[Federal Register Volume 64, Number 59 (Monday, March 29, 1999)]
[Notices]
[Pages 14950-14951]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 99-7598]
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NUCLEAR REGULATORY COMMISSION
[Docket Nos. 50-269, 50-270, and 50-287]
Duke Energy Corporation; Oconee Nuclear Station, Units 1, 2, and
3 Environmental Assessment and Finding of No Significant Impact
The U.S. Nuclear Regulatory Commission (the Commission) is
considering issuance of an exemption from the requirements of Title 10
of the Code of Federal Regulations (10 CFR) Part 50, Section 50.60 and
Appendix G to the Duke Energy Corporation (the licensee) for operation
of the Oconee Nuclear Station, Units 1, 2, and 3, located in Oconee
County, South Carolina.
Environmental Assessment
Identification of the Proposed Action
The proposed action would exempt the licensee from the provisions
in 10 CFR Part 50, Section 50.60 and Appendix G. The NRC has
established requirements in 10 CFR Part 50 to protect the integrity of
the reactor coolant pressure boundary (RCPB) in nuclear power plants.
As part of these requirements, 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 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.
As a result, to approve its amendments to the TS P-T limit curves,
the licensee requested in its submittal dated October 15, 1998, that
the staff exempt Oconee Units 1, 2, and 3 from the application of
specific requirements of 10 CFR Part 50, Section 50.60 and Appendix G
and substitute use of the American Society of Mechanical Engineers
(ASME) Code Case N-514, ``Low Temperature Overpressure Protection
Section XI, Division 1.'' This would 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 pressure transient. The submittal was supplemented by
letters dated December 15, 1998, and January 11 and 21, 1999.
The Need for the Proposed Action
The licensee has noted in its submittal of October 15, 1998, that
the underlying purpose of the regulations is to establish limits to
protect the RPVs from brittle failure during low temperature operation
and that the LTOP provides a physical means of protecting these limits.
As a means of determining the LTOP enable temperature, the licensee
proposed to use the 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 pressure transient. The use of this Code
[[Page 14951]]
Case in lieu of 10 CFR Part 50, Appendix G requires approval of an
exemption.
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 percent allowed by 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 proposed 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 and that reactor vessel pressure would not exceed 110
percent of the P-T limit allowables, which 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
Regulatory Guide (RG) 1.99, Rev. 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, Rev. 2; (3) an assumed 1/4 thickness flaw with
a 6:1 aspect ratio; and (4) a limiting material toughness based on
dynamic crack arrest data.
The staff agrees that an exemption would be required to approve the
use of Code Case N-514 in lieu of 10 CFR Part 50, Appendix G. The staff
examined the licensee's rationale to support the exemption request and
agrees that the use of Code Case N-514 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, Rev.
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.
Environmental Impacts of the Proposed Action
The Commission has completed its evaluation of the proposed action
and concludes that exemption from the requirements of 10 CFR Part 50,
Section 50.60 and Appendix G, to permit the LTOP setpoints to be
established in accordance with the Code Case (e.g., at a level 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 Oconee Units 1, 2, and 3 reactor vessels. The proposed
action will not increase the probability or consequences of accidents,
no changes are being made in the types of any effluents that may be
released offsite, and there is no significant increase in occupational
or public radiation exposure. Therefore, there are no significant
radiological environmental impacts associated with the proposed action.
With regard to potential nonradiological environmental impacts, the
proposed action does not involve any historic sites. It does not affect
nonradiological plant effluents and has no other environmental impacts.
Therefore, there are no significant nonradiological impacts associated
with the proposed action.
Accordingly, the Commission concludes that there are no significant
environmental impacts associated with the proposed action.
Alternatives to the Proposed Action
As an alternative to the proposed action, the staff considered
denial of the proposed action (i.e., the ``no-action'' alternative).
Denial of the application would result in no change in current
environmental impacts. The environmental impacts of the proposed action
and the alternative action are similar.
Alternative Use of Resources
This action does not involve the use of resources not previously
considered in the ``Final Environmental Statement Related to the
Operation of the Oconee Nuclear Station, Units 1, 2, and 3,'' dated
March 1972.
Agencies and Persons Consulted
In accordance with its stated policy, on February 24, 1999, the
staff consulted with the South Carolina State official, Henry Porter of
the Division of Radioactive Waste Management, Bureau of Land and Waste
Management, Department of Health and Environmental Control, regarding
the environmental impact of the proposed action. The State official had
no comments.
Finding of No Significant Impact
On the basis of the environmental assessment, the Commission
concludes that the proposed action will not have a significant effect
on the quality of the human environment. Accordingly, the Commission
has determined not to prepare an environmental impact statement for the
proposed action.
For further details with respect to the proposed action, see the
licensee's letter dated October 15, 1998, as supplemented December 15,
1998, and January 11 and 21, 1999, which are available for public
inspection at the Commission's Public Document Room, The Gelman
Building, 2120 L Street, NW., Washington, DC, and at the local public
document room located at the Oconee County Library, 501 West South
Broad Street, Walhalla, South Carolina.
Dated at Rockville, Maryland, this 24th day of March 1999.
For the Nuclear Regulatory Commission.
Herbert N. Berkow,
Director, Project Directorate II-2, Division of Licensing Project
Management, Office of Nuclear Reactor Regulation.
[FR Doc. 99-7598 Filed 3-26-99; 8:45 am]
BILLING CODE 7590-01-P
