ML17250B362
| ML17250B362 | |
| Person / Time | |
|---|---|
| Site: | Oyster Creek |
| Issue date: | 07/10/1990 |
| From: | Dromerick A Office of Nuclear Reactor Regulation |
| To: | Fitzpatrick E GENERAL PUBLIC UTILITIES CORP. |
| References | |
| TAC-75064, NUDOCS 9007160080 | |
| Download: ML17250B362 (5) | |
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Docket No. 50-219 UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D. C. 20555 July 10, 1990 Mr. E. E. Fitzpatrick Vice President and Director Oyster Creek Nuclear Generating Station P.O.
Box 388 Forked River, New Jersey 08731
Dear Mr. Fitzpatrick:
SUBJECT:
REVIEW OF OYSTER CREEK DRYWELL CONTAINMENT STRUCTURAL INTEGRITY (TAC No. 75064)
References:
1.
GPU Nuclear "Safety Evaluation on Steel Shell Plate Thickness Reduction" SE No. 00243-002, Rev. 4, Dated February 16, 1990 2.
Letter to NRC from J.
C. Devine of GPU Nuclear, Dated April 11, 1990 In February 1990 GPU Nuclear Corporation (GPUN), the licensee of the Oyster Creek Nuclear Generating Station informed NRC staff that based on UT measurements made in February there is evidence of possible ongoing corrosion at elevation 50' 2", which is above the sand bed region, at a rate greater than previously estimated.
As a result GPUN projected that the minimum thickness of the drywell shell will be reached in August of 1991 instead of in June 1992 as previously projected.
In addition the licensee has found the cathodic protection system (CPS) is less effective than expected.
In view of these findings the staff was concerned with the continuous deterioration of the drywell shell and its effect on the structural integrity of the drywell.
On March 8, a conference call between GPUN representatives and NRC staff was held.
The staff requested GPUN to submit a plan for short and long term actions to address the degraded condition of the drywell.
In response to the staff's request GPUN submitted Reference 2 which is summarized as follows.
(A) During the 12 UJ outage (March 26 through April 3, 1990),
GPUN conducted a
more extensive examination than than performed in February 1990.
It consisted of inspecting areas in the sand bed and at elevation 50' 2" and additional areas in these same regions previously found to exhibit lower corrosion rates, and areas in the upper cyclinder at elevation 8 7' 5".
In addition to UT measurements, a 2" diameter core plug was taken from drywell bay 13A in the sand bed together with the removal of a sand sample.
From the evaluation of ORQ00219 pDR 'DOCK p
P
Mr. E.
E. Fitzpatrick July 10, 1990 the UT measurements taken in the UJ outage, GPUN found that the safe operation of Oyster Creek through August 1991 can be assured as indicated in Reference 1
is still valid.
(B)
GPUN has formulated a work plan which consists of the following elements:
(1)
Au mented Data Ac uisition - Measurements will be made at locations not yet inspecte 1n or er to augment the data acquired as a measure to provide high statistical confidence that the inspection program instituted does in fact characterize the entire drywell.
(2) Corrosion Miti ation - The existing cathodic protection system is being eva uate or >ts effectiveness and for possible enhancement.
Other methods of mitigation are under consideration.
Measures to prevent or retard intrusion of water into the gap and sand bed are being taken.
(3) Structural Anal sis - Use of state-of-the-art techniques for modelling and analyzing t e vessel is being considered in conjunction with the use of the actual material properties.
(4) Dr well Modification/Re air - A study has been made for various options suc as se ecte p a e replacement, doubled plates, weld overlay or stiffeners for structural repair in the sand bed region and other areas.
Factors such as constructabi lity and radiation exposure are to be taken into consideration.
A preferred repair option will be selected before the 13R outage, and steps will be taken to be ready for implementing that option if and when it is required.
In accordance with GPUN, the effort outlined above under (A) is to confirm safe operation of Oyster Creek through the 13R outage until August 1991 as indicated in Reference 1, and the effort under (B) (1), (2) and (3) is to establish the basis for continued operation until the 14R outage.
The effort in (B)(4) above for longer term is formulated as a repair contingency plan.
From the information provided by GPUN under (A) above it can be stated with reasonable confidence that the Oyster Creek drywell minimum thickness will not be violated until at least August 1991 as indicated in Reference 1.
However the staff has some reservations on GPUN's use of the effort in (B) (1), (2) and (3) as a basis for continued operation until the 14R outage, especially GPUN's intention to use strength values of the drywell steel in the certified material test reports (CMTRS).
GPUN's rationale for such an approach is that in the evaluation of the cylinder portion (EL 8 7' 5")
GPUN used the allowable stress derived from CMTRs with the approval of NRC.
However, from an AISI survey of test results for thousands of individual product samples, it has been found that strength levels vary as much as 20K from the CMTR test values.
Therefore it is the staff's position that minimum specified strength values (e.g, ASME Code minimum
Mr.
E.
E. Fitzpatrick July 10, 1990 strength values) should be used as the basis for allowable stresses in the stress re-evaluation of degraded components.
Consequently GPUN cannot predicate drywell integrity on CMTR values.
We believe that plans should be made for the implementation of the drywell repair by August 1991 not relying on favorable results of the effort in (B)(1),
(2) and (3) to justify continued operation until the 14R outage.
If the reanalysis effort includes considering changes to the design basis of the
- plant, a license amendment will be required.
At the same time GPUN should continue the inspection as presently instituted.
We will arrange
-a meeting with your staff during late August or early September at our Rockville office to hear the status of your work plan and discuss the NRC staff's concerns noted in this letter.
Sincerely, Original signed by cc:
See next page Alexander W. Dromerick, Senior Project Manager Project Directorate I-4 Division of Reactor Projects - I/II Office of Nuclear Reactor Regulation DISTRIBUTION Docket=file--
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Mr. E.
E. Fitzpatrick Oyster Creek Nuclear Generating Station Oyster Creek Nuclear Generating Station CC:
Ernest L. Blake, Jr.
Shaw, Pittman, Potts and Trowbridge 2300 N Street, NW Washington, D.C.
20037 J.B. Liberman, Esquire Bishop, Liberman, Cook, et al.
1155 Avenue of the Americas New York, New York 10036 Regional Administrator, Region I U.S. Nuclear Regulatory Commission 475 Allendale Road King of Prussia, Pennsylvania 19406 BWR Licensing Manager GPU Nuclear Corporation 1 Upper Pond Road Parsippany, New Jersey 07054 Mayor Lacey Township 818 West Lacey Road Forked River, New Jersey 08731 Licensing Manager Oyster Creek Nuclear Generating Station Mail Stop:
Site Emergency Bldg.
P. 0.
Box 388 Forked River, New Jersey, 08731 Resident Inspector c/o U.S.
NRC Post Office Box 445 Forked River, New Jersey 08731 Commissioner New Jersey Department of Energy 101 Commerce Street
- Newark, New Jersey 07102 Kent Tosch, Chief New Jersey Department of Environmental Protection Bureau of Nuclear Engineering CN 415
- Trenton, New Jersey 08625