ML25209A543
| ML25209A543 | |
| Person / Time | |
|---|---|
| Site: | 07201032 |
| Issue date: | 07/28/2025 |
| From: | Holtec |
| To: | Office of Nuclear Material Safety and Safeguards |
| Shared Package | |
| ML25209A538 | List: |
| References | |
| 5018125 | |
| Download: ML25209A543 (1) | |
Text
HOLTEC INTERNATIONAL COPYRIGHTED MATERIAL REPORT HI-2114830 Proposed Rev. 11D 4-46
[
PROPRIETARY INFORMATION WITHHELD IN ACCORDANCE WITH 10CFR2.390
]
[
PROPRIETARY INFORMATION WITHHELD IN ACCORDANCE WITH 10CFR2.390
] For overpacks installed with temperature monitoring equipment, the difference between the average overpack air outlet temperature and ISFSI ambient temperature shall be computed. This difference shall be compared against the difference between the measured average overpack air outlet temperature and the ISFSI ambient temperature. The measured difference being less than or equal to the computed value provides assurance that the predicted temperatures remain below allowable limits during long-term storage conditions, as described in SR 3.1.2.
[
PROPRIETARY INFORMATION WITHHELD IN ACCORDANCE WITH 10CFR2.390
]
4.4.9 Initial Helium Backfill Pressure Limits for Candidate Heat Load Pattern
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PROPRIETARY INFORMATION WITHHELD IN ACCORDANCE WITH 10CFR2.390 to Holtec Letter 5018125 NON-PROPRIETARY INFORMATION Page 1 of 7
HOLTEC INTERNATIONAL COPYRIGHTED MATERIAL REPORT HI-2114830 Proposed Rev 11D 4.II-8 v)
The air flow in the annulus between the MPCs and overpacks is simulated by the k-turbulence model with the transitional option enabled consistent with the approach in Section 4.4.1.
vi)
Thermal models incorporate all modes of heat transfer (conduction, convection and radiation) in a conservative manner.
vii)
The Discrete Ordinates (DO) model, consistent with Section 4.4.1, is deployed to compute radiation heat transfer.
4.II.4.2 Screening Evaluations 4.II.4.2.1 Limiting MPC Configuration Screening calculations are performed for various heat load patterns identified in Chapter 2.II and MPC designs allowed for storage in Extended configuration. The computed peak fuel cladding temperatures for all allowable MPCs is summarized in Table 4.II.4.1. The most limiting MPC and heat load configuration is adopted for all subsequent evaluations.
4.II.4.2.2 Mesh Sensitivity Studies To achieve grid independent CFD results, a grid sensitivity study is performed on the HI-STORM FW extended thermal model. The grid refinement is performed in the entire domain i.e. for both fluid and solid regions in both axial and radial directions following the guidance in NUREG-2215.
Non-uniform meshes with grid cells clustered near the wall regions are generated to resolve the boundary flow near the walls.
A number of grids are generated to study the effect of mesh refinement on the fuel and component temperatures. All sensitivity analyses were carried out for the case of bounding configuration in Table 4.II.4.1. Table 4.II.4.2 provides a summary of the different sets of grids evaluated and corresponding PCT results. The PCT is essentially the same for all the meshes. Therefore, it can be concluded that Mesh 1 is reasonably converged and is therefore adopted for all licensing basis calculations. To provide further assurance of convergence, the sensitivity results are evaluated in accordance with NUREG-2215 and grid convergence index (GCI), which is a measure of the solution uncertainty, is computed [4.II.1]. The GCI confirms the apparent order of the method is similar to the order of the method.
4.II.4.3 Test Model The rationale for not requiring an experimental test model provided in Section 4.4.3 remains applicable in its entirety.
4.II.4.4 Normal Condition of Storage 4.II.4.4.1 Maximum Temperatures to Holtec Letter 5018125 NON-PROPRIETARY INFORMATION Page 2 of 7
HOLTEC INTERNATIONAL COPYRIGHTED MATERIAL REPORT HI-2114830 Proposed Revision 11D 9.II-4
- 15. Install the HI-STORM FW Redundant Closure Lid.
- 16. Perform the HI-STORM FW surface dose rate measurements in accordance with the Technical Specifications. Measured dose rates must be compared with calculated dose rates that are consistent with the calculated doses that demonstrate compliance with the dose limits of 10CFR72.104(a).
- 17. Secure HI-STORM FW Lower Cask Body to the transporter device as necessary.
- 18. Transfer the HI-STORM FW Lower Cask Body to its designated storage location at the appropriate pitch.
- 20. Position the HI-STORM FW Upper Cask Body at designated MPC transfer location and perform transfer sequence outlined for the HI-STORM FW Lower Cask Body.
- 21. Install the HI-STORM FW Extended Closure Lid.
- 22. Using transporter, transfer the HI-STORM FW Upper Cask Body to storage pad and position it near to the HI-STORM FW Lower Cask Body.
- 23. Remove the Redundant Closure Lid from the HI-STORM FW Lower Cask Body.
- 24. Lift the HI-STORM FW Upper Cask Body and position it on the Lower Cask Body.
- 25. Secure the HI-STORM FW Upper Cask Body on the Lower Cask Body using High Strength Bolts.
- 26. Attach the HI-STORM FW temperature elements (if used) and screens.
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HOLTEC INTERNATIONAL COPYRIGHTED MATERIAL REPORT HI-2114830 Proposed Revision 11D 9.II-9 9.II.4 PROCEDURE FOR UNLOADING THE HI-STORM FW EXTENDED CONFIGURATION FUEL IN THE SPENT FUEL POOL The unloading procedures for the HI-STORM FW Extended Configuration system shall follow the steps as outlined in the main chapter sections 9.4.1, 9.4.3, 9.4.4, and 9.4.5. In addition, specific instructions for removing the HI-STORM Extended Configuration lid and closure bolts are provided below in section 9.4.2.
9.II.4.2 HI-STORM FW Extended Configuration Recovery from Storage
- 1. Unsecure the closure bolts that connect both casks together and the casks to the ISFSI pad.
- 2. Prepare for transferring the HI-STORM FW Upper Cask Body to the designated location for MPC transfer. Ensure the Redundant Closure Lid is staged and easily accessible.
- 3. Once the Upper Cask Body is removed, place the Redundant Closure Lid onto the Lower Cask Body.
- 4. Unsecure the anchor bolts that connects the lower casks to the ISFSI pad.
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HOLTEC INTERNATIONAL COPYRIGHTED MATERIAL REPORT HI-2114830 Proposed Revision 11D 10.II-3 Table 10.II.1.2 HI-STORM FW EXTENDED CONFIGURATION ACCEPTANCE CRITERIA Note:
The acceptance criteria outlined in Table 10.1.2 of Chapter 10 for the HI-STORM FW system is applicable to HI-STORM FW Extended Configuration system, with the addition of maintenance and inspection requirements for the bolts connecting the upper and lower overpacks.
- 1. The HI-STORM bolts connecting the upper and lower overpacks are periodically visually inspected, actuated, and lubricated to ensure proper functionality during disassembly of the upper overpack for recovery of a loaded MPC.
Table 10.II.1.5 REFERENCE ASME CODES FOR CODE WELD INSPECTIONS AND INSPECTION CRITERIA OF HI-STORM FW EXTENDED CONFIGURATION Note:
The ASME codes outlined in Table 10.1.5 of Chapter 10 for the HI-STORM FW system are applicable to HI-STORM FW Extended Configuration system.
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HOLTEC INTERNATIONAL COPYRIGHTED MATERIAL REPORT HI-2114830 Proposed Rev. 11D 12.II-11 iv.
Criticality There is no effect on the criticality control features of the system as a result of this event.
The criticality analysis is unaffected because under the flooding condition water does not enter the MPC cavity and therefore the reactivity would be less than the loading condition in the fuel pool, which is presented in Section 6.1.
- v.
Confinement There is no effect on the confinement function of the MPC as a result of this event. As discussed in the structural evaluation above, all stresses remain within allowable values, assuring Confinement Boundary integrity.
vi.
Radiation Protection Since there is no degradation in shielding or confinement capabilities as discussed above, there is no effect on occupational or public exposures as a result of this event.
Based on this evaluation, it is concluded that the flood accident does not affect the safe operation of the HI-STORM FW Extended System.
12.II.2.2.3 Flood Dose Calculations Since the flood accident produces no leakage of radioactive material and no reduction in shielding effectiveness, there are no adverse radiological consequences.
12.II.2.2.4 Flood Accident Corrective Action As shown in the analysis of the flood accident, the HI-STORM FW Extended System sustains no damage as a result of the flood. At the completion of the flood, exposed surfaces may need debris and adherent foreign matter removal.
Upon detection of the flood accident, the ISFSI operator shall assign personnel to remove the debris with mechanical and manual means as necessary. After uncovering the storage overpack, the storage overpack shall be visually and radiologically inspected for any damage. The loaded MPC shall be removed from the storage overpack with the HI-TRAC VW transfer cask to allow complete inspection of the overpack air inlets and outlets, and annulus. Removal of obstructions to the air flow path shall be performed prior to the re-insertion of the MPC. The sites emergency action plan shall include provisions for the implementation of this corrective action.
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HOLTEC INTERNATIONAL COPYRIGHTED MATERIAL REPORT HI-2114830 Proposed Rev. 11D 12.II-14 include, for example, spraying water into the air outlet opening using pumps or fire-hoses or blowing air into the air outlet opening, to directly cool the MPCs.
12.II.2.4 Burial Under Debris 12.II.2.4.1 Cause of Burial Under Debris Complete burial of the FW Extended System under debris is not a credible accident. During storage at the ISFSI, there are no structures above the casks that may collapse and surround them. The minimum regulatory distance(s) from the ISFSI to the nearest site boundary and the controlled area around the ISFSI concrete pad precludes the proximity of substantial amounts of vegetation.
There is no credible mechanism for the Extended System to become completely buried under debris. However, for conservatism, complete burial under debris is considered. Blockage of the overpack air inlet openings has already been considered in Section 12.II.2.
12.II.2.4.2 Burial Under Debris Analysis Burial of the Extended System does not impose a condition that would have more severe consequences for criticality, confinement, shielding, and structural analyses than that performed for the other accidents analyzed. The effect of the overlaid debris would be to provide additional shielding to reduce radiation doses. The accident external pressure considered in this FSAR (see Table 2.2.1) during the flood bounds any credible pressure loading caused by the burial under debris.
Burial under debris can affect thermal performance because the debris acts as an insulator and heat sink. This will cause the storage system and fuel cladding temperatures to increase. A thermal analysis has been performed to determine the time for the fuel cladding temperatures to reach the accident condition temperature limit during a burial under debris accident.
- i.
Structural The structural evaluation of the MPC enclosure vessel for accident external internal pressure conditions set in Table 2.1.1 bounds the pressure calculated for this event.
Therefore, the resulting stresses from this event are well within the allowable values, as demonstrated in Section 3.4.
ii.
Thermal The fuel cladding and MPC integrity is evaluated in Subsection 4.II.6.2. The evaluation demonstrates that the fuel cladding and confinement function of the MPC are not compromised even if the burial event lasts for a substantial duration.
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