1CAN120601, Supplement to License Amendment Request to Support the Use of Metamic Poison Insert Assemblies in the Spent Fuel Pool
| ML063610336 | |
| Person / Time | |
|---|---|
| Site: | Arkansas Nuclear  |
| Issue date: | 12/14/2006 |
| From: | Eichenberger J Entergy Operations |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| 1CAN120601 | |
| Download: ML063610336 (9) | |
Text
Entergy Entergy Operations, Inc.
1448 S.R. 333 Russellville, AR 72802 Tel 479-858-4702 John R. Eichenberger Acting Director, Nuclear Safety Assurance 1CAN 120601 December 14, 2006 U.S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555
SUBJECT:
Supplement to License Amendment Request to Support the Use of Metamic Poison Insert Assemblies in the Spent Fuel Pool Arkansas Nuclear One, Unit 1 Docket No. 50-313 License No. DPR-51
REFERENCES:
- 1. Letter to the NRC dated July 27, 2006, "License Amendment Request to Support the Use of Metamic Poison Insert Assemblies in the Spent Fuel Pool" (1CAN070603)
- 2. Letter to the NRC dated October 4, 2006, "Supplement to License Amendment Request to Support the Use of Metamic Poison Insert Assemblies in the Spent Fuel Pool" (1CAN100601)
- 3. Letter to the NRC dated October 9, 2006, "Supplemental Information to License Amendment Request to Support the Use of Metamic Poison Insert Assemblies in the Spent Fuel Pool" (1CAN100602)
Dear Sir or Madam:
By letter (References 1, 2 and 3), Entergy Operations, Inc. (Entergy) proposed a change to the Arkansas Nuclear One, Unit 1 (ANO-1) Technical Specifications (TSs) to support the use of poison panel insert assemblies in the ANO-1 spent fuel pool.,
On October 23, 2006, Entergy received a request for additional information regarding the proposed change. As a result, 10 questions were determined to need formal response.
Entergy's response is contained in Attachment 1.
There are no technical changes proposed. The original no significant hazards consideration included in Reference 1 is not affected by any information contained in the supplemental letter. There are no new commitments contained in this letter.
1CAN 120601 Page 2 of 2 If you have any questions or require additional information, please contact Dana Millar at 601-368-5445.
I declare under penalty of perjury that the foregoing is true and correct. Executed on December 14, 2006.
Sincerely, JRE/DM Attachments:
- 1. Response to Request For Additional Information cc: Dr. Bruce S. Mallett Regional Administrator U. S. Nuclear Regulatory Commission Region IV 611 Ryan Plaza Drive, Suite 400 Arlington, TX 76011-8064 NRC Senior Resident Inspector.
Arkansas Nuclear One P. 0. Box 310 London, AR 72847 U. S. Nuclear Regulatory Commission Attn: Ms. Farideh Saba MS 0-8 B1 Washington, DC 20555-0001 Mr. Bernard R. Bevill Director Division of Radiation Control and Emergency Management Arkansas Department of Health and Human Services P. 0. Box 1437 Slot H-30 Little Rock, AR 72203-1437
Attachment 1 To 1CAN120601 Response to Request for Additional Information to 1CAN120601 Page 1 of 6 Response to Request for Additional Information Related to License Amendment Request to Support the Use of Metamic Poison Insert Assemblies in the Spent Fuel Pool Structural/Seismic Question 1 Referring to the last paragraphof page 6 of 50, discuss the fluid-structure analysis study performed and the results of the study that form the basis for Entergy's assertion that use of SOL VIA in seismic response modeling of the racks, fuel assemblies and inserts was adequate. Since both materialproperty and seismic response characteristicsof metamic panels are not as well defined as that of other commonly used materials (e.g., carbon steel.
rebarand concrete), discuss any experimental data that were used as the basis for Entergy's conclusion that good agreement on the behaviorof the beam/stick model was demonstrated.
Enterqy's Response The fluid-structure study consisted of modeling a 3D square structure (a box on feet) representative in general of one rack using shell elements. This study structure was effectively contained in a pool with fluid elements surrounding it. For comparison, the same methodology as used for the rack analysis was used to develop a beam model of the study structure, with hydrodynamic added mass effects also considered the same as for the rack analysis. The fluid/structure model and the associated beam model were analyzed using the same time-history input. Displacement results were comparable and in good agreement.
Hence it was concluded the beam model representation of the racks for the dynamic analysis provided comparable results to consideration of a more detailed model including fluid elements.
The study was analytical with the goal of assessing the dynamic analysis modeling of the racks and no experimental data was considered. The Metamic material was not specifically included, and has no relevance to the conclusions.
Question 2 The last paragraphof Section 3.2, Equation of Motion (page 7 of 50) states that the WPMR is modeled by combining the eight modules and including the appropriateoff-diagonal stiffness matrix and mass matrix terms... Discuss key non-linear attributesthat were modeled in the WPMR analysis that reflect the interactionsbetween the modules and, that between a module and its adjacent spent fuel wall. Discuss the extent of experimental verification implemented with respect to the above modeling of the non- linearattributes. Also, with respect to Section 3.5, "Impact Behavior" (page 8 of 50), discuss pertinent experimentalresults that support the validity of Entergy's use of the Gapped-Truss elements in SOL VIA code.
Enterqy's Response Non-linear attributes in the WPMR include gaps or clearances between the racks and between the racks and the pool, the free-sliding and lift-off potential for the racks relative to their support on the pool floor, and the accounting for potential impact effects. Experimental to 1CAN 120601 Page 2 of 6 verification was not implemented. Methodology used is consistent with industry practice (Reference NUREG/CR-5912, "Review of the Technical Basis and Verification of Current Analysis Methods Used to Predict Seismic Response of Spent Fuel Storage Racks") for analysis of spent fuel racks, shielding blocks, and dry fuel casks. Use of the non-linear gap element (identified as a Gapped Truss element type) in SOLVIA simply provided a means to account for the gaps between the model components and impact forces if those gaps closed during the analysis. The "gapped truss" element is an axial force member, and hence is effectively a spring. The non-linear gap option allows it to be a compression-only element when the gap is closed, and to carry or transmit no loads when the gap is open.
Question 3 Referring to Section 3.8, Poison Insert Analysis Methodology (page 9 of 50), discuss the basis for treating the poison inserts as additional beam elements in the structuralmodel consideringthe fact that the rattling space for poison inserts are much smaller than that of fuel assemblies within a rack cell. Additionally, with respect to the first paragraphof Section 4.8, Poison Insert Modeling, of page 16 of 50, provide basic materialproperties that are used for defining the metamic inserts modeled as a single elastic beam element in a single region 3 rack analysis. Specifically, discuss the appropriatenessof the elastic beam element treatment of the metamic inserts accounting for its materialcharacteristics(e.g., material brittleness), rack specific geometric layout, (e.g., gaps between cell walls and the inserts),
constraints,and potential differences between the stress-strainrelationshipof the metamic inserts and that of the stainless steel cells.
Entercqy's Response The poison inserts were originally designed to be wedged in the flux traps. With redesign of the inserts, nominal gaps or clearances within the flux traps were possible and likely to exist.
Because of potential for the inserts to now "rattle" within the flux traps during a seismic loading event, some manner to account for the impact loads on the inserts (which were presumed inevitable because of the smaller gaps compared to the fuel elements) was required, and including them explicitly in the model was an appropriate way to obtain these load effects. The inserts were modeled in the same manner as the fuel elements, which permitted them to slide, uplift, and close and open the lateral gaps between the inserts and the flux trap walls.
The Metamic inserts were modeled based on the full composite of all the components of the inserts. This included the stainless steel wrapper channels, the Metamic panels, the channel shaped bands which hold the inserts in the wrapper channels, and the stiffener plates which hold the two wrapper channel sections together. While the Metamic panels were modeled using their material properties, (SY = 33.1 ksi, Su=40.67 ksi, and E=12.4 x 106 psi) this was done only for completeness since the stiffness (structural) contribution to the overall properties of the assembled inserts is small. For example, the wrapper panels have a modulus of elasticity of about twice that of the Metamic panels. Additionally, because the Metamic panels are held in the wrapper channels by the bands without any significant clamping force, no shear transfer occurs between the Metamic panels and the wrapper channels and hence no composite action occurs (i.e. the behavior for bending of the panels and relative to the wrapper panels is analogous to stacked loose plates). This gives a relative El (moment of inertia times modulus of Elasticity) relationship of about 30000:1 for the to 1CAN 120601 Page 3 of 6 wrapper channel assembly compared to the Metamic panels. This means the wrapper channel assemblies control the structural behavior (they are much stronger and stiffer) with no significant contribution from the Metamic panels. Additionally, the yield stress of the stainless steel wrapper plates is about 70% of that for the Metamic panels. Since the wrapper plate assemblies control the displacement and deflections of the inserts including the Metamic panels, and because they did not yield, the Metamic panels are effectively protected by the wrapper panel assemblies and their relatively small ductility range (brittleness) is not a concern. Stress-Strain differences are appropriately considered by use of the proper modulus of elasticity for the different materials since everything remained elastic. Hence, consideration of Metamic insert assembly as a beam within the flux traps with the gaps modeled is appropriate.
Question 4 Discuss the specific studies that were performed to confirm that sloshing was negligible at the top of the rack as indicatedin item j of page 13 of 50.
Enterqy's Response No specific study was performed relative to sloshing. This was an observation from the results of the fluid-structure study described in response to RAI question 1 above. The ANO-1 spent fuel pool is approximately 23 feet wide x 44 feet long x 42 feet deep. The spent fuel racks extend to about 15 feet above the floor. A conservative estimate of the sloshing wave height at the top of the pool is about 3.85 feet. The depth of influence for sloshing (convective) load effects can be considered as twice this or 7.7 feet. This is a significant distance above the top of the racks, and hence sloshing loads are not a concern.
Question 5 With respect to Section 6. 1, Single Rack Analysis of page 21 of 50, elaborate more on the analysis results with a discussion of some numericalfindings that support Entergy's assertion that the additional2000 lbfmass rigidly attached to the rack 24" above the top of the cell structurehas an insignificant effect on the rack module analysis results.
Enterqy's Response Due to the magnitude of the added mass to account for hydrodynamic effects, the 2000 lbf mass adds only a fractional increase to the mass of the racks dynamically, and analyses including the 2000 lb mass show no differences in results than the analyses without it.
to 1CAN 120601 Page 4 of 6 Question 6 With respect to Figure 8.1 - Maximum DisplacementPlots, clarify the meanings of "Original,"
"Max. Disp," and "Zone ZI." RegardingFigure 8.2, Cell Impact Force Plots, Single Rack Model, clarify the meaning of "EG 4 E P 1 Force -R."
Enterqy's Response "Original" refers to the original undisplaced model, and indicates that the original position is indicated by the dashed lines. "Max. Disp." is the maximum displacement~of any part of the model at the time indicated. "Zone Z1" is the method by which a portion of the full model can be defined in SOLVIA for convenience of plotting and reviewing results.
"EG 4" indicates the element is part of Element Group 4 as defined in the SOLVIA input.
"E P 1" indicates the results are at element integration point 1 (note these elements are of course one-dimensional and as such have only one integration point). "Force -R" indicates the axial force result for the element.
Question 7 Section 8.10, Comparison of Analysis Results to Westinghouse Ref. (9) Results, states that "This comparison is a further validation of the S&A Ref (5) evaluation and that the use of Westinghouse results for the Wrapper welds, cell seam weld and cell-to-cell weld is justified."
Explain any potential issues that may arise from the Entergy's use of the Westinghouse results for the Wrapper welds, cell seam weld and cell-to-cell weld, and their implication on the Region 3 rack seismic response. As applicable, discuss differences between the above mentioned Westinghouse welds and those used by Entergy's Region 3 racks with the inserted poison.
EnterQv's Response The Region 3 racks are Westinghouse racks, and the Westinghouse analysis is the basis for their original qualification. Because the S&A results show that the addition of the Metamic inserts effectively did not change the seismic behavior and response of the racks, the rack welds as qualified by Westinghouse are not subjected to additional forces due to the addition of the Metamic inserts to the racks, and hence the Westinghouse analysis and qualification of the welds remains valid. The Metamic insert components and welds were analyzed and qualified in the present calculation using the results of the present analysis.
to 1CAN 120601 Page 5 of 6 Question 8 Referring to second paragraphof page 44 of 50, explain and justify with pertinentreferences for the method used by Holtec in specifying a conservative hydrodynamic pressure resulting from the seismic displacement of the racks.
Enterqy's Response Reference to Holtec's analysis in this paragraph was relative to the initial submittal, and should have been updated to reference the Stevenson & Associates analysis performed subsequent to Holtec's.
The pool structure analysis was updated using load results from the updated rack analyses done by Stevenson & Associates. Additionally, the 5000 lb loads indicated were also included in the pool structure analysis update. For consideration of hydrodynamic pressure loads from the rack movements on the walls, it was observed in the fluid/structure study described in response to RAI question 1 above, that the effective pressure on the pool walls during seismic loading was less than or equal to that for the pool water alone. Original design/qualification of the pool and the reanalysis performed for the reracking in 1982 both considered the effect of the water due to seismic inertial effects and the magnitude of this loading effectively covered pressure differences potentially caused by the movement of the racks.
Coupon Sampling Program Question 1 On page 14 of your July 27, 2006 license amendment, you stated that measurements to be performed at each inspection will be as follows: physical observations,length, width, thickness, weight, density and neutron attenuationtesting. Please provide your acceptance criteriafor these parametersand the basis for this criteria.
Enterqy's Response The acceptance criterion for each of the parameters is as follows. The basis for the criterion is either existing coupon sampling programs or reasonable limits that assure further evaluation.
Physical observation - visual examination and photography Upon receipt of a coupon for testing, the exposed coupon should be carefully examined and photographed to document the appearance of the coupon, noting any sign of degradation that may be observed. Special attention will be paid to any edge or corner defects and to any discoloration, swelling, or surface pitting that might exist.
to 1CAN 120601 Page 6 of 6 Dimensional Measurements - length, width, and thickness Measurements on post-irradiated coupons will be made at the same approximate locations used for pre-irradiation characterization measurements and recorded. Length and width dimensions shall not exceed +/- 0.125 inches when compared to the initial width or length.
Thickness is used to monitor swelling and an increase in thickness at any point shall not exceed +/- 0.01 inches of the initial thickness at that point.
Weight and density The weight of each coupon should be obtained within +/- 5% of the initial coupon weight.
Neutron Attenuation Post-irradiated coupons that exhibit a decrease of no more than 5% in Boron-10 content, as determined by neutron attenuation or chemical analysis, is acceptable. This is the same as a requirement for no loss of boron within the accuracy of the measurement.
Changes in excess of any acceptance criteria may require investigation and engineering evaluation which may include early retrieval and measurement of one or more of the remaining coupons to provide corroborative evidence that the indicated change(s) is real. If the deviation is determined to be real, an engineering evaluation shall be performed to identify further testing or any corrective action that may be necessary.
Question 2 On page 13 of your July 27, 2006, your Sample Coupon Measurement Schedule calls for a coupon to be removed every two years for the first three intervals and thereafterevery 4 to 5 years over the service life of the inserts. It is not clear to the staff whether you plan to remove a new coupon every intervalin addition to the coupon removed the previous interval. Please clarify how many coupons you plan to remove every interval.
Entergy's Response A different coupon is removed each sample period. For example, coupon #1 is removed and analyzed after two (2) years exposure in the Spent Fuel Pool (SFP) environment. Coupon #2 is removed and analyzed after four (4) years of exposure in the SFP or two (2) years elapsed time since the first sample. Coupon #3 is removed after six (6) years of exposure or two (2) years elapsed time since the last (2 nd) sample. Coupons #4 through #10 will be removed at the intervals specified in the sample coupon measurement schedule on page 13. A minimum of ten (10) coupons were chosen to adequately cover the expected lifetime without reinserting a previously sampled coupon. When coupon #10 is removed, the accumulated exposure time will be forty (40) years; the expected lifetime of the poison insert assemblies. The sampled coupons may optionally be returned to the pool and remounted on the tree at the discretion of the reviewing engineer.