01-26694. Arizona Public Service Company, Palo Verde Nuclear Generating Station, Unit 3; Exemption

1.0 Background

The Arizona Public Service Company (APS/licensee) is the holder of Facility Operating License No. NPF-74 which authorizes operation of the Palo Verde Nuclear Generating Station (PVNGS), Unit 3. The license provides, among other things, that the facility is subject to all rules, regulations, and orders of the U.S. Nuclear Regulatory Commission (NRC, the Commission) now, or hereafter in effect.

The facility consists of a pressurized water reactor located in Maricopa County in Arizona.

2.0 Request/Action

Title 10 of the Code of Federal Regulations (10 CFR), part 50, discusses fuel performance requirements for fuel used in light water nuclear power reactors. The requirements refer specifically to cladding types of zircaloy or ZIRLO, and do not address other cladding material. Since advanced zirconium based cladding materials do not conform to the two designations specified in the code, an exemption is required.

APS requested a temporary exemption from the requirements of 10 CFR 50.44, 10 CFR 50.46, and 10 CFR part 50, appendix K, for PVNGS, Unit 3, by letter dated March 2, 2001, as supplemented on August 28, 2001, and September 25, 2001. The exemption would allow continued testing of a lead fuel assembly (LFA) containing fuel rods fabricated with an advanced zirconium based cladding material, designated as Alloy A. This cladding material has been previously approved for limited use and testing at PVNGS in letters dated July 17, 1992, and February 4, 1997. The requested exemption extension would allow the Unit 3 LFA to exceed the already approved operating cycles.

Part 50 of 10 CFR specifies standards and acceptance criteria only for fuel rods clad with zircaloy or ZIRLO. As noted above, APS was granted an exemption to use Alloy A in a limited number of pins starting in Cycle 4 and continuing through Cycle 6 in Unit 3. Based on the success of this advanced cladding, APS was granted an additional exemption to extend the burnup for a limited number of pins clad with Alloy A during Cycle 7. As part of the second exemption, APS was allowed to use a full assembly of the Alloy A clad in Unit 3 for three operating cycles, starting in Cycle 7. Based on the results of physical examination and measurements that have confirmed the superior performance of Alloy A, and NRC's prior approval for a limited number of pins, APS has requested an exemption to extend the burnup into Cycle 10 for the full assembly of Alloy A fuel rods.

Section 50.44 (a) of 10 CFR states, “Each boiling or pressurized light-water nuclear power reactor fueled with oxide pellets within cylindrical zircaloy or ZIRLO cladding, must, as provided in paragraphs (b) through (d) of this section, include means for control of hydrogen gas that may be generated, following a postulated loss-of-coolant accident (LOCA).”

Section 50.46(a)(1)(i) of 10 CFR states, “Each 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 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 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.”

Section 50.46 of 10 CFR continues on to delineate specifications for peak cladding temperature, maximum hydrogen generation, coolable geometry, and long-term cooling. Sections 50.44 and 50.46 of 10 CFR specifically refer to fuel with zircaloy or ZIRLO cladding; the use of fuel clad with zirconium-based alloys that do not conform to either of these two designations requires an exemption from this section of the Code.

Appendix K, paragraph I.A.5, of 10 CFR part 50 states, “The rate of energy release, hydrogen generation, 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 cladding. The use of fuel with zirconium-based alloys that do not conform to either of these two designations requires an exemption from this section of the Code.

APS believes that special circumstances are present, pursuant to 10 CFR 50.12(a)(ii), to warrant granting the exemption request.

3.0 Discussion

Pursuant to 10 CFR 50.12, the Commission may, upon application by an 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. These circumstances include the special circumstances as set forth in 10 CFR 50.12(a)(2)(ii), which states that special circumstances 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.”

The underlying purpose of 10 CFR 50.44 is to ensure that there is an adequate means of controlling generated hydrogen. The hydrogen produced in a post-LOCA scenario comes from a metal-water reaction. In the previous exemptions, it was concluded that the use of the Baker-Just equation to determine the metal-water reaction rate is conservative for Alloy A cladding. Therefore, the amount of hydrogen generated by metal-water reaction in these materials will be within the design basis of Palo Verde Unit 3.

Section 50.46 of 10 CFR identifies acceptance criteria for ECCS system performance at nuclear power facilities. The effectiveness of the ECCS in Palo Verde Unit 3 will not be affected by the reinsertion of the LFA. Due to the similarities in the material properties of Alloy A to zircaloy, and the location of the LFA in a non-limiting location, it can be concluded that the ECCS performance in Palo Verde Unit 3 will not be adversely affected.

The intent of paragraph I.A.5 of Appendix K to 10 CFR part 50 is to apply an equation for rates of energy release, hydrogen generation, and cladding oxidation from a metal-water reaction which conservatively bounds all post-LOCA scenarios. CEN-429-P, Rev. 00-P, “Safety Analysis Report for Use of Advanced Zirconium Based Cladding Material in PVNGS Unit 3 Lead Fuel Assemblies,” August 1996, verifies that due to the similarities in the composition of the Alloy A cladding and zircaloy, the application of the Baker-Just equation will continue to conservatively bound all post-LOCA scenarios.

The staff examined the licensee's rationale to support the exemption requests and concluded that continued use of advanced zirconium based cladding materials would meet the underlying purpose of 10 CFR part 50.

Based upon the considerations discussed in this exemption, the staff concludes that the information provided by APS and the actions described in the application form an acceptable basis for extending the exemption for another cycle.

The safety evaluation may be examined, and/or copied for a fee, at the NRC's Public Document Room, located at One White Flint North, 11555 Rockville Pike (first floor), Rockville, Maryland. Publicly available records will be accessible electronically from the ADAMS Public Library component on the NRC Web site, http://www.nrc.gov (the Public Electronic Reading Room).

Therefore, the staff concludes that pursuant to 10 CFR 50.12(a)(2)(ii), special circumstances exist as discussed in Section 3.0 above, and granting this exemption will not present an undue risk to the public health and safety and is consistent with the common defense and security.

4.0 Conclusion

Accordingly, the Commission has determined that, pursuant to 10 CFR 50.12(a), the exemption is authorized by law, will not endanger life or property or common defense and security, and is, otherwise, in the public interest. Also, special circumstances are present. Therefore, the Commission hereby grants Arizona Public Service Company, et al., an exemption from the requirements of 10 CFR 50.44, 10 CFR 50.46, and 10 CFR part 50, appendix K, for Palo Verde Nuclear Generating Station, Unit 3.

Pursuant to 10 CFR 51.32, the Commission has determined that the granting of this exemption will not have a significant effect on the quality of the human environment (66 FR 52644).

This exemption is effective upon issuance.

Dated at Rockville, Maryland, this 16th day of October 2001.

For the Nuclear Regulatory Commission.

John A. Zwolinski,

Director, Division of Licensing Project Management, Office of Nuclear Reactor Regulation.