ML20035C688
| ML20035C688 | |
| Person / Time | |
|---|---|
| Site: | Vogtle  |
| Issue date: | 04/01/1993 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20035C687 | List: |
| References | |
| NUDOCS 9304080319 | |
| Download: ML20035C688 (5) | |
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SAFETY EVALVATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT NO. 62 TO FACILITY OPERATING LICENSE NPF-68 AND AMENDMENT NO. 41 TO FACILITY OPERATING LICENSE NPF-81 EORGIA POWER COMPANY. ET AL.
V0GTLE ELECTRIC GENERATING PLANT. UNITS 1 AND 2 DOCKET NOS. 50-424 AND 50-425
1.0 INTRODUCTION
By "ELV-04052, Application for Amends to Licenses NPF-68 & NPF-81,revising Tech Spec 5.3.1 to Permit Limited Substitution of [[Atomic Element" contains a listed "[" character as part of the property label and has therefore been classified as invalid. Alloy or Stainless Steel Filler Rods for Fuel Rods Per NRC Approved Applications|letter dated November 5, 1992]], as supplemented March 29, 1993, Georgia Power Company, et al. (the licensee) proposed license amendments to change the Technical Specifications (TS) for Vogtle Electric Generating Plant (Vogtle or the facility), Units 1 and 2.
The proposed amendments would revise Technical Specification (TS) 5.3.1, " Design Features -- Fuel Assemblies," in accordance with NRC Generic Letter (GL) 90-02, " Alternative Requirements for Fuel Assemblies in the Design Features Section of Technical Specifications," as issued February 1, 1990, and supplemented July 31, 1992.
Specifically, the amendments would supplement Vogtle TS 5.3.1 by adding that:
Limited substitutions of zirconium alloy or stainless steel filler rods for fuel rods, in accordance with NRC-approved applications of fuel rod configurations, may be used.
Fuel assemblies shall be limited to those fuel designs that have been analyzed with applicable NRC staff-approved codes and methods, and shown by tests or analyses to comply with all fuel safety design bases. A limited number of lead test assemblies that have not completed representative testing may be placed in non-limiting core regions.
By letter of March 29, 1993, the licensee provided additional information in support of the application for amendments.
This additional information does not affect the NRC staff's notice of no significant hazards consideration determination as published in the Federal Reaister (58 FR 6820 dated February 2, 1993, as corrected by 58 FR 8434 dated February 12, 1993).
2.0 BACKGROUND
Requirements for fuel assemblies in TS Section 5, " Design Features," specify the quantity of fuel assemblies and the number of fuel rods per assembly.
In GL 90-02 and its supplement, the NRC recognized that flexibility to use filler rods is desirable to permit timely removal of fuel rods that are found to be leaking during a refueling outage or are determined to be probable sources of future leakage.
This improvement to provide for reconstitution of fuel assemblies using filler rods would result in reductions in future occupational radiation exposure and plant radiological releases.
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Notwithstanding this advantage, the NRC staff recognized in the GL that the substitution of filler rods for fuel rods would be acceptable only when justified by cycle-specific reload analyses using an NRC-approved methodology.
The' license's reload analysis would be required to demonstrate that existing design limits and safety analyses criteria are met in advance of the next operating cycle.
The GL provided a model TS that could be used by licensees to propose TS changes.
Upon receiving several applications to implement GL 90-02, the NRC staff realized that certain ambiguity in the GL had prompted some licensees to incorrectly assume that their currently approved analytical methods were applicable to proposed configurations permitted by the model TS in GL 90-02.
Therefore, on July 31, 1992, the NRC staff issued Supplement 1 to GL 90-02 to clarify the limitations on the application of NRC-approved analytical methods used in the analysis of reconstituted fuel and to request that licensees interpret the phrase "NRC-approved methodology" in the TS accordingly. The NRC staff considers an NRC-approved methodology to be any methodology that the NRC staff has explicitly approved in a written safety evaluation. However, that NRC-approved methodology must be used only for the purpose and the scope of application specified in the reviewed document as approved or modified in the NRC approval documentation.
In general, the scope of application for generic methods is limited to fuel configurations that are represented by fuel assembly test configurations used to validate an approved methodology.
Supplement I stated, in part, that:
When responding to GL 90-02, licensees should have evaluated the applicability of the test data used to derive the correlations and limits for the departure from nucleate boiling ratio (DNBR)...
for proposed configurations. The licensees should also have considered the effect on the mechanical design such as the effect of differential thermal expansion on the proper seating of the fuel rod or on the relaxation of the spacer ' spring which could lead to fretting wear.
In addition, the licensees should have analyzed changes in the fuel design that affect the grid strength or the mass, stiffness, and fundamental frequency of the fuel assembly to ensure that the seismic and loss-of coolant accident (LOCA) design loading conditions will not cause any structural deformation that could prevent fuel coolable geometry or control rod insertion.
The GL Supplement revised the previous model TS to be consistent with realistic reconstitution configurations, and encouraged licensees and fuel vendors to submit generic topical reports that justify the specified fuel configurations with filler rods and that define and justify the analytical methods for core analysis to support fuel reconstitution.
3.0 EVALUATION In response to NRC concerns and a growing trend in the use of reconstituted assemblies in the last few years, Westinghouse Electric Corporation submitted for NRC review and approval a proprietary topical report, WCAP-13060-P,
" Westinghouse Fuel Assembly Reconstitution Evaluation Methodology," dated
. September 1991.
The report provided results of a mechanical evaluation demonstrating that the effects of reconstitution with a significant percentage of filler rods would be acceptable for Westinghouse fuel assembly designs.
The methodology is intended for use during core reload analyses and would be applied to Westinghouse fuel assembly designs that incorporate solid replacement rods of stainless steel, Zircaloy-4, or ZlRLO" and that use mixing vane grids.
Based on other evaluations of the safety aspects of reconstitution, performed by the functional disciplines (Thermal-Hydraulic, Nuclear, Fuel Rod Performance, LOCA and non-LOCA), the report found that the effects of fuel assembly reconstitution on reactor core performance would be minimal.
The report described the methodology that would be used each cycle to evaluate applicable design criteria associated with reconstituted fuel assemblies that use solid filler rods in place of uranium filled fuel rods.
WCAP-13060-P is intended to complement the NRC approved WCAP-9272-P-A,
" Westinghouse Reload Safety Evaluation Methodology," that addresses the analytical and safety aspects of the reload design activity.
The NRC staff reviewed the fuel assembly reconstitution evaluation methodology described in WCAP-13060-P in accordance with Section 4 of the Standard Review Plan. As noted by letter of hrch 30, 1993, the NRC staff found the reconstitution methodology to be acceptable for use in licensing applications involving core reload analyses for Westinghouse fuel assembly designs that incorporate solid replacement rods of stainless steel, Zircaloy-4, or ZIRLO" and that use mixing vane grids.
By letter of March 29, 1993, the licensee provided results of reconstitution analyses for Vogtle Unit 1, fuel cycle 5.
Upon examination of the fuel assemblies during the refueling outage at the end of fuel cycle 4, the licensee determined that one fuel rod in a VANTAGE-5 fuel assembly was leaking and should be replaced with a solid stainless steel rod.
The leaking fuel rod (shown at grid location 9-K in Figure 2 of licensee's letter) was located two spaces from the center of the fuel assemble.
The VANTAGE-5 fuel assembly containing the damaged fuel rod had experienced one cycle of operation and, after reconstitution, would be reloaded within the central region of the core (grid location 7-F in the core loading pattern in Figure 1 of the licensee's letter).
The licensee's evaluations of the safety aspects of reconstitution, performed by the functional disciplines (Thermal-Hydraulic, Nuclear, Fuel Rod Performance, LOCA and non-LOCA), showed that the effects of the proposed fuel assembly reconstitution on the Vogtle I cycle 5 core performance would be minimal.
The NRC staff has reviewed the licensee's submittals and finds that the Vogtle analyses are based upon the methodology of WCAP-13060-P.
The VANTAGE-5 fuel assembly, which is designed to be reconstitutable, provides adequate coolant mixing with the use of mixing vane grids.
The NRC staff's approval of WCAP-13060-P was contingent upon analytical confirmation that the exact configuration and associated core power j
distribution of proposed reconstituted assemblies does not introduce a change in radial gradients in the flow and enthalpy distribution that could invalidate the applicability of the critical heat flux correlation used for
4 predicting departure from nucleate boiling (DNB).
In this respect, the licensee's evaluation for Vogtle Unit I cycle 5 concluded:
Fuel reconstitution may result in a flow redistribution among fuel assemblies due to a change in radial power gradient. The corewide effects on enthalpy rise and DNB was evaluated.
The Vogtle reconstituted Cycle 5 loading pattern is less limiting than the evaluation in Reference 10 [WCAP-13060-P, March 1993].
For Vogtle Unit 1 Cycle 5, the corewide effects are negligible.
Fuel reconstitution may also affect the core average heat flux due to a reduced heat transfer area.
However, one solid filler rod replacing the damaged fuel rod in the Vogtle Unit 1 Cycle 5 loading pattern had a negligible effect on DNB due to the slight increase in core average heat flux. The specific evaluations which were performed for Vogtle Unit 1 Cycle 5, considering the exact configuration and associated core power distribution of the reconstituted assembly, confirmed that the reconstituted assembly was bounded by a regular assembly in DNB analyses and the DNB design basis was met.
The NRC staff agrees with the licensee's conclusion and finds that the above condition associated with approval of WCAP-13060-P is satisfied.
The NRC staff also finds that the substitution of one stainless steel filler rod for one fuel rod, as proposed, is well within the conditions for which the methodology of WCAP-13060-P applies and, thus, the evaluations are consistent with Supplement I to GL 90-02.
The licensee's analyses provided acceptable results and demonstrate that all existing design and safety criteria continue to be met.
Accordingly, the NRC staff concludes that the proposed reconstitution for Vogtle Unit 1, cycle 5 is acceptable.
The requirement to use NRC-approved methodology as clarified by Supplement I to GL 90-02 to demonstrate that existing design basis and safety criteria are met, ensures adequate controls upon future core alterations. As noted in GL 90-02, the NRC staff finds that these controls are also acceptable for the use of a limited number of lead test assemblies in non-limiting core regions.
If the results of 10 CFR 50.59 analyses, performed in accordance with NRC-approved methodology, are determined by the licensee to meet all existing design bases and safety criteria, and not to give rise to an unreviewed safety question or to require a change to the TSs, then the proposed core loading and its subsequent operation with lead test assemblies or with Westinghouse assemblies with mixing vanes that are reconstituted with solid Zircaloy-4, ZIRLO*, or stainless steel filler rods do not require prior NRC staff approval.
Results of such analyses will be reflected in the Core Operating Limits Report (COLR) and periodic updates of the Final Safety Analysis Report, as appropriate.
The NRC staff has also reviewed the supplemental text that the licensee proposes to add to TS 5.3.1 and finds it to be identical to the text proposed
. by the model TS of Supplement 1 to GL 90-02. The proposed change to the TS is, therefore, acceptable.
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4.0 STATE CONSULTATION
In accordance with the Commission's regulations, the Georgia State official was notified of the proposed issuance of the amendments. The State official had no comments.
5.0 ENVIRONMENTAL CONSIDERATION
The amendments change a requirement with respect to the installation or use of facility components located within the restricted area as defined in 10 CFR Part 20.
The NRC staff has determined that the amendments involve no significant increase in the amounts, and no significant change in the types, of any effluents that may be released offsite, and that there is no significant increase in individual or cumulative occupational radiation i
exposure. The Commission has previously issued a proposed finding that the amendments involve no significant hazards consideration, and there has been no public comment on such finding (58 FR 6820 dated February 2,1993, as corrected by 58 FR 8434 dated February 12, 1993).
Accordingly, the amendments meet the eligibility criteria for categorical exclusion set forth in 10 CFR 51.22(c)(9).
Pursuant to 10 CFR 51.22(b) no environmental impact statement or environmental assessment need be prepared in connection with the issuance of the amendments.
6.0 CONCLUSION
The Commission has concluded, based on the considerations discussed above, that:
(1) there is reasonable assurance that the health and safety of the public will not be endangered by operation in the proposed manner, (2) such activities will be conducted in compliance with the Commission's regulations, and (3) the issuance of the amendments will not be inimical to the common defense and security or to the health and safety of the public.
Principal Contributors: D. Hood S. Wu Date:
April 1, 1993 l
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