[Federal Register Volume 62, Number 187 (Friday, September 26, 1997)]
[Notices]
[Pages 50630-50632]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 97-25631]


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NUCLEAR REGULATORY COMMISSION

Docket No. 50-390


Tennessee Valley Authority; Watts Bar Nuclear Plant, 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 for amendment to Facility Operating License No. NPF-90, 
issued to Tennessee Valley Authority, (TVA), for operation of the Watts 
Bar Nuclear Plant (WBN), Unit 1, located in Rhea County, Tennessee.

Environmental Assessment

Identification of Proposed Action

    The proposed action would allow the licensee to utilize the 
American Society of Mechanical Engineers Boiler and Pressure Vessel 
Code (ASME Code) Case N-514, ``Low Temperature Overpressure 
Protection'' to determine its low temperature overpressure protection 
(LTOP) setpoints and is in accordance with the licensee's application 
for exemption dated June 20, 1997. The proposed action requests an 
exemption from certain requirements of 10 CFR 50.60, ``Acceptance 
Criteria for Fracture Prevention Measures for Lightwater Nuclear Power 
Reactors for Normal Operation,'' to allow application of an alternate 
methodology to determine the LTOP setpoints for the Watts Bar Nuclear 
Plant.
    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 Watts Bar 
reactor vessel material.
    In determining the PORV setpoint for LTOP events, the licensee 
proposed the use of safety margins based on an

[[Page 50631]]

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.
    The proposed alternate to the methodology of Appendix G 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,'' which has 
been 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 philosophy used to develop Code Case N-514 guidelines is to 
ensure that the LTOP limits are still below the pressure/temperature 
(P/T) limits for normal operation, but 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 philosophy protects the pressure vessel from LTOP events, and 
still 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.

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. Appendix 
G of 10 CFR Part 50 defines 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 an LTOP system. The LTOP 
system includes pressure relieving devices in the form of power-
operated relief valves (PORVs) that are set at a pressure below the 
LTOP enabling temperature that would prevent the pressure in the 
reactor vessel from exceeding the P/T limits of 10 CFR Part 50, 
Appendix G. To prevent these valves from lifting as a result of normal 
operating pressure surges (e.g., reactor coolant pump (RCP) starting 
and shifting operating charging pumps) with the reactor coolant system 
in a solid water condition, the operating pressure must be maintained 
below the PORV setpoint.
    In addition, to prevent damage to RCP seals, the operator must 
maintain a minimum differential pressure across the RCP seals. Hence, 
the licensee must operate the plant in a pressure window that is 
defined as the difference between the minimum required pressure to 
start an RCP and the operating margin to prevent lifting of the PORVs 
due to normal operating pressure surges. 10 CFR Part 50, Appendix G, 
safety margin adds instrument uncertainty in the LTOP setpoint. The 
licensee's current LTOP analysis indicates that using this 10 CFR Part 
50, Appendix G, safety margin to determine the PORV setpoint would 
result in an operating window between the LTOP setpoint and the minimum 
pressure required for RCP seals which is significantly restricted when 
physical conditions such as PORV overshoot, RCP Delta Ps, and static 
head corrections are taken into account in setpoint determination. 
Operating with these limits could result in the lifting of the PORVs or 
damage to the RCP seals during normal operation. Using Code Case N-514 
would allow the licensee to recapture most of the operating margin that 
is lost by factoring in the instrument uncertainties in the 
determination of the LTOP setpoint. The net effect of using Code Case 
N-514 is that the setpoint will not change significantly with the next 
setpoint analysis. Therefore, the licensee proposed that in determining 
the setpoint for LTOP events for Watts Bar, the allowable pressure be 
determined using the safety margins developed in an alternate 
methodology in lieu of the safety margins required by 10 CFR Part 50, 
Appendix G. The alternate methodology is consistent with the ASME Code 
Case N-514. The content of this Code Case had been incorporated into 
Appendix G of Section XI of the ASME Code and published in the 1993 
Addenda to Section XI.
    An exemption from 10 CFR 50.60 is required to use the alternate 
methodology for calculating the maximum allowable pressure for LTOP 
considerations. By application dated June 20, 1997, the licensee 
requested an exemption from 10 CFR 50.60 to allow it to utilize the 
alternate methodology of Code Case N-514 to compute its LTOP setpoints.

Environmental Impacts of the Proposed Action

    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 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.
    Accordingly, the Commission concludes that there is no significant 
environmental impact associated with this action.

Alternatives to the Proposed Action

    Since the Commission has concluded there is no significant 
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.

[[Page 50632]]

Alternative Use of Resources

    This action does not involve the use of any resources not 
previously considered in the Final Environmental Statement, Supplement 
No 1, for WBN Units 1 and 2, dated April 1995.

Agencies and Persons Consulted

    In accordance with its stated policy, on August 21, 1997 the staff 
consulted with the Tennessee State official, Mr. J. Graves of the 
Division of Radiological Health, regarding the environmental impact of 
the proposed action. The State official had no comments.

Finding of No Significant Impact

    Based upon this 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 June 20, 1997, which is 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 Chattanooga-Hamilton County Library, 1001 
Broad Street, Chattanooga, Tennessee.

    Dated at Rockville, Maryland, this 22nd day of September 1997.

    For the Nuclear Regulatory Commission.
Frederick J. Hebdon,
Director, Project Directorate II-3, Division of Reactor Projects--I/II.
[FR Doc. 97-25631 Filed 9-25-97; 8:45 am]
BILLING CODE 7590-01-P