ML14183A581
| ML14183A581 | |
| Person / Time | |
|---|---|
| Site: | Robinson  |
| Issue date: | 09/19/1994 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML14183A580 | List: |
| References | |
| 92-01, 92-1, NUDOCS 9409220090 | |
| Download: ML14183A581 (4) | |
Text
- cR~ REGU4 1 UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION EQUIVALENT MARGINS EVALUATION ON UPPER SHELF ENERGY FOR H.B. ROBINSON, UNIT NO. 2 BELTLINE MATERIALS 1.0 REVIEW
SUMMARY
By letter dated June 20, 1994, the Carolina Power & Light Company (CP&L or the licensee) requested NRC review and approval of an upper shelf energy (USE) equivalent margins analysis (EMA) performed for the reactor vessel limiting beltline materials of the H. B. Robinson Steam Electric Plant, Unit No. 2 (HBR2). The required data and EMA were submitted by letters dated July 6, 1992; August 19, October 27, November 29, and December 21, 1993; and June 13, 1994. The licensee has confirmed the applicability of the Westinghouse Owners' Group (WOG) Report, WCAP-13587, Revision 1, to HBR2. Revision 1 of WCAP-13587 provided a bounding EMA for WOG plants and it has been previously reviewed and approved by the NRC.
The NRC has reviewed the above-referenced submittals and determined that the licensee used methodology, modeling procedures, and acceptance criteria that fall within the scope of Draft Regulatory Guide DG-1023, the American Society of Mechanical Engineers Boiler and Pressure Vessel Code (the ASME Code),
Section XI, Appendix K, and ASME Code Case N-512. The NRC has completed a review of the information available on the limiting beltline materials for upper shelf energy and the EMA. On the basis of our review, it has been determined that the margins of safety against fracture which exist for the HBR2 beltline materials are equivalent to those required by Appendix G of the ASME Code, and therefore, compliance with 10 CFR Part 50, Appendix G, has been demonstrated to the end of license (EOL).
2.0 INTRODUCTION
Following the submittal of the licensee's response to Generic Letter 92-01 regarding HRB2 (July 6, 1992) and the subsequent responses to NRC requests for additional information, it has been established that the USE values for two of the reactor pressure vessel (RPV) beltline materials will fall below 50 ft-lbs before the EOL and a third material will be at 50 ft-lbs at EOL:
Beltline I.D.
Material Initial USE EOL USE (ft-lbs.)
(ft-lbs.)
Upper Shell Plate W10201-1 A302 Gr A 54 42 Intermediate Shell Plate W10201-4 A302 Gr A 62 46 Upper Shell Plate W10201-3 A302 Gr A 62 50 ENCLOSURE 9409220090 940919 PDR ADOCK 05000261 P
-2 As described above, the licensee has provided an EMA of the HBR2 reactor vessel limiting beltline materials for NRC review and approval.
This analysis is intended to demonstrate, via fracture mechanics, the existence of margins of safety that are equivalent to those required by Appendix G of ASME Code Section III for the RPV beltline materials falling below the NRC screening criteria of 50 ft-lb USE during the operating life of the RPV as outlined in 10 CFR Part 50, Appendix G.
3.0 APPLICABLE REGULATORY REQUIREMENTS AND GUIDELINES The regulatory guidelines concerning upper shelf safety margins are contained in Appendix G of 10 CFR Part 50. The requirements state that the initial unirradiated USE at the start of vessel life shall be no less than 75 ft-lb and that the vessel must maintain a USE of no less than 50 ft-lb throughout its service life. If there is reason to believe that any beltline material might fall below the 50 ft-lb threshold prior to EOL, an analysis demonstrating the existence of "margins of safety against fracture equivalent to those required by Appendix G of the ASME Code," is required. This analysis is subject to the approval of the Director, Office of Nuclear Reactor Regulation.
The NRC has accepted guidelines for the performance of EMAs. These guidelines are contained in the ASME Code,Section XI, Appendix K, ASME Code Case N-512 and Draft Regulatory Guide DG-1023, "Evaluation of Reactor Pressure Vessels With Charpy Upper-Shelf Energy Less Than 50 Ft-Lb."
Draft Regulatory Guide DG-1023 has incorporated the criteria of ASME Code Case N-512 and provides supplemental information on material properties and transient selection.
Since a majority of licensees do not have fracture toughness information for their limiting beltline materials, Charpy V-Notch (CVN) data is typically used to estimate the fracture toughness. Regulatory Guide 1.99, Revision 2, provides a procedure for estimation of the decrease in CVN USE as a function of copper content and fluence. Further, NUREG/CR-5729 provides empirically derived models for predicting the material fracture toughness (J-R curves) from CVN data or chemical composition and fluence. The NUREG/CR-5729 models are applicable to the majority of RPV materials.
4.0 EVALUATION The NRC finds the EMA reported in WCAP-13587, Revision 1, to be applicable to the HRB2 limiting RPV beltline materials with the exception of the method used for determination of the fracture toughness (J-R curves, J te p J o.)
for the A302 material.
The WCAP-13587, Revision 1, analysis consi erel the6T C(T) J R curve data of NUREG CR/5265 to be a lower bound for a 50 ft-lb A302 plate.
The 6T data were adjusted for lower USE values by decreasing JmteriL by 3% per ft-lb of CVN energy. This rate of decrease corresponds to the rate determined from the Charpy model of NUREG/CR-5729. The NRC also considers the 6T A302 data of NUREG/CR-5265 to be a lower bound for A302 plate.
-3 However, the NRC finds the overall J-R Curve adjustment procedure reported in WCAP-13587, Revision 1, for A302 plate to be unacceptable for the following reasons:
(1) The percent decrease in Ju teria calculated to EOL for the limiting A302 material assumed that the material in NUREG/CR-5265 had an USE of 50 ft lb. However, the actual USE for the A302 material in NUREG/CR-5265 is 53 ft-lb. Therefore, the percent decrease in J t for the most limiting A302 plate in the HRB2 beltline (Upper"'lgfi Plate W10201-1, 42 ft-lbs USE) should be approximately 33% as opposed to the 24% reported in WCAP-13587, Revision 1.
(2) The Jmnter data were not temperature corrected. The WCAP-13587, Revision i analysis was performed using a temperature of 390.50F. The data from NUREG/CR-5265 were generated at a temperature of 180 0F. The NRC maintains that a temperature correction is necessary. One method that has been proposed for determining the decrease in J eriat with temperature for NUREG/CR-5265 material is contained in re erence 1.
Using the equation provided in this reference, the decrease in Jmaterial with temperature from 1800F to 390aF is approximately 34%.
Adjusting the analysis to account for the above yields a June
, value at 0.1 inches of crack extension (J01), which is significantly less tan that obtained in WCAP-13587, Revision 1. To meet the criteria of ASME Code Case N 512, Jmateriak must be greater than J l (the driving force for fracture).
The Jewie is calculated for a postu ated flaw in the vessel wall with loading conditions and safety factors which vary for normal operating, upset, emergency and faulted conditions (levels A, B, C and D).
In the NRC assessment of WCAP-13587, Revision 1, levels A and B were found to be controlling for WOG plants [Ref. 2].
To demonstrate "equivalent margins", the J lied must be less than or equal to the J eria at 0.1 inches of crack exTension and the dJ/daapLied must be less Ian the J-R curve slope (dJ/da) evaluated at Jappied materiaL*
In addition to the above considerations, the NRC also found that the WCAP-13587, Revision 1, analysis had conservatively compared the applied driving force for an axial flaw with the material resistance for the weak orientation which corresponds to the circumferential flaw (i.e., meeting the criteria under these conditions assures that the criteria will also be met when the values are compared as suggested by the Code Case.) A conference call [Ref. 3] with the Westinghouse Electric Corporation and the licensee confirmed that this conservative analysis was performed for all of the cases evaluated. The NRC considers this analysis to be overly conservative. In a letter to the NRC dated December 21, 1993, the licensee demonstrated that the appropriate comparison of the applied and material values shows that the Code Case N-512 criteria were met. The letter also addressed the USE adjustment and temperature correction concerns for A302 plate that were discussed previously.
The NRC has concluded that with the modifications contained in the letter to the NRC dated December 21, 1993, the EMA performed in WCAP-13587, Revision 1, demonstrates margins of safety against fracture for the HBR 2 limiting beltline materials that are equivalent to those required by the ASME Code,
-4 Appendix G. The licensee has, therefore, demonstrated compliance with the USE requirements of 10 CFR Part 50, Appendix G, to EOL.
5.0 CONCLUSION
The NRC, in its evaluation of the EMA submitted by the licensee for the RPV beltline materials of HBR2, concludes:
(1) The licensee has employed methodology consistent with the guidelines of the ASME Code,Section XI, Appendix K, ASME Code Case N-512 and DG-1023 which the NRC finds acceptable for analyses of this type.
(2) NRC concerns with the materials fracture resistance aspects of the EMA as originally performed in WCAP-13587, Revision 1, were adequately addressed in the licensee's letter to the NRC dated December 21, 1993.
(3) The EMA performed in WCAP-13587, Revision 1, with the modifications contained in the letter to the NRC dated December 21, 1993, demonstrates margins of safety against fracture for the HBR2 limiting beltline materials that are equivalent to those required by the ASME Code, Appendix G. The licensee has, therefore, demonstrated compliance with the USE requirements of 10 CFR Part 50, Appendix G to EOL.
6.0 REFERENCES
[1]
Memorandum, A.L. Hiser and S.N.M. Malik, USNRC to K.R. Wichman, USNRC, "J-R Curves for Low Toughness A302 B Plate," USNRC, September 9, 1993.
[2]
Letter from Wayne Hodges, USNRC to William Rasin (NUMARC), "Safety Assessment of Report WCAP-13587, Revision 1, "Reactor Vessel Upper Shelf Energy Bounding Evaluation for Westinghouse Pressurized Water Reactors,"
April 21, 1994.
[3]
Conference Call, NRC, Carolina Power & Light and Westinghouse Electric Corporation, December 13, 1993.
Principal Contributor: E. Hackett Dated:
September 19, 1994