ML18092B538
| ML18092B538 | |
| Person / Time | |
|---|---|
| Site: | Salem  |
| Issue date: | 04/24/1987 |
| From: | NRC |
| To: | |
| Shared Package | |
| ML18092B537 | List: |
| References | |
| NUDOCS 8704300099 | |
| Download: ML18092B538 (3) | |
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UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D. C. 20555 SAFETY EVALUATION REPORT ON REPAIR OF SERVICE WATER SYSTEM PIPING AT SALEM GENERATING STATION UNIT 2 PUBLIC SERVICE ELECTRIC ANO GAS COMPANY (PSE&G)
During hydrostatic testing of the service water system piping at Salem Unit 2 perfonned in November 1986, a pin hole leak was observed in the fan cooler section of the piping. The degradation was identified as pitting. The piping is 3 inch schedule 40 type 316 stainless steel. Radiography of all of the approximately 1200 weld joints in this piping was subsequently performed.
In a letter dated December 12, 1986, PSE&G provided infonnation to document the extent of the degradation, their engineering analysis of the degraded piping, and their proposed repair.
The diameter and depth of the observed pitting was determined by radiography based upon comparisons of radiographic densities with calibrated radiographs.
The pitting was determined to be generally rounded, running from 1/16 inch to 3/16 inch in diameter, with about one to three significant pits in 40 to 501' of the joint areas.
In worst cases 10 to 15 significant pits were observed in
~ single joint area.
In virtually all cases, the pitting attack was located at or near the WPld joints.
In their analysis of the degraded piping, PSE&G assumed that the whole piping wall thickness was reduced by the worst obsP.rved flaw at the weld joint. The stress analysis was based upon ANSI 831.1 equations with appropriate use of stress intensification factors.
Based upon a conservative combination of loads and the observed flaw growth rate, a minimum remaining thickness of 0.12 inch was required for an additional service perirtd of-16 months.
A total of 99 areas with remaining wall less than this minimum were repaired by 0.12 inch thick external weld overlays of Inconel 625, 360° around the pipe,
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for widths ranging from about Ii inches to 2 inches.
An overlay of 0.12 inch thickness was determined to be sufficient for providing structural integrity under all design basis loadings.
PSE&G h~s had previous experience with the use of Inconel 625 welds with 316 stainless steel piping in this system. Subsequent inspection of this piping revealed that the Inr.onel 625 weldment remained in excellent condition.
Any pitting near.the weld stopped at the Inconel weld material.
The licensee has committed to perform an in-service inspection of weld joints in the Unit 2 fan cooler piping on a sampling basis within six months to verify the predicted ffaw growth rates. Additional engineering assessment will be conducted at that time.
On December 4, 1986,-NRR and Region I staff met with representatives of PSE&G at which time the infonnation outlined above was discussed.
The licPnsee informed the staff that they were performing the weld overlay in accordance with the original fabrication specification and were, therefore, in compliance with NRC regulations. The licensee is required to perform all inspections and repairs in accordance with the requirements in 10 CFR 50.55a, section (g),
"Inservice Inspection Requirements." This section indicates that the
- inspection and repa*ir program must meet Section XI of the ASME Code.
The applicable edition ar.d addenda of Section XI of the ASME Code for Salem-2 specifies a repair procedure and allows the licensee to utilize the repair procedure specified in the original fabrication specifications. 'The proposed method does not conform to the repair procedure in Section XI of the ASME Code.
In addition, after reviewing the original fabrication specifications, the staff determined that the weld overlay described in the original fabrication specification was not intended for repair of service induced flaws.
Hence, the proposed overlay method is not in ~ompliance with the requirements in 10 CFR 50.55a, subsection (g).
However, 10 CFR 50.55a paragraph (a)(3) pennits alternative requirements to section (g) when authorized by the Director of the Office of Nuclear Reactor Regulation.
Paragraph (a)(3) requires that the applicant demor.strate that (i) the proposed alternative would provide an acceptable level of quality and safety, or (ii,) compliance with the specified requirements of the section would result in hardship or unusual difficulties without a compensating increase in the level of quality and safety.
Based upon our review and evaluation of the analysis and repair methods discussed at that meeting and the documentation provided in the December 12, 1986, letter from PSE&G, we have concluded that the weld overlay repairs together with the radiograph inspections and supporting engineering analysis constitute an acceptable repair method for the pitting degradation observed in the service water system fan cooler piping at Salem Unit 2.
The radiographic inspection, engineering analysis and weld overlay repair method represents an alternative procedure which provides an acceptable level of quality and safety. Hence, the proposed method has demonstrated, compliance with the' criteria in 10 CFR 50.55a paragraph (a)(3). This repair method is considered acceptable for a period of 16 months and justifications for operation of this piping for periods in excess of 16 months must be supported by the licensee and approved by the NRC.
We have further concluded that if similar degradation is observed at Salem Unit 1, repair in accordance with the methods evaluated in this safety evaluation report may be performed and subsequent operation for a period of 16 months would similarly be acceptable.
Principal Contributor:
B. Elliot