIEF: Me i d_

W/3 CYS FOR ACTION LIC.. ASST.: In 4* 94 m v/ I as ACRS16 LIS CZEG/SEP-@ LA A5 c A- T /f N- 2 o -7 (,,

INTERNAL DISTRIBUTION

_1 u ty: FTI3 J NRC PDR -

I & E (2)

MIPC SCHROEDER/IPPOLIIU ROUS' ION NOVAK/ CHECK GRIMES CASE BUTLER HANAUER TEDEGCO/MACCARY EISENHUT EAER ,

SHAO VOLLMER/FUNCH _.,

KREd5R/J. COLLINS a AOi 9/

)MVi '

EXTERNAL DISTRIBUTION CCNTROL NUMBER LPDR: H a r ris un A  %

TIC: "

2Og NcIC: , , ,m 77 ww I '

Gjw s

/_. y MMin FOR PMouSESS METROPOLITAN EDISON COMPANY _ __ .

POST OFFICE BOX 542 READING, PENNSYLVANI A 19603 TELEPHONE 215 - 929-:601 November h, 1976 GQL 15h6 e

tra w'/ ,

Mr. J. P. O'Reilly, Directar - l ', ,'.

Office of Inspections and Enfcreement, Region I I '

U. S. Nuclear Regulatory Cc lssicn jp#*{ d~

631 Park Avenue p)/; -

King of Prussia, PA 19h06 'p , ..

Dear Sir:

E Decket No. 50-289 Cperating License No. DPR-50 In accordance .ith the Technical Specifications of our Three Mile Island Nuclear Sts ion Unit 1 (TMI-1), we are reperting the folleving reportable ccer.rr7 nee C. \ a 1 -=s (1) Report Nunter: ER 76-37/lT 'M jy ec ~ n (2a) Required Report Data: 11/h/76 /g (2b) Date of Occurrence: 10/22/76 f.....--- -

C

-b e.3 (3) Facility: Three Mile Island Nuclear Station - Unit I , - -

(h) Identificaticn of Occurrence: ' -

Title:

Overlap Eetween Centrol Red Group Six (6) and Seven (7) Exceeding The Allevable Thirty (305) Percent.

Type: A reportable cccurrence as defined by Technical Specificaticns ti .9 2. A (2 ) , in that the overlap between Control Red Grcun six and seven exceeded thirty percent thus leading to cperation or sne unit or affected systems when any parameter or opera:icn subject to a limiting conditien is less conservative than the least ecnservative aspect of the limiting condition for operation as established in Technical Specifications 3.5 2 5a.

(5) Conditions Prior to Oc,:urrence:

Power; Core: Sh% FRZR Level: 219 inches Elec: 387 MWe FRZR Temp.: 6h7cy .

RC Flev: 138 x 106 lbs/hr. j h k9 RC Pressure; 2175 psig RC Temp., 579 F.

".Mr. J. P. O'Reilly GQL 15h8 (6) Description of Occurrence:

A: 0305 hours0.00353 days <br />0.0847 hours <br />5.042989e-4 weeks <br />1.160525e-4 months <br /> on October 21, 1976, after reactor power had been reduced to approximately fifty (50".) percent fer condenser tube repairs the fuse for the Grcup 6 progra==er noter failed. Tne blown fuse resulted in a " ctcr fault" signal trippiis the rod centrol syste to manual. Group 7 centinued to respond to manual signals (required due to build-in of Xenon) since it was enabled by the autc=atic sequences. Group 6 remained stationary because cf the blevn fuse. The control roc cperator was aware cf the change in the overlap and was monitcring overlap on the console indication while the motor fault signal was being investigated. (Overlap is net directly indicated, it must be e q uted frc group average position indication).

Althcugh the operator was aware that the Technical Specification limit was being apprcached, the violation did not beccre apparent until the ec=puter printcut was obtained. The cc=puter printcut indicated 32". overicp.

I=cedistely a shutdown margin was calculated and verified adequate while the blcvn fuse was being evaluated. Group 6 was transferred to the Auxiliary Pcver Supply and the everlap condition was corrected. The Group 6 Regulating Pcver Supply was rencved frc service for repair.

(T) Designation of Apparent Cause of Occurrence:

The cause of this occurrence has been determined to be both material and trccedural in that the blevn fuse was caused by a failed diode bridge in the direction detector circuit and the Technical Specification violation occurred because of inadequate procedural guidance regarding monitoring overlap when a sequence fault signal is present.

(8) Analysis of Occurrence:

It has been determined that the cccurrence did not constitute a threat to the health and safety of the public in that the reacter was operating at a reduced pcVer and imbalance and red index were vell within the required limits.

(9) Corrective Action:

In additicn to the i==ediate corrective action described above,the Group 6 Regulating Power Supply has been repaired and returned to service. The Response-to-Alar = Procedure, Control Red Drive Sequence Fault, has been reviewed and vill be revised to include specific =cnitoring requirements when the alarm is present.

The Plant Operators Review Cc=rittee and Unit Superintendent have reviewed and approved the above corrective action and have taken steps to assure its ec=pletion.

(10) Failure Data:

The failed ecmpenent resulting in the blevn fuse was the dicde bridge en the direction errer switch assembly.

p,r. J. P. O'Reilly GQL 15k8

Description:

Direction Error Switch Asse=bly Manufacturer: Diamond Pcver Speciality Co.

Part Nuder: 705271-10h5 Cause: Randem Failure (sher i)

Similar Events:

None Sincerely, R. C A/nold Vice President RCA:DGM:kl 148\ 195