ML25231A288
| ML25231A288 | |
| Person / Time | |
|---|---|
| Site: | 07109225 |
| Issue date: | 06/26/2025 |
| From: | Storage and Transportation Licensing Branch |
| To: | |
| References | |
| Download: ML25231A288 (1) | |
Text
10 CFR 71.95 REPORT EVALUATION FORM Docket No.: 71-9225 Package Model No.: NAC-LWT Cask (Certificate of Compliance No. 9225)
Report Submitted By: NAC International Report Date: June 26, 2025 Report ADAMS Accession No.:
ML25178C679 Review the incoming report to determine if additional Commission or staff action is warranted. The review should consider whether the report identifies a generic defect or problem with the package design and the safety significance of the issue.
Note that a high safety significance represents a potential for significant radiation exposure, medium safety significance represents a potential for some moderate radiation exposure, and low safety significance represents little or no potential for radiation exposure.
- 1. The report identifies:
__ Significant reduction in the effectiveness of a package during use;
__ Defect with a safety significance; Shipment in which conditions of the approval were not observed.
- 2. What is the safety significance? ___ High
__ Medium Low
- 3. Summary of the report:
Background
Date of Notification: April 30, 2025 Notification Method: Teleconference with the NRC Issue Identified: An inconsistency within SAR Section 2.6.7.4.7 and its implementation approach.
Inspection
Reference:
NRC Inspection Report 71-0018-2025-201 conducted in January at the NAC Corporate Offices.
Reportable Condition Impact Limiter Lug Hole Size:
During the preparation of changes to the LWT [Legal Weight Truck Cask System] Safety Analysis Report (SAR) related to the impact limiter lug hole size, it was identified that the normal condition impact limiter attachment analysis was improperly used to address broken impact limiter tabs found during transport.
Structural Evaluations:
SAR Section 2.6.7.4.7 contains structural evaluations of the impact limiter attachment lugs, which are critical for ensuring the impact limiters remain attached during normal and accident conditions.
2 10 CFR 71.95 REPORT EVALUATION FORM Docket No.: 71-9225 Package Model No.: NAC-LWT Cask (Certificate of Compliance No. 9225)
Report Submitted By: NAC International Report Date: June 26, 2025 Report ADAMS Accession No.:
ML25178C679 Criteria for Attachment Normal Handling and Transport:
Impact limiters must remain attached to the cask body to perform their impact-limiting function.
Initial Impact:
During a free drop (normal or accident), the limiter making initial contact must remain in position.
Secondary Impact:
The limiter on the opposite end must remain attached during the initial impact to absorb the secondary impact.
Nonconformance and Analysis Nonconformance Reports (NCRs):
Casks arrived with broken impact limiter attachment lugs, indicating fewer than four effective lugs per limiter. These deficiencies were documented but dispositioned as repairs without NRC notification.
Normal Condition Evaluation:
The SAR stated that only two of the four attachment points for each limiter were assumed effective for normal condition evaluation. However, this did not consider the required initial conditions for accident evaluation, which requires all four lugs to remain intact.
Licensing Drawings:
Neither the CoC nor the licensing drawings allowed for fewer impact limiter attachment lugs during shipment.
Requirements and Analysis Impact Limiter Drawings:
Specific drawings for upper and lower impact limiters were referenced.
Design Criteria:
The method of attachment of the impact limiters to the cask body must satisfy three criteria to ensure proper performance during normal and accident conditions.
Stress Calculations:
The SAR conservatively used a maximum acceleration of 30 g for stress calculations, assuming four attachment points.
3 10 CFR 71.95 REPORT EVALUATION FORM Docket No.: 71-9225 Package Model No.: NAC-LWT Cask (Certificate of Compliance No. 9225)
Report Submitted By: NAC International Report Date: June 26, 2025 Report ADAMS Accession No.:
ML25178C679 Impact on Operability No Impact on Operability:
When broken lugs were found, the casks were taken out of service and repaired as required by NACs Quality Assurance program. No shipments were initiated with broken attachment points, and no incidents resulted in material release, injury, or exposure.
Extent of Condition Multiple NCRs:
Over the past 16 years, multiple NCRs identified broken lugs upon receipt at the destination. No shipments arrived with more than two broken lugs per impact limiter.
Safety Consequences and Implications The NAC-LWT impact limiter system has four redundant attachment lugs. No safety consequences were associated with using the NAC-LWT with reduced impact limiter attachment points. No shipments were initiated with broken or cracked impact limiter attachment points, and no events resulted in the release of material, injury to personnel, or exposure.
The CoC holders updated analyses included in the report demonstrate that the impact limiters would function as designed in an accident with only two impact limiter lugs engaged. Repairs were made in accordance with NACs Quality Assurance program, ensuring that the casks were taken out of service and repaired as required.
- 4. Corrective actions taken by the licensee:
Documentation Conditions Documented:
The conditions described in the report have been documented in accordance with NACs Quality Assurance Program.
Records:
Conditions are recorded in FR 25-003 and CAR 25-004.
Updates Licensing Basis Analysis:
Updates to the licensing basis analysis for the impact limiter attachment lug hole size.
4 10 CFR 71.95 REPORT EVALUATION FORM Docket No.: 71-9225 Package Model No.: NAC-LWT Cask (Certificate of Compliance No. 9225)
Report Submitted By: NAC International Report Date: June 26, 2025 Report ADAMS Accession No.:
ML25178C679 SAR Changes:
Changes to the SAR to address the impact limiter attachment analysis.
Enclosures:
Changes to the Certificate of Compliance (CoC) and SAR are detailed in Enclosures 1, 2, 3, and 4 of the notification.
Long-term Modifications Impact Limiter Issue:
NAC is developing a long-term modification to address the impact limiter issue.
Testing:
Testing potential lug replacement options.
Future Application:
An application to make these modifications to the impact limiter design is expected to be submitted within the next 12 months.
- 5. Staff comments:
The NRC staff reviewed the subject report dated June 26, 2025, and noted that despite the noncompliance with the Certificate of Compliance, there were no adverse safety consequences or implications due to the redundant design and proper handling of the casks.
Furthermore, the staff noted that the corrective actions by NAC International ensure the identified issues are addressed both in the short term through documentation and updates, and in the long term through ongoing testing and planned modifications.
- 6. Staff conclusion:
The report does NOT identify generic design or license/certificate issues that warrant additional Commission or staff action. This report is considered closed.
There is a need to take additional action. Provide a summary of the bases and recommended actions:
ML25231A288 OFFICE NMSS/DFM NMSS/DFM NMSS/DFM NAME TLiu SFiguoroa YDiaz-Sanabria DATE 8/20/2025 8/21/2025 9/8/2025