[Federal Register Volume 64, Number 63 (Friday, April 2, 1999)]
[Notices]
[Pages 16005-16006]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 99-8163]
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NUCLEAR REGULATORY COMMISSION
[Docket Nos. 50-269, 50-270, and 50-287]
In the Matter of Duke Energy Corporation; (Oconee Nuclear
Station, Units 1, 2, and 3); Exemption
I
The Duke Energy Corporation (Duke/the licensee) is the holder of
Facility Operating License Nos. DPR-38, DPR-47, and DPR-55, that
authorize operation of the Oconee Nuclear Station, Units 1, 2, and 3
(Oconee), respectively. The licenses provide, among other things, that
the facilities are subject to all rules, regulations, and orders of the
U.S. Nuclear Regulatory Commission (the Commission) now or hereafter in
effect.
The facilities consist of pressurized water reactors located on
Duke's Oconee site in Seneca, Oconee County, 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.'' Pressurized water reactor licensees
have installed cold overpressure mitigation systems/low temperature
overpressure protection (LTOP) systems in order to protect the reactor
coolant pressure boundaries (RCPBs) from being operated outside of the
boundaries established by the P-T limit curves and to provide pressure
relief of the RCPBs during low temperature overpressurization events.
The licensee is required by the Oconee Units 1, 2, and 3 Technical
Specifications (TSs) 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 Oconee Units 1, 2, and 3 TSs.
In the submittal of October 15, 1998, the licensee requested that
the staff exempt Oconee Units 1, 2, and 3 from the application of
specific requirements of 10 CFR part 50, Sec. 50.60 and appendix G.
Specifically, the licensee proposed to use the American Society of
Mechanical Engineers (ASME) Code Case N-514 to permit setting the
pressure setpoint of the facility's LTOP such that the P-T limits
required by 10 CFR part 50, appendix G could be exceeded by 10 percent
during a low temperature overpressure transient.
The licensee noted that the underlying purpose of the subject
regulations is to establish limits to protect the RPVs from brittle
failure during low temperature operation and the LTOP provides a
physical means of protecting these limits.
The Reactor Coolant System P-T operating window at low temperatures
is defined by the LTOP setpoint. Implementation of an LTOP setpoint
without the additional margin of 10
[[Page 16006]]
percent allowed by the ASME Code Case N-514 would restrict the P-T
operating window and would potentially result in undesired actuation of
the LTOP system. This constitutes an unnecessary burden that can be
alleviated by the application of the Code Case and reduce the potential
for an undesired lift of the LTOP valve.
The licensee stated that establishing the LTOP pressure setpoints
in accordance with the provisions in Code Case N-514 would provide an
acceptable level of safety against overpressurization events of the
Oconee RPVs. The licensee stated that establishing the LTOP setpoints
in accordance with N-514 provisions such that the vessel pressure would
not exceed 110 percent of the P-T limit allowables would still provide
an acceptable level of safety and mitigate the potential for an
inadvertent actuation of the LTOP. The Code Case dictates that when the
LTOP system is enabled, the peak pressure resulting from an LTOP
design-basis transient will not exceed 110 percent of the pressure
limits established by the P-T limit curves for the plant, as required
by 10 CFR part 50, appendix G, and by appendix G to the Code. The Code
Case also requires that the LTOP system be enabled at a temperature of
200 deg.F or at a temperature value equivalent to the sum of the
limiting adjusted reference temperature (ART) + 50 deg.F, whichever is
greater. The staff has previously found for several other nuclear power
plants that Code Case N-514 provides an ``acceptable level of safety''
based on the amount of conservatism that has been explicitly
incorporated into the methodologies for generating P-T limit curves, as
prescribed in 10 CFR part 50, appendix G; appendix G to the Code; and
RG 1.99, Revision 2. The conservatism includes: (1) a safety factor of
2 on the pressure stresses; (2) a margin factor applied to the
calculation of ART values in accordance with the methodology of RG
1.99, Revision 2; (3) an assumed flaw of one-fourth of the vessel
section thickness from the inside wetted surface in the vessel beltline
region with a 6:1 aspect ratio; and (4) a limiting material toughness
based on dynamic crack arrest data. The staff has reviewed the proposed
application of this Code Case to Oconee Units 1, 2, and 3, and found it
to be acceptable.
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. As stated in 10 CFR
50.12(a)(2)(ii), special circumstances exist when application of the
regulation would not serve or is not necessary to achieve the
underlying purpose of the rule. The staff has determined that an
exemption would be required to approve the use of Code Case N-514. The
staff has further determined that special circumstances are present, in
that application of the regulation under these circumstances is not
necessary to achieve the underlying purpose of the rule and use of Code
Case N-514 would meet the underlying intent of the regulation. 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 permitting the LTOP setpoints to be established at the level
specified in the Code Case (e.g., less than or equal to 110 percent of
the limit defined by the P-T limit curves) 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-514 may be used to establish the LTOP
setpoints for the Oconee Units 1, 2, and 3 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 Duke an
exemption from the requested specific requirements of 10 CFR part 50,
Sec. 50.60 and appendix G, for Oconee Nuclear Station, Units 1, 2, and
3.
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 14950, dated March 29,
1999).
This exemption is effective upon issuance.
Dated at Rockville, Maryland, this 29th day of March 1999.
For the Nuclear Regulatory Commission.
Samuel J. Collins,
Director, Office of Nuclear Reactor Regulation.
[FR Doc. 99-8163 Filed 4-1-99; 8:45 am]
BILLING CODE 7590-01-P
