ML25273A363
| ML25273A363 | |
| Person / Time | |
|---|---|
| Site: | HI-STORM 100 |
| Issue date: | 09/18/2025 |
| From: | Storage and Transportation Licensing Branch |
| To: | |
| Shared Package | |
| ML25273A361 | List: |
| References | |
| Download: ML25273A363 (1) | |
Text
POTENTIAL PROPRIETARY INFORMATION Proposed Resolution - Holtec HI-STORM UMAX Amendment 5 Impact on Seismic Analysis due to Long-Term Temp Increase Structural Issue The NRC staff is proposing the following to bring this item to resolution:
Request the applicant to update FSAR table 3.4.12A appropriately to flag the reduced safety margin for the amendment 5 version B1/B2 and update proposed table 2.3.7, revision 8B, Off-Normal and Accident Condition Temperature Limits to 350 deg F for the self-hardening engineered subgrade (SES) in space A for the amendment 5 version B1/B2.
o Using a risk-informed approach, the staff took a closer look at the previously approved package, FSAR revision 7. The staff was able to identify a safety basis to resolve the technical concern with some assumptions and the following rationale and a request to the applicant for a minor revision to the FSAR for the amendment 5 version B1/B2 package. Based on the sensitivity study for increased concrete temperature in calculation 7A of HI-2125228, revision 18, and considering 25% reduction in concrete strength at 300 deg F sustained temperature, the staff estimates approximately 19% increase to the table 5 in the maximum impact force on the multi-purpose canister (MPC) guide plate after applying amplification factors for soil parameter uncertainty and gap sensitivity studies. Based on this, the current safety margin in the critical components (MPC and MPC guide) will be reduced for amendment 5 version B1/B2, but the safety factor will still be greater than 1.0. Therefore, the NRC staff finds it acceptable.
Further, note that per table 6.9 of HI-2230586, revision 2, latest thermal analysis, the maximum off-normal and accident condition temperature in space A concrete is [ ]. Since there is no clear basis or justification for the proposed 600 deg F allowable temperature in accident conditions and due to the reduced design margin in critical MPC components, the allowable should be limited to 350 deg F in table 2.3.7 of the FSAR.