ML23278A228

Enclosure - HI-STORM FW Amd 7 Clarification Discussion (10/04/2023)

ML23278A228
Person / Time
Site:	07201032
Issue date:	10/04/2023
From:	Christian Jacobs Storage and Transportation Licensing Branch
To:	Holtec
Shared Package
ML23278A227	List: ML23278A228 ML23278A229
References
EPID L-2021-LLA-0053, CAC 001028
Download: ML23278A228 (4)

Text

Clarification discussion between Holtec and NRC staff on 10/4/2023 Enclosure The purpose of this call is to discuss Holtecs proposed approach to supplement its responses to the March 23, 2023, Requests for Additional Information (RAIs) relating to the CBS basket designs. The NRC staff proposes the following items for discussion:

1. Is the MPC-37 CBS a component of the HI-STORM FW system? The staff believes that clearly stating the status of MPC-37 CBS (and MPC-89 CBS) would provide clarity for both industry and NRC.

Previously, it was unclear to the staff whether or not the MPC-37 CBS was added to the system via a 72.48 change prior to the amendment and was a component of the system as proposed in the amendment. On June 30, 2023, Holtec submitted Proposed Revision 10I of the SAR, which clarified SAR descriptions of the CBS basket designs. These SAR changes included a more detailed list of the system components in table 1.0.1, which now clearly does not include MPC-37 CBS as a basket design for the system.

The SAR changes also provided updates to section 3.4.4.1.4d clarifying that Holtec is comparing the MPC-37P CBS basket design to the MPC-37 CBS basket design for the tip-over assessment. As stated above, the staffs current understanding is that MPC-37 CBS is not a component of the system. However, the tipover analysis of the MPC-37 CBS in Appendix C of HI-2200503, Analysis of the Non-Mechanistic Tipover Event of the Loaded HI-STORM FW Version E Storage Cask, is included in the SAR by reference and is part of the safety basis of MPC-37P CBS described in section 3.4.4.1.4d. Thus, the staff views the tipover analysis of the MPC-37 CBS as new information submitted as part of this amendment to support the MPC-37P CBS.

The staff would like confirmation that Holtec is requesting that the staff approve the MPC-37P CBS (using the MPC-37 CBS tipover analysis) in Amendment 7, but not the MPC-37 CBS basket design.

Additionally, is Holtec planning to include the MPC-37 CBS tipover analysis among the revised analyses to support the basket design criteria? It was not in the list forwarded by Denise Elisio in an email on October 2, 2023.

Holtec Response: Holtec understands that MPC-37-CBS has been used in some of the previously submitted information to support the MPC-37P. Holtec plans to submit the MPC-37-CBS information (i.e., calc package/stress criteria and deflection measurements) in the RAI response in November 2023.

2. Other than the MPC-37 CBS tipover discussed above, is any other information regarding the MPC-37 CBS basket design part of a requested change in Amendment 7?

Holtec Response: MPC-37-CBS is not in the scope of review for FW A7. However, Holtec will submit information that demonstrates how the MPC-37-CBS meets the stress criteria as mentioned in answer to clarification #1. This information is needed in support of approval of MPC-37P.

Clarification discussion summary between Holtec and NRC staff on 10/4/2023

3. Is any information regarding the MPC-89 CBS basket design part of a requested change in Amendment 7?

The staffs understanding is that Holtec incorporated the MPC-89 CBS basket design into the FSAR using the 10 CFR 72.48 change process, so Holtec is not requesting that the staff review and approve the MPC-89 CBS basket design in Amendment 7.

Holtec Response: MPC-89-CBS is not in the scope of review for FW A7. Holtec is not requesting NRC to review the MPC-89-CBS. However, Holtec will also submit information that demonstrates how the MPC-89-CBS meets the stress criteria that was discussed in clarification #1.

4. Is there any proposed change in Amendment 7 regarding the Method of Evaluation (MOE) for Differential Thermal Expansion (DTE) of the HI-STORM FW system components?

The staff requested information about maintaining a combined radial gap between the basket, shims, and enclosure vessel in the event of DTE in the March 23,2023, RAI 3-14.

The staffs understanding at that time was that Holtec was applying the previously approved MOE for DTE, which consisted of performing an analysis to demonstrate that a combined radial gap between these components was always maintained so that no interference occurred and thus no stress analysis was necessary. The staffs RAI requested this analysis demonstrating that the combined radial gap was maintained for the basket designs added in Amendment 7 (i.e., MPC-44 CBS and MPC-37P CBS).

Holtecs May 8, 2023, response indicated that the MPC-37 CBS and MPC-89 CBS basket designs do not maintain the combined radial gap and have a slight interference at the maximum design basis heat load. Holtec also made changes in Proposed Revision 10I of the SAR discussing the MOE for DTE for the MPC-37 CBS and MPC-89 CBS (e.g., section 3.4.4(a)(i)).

It is not clear to the staff if this information in the RAI response was just for general discussion of DTE, since the MPC-37 CBS and MPC-89 CBS are not being added as proposed changes in Amendment 7, or if Holtecs intent was to seek staff approval of the MOE in Amendment 7. It appears to the staff that this is a different MOE for DTE that applies only to MPC-37 CBS and MPC-89 CBS, which means the DTE methodology would not be formally approved by the staff. The staff requests Holtec to clarify whether Holtec is seeking approval of the MOE for DTE in Amendment 7.

Holtec Response: Holtec plans to provide updated FSAR pages in the November 2023, response, that includes a generic approach that clearly articulates a proposed change (i.e., the MOE for DTE) that can be used for all baskets in the FW system.

Holtec will be requesting NRC to approve this new scope change item (i.e., the generic MOE) in FW A7 to be used for all baskets in the FW system.

5. If Holtec considers the MOE for DTE that allows the combined radial gap to close to be a proposed change in Amendment 7, the staff would like to discuss Holtecs reasoning for classifying the resulting interference stresses as peak stresses following the ASME code.

Clarification discussion summary between Holtec and NRC staff on 10/4/2023 On June 14, 2023, Holtec and the staff held a clarification call and briefly discussed the issue of classifying these thermal interference stresses as peak stresses. Holtec noted that the interference was very small and thus little distortion would occur. The staff noted that, even if the distortions were small in the cases of MPC-37 CBS and MPC-89 CBS, it was not apparent why these stresses, generally, would not be capable of producing distortions, and thus be classified as peak stresses.

On June 30, 2023, Holtec supplemented its May 8, 2023, response to RAI 3-14 to clarify that if stresses did arise due to DTE interference, Holtec will evaluate these stresses per the ASME code. Holtec also included Proposed Revision 10I of the SAR on June 30, 2023, which included changes clarifying that this interference was a peak stress and only to be considered in evaluating fatigue.

The staff is concerned that Holtecs conclusion that the DTE interference would only need to be considered in evaluating fatigue may not apply to all applications for basket design. In the staffs view, the classification of a stress under the ASME code should not be based on a specific stress result but on the mechanism causing the stress. It appears to the staff that significant interference caused by thermal expansion would theoretically be possible in a different basket design and could generate large distortions so should be considered in the design of the MPC. Because of this, the staff does not agree that these interference stresses can be categorically classified as peak stresses under the ASME code. The staff recognizes that the small magnitude of the interference stresses in the case of MPC-89 CBS and MPC-37 CBS could form the basis of an engineering judgement assessment of the effects of the DTE on cask components.

The staff believes that correctness and clarity of the specific aspects of the methodology in the MOE (including its elements) is important to enabling its use in future 10 CFR 72.48 evaluations.

Holtec Response: Holtec understands that NRC staff does not agree that these thermal interference stresses can be generically classified as peak stresses.

However, NRC staff does agree that engineering judgment may be used to classify these stresses for the MPC-37-CBS and MPC-89-CBS as overall being low. By establishing an allowable interference generically, an argument may be possible to use engineering judgment generically. Holtec may consider establishing a limit based on technical analysis.

6. If Holtec is prepared to do so at this time, the staff would like to discuss its proposed approach to revise analyses of the HI-STORM FW baskets to support the basket design criteria. The staff views this an opportunity for Holtec to obtain feedback prior to a significant amount of work being done.

Holtec Response: Holtecs intention is that the proposed MOE (i.e., new scope change) will maintain the current deflection criteria. In addition, the MOE will include an additional primary stress check for all baskets in the FW system. Holtec is

Clarification discussion summary between Holtec and NRC staff on 10/4/2023 requesting that NRC approve the generic MOE based on the revised calc packages for all metamic baskets in the FW system.