[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
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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
