[Federal Register Volume 62, Number 22 (Monday, February 3, 1997)]
[Notices]
[Pages 5061-5062]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 97-2537]


-----------------------------------------------------------------------

NUCLEAR REGULATORY COMMISSION
[Docket Nos. 50-266 and 50-301]


Wisconsin Electric Power Company (Point Beach Nuclear Plant, Unit 
Nos. 1 and 2); Exemption

I

    Wisconsin Electric Power Company (the licensee) is the holder of 
Facility Operating License Nos. DRP-24 and DRP-27, which authorize 
operation of the Point Beach Nuclear Plant, Units 1 and 2, 
respectively. The licenses provide, among other things, that the 
licensee is subject to all rules, regulations, and orders of the 
Commission now or hereafter in effect.
    The facility consists of two pressurized-water reactors located at 
the licensee's site in Manitowoc County, Wisconsin.

II.

    In its letter dated July 1, 1996, as supplemented November 18, 
1996, the licensee requested an exemption from the Commission's 
regulations. Title 10 of the Code of Federal Regulations, Part 50, 
Section 60 (10 CFR 50.60), ``Acceptance Criteria for Fracture 
Prevention Measures for Lightwater Nuclear Power Reactors for Normal 
Operation,'' states that all lightwater nuclear power reactors must 
meet the fracture toughness and material surveillance program 
requirements for the reactor coolant pressure boundary as set forth in 
Appendices G and H to 10 CFR Part 50. Appendix G to 10 CFR Part 50 
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 Appendices G and H 
to 10 CFR Part 50 may be used when an exemption is granted by the 
Commission under 10 CFR 50.12.
    To prevent low-temperature overpressure transients that would 
produce pressure excursions exceeding the P/T limits of Appendix G to 
10 CFR Part 50 while the reactor is operating at low temperatures, the 
licensee installed a low-temperature overpressure protection (LTOP) 
system. The system includes pressure-relieving devices called power-
operated relief valves (PORVs). The PORVs are set at a pressure low 
enough so that if an LTOP transient occurred, the mitigation system 
would prevent the pressure in the reactor vessel from exceeding the P/T 
limits of Appendix G to 10 CFR Part 50. To prevent the PORVs from 
lifting as a result of normal operating pressure surges (e.g., reactor 
coolant pumps starting or stopping) with the reactor coolant system in 
a water solid condition, the operating pressure must be maintained 
below the PORV setpoint. The maximum LTOP setpoint of 425 psig was 
approved May 20, 1980, with the issuance of Amendments 45 (DPR-24) and 
60 (DPR-27) to the Point Beach operating licenses. This LTOP system 
received pressure input from the sensing taps located in the reactor 
coolant system hot leg and at the pressurizer. Subsequent evaluation 
determined that the methodology used to determine the LTOP system 
setpoint did not account for the differential pressure across the core 
during reactor coolant pump operation. A recent Westinghouse 
calculation (NSAL 93-005) indicated that with both reactor coolant 
pumps operating, the pressure at core midplane may be as much as 63 
psig higher than at the pressure sensing points. To account for this 
differential pressure, which could cause the reactor vessel midplane 
pressure to exceed the ASME Section XI, Appendix G limits, the licensee 
implemented an administrative requirement in 1993 allowing only one 
reactor coolant pump in operation when reactor coolant temperature is 
below 160 oF. Plant operation with this restriction places an

[[Page 5062]]

unnecessary burden on plant operators to ensure safety limits are 
maintained.
    The licensee has requested the use of the American Society of 
Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code) Case 
N-514, ``Low Temperature Overpressure Protection,'' which allows 
exceeding the pressure of the P/T limits of 10 CFR Part 50, Appendix G, 
by 10 percent. ASME Code Case N-514, the proposed alternate 
methodology, is consistent with guidelines developed by the ASME 
Working Group on Operating Plant Criteria 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. ASME Code Case N-514 has been 
approved by the ASME Code Committee. The content of this code case has 
been incorporated into Appendix G of Section XI of the ASME Code and 
published in the 1993 Addenda to Section XI.

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. Special circumstances are 
present whenever, according to 10 CFR 50.12(a)(2)(ii), ``Application of 
the regulation in the particular circumstances would not serve the 
underlying purpose of the rule or is not necessary to achieve the 
underlying purpose of the rule.''
    The underlying purpose of 10 CFR 50.60, Appendix G, is to establish 
fracture toughness requirements for ferritic materials of pressure-
retaining components of the reactor coolant pressure boundary to 
provide adequate margins of safety during any condition of normal 
operation, including anticipated operational occurrences, to which the 
pressure boundary may be subjected over its service lifetime. Section 
IV.A.2 of this appendix requires that the reactor vessel be operated 
with P/T limits at least as conservative as those obtained by following 
the methods of analysis and the required margins of safety of Appendix 
G of the ASME Code, Section XI.
    Appendix G of Section XI of the ASME Code requires that the P/T 
limits be calculated (a) using a safety factor of 2 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 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 Point Beach 
reactor vessel material.
    In determining the setpoint for LTOP events, the licensee proposed 
to use safety margins based on an alternate methodology consistent with 
the ASME Code Case N-514 guidelines. The ASME Code Case N-514 allows 
determination of the setpoint for LTOP events such that the maximum 
pressure in the vessel would not exceed 110 percent of the P/T limits 
of the existing ASME Code, Section XI, Appendix G. This approach 
results in a safety factor of 1.8 on pressure. All other factors, 
including assumed flaw size and fracture toughness, remain the same. 
Although this methodology would reduce the safety factor on pressure, 
it was demonstrated in the Bases of the ASME Code Case N-514 that due 
to the isothermal nature of LTOP events, the margin with respect to 
toughness for LTOP transients is within the range provided by ASME, 
Section XI, Appendix G for normal heatup and cooldown in the low 
temperature range. Thus, applying Code Case N-514 will satisfy the 
underlying purpose of 10 CFR 50.60 for fracture toughness requirements. 
Further, by relieving the operational restrictions, the potential for 
undesirable lifting of the PORV would be reduced, thereby improving 
plant safety.

IV

    For the foregoing reasons, the NRC staff has concluded that the 
licensee's proposed use of the alternate methodology in determining the 
acceptable setpoint for LTOP events will not present an undue risk to 
public health and safety and is consistent with the common defense and 
security. The NRC staff has determined that there are special 
circumstances present, as specified in 10 CFR 50.12(a)(2)(ii), in that 
application of 10 CFR 50.60 is not necessary in order to achieve the 
underlying purpose of this regulation.
    Accordingly, the Commission has determined that, pursuant to 10 CFR 
50.12(a), an 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 an exemption from the 
requirements of 10 CFR 50.60 such that in determining the setpoint for 
LTOP events, the Appendix G curves for P/T limits are not exceeded by 
more than 10 percent. This exemption is applicable only to LTOP 
conditions during normal operation.
    Pursuant to 10 CFR 51.32, the Commission has determined that the 
granting of this exemption will not have a significant effect on the 
quality of the human environment (61 FR 66062).
    This exemption is effective upon issuance.

    For the Nuclear Regulatory Commission.

    Dated at Rockville, Maryland, this 27th day of January 1997.
Frank J. Miraglia
Acting Director, Office of Nuclear Reactor Regulation.
[FR Doc. 97-2537 Filed 1-31-97; 8:45 am]
BILLING CODE 7590-01-P