[Federal Register Volume 73, Number 63 (Tuesday, April 1, 2008)]
[Notices]
[Pages 17384-17386]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: E8-6630]
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NUCLEAR REGULATORY COMMISSION
[Docket No. 50-368]
Entergy Operations, Inc.; Arkansas Nuclear One, Unit 2; Exemption
1.0 Background
Entergy Operations, Inc. (Entergy, licensee), is the holder of
Facility Operating License No. NPF-6 which authorizes operation of the
Arkansas Nuclear One, Unit 2 (ANO-2). The license provides, among other
things, that the facility is subject to all rules, regulations, and
orders of the Nuclear Regulatory Commission (NRC, the Commission) now
or hereafter in effect.
The facility consists of a pressurized-water reactor (PWR) located
in Pope County, Arkansas.
2.0 Request/Action
Title 10 of the Code of Federal Regulations (10 CFR) Sec. 50.46,
``Acceptance criteria for emergency core cooling systems for light-
water nuclear power reactors,'' requires, among other items, that
``[e]ach boiling or pressurized light-water nuclear power reactor
fueled with uranium oxide pellets within cylindrical zircaloy or ZIRLO
cladding must be provided with an emergency core cooling system (ECCS)
that must be designed so that its calculated cooling performance
following postulated loss-of-coolant accidents [(LOCAs)] conforms to
the criteria set forth in paragraph (b) of this section.'' Appendix K
to 10 CFR part 50, ``ECCS Evaluation Models,'' requires, among other
items, that the rate of energy release, hydrogen generation, and
cladding oxidation from the metal/water reaction shall be calculated
using the Baker-Just equation. The regulations of 10 CFR 50.46 and 10
CFR part 50, Appendix K, make no provision for use of fuel rods clad in
a material other than zircaloy or ZIRLO. Since the chemical composition
of the Optimized ZIRLOTM alloy differs from the
specifications for zircaloy or ZIRLO, a plant-specific exemption is
required to allow the use of the Optimized ZIRLOTM alloy as
a cladding material at ANO-2. Therefore, by letter dated April 24,
2007, the licensee requested the use of the Optimized
ZIRLOTM for fuel rod cladding at ANO-2.
3.0 Discussion
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.
Authorized by Law
This exemption results in changes to the operation of the plant by
allowing the use of the Optimized ZIRLOTM as fuel rod
cladding material in lieu of zircaloy or ZIRLO. As stated above, 10 CFR
50.12 allows the NRC to grant exemptions from the requirements of 10
CFR part 50. The NRC staff has determined that granting of the
licensee's proposed exemption will not result in a violation of the
Atomic Energy Act of 1954, as amended, or the Commission's regulations.
Therefore, the exemption is authorized by law.
No Undue Risk to Public Health and Safety
By letter dated June 10, 2005, the NRC staff approved Westinghouse
Topical Report WCAP-12610-P-A and CENPD-404-P-A, Addendum 1-A,
``Optimized ZIRLOTM'' (Agencywide Documents Access and
Management System (ADAMS) Accession No. ML051670408). The NRC staff
approved the use of Optimized ZIRLOTM as a fuel cladding
material based on: (1) Similarities with standard ZIRLOTM,
(2) demonstrated material performance, and (3) a commitment to provide
irradiated data and validate fuel performance models ahead of burnups
achieved in batch application. The NRC staff's safety evaluation for
Optimized ZIRLOTM includes 10 conditions and limitations for
its use. In addition, the NRC's June 10, 2005, safety evaluation for
Optimized ZIRLOTM recommends that the computer codes used to
perform fuel design safety analyses incorporate the material properties
of Optimized ZIRLOTM.
The underlying purpose of 10 CFR 50.46 is to establish acceptance
criteria for ECCS performance. The applicability of these ECCS
acceptance criteria has been demonstrated by Westinghouse. Ring
compression tests performed by Westinghouse on Optimized ZIRLO
TM (documented in Appendix B of WCAP-
[[Page 17385]]
12610-P-A and CENPD-404-P-A, Addendum 1-A ``Optimized ZIRLO
TM,'' July 2006, ADAMS Accession No. ML062080576)
demonstrate an acceptable retention of post-quench ductility up to 2200
degrees Fahrenheit [[deg]F] and 17 percent equivalent clad reacted 10
CFR 50.46 limits. Furthermore, oxidation measurements provided by the
licensee (by letter dated November 6, 2007, ``SER [Safety Evaluation
Report] Compliance with WCAP-12610-P-A & CENPD-404-P-A Addendum 1-A
`Optimized ZIRLO TM','' LTR-NRC-07-58, ADAMS Accession No.
ML073130562), illustrate that oxide thickness (and associated hydrogen
pickup) for Optimized ZIRLO TM at any given burnup would be
less than both Zircaloy-4 and ZIRLO TM. Hence, Optimized
ZIRLO TM would be expected to maintain better post-quench
ductility. This finding is based on an ongoing LOCA research program at
Argonne National Laboratory which has identified a strong correlation
between cladding hydrogen content (due to in-service corrosion) and
post-quench ductility.
Utilizing currently approved LOCA models and methods, Westinghouse
performed a plant-specific evaluation and found that the Optimized
ZIRLO TM fuel rods will satisfy the 10 CFR 50.46 acceptance
criteria. Therefore, the exemption request continues to ensure that the
underlying purpose of the rule is achieved.
Paragraph I.A.5 of Appendix K to 10 CFR part 50 states that the
rates of energy, 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 Optimized ZIRLO TM cladding for determining
acceptable fuel performance. Metal-water reaction tests performed by
Westinghouse on Optimized ZIRLO TM (documented in Appendix B
of WCAP-12610-P-A and CENPD-404-P-A, Addendum 1-A) demonstrate
conservative reaction rates relative to the Baker-Just equation. Thus,
a prohibition on the use of Optimized ZIRLO TM is not
necessary for the licensee to achieve the underlying purpose of
paragraph I.A.5 of Appendix K in these circumstances.
Based on the above, no new accident precursors are created by using
Optimized ZIRLO TM, thus, the probability of postulated
accidents is not increased. Also, based on the above, the consequences
of postulated accidents are not increased. In addition, the licensee
will use NRC-approved methods for the reload design process for ANO-2
reloads with Optimized ZIRLO TM. Therefore, there is no
undue risk to public health and safety due to using Optimized ZIRLO
TM.
Special Circumstances
Special circumstances, in accordance with 10 CFR 50.12(a)(2)(ii),
are present whenever 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. In this
circumstance, neither 10 CFR 50.46 nor 10 CFR part 50, Appendix K,
explicitly allows the use of Optimized ZIRLO TM as a fuel
rod cladding material.
The underlying purpose of 10 CFR 50.46 is to ensure that facilities
have adequate acceptance criteria for the ECCS. Based upon results of
metal-water reaction tests and ring-compression tests which ensure the
applicability of ECCS models and acceptance criteria and the use of
approved LOCA models to ensure compliance to 10 CFR 50.46 acceptance
criteria, the staff finds it acceptable to grant an exemption from the
10 CFR 50.46 and Appendix K to 10 CFR part 50 to allow the use of
Optimized ZIRLO TM in future reloads at ANO-2.
On June 10, 2005, the NRC staff approved WCAP-12610-P-A and CENPD-
404-P-A, Addendum 1-A, in which Westinghouse demonstrated that the
effectiveness of the ECCS will not be affected by a change from
zircaloy to Optimized ZIRLO TM. The analysis described in
the WCAP-12610-P-A and CENPD-404-P-A also demonstrated that the ECCS
acceptance criteria applied to reactors fueled with zircaloy fuel rod
cladding are also applicable to reactors fueled with Optimized ZIRLO
TM WCAP-12610-P-A and CENPD-404-P-A fuel rod cladding.
The underlying purpose of 10 CFR part 50, Appendix K, paragraph
I.A.5, is to ensure that cladding oxidation and hydrogen generation are
appropriately limited during a LOCA and conservatively accounted for in
the ECCS evaluation model. Appendix K to 10 CFR part 50 requires that
the Baker-Just equation be used in the ECCS evaluation model to
determine the rate of energy release, cladding oxidation, and hydrogen
generation. In WCAP-12610-P-A and CENPD-404-P-A, Addendum 1-A ,
Westinghouse demonstrated that the Baker-Just model is conservative in
all post-LOCA scenarios with respect to the use of the Optimized
ZIRLOTM as a fuel rod cladding material, and that the amount
of hydrogen generated in an Optimized ZIRLOTM core during a
LOCA will remain within the ANO-2 design basis.
Optimized ZIRLOTM is a niobium-tin-iron (Nb-Sn-Fe)
zirconium (Zr) based alloy with a microstructure comprised of a body-
centered cubic ZrNb phase and a close-packed hexagonal ZrNbFe phase
homogeneously distributed throughout the zirconium matrix. Optimized
ZIRLOTM fuel cladding is different from standard
ZIRLOTM in two respects: (1) The Sn content is lower, and
(2) the microstructure is different. This difference in Sn content and
microstructure can lead to differences in some material properties.
Most of the material properties of standard ZIRLOTM and
Optimized ZIRLOTM are the same within the uncertainty of the
data and, therefore, use of standard ZIRLOTM properties for
safety analyses is acceptable. The NRC staff has reviewed the
licensee's request to use Optimized ZIRLOTM for PWR fuel
mechanical designs as described in WCAP-12610-P-A and CENPD-404-P-A,
Addendum 1-A. In the June 10, 2005, safety evaluation for WCAP-12610-P-
A and CENPD-404-P-A, Addendum 1-A, the NRC staff concluded that, to the
extent specified in the NRC staff's evaluation, the Optimized
ZIRLOTM properties and mechanical design methodology are
acceptable for referencing in fuel reload licensing applications.
Therefore, since the underlying purposes of 10 CFR 50.46 and 10 CFR
part 50, Appendix K, paragraph I.A.5 are achieved through the use of
the Optimized ZIRLOTM as a fuel rod cladding material, the
special circumstances required by 10 CFR 50.12(a)(2)(ii) for the
granting of an exemption from 10 CFR 50.46 and Appendix K to 10 CFR
part 50, exist.
Summary
The NRC staff has reviewed the licensee's request to use the
Optimized ZIRLOTM for fuel rod cladding in lieu of zircaloy
or ZIRLO. Based on the NRC staff's evaluation, as set forth above, the
NRC staff concludes that the exemption is authorized by law, will not
present an undue risk to public health and safety, and is consistent
with the common defense and security. In addition, the NRC staff
concludes that the underlying purposes of 10 CFR 50.46 and Appendix K
to 10 CFR part 50, are achieved through the use of the Optimized
ZIRLOTM alloy. Therefore, pursuant to 10 CFR 50.12(a), the
NRC staff concludes that the use of the Optimized ZIRLOTM
alloy for fuel rod cladding is acceptable and the exemption from 10 CFR
50.46 and Appendix K to 10 CFR part 50, is justified. Although the use
of Optimized ZIRLOTM is allowed, the other requirements of
10 CFR 50.46 and
[[Page 17386]]
Appendix K to 10 CFR part 50 apply to the use of Optimized
ZIRLOTM. The conditions and limitations on the use of
Optimized ZIRLOTM will be discussed in the staff's action on
the license amendment request submitted by the applicant dated April
24, 2007.
4.0 Conclusion
Accordingly, the Commission has determined that, pursuant to 10 CFR
50.12(a), the 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. Also, special circumstances are present.
Therefore, the Commission hereby grants Entergy an exemption from the
requirements of 10 CFR 50.46 and Appendix K to 10 CFR Part 50, for ANO-
2.
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 as published in the Federal Register
on March 10, 2008 (73 FR 12779). This exemption is effective upon
issuance.
Dated at Rockville, Maryland, this 19 day of March 2008.
For the Nuclear Regulatory Commission.
Catherine Haney,
Director, Division of Operating Reactor Licensing, Office of Nuclear
Reactor Regulation.
[FR Doc. E8-6630 Filed 3-31-08; 8:45 am]
BILLING CODE 7590-01-P