ML20079K840
| ML20079K840 | |
| Person / Time | |
|---|---|
| Site: | Oyster Creek |
| Issue date: | 10/28/1991 |
| From: | Devine J GENERAL PUBLIC UTILITIES CORP. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| Shared Package | |
| ML20079K841 | List: |
| References | |
| 5000-91-2079, C321-91-2260, GL-88-01, GL-88-1, NUDOCS 9111050038 | |
| Download: ML20079K840 (4) | |
Text
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GPU Nuclear Corporation fl EE l
38 One Upper Pond Road M
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Paruppany, New Jersey 07054 201-316-7000 T ELE X 130 482 Writer's Direct Dial Number October 28, 1991 5000-91-2079 C321-91-2260 4
U. S. Nuclear Regulatory Commission Washington, D.C.
20555 Attention:
Document Control Desk Gentlemen:
Subject:
Oyster Creek Nuclear Generating Station Docket No. 50 219 Facility License No. DPR-16 Isolation Condenser Pipe Replacement Leak-Before-Break Evaluation During the recent Cycle 13R refueling outage at Oyster Creek, GPU Nuclear (GPUN) replaced piping and valves outside containn.ent as well as the piping inside the penetration guard pipes in the Isolation Condenser (IC) System.
This work was performed to improve safety and to resolve three open issues. These issues were identified in our letter (5000 86-1086) dated November 25, 1986.
The primary purpose of that letter was to address a concern regarding a postulated high energy line break (HELB) in the IC piping inside the penetration guard pipe. Our assessment concluded that any modifications resulting from the resolution of that issue should be performed as part of en integrated change intended to resolve all three issues. Further information regarding the scope of work and schedule was contained in our letter (5000 08-1604) dated July 27, 1988. On January 10, 1990, GPU Nuclear met with the NRC staff to discuss the intended resolutions and planned modifications.
The issues and resolutions are as follows:
1)
Uninspectable Welds S
Generic Letter 88-01, "NRC Position on IGSCC in BWR Austenitic g
Stainless Steel Piping" requires weldments in boiling water reactor Not piping in contact with reactor coolant and susceptible to 38 intergranular stress corrosion cracking (IGSCC) to be inspected W
ultrasonically (UT), sleeved or local leak detection applied.
Weldments in IC process piping enclosed by the penetration guard
-$5 l'
pipes are not inspectable. Therefore, during the 13R outage, piping 88 enclosed by the guard pipe in all four IC penetraticns was replaced with IGSCC resistant Nuclear Grade 316 stainless steel seamless pipe l
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and all reactor coolant pressure retaining weids inside the guard 3
pipes were eliminated. A flued collar penetration fitting welded to ou the outside surface of the new piping replaced the former flue head fitting.
GPU Nuclear Corporation is a subsid:ary of General Pubhc Utahties Corporation
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C321-91-2260 Page 2 2)
Pioe Break Outside Containment The result of the review conducted under Systematic Evaluation Program (SEP) Topic 111-5.8, " Pipe Break Outside Containment," were documented by the NRC staff in the Integrated Plant Safety Assessment Report (IPSAR) for Oyster Creek (NUREG 0822, January, 1983).
As stated in Section 4.10(2) of the IPSAR:
"The emergency condenser steam lines have two automatic isolation valves outside and adjacent to the drywell. A break between these valves with a failure of the first isolation valve or a pipe break between the second valve and the i
condenser resulting in pipe whip such that the isolation valves would not close would both result in a LOCA outside containment. The physical arrangement and space availability preclude installation of restraints.
In addition, it is not practical ta install an isolation valve inside the crywell."
In order to resolve the concern described above, GPUN submitted fracture mechanics analyses and a leak detection evaluation by letters dated May 18, 1982 and October 16, 1984 for the IC piping.
These studies were performed utilizing SEP guidelines to show that through wall cracks in the piping would remain stable under loading, leakage is detectable and sufficient time would be available to isolate and correct the problem. At a meeting on february 11, 1987, the staff informed GPUN that new criteria was being developed associated with the impending broad scope rule change for General Design Criteria (GDC) 4 and that a leak before-break (LBB) evaluation of IC piping would have to be based on the new guidelines.
The revision to GDC 4 was effective on November 27, 1987 and the guidelines were issued as a draft Standard Review Plan (SRP) Section 3.6.3 on August 28, 1987.
GPUN evaluated the new LBB requirements in relation to the 10 piping outside containment and revised the modification scope accordingly.
As presented to the staff on January 10, 1990, the IC piping on all steam inlet and condensate outlet lines has been replaced with IGSCC resistant material from the first elbow inside the drywell, through the penetration and thence outside the drywell to the IC nozzles.
In addition, all six isolation valves outside containment have been replaced with IGSCC resistant material in accordance with NUREG 0313. Rev. 2.
All new pressure retaining weld joints have been 100%
UT inspected and will be stress improved, if possible, no later than the next (Cycle 14R) refueling outage. Thus, the IC piping outside the drywell conforms to the staff position on resistance to IGSCC for the application of LBB.
The IC piping outside containment has been evaluated using the guidance in draf t SRP Section 3.6.3.
The evaluation is contained in our consultant's report (HPR-1226, Vols. I and II) which is attached. We believe that the report provides an adequate basis to resolve SEP Topic 111-5.B for the IC System.
C321-91-2260 Page 3 3.
HELB Inside IC Penetration Guard Pio n The original design basis for IC piping penetrations included consideration of 1.0 PxA loads due to assumed process line breaks inside the penetration guard pipes.
Recently, GPUN performed analyses of IC penetration pipe break loads using a more refined load definition to characterize the flow effects during such a break.
The new load definition methodology took into account pressure, momentum and flow turning effects int,ide the guard pipe geometry. The results of IC penetration structural analyses using the refined pipe break loads were submitted to the NRC by GPUN letters 5000 86-1031 dated September 17, 1986, 5000 86-1086 dated November 25, 1986 and 5000-881604 dated July 27, 1988.
We concluded that a pipe break in 10 condensate return piping within penetration X-5A could overstress the drywell shell.
Until a more permanent solution could be implemented GPUN committed to precautionary measures to assure the absence of pr1 cess line leaks inside the affected penetration guard pipe.
These measures, described in our November 25, 1986 letter, were implemented because the most likely cause of a pipe break is the presence of unstable throughwall cracks in the heat affected zone of circumferential pipe welds and because of the inability to inspect process line welds within the IC penetration guard pipes.
The IC penetration piping replacement, performed during the 13R outage, eliminates the need to assume pipe breaks inside the penetration guard pipes, and therefore eliminates the need to make any local drywell modifications.
There is no longer a need to assume pipe breaks within penetrations, since the new penetration piping is IGSCC resistant material, and the new piping design with the flued collar eliminates all reactor coolant pressure retaining welds inside the penetration guard pipes.
A new pipe stress analysis confirms that stresses and fatigue usage of the process piping and flued collar attachment at each penetration are acceptable.
The new process piping is heavier wall (Schedule 100) than the original Schedule 80 piping to help assure stresses are acceptable. In addition, the flued collar attachment welds are 100%
volumetrically examinable in service.
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C321 91-2260 Page 4 Since the IC penetration modifications eliminated reactor coolant pressure retaining welds inside the penetration guard pipes, the possibility of IGSCC induced leakage is eliminated. Therefore, for this issue, the precautionary measures regarding increase in unidentified leakage rate, periodic visual inspection of the affected penetration and the employment of diagnostic techniques to assure the absence cf a leak in the affected penetration are discontinued.
In conclusion, we believe that IC piping, valve and penetration piping replacement has resulted in a net improvement to safety and resolves the open issues as discussed above.
Ver trul)yours, u
J. C. DeVine, Jr.
Vice President and Director Technical functions J00/PFC/amk cc: Administrator, Region 1 NRC Resident Inspector NRC Project Manager - Oyster Creek l
.