[Federal Register Volume 65, Number 172 (Tuesday, September 5, 2000)]
[Notices]
[Pages 53769-53770]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 00-22648]


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NUCLEAR REGULATORY COMMISSION

[Docket Nos. 50-321 and 50-366]


In the Matter of Southern Nuclear Operating Company, Inc.; (Hatch 
Units 1 and 2)

Exemption

I

    The Southern Nuclear Operating Company, Inc. (the licensee) is the 
holder of Facility Operating License Nos. DPR-57 and NPF-5 which 
authorize operation of the Hatch, Units 1 and 2. The license provides, 
among other things, that the facility is subject to all rules, 
regulations, and orders of the U.S. Nuclear Regulatory Commission (the 
Commission) now or hereafter in effect.
    The facility consists of boiling water reactors (Units 1 and 2) 
located on the licensee's Hatch site in Georgia. This exemption refers 
to both units.

II

    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 appropriate requirements on * * 
* the pressure-temperature limits and minimum permissible temperature 
must be met for all conditions.'' Appendix G of 10 CFR Part 50 
specifies that the requirements for these limits are the American 
Society of Mechanical Engineers (ASME) Code, Section XI, Appendix G 
limits.
    To address provisions of amendments to the technical specifications 
(TS) P-T limits, the licensee requested in its submittal dated June 1, 
2000, that the staff exempt Hatch, Units 1 and 2 from application of 
specific requirements of 10 CFR Part 50, Section 50.60(a) and Appendix 
G and substitute use of ASME Code Cases N-588 and N-640. In addition to 
the primary function in permitting the postulation of a 
circumferentially-oriented flaw (in lieu of an axially-oriented flaw) 
for the evaluation of the circumferential welds in RPV P-T limit 
curves, Code Case N-588 also provides a new set of equations for 
calculating stress intensity factors due to pressure and thermal 
gradient for axial flaws. Although the licensee did not use the primary 
function of Code Case N-588, it employed the new set of equations for 
calculating stress intensity factors for axial flaws. Since these 
equations usually give lower stress intensity factors, using Code Case 
N-588 for establishing the P-T limits would be less conservative than 
the methodology currently endorsed by 10 CFR Part 50, Appendix G, and 
therefore, an exemption to apply the Code Case would be required by 10 
CFR 50.60. Code Case N-640 permits the use of an alternate reference 
fracture toughness (KIC fracture toughness curve instead of 
KIa fracture toughness curve) for reactor vessel materials 
in determining the P-T limits. Likewise, since the KIC 
fracture toughness curve shown in ASME Section XI, Appendix A, Figure 
A-2200-1 (the KIC fracture toughness curve) provides greater 
allowable fracture toughness than the corresponding KIa 
fracture toughness curve of ASME Section XI, Appendix G, Figure G-2210-
1 (the KIa fracture toughness curve), using Code Case N-640 
for establishing the P-T limits would be less conservative than the 
methodology currently endorsed by 10 CFR Part 50, Appendix G, and 
therefore, an exemption to apply the Code Case would also be required 
by 10 CFR 50.60.
    The proposed amendment will revise the P-T limits in the Technical 
Specifications for Hatch, Units 1 and 2 related to the heatup, 
cooldown, and inservice test limitations for the reactor coolant system 
(RCS) for a series of specified Effective Full Power Years (EFPYs) up 
to 54 EFPYs for both units.

[[Page 53770]]

Code Case N-588

    The licensee has proposed an exemption to allow use of ASME Code 
Case N-588 in conjunction with ASME Section XI, 10 CFR 50.60(a) and 10 
CFR Part 50, Appendix G to determine the P-T limits.
    The proposed amendments to revise the P-T limits in the TSs for 
both units rely in part on the requested exemption. Since the limiting 
beltline materials for both units are plates, the proposed P-T limits 
did not use the primary function of Code Case N-588, i.e., to postulate 
a circumferentially-oriented reference flaw as the limiting flaw in a 
RPV circumferential weld. However, the proposed P-T limits employed the 
new set of equations for calculating stress intensity factors for the 
postulated axial flaw.
    Postulating the Appendix G reference flaw (an axially-oriented 
flaw) in a circumferential weld is physically unrealistic and overly 
conservative because the length of the flaw is 1.5 times the vessel 
thickness, which is much longer than the width of the reactor vessel 
girth weld. Industry experience with the repair of weld indications 
found during preservice inspection and data taken from destructive 
examination of actual vessel welds confirms that all detected flaws are 
small, laminar in nature, and do not transverse the weld bead 
orientation. Therefore, any potential defects introduced during the 
fabrication process and not detected during subsequent nondestructive 
examinations would only be expected to be oriented in the direction of 
weld fabrication. For circumferential welds this indicates a postulated 
defect with a circumferential orientation. The above mentioned reasons 
are the bases for the staff to approve previous applications of Code 
Case N-588 from other licensees to their P-T limits with the 
circumferential weld as the limiting beltline material. These approvals 
also permit the use of the improved set of equations for calculating 
stress intensity factors due to pressure and thermal gradient for axial 
flaws to establish P-T limits to protect the RCS pressure boundary from 
failure during hydrostatic testing, heatup, and cooldown when the 
limiting beltline material is not a circumferential weld.
    Consistent with previous approvals for using Code Case N-588, the 
NRC staff concurs that relaxation of the ASME Section XI, Appendix G 
requirements by application of ASME Code Case N-588 is acceptable and 
would maintain, pursuant to 10 CFR50.12(a)(2)(ii), the underlying 
purpose of the ASME Code and the NRC regulations to ensure an 
acceptable margin of safety.

Code Case N-640 (formerly Code Case N-626)

    The licensee has proposed an exemption to allow use of ASME Code 
Case N-640 in conjunction with ASME Section XI, 10 CFR 50.60(a) and 10 
CFR Part 50, Appendix G to determine P-T limits.
    The proposed amendment to revise the P-T limits for Hatch, Units 1 
and 2 rely in part on the requested exemption. These revised P-T limits 
have been developed using the KIc fracture toughness curve, 
in lieu of the KIa fracture toughness curve, as the lower 
bound for fracture toughness.
    Use of the KIc curve in determining the lower bound 
fracture toughness in the development of P-T operating limits is more 
technically correct than the KIa curve since the rate of 
loading during a heatup or cooldown is slow and is more representative 
of a static condition than a dynamic condition. The KIc 
curve appropriately implements the use of static initiation fracture 
toughness behavior to evaluate the controlled heatup and cooldown 
process of a reactor vessel. The staff has required use of the initial 
conservatism of the KIa curve since 1974 when the curve was 
codified. This initial conservatism was necessary due to the limited 
knowledge of RPV materials. Since 1974, additional knowledge has been 
gained about RPV materials which demonstrates that the lower bound on 
fracture toughness provided by the KIa curve is well beyond 
the margin of safety required to protect the public health and safety 
from potential RPV failure. In addition, P-T curves based on the 
KIc curve will enhance overall plant safety by opening the 
P-T operating window with the greatest safety benefit in the region of 
low temperature operations.
    Consistent with previous approvals for using Code Case N-640, the 
NRC staff concurs that this increased knowledge permits relaxation of 
the ASME Section XI, Appendix G requirements by application of ASME 
Code Case N-640, while maintaining, pursuant to 10 CFR 50.12(a)(2)(ii), 
the underlying purpose of the ASME Code and the NRC regulations to 
ensure an acceptable margin of safety.

III

    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 exemptions would be required to approve 
the use of Code Cases N-588 and N-640. The staff examined the 
licensee's rationale to support the exemption requests and concurred 
that the use of the code cases would meet the underlying intent of 
these regulations. Based upon a consideration of the conservatism that 
is explicitly incorporated into the methodologies of 10 CFR Part 50, 
Appendix G; Appendix G of the Code; and RG 1.99, Revision 2 the staff 
concluded that application of the code cases as described would provide 
an adequate margin of safety against brittle failure of the RPV and 
that application of the specific requirements of 10 CFR Part 50, 
Section 50.60(a) and Appendix G is not necessary to achieve the 
underlying purpose of the rule. This is also consistent with the 
determination that the staff has reached for other licensees under 
similar conditions based on the same considerations. Therefore, the 
staff concludes that requesting exemption under the special 
circumstances of 10 CFR 50.12(a)(2)(ii) is appropriate and that the 
methodology of Code Cases N-588 and N-640 may be used to revise the P-T 
limits for Hatch, Units 1 and 2.

IV

    Accordingly, the Commission has determined that, pursuant to 10 CFR 
50.12(a), the exemption is authorized by law, will not endanger life or 
property or common defense and security, and is, otherwise, in the 
public interest. Therefore, the Commission hereby grants Southern 
Nuclear Operating Company, Inc. an exemption from the requirements of 
10 CFR Part 50, Section 50.60(a) and 10 CFR Part 50, Appendix G, for 
Hatch, 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 (65 FR 52140).
    This exemption is effective upon issuance.

    Dated at Rockville, Maryland, this 29th day of August 2000.

    For the Nuclear Regulatory Commission.
John A. Zwolinski,
Director, Division of Licensing Project Management, Office of Nuclear 
Reactor Regulation.
[FR Doc. 00-22648 Filed 9-1-00; 8:45 am]
BILLING CODE 7590-01-P