NL-16-2513, Response to Follow-up Request for Information Regarding Reactor Pressure Vessel Threads-in-Flange Examination Requirement
| ML16328A374 | |
| Person / Time | |
|---|---|
| Site: | Vogtle, Farley  |
| Issue date: | 11/23/2016 |
| From: | Pierce C Southern Nuclear Operating Co |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| NL-16-2513 | |
| Download: ML16328A374 (6) | |
Text
~ Southern Nuclear NOV 2 3 2016 Docket Nos.: 50-348 50-424 50-425 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D. C. 20555-0001 Charles R. Pierce Regulatory Affairs Director Vogtle Electric Generating Plant-Units 1 & 2 Joseph M. Farley Nuclear Plant-Unit 1 40 lnvcmcs~ Center Parkway Post Oflicc Box I 295 Bimtingham. AI 352~2 205 992 7872 td 205 992 760 I fax crpi~rcc@southcmcu.cum NL-16-2513 Response to Follow-up Request for Information Regarding Reactor Pressure Vessel Threads-in-Flange Examination Requirement Ladies and Gentlemen:
By application dated August 4, 2016 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML16221A072), as supplemented by letter dated October 24, 2016 (ADAMS Accession No. ML16298A049} Southern Nuclear Operating Company (SNC) submitted Alternative VEGP-ISI-ALT-11, Version 2.0, for the Vogtle Electric Generating Plant, Units 1 and 2, and Alternative FNP-ISI-AL T-19, Version 2.0, for the Joseph M. Farley Nuclear Plant, Unit 1. These Alternatives propose to eliminate the reactor pressure vessel (RPV) threads-in-flange examination requirement as an alternative to certain requirements of Section XI of the American Society of Mechanical Engineers Boiler and Pressure Vessel Code for inservice inspection of RPV components.
By letter dated November 16, 2016, the Nuclear Regulatory Commission (NRC) staff requested additional information to complete its review. The Enclosure provides the SNC response.
This letter contains no NRC commitments. If you have any questions, please contact Ken McElroy at 205.992.7369.
RZ."fte:tted, C. R. Pierce Regulatory Affairs Director CRP/RMJ
Enclosure:
SNC Response to NRC Request for Additional Information
U.S. Nuclear Regulatory Commission NL-16-2513 Page2 cc:
Southern Nuclear Operating Company Mr. S. E. Kuczynski, Chairman, President & CEO Mr. D. G. Bost, Executive Vice President & Chief Nuclear Officer Ms. C. A. Gayheart, Vice President - Farley Mr. D. R. Madison, Vice President-Fleet Operations Mr. B. K. Taber, Vice President-Vogtle 1 & 2 Mr. M. D. Meier, Vice President-Regulatory Affairs Mr. B. J. Adams, Vice President-Engineering Ms. B. L. Taylor, Regulatory Affairs Manager-Farley Mr. D. D. Sutton, Regulatory Affairs Manager-Vogtle 1 & 2 RType: Farley=CFA04.054; Vogtle=CVC?OOO U.S. Nuclear Regulatorv Commission Ms. C. Haney, Regional Administrator Mr. S. A. Williams, NRR Project Manager-Farley Mr. E. T. Coffman, Senior Resident Inspector-Vogtle 1 & 2 Mr. P. K. Niebaum, Senior Resident Inspector-Farley Mr. R. E. Martin, NRR Project Manager-Vogtle 1 & 2
Vogtle Electric Generating Plant-Units 1 & 2 Joseph M. Farley Nuclear Plant-Unit 1 Response to Follow-up Request for Information Regarding Reactor Pressure Vessel Threads-in-Flange Examination Requirement Enclosure SNC Response to NRC Request for Additional Information
Enclosure to N L 2513 SNC Response to NRC Request for Additional Information Follow-up RAI-1 (Related to NRC RAI-5, Question 2a)
The licensee's response to the previous RAI-5, Question 2a, indicated that, "Thermal loads are applied as uniform surface convection on the inside surface only." This response did not clarify how the heatup transient was applied. Please provide: (a) the thermal boundary conditions for the top, bottom, and RPV flange outer surfaces to confirm that this part of modeling is appropriate, and (b) a revision of the response to this RAI regarding how the heatup transient was applied to the thermal model since the application of thermal loads was not answered clearly.
Revised Response Related to RAI-5, Question 2a:
Internal pressure is applied uniformly on the inside surface of the model, and an endcap load is applied to the bottom surface. Thermal loads are applied as uniform surface convection on the inside surface only, using a conservative surface heat transfer coefficient (HTC) of 10,000 Btu/hr/ft2, while the top, bottom, RPV outer, and circumferential symmetry planes surfaces are assumed adiabatic thermal boundary conditions. The figure below shows the applied temperature on the inside surface of the model (shown in RED), which was a linear ramp from 70°F to 600°F at rate of 1 00°F/hour using a HTC of 10,000 Btu/hr/ft2* No temperature or HTC was applied on the above mentioned other surfaces of the model.
Temperature was applied on the inside surface of the Follow-up RAI-2 (Related to NRC RAI-5, Question 3)
Regarding selection of heatup transient instead of cooldown transient in the FEM analysis, the licensee's response to NRC RAI-5, Question 3 states that, "Since heatup and cooldown have the same temperature change rate, in linear elastic analysis they will produce identical maximum and minimum stress range for crack growth calculation, despite an opposite time history." The above description of stresses is not consistent with the similar P-T limits E-1
Enclosure to NL-16-2513 SNC Response to NRC Request for Additional Information application (ignoring the crack growth part because it does not apply to the P-T limit application), of which the cooldown transient will create tensile stresses in the RPV inner wall and compressive stresses in the outer wall, and vice versa for the heatup transient. Please provide additional discussion on your response to NRC RAI-5, Question 3 to justify that heatup and cooldown transients will produce identical maximum and minimum stress ranges.
Revised Response Related to RAI-5, Question 3:
Since heatup and cooldown have the same temperature change rate, in linear elastic analysis they will produce identical maximum and minimum stress range for crack growth calculation, despite an opposite time history. This assumes a single material and no pressure loading.
For heatup, the RPV starts from a stress-free steady state of 70°F to a stress-free steady state of 600°F. For cooldown, the RPV starts from a stress-free steady state of 600°F to a stress-free steady state of 70°F. During the transients, heatup and cooldown produce maximum tensile and maximum compressive stresses at opposite time points of the transient history, and produce the same stress range (maximum stress minus minimum stress) at each node point. Therefore, only one transient needs to be analyzed, and the heatup transient was chosen. The combined number of cycles from heatup and cooldown were used in the subsequent fatigue crack growth calculation.
Follow-up RAI-3 (Related to NRC RAI-5, Question 4a)
The licensee's response to NRC RAI-5, Question 4a indicated that, "the FEM model for the applied K determination is the same as the FEM model for the stress determination." Please clarify how loads are applied to both the FEM model for the stress determination and the FEM model for the applied K determination.
Revised Response Related to RAI-5, Question 4a:
It is confirmed that the FEM model for the applied K determination is the same as the FEM model for the stress determination. The loads were applied on the two models using an identical approach. The purpose of performing the stress determination on the model without crack tip elements was to determine the appropriate location to insert the crack tip elements.
Once that location is identified, the analyses were repeated using the model with crack tip elements to determine the K results. For example:
Internal pressure was applied uniformly on the inside surface of the stress and crack tip elements models.
Convective heatup heat transfer load was applied on the inside surface of the stress and crack tip elements models to determine temperature. Then the temperature results were imported to the corresponding stress or crack tip elements models to determine the stress or K results.
Follow-up RAI-4 (Related to NRC RAI-5, Question 6)
The licensee's response to NRC RAI-5, Question 6 indicated that, the maximum calculated K at any crack depth is about 20 ksi"in. This requires a K1c of 20"10 = 3.2 ksi"in." The K1c of 3.2 ksi"in may be a misprint of 63.2 ksi"in. Please provide the operating temperature at the time when K is 20 ksi"in to justify that, "an AT NDT of up to 70°F will not affect the results."
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Enclosure to N L 2513 SNC Response to NRC Request for Additional Information Response Follow-up RAI-4:
The correct K1c to be used is 63.2 ksivin. Recognizing that only the heatup transient was used in the analysis as explained above, the temperature at the time and location where K = 20 ksivin is 528°F. This of course would be different in the case of the cooldown transient.
Nevertheless, the minimum temperature considering either of the two transients would be 70°F which is higher than the RT NDT of the flange regions of VEGP and FNP (the RT NoT for the flange region is 20°F for VEGP Unit 1, 1 0°F for VEGP Unit 2, and 60°F for FNP Units 1 and 2).
Hence, the acceptance criterion of IWB-3612 of ASME Code Section XI would be met at all temperatures.
E-3