ML18127A650

LER 1978-011-01 for St. Lucie Unit 1, Update Concerning When Upper Guide Structure Was Removed (Refueling Shutdown), 3 (of 45) Incore Instrument Thimbles Remained in the Core

ML18127A650
Person / Time
Site:	Saint Lucie
Issue date:	08/08/1978
From:	Schmidt A Florida Power & Light Co
To:	O'Reilly J NRC/IE, NRC/RGN-II
References
PRN-LI-78-215 LER 1978-011-01
Download: ML18127A650 (7)

Text

REGULATORY IN -ORMATION DISTRIBUTION SYSTEM (BIDS >

DI TRIBUTION FOR INCOMING MATERIAL 50-335 REC: OREILLY J P ORG: SCllMIDT A D DOCDATE: Oe/08/78 NRC FL PWR 5 LIGl.lT DATE RCVD: 08/15/78 DOCTYPF: I ETTER NOTARIZED: NO COPIES RECEIVED

SUBJECT:

LTR 1 ENCL 1 UPDATE TO LICENSEE EVENT REPT 50-335/78-11 ON 04/15/78 CONCERNING REMOVAL OF THE UPPER GUIDE STRUCTURE AND THREE<3) OF THE 45 INCORE INSTRU Tl lIMBLES REMAINED IN TIRE CORL.,

PLANT NAME: ST LUCIE 51 REVIEWER INITIAL: XBT DISTRIBUTOR INITIAL:

~>+>>~>~>~>+~>++<.++++++ DISTRIBUTION OF Tl IIS MATERIAL IS AS FOLLOWS INCIDENT REPORTS

<DISTRIBUTION CODE A002)

FOR ACTION: ORBI4 BC+~~W/4 ENCL INTERNAL: +W/ENCL NRC PDR44~W/ENCL I 5 E~~~W/2 ENCL MIPC++W/3 ENCL I 5 C SYSTEMS BR+4W/ENCL EMERGENCY PLAN BR++W/ENCL NOVAK/CHECKS~ W/ENCL EEB<<~W/ENCL AD FOR ENG~~~~W/ENCL ,

PLANT SYSTEMS BR<<W/ENCL HANAUER~4 W/ENCL AD FOR PLANT SYSTEMS>+W/ENCL AD FOR SYS 8c PROJ+4W/ENCL REACTOR SAFETY BR~~W/ENCL ENGINEERING BR~H~W/ENCL VOLLMER/BUNCH>+W/ENCL KREGER/J. COLLINS~H~ll/ENCL POWER SYS BR4+W/ENCL K SEYFRIT/IE%+W/ENCL EXTERNAL: LPDRi$

FT PIERCE> FL<<~W/ENCL TICI LI Z CARTER~~4W/ENCL NS I C4~W/ENCL ACRS CAT B4~4W/16 ENCL DISTRIBUTION: LTR 45 ENCL 45 CONTROL NBR: 782230311 SI ZE: 3P 8b4Ht %8Hf+8s 8f %C CHI k%%%%+df% 3HHI MHHFSHI )Hl+%8f THE END  %%%%%%c.%%%%%M%4%%%0%%%%%%%%%%%

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S FLORIOA POWER & UGHT COMPANY August 8, 1978 C7 OQ PRN-LI-78-215 c" GQ f"1~

~ CD"1 R~> ~CD Mr. James P. O'Reilly, Director, Region II CA CD Office of Inspection. and Enforcement U. S. Nuclear Regulatory Commission 230 Peachtree Street, N. W., Suite 1217 Atlanta, Georgia 30303

Dear Mr. O'Reilly:

N REPORTABLE OCCURRENCE 335-78-11 ST. LUCIE UNIT 1 DATE OP OCCURRENCE: MARCH'6, 1978 .;

INCORE INSTRUMENT THIMBLES UPDATE REPORT NO. 1 The attached Licensee Event Report is being submitted to update our initial report of April 28, 1978.

Very truly yours, yacc:

D. Schmidt Vice President Power Resources MAS/cpc Attachment Harold P. Reis, Esquire Director, Office of Inspection and Enforcement (40)

Director, Office of Management Information and Program Control (3) 7822303ii PEOPLE ... SERVING PEOPLE

LICENSEE EVENT REPClRT Tat tLal Report UPDATE yl xil 28, 1978 I CONTROL BLOCK: (PLEASE PAINT AlLL AEOLIIAED INFOAMATIOhl3 1

UCENSEE UCENSE EVENT NAME LICENSE NUaiBER TYPE TYPE F L S L S 1 0 0 0 0 0 0 0 0 0 4 1 1 1 1

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7 89 14 15 25 26 30 31 32

'EPORT REPORT

. CATC TORY TYPE SOURCE OOCIIET NUMBER EVENT OATE REPORT OATS

[OD1JCONT ~T L 0 5 0 0 3 3 5 0 4 1 5 7 8 0 8 0 8 7 8 7 8 57 58 59 60 61 68 69 ~ . 74 75 60 I

EVENT OESCRIPTION Q~g chez the Upper Guide Structure (UGS) was removed (refueling shutdown), 3 (of 45) incoxe 7 8 9 80 0 3 instrument thimbles (or scabbaxds) remained in the core. All three showed kvidence t 7 8 9 80 that a clean separation (no loose pieces) had occurred befoxe plant'ooldown. Each 7 8 9 L ' 80 l00m seperation.was at the point of attachment to the UGS instrument plate. These thimbles

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axe not pxessure boundaries; they act as "bushings" to support the incoxe detectors anH 7 8 9 PRhIE 60 SYSTEM CAUSE COMPOAIBIT COMPO N ONT COOE COOS COMPONENT COOE MAIeUFACIQAER 1007j ~RA ~B X fi X X X N C 4 9 0 7 8 9 10 11 . 12 17 43 . 44 47 CAUSE OESCRIPTION JOB An investigation to determine the'cause of'he broken thimbles was 'pexformed by the

'0 7 8 9 60 vendor. Results of the investigation show that the thimbles fractured by fatigue Q~ g 7 8 9 80

~10 at a 1ocati,on where stresses were concentrated due to the deep thxead at the end of the 7 89 ~

FACUIY METHOO OF STATUS 3L POWER OTHER STATUS ~ OISCOVERY OISCOVERY OESCRIPTION

~B ~00 0 N/A N/A fiick 7 8 9 10 12 13 44 45 46 80 FORM OF ACTIVITY COATENT Q~g RELEAS'EO

~Z ~, OF RELEASE Z

AMOUNT OF ACTIVITY N/A LOCATION OP RELEASE N/A 7 8 9 10 11 44 45 80 PERSONNEL EXPOSURES

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NUMBER TYPE OESCRI~iON

~i3 ~00 0 Z N/A 7 8 9 .

11 12 13 80 PERSONNEL INJURIES Lq a 8 9

~00 NUMBCR 11 DESCRIPTION 12 60 PROBABLE CONSEQUENCES Q1 5 These thimbles are'ot' pressure boundary.

7 8 9 LOSS OR OAMAGE TO FACIUTY TYPE OESCRIPTION

~Z N/A 7 89 10 80 PUBLIClTY N/A 7 89 ~ 80 AOOITIONAL FACTORS

~16 See Page 2 for continuation of Event and Cause Descriptions.

7 89 7 89 80 M. A. Schoppman PHONE 305 55 2-3802 CP'0 1ST e $ 07

0 PORTABLE OCCURRENCE 335-78-11 LICENSEE EVENT REPORT UPDATE //1 PAGE THO Event Description (continued) to prevent. detector movement in the fuel assembly CEA guide tubes. Although evidence showed that the thimbles separated be'fore the plant shutdown, there was no effect on plant operation because the associated detectors were still fully operable and the system is designed with a high degree of redundancy.

The thimbles were repaired and returned to.service. This is the first event of its type at St. Lucie.'335-78-11)

Cause Descri tion (continued) extension tube (mechanical stresses) and the fillet weld over the threaded portion (residual'nd mechanical stresses). The repair of the. broken thimble has been conducted to assure resistance to this type of fatigue failure.

Although it is possible that one or more thimbles of the type that did break could break during future operation,- the vendor does not have any information that this will occur. This identical design is used in one other vendor plant that has been in operation six months longer than St., Lucie 1 and has had no failures. The vendor has evaluated the mechanical implications of one or moxe thimbles breaking during operation and has determined that the thimble is completely entrapped in its guide path, so that even though broken it cannot migrate to another location and cause damage to fuel or other components.

Although the three thimbles appear to have been broken for a period of time prior to shutdown, all three in-core instruments in those positions were. still functionirig. Due to the redundance of the in-core instrument system, the loss of one or more instruments could be tolerated even if the broken ICI thimble caused the in-core instrument to fail. In addition, operation with failed in-core detectors. ~s a reviewed issue addressed by technical specifications.

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