Duke Energy Corporation et al., (the licensee) is the holder of Facility Operating License Nos. NPF-35 and NPF-52, which authorize operation of the Catawba Nuclear Station, Units 1 and 2. The licenses provide, 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 two pressurized water reactors located in York County, South Carolina.
Title 10 of the Code of Federal Regulations (10 CFR) part 50, section 50.46 and appendix K identify requirements for calculating emergency core cooling system (ECCS) performance for reactors containing fuel with Zircaloy or ZIRLO cladding, and 10 CFR 50.44 identifies requirements for the control of hydrogen gas generated in part from a metal-water reaction between the reactor coolant and reactor fuel having Zircaloy or ZIRLO cladding.
The licensee has requested, in its letter dated December 3, 2002, as supplemented by letter dated April 8, 2003, a temporary exemption to 10 CFR 50.44, “Standards for combustible gas control system in light-water-cooled power reactors,” 10 CFR 50.46, “Acceptance criteria for emergency core cooling systems for light-water nuclear power reactors,” and appendix K to 10 CFR part 50, “ECCS Evaluation Models,” that would allow the Catawba Nuclear Station, Units 1 and 2 to operate using eight lead test assemblies (LTAs) with a tin composition that is nominally below the lower bound licensed limit of 0.80 percent, as specified in WCAP-12610-P-A, “VANTAGE+ Fuel Assembly Reference Core Report,” in non-limiting core locations. The purpose of the LTAs is to obtain data that would allow the optimization of ZIRLO corrosion resistance, in order to support improved fuel performance and reliability at increased burnup levels.
Pursuant to 10 CFR 50.12, “Specific exemptions,” 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. Under section 50.12(a)(2), special circumstances include, among other things, when the application of the regulation would not serve, or is not necessary to achieve, the underlying purpose of the rule.
The underlying purpose of 10 CFR 50.44, 10 CFR 50.46, and appendix K to 10 CFR part 50, is to establish requirements for the calculation of ECCS performance, and acceptance criteria for that performance, in order to assure that the ECCS functions to transfer heat from the reactor core following a loss-of-coolant-accident, such that (1) fuel and clad damage that could interfere with continued effective core cooling is prevented, and (2) clad metal-water reaction is limited to specified amounts.
The mechanical properties of the low-tin ZIRLO in the LTAs are very similar to those of the approved ZIRLO, since both of these alloys are zirconium-based materials with slight variations in tin content. The licensee will perform an evaluation of the fuel rod design using the same methods used for the current robust fuel assembly design. No new or altered design limits need to be applied, nor are any required for this program for the purposes of 10 CFR part 50, appendix A, “General Design Criteria for Nuclear Power Plants,” Criterion 10, “Reactor Design” (GDC 10). The licensee has evaluated the three areas of the mechanical design that could potentially be impacted by low-tin ZIRLO, namely, material properties, corrosion and thermal creep. The staff evaluated the data provided to substantiate that the material properties are similar to Zircaloy and that the corrosion and thermal creep will remain within established acceptance criteria. The NRC staff concludes that the data show that the selected LTA mechanical design will satisfy established acceptance criteria and should perform safely in the Catawba Nuclear Station.
The licensee has performed evaluations of the impact of the LTAs on the nuclear design. The approved reload methodologies can be used to model the LTAs since the features of the LTAs do not challenge the validity of the standard methodologies. The licensee has limited the number of LTAs to eight, and all of the LTAs will be placed in non-limiting locations in the Start Printed Page 47371core. The licensee will use the approved reload methodologies for the Catawba Nuclear Station reload design containing the LTAs. Given the limited number of LTAs to be installed and the installation in non-limiting locations, the NRC staff concludes that the LTA core design is acceptable for use in the Catawba Nuclear Station.
10 CFR 50.46 identifies acceptance criteria for ECCS performance at nuclear power plants. The material properties of the low-tin ZIRLO are similar to those of the current ZIRLO cladding. Because the current analyses are done with material properties that approximate the low-tin ZIRLO properties, the current ECCS analysis remains applicable and unchanged for the LTAs. Therefore, the NRC staff concludes that the ECCS performance of the Catawba Nuclear Station will not be adversely affected by the insertion of eight low-tin ZIRLO LTAs. As such, the licensee has achieved the underlying purpose of 10 CFR 50.46. The staff has also concluded that should these LTAs fail, the consequences will be bounded by the current analyses for fuel failures and radiological assessments because the source term will not be affected by a different cladding material.
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 determining acceptable fuel performance of advanced zirconium-based alloys. The underlying intent of this portion of the appendix, however, is to ensure that analysis of fuel response to LOCAs is conservatively calculated. Due to the similarities in the chemical composition between the low-tin ZIRLO and ZIRLO, the application of the Baker-Just equation in the analysis of low-tin ZIRLO clad fuel will conservatively bound all post-LOCA scenarios. Thus, the underlying purpose of the rule will be met. Therefore, special circumstances exist to grant an exemption from appendix K to 10 CFR part 50 that would allow the licensee to apply the Baker-Just equation to low-tin ZIRLO.
The purpose of 10 CFR 50.44 is to ensure that means are provided for the control of hydrogen gas that may be generated following a LOCA. The hydrogen produced in a post-LOCA scenario comes from a metal-water reaction. Tests performed by Westinghouse on the low-tin ZIRLO alloy have demonstrated that the reduction in tin content will have no significant effect on current assessments of hydrogen gas production. As such, the licensee has met the underlying purpose of 10 CFR 50.44.
The NRC staff examined the licensee's rationale to support the exemption request and, for the reasons set forth above, concludes that allowing these eight LTAs with a nominally lower tin composition would meet the underlying purpose of 10 CFR 50.44, 10 CFR 50.46, and appendix K to 10 CFR part 50. Further, the NRC staff has determined that the reduction in tin content will have no significant effect on current assessments of a metal-water reaction, and that the mechanical design of the LTAs would perform satisfactorily. Therefore, ECCS performance will not be adversely affected and application of 10 CFR 50.44, 10 CFR 50.46 and 10 CFR part 50, appendix K, is not necessary to achieve their underlying purpose.
Based upon the considerations above, the NRC staff concludes that, pursuant to 10 CFR 50.12(a)(2), the granting of this exemption is acceptable.
For the reasons set forth above, 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 Duke Energy Corporation an exemption from the requirements of 10 CFR part 50, section 50.44, section 50.46, and appendix K to 10 CFR part 50, with respect to the use of low-tin ZIRLO LTAs at the Catawba Nuclear Station.
This exemption is effective upon issuance.Start Signature
Dated at Rockville, Maryland, this 4th day of August 2003.
For The Nuclear Regulatory Commission.
Herbert N. Berkow,
Acting Director, Division of Licensing Project Management, Office of Nuclear Reactor Regulation.
[FR Doc. 03-20240 Filed 8-7-03; 8:45 am]
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