[Federal Register Volume 69, Number 139 (Wednesday, July 21, 2004)]
[Notices]
[Pages 43633-43635]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 04-16532]


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NUCLEAR REGULATORY COMMISSION

[Docket Nos. 50-327 and 50-328]


Tennessee Valley Authority, Sequoyah Nuclear Plant, Unit Nos. 1 
and 2; Exemption

1.0 Background

    The Tennessee Valley Authority (TVA, the licensee) is the holder of 
Facility Operating License Nos. DPR-77 and DPR-79, which authorize 
operation of the Sequoyah Nuclear Plant (facility or SQN), Unit Nos. 1 
and 2, respectively. The licenses provide, 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 
Hamilton County, Tennessee.

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. TVA requested that 
they be able to use Westinghouse Report WCAP-15315, ``Reactor Vessel 
Closure Head/Vessel Flange Requirements Evaluation for Operating PWR 
[Pressurized-Water Reactor] and BWR [Boiling-Water Reactor] Plants'' in 
lieu of 10 CFR, Appendix G, Footnote 2 to Table 1.

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. Therefore, in determining 
the acceptability of the licensee's exemption request, the staff has 
performed the following regulatory, technical, and legal evaluations to 
satisfy the requirements of 10 CFR 50.12 for granting the exemption.

3.1 Regulatory Evaluation

    It is stated in 10 CFR part 50, Appendix G 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 SQN Units 1 
and 2 Technical Specifications (TSs) to implement a pressure-
temperature limits report (PTLR) for each unit, TVA requested in its 
submittal dated September 6, 2002, that the staff exempt SQN 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 initial technical basis for this exemption request was 
submitted on December 19, 2002. The requirements from which TVA 
requested that SQN 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.'' 
The proposed action is in accordance with the licensee's

[[Page 43634]]

application for exemption contained in its September 6, 2002, 
submittal, and is needed to support the TS amendments that are 
contained in the same submittal. The proposed amendments will revise 
the SQN Units 1 and 2 TSs to permit the implementation of a PTLR for 
each unit.
    TVA's final, complete technical basis for the requested exemption 
was submitted to the NRC by letters dated June 24, 2003, and December 
18, 2003. The licensee's June 24, 2003, letter included as an 
attachment Westinghouse report WCAP-15984-P, Revision 1, ``Reactor 
Closure Head/Vessel Flange Requirements Evaluation for SQN Units 1 and 
2.'' This revision of WCAP-15984 updated information provided in WCAP-
15984-P, Revision 0, which had been submitted to the staff on December 
19, 2002. The licensee's December 18, 2003, letter provided responses 
to specific questions raised by the NRC staff to clarify information in 
WCAP-15984-P, Revision 1.

3.2 Technical Evaluation

    WCAP-15984-P, Revision 1 included a fracture mechanics analysis of 
postulated flaws in SQN Units 1 and 2 RPV closure flange regions under 
boltup, 100 degrees Fahrenheit per hour ([deg]F/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 SQN Units 1 and 2 beltline materials. 
Westinghouse performed finite element modeling to calculate the 
stresses present at critical locations within the flange region and 
determined that the 100 [deg]F/hr heatup transient was the most severe 
condition with the upper head-to-flange weld being the most limiting 
location. With these stresses, Westinghouse calculated the applied 
stress intensity (KI applied) 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 90 percent of the 
thickness of the component wall. The KI applied values were 
calculated 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 KI applied 
values to ASME Code lower bound static crack initiation fracture 
toughness (KIC) values determined from the nil-ductility 
transition reference temperature (RTNDT) values for the SQN 
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 SQN 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-15984-P, Revision 1 and the 
analysis which 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 which used 
ASME Code lower bound crack arrest/dynamic test 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 which established the requirements in 10 CFR 
part 50, Appendix G was justified based on the more limited knowledge 
of RPV material behavior that was available in the early eighties. 
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 the licensees use of ASME Code Cases N-640 and N-641.
    The minimum KIC value given in ASME Code for a RPV 
steel, regardless of material RTNDT value or temperature, is 
33.2 ksi[radic]in. This value represents the ``lower shelf'' of the 
ASME Code KIC curve. Based on information in WCAP-15984-P, 
Revision 1 and the licensee's December 18, 2003, response to NRC staff 
questions, it is apparent that the KIapplied for any flaw up 
to \1/4\ of the wall thickness (\1/4\ T) at the limiting location 
(refer to WCAP-15984-P, Revision 1, Figure 4-2), would not exceed 33.2 
ksi[radic]in (including staff consideration of ASME Code structural 
factors) until between 1 and 2 hours into the 100[deg]F/hr heatup 
transient. The temperature at the tip of postulated flaws up to \1/4\ T 
size would be adequate at that point in time to ensure that the 
limiting SQN flange materials would exhibit fracture toughness 
properties in excess of ASME Code ``lower shelf'' behavior.
    Hence, the analysis provided in WCAP-15984-P, Revision 1 has 
demonstrated that, for the most limiting transient addressed by 10 CFR 
Part 50, Appendix G, the combination of factors which would have to 
exist (high stresses in the RPV flange region along with the metal of 
the flange region being at low temperature) cannot exist 
simultaneously, and the structural integrity of the SQN 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 
SQN 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 SQN 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.

3.3 Legal Basis for Exemption

    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. The staff accepts the 
licensee's determination that an exemption would be required to permit 
TVA to not meet those requirements related to the application of 
Footnote 2 to Table 1 of 10 CFR part 50, Appendix G. The staff examined 
the licensee's rationale to support the exemption request and agrees 
that based on the information provided in WCAP-15984-P, Revision 1 and 
TVA's December 18, 2003, letter, an acceptable technical basis has been 
established to exempt SQN Units 1 and 2 from requirements related to 
the application of Footnote 2 to Table 1 of 10 CFR part 50, Appendix G. 
The technical basis provided by TVA has established that an adequate 
margin of safety against brittle failure would continue to be 
maintained for SQN 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-

[[Page 43635]]

critical conditions and RPV hydrostatic and leak test conditions. 
Hence, the 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 requirements related to the 
application of Footnote 2 to Table 1 of 10 CFR part 50, Appendix G. 
Therefore, the staff concludes that requesting the exemption under the 
special circumstances of 10 CFR 50.12(a)(2)(ii) is appropriate, and 
should be granted to TVA 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 SQN 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 TVA an exemption from those 
requirements related to the application of Footnote 2 to Table 1 of 10 
CFR part 50, Appendix G, for SQN Units 1 and 2.
    Pursuant to 10 CFR 51.32, the Commission has determined that the 
granting of this exemption will not result in any significant effect on 
the quality of the human environment (69 FR 32372).
    This exemption is effective upon issuance.

    Dated in Rockville, Maryland, this 7th day of July, 2004.
    For the Nuclear Regulatory Commission.

Ledyard B. Marsh,
Director, Division of Licensing Project Management, Office of Nuclear 
Reactor Regulation.
[FR Doc. 04-16532 Filed 7-20-04; 8:45 am]
BILLING CODE 7590-01-P