ML070660182
| ML070660182 | |
| Person / Time | |
|---|---|
| Site: | Oyster Creek |
| Issue date: | 03/16/2007 |
| From: | Catherine Haney Plant Licensing Branch III-2 |
| To: | Webster R Rutgers Environmental Law Clinic |
| Miller G, NRR/DORL, 415-2481 | |
| Shared Package | |
| ML070660192 | List: |
| References | |
| TAC MD4081, Y020070015 | |
| Download: ML070660182 (2) | |
Text
March 16, 2007 Mr. Richard Webster Attorney at Law Rutgers Environmental Law Clinic 123 Washington Street Newark, NJ 07102-3094
Dear Mr. Webster:
This letter responds to the concerns raised in your e-mail dated November 9, 2006, to Mr. Roy Fuhrmeister in the Nuclear Regulatory Commissions (NRCs) Region I Office. Your concerns involved the material condition of the containment drywell shell at the Oyster Creek Nuclear Generating Station (Oyster Creek) and the potential for corrosion of the containment drywell shell to compromise its ability to perform its design function. You stated that Preliminary Notification (PN) PN-I-06-012, dated November 11, 2006, did not assess whether restart of Oyster Creek was justified because the PN did not assess what area of the drywell shell was thinner than the American Society of Mechanical Engineers, Boiler and Pressure Vessel Codes (ASME Codes) required thickness of 0.736 inches. You indicated that the licensee must show that a total area thickness of 0.736 inches with a one square-foot area in each bay no thinner than 0.536 inches in order for the General Electric (GE) modeling to be bounding and that the NRC staff indicated at an October 3, 2006, Advisory Committee on Reactor Safeguards (ACRS) meeting that the total thinned area (per bay) was less than four square feet.
In your e-mail, you asked: (1) what was the NRCs assessment of the area in each bay that is thinner than 0.736 inches, (2) how was this assessment derived and what was the associated uncertainty, and (3) how can the NRC rely upon the GE modeling (arguing that the vessel is non-spherical, that the analysis does not account for asymmetric buckling, and that the analysis does not model multiple areas thinner than 0.736 inches in each bay)?
In reference to your comment regarding the NRC staff's statements during the October 3, 2006, ACRS meeting, it is important to note that the staffs discussion of a thinned area of less than four square feet referred to conservative assumptions in the Sandia National Laboratories (SNL) analysis to encompass possible degradation in bays 1 and 13 later published in January 2007 (Agencywide Documents Access and Management System accession number ML070120395). This confirmatory analysis was performed by SNL in support of the NRC staff's review of the Oyster Creek License Renewal Application and is not a part of the Oyster Creek licensing basis.
The GE analysis, which is the current licensing basis for the structural integrity of the drywell shell, conservatively assumed a uniform drywell shell thickness of 0.736 inches in the sandbed region. To account for actual plant conditions where local thinning of the drywell shell liner was observed, subsequent calculations were performed that showed that the Oyster Creek drywell shell has adequate margin against buckling in accordance with ASME Code assuming a one square-foot area thinner than 0.736 inches but thicker than 0.536 inches. Although the calculation was performed for one typical bay, the evaluation results would remain valid, should
R. Webster thinning occur in multiple bays, as long as the thinned zones are limited to a one square-foot area of a thickness not less than 0.536 inches. Additionally, a calculation was performed to show that the drywell shell had adequate margin against buckling assuming an area less than 2.5 inches in diameter (approximately 5 square inches) and thinner than 0.536 inches but thicker than 0.49 inches. These areas of the localized thinning were chosen to bound the observed plant conditions. These degraded conditions were evaluated and determined to meet ASME Code standards.
During the 2006 Oyster Creek refueling outage (RFO) 21, which took place from October 15 to November 11, 2006, AmerGen Energy Company, LLC (AmerGen) conducted measurements of the drywell shell liner thickness. The NRC staff observed AmerGens activities and evaluated the results as they became available. From the measurements taken during RFO 21, the NRC staff concluded that there was no evidence of significant reduction in the drywell shell thickness.
Given that the measurements taken during RFO 21 show that the condition of the drywell shell remains within the current licensing basis for Oyster Creek, the NRC staff found startup and operation of Oyster Creek to be acceptable for the upcoming operational cycle.
Recognizing that the buckling capacity of the drywell shell is sensitive to imperfections and non-linearity in geometry, the ASME Code reduces the allowable stresses by 79% when a structure is subjected to biaxial compression (e.g., external pressure). The NRC staff does not believe that the identified degradation at Oyster Creek invalidates this approach, thus the GE analysis bounds current plant conditions and is supportive of safe plant operation.
I trust this letter has been responsive to your request.
Sincerely,
/ra/
Catherine Haney, Director Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. 50-219 cc: See next page
R. Webster thinning occur in multiple bays, as long as the thinned zones are limited to a one square-foot area of a thickness not less than 0.536 inches. Additionally, a calculation was performed to show that the drywell shell had adequate margin against buckling assuming an area less than 2.5 inches in diameter (approximately 5 square inches) and thinner than 0.536 inches but thicker than 0.49 inches. These areas of the localized thinning were chosen to bound the observed plant conditions. These degraded conditions were evaluated and determined to meet ASME Code standards.
During the 2006 Oyster Creek refueling outage (RFO) 21, which took place from October 15 to November 11, 2006, AmerGen Energy Company, LLC (AmerGen) conducted measurements of the drywell shell liner thickness. The NRC staff observed AmerGens activities and evaluated the results as they became available. From the measurements taken during RFO 21, the NRC staff concluded that there was no evidence of significant reduction in the drywell shell thickness.
Given that the measurements taken during RFO 21 show that the condition of the drywell shell remains within the current licensing basis for Oyster Creek, the NRC staff found startup and operation of Oyster Creek to be acceptable for the upcoming operational cycle.
Recognizing that the buckling capacity of the drywell shell is sensitive to imperfections and non-linearity in geometry, the ASME Code reduces the allowable stresses by 79% when a structure is subjected to biaxial compression (e.g., external pressure). The NRC staff does not believe that the identified degradation at Oyster Creek invalidates this approach, thus the GE analysis bounds current plant conditions and is supportive of safe plant operation.
I trust this letter has been responsive to your request.
Sincerely,
/ra/
Catherine Haney, Director Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. 50-219 cc: See next page DISTRIBUTION: Yellow 020070015 PUBLIC LPL1-2 R/F RidsNrrPMGMiller RidsNrrDorlLpl1-2(HChernoff)
RidsOgcRp RidsAcrsAcnwMailCenter RidsRgn1MailCenter(GMatakas)
RidsNrrDpr RidsNrrAdro(BBoger)
RidsEdoMailCenter RidsOgcMailCenter RidsNrrOd(JDyer/MWeber)
RidsNrrPmas(RMitchell)
RidsOcaMailCenter KManoly RidsNrrPMDWilliams RidsNrrLAMOBrien RidsNrrDorl(CHaney/TMcGinty)
MYoung RidsNrrAdes(JGrobe)
RidsOpaMail RidsSecyMailCenter RidsNrrWpcMail (paper copy to MS O-5-A4)
Package Accession Number: ML070660192 Incoming Accession Number: ML070260177 Response Accession Number: ML070660182 OFFICE LPL1-2/PM LPL1-2/LA LPL1-2/BC DE/EMCB/BC RGN-1/DRP/BC NAME GEMiller REnnis for MOBrien HChernoff KManoly RBellamy SBarber for (via Phone)
DATE 3/16/07 3/15/07 3/15/07 3/15/07 3/15/07 OFFICE DLR/RLRA/PM OGC DORL/D NAME DAshley NDudley for MYoung CHaney (Tim McGinty for)
DATE 3/14/07 3/15/07 3/16/07 OFFICIAL RECORD COPY
Oyster Creek Nuclear Generating Station Site Vice President - Oyster Creek Nuclear Generating Station AmerGen Energy Company, LLC P.O. Box 388 Forked River, NJ 08731 Senior Vice President of Operations AmerGen Energy Company, LLC 200 Exelon Way, KSA 3-N Kennett Square, PA 19348 Kathryn M. Sutton, Esquire Morgan, Lewis, & Bockius LLP 1111 Pennsylvania Avenue, NW Washington, DC 20004 Kent Tosch, Chief New Jersey Department of Environmental Protection Bureau of Nuclear Engineering CN 415 Trenton, NJ 08625 Vice President - Licensing and Regulatory Affairs AmerGen Energy Company, LLC 4300 Winfield Road Warrenville, IL 60555 Regional Administrator, Region I U.S. Nuclear Regulatory Commission 475 Allendale Road King of Prussia, PA 19406-1415 Mayor of Lacey Township 818 West Lacey Road Forked River, NJ 08731 Senior Resident Inspector U.S. Nuclear Regulatory Commission P.O. Box 445 Forked River, NJ 08731 Director - Licensing and Regulatory Affairs AmerGen Energy Company, LLC Correspondence Control P.O. Box 160 Kennett Square, PA 19348 Manager Licensing - Oyster Creek Exelon Generation Company, LLC Correspondence Control P.O. Box 160 Kennett Square, PA 19348 Regulatory Assurance Manager Oyster Creek AmerGen Energy Company, LLC P.O. Box 388 Forked River, NJ 08731 Assistant General Counsel AmerGen Energy Company, LLC 200 Exelon Way Kennett Square, PA 19348 Ron Bellamy, Region I U.S. Nuclear Regulatory Commission 475 Allendale Road King of Prussia, PA 19406-1415 Correspondence Control Desk AmerGen Energy Company, LLC 200 Exelon Way, KSA 1--1 Kennett Square, PA 19348 Oyster Creek Nuclear Generating Station Plant Manager AmerGen Energy Company, LLC P.O. Box 388 Forked River, NJ 08731