Southern Nuclear Operating Company, Inc., Vogtle Electric Generating Plant, Units 1 and 2; Exemption, 16877-16879 [E5-1450]

Agencies

• NUCLEAR REGULATORY COMMISSION

[Federal Register Volume 70, Number 62 (Friday, April 1, 2005)]
[Notices]
[Pages 16877-16879]
From the Federal Register Online via the Government Printing Office [www.gpo.gov]
[FR Doc No: E5-1450]


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NUCLEAR REGULATORY COMMISSION

[Docket Nos. 50-424 and 50-425]


Southern Nuclear Operating Company, Inc., Vogtle Electric 
Generating Plant, Units 1 and 2; Exemption

1.0 Background

    Southern Nuclear Operating Company, Inc. (SNC, or the licensee) is 
the holder of Facility Operating License Nos. NPF-68 and NPF-81 that 
authorize operation of the Vogtle Electric Generating Plant, Units 1 
and 2 (Vogtle, Units 1 and 2). The license provides, among other 
things, that the facility is subject to all rules, regulations, and 
orders of the Nuclear Regulatory Commission (NRC, the Commission) now 
or hereafter in effect.
    The facility consists of two pressurized water reactors located in 
Burke County, Georgia.

2.0 Request/Action

    Title 10 of the Code of Federal Regulations (10 CFR) part 50, 
Appendix G requires that pressure-temperature (P-T) limits be 
established for reactor pressure vessels (RPVs) during normal operating 
and hydrostatic or leak rate testing conditions. Specifically, 10 CFR 
part 50, Appendix G states that ``[t]he minimum temperature 
requirements * * * pertain to the controlling material, which is either 
the material in the closure flange or the material in the beltline 
region with the highest reference temperature. * * * the minimum 
temperature requirements and the controlling material depend on the 
operating condition (i.e., hydrostatic pressure and leak tests, or 
normal operation including anticipated normal operational occurrences), 
the vessel pressure, whether fuel is in the vessel, and whether the 
core is critical. The metal temperature of the controlling material, in 
the region of the controlling material which has the least favorable 
combination of stress and temperature, must exceed the appropriate 
minimum temperature requirement for the condition and pressure of the 
vessel specified in Table 1 [of 10 CFR part 50, Appendix G].'' Footnote 
2 to Table 1 in 10 CFR Part 50, Appendix G specifies that RPV minimum 
temperature requirements related to RPV closure flange considerations 
shall be based on ``[t]he highest reference temperature of the material 
in the closure flange region that is highly stressed by bolt preload.''
    In order to address provisions of amendments to modify the Vogtle, 
Units 1 and 2 Technical Specifications to revise the pressure-
temperature limits report methodology for each unit, SNC requested in 
its submittal dated February 26, 2004, that the staff exempt Vogtle, 
Units 1 and 2 from the application of specific requirements of 10 CFR 
part 50, Appendix G, as they pertain to the establishment of minimum 
temperature requirements, for all modes of operation addressed by 10 
CFR part 50, Appendix G, based on the material properties of the 
material of the RPV closure flange region that is highly stressed by 
the bolt preload. The licensee's technical basis for this exemption 
request is contained in Enclosure 4 of its February 26, 2004, 
submittal: WCAP-16142-P, Revision 1, ``Reactor Vessel Closure Head/
Vessel Flange Requirements Evaluation for Vogtle Units 1 and 2,'' and a 
response to an NRC staff request for additional information contained 
in an SNC letter dated October 22, 2004. The requirements from which 
SNC requested that Vogtle, Units 1 and 2 be exempted shall be referred 
to, for the purpose of this exemption, as those requirements related to 
the application of footnote (2) to Table 1 of 10 CFR part 50, Appendix 
G.
    WCAP-16142-P, Revision 1 included a fracture mechanics analysis of

[[Page 16878]]

postulated flaws in the Vogtle, Units 1 and 2 RPV closure flange 
regions under boltup, 100 [deg]F per hour (/hr) heatup, 100 [deg]F/hr 
cooldown, and steady-state conditions, with the heatup and cooldown 
transients being modeled in accordance with what would be permissible 
using P-T limit curves based on the most limiting Vogtle, Units 1 and 2 
beltline materials. Westinghouse performed finite element analyses to 
calculate the stresses present at the flange region and determined two 
limiting locations: (1) The top head dome-to-torus weld at the end of 
the 100 [deg]F/hr heatup transient, and (2) the torus-to-flange weld at 
the boltup condition. With these stresses, Westinghouse calculated the 
applied stress intensity factor (Kapplied) for semi-elliptical, outside 
diameter initiated, surface breaking flaws with an aspect ratio (length 
vs. depth) of 6:1, and with depths ranging from 0 to 80 percent of the 
thickness of the component wall. The Kapplied values were calculated by 
using the Raju-Newman stress intensity factor influence coefficients 
for external surface cracks in cylindrical vessels and is in accordance 
with the American Society of Mechanical Engineers Boiler and Pressure 
Vessel Code (ASME Code) Section XI, Appendix G, Subparagraph G-2220 
requirements for the analysis of flange locations. Westinghouse then 
compared these K applied values to ASME Code lower bound plane strain 
fracture toughness (KIc) values determined from the nil-ductility 
transition reference temperature (RTNDT) values for the Vogtle, Units 1 
and 2 RPV closure flange materials. Westinghouse also provided an 
assessment of the potential for changes in the material RTNDT values 
for the Vogtle, Units 1 and 2 RPV closure flange materials due to 
thermal aging resulting from exposure to the RPV operating environment.
    The use of ASME Code KIc as the material property for the fracture 
mechanics analysis represents the most significant change between the 
analysis provided in WCAP-16142-P, Revision 1 and the analysis that was 
performed as the basis for establishing the minimum temperature 
requirements in 10 CFR part 50, Appendix G. The minimum temperature 
requirements related to footnote (2) to Table 1 of 10 CFR part 50, 
Appendix G were incorporated into the Code of Federal Regulations in 
the early 1980s and were based on analyses that used ASME Code lower 
bound crack arrest fracture toughness (KIA) as the parameter for 
characterizing a material's ability to resist crack initiation and 
propagation. The use of ASME Code KIA is always conservative with 
respect to the use of ASME Code KIC for fracture mechanics evaluations, 
and its use in the evaluations that established the requirements in 10 
CFR part 50, Appendix G was justified based on the limited knowledge of 
RPV material behavior that was available in the early 1980s. However, 
the use of ASME Code KIC, not ASME Code KIA, is consistent with the 
actual physical processes that would govern flaw initiation under 
conditions of normal RPV operation, including RPV heatup, cooldown, and 
hydrostatic and leak testing. Based on our current understanding of the 
behavior of RPV materials, the NRC staff has routinely approved 
licensees' utilization of ASME Code KIC as the basis for evaluating RPV 
beltline materials to demonstrate compliance with the intent of 10 CFR 
part 50, Appendix G through licensees' use of ASME Code Cases N-640 and 
N-641, which have been incorporated into Appendix G to Section XI of 
the 2001 Edition through the 2003 Addenda of the ASME Code endorsed in 
10 CFR 50.55a.
    Information in WCAP-16142-P, Revision 1 and the licensee's October 
22, 2004, response to NRC staff questions indicated that the resulting 
margin (KIC/Kapplied) from the fracture mechanics 
analysis is 3.19 for the boltup condition and 4.06 for the heatup 
condition, assuming that the crack depth is one tenth of the wall 
thickness (1/10t). The margins show that the boltup condition with 
lower Kapplied (about one half the Kapplied of 
the heatup condition) is more limiting because the low temperature 
associated with the boltup condition gives a much lower KIC 
value. Using these calculated margins and the Kapplied plot 
shown in WCAP Figures 4-1 and 4-2, the NRC staff found that the ASME 
Code Appendix G margin of 2 can be maintained for a flaw much deeper 
than 1/10t at these limiting locations.
    In summary, the analysis provided in WCAP-16142-P, Revision 1 has 
demonstrated that, for the most limiting transient addressed by 10 CFR 
Part 50, Appendix G, the combination of factors (high stresses in the 
RPV flange region along with low temperature at the metal of the flange 
region) cannot exist simultaneously, and the structural integrity of 
the Vogtle, Units 1 and 2 RPV closure flange materials will not be 
challenged by facility operation in accordance with P-T limit curves 
based consideration of Vogtle, Units 1 and 2 beltline materials. 
Therefore, the more conservative minimum temperature requirements 
related to footnote (2) to Table 1 of 10 CFR Part 50, Appendix G are 
not necessary to meet the underlying intent of 10 CFR Part 50, Appendix 
G, to protect the Vogtle, Units 1 and 2 RPVs from brittle failure 
during normal operation under both core critical and core non-critical 
conditions and RPV hydrostatic and leak test conditions.

3.0 Discussion

    Pursuant to 10 CFR 50.12, the Commission may, upon application by 
any interested person or upon its own initiative, grant exemptions from 
the requirements of 10 CFR Part 50 when (1) the exemptions are 
authorized by law, will not present an undue risk to public health or 
safety, and are consistent with the common defense and security; and 
(2) when special circumstances are present. These circumstances include 
the special circumstances where application of the regulation in the 
particular circumstances is not necessary to achieve the underlying 
purpose of the rule.
    The underlying purpose of 10 CFR Part 50, Appendix G, footnote (2) 
to Table 1 is to protect the integrity of the reactor coolant pressure 
boundary during hydrostatic pressure and leak tests, and during normal 
operations, including heatup, cooldown, and operational occurrences. 
This is accomplished through these regulations that, in part, specify 
the minimum temperature requirements in the closure flange region. The 
NRC staff accepts the licensee's determination that an exemption would 
be required to permit SNC to not meet those requirements related to the 
application of footnote (2) to Table 1 of 10 CFR Part 50, Appendix G. 
The NRC staff examined the licensee's rationale to support the 
exemption request. Based on a consideration of the information provided 
in WCAP-16142-P, Revision 1 and SNC's October 22, 2004 letter, an 
acceptable technical basis has been established to exempt Vogtle, Units 
1 and 2 from requirements related to footnote (2) to Table 1 of 10 CFR 
Part 50, Appendix G. The technical basis provided by SNC has 
established that an adequate margin of safety against brittle failure 
would continue to be maintained for the Vogtle, Units 1 and 2 RPVs 
without the application of those requirements related to the 
application of footnote (2) to Table 1 of 10 CFR Part 50, Appendix G, 
for normal operation under both core critical and core non-critical 
conditions and RPV hydrostatic and leak test conditions.
    Therefore, the NRC staff concludes that, pursuant to 10 CFR 
50.12(a)(2)(ii), the underlying purpose of 10 CFR part 50, Appendix G 
will be achieved without the application of those

[[Page 16879]]

requirements related to the application of footnote (2) to Table 1 of 
10 CFR part 50, Appendix G, and the proposed exemption should be 
granted to SNC such that those requirements related to the application 
of footnote (2) to Table 1 of 10 CFR part 50, Appendix G need not be 
applied to Vogtle, Units 1 and 2.

4.0 Conclusion

    Accordingly, the Commission has determined that, pursuant to 10 CFR 
50.12(a), the exemption is authorized by law, will not present an undue 
risk to the public health and safety, and is consistent with the common 
defense and security. Also, special circumstances are present. 
Therefore, the Commission hereby grants SNC an exemption from the 
requirements 10 CFR Part 50, Appendix G, Table 1, footnote (2), for 
Vogtle, Units 1 and 2.
    Pursuant to 10 CFR 51.32, the Commission has determined that the 
granting of this exemption will not have a significant effect on the 
quality of the human environment (70 FR 13215).
    This exemption is effective upon issuance.

    Dated at Rockville, Maryland, this 24th day of March 2005.

    For the Nuclear Regulatory Commission
Ledyard B. Marsh,
Director, Division of Licensing Project Management, Office of Nuclear 
Reactor Regulation.
[FR Doc. E5-1450 Filed 3-31-05; 8:45 am]
BILLING CODE 7590-01-P