ML20248J243

Safety Evaluation Accepting Util 880122,0601,0714 & 0816 Submittals Re Insp Results,Mitigation,Flaw Evaluations & Overlay Repairs of Welds Susceptible to IGSCC to Support Operation of Unit 2,for Another 18-month Fuel Cycle

ML20248J243
Person / Time
Site:	Quad Cities
Issue date:	10/03/1989
From:	Office of Nuclear Reactor Regulation
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ML20248J241	List: ML20248J238 ML20248J243
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NUDOCS 8910130164
Download: ML20248J243 (4)

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-,. ATTACHMENT 1 .

SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATING TO WELD INSPECTIONS AND REPAIRS.FOR INTERGRANULAR STRESS CORR 0SION CRACKING COMMONWEALTH EDISON COMPANY QUAD CITIES UNIT 2 DOCKET NO. 50-265

1.0 INTRODUCTION

The staff reviewed submittals from Commonwealth Edison Company (CECO, the licensee) dated January 22, June 1, June 13, July 14, and August 16, 1988, regarding inspection results, mitigation, flaw evaluations, and overlay repairs of welos susceptible to Intergranular Stress Corrosion Cracking (IGSCC) to support continued operation of Quad Cities Unit 2, in its present configuration, for another 18-month fuel cycle. During the Unit 2 refueling outage from March 14 through May 22, 1983, 157 Class 1 piping welds susceptible to IGSCC in various austenitic stainless steel piping systems were ultrasonically examined.

The results of the inspection showed that flaw indications were observed in 19 welds. These included eleven 12-inch and six 28-inch recirculation system welds and two 6-inch reactor water cleanup (RWCU) system welds. Twelve of these walds did not have previously identified flaws. Overlay repairs were j applied to 13 of the 19 flawed welds. Six 28-inch flawed welds were justified q for continued operation without overlay repair by fracture mechanics evaluation.

A total of 47 welds in the core spray, residual heat removal, and recirculation systems were stress improved using the mechanical stress improvement process (MSIP).

2.0 DISCUSSION 4

2.1 Inspection Scope The licensee reported that there are 242 Class 1 piping welds in Quad Cities Unit 2, subject to IGSCC inspection. Of these, 157 welds were inspected during the 1988 refueling outage. The original sample size of 80 welds was determined in accordance with the guidelines in Generic Letter 84-11, and was expanded to 157 welds after flaws were found in the original and expanded samples.

1 The staff concludes that the inspection scope for Class 1 piping meets the staff  !

requirements and the guidelines in Generic Letter 84-11 since more than 64% of l the IGSCC susceptible welds were inspected during this outage.  !

2.2 Ultrasonic Examination The licensee reported that the IGSCC inspection was performed by Electric Power Reseach Institute (EPRI) Nondestructive Examination (NDE) Center qualified personnel. These examiners also passed the latest requalification program. Weld overlays were ultrasonically examined in accordance with CECO

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procedures which comply with EPRI developed weld overlay examination techniques.

General Electric (GE) performed the ultrasonic examination (UT) for the 1

-licensee using either the manual or. automatic techniques. In the cases of end cap-to-header weld overlay. both. automated and manual techniques were used.

During this outage IGSCC-like flaw indications were found-in nine 12-inch .

recirculation risers welds, one 28-inch recirculation weld, and two 6-inch RWCU welds. Consequently, the inspection sample was. expanded to include 100%

of the 12-inch and larger recirculation system piping welds (exclusive of

' nozzle-to-safe end welds).and 100% of the accessible Class 1 RWCU piping welds.

In addition, as requested per NRC Safety Evaluation Report (SER) dated March 6, 1987, welds 285-F14 and 28S-S12 were inspected (no indications were identified).

In the examination of nine unrepaired welds (two 12-inch and seven 28-inch recirculation welds), flaw growth was found in'two 12-inch and one 28-inch welds.

The indications in two previously flawed 28-inch recirculation welds _(02AS-56 and 02BS-F14) were determined not to be IGSCC related . However, the staff reconnends that CECO examine these two welds during the next refueling outage to confirm the inspection results reported in this outage.

Fourteen of twenty weld overlay. repairs performed during the 1986 refueling outage were re-examined this outage. Eleven of the fourteen weld overlay examinations reported no indications in the weld overlay-material. The flaws in the overlays of welds 02AS9, 02AS10 and 02BS-S3 were minor and the remaining.-

ligament of the overlays were reported to exceed the full structural design thickness. .

An NRC Region III inspector selectively reviewed the ultrasonic examination i procedures and data, and held discussions with the examiners regarding the i non-destructive examinations performed during this refueling outage. The inspector concluded in his report numbered 50-265/88006' dated June 28, 1988, that nun-destructive examinations were performed by qualified personnel and that no violations of NRC requirements were identified.

2.3 Weld Overlay Repair During this refueling outage, fifteen weld overlays were applied. Thirteen weld overlays were applied to eleven welds found flawed in this outage, and to two previously flawed welds. 'Two weld overlays were applied to unflawed locations (02C-54 and 02H-S4) to balance and reduce the weld overlay shrinkage stress in the recirculation system. Structural Integrity Associates Incorporated I (SIA) performed the overlay design evaluation for the licensee and all of the overlays were designed to meet the " standard" weld overlay design basis of NUREG-0313, Revision 2. The as-built overlay d bensions were reported to meet the design dimensions in all cases. Structural Integrity Associates also performed piping stress analysis in the recirculation and RWCU systems resulting from overlay induced shrinkages. The piping stresses were determined to meet ASME Code,Section III requirements. The largest shrinkage stress was calculated to be 18.8 Ksi at the recirculation riser safe end to nozzle and pipe joints.

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j. 3 Weld 02A-S10 (recirculation header to end cap) was overlay repaired during the l

1986 outage and was reinspected this outage as requested in NRC Safety Evaluation Report dated March 6, 1987. There was no significant changes to indications in the overlay. After reinspection, a large portion of the weld overlay was i

removed by machining. Liquid penetration (PT) examinations were performed at j various stages of machining and no flaws were detected. The overlay was l reapplied after machining. The overlays of two RWCU welds outside of the {

drywell were intended for limited service. For ALARA consideration, these J overlays were not surface finished for ultrasonic examination. To prevent {

steam blow out from axial flaws, the first layer of the overlays on these RWCU welds was applied with the system drained. The first layer was not considered in the design thickness.

The staff concludes that the weld overlay repairs performed during this outage are acceptable.

2.4 Flaw Evaluation i Structural Integrity Associates performed flaw evaluations for the licensee on six 28-inch recirculation welds to justify continued service without over-lay repair. Five welds (02D-F12, 02AS-F14, 02AS-512, 02BD-F8, and 02BS-512) werefoundflawedinpreviousoutagesandoneweld(02AD-S6)wasfoundflawed during this outage. In weld 02BD-F8, two new flaws and some growth of the old flaws were reported. There was no significant flaw growth in the other four previously flawed welds. Ashortandshallow(7%throughwall)circumferential flaw was found in weld 02AD-56. InductionHeatingStressImprovement(IHSI) had been performed on these welds in a previous outage, and the treatment records reviewed by the licensee were confirmed to be within the EPRI guidelines.

- The licensee also reviewed the original construction radiographs of these welds and observed strong evidence of ID grinding and/or wide weld roots. Structural Integrity Associates' flaw evaluations followed the guidelines in NUREG-0313, l Revision 2. Weld residual stresses were conservatively assumed as "as-welded" i and a bounding overlay shrinkage stress of 1 ksi was assumed for crack growth I calculations, since the actual overlay induced shrinkage stress was less than 1 500 psi in these welds. The results of SIA's flaw evaluations showed that all six 28-inch recirculation welds were acceptable without repair for at least another 18-month fuel cycle.  ;

Twenty-three IGSCC indications and fifty-three contamination cracks were reported in the re-applied overlay of the end cap weld 02A-510. Three boat samples were removed from the overlay at locations with reported indications j and no defects were found. Structural Integrity Associates performed a l 3-dimensional finite element stress analysis of the overlay, which assumed all {

these indications were true cracks. The results of SIA's stress analysis j showed all applicable ASME Code limits were satisfied. Because of reported UT )

indications in the overlay, the licensee indicated that the subject end-cap i will be inspected in accordance with Category F schedule (for welds with inadequate mitigation).

The staff concludes that SIA's flaw evaluations meet the guidelines in NUREG-0323, Revision 2 and are acceptable.

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, 2.5 Mechanical Stress Improvement Process (MSIP)

A total of 47' welds in the core spray, residual heat removal (LPCI), and recircu-lation systems were stress improved using mechanical stress improvement process (MSIP). Of these'47 welds, 33 were not included in the scope of either the initial or expanded UT examinations.

2.6 Induction Heating Stress Improvement j

All ten recirculation welds found flawed during this outage were IHSI treated in 1984 Most of these flaws were axially oriented and a few short circumferen-tial flaws were also reported. An initial review by SIA of the IHSI treatment records, original construction radiographs, and UT examination history indicated that the IHSI treatments were all within the current guidelines, and there is strong evidence of ID grinding and/or wide weld roots in each of these welds..

Because cracking of IHSI treated welds has been found in a number of operating BWR plants, the staff has generic concerns regarding the effectiveness of IHSI i treatment in mitigating IGSCC. To ensure timely detection of IGSCC, the staff recommends that the licensee should consider inspecting 50% of the IHSI treated <

welds during each of the next two refueling outages.

2.7 Augmented Leakage Monitoring Program The licensee did not describe an augmented leakage monitoring program in their i submittals. Thus, the NRC staff reconsnends that CECO follow the guidelines on leak detection in NUREG-0313, Revision 2. i 3.0 Conclusion l

Based upon a review of the licensee's submittals, the staff concludes that CECO has adequately addressed IGSCC in Class 1 piping with respect to inspections, repairs, and litigations performed during the Quad Cities, Unit 2, Spring 1988 refueling outage, and that these activities were performed in accordance with

-the guidelines in Generic letter 84-11. In addition, the staff also concludes 4 that Quad Cities Unit 2 can be safely operated for another-18-month fuel cycle '

in the present configuration.

Principal Contributor: William Koo Dated: October 3,1989

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