ML20206E226

Safety Evaluation Concluding That Proposed Alternatives Will Result in Acceptable Level of Quality & Safety.Authorizes Use of Code Case N-504 for Weld Overlay Repair of FW Nozzle Weld at Pnpp & Use of Table IWB-3514

ML20206E226
Person / Time
Site:	Perry
Issue date:	04/29/1999
From:	NRC (Affiliation Not Assigned)
To:
Shared Package
ML20206E214	List: ML20206E211 ML20206E226
References
NUDOCS 9905050057
Download: ML20206E226 (4)

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, f*Ph p & UNITED STATES g j NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 30056-0001 o

SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION ALTERNATIVES TO ASME CODE REQUIREMENTS FOR REPAIR AND INSPECTION OF A FEEDWATER NOZZLE TO SAFE-END WELD FIRSTENERGY NUCLEAR POWER COMPANY PERRY NUCLEAR POWER PLANT DOCKET NO. 50-440

1.0 INTRODUCTION

By letters dated March 25 and April 1,1999, the FirstEnergy Nuclear Operating Company (the licensee), proposed an altemative to the American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code),Section XI repair requirements along with a separate attemative to the ASME Code, Section til ultrasonic examination acceptance criteria under 10 CFR 50.55a(a)(3). The proposed attematives consist of the use of Code Case N-504,

" Alternative Rules for Repair of Class 1,2 and 3 Austenitic Stainless Steel Piping," to perform a weld overlay repair on a feedwater nozzle to safe-end weld N4C-KB at the Perry Nuclear Power Plant (PNPP), and the use of ASME Section XI acceptance criteria of Table IWB-3514-3 for the laminar flaws when inspecting the overlay repaired weld in accordance with Code Case N-416-1, *Altemative Pressure Test Requirement for Welded Repairs or installation of Replacement items by Welding, Class 1,2 and 3,Section XI, Division," respectively. The subject weld was found cracked during refuel outage (RFO) 2. Mechanical stress improvement process (MSIP) was applied to mitigate the cracking during RFO 3. The safe-end was fabricated from SA-508, Class 1 (P1 Group 2) material and the nozzle was made of SA-508, Class 11 (P3 Group 3) material. Both the nozzle and the safe-end are buttered with Alloy 182 and the weld was made with Alloy 82 filter. The subject weld is a dissimilar metal weld. The flaw was reported to be initiated in the butter at the safe-end side and extended into the weld.

The licensee proposed to perform a weld overlay repair on the subject weld during the current refueling outage (RF0 7) which began on March 26,1999.

Pursuant to 10 CFR 50.55(a)(3), proposed attematives to the requirements of 10 CFR 50.55a(g) may be used when authorized by the NRC. The licensee must demonstrate that (1) the proposed altemative would provide an acceptable level of quality and safety ((a)(3)(i)), or (2) compliance with the requirements of 10 CFR 50.55a(g) would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety ((a)(3)(ii)).

ENCLOSURE 9905050057 990429 l PDR ADOCK 05000440  ;

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I 2.0 EVALUATION 2.1 ASME Section XI Code Reoair Reauirement The current applicable ASME Section XI Code to PNPP is the 1989 Edition with no addenda. Article IWB-4000, " Repair Procedures," of the subject Section XI Code Edition provides rules and requirements for repair of the pressure retaining boundary for Class 1 components and their supports. To perform the Code repair, Sub-art,icle IWB-4120 l

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

2.1.1 Proposed Alternative The licensee proposed to use the Code Case N-504 as an alternative to the ASME Code,Section XI, IWB-4000 requirements for repair to perform weld overlay repair on the subject feedwater nozzle weld at PNPP.

2.1.2 Licensee's Basis for the Proposed Altemative The licensee's bases for the proposed alternative to the Section XI Code repair requirements are summarized below:

(1) It is not practical to perform the Code repair, which requires the removal of the defect from the degraded component as the defect was connected to the inner diameter surface of the component. Therefore, it is necessary to use the Code Case N-504 for weld overlay repair of the subject feedwater nozzle weld.

(2) The overlay is designed as a full structural overlay in accordance with the ASME Code Case E L cod the guidelines in NUREG-0313, Revision 2 to assure the structuralintegrity of the repaired weld. The designed overlay will cover the subject weld and portion of'he safe-end adjacent to the weld.

(3) The weld ovety made of Alloy 52 (ASME Code Case 2142) or Alloy 152 (ASME 2143) is resis' ant to intergranular stress corrosion cracking (IGSCC).

(4) Because of the relatively low carbon content (0.23 percent) in the safe-end material (carbon steel), a temper bead welding technique to fabricate the proposed overlay mpair is not required because the potential of hardening the safe-end material by welding is low. However, as a conservative approach, a qualified temper bead welding technique will be applied for the first three overlay layers to ensure a high quality overlay.

2.1.3 Sts*f Evaluation The licensee propo.ed attemative to Section Xi Code repair is based on the use of the Code Case N-504 to perform a weld overlay repair on the subject feedwater noz;le to i - . . . _.

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safe-end weld. The subject nozzle weld is a dissimilar metal weld (austenitic material to ferritic material) and a portion of the weld overlay will extend from the austenitic weld into the safe-end made of carbon steel material (P1 Group 2). The staff notes that, in Regulatory Guide 1.147, the approved use of the Code Case N-504 is for applying the austenitic weld over on the austenitic material. Therefore, the licensee proposed altemative will extend the application of Code Case N-504 to apply the austenitic weld overlay on the ferritic material. The licensee proposed to use either Alloy 52 or Alloy 152 for the weld overlay repair. This is acceptable because these materials have been approved by the staff and used 'successfully in the past on a similar welding application.

2.2 ASME Section 111 Code Acceptance Criteria for Ultrasonic Examination When performing pressure testing in a'ecordance with Code Case N-416-1, the Code Case requires that the acceptance criteria of the non-destructive examinations (NDE) shall be in accordance with the applicable sub-article of the ASME Section lil,1992 Edition with no addendum. For the ultrasonic examination, the acceptance criteria is provided in sub-article NB-5330.

2.2.1 Licensee Proposed Alternative The licensee proposed the acceptance criteria of ASME Code Section XI as an alternative to the Section lll requirements for the laminar flaws in the weld overlay repair, in ASME Code Section XI, the allowable laminar flaws for the dissimilar metal weld are provided in Table IWB-3514-3 for ultrasonic examination.

2.2.2 Licensee's Basis for the Proposed Alternative The licensee's bases for the proposed alternative to ASME Section 111 Code acceptance criteria for the laminar flaws are summarized below:

(1) In ASME Code Section 111 of 1992 Edition and Code Case N-504, there are no specific acceptance criteria for the laminar flaws for pre-service examination. l (2) Since the weld overlay repair is proposed to be an attemative to the ASME Section XI Code repair, it is appropriate to apoly the Code Section XI acceptance criteria for the laminar flaws when inspecting t!.: overlay repaired weld in accordance with Code Case N-416-1.

2.2.3 Staff 0 valuation The licensee proposed the use of ASME Code,Section XI, Table IWB-3514, as an alternative for the NDE acceptance criteria of the ASME Code, Section 111, for the laminar flaws in the weld overlay repair. This is acceptable because the laminar flaws j

, are not expected to impact the structural integrity of the subject overlay repaired weld. I Furthermore, if the Code repair were performed to correct such benign lamination, it might result in an adverse residual stress profile in the subject nozzle weld that could promote initiation and growth of stress corrosion cracking. The licensee proposed  !

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, .s alternative has been approved by the staff in other plants for a similar weld overlay repair.

On the basis of a review of the licensee's submittal, the staff has determined that the licensee proposed alternatives as discussed above for the weld overlay repair of the subject feedwater l nozzle weld at PNPP is acceptable because it will provide assurance of weld integrity.

3.0 .Cfj 'CLUSION On the basis of a review of the licensee's submittal, the staff concludes that the proposed alternatives will result in an acceptable level of quality and safety. Therefore, pursuant to 10 CFR 50.55a(a)(3)(i), the staff authorizes the use of Code Case N-504 for the weld overlay repair of the subject feedwater nozzle weld at PNPP and the use of ASME Code Section XI, Table IWB-3514, for the acceptance criteria of the laminar flaws when performing ultrasonic examination of the overlay repaired weld.

Contact:

W. Koo Date: April 29, 1999 l

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