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.
Title 10 of the Code of Federal Regulations (10 CFR) § 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.
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-Start Printed Page 1738512610-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 [°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, 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.
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 Start Printed Page 17386Appendix 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.
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.Start Signature
Dated at Rockville, Maryland, this 19 day of March 2008.
For the Nuclear Regulatory Commission.
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