ML17335A297

Informs of Plans for Resolving Issue of Thin Pipe Wall Section Discovered in Section of Plant Main Steam Sys,Per 980804 Conversation with NRC

ML17335A297
Person / Time
Site:	Cook
Issue date:	10/16/1998
From:	Powers R INDIANA MICHIGAN POWER CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
AEP:NRC:1098C, NUDOCS 9810200183
Download: ML17335A297 (4)

Text

REGULA'i Y INFORMATION DISTRIBUTI i~ 'SYSTEM (RIDS)

/ ACCESSION NBR:9810200183 DOC.DATE: 98/10/16 NOTARXZED: NO DOCKET I FACIE:50-315 Donald C. Cook Nuclear Power Plant, Unit 1, Indiana M 05000315 AUTA.NAMFi, -i AUTHOR AFFILIATION POWERS,R.P. Indiana Michigan Power Co. (formerly Indiana & Michigan Ele RECIP.NAME RECIPIENT AFFILIATION Records Management Branch (Document Control Desk)

SUBJECT:

Informs of plans for resolving issue of thin pipe wall section discovered in section of plant main steam sys,per 980804 conversation with DISTRIBUTION CODE: A001D COPIES RECEIVED:LTR ENCL SIZE:

TITLE: OR Submittal: General Distribution NRC.-'OTES:

T E

RECIPIENT COPIES RECIPIENT COPIES 0 ID CODE/NAME LTTR ENCL ID CODE/NAME LTTR ENCL PD3-3 LA PD3-3 PD STANG, J INTERNAL: E CEN ER 01 NRR/DE/ECGB/A NRR/DE EMCB NRR/DRCH/HICB iNRR/DSSA/SPLB NRR/DSSA/SRXB NUDOCS-ABSTRACT OGC/HDS3 EXTERNAL: NOAC NRC PDR D

NOTE TO ALL "RIDS" RECIPIENTS:

PLEASE HELP US TO REDUCE WASTE. TO HAVE YOUR NAME OR ORGANIZATION REMOVED FROM DISTRIBUTION LISTS OR REDUCE THE NUMBER OF COPIES RECEIVED BY YOU OR YOUR ORGANIZATION, CONTACT THE DOCUMENT CONTROL DESK (DCD) ON EXTENSION 415-2083 TOTAL NUMBER OF COPIES REQUIRED: LTTR 13 ENCL

Indiana Michigan~

Power Company 500 Circle Drive ~

Buchanan, Ml 491071373 AEP NRC: 1098C October 16, 1998 Docket No: 50-315 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Mail Stop 0-Pl-17 Washington, D. C. 20555-0001 Gentlemen:

Donald C. Cook Nuclear Plant Unit 1 MAIN STEAM SYSTEM PIPE WALL THINNING

References:

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1...Letter, AEP:NRC:1098A, ",Donald C. -Cook Nuclear, Plant Unit 1, MAIN STEAM SYSTEM-PIPE,,WALL THINNING", dated April 17, 1997.

2. Letter AEP:NRC:1098B, "Donald C., Cook Nuclear -Plant Unit 1, MAIN STEAM SYSTEM PIPE-WALL THINNING", dated May 5, 1997.

The purpose of this letter is to inform you of our plans for resolving the issue of a thin pipe wall section discovered in a section of the unit 1 main steam system. This information was requested during an August 4, 1998, conversation with members of the NRC staff.

During the 1995 unit 1 refueling outage, the erosion-corrosion program identified that the wall thickness of the main steam piping in the extrados of the bend (1-MS-1) was less than the code allowable primary calculation (equation 3) in the ASME B31.1 code, 1967 Edition. It was determined that this piping was acceptable for cycle 15 with the condition that thickness measurements be taken again during the next refueling outage (U1R97). -

Wall thickness measurements were again performed in 1997. The results were comparable with the 1995 results indicating that erosion-corrosion is not active in this piping.

As the measured wall thickness was determined to be less than the code allowable primary calculation (equation 3, B31.1), we performed an, alternate code acceptable calculation using the actual ultimate tensile strength. from the certified material test report (CMTR) to compute: the"allowable stress.. The alternate code-acceptable minimum wall thickness calculation, based on the F

computed allowable stress using the lowest value ultimate tensile 98i0200183I 9810i'6. ,

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U.S. Nuclear Regulatory Commission AEP:NRC:1098C Page 2 strength of seven lots of material listed on the CMTR, is 0.828".

The minimum measured wall thickness in the pipe was 0.843". This information was transmitted to the NRC via reference 1.

The use of CMTR data was unacceptable to the NRC, 'nd a relief request for one cycle of operation was submitted via reference 2.

We have removed a boat sample from the surface of the unit 1 main steam pipe sweep downstream of steam generator one. The boat sample was machined into a round tensile pull specimen and pulled within a tens'le te t m chine. The ltimat" "ensi'e strength (UTS) test result obtained from the main steam line exceeded the minimum tensile strength required. However, it did not meet or exceed the UTS value we needed to establish a new minimum pipe wall thickness that would be lower than the actual pipe wall thickness measured. The required design minimum UTS is 70 ksi.

The actual measured UTS was 74.6 ksi. To establish a new minimum pipe wall thickness that would deem the actual pipe wall thickness acceptable, we needed to have a UTS value of 75.4 ksi.

As a result of this tensile test, we will perform an internal base metal buildup of the existing pipe. A small section of pipe will be removed from the pipe sweep, thus allowing access to the internal surface of the pipe sweep. The pipe wall thickness will be increased by performing a base metal weld buildup on the internal surface of the pipe pr'or to unit 1 restart. The small section of pipe will then be welded back in place. The base metal buildup will increase the pipe wall thickness to a value that exceeds the minimum pipe wall thickness required by the piping design code, B31.1, thus complying with our FSAR.

Based on the results of the tensile test and our plans to build up the base metal of the piping, the relief request submitted via reference 2 is no longer required and is superceded by this submittal.

Sincerely, R. P. Powers Vice President

/jmc ce J. A. Abramson J. L. Caldwell MDEQ DW & RPD NRC Resident Inspector J. R. Sampson