[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