ML23321A219

International, NRC Clarification Questions from EA-23-044 Holtec Pec Presentation ML23297A261 (Edited Excerpt from the Pec Transcript ML23307A107)

ML23321A219
Person / Time
Site:	Holtec
Issue date:	11/17/2023
From:	Holtec
To:	Office of Nuclear Material Safety and Safeguards
Shared Package
ML23321A216	List: ML23321A217 ML23321A219 ML23321A220
References
5014791, EA-23-044
Download: ML23321A219 (1)

Text

Atachment 2 to Holtec Leter 5014791 NRC Clari"caon Quesons from EA-23-044 Holtec PEC presentaon ML23297A261 (edited excerpt from the PEC transcript ML23307A107)

QUESTION 1: Relang to Slide 10, your response to Item 1. While there were geometric changes to the model, the "rst example of Apparent Violaon A was that Holtec changed an element of an MOE by using a new modeling assumpon to model the bolts with nodal constraints. Is Holtec suggesng that the use of nodal constraints is a geometric change, or a dimensional change or an input change and not an element change? If so, could you elaborate on that?

Additional Information on Apparent Violations Response to Item 1 HOL T EC I N T ER.NATIO NA L

\f'The corner welds described in FSAR Revision 21 are between intersecting Metamic panels within the actual basket structure, there are no welds between "the standard basket and shims"

\f'Holtec uses NEI 12-04 as 72.48 program basis, as endorsed by NRC in Reg Guide 3.72

\f'NEI 12-04 specifically discusses dimensional changes as input changes which are different than methodology which is "calculational framework" which tend to involve a mathematical expression

\f'Holtec modeled the accurate dimensional and physical changes that occurred with the CBS design change and did not change the calculational framework of the analysis

\f'Previously established understanding of NRC guidance was that a change to the FEA model to accord with geometric changes was not automatically considered a change to the methodology Definition of "method of evaluation" in NEl-12-04 is based on "calculational framewo rk" Examples of mathematical models that would be a change in methodology are methods of heat transfer and material performance - not geometrical changes www.holtec.com I Page 10 RESPONSE TO QUESTION 1:

The introducon of the CBS bolts is a geometric change to the MPC fuel basket, which leads to an input change to the analycal model. Holtecs posion that this is not an MOE change is further substanated by the fact that the corner welds in the original basket design were also modeled using nodal constraints.

In other words, the corner welds themselves, like the CBS bolts, were not modeled explicitly using a disnct element type and/or material model, but instead their eect was simulated in the "nite element model by merging the interfacing nodes between two adjacent elements represenng the Metamic-HT basket panels. Thus, the change from the original fuel basket design with corner welds to the CBS basket design simply entailed releasing the merged nodes at the corner locaons (to eliminate the fricon-sr welds) and introducing a new set of nodal constraints to represent the bolted connecons between the fuel basket panels and the CBS shims.

Page 1 of 16

Atachment 2 to Holtec Leter 5014791 QUESTION 2:

My next queson relates to Slide 12, which is Holtec's response to Item 2. While welds for the previous basket design with the extruded version of the shims are not welded to the shims, the second example of apparent violaon A was that Holtec used a new or dierent MOE by assuming the impact load is directly transferred between the shims and the basket without inducing load in the bolts. Is Holtec suggesng that this assumpon is not a new MOE because of the weld locaon in the previous design? If so, could you elaborate?

Additional Information on Apparent Violations HOLTEC I NTEl{N A TIO NA L Response to Item 2 v As in item 1, this is a direct result of the change in geometry of the basket/shim configu ration

• The corner welds described in FSAR Revision 21 are between intersecting Metamic panels within th e actual basket structure

• There are no welds between " the standard basket and shims" v For the standard (FSW-based) basket design, there is no physical connection between the fuel basket and the shims if Evaluation performed for friction stir welds used direct outputs from the ANSYS simulation

• Friction Stir Welds were an integral part of the standard basket design - not the shims v Bolts are a separate physical component

• A separate analysis was performed as necessary to demonstrate their suitabilit y for the solid shims if Not considered a change in methodology- if welds still existed they would have been analyzed using the previously established method

\/'Since the CBS basket introduced a different component it was analyzed using a bounding load consistent with the FEA model framework www.holtec.com I Page 12 RESPONSE TO QUESTION 2:

The design philosophy that the lateral impact load is directly transferred between the shims and the basket is not new to the CBS basket design. The same load transfer mechanism exists in the original MPC-68M design, where the basket shims are disconnected and installed independently from the Metamic-HT fuel basket. In fact, it was this original design philosophy that movated the design of the CBS atachment bolts. Speci"cally, the bolt holes in the CBS shims are oversized with respect to the CBS bolt diameter to allow enough relave movement between the CBS shims and the Metamic-HT fuel basket such that when a lateral impact or side load occurs, the intervening CBS shims are pressed into contact with the fuel basket before the CBS bolts make contact with the bolt hole diameter and develop a shear load. In summary, the load transfer mechanism between the shims and the fuel basket, under lateral loading, is the same in the CBS basket design as it was in the original basket design, and moreover, the CBS bolted joints were designed speci"cally with this design imperave in mind. Therefore, this is not a new or dierent MOE.

Page 2 of 16

Atachment 2 to Holtec Leter 5014791 QUESTION 3:

My next queson also relates to Slide 12. Holtec states that a separate analysis was performed as necessary to demonstrate bolt suitability for the solid shims. Could you explain what that analysis was and what bolt suitability entails? When you say, as necessary, how did you determine when that analysis was necessary? In cases when this analysis was determined to be unnecessary, what was the jus"caon for this? Were these analyses and the decision on whether to perform them part of an MOE approved by the NRC for this applicaon?

Additional Information on Apparent Violations HOLTEC I NTEl{N A TIO NA L Response to Item 2 v As in item 1, this is a direct result of the change in geometry of the basket/shim configu ration

• The corner welds described in FSAR Revision 21 are between intersecting Metamic panels within th e actual basket structure

• There are no welds between " the standard basket and shims" v For the standard (FSW-based) basket design, there is no physical connection between the fuel basket and the shims if Evaluation performed for friction stir welds used direct outputs from the ANSYS simulation

• Friction Stir Welds were an integral part of the standard basket design - not the shims v Bolts are a separate physical component

• A separate analysis was performed as necessary to demonstrate their suitabilit y for the solid shims if Not considered a change in methodology- if welds still existed they would have been analyzed using the previously established method

\/'Since the CBS basket introduced a different component it was analyzed using a bounding load consistent with the FEA model framework www.holtec.com I Page 12 RESPONSE TO QUESTION 3:

The CBS bolts are generally not in the primary load path during a lateral impact event as discussed above in Holtecs response to Queson 2. Therefore, in the vast majority of cases, an explicit stress analysis of the CBS bolts is not necessary for the non-mechanisc pover event. The only excepon is the solid shim present in the MPC-68M CBS basket, which is iden"ed in Figure 1 below (excerpted from Holtec drawing 12035).

Page 3 of 16

Atachment 2 to Holtec Leter 5014791

[PROPRIETARY INFORMATION WITHHELD PER 10CFR2.390]

Figure 1 - CBS Solid Shim Locaons for MPC-68M CBS Basket Assembly At the 8 locaons iden"ed above, the solid shim provides direct support to the adjacent cell wall associated with the corner cell locaon, parcularly when the impact load is perpendicular to the bolt axis (as shown in Figure 1). In this scenario, the solid shim and its atachment bolts must resist 50% of the ampli"ed weight of the cell wall plus the stored fuel assembly located in the corner cell to account for the pover event. Only half of the weight is considered because the total load acng on the cell wall is supported at both ends of the unsupported span. The stress analysis of the CBS bolts for this loading condion is documented in Supplement 79 of HI-2012787, which shows that the primary shear stress in the bolts, at the maximum design basis deceleraon of 60g, is less than the Level D stress limit per ASME Secon III, Appendix F.

The pover model for the MPC-68M CBS is described in the HI-STORM 100 FSAR Secon 3.III.4.4.3.1, which states the following regarding the CBS solid shims and their atachment bolts:

At the eight perimeter corners, the intersecng basket panels are bonded together in the "nite element model to model shim and bolts at these locaons. Bolts at these perimeter corners are quali"ed using strength of material formulaons.

Bolts did not exist in any previous design, so no method of evaluaon existed in any prior NRC approved applicaon.

Page 4 of 16

Atachment 2 to Holtec Leter 5014791 QUESTION 4:

My next queson relates to Slide 15. That is your response to Item 3. Holtec states that the analysis of both canisters is the same. Which canisters is Holtec referring to? In which analyses? HI-2188448 for MPC-32M, and supplement 79 of HI-20127874 for MPC-68M-CBS? Sorry, that was a queson. That was me suggesng that those are maybe the two analyses that youre referring to but seeking clari"caon for that.

Additional Information on Apparent Violations HOLTEC I NTEl{N ATIONAL Response to Item 3 V-This item was explicitly addressed in the revised 72.48 evaluations provided to the NRC via the audit-related SharePoint site on May 23, 2023 V-While the original MPC-68M analysis did use an elastic material model, the use of a bilinear material model in the MPC-68M-CBS analysis meets both criteria in NEI 12-04 to NOT be considered a change in methodology MPC-32M, which was licensed in the same docket as the MPC-68M, used a bilinear material model for the shims in the tipover analysis from the time of its initial approval.

Analysis of both canisters is the same, with the same scenario applied, therefore this meets the NEI 12-04 definition of " approved for the intended function."

v Additionally, Holtec performed a run with the CBS sty le shims using an elastic material model and demonstrated that the results are essentially the same as the bilinear model, meeting the first criteria in NEI 12-04.

This was provided to the NRC on May 23, 2023 N El 12-04, Section 6.8: (c)(2)(vUI). In general, licensees or CoC holders can make changes to MOEs without first obtaining a license amendment or cask CoC amendment In two ways:

I . Changing one or more elements of the MOE, provided the results are essentially the same as, or more conservative than, previous results or Mi@@iiiiHiiiMJ..-

RESPONSE TO QUESTION 4:

The statement on Slide 15 saying the analysis of both canisters is the same, indicates that both analyses are the same and is intended to mean that the analysis of a pover of the HI-STORM 100 system containing the MPC-32M is the same as the analysis of the pover of the HI-STORM 100 system containing the MPC-68M. The reviewer is correct in that HI-2188448 Rev. 3 contains the pover analysis of the MPC-32M (only allowed for storage in the HI-STORM 100S Version E), which uses the bilinear material model. The pover analyses for the MPC-68M and MPC-68M-CBS are in various reports depending on the HI-STORM 100 overpack design. HI-2188448 Rev 3 contains the MPC-68M and MPC-68M-CBS in the HI-STORM 100S Version E. HI-2012787 Rev. 40 contains the MPC-68M and MPC-68M-CBS in other overpack variants.

Page 5 of 16

Atachment 2 to Holtec Leter 5014791 QUESTION 5:

It is the Sta's understanding that MPC-68M-CBS was analyzed as a basket slice in ANSYS while MPC-32M was analyzed as a half-symmetry model in LS-DYNA, among other dierences. Is this incorrect? How does Holtec view these analyses as the same?

RESPONSE TO QUESTION 5:

The reviewer is parally correct. The soware used in the analysis of the MPC-68M-CBS is dierent depending on the storage overpack used. The original MPC-68M licensing basis pover analyses were performed, reviewed, and approved in HI-STORM 100 overpack styles in ANSYS. For the newer HI-STORM 100 overpack styles, such as the HI-STORM 100S Ver E, pover analyses of the MPC-68M were performed in LS-DYNA. Those analyses are what are referred to as the same. The intent of the same statement was not that the ANSYS and LS-DYNA evaluaons were the same, but that each canister and overpack were run in the same methodology as was originally licensed. Also, the analysis of the MPC-68M in the HI-STORM 100S Ver E (and therefore the MPC-68M-CBS in the HI-STORM 100S Ver E) was the same as the MPC-32M in the HI-STORM 100S Ver E.

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Atachment 2 to Holtec Leter 5014791 QUESTION 6:

My next queson also relates to Slide 15. Where was the previously approved method for calculang a bilinear material model for MPC-32M discussed? Is it Appendix B of HI-2188448 Revision 0? Which amendment added MPC-32M? Was the FSAR updated to re"ect the change in material model for the shims? Why was a bilinear material model developed for MPC-32M shims? Did these shims exceed the yield stress?

Additional Information on Apparent Violations HOLTEC I NTEl{N ATIONAL Response to Item 3 V-This item was explicitly addressed in the revised 72.48 evaluations provided to the NRC via the audit-related SharePoint site on May 23, 2023 V-While the original MPC-68M analysis did use an elastic material model, the use of a bilinear material model in the MPC-68M-CBS analysis meets both criteria in NEI 12-04 to NOT be considered a change in methodology MPC-32M, which was licensed in the same docket as the MPC-68M, used a bilinear material model for the shims in the tipover analysis from the time of its initial approval.

Analysis of both canisters is the same, with the same scenario applied, therefore this meets the NEI 12-04 definition of " approved for the intended function."

v Additionally, Holtec performed a run with the CBS sty le shims using an elastic material model and demonstrated that the results are essentially the same as the bilinear model, meeting the first criteria in NEI 12-04.

This was provided to the NRC on May 23, 2023 N El 12-04, Section 6.8: (c)(2)(vUI). In general, licensees or CoC holders can make changes to MOEs without first obtaining a license amendment or cask CoC amendment In two ways:

I . Changing one or more elements of the MOE, provided the results are essentially the same as, or more conservative than, previous results or Mi@@iiiiHiiiMJ..-

RESPONSE TO QUESTION 6:

The previously approved method for calculang a bilinear material model for MPC-32M shims is discussed at several locaons in HI-2188448, speci"cally Secon 5.3, Secon E.2 in Appendix E, and Secon H.2 in Appendix H. The input values de"ning the bilinear material model are developed in Appendix B of HI-2188448. The MPC-32M in the HI-STORM 100S Version E overpack was included in Amendment 15. The FSAR was revised at that me (March 2019) and submited to NRC sta with the Amendment 15 applicaon (ML19092A181). The FSAR corresponding to Amendment 15 approval does not detail the speci"c material model for the basket shims. The bilinear material model developed for the MPC-32M shims was chosen because the maximum stress in the shim was expected to be in the post-elasc range, as discussed in LR-171, provided to the NRC in May 2023. Minor exceedance of the yield stress occurs in very localized areas.

Page 7 of 16

Atachment 2 to Holtec Leter 5014791 QUESTION 7:

My next quesons also relate to Slide 15. Holtec menons performing a "nite element analysis with the CBS using an elasc material model. Did the shim remain in the elasc region in the "nite element analysis?

If so, why was the bilinear material model needed previously? If not, how is an elasc material model valid for characterizing the behavior of the shims in the "nite element analysis? Which results are essenally the same between the elasc CBS model, the bilinear CBS model, and the model for the previous design? And "nally, did the elasc and bilinear CBS models include any other changes from the model for the previous design?

Additional Information on Apparent Violations HOLTEC I NTEl{N ATIONAL Response to Item 3 V-This item was explicitly addressed in the revised 72.48 evaluations provided to the NRC via the audit-related SharePoint site on May 23, 2023 V-While the original MPC-68M analysis did use an elastic material model, the use of a bilinear material model in the MPC-68M-CBS analysis meets both criteria in NEI 12-04 to NOT be considered a change in methodology MPC-32M, which was licensed in the same docket as the MPC-68M, used a bilinear material model for the shims in the tipover analysis from the time of its initial approval.

Analysis of both canisters is the same, with the same scenario applied, therefore this meets the NEI 12-04 definition of " approved for the intended function."

v Additionally, Holtec performed a run with the CBS sty le shims using an elastic material model and demonstrated that the results are essentially the same as the bilinear model, meeting the first criteria in NEI 12-04.

This was provided to the NRC on May 23, 2023 N El 12-04, Section 6.8: (c)(2)(vUI). In general, licensees or CoC holders can make changes to MOEs without first obtaining a license amendment or cask CoC amendment In two ways:

I. Changing one or more elements of the MOE, provided the results are essentially the same as, or more conservative than, previous results or wi1;;;;;..;;,;w;..-

RESPONSE TO QUESTION 7:

In response to the NRCs April 2023 debrief, Holtec updated the four 72.48 evaluaons. One of those updates included performing an analysis of the MPC-68M-CBS using the linear elasc material model for the shims. The linear elasc soluon for the MPC-68M-CBS showed [

PROPRIETARY INFORMATION WITHHELD PER 10CFR2.390

]

Holtec made a conservave decision to use a bilinear material model for the quali"caon of the MPC-68M-CBS because it maximizes the strains and deformaon of the CBS shims and, by doing so, places greater demand on the fuel basket to meet its allowable de"econ limit. Holtec believes the bilinear model is more appropriate for characterizing the physical condions in the CBS style basket, but due to stas concerns, a comparison of the linear elasc material model and the bilinear material model was performed. As stated in the revised 72.48 and Posion Paper LR-171, the deformaon in the fuel basket, which is the FSAR stated acceptance criterion for the pover analysis, shows no substanve dierence with the dierent material models in the shim. The changes from the previous design are the changes described to modify the shims to the bolted design. However, the comparison and results described above are a direct comparison between the same models with only the material model changed between bilinear and linear elasc. Lastly, the decision to use a linear elasc material model for the basket shims in the Page 8 of 16

Atachment 2 to Holtec Leter 5014791 original quali"caon of the MPC-68M (i.e., non-CBS basket) is jus"ed since even the maximum local stress in the shims is below the material yield stress.

QUESTION 8:

My next quesons relate to slide 17, which is Holtec's response to Item 4. Did Holtec demonstrate that the primary stresses in the CBS basket shims remain below the yield strength? If so, where is that documented? In the FSAR or Supplement 79 of HI-2012787? If not, which demonstraon is referred to in the sub-bullet that is not replaced by the peak stress comparison? Is this how the previous design was analyzed, meaning, did the analysis of the standard shims demonstrate that only the primary stresses were below yield?

Additional Information on Apparent Violations *****

HOLTEC

\NT EKN ATIONA L Response to Item 4

,f'Primary stresses in the standard basket shims, as well as the CBS basket shims, remain below the material yield strength during non-mechanistic tipover ifOnly peak stresses are compared to the material ultimate strength in the supporting calculation package (supplement 79 of Hl-2012787) ifThe same calculation package indicates that this is "conservative as primary membrane plus bending stress is lower".

,fThis is not a different MOE because the primary stresses in the CBS basket shims still remain below yield, just as in the standard shims and described in the FSAR.

The additional comparison performed in the calculation package does not replace that demonstration.

www.holtec.com I Page 17 RESPONSE TO QUESTION 8:

Yes, Holtec demonstrated in Supplement 79 of HI-2012787 that the primary stresses in the CBS basket shims remain well below the yield strength. [

PROPRIETARY INFORMATION WITHHELD PER 10CFR2.390

] With regard to the analysis of the standard shims for the MPC-68M, there was no need to perform stress linearizaon since even the peak stress was below the yield stress of the material. Therefore, it was readily apparent that the primary stresses in the standard shims for the MPC-68M were also below yield.

Page 9 of 16

Atachment 2 to Holtec Leter 5014791 QUESTION 9:

More quesons on Slide 17. What does Holtec mean by peak stresses in this context? How is Holtec categorizing the stresses as peak or primary, and is that dierent than the stress categorizaon in the previous analysis? Why was the peak stress comparison performed?

Additional Information on Apparent Violations *****

HOLTEC I N TE KNATIONA L Response to Item 4

\f'Primary stresses in the standard basket shims, as well as the CBS basket shims, remain below the material yield strength during non-mechanistic tipover

\/'Only peak stresses are compared to the material ultimate strength in the supporting calculation package (supplement 79 of Hl-2012787)

\/'The same calculation package indicates that this is "conservative as primary membrane plus bending stress is lower".

\f'This is not a different MOE because the primary stresses in the CBS basket shims still remain below yield, just as in the standard shims and described in the FSAR.

The additional comparison performed in the calculation package does not replace that demonstration.

www.holtec.com I Page 17 RESPONSE TO QUESTION 9:

In the context of Slide 17 and Supplement 79 of HI-2012787, the use of the term peak stress means the maximum computed stress at any point in the basket shims regardless of its locaon. Thus, peak stresses include the eects of local structural disconnuies and stress concentraons where present. Whereas primary stresses are linearly varying over the cross secon, and are necessary to sasfy basic force and moment equilibrium.

The peak stress in the basket shims was compared to the yield stress in the original analysis of the MPC-68M for comparison only. In other words, since the peak stress was below the yield point, it was obvious that primary stresses were not a concern. For the MPC-68M-CBS, the peak stress in the CBS exceeded the material yield stress, so a disncon was made between peak and primary stresses in Supplement 79 of HI-2012787.

Page 10 of 16

Atachment 2 to Holtec Leter 5014791 QUESTION 10:

My next queson relates to Slide 19. That's Holtec's response to Item 5. Holtec states that the results for ANSYS Rev 17 have been shown to be essenally the same. Which results from Rev 17 were shown to the same as which other results?

Additional Information on Apparent Violations *****

HOLTEC I N TE KNATIONA L Response to Item 5

'1'For ANSYS Rev 17, the results have been shown to be essentially the same between the two codes, thus meeting the second criteria in NEI 12-04

'1' Holtec's QA program mandates that a new version of a Code be requalified to establish its validity before use in any safety-significant project The code is run and shows the same results Hl-2012627 provides this QA qualification for ANSYS

'1'The Holtec quality validation process for computer codes is well established v Rev 17 is a valid edition of the Code-fully compliant with Holtec QA.

v We recognize that this could have been more clearly documented within the 72.48 evaluation www.holtec.com I Page 19 RESPONSE TO QUESTION 10:

Both ANSYS Version 11.0 and Version 17.1 have been independently validated by Holtec in HI-2012627 by solving a set of 39 test problems and comparing the results against published target values. The speci"c test problems are 2, 5, 7, 27, 28, 32, 34, 38, 42, 45, 58, 62, 63, 66, 70, 92, 93, 95, 96, 97, 99, 102, 105, 107, 109, 113, 125, 128, 131, 147, 160, 161, 191, 193, 195, 211, 217, 227, and 228 from the ANSYS Mechanical APDL Veri"caon Manual. These test problems show the same results between both ANSYS versions for a variety of analysis types, element types, material models, boundary condions, etc..

Page 11 of 16

Atachment 2 to Holtec Leter 5014791 QUESTION 11:

My next quesons relate to Slide 21. That's Holtec's response to Item 6. Sorry, I don't have new quesons here. These would basically be, as Holtec points out, this item is very similar to Item 2, so I would have the same quesons for Item 2. This is just related to the FW, whereas Item 2 was for the HI-STROM 100.

Then also on Slide 24, as Holtec points out, this item is related to Item 1, so I would have the same quesons as I did for Item 1, which were my quesons on Slide 10.

Additional Information on Apparent Violations HOLTEC I NT El{N A TIO NA L Response to Item 6

\/'Similar to item 2, this is a direct result of the change in the basket/shim geometry

• The corner welds described in the FSAR are between intersecting Metamic panels within the actual basket structure, there are no welds between "the standard basket and shims" if For the standard basket design, there is no physical connection between the fuel basket and the shims, and therefore there is no FSAR method for evaluating basket-to-shim connections ifThe evaluation performed for the Friction Stir Welds used direct outputs from the ANSYS simulation because those were an integral part of the standard basket (not the shims)

\/'This was not a change in methodology - if basket welds still existed they would have been analyzed the using previously established method

\/'Since the CBS basket variant introduced a different component (bolted shims), the bolts were analyzed using a bounding load consistent with the FEA model framework www.holtec.com I Page 21 RESPONSE TO QUESTION 11:

As stated above, the introducon of the CBS bolts is a geometric change to the MPC fuel basket, which leads to an input change to the analycal model. Holtecs posion that this is not an MOE change is further substanated by the fact that the corner welds in the original basket design were also modeled using nodal constraints. In other words, the corner welds themselves, like the CBS bolts, were not modeled explicitly using a disnct element type and/or material model, but instead their eect was simulated in the "nite element model by merging the interfacing nodes between two adjacent elements represenng the Metamic-HT basket panels. Thus, the change from the original fuel basket design with corner welds to the CBS basket design simply entailed releasing the merged nodes at the corner locaons (to eliminate the fricon-sr welds) and introducing a new set of nodal constraints to represent the bolted connecons between the fuel basket panels and the CBS shims.

Finally, as with the HI-STORM 100 System (see QUESTION 2 above), the design philosophy that the lateral impact load is directly transferred between the shims and the basket is not new to the CBS basket designs included in the HI-STORM FW FSAR. The same load transfer mechanism exists in the original MPC-37 and MPC-89 designs, where the basket shims are disconnected and installed independently from the Metamic-HT fuel basket.

Page 12 of 16

Atachment 2 to Holtec Leter 5014791 QUESTION 12:

So, my next queson is for Slide 26. That relates to Holtec's response to Item 8. For the CBS results, were plasc strains limited to areas beyond the acve fuel region? What were the structural basket criteria, and how has Holtec demonstrated the CBS baskets meet these criteria?

Additional Information on Apparent Violations *****

HOLTEC I N TE KNATIONA L Response to Item 8

'\f'We submit that this is NOT a change in methodology- the results in the FSAR for the MPC-37-CBS basket are the same as those presented for the original design of the MPC-37

'1'The Holtec FSAR presented strain results in figures for the MPC-37

'\f'For the MPC-37-CBS basket figures were also included in the FSAR to show strain results throughout the basket

'\f'For both the original and CBS basket designs, the FSAR figures support the same conclusion that the basket meets the structural basket criteria www.holtec.com I Page 26 RESPONSE TO QUESTION 12:

The structural basket criteria for the Metamic-HT baskets has always been the de"econ based criteria in Chapter 2 of the HI-STORM FW FSAR. In the original licensing of HI-STORM FW, Holtec met that criteria by demonstrang that the plasc strains were limited to very small areas outside the acve fuel region.

Similarly for the CBS variants of those canisters, Holtec has demonstrated that plasc strains are either outside the acve fuel region or limited to very small, localized areas within the acve fuel region.

Page 13 of 16

Atachment 2 to Holtec Leter 5014791 QUESTION 13:

My next quesons relate to Slide 29. This is Holtec's response to Item 9. Was the allowance for basket-to-shell interference added as part of an amendment to the HI-STORM FW system? In which revision of the FSAR was the allowance for basket-to-shell interference added? In which revision to the FSAR was the CBS design added? Which non-CBS baskets have basket-to-shell interference? How did Holtec address this interference, and where is this documented?

Additional Information on Apparent Violations HOLTE C I N T El{N A TIO NA L Response to Item 9 ifThe Holtec FSAR, Paragraph 3.1.l(i) addresses the allowance for baskeHo-shell interference ifThe allowance for interference was not addressed in the 72.48 evaluations for the CBS baskets because it existed prior to these design modifications:

• Differential Themial Expansion (DTE): The stress arising from the differential thermal expansion between the fuel basket and the MPC shell is mitigated by providing a presaibed nominal gap at their interface locations. The radial gap is selected to produce modest local compatibility stresses at the basket panel-to-shell j1.111ction which are classified as peak stresses in NB-3213.11 and NB-3213. B (b) that produce no significant distortion, and are important only in determining the cyclic fl.tigue life ofthe component. The magnitude of the peak stress will vary al the different basket panel-to-shell interface locations and with the canister' s heat generation rate. At low heat loads and ambient conditions, a positive gap will exisi at most interface locations. The progressive reduction in the gap with increasing heat load ensures improved heat transmission across the basket-to-,shell interfl.ce which enhances the thermal capacity.

www.holtec.com I Page 29 RESPONSE TO QUESTION 13:

A change was made to the HI-STORM FW FSAR (Rev 6) which modi"ed Chapter 3 to account for basket-to-shell interference and was evaluated in accordance with 10 CFR 72.48. This 72.48 evaluaon was completed in August of 2020, and was provided to the inspecon team during the inspecon. This change was formally incorporated into the HI-STORM FW FSAR in Revision 7. The MPC-89 was the "rst CBS basket in the HI-STORM FW system and the change was evaluated in accordance with 72.48, which was completed in May 2020. This change was also formally incorporated into FW FSAR Revision 7. Currently, only the MPC-37 CBS and MPC-89 CBS baskets have basket-to-shell interference. The maximum basket-to-shell interference value was documented in FSAR Table 4.4.6. The value is so small that engineering judgement was made that it met the revised criteria (shown on the slide above).

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Atachment 2 to Holtec Leter 5014791 QUESTION 14:

Just one more queson, which is in relaon to Slide 12 in the presentaon. Holtec menoned the oversized holes in discussing the assumpon that the shims aren't in the load path. Were these oversized holds depicted in the drawings or the FSAR at the me of the inspecon?

Additional Information on Apparent Violations *****

HOLTEC I N TE KNATIONA L Response to Item 2 v As in item 1, this is a direct result of the change in geometry of the basket/shim configu ration

• The corner welds described in FSAR Revision 21 are between intersecting Metamic panels within the actual basket structure

• There are no welds between "the standard basket and shims" v For the standard (FSW-based) basket design, there is no physical connection between the fuel basket and the shims v'Evaluation performed for friction stir welds used direct outputs from the ANSYS simulation Friction Stir Welds were an integral part of the standard basket design - not the shims v Bolts are a separate physical component

• A separate analysis was performed as necessary to demonstrate their suitability for the solid shims v' Not considered a change in methodology- if welds still existed they would have been analyzed using the previously established method

,f'Since the CBS basket introduced a different component it was analyzed using a bounding load consistent with the FEA model framework www.holtec.com I Page 12 RESPONSE TO QUESTION 14:

When the inspecon began in December 2022, HI-STORM FW FSAR Rev 9 was the most current revision of the FSAR, which contains Drawing 12030 Revision 1 for the MPC-89 CBS basket. The speci"c bolt hole size is not shown on the licensing drawing, but it is shown on the more detailed fabricaon drawing for the basket components and also discussed in Appendix N of HI-2094353, which states:

Bolt holes in the Connuous Basket Shims (CBS) and basket panel extensions are sized so that shims can slide up against basket panels without subjecng bolts to shear loads. In other words, impact load is directly transferred from shims to basket panels during pover.

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Atachment 2 to Holtec Leter 5014791 QUESTION 15:

And I have one "nal queson, which relates to Slide 33. Which is Holtec's response to apparent violaon C. In Holtec's view, is the p-over analysis part of the licensing basis for HI-STORM 100 or HI-STORM FW?

In Holtec's view, what is the purpose for the p-over analysis? Why has Holtec submited a p-over analysis as part of the FSAR, and where has Holtec demonstrated that no credible events could cause a p-over?

Additional Information on Apparent Violations HOLTEC INT El{N A TIO NA L Response to Apparent Violation C if As discussed in the response Item 9 (AV A), Holtec submits that the revised analyses for the CBS style baskets were controlled in a manner commensurate with the original Metamic-HT Friction Stir Welded baskets

\f'The technical evaluations were accurate for the revised physical configuration, and the methodology used is consistent with NRC position as indicated by prior NRC approvals

\f'Holtec evaluated the full scope of safety analyses (thermal, criticality, structural, shielding) from the standard basket for all CBS basket variants

\1' Additionally, the tip over analysis is described throughout both the HI-STORM 100 and HI-STORM FW FSARs as non-mechanistic and it is demonstrated that no credible events could tip over the cask www.holtec.com I Page 33 RESPONSE TO QUESTION 15:

Holtec understands that a pover analysis is part of the licensing basis for both HI-STORM 100 and HI-STORM FW FSARs. This analysis was introduced at the inial licensing of both systems as it is a clear expectaon of NRC sta in the standard review plan for dry storage systems (NUREG-1536 at the me of inial license). The FSARs state in Chapter 2 that the freestanding loaded overpacks of each system is demonstrated by analysis to remain kinemacally stable under all design basis environmental phenomena (tornado, earthquake, etc.) and postulated accident condions. The analyses for each of those events are in Chapter 3 of the FSARs, and each one shows that the cask remains vercally oriented, therefore the pover event is described as non-mechanisc throughout all licensing documentaon. The SER for the original revision of the HI-STORM 100 CoC echoes this philosophy stang, The overpack will not pover as a result of a credible natural phenomenon, including tornado wind and a tornado-generated missile, a seismic event, or a "ood. However, to demonstrate the defense-in-depth features of the design, a non-mechanisc pover scenario per NUREG-1536 was analyzed.

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