[Federal Register Volume 62, Number 48 (Wednesday, March 12, 1997)]
[Notices]
[Pages 11482-11483]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 97-6342]
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NUCLEAR REGULATORY COMMISSION
[Docket No. 50-313]
Entergy Operations, Inc.; Arkansas Nuclear One, Unit 1
Environmental Assessment and Finding of No Significant Impact
The U.S. Nuclear Regulatory Commission (the Commission) is
considering issuance of an exemption from certain requirements of its
regulations to Facility Operating License No. DPR-51, issued to Entergy
Operations, Inc. (the licensee), for operation of Arkansas Nuclear One,
Unit 1 (ANO-1), located in Pope County, Arkansas.
Environmental Assessment
Identification of the Proposed Action
The proposed action would allow the licensee to utilize American
Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code
(Code) Case N-514, ``Low Temperature Overpressure Protection'' to
determine its low temperature overpressure protection (LTOP) setpoints.
By application dated November 26, 1996, the licensee requested an
exemption from certain requirements of 10 CFR 50.60, ``Acceptance
Criteria for Fracture Prevention Measures for Lightwater Nuclear Power
Reactors for Normal Operation.'' The exemption would allow application
of an alternate methodology to determine the LTOP setpoints for ANO-1.
The proposed alternate methodology is consistent with guidelines
developed by the ASME Working Group on Operating Plant Criteria (WGOPC)
to define pressure limits during LTOP events that avoid certain
unnecessary operational restrictions, provide adequate margins against
failure of the reactor pressure vessel, and reduce the potential for
unnecessary activation of pressure relieving devices used for LTOP.
These guidelines have been incorporated into Code Case N-514, ``Low
Temperature Overpressure Protection.'' Code Case N-514 has been
approved by the ASME Code Committee and incorporated into Appendix G of
Section XI of the ASME Code and published in the 1993 Addenda to
Section XI. However, 10 CFR 50.55a, ``Codes and Standards,'' and
Regulatory Guide 1.147, ``Inservice Inspection Code Case
Acceptability,'' have not been updated to reflect the acceptability of
Code Case N-514.
The Need for the Proposed Action
Pursuant to 10 CFR 50.60, all lightwater nuclear power reactors
must meet the fracture toughness requirements for the reactor coolant
pressure boundary as set forth in 10 CFR Part 50, Appendix G. 10 CFR
Part 50, Appendix G, defines pressure/temperature (P/T) limits during
any condition of normal operation including anticipated operational
occurrences and system hydrostatic tests, to which the pressure
boundary may be subjected over its service lifetime. It is specified in
10 CFR 50.60(b) that alternatives to the described requirements in 10
CFR Part 50, Appendix G, may be used when an exemption is granted by
the Commission under 10 CFR 50.12.
To prevent transients that would produce excursions exceeding the
10 CFR Part 50, Appendix G, P/T limits while the reactor is operating
at low temperatures, the licensee installed the LTOP system. The LTOP
system includes the electromatic relief valve (ERV) that is set to the
LTOP mode when reactor pressure and temperature are reduced. The ERV
prevents the pressure in the reactor vessel from exceeding the P/T
limits of 10 CFR Part 50, Appendix G. However, to prevent ERV from
lifting as a result of normal operating pressure surges, some margin is
needed between the normal operating pressure and the ERV setpoint.
To meet the 10 CFR Part 50, Appendix G P/T limits, the ERV would be
set to open at a pressure very close to the normal pressure inside the
reactor. With the ERV setpoint close to the normal operating pressure,
minor pressure perturbations that typically occur in the reactor could
cause the ERV to open periodically. This is undesirable from the safety
perspective because after every ERV opening there is some concern that
the ERV may not reclose. A stuck open ERV would continue to discharge
primary coolant and reduce rector pressure until the discharge pathway
was closed by operator action.
Code Case N-514 would permit a slightly higher pressure inside the
reactor during shutdown conditions. The ability to maintain a higher
pressure in the reactor would allow a higher ERV setpoint and the
likelihood for inadvertent opening of the ERV would be reduced.
Environmental Impacts of the Proposed Action
Appendix G of the ASME Code requires that the P/T limits be
calculated: (a) using a safety factor of two on the principal membrane
(pressure) stresses, (b) assuming a flaw at the surface with a depth of
one quarter (\1/4\) of the vessel wall thickness and a length of six
(6) times its depth, and (c) using a conservative fracture toughness
curve that is based on the lower bound of static, dynamic, and crack
arrest fracture toughness tests on material similar to the ANO-1
reactor vessel material.
Code Case N-514 guidelines are intended to ensure that the LTOP
limits are still below the pressure/temperature (P/T) limits for normal
operation, but to allow the pressure that may occur with activation of
pressure relieving devices to exceed the P/T limits, provided
acceptable margins are maintained during these events. This approach
protects the pressure vessel from LTOP events, and maintains the
Technical Specifications P/T limits applicable for normal heatup and
cooldown in accordance with 10 CFR Part 50, Appendix G and Sections III
and XI of the ASME Code.
In determining the ERV setpoint for LTOP events, the licensee
proposed the use of safety margins based on an alternate methodology
consistent with the proposed ASME Code Case N-514 guidelines. ASME Code
Case N-514 allows determination of the setpoint for LTOP events such
that the maximum pressure in the vessel will not exceed 110% of the P/T
limits of the existing ASME Appendix G. This results in a safety factor
of 1.8 on the principal membrane stresses. All other factors, including
assumed flaw size and fracture toughness, remain the same. Although
this methodology would reduce the safety factor on the principal
membrane stresses, use of the proposed criteria will provide adequate
margins of safety to the reactor vessel during LTOP transients.
Use of Code Case N-514 safety margins will reduce operational
challenges during low-pressure, low-temperature operations. In terms of
overall safety, the safety benefits desired
[[Page 11483]]
from simplified operations and the reduced potential for undesirable
opening of ERV will more than offset the reduction of the principal
membrane safety factor. Reduced operational challenges will reduce the
potential for undesirable impacts to the environment.
The change 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 the
allowable individual or cumulative occupational radiation exposure.
Accordingly, the Commission concludes that there are no significant
radiological environmental impacts associated with the proposed action.
With regard to potential nonradiological impacts, the proposed
action involves features located entirely within the restricted area as
defined in 10 CFR Part 20. It does not affect nonradiological plant
effluents and has no other environmental impact. Accordingly, the
Commission concludes that there are no significant nonradiological
environmental impacts associated with the proposed action.
Alternatives to the Proposed Action
Since the Commission has concluded there is no measurable
environmental impact associated with the proposed action, any
alternatives with equal or greater environmental impact need not be
evaluated. As an alternative to the proposed action, the staff
considered denial of the proposed action. 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 any resources not
previously considered in the Final Environmental Statement for ANO-1.
Agencies and Persons Consulted
In accordance with its stated policy, on January 28, 1996, the
staff consulted with the Arkansas State official, Mr. David Snellings,
Director of the Division of Radiation Control and Emergency Management,
regarding the environmental impact of the proposed action. The State
official had no comments.
Finding of No Significant Impact
Based upon 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 November 26, 1996, which is available for
public inspection at the Commission's Public Document Room, 2120 L
Street, NW., Washington, DC, and at the local public document room
located at the Tomlinson Library, Arkansas Tech University,
Russellville, AR 72801.
Dated at Rockville, Maryland, this 7th day of March 1997.
For the Nuclear Regulatory Commission.
George Kalman,
Senior Project Manager, Project Directorate VI-1, Division of Reactor
Projects III/IV, Office of Nuclear Reactor Regulation.
[FR Doc. 97-6342 Filed 3-11-97; 8:45 am]
BILLING CODE 7590-01-P
