ML17329A089

Forwards MT-MNA-035(91), Metallurgical Investigation of Wall Thinning & Leakage of Bmi Thimble Tubing at DC Cook Unit 2. Replacement Thimble Tubes Will Be Chrome Plated at Tube Surfaces

ML17329A089
Person / Time
Site:	Cook
Issue date:	07/15/1991
From:	Fitzpatrick E INDIANA MICHIGAN POWER CO. (FORMERLY INDIANA & MICHIG
To:	Murley T NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
Shared Package
ML17329A090	List: ML17329A089 ML17329A091
References
AEP:NRC:1059C, NUDOCS 9107230253
Download: ML17329A089 (4)

Text

. AGGELERATED DEMONSTR"ION SYSTEM DISTRIBUTION e)

Ytc REGULATORY INFORMATION DISTRIBUTION SYSTEM (RIDS)-

ACCESSION NBR:9107230253 DOC.DATE: 91/07/15 NOTARIZED: NO DOCKET FACIL:50-316 Donald C. Cook Nuclear Power Plant, Unit 2, Indiana 6 05000316 AUTH. NAME AUTHOR AFFILIATION, .

FITZPATRICK,E. Indiana Michigan Power Co. (formerly Indiana 6 Michigan Ele RECIP.NAME RECIPIENT AFFILIATION MDRLEY,T.E. Document Control Branch (Document Control Deck)~D

SUBJECT:

Forwards MT-MNA-035(91), "Metallurgical Investigation of I Wall Thinning & Leakage of BMI Thimble Tubing at DC Cook Unit 2." Replacement thimble tubes will be chrome plated at tube surfaces. D DISTRIBUTION CODE: A001D TITLE: OR COPIES RECEIVED:LTR Submittal: General Distribution ENCL SIZE: +33 s NOTES:

RECIPIENT A

COPIES RECIPIENT COPIES ID CODE/NAME LTTR ENCL ID CODE/NAME LTTR ENCL D PD3-1 LA 1 1 PD3-1 PD 1 1 COLBURN,T. 2 2 D

INTERNAL: NRR/DET/ECMB 7D 1 1 NRR/DET/ESGB 1 1 NRR/DOEA/OTSB11 1 1 NRR/DST 8E2 1 1 NRR/DST/SELB 7E 1 1 NRR/DST/SICB8H7 1 1 NRR/DST/SRXB 8E 1 1 NUDOCS-ABSTRACT 1 1 OC LFMB 1 0 OGC/HDS2 1 0 01 1 1 RES/DSIR/EIB 1 1 EXTERNAL: NRC PDR 1 1 NSIC 1 1 D

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D NOTE TO ALL "RIDS" RECIPIENTS:

PLEASE HELP US TO REDUCE WASTE! CONTACT THE DOCUMENT CONTROL DESK, ROOM Pl-37 (EXT. 20079) TO ELIMINATEYOUR NAME FROM DISTRIBUTION LIPID FOR DOCUMENTS YOU DON'T NEED!

TOTAL NUMBER OF COPIES REQUIRED: LTTR 18 ENCL 16

Indiana Michigan Power Company P.O. Box 16631 4 Columbus, OH 432$ 6 R

AEP'NRC:1059C Donald C. Cook Nuclear Plant Units 1 and 2 Docket Nos. 50-315 and 50-316 License Nos. DPR-58 and DPR-74 THIMBLE TUBE ROOT CAUSE U. S. Nuclear Regulatory Commission Document Control Desk Washington, D. C. 20555 Attn: T. E. Murley July 15, 1991

Dear Dr. Murley:

The purpose of this letter is to respond to requests made by your staff during a meeting held on April 11, 1991 users in your Rockville, Maryland offices, at which we presented a report regarding thimble tube wear mitigation activities at the Donald C. Cook Nuclear Plant. During that meeting we committed to provide you an updated status report and a copy of a Westinghouse report which contains the results from the hot cell laboratory examination of two thimble tubes taken from the Cook Nuclear Plant Unit 2 reactor. A copy of the Westinghouse report is attached. Six copies are being sent with Mr. Colburn's copy of this letter for NRC internal distribution and Status Re ort We have chosen to reposition or replace as many thimble tubes as necessary during the 1992 refueling outages to ensure that no thimble tube will develop a leak during the subsequent operating cycle for each Cook Nuclear Plant unit. Our thimble tube wear criteria for repositioning and replacement are currently 308 and 65% wall loss, respectively. If less than approximately 6 of the 58 thimble tubes in each unit require replacement, we may decide at that time to isolate those tubes using the isolation valve at the seal table and replace them at a later date.

Replacement thimble tubes will be chrome plated at tube surfaces corresponding to the locations in the reactor where the thimble pi07gg0P53 9'107i5 05000316

~ PDR "3 ADOCK p PDR

Dr. T. E. Murley AEP:NRC:1059C tubes are susceptible to wear, i.e., the fuel assembly lower nozzle and the lower core plate area. Contracts for the purchase of chrome plated thimble tubes and for the manpower services to remove, reposition, and replace thimble tubes are currently in the AEPSC approval process.

We have also chosen not to install any hardware modifications to the lower core plate or fuel assembly lower nozzle to mitigate thimble tube wear at this time. We believe that the addition of the chrome plating will reduce the amount of thimble tube wear found at the Cook Nuclear Plant. After one cycle of operation for each Cook Nuclear Plant unit, we will eddy current inspect each thimble tube to quantify the benefit of the chrome plating and to determine if additional hardware changes to further mitigate thimble tube wear are required.

Westin house Hot Cell Laborator Results Attached is MT-MNA-035(91), "Metallurgical Investigation of Wall Thinning and Leakage of the BMI Thimble Tubing at D. C. Cook Unit 2", dated January 1991. The results presented in this report, which indicate that the thimble tube wear is caused by flow-induced vibration, provided the basis for our root cause evaluation determination.

This document has been prepared following Corporate procedures that incorporate a reasonable set of controls to ensure its accuracy and completeness prior to signature by the undersigned.

Sincerely, Pg~pm Vice President eh Attachment cc: D. H. Williams, Jr.

A. A. Blind - Bridgman J. R. Padgett G. Charnoff NFEM Section Chief A. BE Davis - Region III-NRC Resident Inspector Bridgman

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