ML24222A860
| ML24222A860 | |
| Person / Time | |
|---|---|
| Site: | Holtec |
| Issue date: | 08/09/2024 |
| From: | Holtec |
| To: | Office of Nuclear Material Safety and Safeguards |
| Shared Package | |
| ML24222A858 | List: |
| References | |
| 5014982 | |
| Download: ML24222A860 (1) | |
Text
Attachment 1 to Holtec Letter 5014982 Amendment Request 1014-19
SUMMARY
OF PROPOSED CHANGES
All changes to the CoC and FSAR are marked in the subsequent attachments. Changes that have occurred as part of prior applications are not marked as changes.
Proposed Change #1 Update the Acceptance Criteria and Method of Evaluation (MOE) for the HI-STORM 100 tipover accident described in the FSAR for equipment combinations involving MPCs with Metamic -HT baskets. This involves applying a new stress-based criteria and completing new evaluations consistent with the new tipover Acceptance Criteria and MOE established in HI-STORM FW Amendment 7. The NRCs acceptance of this can be found in Reference [1] Attachment 1 (NRCs Preliminary Safety Evaluation Report for HI-STORM FW Amendment 7). This also involves some adjustment of the existing deflection criteria.
Reason for Proposed Change #1 This amendment is needed to obtain NRC approval of a new acceptance criteria and methodology for the non-mechanistic tipover analysis. It became clear during a recent review of a HI-STORM FW amendment that there was a disconnect on the understanding of acceptance criteria and requirements for the non-mechanistic tipover analysis. Therefore, this amendment aligns the HI -STORM 100 with the lessons learned from that HI-STORM FW amendment. The adjustment of the existing deflection criteria provides a more reasonable set of acceptance criteria in tandem with the additional new stress-based criteria.
Justification for Proposed Change #1 The proposed change in this LAR is not removing any existing acceptance criteria and is adding additional structural acceptance criteria for the tipover event and an accompanying MOE. The proposed changes are consistent with the new tipover Acceptance Criteria and MOE established in HI-STORM FW Amendment
- 7. The NRCs acceptance of this can be found in Reference [1] Attachment 1 (NRCs Preliminary Safety Evaluation Report for HI-STORM FW Amendment 7). The adjustment of the existing deflection criteria does not require any additional analysis, and all criticality control conclusions can be drawn from the existing analyses.
Safety Significance of Proposed Change #1 The proposed changes are consistent with the new tipover Acceptance Criteria and MOE established in HI-STORM FW Amendment 7. The NRCs acceptance of this can be found in Reference [1] Attachment 1 (NRCs Preliminary Safety Evaluation Report for HI-STORM FW Amendment 7).
Furthermore, the NRC staff has issued a safety determination Reference [2] that indicates the consequences of a basket failure have no safety significance based on the fact that the confinement boundary is maintained. The hypothetical tipover accident is the most significant challenge of the structural performance of the basket. The primary safety function is to prevent a criticality event, and the criticality assessment in Reference [2] determined no safety concerns under a hypothetical tipover including basket failure.
The staff assessment (Reference [2]) concludes that the MPC, which is the confinement boundary, maintains its structural integrity during a tipover event and, the staff concludes that the MPC confinement boundary maintains its structural integrity and no water is able to enter the interior of the MPC during
Page 1 of 3 Attachment 1 to Holtec Letter 5014982 Amendment Request 1014-19
SUMMARY
OF PROPOSED CHANGES accident conditions. The staff also acknowledges that consistent with the FSAR, the cladding is not relied on for any safety conclusions, there is no requirement to demonstrate structural integrity of the cladding.
Retrievability requirements continue to be met, since as stated above, the MPC maintains its integrity.
The staff also considered natural phenomena hazards (NPH) and concluded, the structural failure of the fuel baskets during these NPH accident conditions is unlikely. However, even if a basket failure occurs, the criticality evaluation below demonstrates that the fuel will be maintained subcritical. Therefore, the staff concludes that the NPH accident conditions do not result in significant safety consequences for the HI-STORM 100 storage system with the CBS fuel basket designs, (Reference [2]).
Finally, the structural assessment considered the handling operations for the dry cask storage systems. The system is either handled with single failure proof devices where a drop is considered non-credible or held to a lift height which has been demonstrated acceptable via a drop analysis. The drop analysis shows that there are no significant loads on the basket that would challenge the structural integrity. Therefore, a similar conclusion to that for the non-mechanistic tip-over can be made for dry cask handling accident conditions. The MPC confinement boundary maintains its structural integrity and no water can enter the interior of the MPC. Should the fuel basket fail to maintain its structural integrity during stack-up the fuel will be maintained in a subcritical condition, (Reference [2]).
Since the proposed change #1 in this LAR is not removing any existing acceptance criteria and is adding additional acceptance criteria and an accompanying MOE, the low safety significance established by the NRC in Reference [2] should apply to this proposed change. The confinement boundary is completely unchanged by the introduction of the new tipover methodology, and therefore the change remains within the low safety determination already made by the NRC staff.
Minor Changes:
- Added Table 1.0.4 in FSAR Chapter 1 explicitly listing allowed equipment combinations for reader clarity. This also involved deleting a table that was no longer needed and updating some cross-references in other sections of the FSAR.
- Mirrored clarifications made to the FW FSAR related to the structural evaluation of the tipover event in FW Amendment 7 (corrected usage of terms total versus permanent deflection, clarified active fuel region, etc.).
- Changes to the FSAR and CoC related to fuel weight, solid shim thickness, and pad characteristics to align with the new tipover analysis described in Change 1.
- Update the statements in FSAR Section 3.II.2 related to CG eccentricities in the evaluation of lifting devices (as was done in HI-STORM FW Amendment 7). The previous FSAR commitment does not stem from any requirement in NUREG -0612 or ANSI N14.6. This FSAR requirement is unnecessary since ANSI N14.6 mandates increased design factors of 6 and 10 with respect to material yield and ultimate strength, which adequately compensates for small CG variations.
Page 2 of 3 Attachment 1 to Holtec Letter 5014982 Amendment Request 1014-19
SUMMARY
OF PROPOSED CHANGES
References:
[1] NRC Memorandum, User Need Memo for Rulemaking for the HI-STORM Flood/Wind Multipurpose Canister Storage System, CoC No. 1032, Amendment 7 , dated May 7, 2024, ML23030B791
[2] NRC Memorandum, Safety Determination of a Potential Structural Failure of the Fuel Basket During Accident Conditions for the HI-STORM 100 and HI-STORM Flood/Wind Dry Cask Storage Systems, dated January 31, 2024, ML24018A085
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