[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
