ML20207D370
| ML20207D370 | |
| Person / Time | |
|---|---|
| Site: | Quad Cities  |
| Issue date: | 12/24/1986 |
| From: | Turbak M COMMONWEALTH EDISON CO. |
| To: | Harold Denton Office of Nuclear Reactor Regulation |
| References | |
| 2553K, NUDOCS 8612300387 | |
| Download: ML20207D370 (3) | |
Text
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) Commonwealth Edloon
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One First Nabonel Piara. Chicago, Illinois
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7 Address Reply to: Poet Omco Box 767 k/ Chica0o, tilinois 60600 0767 December 24, 1986 Mr. Harold R. Denton, Director Office of Nuclear Reactor Regulation U.S. Nuclear Regulatory Commission Washington, DC 20555
Subject:
Quad Cities Station Unit 2 Inservice Inspection Information NRC Docket No. 50-265 1
Dear Mr. Denton:
i The Quad Cities Unit 2 refueling outage is nearing completion with l
startup planned for January 18, 1987.
In applying the inservice inspection (ISI) plan, additional IGSCC was found in the recirculation system resulting in all susceptible recirculation system piping welds being examined.
Prior to this outage, Unit 2 had 14 (fourteen) weld overlays.
These 14 overlays were upgraded to full structural thickness criteria and were surfaced for UT examination using EPRI techniques. The additional IGSCC resulted in 6 (six) additional weld overlays being applied, also to full structural requirements.
The UT examinations of 19 (nineteen) of the overlays confirmed that full structural thickness requirements were met. One overlay on an end cap weld was found to have axial crack indications into the weld overlay to the extent that full structural criteria were not met. The attachment provides information on the cap weld. We request NRC review the acceptability of leaving the weld in its present condition. The system pressure test is scheduled for Monday, December 29 and a response by that date is requested.
please direct any additional questions regarding this issue to this office.
Very truly yours, Y.S.(
M. S. Turbak Operating Plant Licensing Director cc: Resident Inspector - Quad Cities T. S. Note 11a - NRR M. C. parker 8612300387 861224
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PDR ADOCK 05000265
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Ultras:nic Exanination and Disposition End Cap Weld 02A-S10 Quad-Cities Unit 2 Fall 1986 Outage
Background
02A-S10 is a 22-inch recirculation end cap-to-header weld. Circumferentially-oriented IGSCC flaw indications have been reported in this weld since the 1983 refueling outage ultrasonic examinations. This weld was also treated with induction heating stress improvement (IHSI) during the 1983 refueling cutage. A flawed pipe analysis of the flaws in this weld was performed by Nutech and demonstrated the acceptability of continued operation without weld overlay repair.
The details of this analysis are contained in the flaw analysis and disposition report submitted to the NRC by Commonwealth Edison.
1986 Ultrasonic Examination Results/ Repair Activities Manual ultrasonic examinations during the 1985 and 1986 refueling outages revealed no significant changes in the circumferential flaw indications.
Two axial flaw indications were observed in the most recent (1986) manual UT examination.
In order to more accurately quantify the circumferential extent of the finw indications, an automatic ultrasonic examination was performed during the current outage. While this examination confirmed the circumferential flaws, several additional axial flaw indications were detected with the automatic examinations. Although a two layer design overlay (0.125 inches thick) would have been a sufficient repair, a " full structural" weld overlay repair was designed for this particular weld with a thickness of 0.380 inches. This design was applied because of the difficulty in setting up for welding (an extension piece on the end cap was needed).
The station wanted a conservctive overlay to avoid any possibility of future welding.
Several " steam blow-outs" indicative of through-wall axial IGSCC flaws were observed during the weld overlay application. These were repaired using the shielded metal arc welding (SMAW) process, with at least one final weld overlay layer applied using automatic gas tungsten arc welding (GTAW). The base metal surface passed liquid penetrant (PT) examination prior to weld overlay application and the first weld overlay layer was " discarded" due to a delta ferrite content below 7.5 FN.
Ultrasonic Eyamination of the Weld Overlay Repaired Weld Following welding and surface conditioning, a post-weld overlay ultrasonic examination was performed in accordance with the Commonwealth Edison procedure and in compliance with industry (EPRI) and NRC-approved criteria. This examination revealed several axial flaw indications, seven of which had a aining ligament equal to or less than the minimum weld overlay design r
thickness. The minimum remaining ligament measured was 0.28 inches. These flaws are associated with steam blow-out repairs during the weld overlay application.
In addition, a two-inch long circumferentially-oriented flaw indication was observed at a remaining ligament (depth from outside surface of weld overlay) of 0.42 inches.
This remaining ligament places this flaw indication very close to the weld overlay / original pipe outside diameter interface.
Examination of this specific area by a CECO-SMAD Level III determined that this indication is a circumferential crack associated with two axial indications.
The examinations of weld overlays at Quad-Cities Unit 2 during the Fall 1986 outage were performed to a CECO procedure based on techniques developed by EPRI. The EPRI techniques for examination of weld overlays utilize dual element, pitch catch, focused refracted "L" wave transducers.
For the overlay weld metal, the primary examination is performed using 70 degree transducers, supplemented with OD creeping wave transducers at the option of the examiner.
Base metal under the overlay is examined using 60 degree transducers. The examinations are made in two directions for both circumferential1y and axially oriented flaws.
The UT calibration standard is an overlayed piece of pipe made from the same material as the pipe being examined. A 1/16-inch side-drilled hole at the weld overlay / base metal interface is used to calibrate the sensitivity of the UT instrument.
The signal is maximized and set to 80% of Full Screen Height.
Calibration blocks are used for the sweep range calibration. These blocks are made of similar material and have holes or notches located at 0.100 inch depth increments, similar to the EPRI crack sizing calibration blocks. The sweep range is set to one or two inches, depending on the volume of examination.
The EPRI technique for depth measurement depends on finding the tip of the crack.
Laboratory work has demonstrated the technique to be reliable.
Once a crack tip indication is found, the examiner evaluates the information from the direction of examination and transducer angles used and makes a depth call.
This call establishes the remaining ligament of sound metal between the crack tip and the outside surface of the weld overlay.
The accuracy of depth sizing is dependent on the smoothness of the overlay surface. The CECO specification requires a long-range maximum roughness of 1/64 inch per inch compared to the EPRI recommendation of 1/32 inch per inch maximum. This degree of smoothness assures accurate depth readings from the sweep location of an indication on the instrument screen.
Discussion In the case of each flaw, sufficient remaining ligament exists over the flaw to satisfy the required weld overlay thickness criteria.
For the axially-oriented flaws, the minimum leakage barrier thickness of two layers or 0.125 inches is satisfied, even considering propagation of the deepest observed flaw due to fatigue (a conservatively calculated flaw growth by fatigue of 0.030 inches in five years or 0.146 inches in thirty years).
For the circumferentially-oriented flaw, the remaining ligament places the flaw at the weld overlay interface.
This remaining ligament includes both the
" discarded" first weld overlay layer and the calculated full structural weld overlay thickness of 0.380 inches.
Planned Actions This weld overlay will be examined at the next refueling outage.
Based on the results of this examination, further examinations and/or repair activities will be determined at that time.
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