ML20199G987
| ML20199G987 | |
| Person / Time | |
|---|---|
| Site: | Wolf Creek, Callaway  |
| Issue date: | 01/20/1999 |
| From: | Mel Gray NRC (Affiliation Not Assigned) |
| To: | NRC (Affiliation Not Assigned) |
| References | |
| TAC-MA1113, TAC-MA1294, NUDOCS 9901250083 | |
| Download: ML20199G987 (28) | |
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U h LICENSEES: Wolf Cresk Nuclsar Op: rating Corporation Union Electric Company FACILITIES: Wolf Creek Generating Station, Unit 1 Callaway Plant, Unit 1 I
SUBJECT:
MEETING WITH WOLF CREEK NUCLEAR OPERATING CORPORATION (WCNOC) AND UNION ELECTRIC COMPANY (UE) REGARDING PROPOSED TECHNICAL SPECIFICATION AMENDMENTS FOR WOLF CREEK AND CALLAWAY PLANTS (TAC NOS. MA1294 AND MA1113)
On October 14 and 15,1998, meetings were held between Wolf Creek Nuclear Operating Corporation (WCNOC), Union Electric (UE), and the Nuclear Regulatory Commission (NRC) staffs to discuss topics related to proposed technical specification changes that support modifications to increase the spent fuel pool (SFP) capacity at the Wolf Creek Nuclear Generating Station and Callaway.
On October 14,1998, topics that required only non-proprietary information responses were discussed. On October 15,1998, topics that required both proprietary and non-proprietary information responses were discussed. Attachment 1 is a list of attendees. Attachment 2 provides a summary of each topic discussed. The topic summaries in Attachment 2 are grouped by proprietary and non-proprietary category.
At the conclusion of the meeting, the NRC staff identified six topics that required additional information (topics 9,13,26,27,29,30). WCNOC and UE personnel committed to provide this information in a timely manner to support the review schedule for the proposed issuance of the license amendments. ORIGINAL SIGNED BY:
Mel Gray, Project Manager Project Directorate IV-2 l Division of Reactor Projects - lil/IV Office of Nuclear Reactor Regulation l
Docket No. 50-482 DISTRIBUTION: (Hard Copy) and 50-483 Docket ACRS l PUBLIC PDIV-2 Reading i Attachments: 1. List of Meeting Attendees KThomas OGC l 2. Summary of Discussion Topics MGray GBagchi l YKim RRothman cc w/atts: See next page EPeyton l
DISTRIBUTION: (E-Mail)
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2 NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20565-0001 b ,,,,, 8 January 20, 1999 LICENSEES: Wolf Creek Nuclear Operating Corporation -
Union Electric Company FACILITIES: Wolf Creek Generating Station, Unit 1 Callaway Plant, Unit 1
SUBJECT:
MEETING WITH WOLF CREEK NUCLEAR OPERATING CORPORATION (WCNOC) AND UNION ELECTRIC COMPANY (UE) REGARDING PROPOSED TECHNICAL SPECIFICATION AMENDMENTS FOR WOLF CREEK AND CALLAWAY PLANTS (TAC NOS. MA1294 AND MA1113)
On October 14 and 15,1998, meetings were held between Wolf Creek Nuclear Operating Corporation (WCNOC), Union Electric (UE), and the Nuclear Regulatory Commission (NRC) staffs to discuss topics related to proposed technical specification changes that support modifications to increase the spent fuel pool (SFP) capacity at the Wolf Creek Nuclear Generating Station and Callaway.
On October 14,1998, topics that required only non-proprietary information responses were discussed. On October 15,1998, topics that required both proprietary and non-proprietary information responses were discussed. Attachment 1 is a list of attendees. Attachment 2 provides a summary of each topic discussed. The topic summaries in Attachment 2 are grouped by proprietary and non-proprietary category.
At the conclusion of the meeting, the NRC staff identified six topics that required additional information (topics 9,13,26,27,29,30). WCNOC and UE personnel committed to provide this information in a timely manner to support the review schedule for the proposed issuance of the license amendments.
Mel Gray, Project Manager Project Directorate IV-2 Division of Reactor Projects - lil/IV Office of Nuclear Reactor Regulation Docket Nos. 50-482 and 50-483 Attachments: 1. List of Meeting Attendees
- 2. Summary of Discussion Topics
, cc w/atts: See next page 1
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l cc w/encis:
Jay Silberg, Esq. Chief Operating Officer Shaw, Pittman, Potts & Trowbridge Wolf Creek Nuclear Operating Corporation 2300 N Street, NW P. O. Box 411 l Washington, D.C. 20037 Burlington, Kansas 66839 i
Regional Administrator, Region IV Supervisor Licensing U.S. Nuclear Regulatory Commission Wolf Creek Nuclear Operating Corporation
- 611 Ryan Plaza Drive, Suite 1000 P.O. Box 411 Arlington, Texas 76011 Burlington, Kansas 66839 Senior Resident inspector U.S. Nuclear Regulatory Commission U.S. Nuclear Regulatory Commission Resident inspectors Office
- P. O. Box 311 8201 NRC Road i Burlington, Kansas 66839 Steedman, Missouri 65077-1032 l Chief Engineer Mr. Otto L. Maynard l Utilities Division President and Chief Executive Officer Kansas Corporation Commission Wolf Creek Nuclear Operating Corporation 1500 SW Arrowhead Road Post Office Box 411 Topeka, Kansas 66604-4027 Burlington, Kansas 66839 l
Office of the Governor ;
State of Kansas !
Topeka, Kansas 66612 l
Attomey General Judicial Center 301 S.W.10th 2nd Floor Topeka, Kansas 66612 County Clerk Coffey County Courthouse Burlington, Kansas 66839 Vick L. Cooper, Chief Radiation Control Program Kansas Department of Health and Environment l Bureau of Air and Radiation Forbes Field Building 283 Topeka, Kansas 66620 l
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cc w/encls:
Professional Nuclear Mr. Otto L. Maynard Consulting, Inc. President and Chief Executive Officer 19341 Raines Drive Wolf Creek Nuclear Operating Corporation Derwood, Maryland 20855 Post Office Box 411 Burlington, Kansas 66839 John O'Neill, Esq.
Shaw, Pittman, Potts & Trowbridge Mr. Dan I. Bolef, President 2300 N. Street, N.W. Kay Drey, Representative Washington, D.C. 20037 Board of Directors Coalition for the Environment Mr. H. D. Bono 6267 Delmar Boulevard Supervising Engineer University City, Missouri 63130 Quality Assurance Regulatory Support Union Electric Company Mr. Lee Fritz Post Office Box 620 Presiding Commissioner Fulton, Missouri 65251 Callaway County Court House 10 East Fifth Street U.S. Nuclear Regulatory Commission Fulton, Missouri 65151
! Resident inspector Office 8201 NRC Road Mr. Alan C. Passwater, Manager Steedman, Missouri 65077-1302 Licensing and Fuels Union Electric Company Mr. J. V. Laux, Manager Post Office Box 66149 Quality Assurance St. Louis, Missouri 63166-6149 Union Electric Company Post Office Box 620 Mr. Garry L. Randolph Fulton, Missouri 65251 Vice President and Chief Nuclear Officer Union Electric Company Manager- Electric Department Post Office Box 620 Missouri Public Service Commission Fulton, Missouri 65251 301 W. High Post Office Box 360 l Jefferson City, Missouri 65102 l Regional Administrator, Region IV
! U.S. Nuclear Regulatory Commission l Harris Tower & Pavilion
! 611 Ryan Plaza Drive, Suite 400 Arlington, Texas 76011-8064 Mr. Ronald A. Kucera, Deputy Director Department of Natural Resources P.O. Box 176
. Jefferson City, Missouri 65102 4
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9 MEETING WITH WOLF CREEK NUCLEAR OPERATING CORPORATION AND UNION ELECTRIC COMPANY l 1
l LIST OF MEETING ATTENDEES ,
l OCTOBER 14,1998 ;
I l
l WOLF CREEK NUCLEAR OPERATING CORPORATION
- Ron Holloway
! UNION ELECTRIC COMPANY Richard Lutz i Dave Shafer Timothy Hermann
! HOLTiTC INTERNATIONAL i <
Alan Soler
- Scott Pellet MR.Q Yong Kim Goutam Bagchi Giuliano DeGrassi (Brookhaven National Laboratory) l Joseph Braverman (Brookhaven National Laboratory) l- Robert Rothman j Mel Gray t
l OTHER ATTENDEES l
! Tom Lehman (Florida Power Corporation) l Jim Andrachek (Westinghouse Corporation)
William Lapay (Westinghouse Corporation) 9 1
1 i l
MEETING WITH WOLF CREEK NUCLEAR OPERATING CORPORATION AND UNION ELECTRIC COMPANY LIST OF MEETING ATTENDEES OCTOBER 15,1998 l
WOLF CREEK NUCLEAR OPERATING CORPORATION Ron Holloway UNION ELECTRIC COMPANY Richard Lutz Dave Shafer Timothy Hermann HOLTEC INTERNATIONAL Alan Soler Scott Pellet NLR_Q Yong Kim ,
Goutam Bagchl !
Giuliano DeGrassi (Brookhaven National Laboratory)
Joseph Braverman (Brookhaven National Laboratory) ;
Mel Gray l
l 4
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SUMMARY
OF DISCUSSION TOPICS Reference. Holtec Intemational Report No. HI-971769, entitled " Licensing Report for Reracking of the Callaway and Wolf Creek Nuclear Plants for Union Electric and WCNOC." Union Electric submitted this report as Enclosure 3 (proprietary version) and Enclosure 4 (non-proprietary version) in application for amendment dated February 24,1998. WCNOC submitted this report i as Attachment 1 (proprietary version) and Attachment 2 (non-proprietary version) in application for amendment dated March 20,1998.
I Non-Proprietary Discussion Toolcs:
l Item 2
! Explain how the welding between cells *detunes" the rack from the seismic input as stated on page 2-12 of the Reference.
Discussion:
- Holtec International personnel explained their philosophy of designing the cell-to-cell weld sizes and locations to ensure that the fundamental frequency of the rack falls outside of the response I spectra peak range. They cited parametric studies performed for Zion Nuclear Plant to study the sensitivity of rack response to changes in weld lengths. These studies indicated that an optimum weld configuration could be achieved to minimize the rack displacements. The study also demonstrated that pedestal forces are relatively insensitive to the weld length, it was noted, however, that the studies were specific to the Zion plant design and earthquake loading.
The staff also expressed concerns over the discontinuity of the welds with regard to shear l
' transfer through the rack superstructure. This issue was discussed further under other topics.
Status: Closed item 3 The safety assessment for Wolf Creek states that the gaps between the racks and pool walls vary from 3/4 inches to 7.43 inches. Figure 1.2 of the Reference shows gaps of 1 inch to 7.43 ,
inches. What are the correct dimensions of the gaps? !
Discussion:
L The licensee clarified the inconsistency in gap dimensions by indicating that the referenced Holtec report provides the nominal gaps which are as small as one inch. The dimension provided in the licensee's safety assessment report was the minimum gap which can be as small as 3/4 inch when dimensionel tolerances are considered.
Status: Closed i I
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! Item 4 Are the gaps between the racks and between the racks and the poc! wa!! measured at the !
baseplates or at a higher elevation? If the gaps between the top and bottom of the fuel rack l are different, provide values at both elevations.
Discussion:
Holtec personnel clarified the locations of the gap dimensions indicated in the licensing report.
The gaps reflect the nominal dimensions between the outer surface of the rack walls (excluding l sheathing) and the adjacent rack walls or poolliner plate. The rack-to-pool gaps are 1/4 inch I smaller at the baseplate due to baseplate extension. At rack-to-rack locations, baseplates have l
extensions of 3/4 inch and are nominally in contact to provide a nominal gap of 1.5 inches between rack walls. Holtec personnelindicated that the baseplate extensions were appropriately considered in the seismic analysis.
Status: Closed item 5 Provide the dimensions of the bearing pads used to transfer the dead load of the racks to the
! spent fuel pool floor.
Discussion:
Holtec personnel provided the dimensions of the three sizes of support pedestal bearing pads.
They are 14" square,19" by 26", and 26" square for one, two and four pedestals, respectively.
All pads are 1.5" thick.
Status: Closed ltem 6 l
- Provide additional design information on the platforms which will be used to support the spent fuel racks in the cask loading pit. Include a description of how they will be supported and connected to the pool.
l l Discussion:
The licensees provided a description of the Cask Loading Pit support platforms. The platforms are fabricated from structural members and are designed to the requirements of ASME Section ll1 Subsection NF. The peak vertical and horizontal loads from the rack dynamic analysis are used in the design of the platform members. The rack pedestals rest on 10.5 inch square supporting plates at the top of the platforms. The platforms are not connected to the poolliner l but simply rest on the liner plate as freestanding structures.
Status: Closed
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l Item 7 Identify all interim spent fuel pool configurations, including those which will have both existing and new fuel racks. Provide the maximum length of time for which the pool will remain in each interim configuration.
Discussion: )
The licensees explained that all of the existing racks in the spent fuel pool will be removed and j replaced during the first campaign. A fuel and rack shuffle scheme was prepared defining all of 1 the sequences and stages necessary to complete the campaign. The interim configurations will l exist for short periods of time during construction only with each configuration existing for much less than 30 days.
l Status, Closed
- Item 8 Provide a description and sketch of the existing spent fuel racks. Are the current racks free standing or are they attached to the pool floor and/or walls?
Discussion:
l The licensees explained that the existing racks are constructed from square tubes welded
! together to form a honeycomb structure. A typical fuel rack drawing was reviewed. The racks are free standing with pairs of modules mechanically fastened together at the top. Holtec personnel performed additional seismic analyses of these racks to demonstrate that no lateral l supports are required during the construction phase.
Status: Closed l
Item 9 l Figures 7.2.1,7.2.2 and 7.2.4 in the Reference show an additional bar around the top perimeter of a fuel rack. This is not in agreement with Figure 2.1.1 of the Reference. What is the current configuration?
l l Discussion:
! Holtec personnel indicated that figures in the referenced report which show a bar around the i l top perimeter of the rack were leftover from generic material previously developed for other l l projects and were solely intended to indicate the orientation of the impactor and target for a !
- typical" rack structure during drop scenarios. No such bars are included in this design. The !
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staff expressed a concem about including the correct fuel rack design drawings in the FSAR update. The licensees agreed to address this concern.
Status:
The licensees will provide a response to clarify this aspect of the rack design and will address whether any changes in the FSAR are needed.
Item 10 l I
Provide a detailed description of the methodology used to verify and benchmark all of the I computer programs used in the seismic and structural analysis of the spent fuel racks and pool. l i
Discussion: l l
Holtec personnel stated that the following computer programs were used in this project:
ANSYS, LSDYNA-3D, DYNARACK, and STARDYNE. The programs were validated under Holtec's Quality Assurance program. Validation of the commercially available programs was l performed by running sample problems and comparing against known results. The validation 1 of Holtec's DYNARACK program involved an extensive benchmarking effort which was ,
described in detail in a report which was submitted to NRC in the recent Waterford 3 reracking license amendment which was subsequently approved by the staff on July 10,1998. The staff expressed concerns about the adequacy of both analytical and experimental verification of results. There was some further discussion regarding benchmarking against other programs such as ANSYS. Holtec personnelindicated that other programs have limited capabilities in the area of fluid coupling but they would be willing to work with the staff in developing and analyzing additional benchmark problems in the future.
Status: Closed item 12 With respect to the single safe shutdown earthquake (SSE) artificial time history used for stress analysis as mentioned in the applications, provide the following:
a) A comparison between the response spectrum (RS) of the artificial time history and the licensing basis design RS in the final safety analysis report (FSAR).
b) Demonstrate the adequacy of the artificial time history including a demonstration of the extent of conformance to a target power spectral density (PSD) function of the artificial time history iri accordance with guidance provided in Standard Review Plaa Section 3.7.1.
.o em 5-Discussion:
Holtec personnel presented a set of figures showing comparisons of the response spectra and the power spectral density (PSD) of the artificial time history set with the corresponding target j response spectra and PSD curves. The curves were based on 4 percent damping for SSE and :
2 percent damping for OBE and were shown to envelope the target curves in accordance with the requirements of SRP Section 3.7.1.
Status: Closed item 14 ;
1 Clarify the function of shear and bending springs in Figure 6.5.4 of the applications. They ,
appear to represent hinges at the center elevation (H/2) of the rack. l Discussion:
Holtec personnel explained that the shear and bending elements depicted in the figure are not hinges but are stiffness elements pictorially described at the center elevation of the rack module. The stiffness elements are mathematically described by stiffness matrices derived ,
from classical complementary energy principles and are equivalent to exact solutions based on i elastic beam and rod theory. The staff questioned the adequacy of representing the rack as a beam structure and whether shear was properly represented. This was discussed further under other topics.
Status. Closed item 18 Provide the specific values of the friction coefficients used in the cases where a random Gaussian distribution was assumed. Were different values assigned to each support leg of each rack? Were any sensitivity studies performed to investigate the limits of response for other randomly selected values? Can any conclusions be drawn with regard to identifying a bounding case by comparing the results of the random case with the results of the cases with upper and lower limits of friction coefficient?
Discussion:
Holtec personnel presented a complete list of coefficient of friction (COF) values for a i
representative random Gaussian distribution sitnulation. The values were based on a mean of l 0.5 and a standard deviation based on tests performed by Rabinowicz with lower and upper limits of 0.2 and 0.8. The sample data illustrated that different friction coefficients are assigned I randomly to each of the four support pedestals in each horizontal direction for each rack. A l different random set was generated for each of the five random load cases analyzed under this project. Sensitivity studies were not performed for this project. However, Holtec personnel indicated that based on the comparisons of results of the random COF load cases with those using the two extreme values (0.2 and 0.8) for this project and other reracking projects, the l
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I l random simulations are most often bounded by the two extreme conditions. The load case with a COF of 0.8 generally provides the highest stresses and rocking displacements while the case with a COF of 0.2 provides the highest sliding displacements.
Status, Closed item 19 i
Figures 6.5.8 and 6.5.9 of the Reference illustrate a half full spent fuel pool with only 8 of the 15 fuel racks installed. Why was this condition analyzed? Is this an interim configuration?
Discussion:
Holtec personnel explained that the 8 rack spent fuel pool configuration was analyzed to establish the results for one possible pool layout which may take place during the construction phase. This analysis was performed prior to the preparation of the installation rack shuffle scheme and may not accurately depict a specific interim configuration but was chosen to l investigate whether any unexpected rack responses could result in the unlikely event that an earthquake occurred during the rack change-out process. This analysis supplemented the single rack analyses which were performed to evaluate the possibility of rack overturning during l the construction phase. Those analyses considered the narrowest racks half filled with fuel to
- maximize the possibility of overturning. The results of both the single rack and 8 rack analysis demonstrated large margins against overturning.
l Status. Closed item 20 I i lt does not appear that half full or empty fuel rack load cases were considered in the whole pool l multi-rack analyses. Such cases may be more bounding with regard to rocking and sliding behavior leading to rack-to-rack or rack-to-wall impacts. Explain why these cases should not be considered.
Discussion:
Holtec personnel pointed out that half-full racks were considered in the single rack runs
! performed for overtuming evaluations. The displacements predicted by those analyses were shown to be smaller than the displacements from the analyses of fully loaded racks in a fully -
i racked pool. In addition, their experience with other rerack analyses has shown that fully l loaded racks most often control the rack stress values over simulations including partially l loaded racks and often control for displacements as well. Empty racks do not control with respect to stresses or displacements. In past analyses of other plants, Holtec personnel had performed a number of simulations to vary only the fuelloading to investigate the effect of these variations on rack response. They investigated diagonally and anti-symmetrically loaded
! racks
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in a variety of combinations and showed that the simulations with partially loaded racks produced similar results to the simulations with completely filled racks.
1 Status: Closed item 21 Since the fuel racks rest on bearing pads, was the potential for fuel racks slipping off the pads (due to combined rack and pad motion) and directly impacting the pool floor evaluated?
Similarly, was slippage of the platforms in the cask loading pit considered?
Discussion:
Holtec personnel concluded that slippage of the racks off the bearing pads was not plausible based on the geometry of the pad and pedestal and the required differential displacement. A differential movement of 9.5 inches would be required for the pedestal to clear the pad. The maximum displacements predicted by the analysis were significantly smaller than this value.
Significant movement of the bearing pad along the liner is unlikely during the short duration of time that a pedestal may lift off the bearing pad. Based on similar reasoning, slippage of the racks off the cask loading' pit platforms was also not considered plausible.
Status: Closed item 27 Were the loads resulting from the local fluid coupling hydrodynamic pressures considered in the evaluation of the fuel racks?
Discussion:
Holtec personnel indicated that the hydrodynamic pressure loads are considered in the equilibrium equations that are computed by DYNARACK. Holtec stated that the primary stress in the cell walls is longitudinal and results from the rack exhibiting beam type stresses during the seismic event. This stress is evaluated by the DYNARACK postprocessor and compared with the allowable limits. Holtec recognizes that the hydrodynamic pressure acting on the flat cell section will induce a stress in the short direction across the cell wall but claimed that the pressure is too small to cause any permanent change in the cell wall dimension that could result in a radiological concern. The staff raised a concern that Holtec's response did not address potential local buckling of the cell walls perpendicular to the affected cell wall to which the pressure loads are transferred. The licensees agreed to provide a calculation to address this concern.
Status:
The licensees will provide a calculation to evaluate local cell wall buckling due to the hydrodynamic pressure loads.
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l Item _2R The loading combination table on page 6-21 of the Reference contains a Service Level B l combination that includes load P, which is the upward force on the r,acks caused by a postulated stuck fuel assembly. The report does not address this load. Provide an explanation l and/or justification for not including this load. I Discussion:
Holtec personnelindicated that the project specification required evaluation of a 5000 lb upward load resulting from a stuck fuel condition. Although it was not reported in the licensing report, the evaluation was performed using hand calculations. The evaluation was performed by conservatively comparing the computed stresses against the Level A allowables.
Status Closed item 29 The load combination table on page 6-21 of the Reference contains thermalloads for normal and accident conditions. However, the report does not provide any information on thermal I stress analysis. Explain why thermal stresses were not included in the analyses and load !
combinations. ,
Discussion:
Holtec personnel described a thermal condition in which the average rack metal temperature is approximately 32'F higher than pool slab liner, if the pedestals are assumed to stick to the liner, a maximum thermal stress of 7800 psi can be developed. The staff questioned why the case of an isolated hot cell was not considered as required by the OT position (Reference to the OT position or OT position paper in these topic discussions refers to document entitled "OT Position for Review and Acceptance of Spent Fuel Storage and Handling Applications",
provided to licensees in NRC letter dated January 18,1979). This condition could result in high shear stresses in the welds connecting the cells. Holtec agreed to provide this calculation.
Status 1 The licensee will provide a calculation on the evaluation of thermal stress resulting from an isolated hot cell.
Item 30 What is the maximum vertical force developed in the support pedestal resulting from the deep drop of a fuel assembly into a corner cell?
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Discussion:
The Reference had indicated that the deep drop of a fuel assembly would result in a vertical i pedestal force lower than the pedestal forces generated during the seismic events (291,000
( lbs.). In the meeting, Holtec stated that the force predicted by the drop analysis was actually 1,050,000 lbs. However, they explained that the ana!ysis contained several very conservative assumptions. The fuel assembly and pedestal were assumed to be rigid. The impact velocity neglected the pressure buildup in the cell. However with all of the conservatisms included, l Holtec personnel demonstrated that the computed force is adequately resisted by the rack structure, bearing pad, liner, and underlying concrete. It was agreed that a description of the analysis would be provided to clarify the statements made in the licensing report.
Status:
l The licensees agreed to submit a formal response on the docket to address this issue.
Item 31 l How was localized severing of the baseplate / cell wall welds determined in the analysis of the accident scenario involving the fuel assembly deep drop through an interior cell?
I Discussion-l l Holtec personnel explained that the LSDYNA3D model includes the welds between the l baseplate and the bottom of the cell wall as finite elements. The stress-strain relationship
! appropriate for the weld material is defined and assigned to the finite element components.
Failure of the welds occurs when the ultimate stress is reached.
I Status: Closed i
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l l Define the acceptance criteria for the rack drop accident. Why is a pierced liner and a 4 inch j indentation into the pool floor acceptable?
Discussion:
Holtec personnel explained that damage from a dropped rack is of no safety consequence l
since the dropped rack does not contain any fuel. Damage to fuelin adjacent racks is precluded by procedorea which require maintaining a horizontal offset distance. Therefore the acceptance criteria !4 based on assuring that catastrophic damage to the pool structure does not take place. Catastrophic damage is taken as rapid loss of the pool water such that the fuel
- is overheated or is allowed to exceed the acceptable K., design margin value of 0.95. This is I based on Section 111.1.5(4) of the OT Position Paper. On this basis, local damage to the pool liner and local concrete crushing is acceptable since the rate of water loss through the leak chase system would be small and can be controlled.
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l Will the increased mass due to the expansion of the spent fuel storage capacity affect the seismic response of the fuel building? If not, provide justification.
I Discussion: j Holtec personnel indicated that the additional mass from the added fuel and racks is small in relation to the mass of the building including the existing pool, racks and fuel. Calculations determined that the mass moment of inertia of the building at any point is changed by a j maximum of only 2.5 percent and the change in weight in any of the structural nodes was a i maximum of 5 percent. On this basis, it was concluded that the changes will have minimal impact on the seismic response of the building.
Status: Closed item 35 in general, a 3-D single-rack (SR) analysis provides more critical information for evaluating 4 structural stability of racks (e.g., tip-over) than a 3-D multi-rack analysis does. However, you l did not perform a 3-D SR analysis. Provide justifications for not performing a 3-D SR analysis.
Discussion:
As was previously discussed (Item 19),3-D single rack analyses were performed to evaluate l rack stability and to investigate response during construction phase configuratians.
Status: Closed l
ltem 36 Describe the method of leak detection in the fuel pool structure. How are leaks monitored? Is there any existing leakage?
Discussion:
1 The licensees explained that the spent fuel pool leak detection system utilizes gravity flow leak collection chases positioned behind the liner plate welds. The leak chases are segregated into isolatable zones to lacilitate leak detection. References to the licensee FSAR sections were provided for more information. The Wolf Creek Plant has experienced spent fuel poolleakage in the past, and those leaks have been repaired.
, Status: Closed item 37
>< e 1
i Discuss the quality assurance and inspection programs to preclude installation of any irregular or distorted rack structure, and to confirm the actual fuel rack gap corsfigurations with respect to the gaps assumed in the DYNARACK analyses after installation of the racks.
Discussion:
The licensee described the inspection procedures that are implemented to ensure the quality of the racks and their proper installation in the pool. They include a visual inspection and pre-installation drag testing of a percentage of the cells. After installation, all cells are drag tested and gaps are checked at various locations using underwater cameras and long handled measuring tools. If test criteria or gap tolerances are exceeded, the racks are reworked or repositioned.
Status: Closed item 38 Describe the plan and procedure for the post earthquake inspection of fuel rack gap configurations.
Discussion:
The licensees indicated that a step will be added to the appropriate existing procedure for responses to natural events to include additional spent fuel pool rack inspection guidance subsequent to an earthquake event. This willinclude an inspection to determine whether the rack-to-rack gaps or peripheral rack-to-wall gaps have changed from their design basis values.
The results will be evaluated and any necessary corrective actions will be taken.
Status: Closed Proprietarv Discussion Topics:
ltem 1 Provide detailed fuel rack geometric and physical design data that was not included in the applications, including missing dimensional data (cell wall thickness, sheathing dimensions, baseplate dimensions, etc.) and weld design details (types, sizes, locations and lengths) for the welds between fuel rack cells, between cells and baseplate, between poison sheathing and cells., and between support legs and baseplate.
Discussion:
The Holtec proprietary rack manufacturing drawings were made available for review. All of the requested information was obtained from these drawings.
Status: Closed
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l item 11 l
Provide a description of the formulation used to simulate fluid coupling in a whole pool multi-rack model. Describe the theory, key assumptions, limitations, and verification of the methodology by experiment. In addition, the fluid coupling equations on page 6-11 of the l Reference include nonlinear terms which are not defined. Do these nonlinear terms account for I the change in gap size during a seismic event? Define and explain.
Discussion:
Holtec personnel provided a more detailed summary of the fluid coupling theory and methodology that is currently implemented in their DYNARACK program for application to whole l pool multi-rack analysis. They explained that the current methodology is based on the same fluid mechanics formulation that was developed for the 2-D multi-rack model for Diablo Canyon fuel racks in 1987. That methodology had been reviewed and found acceptable by the NRC l staff and its consultants. Holtec personnel subsequently undertook an experimental program in .
1988 to benchmark the theory and claimed that the scale model experiments showed that the l theoretical model consistently bounded the test data. The current methodology was also submitted to NRC for review and approval under a recent Waterford 3 reracking license l amendment (Amendment was approved by the NRC staff on July 10,1998). In the current application, Holtec personnel indicated that the fluid coupling terms are based on the initial gaps and do not account for the change in gap during an earthquake. This assumption, however, has been shown to be conservative.
Status: Closed l Item 13 Justify the adequacy of modeling a fuel rack as a 12 degree of freedom structure consisting of single nodes at the top and bottom connected by a single linear elastic element representing beam-like behavior include information on the rack stiffness and frequency.
Discussion:
Holtec personnel's position is that the rack is a relatively rigid structure that exhibits primarily rigid body motion during an earthquake event. The selecticn of six degrees of freedom at the top of the rack and six degrees of freedom at the bottom of the rack provides adequate representation of the rigid body motion and captures the first mode elastic response. Holtec personnelindicated that the stiffness values of the rack models are determined by considering each rack module as a beam with multiple flanges and webs comprised of cell walls. A series of simple frequency calculations were provided to illustrate the high frequencies of the rack for various modes of vibration with and without fuel. The staff, however, questioned whether Holtec personnel had appropriately modeled shear and torsional stiffness in their calculations considering the intermittent welds connecting the fuel rack cells. Holtec and licensee personnel agreed that they would provide another calculation which adequately considers shear and l
torsion.
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l l Status l The licensees will provide a fuel rack frequency calculation which properly considers shear deformation and torsion.
Item 16 The governing equation of motion given on page 6-15 of the Reference does not appear to include a velocity dependent damping term. How is structural damping considered in the analysis? Provide the damping values assumed for linear elastic structures as well as any additional damping associated with impacts.
Discussion Holtec personnel described the method in which structural damping is incorporated into their analysis. The governing equation in the licensing report lumped the damping into the generalized force. The damping values are consistent with those prescribed by Regulatory Guide 1.61 with slightly higher values used for impact damping.
Status: Closed item 16 Provide additional information and justification for modeling the fuel assemblies as five unconnected rattling masses versus modeling them as a beam structure. Why are only five impact elevations assumed? Is the full mass of the fuel assemblies assumed to rattle? How !
are the impact stiffnesses determined? What are their values?
Discussion: 1 l
Holtec personnel stated that modeling the fuel assemblies as five rattling masses is a )
conservative assumption for a number of reasons. An actual fuel assembly would impact at the spacer grid locations which are greater than five. By assuming that there are only five impact locations, unconnected masses, and all fuel assemblies moving in unison, both the local and overallimpact forces on the rack are maximized. Holtec personnel provided the impact stiffnesses and explained that they are based on the local stiffness of the cell wall with the fuel spacer grids assumed rigid. During this discussion, the staff also questioned why the fuel rack j model did not include nodes at the fuel rattling mass elevations. Holtec indicated that this is not I needed because the program can keep track of the deflection of the rack at the fuel mass I elevations based on the displacements and rotations of the top and bottom nodes. Those i deflections are used to determine the fuel impset forues applied to the rack at the appropriate elevations. The staff concluded that this was acceptable as long as the rack deformation can be properly represented by its first mode deflection shape as was discussed in Item 13.
Status: Closed
- Item 17 l
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o*e 1
I i
How rre gap element stiffnesses determined for rack-to-rack and rack-to-pool interfaces?
, Provide the methods and the values.
l Discussion: )
l Holtec personnel presented the stiffness values and the calculations illustrating how he values are determined. l l
Status: Closed j
, I
! Item 22 ,
l
! Provide a brief description of the analytical modeling of the existing spent fuel rack used in the l overturning check analysis. Identify the similarities and differences between the existing rack i model and the new rack model.
Discussion:
l Holtec personnel indicated that the existing spent fuel racks were modeled in the same manner
- as the new racks. They provided information on the differences in component properties due to l differences in construction.
Status, Closed Item 23 l
l Explain how the fuel rack stresses and stress factors are determined directly from the relatively l simple DYNARACK model.
l Discussion:
l Holtec personnel explained their method for determining stresses and stress factors. The l criticallocations which they investigate are at the composite rack cell section at the base of the l rack where the highest
- beam-like* stresses develop during a seismic event, and the support pedestals. The stress factors represent the ratio of actual stress vs. silowable stress.
1 Status: Closed l Item 24 The table on page 6-31 of the Reference provides a summary of the bounding stress factors for l the seismic analyses. However, the critical sections (e.g., cellular cross section, pedestal, etc.)
and their locations are not identified. Please indicate the sections and locations and provide an example to illustrate how these stress factors were determined.
Discussion:
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The criticallocations were discussed in item 23. Holtec presented an example illustrating how their DYNARACK postprocessor computes the stress factors.
I Status: Closed Item 25 Provide the detailed calculations which define allowable impact loads for fuel assembly to cell, rack-to-rack, rack-to-pool wall, and pedestal-to-pool floor locations. What is the allowable impact load for a fuel assembly?
Discussion: j Holtec personnel presented the calculations for the fuel-to-cell allowables and the safety margins for the fuel assembly impact loads. Additional information was presented on the bearing pad calculations which define the pedestal-to-pool floor allowables. In this application, there are no rack-to-pocl wall or cellular structure rack-to-rack impacts. Calculation of impact load allowables for rack-to-rack impacts at the baseplates was covered in the licensing report.
S9_tys_.; Closed item M Provide the detailed calculations on the SSE evaluation of welds summarized in Table 6.9.1 of the Refert;nce.
]
Discussion:
Holtec personnel presented sample calculations and explained the method used to determine i and evaluate the stresses in the rack cell-to-baseplate, pedestal-to-baseplate, and cell-to-cell welds, in reviewing the rack cell-to-baseplate calculation, the staff noted that the weld stress '
considered only direct tension and not shear in the weld. In the other calculations, it was unclear whether shear was appropriately considered. Holtec personnel and the licensees agreed to review their calculations to address shear in all of these welds.
Slatyg The licensees u.!i provide additional information which may include revised calculations that appropriately address shear in the welds.
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lt a w :.
l l l Item 34 Provide a description of the analysis method used to demonstrate that the poolliner will not tear or rupture under the limiting load conditions and that there is no fatigue problem under the specified number of earthquake events.
Discussion:
l Holtec personnel presented a description of the finite element analysis which they performed to evaluate the integrity of the liner for the highest loads at the worst location. The fatigue evaluation used the results of the seismic analysis to determine the maximum number of cycles that may be accumulated for the required number of OBE and SSE events during the life of the plant. Based on the maximum stress level in the liner, the cumulative usage factor was shown to be well below 1.0.
Status: Closed l
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.. .- l Discuss the quality assurance and inspection programs to preclude installation of any irregular or distorted rack structure, and to confirm the actual fuel rack gap configurations with respect to the gaps assumed in the DYNARACK analyses after installation of the racks.
Discussion:
l The licensee described the inspection procedures that are implemented to ensure the quality of l the racks and their proper installation in the pool. They include a visual inspection and pre-l installation drag testing of a percentage of the cells. After installation, all cells are drag tested
! and gaps are checked at various locations using underwater cameras and long handled l measuring tools. If test criteria or gap tolerances are exceeded, the racks are reworked or r4 ositioned.
l Status: Closed item 38 i
Describe the plan and procedure for the post earthquake inspection of fuel rack gap l configurations.
f l
Discussion:
l l The licensees indicated that a step will be added to the appropriate existing procedure for responses to natural events to include additional spent fuel pool rack inspection guidance i subsequent to an earthquake event. This will include an inspection to determine whether the !
rack-to-rack gaps or peripheral rack-to-wall gaps have changed from their design basis values. I l The results will be evaluated and any necessary corrective actions will be taken.
Statys. Closed )
Proprietary Discussion Topics:
I Item 1 Provide detailed fuel rack geometric and physical design data that was not included in the applications, including missing dimensional data (cell wall thickness, sheathing dimensions, baseplate dimensions, etc.) and weld design details (types, sizes, locations and lengths) for the welds between fuel rack cells, between cells and baseplate, between poison sheathing and cells, and between support legs and baseplate.
Discussion:
The Holtec proprietary rack manufacturing drawings were made available for review. All of the requested information was obtained from these drawings.
Status: Closed l
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.* 's llem 11 1 Provide a description of the formulation used to simulate fluid coupling in a whole pool multi- I rack model. Describe the theory, key assumptions, limitations, and verification of the methodology by experiment. In addition, the fluid coupling equations on page 6-11 of the Reference include nonlinear terms which are not defined. Do these nonlinear terms account for the change in gap size during a seismic event? Define and explain.
Discussion:
Holtec personnel provided a more detailed summary of the fluid coupling theory and methodology that is currently implemented in their DYNARACK program for application to whole pool multi-rack analysis. They explained that the current methodology is based on the same fluid mechanics formulation that was developed for the 2-D multi-rack model for Diablo Canyon fuel racks in 1987. That methodology had been reviewed and found acceptable by the NRC staff and its consultants. Holtec personnel subsequently undertook an experimental program in 1988 to benchmark the theory and claimed that the scale model experiments showed that the theoretical model consistently bounded the test data. The current methodology was also submitted to NRC for review and approval under a recent Waterford 3 reracking license amendment (Amendment was approved by the NRC staff on July 10,1998). In the current application, Holtec personnel indicated that the fluid coupling terms are based on the initial gaps and do not account for the change in gap during an earthquake. This assumption, however, has been shown to be conservative.
Status: Closed item 13 Justify the adequacy of modeling a fuel rack as a 12 degree of freedom structure consisting of single nodes at the top and bottom connected by a single linear elastic element representing beam-like behavior. Include information on the rack stiffness and frequency.
Discussion:
Holtec personnel's position is that the rack is a relatively rigid structure that exhibits primarily rigid body motion during an earthquake event. The selection of six degrees of freedom at the top of the rack and six degrees of freedom at the bottom of the rack provides adequate representation of the rigid body motion and captures the first mode elastic response. Holtec personnel indicated that the stiffness values of the rack models are determined by considering each rack module as a beam with multiple flanges and webs comprised of cell walls. A series of simple frequency calculations were provided to illustrate the high frequencies of the rack for various modes of vibration with and without fuel. The staff, however, questioned whether l
Holtec personnel had appropriately modeled shear and torsional stiffness in their calculations l considering the intermittent welds connecting the fuel rack cells. Holtec and licensee personnel agreed that they would provide another calculation which adequately considers shear and torsion, i
1 I
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l Status The licensees will provide a fuel rack frequency calculation which properly considers shear deformation and torsion.
Item 15 The governing equation of motion given on page 6-15 of the Reference does not appear to include a velocity dependent damping term. How is structurai damping considered in the analysis? Provide the damping values assumed for linear elastic structures as well as any additional damping associated with impacts.
Discussion Holtec personnel described the method in which structural damping is incorporated into their ,
analysis. The governing equation in the licensing report lumped the damping into the generalized force. The damping values are consistent with those prescribed by Regulatory ,
Guide 1.61 with slightly higher values used for impact damping.
Status: Closed item 16 Provide additional information and justification for modeling the fuel assemblies as five unconnected rattling masses versus modeling them as a beam structure. Why are only five impact elevations assumed? Is the full mass of the fuel assemblies assumed to rattle? How are the impact stiffnesses determined? What are their values?
Discussion: '
Holtec personnel stated that modeling the fuel assemblies as five rattling masses is a conservative assumption for a number of reasons. An actual fuel assembly would impact at the spacer grid locations which are greater than five. By assuming that there are only five impact locations, unconnected masses, and all fuel assemblies moving in unison, both the local and overallimpact forces on the rack are maximized. Holtec personnel provided the impact stiffnesses and explained that they are based on the local stiffness of the cell wall with the fuel spacer grids assumed rigid. During this discussion, the staff also questioned why the fuel rack model did not include nodes at the fuel rattling mass elevations. Holtec indicated that this is not needed because the program can keep track of the deflection of the rack at the fuel mass elevations based on the displacements and rotations of the top and bottom nodes. Those deflections are used to determine the fuel impact forces applied to the rack at the appropriate elevations. The staff concluded that this was acceptable as long as the rack deformation can be properly represented by its first mode deflection shape as was discussed in item 13.
Status: Closed l
Item 17
- u. .+
l How are gap element stiffnesses determined for rack-to-rack and rack-to-pool interfaces?
Provide the methods and the values.
Discussion:
Holtec personnel presented the stiffness values and the calculations illustrating how the values are determined.
i
- l. Status: Closed Item 22 Provide a brief description of the analytical modeling of the existing spent fuel rack used in the overturning check analysis. Identify the similarities and differences between the existing rack model and the new rack model.
l l _ Discussion:
l Holtec personnel indicated that the existing spent fuel racks were modeled in the same manner I as the new racks. They provided information on the differences in component properties due to differences in construction.
Status: Closed litDL21 l l Explain how the fuel rack stresses and stress factors are determined directly from the relatively l simple DYNARACK model.
! Discussion:
l Holtec personnel explained their method for determining stresses and stress factors. The
. criticallocations which they investigate are at the composite rack cell section at the base of the
! rack where the highest " beam-like" stresses develop during a seismic event, and the support l pedestals. The stress factors represent the ratio of actual stress vs. allowable stress.
Status, Closed Item 24
. The table on page 6-31 of the Reference provides a summary of the bounding stress factors for the seismic analyses. However, the critical sections (e.g., cellular cross section, pedestal, etc.)
and their locations are not identified. Please indicate the sections and locations and provide an example to illustrate how these stress factors were determined.
Discussion:
,, c , ,- - -- ,
- s. .+
l l '
l The critical locations were discussed in item 23. Holtec presented an example illustrating how their DYNARACK postprocessor computes the stress factors.
l
\
Status: Closed l Item 25 Provide the detailed calculations which define allowable impact loads for fuel assembly to cell, rack-to-rack, rack-to-pool wall, and pedestal-to-pool floor locations. What is the allowable impact load for a fuel assembly?
Discussion:
Holtec personnel presented the calculations for the fuel-to-cell allowables and the safety margins for the fuel assembly impact loads. Additionalinformation was presented on the bearing pad calcula'tions which define the pedestal-to-pool floor allowables. In this application, there are no rack-to-pool wall or cellular structure rack-to-rack impacts. Calculation of impact load allowables for rack to-rack impacts at the baseplates was covered in the licensing report.
Status. Closed item 26 Provide the detailed calculations on the SSE evaluation of welds summarized in Table 6.9.1 of ,
the Reference.
Discussion:
Holtec personnel presented sample calculations and explained the method used to determine and evaluate the stresses in the rack cell-to-baseplate, pedestal-to-baseplate, and cell-to-cell welds. In reviewing the rack cell-to-baseplate calculation, the staff noted that the weld stress considered only direct tension and not shear in the weld. In the other calculations, it was unclear whether shear was appropriately considered. Holtec personnel and the licensees agreed to review their calculations to address shear in all of these welds.
StalgE The licensees will provide additional information which may include revised calculations that '
appropriately address shear in the welds.
I
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1 1
Item 34 Provide a description of the analysis method used to demonstrate that the pool liner will not tear or rupture under the limiting load conditions and that there is no fatigue problem under the
, specified number of earthquake events.
l Discussion:
1 i
Holtec personnel presented a description of the finite element analysis which they performed to evaluate the integrity of the liner for the highest loads at the worst location. The fatigue evaluation used the results of the seismic analysis to determine the maximum number of cycles that may be accumulated for the required number of OBE and SSE events during the life of the !
plant. Based on the maximum stress levelin the liner, the cumulative usage factor was shown l l
to be well below 1.0. l l
l Status: Closed l l
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