96-5813. Arizona Public Service Company, et al. (Palo Verde Nuclear Generating Station, Unit No. 2); Exemption  

  • [Federal Register Volume 61, Number 49 (Tuesday, March 12, 1996)]
    [Notices]
    [Pages 10035-10036]
    From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
    [FR Doc No: 96-5813]
    
    
    
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    NUCLEAR REGULATORY COMMISSION
    
    [Docket No. STN 50-529]
    
    
    Arizona Public Service Company, et al. (Palo Verde Nuclear 
    Generating Station, Unit No. 2); Exemption
    
    I
    
        The Arizona Public Service Company, et al. (APS or the licensee), 
    is the holder of Facility Operating License No. NPF-51, which 
    authorizes operation of the Palo Verde Nuclear Generating Station 
    (PVNGS), Unit No. 2, a pressurized-water reactor (PWR) located in 
    Maricopa County, Arizona. This license provides, among other things, 
    that the licensee is subject to all the rules, regulations, and orders 
    of the Commission now or hereafter in effect.
    
    II
    
        Section 50.46 of Title 10 of the Code of Federal Regulations (10 
    CFR 50.46) contains acceptance criteria for emergency core cooling 
    systems (ECCS) for light-water nuclear power reactors fueled with 
    uranium oxide pellets within cylindrical zircaloy cladding. Further, 10 
    CFR 50.46 states that ECCS cooling performance following postulated 
    loss-of-coolant accidents must be calculated in accordance with an 
    acceptable evaluation model. Appendix K to 10 CFR Part 50 contains the 
    required and acceptable features for ECCS evaluation models. Finally, 
    10 CFR 50.44 contains requirements for the control of hydrogen gas that 
    may be generated after a postulated loss-of-coolant accident (LOCA) in 
    light-water power reactors fueled with uranium oxide pellets within 
    cylindrical zircaloy cladding.
    
    III
    
        By letter dated December 20, 1995, APS submitted an amendment 
    request for PVNGS Unit 2 to allow fuel rods clad with advanced 
    zirconium-based alloys to be substituted in two fuel assemblies for up 
    to 40 rods clad with conventional Zircaloy-4. These assemblies would be 
    used for evaluating in-reactor performance during fuel cycles 7, 8, and 
    9.
        By letter dated January 12, 1996, APS submitted a request for an 
    exemption to 10 CFR 50.46, 10 CFR Part 50, Appendix K, and 10 CFR 
    50.44. These regulations refer to the use of zircaloy, but do not 
    clearly specify what is considered zircaloy. Therefore, the use of 
    advanced zirconium-based alloys rather than conventional Zircaloy-4 may 
    not be within the regulatory basis.
        Pursuant to 10 CFR 50.12(a), ``The Commission may, upon application 
    by any interested person or upon its own initiative, grant exemptions 
    from the requirements of the regulations of this part, which are--(1) 
    Authorized by law, will not present an undue risk to the public health 
    and safety, and are consistent with the common defense and security. 
    (2) The Commission will not consider granting an exemption unless 
    special circumstances are present. Special circumstances are present 
    whenever * * * (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 Code of Federal Regulations at 10 CFR 50.46 states: ``Each 
    boiling and pressurized light-water nuclear power reactor fueled with 
    uranium oxide pellets within cylindrical Zircaloy cladding must be 
    provided with an ECCS that must be designed such that its calculated 
    cooling performance following postulated loss-of-coolant accidents 
    conforms to the criteria set forth in paragraph (b) of this section. 
    ECCS cooling performance must be calculated in accordance with an 
    acceptable evaluation model and must be calculated for a number of 
    postulated
    
    [[Page 10036]]
    loss-of-coolant accidents of different sizes, locations, and other 
    properties sufficient to provide assurance that the most severe 
    postulated loss-of-coolant accidents are calculated.'' The Code of 
    Federal Regulations at 10 CFR 50.46 then goes on to give specifications 
    for peak cladding temperature, maximum cladding oxidation, maximum 
    hydrogen generation, coolable geometry, and long-term cooling. Since 10 
    CFR 50.46 specifically refers to fuel with Zircaloy cladding, the use 
    of fuel clad with advanced zirconium-based alloys would, in effect, 
    place the licensee outside the applicability of this section of the 
    Code.
        The underlying purpose of the rule is to ensure that facilities 
    have adequate acceptance criteria for ECCS. The fuel rods clad with the 
    advanced zirconium-based alloys will be identical in design and 
    dimension to the fuel rods clad with conventional Zircaloy-4. The 
    advanced cladding materials used in the demonstration fuel assemblies 
    were chosen based on the improved corrosion resistance exhibited in ex-
    reactor autoclave corrosion tests in both high-temperature water and 
    steam environments. Fuel rods clad with similar types of advanced 
    zirconium-based alloys have been successfully irradiated in high-
    temperature PWRs in Europe.
        The mechanical properties of the clad made from the advanced 
    zirconium-based alloys meet all the mechanical requirements of the 
    conventional Zircaloy-4 procurement specifications. Thus, the cladding 
    and structural integrity of the fuel rods and fuel assemblies that have 
    the advanced zirconium-based alloys will be maintained.
        Therefore, due to these similarities between advanced zirconium-
    based alloys and Zircaloy-4, the advanced alloys are expected to result 
    in clad and fuel performance similar to Zircaloy-4, such that the 10 
    CFR 50.46 LOCA acceptance criteria will be satisfied for the advanced 
    zirconium-based cladding. Thus, the underlying purpose of the rule has 
    been met.
        Strict interpretation of the regulation would render the criteria 
    of 10 CFR 50.46 inapplicable to the advanced zirconium-based alloys, 
    even though analysis shows that applying the Zircaloy criteria to the 
    advanced zirconium-based alloys yields acceptable results.
        A strict application of the regulation in this instance is not 
    necessary to achieve the underlying purpose of the rule. Therefore, 
    special circumstances exist to grant an exemption from 10 CFR 
    50.46(a)(1)(i) that would allow the licensee to apply the acceptance 
    criteria of 10 CFR 50.46 to a reactor with 40 fuel rods clad with 
    advanced zirconium-based alloys.
        The Code of Federal Regulations at 10 CFR 50.44 provides 
    requirements for control of hydrogen gas generated in part by Zircaloy 
    clad fuel after a postulated LOCA. The intent of this rule is to ensure 
    that an adequate means is provided for the control of hydrogen gas that 
    may be generated following a LOCA.
        The hydrogen produced in a post-LOCA scenario comes from cladding 
    oxidation from a metal-water reaction. Most of the high-temperature 
    oxidation occurs in the -phase since the diffusion coefficient 
    for oxygen in the -phase of zirconium is significantly greater 
    than that in -phase zirconium.
        The -phase oxidation resistance of the alloys is expected 
    to be as good as or better than that of Zircaloy-4. It is expected that 
    the alloying element levels adjusted to improve the corrosion 
    resistance of the -phase of these alloys with respect to the 
    -phase of Zircaloy-4 will result in an improvement of the 
    corrosion resistance of the -phase of these alloys as well. It 
    is therefore concluded that the -phase oxidation rate of the 
    alloys will be comparable to or lower than that of Zircaloy-4 and that 
    the Baker-Just correlation will overpredict the -phase 
    oxidation of the alloys. A strict interpretation of the rule in this 
    instance would result in the criteria of 10 CFR 50.44 inapplicable to 
    advanced zirconium-based alloys. Since application of the regulation is 
    not necessary to achieve the underlying purpose of the rule, special 
    circumstances exist to grant an exemption from 10 CFR 50.44 to a 
    reactor containing 40 fuel rods clad with advanced zirconium-based 
    alloys.
        Paragraph I.A.5 of Appendix K to 10 CFR Part 50 states that the 
    rates of energy release, hydrogen generation, and cladding oxidation 
    from the metal-water reaction shall be calculated using the Baker-Just 
    equation. However, since the Baker-Just equation presumes the use of 
    Zircaloy clad fuel, strict application of the rule would not permit use 
    of the equation. The intent of this part of Appendix K, however, is to 
    apply an equation that conservatively bounds all post-LOCA scenarios. 
    Due to the similarities in the composition of the advanced zirconium-
    based alloys and Zircaloy, the application of the Baker-Just equation 
    in the analysis of advanced zirconium-based clad fuel will 
    conservatively bound all post-LOCA scenarios. Since the use of the 
    Baker-Just equation presupposes Zircaloy cladding and post-LOCA 
    scenarios are conservatively bounded, the underlying purpose of the 
    rule will be met. Thus, special circumstances exist to grant an 
    exemption from Paragraph I.A.5 of Appendix K to 10 CFR Part 50 that 
    would allow the licensee to apply the Baker-Just equation to advanced 
    zirconium-based alloys.
    
    IV
    
        Accordingly, the Commission has determined that, pursuant to 10 CFR 
    50.12, this exemption is authorized by law, will not present an undue 
    risk to the public health and safety, and is consistent with the common 
    defense and security. The Commission has determined, pursuant to 10 CFR 
    50.12(a)(2)(ii) that special circumstances exist, as noted in Section 
    III above. Therefore, the Commission hereby grants Arizona Public 
    Service Company, et al., an exemption from 10 CFR 50.46, 10 CFR Part 
    50, Appendix K, and 10 CFR 50.44.
        Pursuant to 10 CFR 51.32, the Commission has determined that 
    granting this exemption will not have a significant impact on the human 
    environment (61 FR 5042).
        This exemption is effective upon issuance and shall expire at the 
    completion of the ninth Unit 2 refueling outage.
    
        Dated at Rockville, Maryland, this 6th day of March 1996.
    
        For the Nuclear Regulatory Commission.
    Elinor G. Adensam,
    Deputy Director, Division of Reactor Projects III/IV, Office of Nuclear 
    Reactor Regulation.
    [FR Doc. 96-5813 Filed 3-11-96; 8:45 am]
    BILLING CODE 7590-01-P
    
    

Document Information

Published:
03/12/1996
Department:
Nuclear Regulatory Commission
Entry Type:
Notice
Document Number:
96-5813
Pages:
10035-10036 (2 pages)
Docket Numbers:
Docket No. STN 50-529
PDF File:
96-5813.pdf