ML24309A289
| ML24309A289 | |
| Person / Time | |
|---|---|
| Site: | Holtec |
| Issue date: | 11/04/2024 |
| From: | Holtec |
| To: | Office of Nuclear Material Safety and Safeguards |
| Shared Package | |
| ML24309A286 | List: |
| References | |
| 5014984, EPID L-2024-LLA-0111, CAC 001028 | |
| Download: ML24309A289 (1) | |
Text
Holtec Response to Request for Additional Information Docket No. 72-1014 Holtec International HI-STORM 100 Multipurpose Canister Storage System Certificate of Compliance No. 1014 Amendment No. 19 RAI 4-1 Provide justification in the final safety analysis report (FSAR) for why the limited combinations of HI-STORM 100 dry cask storage system (DCSS) components are considered to be bounding for other combinations during structural tipover event analyses.
For the overpacks, the analysis results for the HI-STORM 100 overpack containing the Multi-Purpose Canister (MPC)-68M and MPC-68M-CBS fuel baskets are presented in this amendment to the FSAR, while the analyses for the HI-STORM 100S and 100S Version B overpacks, including Type IS which could be heavier for higher density concrete, are not presented even though they contain the same fuel baskets. This implies that the presented combinations are the limiting combinations.
Similarly for the baskets, the analysis of the CBS-type fuel baskets contained in the HI-STORM 100S Versions E and E1 overpacks are presented in the FSAR, but not all non-CBS-type basket analyses are presented. In the FSAR, provide justifications for considering these presented DCSS component combinations as bounding for other baskets or, if the justifications already exist, clearly indicate where they are located in the FSAR.
This information is necessary to demonstrate compliance with 10 CFR 72.236(b) and (l).
Holtec RAI Response:
The tipover analyses for the HI-STORM 100, HI-STORM 100S, and HI-STORM 100S Version B overpacks are largely unchanged in Amendment 19, as they continue to follow the previously approved methodology established in Amendment No. 1 to the HI-STORM 100 FSAR (LAR 1014-1). Unlike the HI-STORM 100S Version E and HI-STORM 100S Version E1, the tipover analyses for the HI-STORM 100, HI-STORM 100S, and HI-STORM 100S Version B involve a two-step process, wherein an initial calculation is performed to determine the peak impact deceleration and then a separate analysis is performed to qualify the MPC fuel basket inside the overpack during a non-mechanistic tipover event. This two-step approach is maintained in Amendment No. 19, except that the previous ANSYS models used to qualify the MPC-68M and MPC-68MCBS have been replaced with the latest enhanced LS-DYNA model. Additional clarifying information is provided below.
The HI-STORM 100 tipover model is fuel basket agnostic. In other words, the MPC, including the internal fuel basket and the stored fuel assemblies, is modeled in LS-DYNA as a solid homogeneous cylinder with the correct external dimensions and total mass. The purpose of the HI-STORM 100 tipover model is to show that the maximum impact deceleration, at a height corresponding to the top of the fuel basket, is less than the design basis limit of 45g per Subsection 2.2.3.2 and Table 3.1.2 of the FSAR, as well as paragraph 3.4.6.a of the HI-STORM 100 CoC, Appendix B. The results for the HI-STORM 100 overpack satisfy this limit for two reference ISFSI pad designs (i.e., Set A & Set B), as shown in FSAR Section 3.4.10.
Following the confirmation of the peak impact deceleration, separate finite element analyses are performed for the various MPC fuel basket types, using a bounding impact deceleration (45 g or greater) as input, to demonstrate compliance with the applicable stress and permanent deflection criteria. The qualifying analyses for the Alloy X fuel baskets (e.g., MPC-24, MPC-32, MPC-68) are discussed in FSAR subparagraph 3.4.4.3.1.1, Page 1 of 16 ATTACHMENT 2 TO HOLTEC LETTER 5014984
Page 2 of 16 and they are not affected by the proposed changes in Amendment No. 19. For the Metamic-HT fuel baskets (i.e.,
MPC-68M and MPC-68MCBS), the qualifying analyses are performed in subparagraph 3.III.4.4.3.1 of Supplement 3.III, which have been updated as part of Amendment No. 19 to replace the former ANSYS finite element models with the so-called enhanced LS-DYNA tipover model (similar to HI-STORM FW Amendment No. 7). It is important to note that the enhanced LS-DYNA model is only used to qualify the MPC-68M and MPC-68MCBS fuel baskets, not any components of the HI-STORM 100 overpack. The qualifying analyses for the HI-STORM 100 overpack, for the non-mechanistic tipover event, are those presented in Chapter 3 of the FSAR, specifically in Sections 3.4.4 and 3.4.10, which have already been approved by the NRC. This is recognized in subparagraph 3.III.4.4.3.1 of Supplement 3.III, which states:
Since the HI-STORM 100 overpack, including its closure lid, have already been evaluated for the non-mechanistic tipover event in Section 3.4 with acceptable results, the focus of the tipover analyses performed herein is the qualification of the MPC-68M and MPC-68MCBS enclosure shells and fuel baskets (i.e., the cask internals).
With regard to the HI-STORM 100S and the HI-STORM 100S Version B, comparative evaluations presented in FSAR Section 3.4.10 have previously established that the peak impact decelerations computed for the HI-STORM 100 overpack are bounding for 100S and 100S Version B overpack types. This method of evaluation was incorporated in the FSAR in Amendment No. 1 (LAR 1014-1) with the introduction of the HI-STORM 100S, and the approved methodology was subsequently followed for the HI-STORM 100S Version B, including the Type IS variant (which employs higher density concrete in the overpack body). The supporting calculations for the Type IS are documented in Attachment H of report HI-2002474, which has been provided per the staffs request (see RAI 4-11).
For the HI-STORM 100S Version E and E1 overpacks, the tipover analyses presented in Supplement 3.II of the FSAR are consistent with the analyses outlined by Holtec during the pre-application meeting on April 24, 2024, and they represent the most limiting DCSS combinations. The tipover analyses presented in the HI-STORM 100 FSAR are based, in part, on insights gained from HI-STORM FW Amendment No.7, which showed that PWR fuel basket types are generally more limiting than BWR fuel basket types due to their higher fuel weights and larger cell sizes. This is discussed in paragraph 3.4.4.1.4e of the HI-STORM FW FSAR and also quantified in FSAR Table 3.4.22. Another trend that was observed from the results in HI-STORM FW Amendment No. 7 is that CBS baskets are generally more limiting than their non-CBS counterpart for the same set of input parameters (i.e., fuel weight, basket temperatures, target foundation) because of the reduced joint fixity at the panel intersections versus the friction-stir welded basket types.
Based on the above considerations, the three most limiting basket types (i.e., MPC-32M, MPC-32MCBS, and MPC-68MCBS) are analyzed for the HI-STORM FW Version E in Supplement 3.II, with only the MPC-68M excluded due to its lesser fuel weight, smaller cell size, and welded basket design. For the HI-STORM FW Version E1, both CBS basket types (i.e., MPC-32MCBS and MPC-68MCBS) are analyzed, and the friction-stir welded basket types (i.e., MPC-32M and MPC-68M) have been excluded. It is noted that the results in Table 3.II.4.14 appear to show that the MPC-32M basket is more limiting than the MPC-32MCBS for the same overpack, but this is not an apples-to-apples comparison since the tipover analysis for the MPC-32MCBS is based on a maximum fuel weight of 1520 lb per assembly versus 2050 lb per assembly for the MPC-32M. The difference in maximum allowable fuel weight speaks directly to the fact that CBS basket types are more limiting than their non-CBS counterpart.
RAI 4-2 Provide a justification and a more detailed explanation of the new averaging method being employed in this amendment for the determination of fuel basket maximum permanent deflections resulting from the tipover event in the FSAR and associated reports.
The analytical steps performed to determine the fuel basket maximum permanent deflection are documented in notes 1 to 7 of FSAR table 3.II.4.14. For this proposed amendment, note 7 of the table is added and allows an averaging approach to be employed for this determination, but it is not clear why an averaging approach was ATTACHMENT 2 TO HOLTEC LETTER 5014984
Page 3 of 16 selected (presumably when steps 1 to 6 do not produce permanent deflection results that meet the dimensionless limit of 0.005 of the fuel basket cell width). Describe why an averaging approach is justified, both from a structural and criticality standpoint.
The averaging approach is not described in the FSAR, so it is not clear exactly how an average basket permanent deflection value is determined. Provide a more detailed description of step 7 that identifies the quantities, locations and timesteps of basket cell/panel measurements required to determine the maximum average deflection value, providing a pictorial example if necessary. Additionally, FSAR sections 6.II.3.1 and 6.III.3 for criticality refer to Chapter 3, however, there does not appear to be any numerical or pictorial proof provided in the discussion, figures, or tables in chapter 3 that indicate that the permanent deflections are in a few areas of the active fuel region of the baskets. It is noted by staff that effective plastic strain contours are provided in report HI-2240678, appendices C and D for the MPC-68M and MPC-68M-CBS baskets in the 100 overpack; however, there is no mention of them in the same report. Staff also notes that no temperature is indicated on these contour plots, which would be linked to material true ultimate and fracture strains. Provide sufficient evidence in chapter 3 of the FSAR to support, or revise as necessary, the statements cited above in the criticality portion of the FSAR, as well as the following statements in FSAR sections 3.II, 3.III, and 3.IV:
The objective of the analysis is to demonstrate that the plastic deformation in the fuel basket is sufficiently limited to the value at which the criticality safety is maintained...
The fuel basket does not experience significant plastic deformation in the active fuel region to exceed the acceptable limits; plastic deformation is essentially limited locally in cells near the top of the basket beyond the active fuel region for MPC-32M basket.
The fuel basket does not experience significant plastic deformation in the active fuel region to exceed the acceptable limits; plastic deformation is essentially limited locally in cells near the top of the basket beyond the active fuel region for MPC-68M basket.
Similar to the MPC-68M basket design, the response of the MPC-68MCBS basket during the tipover event is predominantly elastic with very localized areas of plasticity.
The fuel basket does not experience significant plastic deformation in the active fuel region to exceed the acceptable limits; peak plastic deformation is essentially limited locally in cells near the impact location of the basket for MPC-32M basket.
The fuel basket does not experience significant plastic deformation in the active fuel region to exceed the acceptable limits; peak plastic deformation is essentially limited locally in cells near the impact location of the basket for MPC-68M basket.
This information is necessary to demonstrate compliance with 10 CFR 72.236(b).
Holtec RAI Response:
The new averaging method being employed in this amendment for the determination of fuel basket maximum permanent deflections resulting from the tipover event is justified based on the following:
(i)
The deflection criterion is no longer the sole determinant of the structural integrity of the Metamic-HT fuel baskets as limits have also been established in this amendment (e.g., FSAR sections 2.II.2.6 and 3.II.4.4.2(iii)) for the primary stress and maximum strain (via element erosion criterion) in the fuel basket; (ii)
Evaluating the permanent deflection in terms of the maximum width-averaged value instead of the peak value at the panel mid-span is more aligned with the criticality models described in FSAR sections 6.II.3.1 and 6.III.3, where the fuel basket panels are assumed to be uniformly displaced over the entire width of the panel and length of the active fuel region by an amount equal to 0.5% of the panel width.
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Page 4 of 16 (iii)
The tipover analysis still maintains a degree of conservative relative criticality analysis model, since the former does not allow for length averaging when evaluating deflections. In other words, the 0.5%
deflection limit is met for all basket panels and for all elevations within the active fuel region. This insures that the average panel deflection, accounting for both length and width variations, remains well below the value assumed in the criticality analysis model.
In other words, the primary stress and maximum strain limits introduced in this amendment for the Metamic-HT fuel baskets supersede the permanent deflection limit as the primary indicator of the fuel baskets structural integrity. In fact, one could argue that the permanent deflection limit could be eliminated from the FSAR, except for the fact that the criticality models in Chapter 6 are predicated on a maximum allowable panel deflection. To that end, the permanent deflection limit is maintained in the FSAR, but it has been modified to bring it into closer agreement with the criticality analysis for the Metamic-HT fuel baskets.
The general steps involved in calculating the maximum permanent deflection of a Metamic-HT fuel basket panel are captured in the FSAR in the first note below Table 3.II.4.14. In particular, step 7 of note 1 to Table 3.II.4.14 describes how the maximum width-averaged permanent deflection is calculated from the LS-DYNA tipover results. Per the staffs request, a detailed description of the calculated result in Table 3.III.4 for a MPC-68M inside a HI-STORM 100 overpack on a Set A ISFSI pad is provided in report HI-2240678, with deflection values, locations and time steps of the fuel basket panel measurements.
Since the maximum permanent deflection at the mid-span of the panel is always greater than the maximum average permanent deflection over the full panel width, the averaging method is only employed when necessary (as indicated in step 7 of note 1 to FSAR Table 3.II.4.14). That is to say, if the maximum permanent deflection at the panel mid-span (following steps 1 through 6 in Table 3.II.4.14) is already less than 0.5% of the panel width, then step 7 can be ignored and the safety factor can be conservatively calculated using the maximum permanent deflection at mid-span from step 6. This is, in fact, the case for the majority of the tipover analysis results. The new averaging method is only used for the results in FSAR Table 3.III.4 involving the HI-STORM 100 overpack.
For the HI-STORM 100S Version E and the HI-STORM 100S Version E1 in FSAR Supplement 3.II, and the HI-STORM 100 UVH in Supplement 3.IV, the maximum permanent deflection is not averaged over the width at any panel locations for any fuel basket type, as indicated in note 2 to Tables 3.II.4.14, 3.II.4.15, and 3.IV.4.9.
Regarding the statements in FSAR sections 6.II.3.1 and 6.III.3 indicating that the permanent deflections are only present in a few areas of the basket, they have been revised to provide greater clarity and better reflect the results presented in Chapter 3 of the FSAR. In addition, the identified statements in FSAR Supplements 3.II, 3.III, and 3.IV have also been revised or deleted, as appropriate, to avoid qualitative statements about the nature and extent of the plastic deformation, for which there are no acceptance limits. The updated supplements in FSAR Chapter 3 now refer only to the maximum permanent deflection in the fuel basket panels, which is the basis for structural acceptance.
RAI 4-3 Specify the tipover event analysis foundation model input parameters and resulting impact decelerations of the DCSS components of interest in each applicable section of the FSAR.
The independent spent fuel storage installation (ISFSI) concrete foundation system stiffness (e.g., foundation thickness, concrete compressive strength and soil subgrade modulus) included in the tipover analytical models is not consistent for each version of the HI-STORM 100 model evaluated, and there does not appear to be a reason for the apparent inconsistencies. Identify these stiffness input parameters for the tipover analysis of each DCSS component combination presented in the FSAR, identifying when the employed values may deviate from the stated licensing basis, including a justification for same. It is important to identify these values in the FSAR as the foundation system stiffness parameters employed can limit the parameters of the ISFSI pads where the DCSS can be used.
Similarly, impact deceleration values employed for the evaluation of each component of each version of the HI-STORM 100 DCSS need to be identified in the FSAR. The deceleration values are proportional to the force ATTACHMENT 2 TO HOLTEC LETTER 5014984
Page 5 of 16 received by the cask and its components during tipover and are important in the tipover analysis. However, in some cases, the values stated seem to conflict with those already presented (e.g., the MPC-68M and MPC-68M-CBS baskets in the 100 overpack, presented in FSAR Supplement III, cite a 60-g deceleration), whereas some are not stated at all (e.g., for the UVH overpack in FSAR Supplement IV). Provide deceleration time-history plots for the (original) 100 and UVH overpack evaluations in the FSAR and associated reports.
This information is necessary to demonstrate compliance with 10 CFR 72.236(b) and (l).
Holtec RAI Response:
A generic tipover analysis is performed for each freestanding HI-STORM overpack included in the HI-STORM 100 FSAR. The foundation model input parameters, however, are not the same for all overpacks. The specific set of foundation model input parameters associated with the tipover analysis for a particular HI-STORM establishes the reference ISFSI pad for that overpack version. For example, the reference ISFSI pad parameters for the HI-STORM 100, HI-STORM 100S, and HI-STORM 100S Version B (including Type IS variant) are summarized in FSAR Table 2.2.9, which are different from the reference ISFSI pad parameters for the HI-STORM 100S Version E and Version E1 in FSAR Table 2.II.0.1. For the HI-STORM UVH, the reference ISFSI pad parameters are in FSAR Table 2.IV.0.1.
If a site plans to implement the HI-STORM 100 system under Holtecs Part 72 generic certificate, then the site has two options with respect to the design of their ISFSI pad as it relates to the tipover analysis:
i) show that their ISFSI pad design is bounded by the reference ISFSI pad parameters in the HI-STORM 100 FSAR for the particular HI-STORM version(s) being deployed at the site, or; ii) perform a site-specific tipover analysis using the approved methodology described in Section 3.4 of the HI-STORM 100 FSAR and demonstrate acceptable results for their site-specific foundation parameters.
Thus, the reference ISFSI pad parameters in the FSAR are not absolute design limits, as the site can elect to perform a site-specific tipover analysis to qualify an alternate ISFSI pad design, as discussed in FSAR Subsections 2.2.3.2, 2.II.0.4, and 2.IV.0.1. The reference ISFSI pad designs in the HI-STORM 100 FSAR have evolved over time as new overpack versions have been introduced and tipover analysis methods have changed.
The impact deceleration values due to a tipover event are evaluated and treated differently depending on the overpack version. For example, as discussed in the response to RAI 4-1, the HI-STORM 100, the HI-STORM 100S, and the HI-STORM 100S Version B (including the Type IS variant) have a design basis peak deceleration limit of 45g, as set forth in the HI-STORM 100 CoC. Thus, the component evaluations for those specific overpack versions are informed by a maximum impact deceleration of 45g, except where a higher value is used to impart further conservatism. For example, the stress analyses for the Alloy X fuel basket types in FSAR subparagraph 3.4.4.3.1.1 use a bounding deceleration value of 60g. Similarly, the tipover analyses for the MPC-68M and MPC-68MCBS in Supplement 3.III are conservatively configured such that the maximum deceleration at the top of the fuel basket exceeds 45g.
For the other overpack versions (i.e., HI-STORM 100S Versions E, E1, and UVH), the approach is different, as there is no design basis deceleration limit established in the FSAR or the CoC. The peak impact deceleration can exceed 45g at the top of the fuel basket so long as all of the DCSS components satisfy their respective acceptance limits for the tipover event. This change in the deceleration limit for the newer overpack versions coincided with the change in the tipover analysis method from the original two-step analysis process, as described in the response to RAI 4-1, to the more comprehensive LS-DYNA solution, where the overpack, the MPC, and all of the contents are individually modeled in detail.
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Page 6 of 16 RAI 4-4 Provide the method of evaluation and analyses being employed for the load-bearing MPC-68M-CBS fuel basket corner shim bolts in all applicable FSAR sections and associated reports.
The only FSAR section that addresses the structural evaluation of the load-bearing MPC-68M-CBS basket corner shim bolts is section 3.II.4.4.2(iii), for the Version E and E1 overpacks, where report HI-2188448, Revision 5, Analysis of the Non-Mechanistic Tipover Event of the Loaded HI-STORM 100S Version E Storage Cask, is referenced for further documentation. [Withheld in accordance with 10 CFR 2.390] However, the FSAR section 3.III.4.4.3.1 describing the evaluation of the MPC-68M-CBS in the 100 overpacks, does not address the evaluation of any CBS shim bolts, whether it be the load-bearing corner shim bolts or those with oversized holes.
Appendix D of the referenced report HI-2240678, Revision 0, Analysis of the Non-Mechanistic Tipover Event of the Loaded HI-STORM 100, [Withheld in accordance with 10 CFR 2.390]. Address the method of evaluation and analysis results for the load-bearing MPC-68M-CBS basket corner shim bolts in all applicable FSAR sections and reports.
This information is necessary to demonstrate compliance with 10 CFR 72.236(b).
Holtec RAI Response:
[Withheld in accordance with 10 CFR 2.390]
The MPC-68MCBS is not allowed inside the HI-STORM UVH per FSAR Table 1.0.4, so the CBS bolts and corner shims do not need to be addressed in FSAR Supplement 3.IV or report HI-2210290.
RAI 4-5 Provide discussions of fuel basket stresses and stress contour diagrams associated with the tipover event analyses, in the FSAR and associated reports, for those DSCC combinations included in this amendment.
Similar to what was included in the FSAR for Amendment No. 7 for the HI-STORM FW Metamic-HT baskets and shims, include stress contour diagrams of the fuel basket and shim stresses associated with the tipover event analyses, providing justification for any stresses that exceed the acceptance criterion limits. Staff notes that basket stresses exceeding the prescribed limits are discussed in the analyses detailed in all reports except that for the MPC-68M fuel basket in the UVH overpack.
This information is necessary to demonstrate compliance with 10 CFR 72.236(l).
Holtec RAI Response:
Stress contour plots for the Metamic-HT fuel baskets and basket shims, for each of the DSCC combinations included in Amendment No. 19, are provided in the supporting calculation packages (i.e., HI-2188448, HI-2210290, HI-2240678). The calculation packages, in turn, are referenced in the FSAR. Considering all of the different DCSS combinations and the various temperature zones for the fuel baskets, the number of stress plots is quite significant, totaling almost 100 plots. For that reason, in the initial submittal, Holtec elected to refer to the calculation packages, rather than reproduce the full set of plots in the FSAR. However, in light of this RAI, we have updated Chapter 3 of the FSAR, including Supplements 3.II, 3.III, and 3.IV, to include the stress contour plots for the fuel basket and basket shims for the limiting DCSS combinations (i.e., those that produced the lowest safety factors in FSAR Tables 3.II.4.14, 3.II.4.15, 3.III.4, and 3.IV.4.9). Lastly, the tipover analysis report (HI-2210290) for the UVH overpack has also been updated to include an appropriate discussion of the fuel basket stresses for the MPC-68M in relation to the primary stress limit.
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Page 7 of 16 RAI 4-6 Response submitted separately.
RAI 4-7 Verify that the appropriate enclosure vessel geometry has been included in the structural analysis model for the tipover event evaluation of the HI-STORM 100 overpack containing the MPC-68M and MPC-68M-CBS fuel baskets.
[Withheld in accordance with 10 CFR 2.390] However, per FSAR section 1.II.5, this Drawing is applicable to the 100S Version E and E1 overpacks, and, therefore, seemingly not applicable to an analysis of the HI-STORM 100 overpack. It appears that Drawing 3923, for the MPC Enclosure Vessel, as listed in FSAR section 1.5, would be the appropriate Drawing reference for the HI-STORM 100 overpack. Verify that the correct Drawing reference has been made in the FSAR and that the analysis models for the evaluations of the MPC-68M and MPC-68M-CBS fuel baskets in the HI-STORM 100 overpack, as presented in the FSAR and report HI-2240678, have employed the appropriate enclosure vessel geometry.
This information is necessary to demonstrate compliance with 10 CFR 72.236(b) and (l).
Holtec RAI Response:
[Withheld in accordance with 10 CFR 2.390] As noted in the RAI, the correct drawing number is 3923. This correction has been made in Revision 1 of the report. [Withheld in accordance with 10 CFR 2.390]
[Withheld in accordance with 10 CFR 2.390]
RAI 4-8 Provide justifications, in the FSAR and associated reports, for the fuel basket thermal zones employed in the tipover event structural evaluations of for the HI-STORM 100 DCSS combinations containing the MPC-68M-CBS fuel basket.
The fuel basket thermal loads determined for each structural analysis are stated, either in the FSAR or associated calculation, to be bounding for that type of basket, and their source is stated to be report HI-2043317, revision 57, HI-STORM Thermal-Hydraulic Analysis Supporting up to 36.9 KW High Heat Load Amendment. However, the manner in which these are translated to the modeled thermal zones for the same baskets in different overpacks is not consistent.
For the MPC-68M-CBS basket in 100S Version E and E1 overpacks, [Withheld in accordance with 10 CFR 2.390] In comparing the modeled basket thermal zones presented in the FSAR figures (e.g., 3.II.4.32B, 3.II.4.34B, and 3.III.8) and associated report figures for the same basket, the same thermal analysis results from report HI-2043317 appear to be pictured; however, the basket thermal zones identified for the three separate analyses are disparate in arrangement and temperature range. Provide justifications for these differences.
This information is necessary to demonstrate compliance with 10 CFR 72.236(b) and (l).
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Page 8 of 16 Holtec RAI Response:
The fuel basket temperature zones in the tipover event structural evaluations for the HI-STORM 100 DCSS combinations containing the MPC-68MCBS fuel basket are informed by the thermal analyses documented in report HI-2043317, as correctly noted in the RAI. [Withheld in accordance with 10 CFR 2.390] This is because the configuration of the air inlet and outlet vents for the HI-STORM 100S Version B is most limiting from a thermal standpoint.
While the source of fuel basket temperatures for the MPC-68MCBS is the same for all HI-STORM 100 DCSS combinations, the partitioning and assignment of the temperature zones in the LS-DYNA tipover models vary slightly depending on the circumstances of each tipover analysis. For example, where calculated stresses and/or permanent deflections were closer to the limit values, the temperature zones for a particular DCSS combination may have been refined further to reduce conservatism and improve margins. The tipover analyses were also performed in parallel by different Holtec analysts, which also contributed to the minor differences in fuel basket temperature zones for different DCSS combinations. Regardless of the circumstances, the final temperature zones, as presented in the FSAR figures, bound the actual computed fuel basket temperatures from HI-2043317 for all DCSS combinations.
RAI 4-9 Provide references in the FSAR for the definition of active fuel region for all overpack/enclosure vessel/fuel basket component combinations presented in this amendment.
It appears that the active fuel region for the HI-STORM 100S Version E and E1 overpacks and components is defined in FSAR table 3.II.2.1, as referenced in section 2.II.2.4 of the FSAR. However, there does not appear to be a similar definition referenced for the 100 and UVH overpacks in FSAR sections 2.III and 2.IV, respectively. The definition of active fuel region can determine the area of highest temperatures and therefore the area of least margin to yield stress and ultimate stress.
This information is necessary to demonstrate compliance with 10 CFR 72.236(b) and (l).
Holtec RAI Response:
The active fuel region for the HI-STORM UVH overpack and components is defined in FSAR Table 3.IV.2.1, which is analogous to FSAR Table 3.II.2.1 for the HI-STORM 100S Version E and Version E1. A reference to FSAR Table 3.IV.2.1 has been added in Table 2.IV.2.1 of Supplement 2.IV to establish a clear link between the fuel basket acceptance criteria and the active fuel region for the HI-STORM UVH.
Unlike the HI-STORM 100 Versions E, E1, and UVH, the HI-STORM 100 overpack is a fixed height storage system. Thus, upper and lower fuel spacers are used to vertically position the fuel assemblies inside the MPC cavity. The suggested fuel spacer lengths for various BWR fuel assembly types are given in FSAR Table 2.1.10, which also establishes the relative position of the active fuel region. The tipover analyses in Supplement 3.III for the HI-STORM 100 overpack, with the MPC-68M or MPC-68MCBS inside, are performed based on the maximum length BWR fuel assembly per Table 2.1.10. A reference to FSAR Table 2.1.10 has been added in Section 2.III.0.1 to establish a clear link between the fuel basket acceptance criteria and the active fuel region for the HI-STORM 100.
RAI 4-10 Justify the differences in discretization of the ISFSI pad structural models employed in the tipover event analysis of the HI-STORM 100 overpack containing the MPC-68M and MPC-68M-CBS fuel baskets in comparison to those employed for the other DCSS combinations evaluated in this amendment.
The LS-DYNA finite element models of the ISFSI pads employed in the new analyses for the HI-STORM 100 ATTACHMENT 2 TO HOLTEC LETTER 5014984
Page 9 of 16 overpack, containing the MPC-68M and MPC-68M-CBS fuel baskets, appear to have less discretization at the cask tipover impact point than those employed for the Version UVH, Version E, and Version E1 analyses. Provide the reason for this modeling change and justify the difference, specifically addressing what effect its inclusion might have on the current results for the HI-STORM 100 analyses presented in this amendment.
This information is necessary to demonstrate compliance with 10 CFR 72.236(b).
Holtec RAI Response:
The LS-DYNA finite element models of the ISFSI pads employed in the new analyses for the HI-STORM 100 overpack containing the MPC-68M and MPC-68MCBS are identical to the ISFSI pad models presented in Appendix 3.A, which have been previously approved and are used consistently for all HI-STORM 100 tipover analyses. Similarly, the discretization of the ISFSI pad models for the Version UVH, Version E and Version E1 are consistent with the ISFSI pad models established at the time of their original licensing.
Also, as discussed in the response to RAI 4-1, the new LS-DYNA analyses in Supplement 3.III for the HI-STORM 100 overpack containing the MPC-68M and MPC-68MCBS serve only to demonstrate the structural integrity of the MPC enclosure vessel and the fuel basket for a tipover event resulting in a bounding impact deceleration (i.e., greater than 45g). Since the current finite element model of the ISFSI pad achieves this objective, there is no need to change the mesh density of the pad used in Supplement 3.III.
RAI 4-11 Submit the documents listed below, which are referenced in the submitted supporting calculations, to allow review of analysis model input parameters. If these documents have already been submitted previously, advise of the ADAMS accession number.
- a. HI-2043317, Revision 57, HI-STORM Thermal-Hydraulic Analyses Supporting up to 36.9 kW High Heat Load Amendment.
- c. HI-2002474, Revision 9, Analysis of the Loaded HI-STORM 100 System Under Drop and Tipover Scenarios.
This information is necessary to demonstrate compliance with and 10 CFR 72.236(b).
Holtec RAI Response:
As requested, the three Holtec reports identified above are provided to the NRC as part of this submittal.
RAI 4-12
[Withheld in accordance with 10 CFR 2.390]
This information is necessary to demonstrate compliance with and 10 CFR 72.236(b) and (l).
Holtec RAI Response:
[Withheld in accordance with 10 CFR 2.390]
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Page 10 of 16 RAI 4-13 Provide a reason for reducing the fuel assembly weight limit of the MPC-32M in the 100S Version E overpack in this amendment as well as a justification in the FSAR for the use of the original fuel assembly weight in the tipover evaluation for the MPC-32M basket in the 100S Version E overpack.
FSAR table 2.II.1.1 (and CoC appendix D, table 2.1-1, sections V.A.1.g and V.A.2.g) proposes revising the fuel assembly weight limit for the MPC-32M from 2050 lbs. to 1520 lbs. The evaluation for the MPC-32M fuel basket in the 100S Version E overpack is documented in report HI-2188448, where it is stated in section 5.1 that, rather than the revised value of 1520 lbs., the original fuel assembly weight of 2050 lbs. is employed and is considered to be a conservative input. However, FSAR section 3.A.5 states that, for the tipover event, the most conservatism is introduced into the results by using the minimum weight. Provide a justification in the FSAR that the current results presented for the MPC-32M basket in the 100S version E overpack using the original, heavier fuel assembly weight, produce the bounding tipover analysis results.
This information is necessary to demonstrate compliance with 10 CFR 72.236(b) and (l).
Holtec RAI Response:
The HI-STORM 100S Version E overpack is a lesser used dry storage system, as it is only deployed at one nuclear site: Indian Point Energy Center (IPEC). In HI-STORM 100 Amendment No. 19, the allowable fuel weight for the MPC-32M and MPC-32MCBS is reduced to better align with the needs of IPEC and also to improve design margins with respect to the enhanced LS-DYNA tipover model for the MPC-32MCBS, which is the more limiting of the two fuel basket configurations. That being said the MPC-32M has more strength to support a higher fuel assembly weight, as confirmed by the tipover analysis in HI-2188448 where a bounding fuel weight of 2050 lbs. is used as input for the MPC-32M (versus only 1520 lbs. for the MPC-32MCBS). The HI-STORM 100 FSAR, however, does not differentiate between the MPC-32M and MPC-32CBS in terms of allowable fuel contents, as the limits in FSAR Table 2.II.1.1 apply to both basket types. Hence, fuel assemblies weighing more than 1520 lbs. cannot be loaded in a MPC-32M despite the fact that HI-2188448 conservatively evaluates a higher fuel weight of 2050 lbs.
At the time of its original licensing in 2020 (via HI-STORM 100 Amendment No. 15), the fuel assembly weight limit for the MPC-32M was chosen as 2050 lbs. to match the existing limit for the MPC-32, a stainless steel (Alloy X) welded fuel basket. Moreover, the original tipover analysis for the MPC-32M did not utilize the enhanced LS-DYNA model for Metamic-HT fuel baskets, which was approved in HI-STORM FW Amendment No. 7 (LAR 1032-7) and is the impetus for this HI-STORM 100 amendment. That means that the previous tipover analysis for the MPC-32M was less restrictive as it did not apply any erosion criteria to the fuel basket elements, nor did it place any stress limits on the fuel basket panels. The only acceptance criterion that formerly applied to the tipover analysis of the MPC-32M fuel basket was the permanent deflection limit defined in FSAR Section 2.II.2.6.
Since the tipover analysis for the MPC-32M and MPC-32MCBS inside the HI-STORM 100S Version E are fully revised in Amendment No. 19 using a new fuel basket model and a new set of acceptance criteria, the fuel assembly weight limit is also revised to more closely envelope the loaded fuel assemblies at IPEC. If another site is interested in loading MPC-32M or MPC-32MCBS inside HI-STORM 100S Version E overpacks, under Holtecs generic certificate after this Amendment, then their fuel assemblies must comply with the proposed content limits in FSAR Table 2.II.1.1, including the maximum fuel assembly weight of 1520 lbs. Otherwise they cannot load fuel in a MPC-32M or MPC-32MCBS without a Part 72 license amendment.
Finally, with regard to the referenced statement in FSAR section 3.A.5, it is important to note that the tipover model described in Appendix 3.A is the original tipover model for the HI-STORM 100 overpack, which treats the MPC as a solid homogeneous cylinder having the proper total mass and external dimensions. In other words, the stored fuel assemblies in the MPC and the fuel basket are not modeled explicitly in the same manner as the enhanced LS-DYNA models discussed in Supplements 3.II, 3.III, and 3.IV. The purpose of the tipover model described in Appendix 3.A is only to determine the peak impact deceleration of the MPC measured at a height ATTACHMENT 2 TO HOLTEC LETTER 5014984
Page 11 of 16 corresponding to the top of the fuel basket (see also response to RAI 4-1). In that context, the peak impact deceleration of the solid, homogeneous MPC will increase, if the total mass assigned to the MPC were to decrease (while all other model parameters remain the same). The same inverse relationship does not apply to the mass of a fuel assembly and the impact force it transmits to the supporting fuel basket panels. This is because the impact force is equal to the product of the fuel assembly mass times the peak impact deceleration of the individual fuel assembly. It can be inferred from the analysis of a single mass impacting a spring in FSAR section 3.A.5 that the product of these two quantities is proportional to the square root of the fuel assembly mass. Thus, for stress analysis of a MPC fuel basket during a tipover event it is conservative to use the maximum fuel weight.
RAI 8-1 Address aging management activities related to the proposed changes in this amendment.
As stated in the renewed certificate of compliance for CoC No. 1014, Condition 14, AMENDMENTS AND REVISIONS FOR RENEWED CoC, (A)ll future amendments and revisions to this CoC shall include evaluations of the impacts to aging management activities (i.e., time-limited aging analyses and aging management programs) to ensure they remain adequate for any changes to structures, systems, and components within the scope of renewal. Provide information on aging management for this amendment.
This information is necessary to demonstrate compliance with 10 CFR 236(g).
Holtec RAI Response:
The request to update the Acceptance Criteria and Method of Evaluation (MOE) for the HI-STORM 100 tipover accident described in the FSAR in this amendment as well as the minor changes listed in the SOPC do not add any new components to the system. Additionally, there are no changes to any materials or environments for the existing components. All other acceptance criteria in the FSAR are the same as those in the existing FSAR used as the basis for license renewal. Since there is no change to any component, material, environment, temperature, or pressure there is no change to any aging management requirements due to this amendment.
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Page 12 of 16 Additional Comments/Questions:
AC/Q-1 Include 100S Version B Type IS overpack in FSAR table 1.0.4.
Holtec Response:
Note 5 is added to FSAR Table 1.0.4 explaining that the HI-STORM 100S Version B table entry includes Type IS.
AC/Q-2 Reconcile FSAR section 2.III.0 (for 100 overpack with MPC-68M/68M-CBS baskets) where it says basket shims are NITS, with Drawings 7195 for MPC-68M and 12035 for MPC-68M-CBS, which state shim (and bolts/nuts) are ITS.
Holtec Response:
Section 2.III.0 is updated to clarify the ITS and ITS-B designations of shims in MPC-68M and MPC-68MCBS.
AC/Q-3 Verify that Minimum Permitted Value is the correct title for the column of ISFSI pad data listed in FSAR table 2.II.0.1; it seems that larger pad data values would result in higher cask deceleration values. Similarly, clarify what the title Allowable means for 30 pad thickness in column of FSAR table 2.IV.0.1. Also, provide footnotes to these tables to clearly indicate any analyses within these FSAR sections that do not employ the listed values in their evaluation.
Holtec Response:
Sections 2.II.0.1 and 2.IV.0.1 and the titles in Tables 2.II.0.1 and 2.IV.0.1 are updated to indicate that the pad parameters are the reference parameters. The ISFSI pad design data presented in Tables 2.II.0.1 and 2.IV.0.1 form the basis for the generic tipover analyses documented in calculation packages HI-2188448 (for Version E and Version E1) and HI-2210290 (for Version UVH), respectively. [Withheld in accordance with 10 CFR 2.390]
For simplicity and better configuration control, the Tables 2.II.0.1 and 2.IV.0.1 provide the reference pad design data for the Overpack as opposed to the Overpack with a particular fuel basket combination.
Since all the tipover analyses with different fuel basket configurations in the above mentioned calculation packages either use or bound the reference ISFSI pad design data listed in the FSAR tables, we believe the updates to Tables 2.II.0.1 and 2.IV.0.1 with footnotes indicating added conservatism in the analyses can be avoided. Furthermore, it is also noted that the calculation packages clearly indicate additional conservatism, wherever applicable. Lastly, as noted in response to RAI 4-3, the reference ISFSI pad parameters in the FSAR are not absolute design limits, as the site can elect to perform a site-specific tipover analysis to qualify an alternate ISFSI pad design.
AC/Q-4 FSAR section 3.II.2 mentions table 3.2.5. Clarify whether it should be table 3.II.2.5.
Holtec Response:
Yes, the FSAR section is updated to reflect the correct table number i.e. Table 3.II.2.5.
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Page 13 of 16 AC/Q-5 Verify that the following statement of Supplement II (page 3.II-30) is still applicable, as it was deleted in Supplement IV (page 3.IV-15), or correct:
This is an improvement compared with the approach taken in the HI-STORM 100 tip-over analysis, where the loaded MPC was modeled as a cylinder and therefore the structural integrity of the MPC and fuel basket had to be analyzed separately based on the rigid body deceleration result of the cask.
Holtec Response:
Holtec verifies that the above referenced statement from Supplement 3.II is applicable. The same statement was deleted from Supplement 3.IV not for any technical reasons, but because: (i) Supplement 3.IV, along with the HI-STORM 100 Version UVH, was added to the HI-STORM 100 FSAR after Supplement 3.II, which first introduced the more detailed LS-DYNA tipover model with the MPC contents modelled explicitly, and (ii) the LS-DYNA model description in subparagraph 3.IV.4.3.4 begins by making a comparison to the tipover model employed in Supplement 3.II (as opposed to the HI-STORM 100 tipover analysis). That said the tipover analysis for the HI-STORM 100 Version UVH is an improvement over the HI-STORM 100 tipover analysis. No changes have been made to Supplement 3.II or Supplement 3.IV resulting from this NRC comment.
AC/Q-6
[Withheld in accordance with 10 CFR 2.390]
Holtec Response:
[Withheld in accordance with 10 CFR 2.390]
AC/Q-7 FSAR page 3.III-7, as well as the relevant Holtec report, states that the MPC maximum plastic strain is 8.2%,
but should be 0.82%.
Holtec Response:
This text in the FSAR is updated. No action is needed in the calculation package as a similar statement does not exist in Holtec report HI-2240678.
AC/Q-8 FSAR figure 3.III.8, as well as the relevant Holtec report, for MPC-68M-CBS fuel basket in 100 overpack, the thermal zone diagram title states there is a 270°C region, but it is not labeled in the diagram. Label diagram or delete from the title.
Holtec Response:
The 270°C region is not considered in the MPC-68MCBS fuel basket in the HI-STORM 100 overpack. The title of FSAR Figure 3.III.8 and the calculation package are updated accordingly.
AC/Q-9 Provide a figure in FSAR section 3.IV for fuel basket temperature zones for the MPC-68M fuel basket in the UVH overpack.
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Page 14 of 16 Holtec Response:
Figure 3.IV.4.22 is added to the FSAR showing the MPC-68M fuel basket temperature zones in the HI-STORM 100 Version UVH.
AC/Q-10 It seems that FSAR tables 3.IV.4.6 and 3.IV.4.7, which tabulate plastic strains for the MPC-32M and MPC-68M in the UVH overpack, have been deleted (per indications on proposed FSAR page 3.IV-17). Confirm and indicate table deletion in FSAR.
Holtec Response:
The comment is correct. Holtecs intention was to delete Tables 3.IV.4.6 and 3.IV.4.7 (similar to Tables 3.II.4.12 in Supplement 3.II), but only the text was deleted in previous submittal. Tables 3.IV.4.6 and 3.IV.4.7 have been properly deleted in the latest update to FSAR Chapter 3.
AC/Q-11 Correct FSAR figures 3.IV.4.23 to 3.IV.4.26, where new strain contour is overlapping old strain contour.
Holtec Response:
It appears that the old versions of Figures 3.IV.4.23 to 3.IV.4.26 are shown on top of the new figures in the pdf file that Holtec sent with the initial Amendment 19 submittal. Therefore, the new figures were not visible in the pdf file. This has been corrected in the latest pdf file sent with the RAI responses, which now clearly shows the new strain contours, and the old strain contours are shown with a line struck through them.
AC/Q-12 It is mentioned in the Summary of Proposed Changes document that CG changes in FSAR section 3.II.2 have been made consistent with those in FW 7. Advise what specific changes are being made as well as explaining why they are being made.
Holtec Response:
The changes appear in the last paragraph of Section 3.II.2 (on page 3.II-3), which include deleting the following statement:
The weight information provided above shall be used for designing the lifting and handling ancillary for the HI-STORM cask components.
Consistent with HI-STORM FW Amendment No. 7, this change is being made because the cask lifting ancillaries are designed per ANSI N14.6 with increased safety factors of 6 and 10 with respect to material yield and ultimate strength, which adequately compensates for small CG variations.
In addition, the words unless a more accurate CG height is calculated on a site-specific basis are added to the first sentence of the same paragraph. This aligns with the text in the preceding FSAR paragraph, which allows precise CG data to be obtained, for a specific site, from the Solidworks models linked to the Licensing drawings. This proposed change mirrors the change made to Section 3.2 of the HI-STORM FW FSAR in Amendment No. 7.
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Page 15 of 16 AC/Q-13 FSAR section 3.III.4.4.3.1 states that slotted construction of baskets means no prying, but non-CBS type Metamic-HT baskets are welded at panel seams and exterior corners. Is this statement correct? If not completely correct, clarify the applicability of this statement. Confirm that these baskets are modeled the same way as the HI-STORM FW Amendment No. 7 baskets in this regard.
Holtec Response:
[Withheld in accordance with 10 CFR 2.390] The modeling approach of the fuel basket panel connections is consistent with that followed in HI-STORM FW Amendment 7. Furthermore, the discussion in Section 3.III.4.4.3.1 is with regards to the interior panels at 90 degree corners. This is appropriately clarified in the FSAR.
AC/Q-14 Cite sources in the FSAR for the fuel basket temperature zone presented in the following figures:
- a. 3.II.4.11, 3.II.4.32A, 3.II.4.32B, 3.II.4.34A, and 3.II.4.34B for MPC-32M, MPC-32M-CBS and MPC-68M-CBS in 100S Version E and MPC-32M-CBS and MPC-68M-CBS in 100S Version E1.
- b. 3.III.4 and 3.III.8 for MPC-68M and MPC-68M-CBS in 100.
- c. 3.IV.4.12 for MPC-32M in UVH.
Holtec Response:
Appropriate thermal report references are added to all the noted figures, as well as Figure 3.IV.4.22.
AC/Q-15 For the MPC-68M Drawing 7195, Revision 17, [Withheld in accordance with 10 CFR 2.390].
Holtec Response:
[Withheld in accordance with 10 CFR 2.390]
AC/Q-16 Identify maximum strain of MPC located on FSAR figure 3.II.4.15 (for MPC-32M in 100S version E overpacks).
No red areas of stress contours can be seen from view shown. Provide more information.
Holtec Response:
The FSAR figure 3.II.4.15 is updated with view that reflects the areas where higher plastic strain is developed.
AC/Q-17 Report HI-2188448, Revision 5, for 100S Versions E and E1 overpacks
[Withheld in accordance with 10 CFR 2.390]
Holtec Response:
[Withheld in accordance with 10 CFR 2.390]
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Page 16 of 16 AC/Q-18 Report HI-2210290, Revision 3, for UVH overpack
[Withheld in accordance with 10 CFR 2.390]
Holtec Response:
[Withheld in accordance with 10 CFR 2.390]
AC/Q-19 Response Submitted Separately ATTACHMENT 2 TO HOLTEC LETTER 5014984