05000280/LER-1986-007, :on 860107,two Bolting Studs in Valve Flange MOV-SI-1890B Failed.Caused by Intergranular Stress Corrosion of Bolting Matl.Insp Conducted & Stud Matl Replaced,As Necessary

:on 860107,two Bolting Studs in Valve Flange MOV-SI-1890B Failed.Caused by Intergranular Stress Corrosion of Bolting Matl.Insp Conducted & Stud Matl Replaced,As Necessary

ML20141D055
Person / Time
Site:	Surry
Issue date:	03/31/1986
From:	Saunders R VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.)
To:	NRC OFFICE OF ADMINISTRATION (ADM)
Shared Package
ML20141D059	List: 05000280/LER-1986-007, :on 860107,two Bolting Studs in Valve Flange MOV-SI-1890B Failed.Caused by Intergranular Stress Corrosion of Bolting Matl.Insp Conducted & Stud Matl Replaced,As Necessary ML20141D075
References
86-005A, 86-5A, LER-86-007, LER-86-7, NUDOCS 8604070385
Download: ML20141D055 (5)

LER-1986-007, on 860107,two Bolting Studs in Valve Flange MOV-SI-1890B Failed.Caused by Intergranular Stress Corrosion of Bolting Matl.Insp Conducted & Stud Matl Replaced,As Necessary

Event date:
Report date:
2801986007R00 - NRC Website

text

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With Unit I at 97% on January 7, 1986, 2 bolting studs in *f0V-SI-1890B were observed to have failed. The f ailure mechanism was determined to be intergranular stress corrosion of 410 stainless steel stud material. An inspection of Unit 1 was conducted and stud material of valves containing etuda 2/4 inch diameter and greater, with the same natarial designation or t'iose stainless studs for which no material designation could be determined, were replaced.

An inspection and replacement program for Unit 2 has been completed also. This voluntary report is subnit ted for infornat ton.

A detailed report is attached. The bolting naterial was installed as part of valve bolting material design change issued in 1979.

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Description of the Event With Unit No. 1 at 97% power, on January 7,1986 during a routine inspection, 2 stainless steel studs in a valve flange for the low head safety injection system were observed to have failed. A subsequent review of records and a walkdown revealed studs of the same material designation on other valves.

2.

Safety Consequences and Implications

A detailed engineering analysis, including chemical and metallurgical tests, was performed on the failed material. The subsequent engineering evaluation indicated that the failure mechanism would not cause valve flange f ailure or excessive Icakage as the adjacent studs would satisfactorily absorb the increased stress caused by the stud f ailures.

3.

Cause

A thorough metallurgical and chemical analysis of the f ailed studs and foreign material found on the studs indicated that the failure mechanism was stress corrosion cracking followed by rapid unstable crack growth af ter the critical flaw size was achieved. The bolting material was installed as part of a valve bolting material design change issued in 1979.

4.

Immediate Corrective Action

An inspection of records to identify the valves containing the questionable naterial and a visual walkdown of safety systems in Unit I was conducted. The studs in MOV-SI-1890B were replaced with ASTM A193 B7 type bolting material and an evaluation was initiated.

5.

Additional Corrective Action During the next maintenance outage, which commenced on January 24, 1986, e

an inspection of Unit i valves was conducted.

Studs of 3/4 itch diameter and greater of the material in question were replaced in critical plant systems.

An inspection and replacement of Unit 2 critical valves studs was completed during the February outage. A list of valves which had studs replaced is attached.

In addition, a testing program was initiated to determine the susceptability of suspected stud material of less than 3/4 diameter. A detailed report has been prepared and is attached.

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Action Taken to Prevent Recurrence Material of question is being replaced with AST't A193 B7 type bolting material. Stud replacement in critical systems has been completed for Units 1 and 2.

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Generic Implications As the stud material identified was procured to a unique Virginia Electric and Power Company specification, there appears to be no generic implication.

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o VIRGINIA ELECiniC AND POWER COMPANY Surry Power Station P. O. Box 315 Surry, Virginia 23883 Parch 31, 1986 U.S. Nuclear Regulatory Ccrmissicn Serial No:

86-005A Docunent Control Desk Docket No:

50-280 016 Phillips Building License No:

DPR-32 Washington, D. C.

20555 Gentlemen:

Pursuant to Surry Power Staticn Tedinical Specifications, Virginia Electric and Power Ccrpany hereby subnits the following Licensee Event Report update for Surry Unit 1.

REPORT NLMIER 86-007-01

'Ihis report has been reviewed by the Staticn Nuclear Safety and Operating Ccximittee and will be reviewed by Safety Evaluaticn and Ccntrol.

Very truly yours, R. F. Saunders d Staticn Manager Enclosure cc:

Dr. J. Nelson Grace Regicnal Administrator Suite 2900 101 Marietta Street, hW Atlanta, Georgia 30323 j

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