[Federal Register Volume 62, Number 29 (Wednesday, February 12, 1997)]
[Notices]
[Pages 6564-6565]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 97-3463]



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NUCLEAR REGULATORY COMMISSION

[Docket No. STN 50-530]


Arizona Public Service Company, et al., (Palo Verde Nuclear 
Generating Station, Unit 3); Exemption

I.

    On November 25, 1987, the Commission issued Facility Operating 
License No. NPF-74 to Arizona Public Service Company, Salt River 
Project Agricultural Improvement and Power District, El Paso Electric 
Company, Southern California Edison Company, Public Service Company of 
New Mexico, Los Angeles Department of Water and Power, and Southern 
California Public Power Authority for the Palo Verde Nuclear Generating 
Station, Unit 3. The license provides, among other things, that the 
licensee is subject to all rules, regulations, and orders of the 
Commission now or hereafter in effect.

II.

    Several sections of Title 10 of the Code of Federal Regulations 
discuss requirements for fuel that is used in light water nuclear power 
reactors. Since these requirements refer to specific cladding types of 
zircaloy or ZIRLO, the use of fuel clad with other zirconium-based 
alloys, or any other cladding material, that do not conform to these 
two designations requires an exemption from the code.
    Specifically, 10 CFR 50.44, ``[s]tandards for combustible gas 
control system in light-water-cooled power reactors,'' contains 
requirements for the control of hydrogen gas that may be generated 
after a postulated loss-of-coolant accident in light-water nuclear 
power reactors fueled with uranium oxide pellets within cylindrical 
zircaloy or ZIRLO cladding. Section 50.46 of Title 10 of the Code of 
Federal Regulations, ``[a]cceptance criteria for emergency core cooling 
systems for light water nuclear power reactors,'' contains acceptance 
criteria for emergency core cooling systems (ECCS) for light-water 
nuclear power reactors fueled with uranium oxide pellets within 
cylindrical zircaloy or ZIRLO cladding. Appendix K to Part 50, ``ECCS 
Evaluation models,'' contains the required and acceptable features for 
ECCS evaluation models to meet the requirements of 10 CFR 50.46. 
Paragraph I.A.5 of Appendix K states that the rates of energy release, 
hydrogen concentration, and cladding oxidation from the metal-water 
reaction shall be calculated using the Baker-Just equation. The Baker-
Just equation presumes the use of Zircaloy or ZIRLO clad fuel.
    Testing of advanced clad materials is necessary to provide data to 
justify full-core use of clad materials and a subsequent rule change to 
implement the advanced clad designs.

III.

    By letter dated September 12, 1996, as supplemented by letter dated 
December 13, 1996, Arizona Public Service Company (APS, or the 
licensee), submitted a request for exemption from the requirements of 
10 CFR 50.44, 10 CFR 50.46, and Appendix K to Part 50, to allow use of 
three lead fuel assemblies (LFAs) that contain advanced zirconium-based 
cladding materials. These assemblies would be used to evaluate the 
performance of the advanced cladding materials for three fuel cycles, 
which are cycles 7, 8, and 9.
    Pursuant to 10 CFR 50.12(a), ``[t]he 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 * * *''. As discussed in Section II. 
above, three separate sections of Title 10 to the Code of Federal 
Regulations establish requirements for performance of fuel used in 
light-water nuclear power reactors. These regulations refer to the use 
of zircaloy or ZIRLO cladding material, but do not specify what 
constitutes zircaloy. Therefore, the use of fuel that is clad with 
other zirconium-based alloys may not be within the regulatory basis for 
use of other alloys and would, in effect, place the licensee outside 
the applicability of these sections of the code. The licensee would 
require an exemption to these portions of the code to allow use of 
advanced zirconium-based alloys in its reactor.
    The information provided by the licensee in its September 12, 1996, 
letter demonstrates that the predicted chemical, mechanical, and 
material performance characteristics of the advanced zirconium-based 
cladding is within the parameters approved for zircaloy under 
anticipated operations occurrences and postulated accidents. In 
addition, nominal fuel performance characteristics of the advanced 
zirconium-based clad test rods continue to be the same as, or superior 
to, those experienced with existing Zircaloy-4 fuel rods. The 
information provided in the licensee's December 13, 1996, letter 
demonstrated that although two of the three proposed lead fuel 
assemblies will be in relatively high power and rodded positions during 
Unit 3 Cycle 7, these assemblies will not be in limiting (the highest 
power) regions of the core. The licensee also proposes to include up to 
six fuel rods that have already been exposed for three fuel cycles in 
one of the three fuel assemblies. These rods are being tested to 
determine the effects on the cladding of extended burnup. These rods 
will be measured after Cycle 6, and before use in Cycle 7, to ensure 
that end of cycle (EOC) 7 maximum circumferentially averaged oxide 
thickness projected for each rod transferred will remain below the 
approved oxide thickness limit, and that adequate shoulder gap will 
exist at EOC 7 for each rod using conservative assumptions for fuel rod 
and fuel assembly growth. The staff concludes that the use of advanced 
zirconium-based cladding materials in three lead fuel assemblies in 
non-limiting core locations will not present an undue risk to the 
public health and safety, and is consistent with the common defense and 
security.
    The underlying purpose of 10 CFR 50.44 is to ensure that adequate 
means is provided for the control of hydrogen gas that may be generated 
following a loss of coolant accident (LOCA). The hydrogen produced in a 
post-LOCA scenario comes from cladding oxidation in a metal-water 
reaction. Most of the high temperature oxidation occurs during that 
portion of the LOCA scenario that results in a molecular phase of 
zirconium (the beta-phase) that allows a significantly higher diffusion 
coefficient for oxygen than that molecular phase of zirconium that 
exists during normal operation (the alpha-phase). The beta-phase 
oxidation resistance of the proposed alloys is expected to be as good 
as, or better than, that of the existing Zircaloy-4. In addition, the 
elemental composition used in the proposed alloy to improve the 
corrosion resistance of the alpha-phase of these alloys will also 
improve the corrosion resistance of the beta-phase of these alloys as 
well. The staff therefore concludes that the beta-phase oxidation rate 
of the proposed alloys will be at or lower than that of the

[[Page 6565]]

existing Zircaloy-4. A strict interpretation of the rule in this 
instance would conclude that the criteria of 10 CFR 50.44 are not met 
by advanced zirconium-based alloys, since these alloys are not 
specifically zircaloy or ZIRLO. Since the advanced zirconium-based 
alloys meet the underlying purpose of the rule, strict application of 
the rule to only apply to zircaloy or ZIRLO cladding is not necessary 
to achieve the underlying purpose of the rule. Since strict application 
of 10 CFR 50.44 is not necessary to meet the underlying purpose of the 
rule, special circumstances exist to grant an exemption from this 
regulation to allow a reactor to contain three lead fuel assemblies 
containing fuel rods clad with advanced zirconium-based alloys.
    The underlying purpose of 10 CFR 50.46 is to specify acceptance 
criteria for ECCS performance at light-water nuclear power reactors. 
The fuel rods clad with the advanced zirconium-based alloys will be 
identical in design and dimensions to the fuel rods clad with the 
existing Zircaloy-4. The advanced cladding materials used in the 
proposed fuel assemblies were chosen to improve 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 advanced zirconium-based alloy clad meets all the 
mechanical requirements of the existing Zircaloy-4 procurement 
specifications. Thus the cladding and structural integrity of the fuel 
rods and fuel assemblies with advanced zirconium-based alloy cladding 
will be maintained. In addition, although the staff has not yet 
reviewed and generically approved the overall behaviors of alloys A and 
F to meet the limits of ECCS performance criteria requirements, the 
three lead fuel assemblies will be placed in non-limiting locations 
within the core. Based on the above considerations, the staff concludes 
that the lead fuel assemblies will perform acceptably under postulated 
LOCA conditions. Thus, the underlying purpose of the rule has been met. 
A strict interpretation of the rule in this instance would conclude 
that the criteria of 10 CFR 50.46 are not met by advanced zirconium-
based alloys, since these alloys are not strictly zircaloy or ZIRLO. 
Since the advanced zirconium-based alloys meet the underlying purpose 
of the rule, strict application of the rule to only apply to zircaloy 
or ZIRLO cladding is not necessary to achieve the underlying purpose of 
the rule. Therefore, special circumstances exist to grant an exemption 
from 10 CFR 50.46 that would allow the licensee to apply the acceptance 
criteria of 10 CFR 50.46 to a reactor containing a limited number of 
fuel rods 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 concentration, and cladding oxidation 
from the metal-water reaction shall be calculated using the Baker-Just 
equation. Since the Baker-Just equation presumes the use of zircaloy 
clad fuel, strict application of the rule would not permit use of the 
equation for advanced zirconium-based alloys for determining acceptable 
fuel performance. The underlying intent of this portion of the 
Appendix, however, is to ensure that analysis of fuel response to LOCAs 
is conservatively calculated. Due to the similarities in the 
composition of the advanced zirconium-based alloys and Zircaloy/ZIRLO, 
the application of the Baker-Just equation in the analysis of advanced 
zirconium-based clad fuel will conservatively bound all post-LOCA 
scenarios. Thus, the underlying purpose of the rule will be met. Thus, 
special circumstances exist to grant an exemption from 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, pursuant to 10 CFR 
50.12(a)(i), that an exemption as described in Section III above 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 50.44, 10 CFR 50.46, and Appendix K to 10 CFR 
Part 50 for use of lead fuel assemblies.
    Pursuant to 10 CFR 51.32, the Commission has determined that the 
granting of this exemption will not have a significant impact on the 
quality of the human environment (62 FR 3925).
    This exemption is effective upon issuance.

    For the Nuclear Regulatory Commission.

    Dated at Rockville, Maryland this 4th day of February 1997.
Frank J. Miraglia, Jr.,
Acting Director, Office of Nuclear Reactor Regulation.
[FR Doc. 97-3463 Filed 2-11-97; 8:45 am]
BILLING CODE 7590-01-P