[Federal Register Volume 64, Number 206 (Tuesday, October 26, 1999)]
[Notices]
[Pages 57666-57668]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 99-27950]


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NUCLEAR REGULATORY COMMISSION

[Docket No. 50-395]


South Carolina Electric & Gas Company, V.C. Summer Nuclear 
Station, Unit 1; Exemption

I

    South Carolina Electric & Gas Company (the licensee) is the holder 
of Facility Operating License No. NPF-12, that authorizes operation of 
the V.C. Summer Nuclear Station. 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.

[[Page 57667]]

    The facility consists of a pressurized water reactor located on the 
V.C. Summer Nuclear Station site in Jenkinsville, South Carolina.

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.
    Pressurized water reactor licensees have installed cold 
overpressure mitigation systems/low temperature overpressure protection 
(LTOP) systems in order to protect the reactor coolant pressure 
boundary (RCPB) from being operated outside of the boundaries 
established by the P-T limit curves and to provide pressure relief of 
the RCPB during low temperature overpressurization events. The licensee 
is required by the V.C. Summer Nuclear Station Technical Specifications 
(TS) to update and submit the changes to its LTOP setpoints whenever 
the licensee is requesting approval for amendments to the P-T limit 
curves in the TS.
    Therefore, in order to address the provisions of amendments to the 
TS P-T limits and LTOP curves, the licensee requested in its submittal 
dated August 19, 1999, that the staff exempt V.C. Summer Nuclear 
Station from application of specific requirements of 10 CFR Part 50, 
Section 50.60(a) and 10 CFR Part 50, Appendix G, and substitute use of 
ASME Code Case N-640 as an alternate reference fracture toughness for 
reactor vessel materials for use in determining the P-T limits.
    The proposed action is in accordance with the licensee's 
application for exemption contained in a submittal dated August 19, 
1999, and is needed to support the TS amendment that is contained in 
the same submittal and is being processed separately. The proposed 
amendment would impact the P-T limits of TS 3/4.4 for V.C. Summer 
Nuclear Station related to the heatup, cooldown, and inservice test 
limitations for the Reactor Coolant System to a maximum of 32 Effective 
Full Power Years (EFPY). It will result in a revision to TS 3/4.4.9, 
Pressure/Temperature Limits, to reflect the revised P-T limits of the 
reactor vessel.

Code Case N-640

    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 that the P-T limits meet the 
underlying intent of the NRC regulations.
    The proposed amendment to revise the P-T limits for V.C. Summer 
Nuclear Station relies in part on the requested exemption. The ASME 
Code Case N-640 approach for calculating the allowable limit curves for 
various heatup and cooldown rates specifies that the total stress 
intensity factor, KI, for the combined thermal and pressure 
stresses at any time during heatup or cooldown cannot be greater than 
the reference stress intensity factor, KIC, for the metal 
temperature at that time. KIC is obtained from the reference 
fracture toughness curve, defined in Appendix G to Section Xl of the 
1996 ASME Code. The KIC curve is based on the lower bound of 
static critical KI values measured as a function of 
temperature on specimens of SA-533 Grade B Class 1, SA-508-2, and SA-
508-3 steels.
    Use of the KIc curve in determining the lower bound 
fracture toughness in the development of a P-T operating limits curve 
is more technically correct than the KIa curve. The 
KIc curve appropriately implements the use of static 
initiation fracture toughness behavior to evaluate the controlled heat-
up and cooldown process of a reactor vessel. The licensee has 
determined that the use of the initial conservatism of the 
KIa curve when the curve was codified in 1974 was justified. 
This initial conservatism was necessary due to the limited knowledge of 
reactor pressure vessel materials. Since 1974, additional knowledge has 
been gained about reactor pressure vessel materials, which demonstrates 
that the lower bound on fracture toughness provided by the 
KIIa curve is well beyond the margin of safety required to 
protect the public health and safety from potential reactor pressure 
vessel 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. The two primary 
safety benefits in opening the low temperature operating window are a 
reduction in the challenges to RCS power-operated relief valves and 
elimination of RCP impeller cavitation wear.
    Since the RCS P-T operating window is defined by the P-T operating 
and test limit curves developed in accordance with the ASME Section XI, 
Appendix G procedure, continued operation of Summer with these P-T 
curves without the relief provided by ASME Code Case N-640 would 
unnecessarily restrict the P-T operating window. This restriction 
requires, under certain low temperature conditions, that only one 
reactor coolant pump in a reactor coolant loop be operated. The 
licensee has found from experience that the effect of this restriction 
is undesirable degradation of reactor coolant pump impellers that 
results from cavitation sustained when either one pump or one pump in 
each loop is operating. Implementation of the proposed P-T curves as 
allowed by ASME Code Case N-640 does not significantly reduce the 
margin of safety. Thus, pursuant to 10 CFR 50.12(a)(2)(ii), the 
underlying purpose of the regulation will continue to be served.
    In summary, the ASME Section XI, Appendix G procedure was 
conservatively developed based on the level of knowledge existing in 
1974 concerning reactor pressure vessel materials and the estimated 
effects of operation. Since 1974, the level of knowledge about these 
topics has been greatly expanded. 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 an exemption would be required to approve 
the use of Code Case N-640. The staff examined the licensee's rationale 
to support the exemption request and concurred that the use of the Code 
case would also 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

[[Page 57668]]

the Code case as described would provide an adequate margin of safety 
against brittle failure of the RPVs. 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 the exemption under the special 
circumstances of 10 CFR 50.12(a)(2)(ii) is appropriate and that the 
methodology of Code Case N-640 may be used to revise the LTOP setpoints 
and P-T limits for the Summer reactor coolant system.

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 South Carolina 
Electric & Gas Company an exemption from the requirements of 10 CFR 
Part 50, Section 50.60(a) and 10 CFR Part 50, Appendix G, for the V.C. 
Summer Nuclear Station.
    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 (64 FR 56359).
    This exemption is effective upon issuance.

    Dated at Rockville, Maryland, this 20th day of October 1999.

    For the Nuclear Regulatory Commission.
John A. Zwolinski,
Director, Division of Licensing Project Management, Office of Nuclear 
Reactor Regulation.
[FR Doc. 99-27950 Filed 10-25-99; 8:45 am]
BILLING CODE 7590-01-P