ML040290810
| ML040290810 | |
| Person / Time | |
|---|---|
| Site: | North Anna  |
| Issue date: | 01/22/2004 |
| From: | Hartz L Virginia Electric & Power Co (VEPCO) |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| 04-017 | |
| Download: ML040290810 (11) | |
Text
VIRGINIA ELECTRIC AND POWER COMPANY 10 CFR 50.90 RICHMOND, VIRGINIA 23261 January 22, 2004 U. S. Nuclear Regulatory Commission Serial No.04-017 Attention: Document Control Desk NLOS/ETS Washington, D.C. 20555 Docket Nos. 50-338/339 License Nos. NPF-4/7 VIRGINIA ELECTRIC AND POWER COMPANY NORTH ANNA POWER STATION UNITS I AND 2 PROPOSED TECHNICAL SPECIFICATIONS CHANGES AND EXEMPTION REQUEST FOR USE OF FRAMATOME ANP ADVANCED MARK-BW FUEL REQUEST FOR ADDITIONAL INFORMATION REGARDING ASSESSMENT OF FUEL ASSEMBLY BOW CONCERN Framatome ANP has provided NRC an interim report concerning a reassessment of the methodology for determining power peaking effects of assumed fuel assembly bow.
Framatome's interim report characterizes this as an evaluation of a deviation pursuant to the provisions of 10 CFR 21.21(a)(2). This issue potentially affects the Advanced Mark-BW fuel intended for use in North Anna Units 1 and 2, for which Dominion has requested approval in a licensing amendment request (Serial No.02-167, dated March 28, 2002).
In a December 30, 2003 telephone conference call, the NRC staff requested additional information regarding Dominion's approach to accommodate the fuel assembly bow issue. The requested information is included in Attachment 1 to this letter. All of the information provided is applicable to both North Anna Units 1 and 2.
Please be advised that the approach Dominion has taken to resolve the issue is an interim solution to support the use of Framatome Advanced Mark-BW fuel in North Anna Units 1 and 2. Attachment 1 describes the approach and margins identified as part of the interim resolution of this issue. Dominion expects to incorporate the elements that constitute the final resolution of this issue when available from Framatome ANP.
To support the use of Framatome Advanced Mark-BW fuel in North Anna Unit 2, Cycle 17, we respectfully request the NRC to complete their review and approval of the license amendment and associated exemptions by February 29, 2004. We appreciate your consideration of our technical and schedular requests. If you have any questions or require additional information, please contact us.
Very truly yours, Leslie N. Hartz Vice President - Nuclear Engineering Commitments made in this letter: None 60
cc: U.S. Nuclear Regulatory Commission Region II Sam Nunn Atlanta Federal Center 61 Forsyth Street, SW Suite 23T85 Atlanta, GA 30303 Mr. J. E. Reasor, Jr.
Old Dominion Electric Cooperative Innsbrook Corporate Center 4201 Dominion Blvd.
Suite 300 Glen Allen, VA 23060 Commissioner Bureau of Radiological Health 1500 East Main Street Suite 240 Richmond, VA 23218 Mr. S. R. Monarque Licensing Project Manager Division of Licensing Project Management U.S. Nuclear Regulatory Commission Washington, D.C. 20555 Mr. M. T. Widmann NRC Senior Resident Inspector North Anna Power Station
04-017 Docket Nos.: 50-338/339
Subject:
Proposed Technical Specifications Changes and Exemption Request Framatome ANP Advanced Mark-BW Fuel -Poetential Assembly Bow Concern COMMONWEALTH OF VIRGINIA )
)
COUNTY OF HENRICO )
The foregoing document was acknowledged before me, in and for the County and Commonwealth aforesaid, today by Leslie N. Hartz who is Vice President - Nuclear Engineering of Virginia Electric and Power Company. She has affirmed before me that she is duly authorized to execute and file the foregoing document in behalf of that Company, and that the statements in the document are true to the best of her knowledge and belief.
Acknowledged before me thi.)-Q-a'day of 'ai U(0 2004.
My Commission Expires: 3 /31/64 Notary Public A-. * .--
(SEAL)-~
Serial No.04-017 Docket Nos. 50338/339 Attachment 1 Interim Assessment of Fuel Assembly Bow for Implementation of Advanced Mark-BW Fuel at North Anna Units 1 and 2 Framatome Fuel Transition Program Technical Specification Change Virginia Electric and Power Company (Dominion)
North Anna Power Station Units 1 and 2
Serial No.04-017 Docket Nos. 50-338/339 1.0 General Description 1.1 Issue Definition & Framatome ANP Evaluation Framatome ANP has provided the NRC with an interim report concerning a reassessment of the methodology for determining power peaking effects of assumed fuel assembly bow (Reference 1). Framatome's interim report characterizes this as an evaluation of a deviation pursuant to the provisions of 10 CFR 21.21(a)(2). This issue potentially affects the Advanced Mark-BW fuel intended for use in North Anna Units 1 and 2, for which Dominion has requested approval in a licensing amendment request (Reference 2).
1.2 Key Impacts of Issue The Framatome ANP fuel assembly bow methodology is documented in topical report BAW-10147P-A, Revision 1 (Reference 3). The geometric configuration for assembly bow is defined by Figure 1 in Appendix J of Reference 3 and is illustrated in the attached Figure 1. The methodology assumes that fuel assembly bowing displaces one fuel assembly along its diagonal axis away from its adjacent assemblies until it touches the faces of the two adjacent assemblies on the other side. This assumed displacement increases the water gap between the bowed assembly and its neighbors in the original array.
The Framatome ANP assessment of this issue has concluded that its effects on plant parameters important to design analyses are limited to potential increases in local power peaking. Reference 1 reports that three influences are being investigated for their effect on power peaking associated with the assumed bow condition: the assumed gap size, use of transport versus diffusion theory in the neutronics calculations, and the geometric model used in the calculations.
Framatome has determined that the aggregate effect of these changes is to produce an increase in the local peaking in fuel rods near the regions of increased water gap. Framatome has informed Dominion that this can be characterized as an increase in the local power peaking uncertainty factor that is assumed in design analyses and predictions.
To support the assessment of the assembly bow issue, Framatome has performed neutronic calculations of the assumed assembly configuration for both 15x15 and 17x17 fuel lattices. These calculations included fresh fuel, burned fuel, and cases with and without Gadolinia. For application to North Anna 1 and 2, Framatome has quantified the local increase in peaking factor uncertainty as follows:
Increase in Local Peaking Factor = 7.8% (corner rod near enlarged water gap)
Increase in Local Peaking Factor = 6.5% (peripheral rods adjacent to corner)
Increase in Local Peaking Factor = 4.5% (rod diagonally interior to corner rod) 1 of 7
Serial No.04-017 Docket Nos. 50-338/339 In addition, the potential effects of assembly bowing on calculated power peaking are concentrated in the quadrant of the fuel assembly closest to the increased water gap. The calculated results indicate that the effect of bowing on rod power diminishes for rod ]ocations further away from the' affected corner and actually decreases rod powers on the opposite side of the bowed assembly.
These calculated results are the maximum effect calculated locally, and apply to only a limited portion of the rod axial length since fuel assemblies are pinned at top and bottom to upper and lower core plates, respectively. These effects are thus treated as an increase in total local peaking (typically associated with Heat Flux Hot Channel Factor, Fa). Framatome has assumed for conservatism that these same effects also apply to the integrated rod power (Enthalpy Rise Hot Channel Factor, FAH). This assumption is applied in the North Anna assessment.
2.0 Dominion Evaluation Approach The fuel assembly bow issue represents a nonconformance with respect to certain assumptions in the design analyses that support implementation of Advanced Mark-BW fuel at North Anna 1 and 2. The interim approach taken by Dominion to address the nonconformance involves confirming that its potential effects can be accommodated by increasing the applied total uncertainty factor in reload core design calculations and by demonstrating that the effect can be accommodated within the design margins of the Reference 2 submittal. The design analyses documented in Reference 2 demonstrated acceptable performance assuming values of both Fo and, FAH that are greater than current design limits for North Anna 1 and 2. The specific application of either of these approaches is discussed in Section 3.0 below. The limits of operation that are supported by the analyses of the Advanced Mark-BW fuel are effectively reduced for all fuel cycles (or portions thereof) in which this interim approach is applied.
Resolution of this issue will be monitored through the Dominion corrective action system until a final resolution is available and can be implemented.
3.0 Margin Assessment 3.1 Nuclear Core Design The methodology of Reference 4 defines an approach to obtain the total uncertainty factor for local peaking, Fo. This determination of the total uncertainty factor involves the statistical combination of several uncertainty factors, including the uncertainty due to assembly bow. The statistical combination of uncertainties is applied as a square-root-sum-of-the-squares (SRSS) calculation, consistent with the treatment for the rod bow penalty in Appendix I (Questions 15 & 32) of Reference 3. In Section 4.2.8 of the Dominion licensing application request (Reference 2) it was concluded that the current total 2 of 7
Serial No.04-017 Docket Nos. 50-338/339 peaking factor uncertainty of 1.0815 used for Westinghouse fuel bounded the value obtained from the Framatome calculation.
Subsequently, Framatome has quantified a total uncertainty factor of 1.0988 from a revised calculation that includes the revised peaking penalty of 7.8% due to assembly bow. To conservatively accommodate the effects of fuel assembly bow, Dominion will apply a total uncertainty factor on nuclear core design predictions of Heat Flux Hot Channel Factor, FQ, that bounds the revised Framatome ANP value. The same total uncertainty factor will be applied to Fa measurements obtained during periodic core surveillance. Dominion has confirmed that there will be sufficient margin with respect to design and operating limits to accommodate this total uncertainty factor. This approach ensures that all design and core follow activities which use these results will directly incorporate the potential increase in uncertainty on Fo. Since calculated results will include these effects, comparison to applicable design and surveillance limits will be performed in accordance with current processes.
Several fuel and safety analysis design considerations are either dependent upon F0 or establish limitations upon Fa. These include assessments for fuel centerline melting, loss of coolant accidents, control rod ejection and cladding strain. Application of an increased total F1 uncertainty factor directly in the core design calculations accommodates the effects of fuel assembly bow for these design considerations such that no additional evaluations are necessary.
The North Anna assessment has concluded that the potential increase in Enthalpy Rise Hot Channel Factor, FAH, can be fully accommodated by determining its effect upon the thermal/hydraulic (i.e., DNB) analyses, which is discussed in Section 3.2. The core design calculations will verify that the current Core Operating Limits Report (COLR) limit of 1.49 for FAH is met. A 1.49 limit will also be applied in assessment of FAH measurements obtained during periodic core surveillance.
3.2 Thermal/Hydraulic Design The approach taken to evaluate the DNB effects of fuel assembly bow for the North Anna interim assessment is very conservative. It involves applying the peaking penalty for assembly bow in a deterministic manner rather than including it as a separate radial uncertainty for inclusion in the Statistical Design Limit (SDL). The approach selected involves performing DNB calculations for the fuel assembly subchannels as described below.
The North Anna evaluation has concluded that the unit subchannel represented by the corner fuel rod and the 3 adjacent fuel rods within the bowed fuel assembly has more limiting conditions for DNB analyses than the corner subchannel defined by the corner rod of the bowed assembly and the corner rod from each of the adjacent three fuel assemblies. The conclusion that this unit subchannel is limiting is based upon the following arguments. The corner subchannel benefits directly from the enhanced cooling from the enlarged flow 3 of 7
Serial No.04-017 Docket Nos. 50-338/339 area attributed to the bowed condition whereas the unit subchannel within the bowed assembly does not benefit directly from the larger flow area. Other interior subchannels are less limiting since the effect of bowing on rod power diminishes for rod locations further away from the affected corner and actually decreases rod powers on the-opposite side of the bowed assembly. These arguments are consistent with the conclusions of Reference 3.
The specific penalties for the four rods of the unit subchannel were presented in Section 1.2 as 7.8% (corner rod), 6.5% (two rods adjacent to corner), and 4.5%
(rod diagonally interior to corner). The average of the penalty values for each of these 4 rods results in a peaking penalty of 6.3%. The North Anna interim evaluation applies this increase of 6.3% to the assumed FA&H values across all channels in the assembly, which conservatively bounds both the magnitude and location of the potential increased peaking identified by Framatome ANP.
Averaging the contribution from each rod sufficiently accounts for the identified effects because: 1) the individual rod penalty factors are conservative and 2) the average penalty is applied across all assembly channels.
The thermal/hydraulic design analyses for Departure from Nuclear Boiling (DNB) for the Advanced Mark-BW fuel were reported in Section 4.4 of the report transmitted by Reference 2. The statepoints, which define the thermal margin of the North Anna core with the Advanced Mark-BW fuel assembly, include points on the safety limit line, limiting axial flux shapes at several axial offsets, and the following events: misaligned rod, loss of flow, rod withdrawal at power, locked rotor, rod urgent failure, rod withdrawal from subcritical and steam line break.
These statepoints and their DNBR results were reviewed for the North Anna assessment.
The statepoints that were evaluated in Reference 2 using statistical DNBR methods included a peak FaH of 1.587 and a 1.7% core uprating. Acceptable thermal margin for the Advanced Mark-BW fuel assembly for each of these statepoints was demonstrated in, Reference 2 by comparing the predicted MDNBRs against the Thermal Design Limit. With the exception of the loss of flow and locked rotor events, the DNB analyses met this limit.
Additional DNB analysis cases were performed for the Locked Rotor and Complete Loss of Flow events to accommodate the assembly bow issue. These revised DNB analyses utilized statepoint definitions that were re-evaluated, which involved removal of- the 1.7% power uprating included in the Reference 2 analyses. The results of the revised DNB calculations met the Thermal Design Limit (TDL), assuming a peak FAH of 1.587.
The statepoints, which were evaluated in Reference 2 using deterministic DNBR methods, included a peak FAH of 1.650 and a 1.7% core uprating. Acceptable thermal margin for the Advanced Mark-BW fuel assembly for each of these statepoints was demonstrated by comparing the predicted MDNBRs to the design DNB limit for the specific code/correlation. The DNB analyses met the applicable limits.
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Serial No.04-017 Docket Nos. 50-338/339 An assumed FAH of 1.587 (1.65 for deterministic events) provides margin relative to the current FAH design limit of 1.49 (1.55 for deterministic events) that will be used for the interim assessment of the fuel assembly bow effects. The difference between the current FAH design limit of 1.49 (or 1.55) and the value of 1.587 (or 1.65) assumed in the Reference 2 design analyses accommodates the assumed 6.3% increase in peaking from assembly bow.
North Anna-specific analysis cases were performed to confirm that the applicable statistical design limits (SDLs) provided in Reference 2 remain valid. These analyses demonstrated that the SDL values for both the hot rod and core-wide DNB criteria are met, assuming a FH design limit of 1.49.
4.0 Conclusions The Dominion interim approach to address the fuel assembly bow issue involves application of an increased uncertainty factor to core design predictions and accommodating the increased uncertainty effects by taking credit for available margin in design analyses performed for the Advanced Mark-BW fuel. This interim approach is being adopted by Dominion as a conservative and expedient measure while Framatome ANP pursues final resolution of this issue. Dominion expects to incorporate the elements that constitute the final resolution of this issue when available from Framatome ANP.
4.1 Scope of Interim Assessment This interim assessment has addressed in a conservative manner the potential effects of the fuel assembly bow issue. The scope of the assessment is limited to fuel design considerations and safety analyses which are dependent upon local peaking factors Fa and FAH. Each of these areas was specifically addressed to ensure that the adequacy of design analyses and limits. These effects have been addressed in the nuclear core design, fuel rod design, NSSS safety analysis, and core follow and surveillance activities.
The margin and penalty rackup will be included in the reload safety documentation for any cycles that adopt the approach described herein to accommodate the assembly bow issue. This interim approach will be applied to the initial cycles in both units that use Framatome ANP Advanced Mark-BW fuel.
These cycles are North Anna 2, Cycle 17 which refuels in Spring 2004 and North Anna 1, Cycle 18 which refuels in Fall 2004. It is noted that this approach is conservative for subsequent cycles, since the available thermal/hydraulic margins increase as the proportion of Advanced Mark-BW fuel in the core increases.
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Serial No.04-017 Docket Nos. 50-3381339 4.2 Duration of Interim Assessment The scheduled date for completion of Framatome ANP's assessment of this issue is stated as December 17, 2004 in Reference 1. Dominion will evaluate the continued application of this interim approach for future fuel cycles (or portions thereof) for which this issue applies. This interim approach will be removed upon notification from Framatome ANP that their assessment of this issue is completed and that a final resolution has been developed and can be implemented.
5.0 References
- 1. Letter, James F. Mallay (Framatome ANP) to USNRC, "Interim Report of an Evaluation of a Deviation Pursuant to 10 CFR 21.21(a)(2)," NRC:03:083, December 9, 2003.
- 2. Letter, L. N. Hartz to USNRC, "North Anna Power Station Units 1 and 2 -
Proposed Technical Specifications Changes and Exemption Request Use of Framatome ANP Advanced Mark-BW Fuel," Serial No.02-167, March 28, 2002.
- 3. BAW-10147P-A, Revision 1, "Fuel Rod Bowing in Babcock & Wilcox Fuel Designs," May 1983.
- 4. BAW-10163-P-A, "Core Operating Limit Methodology for Westinghouse-Designed PWRs," June 1989.
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. 4 Serial No.04-017 Docket Nos. 50-338/339 Figure 1 Geometry of Fuel Assemblies X, .
Bundle Pitch Lines -'..
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Spacer Grid Envelopes 7 of 7