ML20211D229

Forwards SG Run Time Analysis Cycle 9 & Probabilistic Operational Assessment of SG Tube Degradation at Songs,Unit 2,for Cycle 9, Which Provides Basis for Determination of Appropriate Insp Intervals for Different Mechanisms

ML20211D229
Person / Time
Site:	San Onofre
Issue date:	09/25/1997
From:	Rainsberry J SOUTHERN CALIFORNIA EDISON CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
Shared Package
ML20211D231	List: ML20211D229 ML20211D236 ML20211D252
References
GL-95-05, GL-95-5, NUDOCS 9709290079
Download: ML20211D229 (2)

Text

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t September 25, 1997 U. S. Nuclear Regulatory Commission Attnt Document Control Desk Washington, D. C. 20555 Gentlemen:

SUBJCCT: Docket No. 50-361 Steam Generator Run Time Analysis for Cycle 9 San Onsfre Nuclear Generating Station, Unit 2

Reference:

February 6,1997LetterfromGregGibson(SCE)totheDocument Control Desk (NRC) Special Report: " Inservice Inspection of Steam Generator Tubes, San Onofre Nuclear Generating Station, Unit 2" In the referenced Special Report to the NRC, Southern California Edison (SCE) committed to provide an assessment of the results of the 1997 San Onofre Unit 2 steam generator inspection to the NRC within 180 days of the end of the 11,97 Unit 2 refueling outage. This assessment has been completed and is enclosed. SCE plans to operate the Unit 2 steam generators for approximately ten (10)monthsthroughJanuary,1998. The enclosed assessment is based on guidance contained in Regulatory Guide (RG) 1.121 " Bases for Plugging Degraded i Pressurized Water Reactor Steam Generator Tubes," Rev 0, August 1976, Generic Letter 95-05 " Voltage Based Repair Criteria for Westinghouse Steam Generator Tubes Affected by Outside Diameter Stress Corrosion Cracking," August 3, 1995, and Draft Regulatory Guide X.XX " Steam Generator Tube Integrity,"

November 1996. One of the major functions of this assessment was to provide a basis for determination of appropriate inspection intervals for different degradation mechanisms.

t The next planned. inspection of tubes for degradation at the top of the

'a e,} tubesheet will occur during the next refueling outage. The structural h integrity performance criteria and the accident leakage criteria of the above gg described regulatory documents can be met throughout a full cycle of operation

,, g without this particular inspection during a mid-cycle outage.

The next-planned inspection of the full length of all tubes with a bobbin probe will occur during a mid. cycle outage. The purpose of this is to project g

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Document Control Desk meeting of the structural integrity criteria for axially oriented primary water stress corrosion cracking at dented eggcrate supports. The probability ,

of burst for this degradation is projected to be within the structural integrity criteria until the mid-cycle inspection. The mid-cycle outage provides an opportunity to identify tubes affected by this degradation and remove them from service. With this action taken, the probability of burst for this degradation is projected to be within the structural integrity j criteria at the end of the cycle.

The next planned inspection of the full length of all tubes with a bobbin probe during the mid-cycle outage will also address axial cracking in tubing freespans and axial cracking at undented eggerate supports. Affected tubes will be identified and removed from service. This will provide added assurance of safe operation. However,'this degradation is considered to be within criteria that would not indicate a need for a mid-cycle inspection.

In summary, SCE considers that safe operation of the San Onofre Unit 2 steam generators is supported by a mid-cycle inspection outage, the enclosed ,

assessments, the end of Cycle 8 repairs, in-situ pressure testing, laboratory  !

results of tubes removed from a steam generator, and operational tube leakage limits. ,

As discussed at the January 30, 1997 meeting SCE is prepared to meet with the NRC to discuss the results of the analyses once the NRC Staff has had an opportunity to review this material.

Very truly yours, Enclosures cc: E. W. Herschoff, Regional Administrator, NRC Region IV K. E. Perkins, Jr., Director, Walnut Creek Field Office, NRC Region IV J. A. Sloan.-NRC Senior Resident inspector, San Onofre Units 2 & 3 M. B. Fields. NRC Project Manager, San Onofre Units 2 and 3 .

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