ML021640649
| ML021640649 | |
| Person / Time | |
|---|---|
| Site: | Oyster Creek |
| Issue date: | 06/03/2002 |
| From: | Gallagher M AmerGen Energy Co |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| 2130-02-20148 | |
| Download: ML021640649 (4) | |
Text
AmerGenM AmerGen Energy Company, LLC www.exeioncorp.com An Exelon/British Energy Company 200 Exelon Way Suite 345 Kennett Square, PA 19348 10 CFR 50.55a June 3, 2002 2130-02-20148 U. S. Nuclear Regulatory Commission Attn: Document Control Desk Washington DC 20555
Subject:
Oyster Creek Generating Station Docket No. 50-219 ASME Section XI Relief Request R17, Revision 1 Response to Request for Additional Information
Reference:
AmerGen letter 2130-01-20195 dated September 14, 2001, "ASME Section XI Relief Request R17, Revision 1" The enclosure to this letter provides a response to a request for additional information concerning the referenced AmerGen Energy Company, LLC (AmerGen) letter. Proposed responses to the questions were discussed during a May 15, 2002 telephone conference with the NRC staff. The referenced relief request pertains to examination coverage for reactor vessel shell axial welds.
Should you have any questions or require any additional information please contact Mr. Paul F.
Czaya at 610-765-5952.
Sincerely, 40/k"PI-AL Michael P. Gallagher Director - Licensing, Mid-Atlantic Regional Operating Group
Enclosure:
ASME Section 11 Code Request R17, Revision 1 Response to Request for Additional Information c: H. J. Miller, Administrator, USNRC Region I R. J. Summers, USNRC Senior Resident Inspector, Oyster Creek Peter S. Tam, USNRC Senior Project Manager, Oyster Creek (Acting)
File No. 01042
/,
Enclosure Response to Request for Additional Information Relief Request R17, Revision 1 Request for Relief from Achieving More Than 90 % of the Examination Volume of Certain Reactor Pressure Vessel Axial Shell Welds
Oyster Creek Generating Station 2130-02-20148 Relief Request R17, Revision 1 Response to Request for Additional Information Page El of 2 NRC Question 1 Were your calculations based on 114 degrees F or 70 degrees F mean RTndt?
Response
The Oyster Creek (OC) evaluation uses OC-specific information together with the methodology from Boiling Water Reactor Vessel and Internals Project (BWRVIP) Report, "BWR Reactor Pressure Vessel Shell Weld Inspection Recommendations (BWRVIP-05)." The OC data includes weld chemistry information and reactor pressure vessel (RPV) dimensions. In the evaluation, a mean RTndt of approximately 60 degrees F was used.
NRC Question 2 Why is your Vessel Failure Probability six times an order of magnitude lower than the BWR fleet?
Response
The failure probabilities are lower for two primary reasons:
a)
OC-specific weld chemistry values were used in the evaluation (Cu = 0.21, Ni = 0.07, initial RTndt = -8'F). These values are significantly lower than the bounding values used in the BWRVIP-05 calculations. This difference has a significant impact on the probability of failure. Note also that, based on Structural Integrity Associates' earlier materials evaluation, the use of -50'F for initial RTndt could have been used. Instead, for conservatism, the combination of RTndt = -8°F and the OC-specific Cu and Ni values were used.
b)
The failure probabilities in BWRVIP-05 were determined using bounding values for weld chemistry and RPV geometry. The BWRVIP-05 analysis used a RPV thickness of 5.25 inches and a diameter of 225.2 inches. This compares with a thickness of over 7 inches and a diameter of 213 inches for the OC vessel. These differences result in a significant reduction in the hoop stress compared to the BWRVIP-05 evaluation, which significantly reduces the failure probability.
Oyster Creek Generating Station 2130-02-20148 Relief Request R17, Revision 1 Response to Request for Additional Information Page E2 of 2 NRC Question 3 What are your values for Conditional Failure Probability and Low Temperature Overpressure (LTOP) Frequency?
Response
The conditional failure probability is 2.5 x 10-9 per year. The LTOP frequency is 1 x 10-3 per year. This results in a total probability of failure of 2.5 x 10-12 per year.