ML20212C448

SER Accepting Alternative to ASME Section XI Code Requirements to Use Code N-432 & N-504-1 for Weld Overlay Repair for Hope Creek Generating Station

ML20212C448
Person / Time
Site:	Hope Creek
Issue date:	10/17/1997
From:	NRC (Affiliation Not Assigned)
To:
Shared Package
ML20212C454	List: ML20212C448 ML20248J582
References
NUDOCS 9710290241
Download: ML20212C448 (3)

Text

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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION l ALTERNATIVE TO ASME SECTION XI CODE RE0VIREMENTS i TO USE CODE CASES N-432 AND N-504-1 FOR WELD OVERLAY REPAIR PUBLIC SERVICE ELECTRIC AND GAS COMPANY HOPE CREEK GENERATING STATION QQCKET NO. 50-354 1.0 .IN1RODUQ[QN

• By letters dated October 9 and 15 1997, the Public Service Electric and Gas Company (PSE&G, the licensee) prop,osed an alternative to the American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code ,

Section XI repair requirements under Title 10 of the Code of Federa)ll Reaulations (10 CFR),10 CFR Section 50.55a(a)(3). The licensee proposed to use Code Cases N-432, " Repair Welding Usin Arc Welding (GTAW) Temper Bead Technique,"g Automatic and N-504-1 "Al or Machine Gat Tungsten-Repair of Class 1, 2, 3 Austenitic Stainless Steel Piping "ternative Rules to perform weld_for overlay repair on a nozzle to safe end weld (NSB) in core, spray piping loop "A" at Hope Creek Generating Station (HCGS). The subject weld was found leaking during a routine tour of the drywell in the current seventh refueling outage. Three pin hole leaks were found at the top of the core spray nozzle-to-safe-end weld. Subsequent ultrasonic examinations have shown that the defect that caused leakage is a circumferential flaw with a length about 4.1 inches on the inside diameter surface of the weld and was located in the Inconel 182 butter region of the weld which is adjacent to the NSB core spray nozzle. The licensee proposed weld overlay repair design has a portion of the overlay extended into the core spray nozzle. The core spray nozzle is made of SA-50B Class 2 low alloy steel. A temper bead welding technique as prescribed in Code Case N-432 is needed to fabricate the weld overlay on the core spray nozzla. The temper bead welding technique is designed to avoid excessively hardening the low alloy steel material when welding is performed on this material.

Pursuant to 10 CFR 50.55(a (3), proposed alternatives to the requirements of demonstrate 10 CFR 50.55a th(g) may be use)d when authorized by the NRC.

The licensee must at 1) the proposed alternative would provide an acceptable level of q'iality 10 CFR and safety 50.55a(g) ((a)(3)(in hardship or uausual difficulty without a1)), or 2) would result compensating increase in the level of quality and safety ((a)(3)(ii)).

ENCLOSURE fogo2}o2 D0 g g g s4 p PDR L

2.0 LYALU&Il0lf 2.1 ASME Section XI Code Requirement The licensee indicated that the 1983 Edition with Summer 1983 Addenda is the '

currently applicable ASME Code to HCGS. Article IWB-4000, " Repair Procedures," of the subject Section XI Code Edition and Addenda provides rules and requirements for repair of the pressure retaining boundary for Class I components and their supports. To aerform Code repair, Subarticle IWB-4120

" procedure" requires that defects s1all be removed from the degraded components prior to performing a repair by welding.

2.2 Proposed Alternative The licensee proposed to use a combination of the requirements from ASME Code Cases N-432 for temper welding and N-5't-1, for austenitic weld overlays as an alternative to the ASME Code,Section XI, IWB-4000 requirements for repair to perform a temper hand weld overlay repair on the subject core spray nozzle weld at HCGS.

2.3 Licensee's Basis for the Proposed Alternative The licensee's basis for the proposed alternative are summarized below:

(1) Using Code Cases N-432 and N-504-1 for weld overlay repair of the subject core spray nozzle weld is necessary because it is not practical to perform the Code repair, which requires the removal of the through-wall defect from the degraded component.

(2) An engineered structural weld overlay is designed in accordance with NUREG-0313, " Technical Report on Material Selection and Processing Guidelines for BWR Coolant Pressure Boundary Piping," and Code Case N-504-1 modified for use on the vessel nozzle and Ni-Cr-Fe safe end and attachment welds. The overlay design assumes the subject core spray nozzle weld to be completely cracked and will restore the code margins in the overlay repair.

(3) The weld overlay made of Inconel 52 or Inconel 152 is resistant to intergranular stress' corrosion cracking (IGSCC) and a beneficial residual compressive field results from shrinkage of the overlay weld.

(4) The temper bead welding technique prescribed in Code Case N-432 is needed to fabricate the weld overlay on low alloy steel component to avoid embrittlement of the low alloy steel without needing a high post weld stress relief.

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4 2.4 Staff Evaluation The licensee proposed alternative to Code repair using the temper welding and austenitic weld requirements from Code Cases N-432 and N-504-1 is discussed above. The staff notes that, while the NRC has separately approved the use of both Code Cases N-432 and 504-1 (for ferritic material and austenitic atory Guide 1.147, the NRC has not previously material, approved t he use of au)tenitic s weld overlays on ferritic material.respectively The , in R proposed alternative will extend the use of temper bead welding technique in i Code (,ase N-432 to the fabric 4'n of weld overlay repair in Code Case N-504-

1. The licensee proposed to de ief %n Inconel 52 or 152 for the weld overlay J repair. This is acceptable WMm these materials have been approved by the  ;

staff and used.successfully in the pst on a similar welding application.

Further these welding materials have enhanced resistance to IGSCC.

The i licensee also identified some modificallons to both Code Cases in order to-accommodate the fabrication and examination of the weld overlay. The staff i

.has reviewed theso modifications and has determined them to be acceptable for assuring material integrity.

On the basis of a review of the licensee's submittal, the staff has determined that the proposed alternative to use Code Cases N-432 and N-504-1 with modifications for the weld overlay repair of the subject core spray nozzle weld at HCGS is acceptable because it will provide assurance of weld integrity.

3.0 CONCLUSION

On the basis of a review of the licensee's submittal, the staff concludes that the proposed alternative will result in acceptable level of quality and safety. Therefore, pursuant to 10 CFR 50.55a(a) the licensee proposed use of Code Cases of N-432(3)(1),

and N-504-1the withstaff authorizes modifications to weld overlay repair of the subject core spray nozzle weld at HCGS.

Principal Contributor: _ W. Koo Date: October 17, 1997

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