ML20245E795
| ML20245E795 | |
| Person / Time | |
|---|---|
| Site: | Quad Cities  |
| Issue date: | 07/13/1989 |
| From: | Stols R COMMONWEALTH EDISON CO. |
| To: | Murley T Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML20245E799 | List: |
| References | |
| 0199T:2-3, 199T:2-3, NUDOCS 8908110369 | |
| Download: ML20245E795 (4) | |
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Comm:nwealth Edison
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72 West Mams Street, Chicago, Ilknois 1m' Post OfEe BEE 7F
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2 A/ Chicago, Illinois 60690 - 0767 July 13, 1989 Dr. Thomas E. Murley, Director Office of Nuclear Reactor Regulation U.S. Nuclear Regulatory Commission WasidngtT,n, DC 20b55
Subject:
Quad Cities Station Unit 1 Inspection Plc., for Piping Susceptible te Intergranular Stress Corrosion Cracking (IGSCC)
!!RC Dockat_NA_iQ-334 References (s):
T.M. Ross letter to T.J. Kovach dated June 6, 1989.
(b):
R. Stols letter to T.E. Murley dated June 9, 1989.
Dr. Murley:
Reference (b) transmitted the Inspection Plan for piping susceptible to Intergranular Stress Corrosion Cracking (IGSCC) for the upcoming Unit 1 l
outage. The Inspection Plan incorporated the recommendations provided in l
Reference (a), with the exception of the recommendation for the Pipelock inspection.
Attachment A provides the justification for the inspection method of the Pipelock.
In eddition, during a May 25, 1989 conference call, the NPC Staff requested that additional intensnation on the affects of shrinkage on the total applied stress in the piping syst em due to application of weld overlays be submitted. The inf ormation is pr ovided in Attachment 3.
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4-1 T.E. Murley July 13, 1989 Please direct any questions you may have regarding this matter to this office.
Very truly yours,
's R.
Stols Nuclear Licensing Administrator 1m Attachments 1:
Justification for Pipelock Inspection 2:
" Applicability of Pipelock as a Remedy for Intergranular Stress Corrosion Cracking in BWRs" 3:
Request for Additional Information Affects of Shrinkage on Total Applied Stress in Piping System 4:
Sustained Stresses at IGSCC Susceptible Weld Locations cc T.M. Ross - Project Manager, HER N.
Koc - NRR R.L. Higgins - Senior Pesident Inspector, Quad Cities 1
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ECIACllMDtT 1 JUSTIFICATJC21 OF PJH4QCE_DiSEECTIQ[i l
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in 1984 and installed with a Pipelock that has not been properly ultrasonically examined. Therefore, this weld should be surface conditioned and ultrasonic-ally examined during the next refueling outage to ensure the effectiveness of the overlay and Pipelock in mitigating IGSCC.
l RESED1iSEt The Pipelock was applied on 02M-S3 as part of a research and development effort in 1983. The design basis of the Pipelock is to retain the pipe integrity in the hypothetical case of full degradation of the welded joint. The load path is redirected around the degraded Weldment through the Pipelock rings which act in a manner analogous to split loose flanges. The Pipelock studs carry the axial tensile loads. The positive locking mechanism holding the rings on the pipe operates without the benefit of friction.
Weld 02M-S3 contained a small axial IGSCC flew prior to installation of the Pipclock. 7e alleviate any concern with minor leakage, a two layer
" leak barrier" overlay was applied first. The Pipelock installed at Quad Cities Plant was designed for application with a weld overlay. The Pipelock and overlay functions in this specific case are complementary. The Pipelock ensures strength and safety while the overlay seals through-the-wall cracks which existed prior to the application of the Pipelock.
The Pipeleck is not only capable of holding the joint together, but also provides compression at the inner surface of the pipe in the weld and heat affected zone (HAZ). Tightening of the studs, holding the Pipelock rings on opposite sides of the weldment, provides compressive stresses in the axial and hoop directions which remain compressive at the inner surface even after pressurizing the pipe.
A typical stress distribution in the 11AZ due to pretightening the studs is contained in Attachment 2.
The Pipelock retardc or eliminates crack growth, and provides defense-in-depth against catastrophic failure. The Pipelock also reduces the stresses in overlaid material which is highly tensile after overlaying.
Overlay material is basically res4stant to stress corrosions and the significant decrease of tension further reduces the potential for leaks.
Pipelocks are deslyned to meet ASME Code Section III requirements for long-term, multi-cycle operation. The installed Pipelock on overlaid weldnents meatsSection XI criteria. The analysis was performed for the load history specified for the life of the plant. The analysis was also performed to the safety requirements defined in the original Qued Cities Plant Piping System design code.
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, Disassembly of the Pipelock for inspection is not required.
Pipelocks by their inherent design, eliminate the need to. inspect the weld and quantify crack depths for safety purposes. The surface over the welded region can be visually inspected without disassembly of the Pipelock.
Inspection during the first outage after installation was carried out in order to retighten nuts on the studs which, as required in the original design, needed adjusting after the first thermal cycle.
Disassembly and reassembly of the Pipelock is not desirable.
In addition to the cost of 0isassembly and reassembly, in terms of man-hours and radiation exposure, the Pipelock would require retorquing after the first fuel cycle after reassembly. A UT inspection is not possible even after disassembly because grooves are machined in the overlay to provi_de a frictional surface for tire Pipe 2ock.
Inspection of the Pipelock has been performed each outage since it was installed.
Inspection is planned for the Pipelock in the future to the same schedule as a Standard Weld Overlay (NUREG-0313, Revision 2, Category E).
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