ML24309A290
| ML24309A290 | |
| Person / Time | |
|---|---|
| Site: | Holtec |
| Issue date: | 11/04/2024 |
| From: | Holtec |
| To: | Office of Nuclear Material Safety and Safeguards |
| Shared Package | |
| ML24309A286 | List: |
| References | |
| 5014984, EPID L-2024-LLA-0111, CAC 001028 | |
| Download: ML24309A290 (1) | |
Text
Table 1.0.4 (continued)
ALLOWABLE HI-STORM 100 OVERPACK AND MPC COMBINATIONS HOLTEC INTERNATIONAL COPYRIGHTED MATERIAL HI-STORM 100 FSAR Proposed Rev. 25a REPORT HI-2002444 1-39 Overpack HI-TRAC MPC HI-TRAC 125D MPC-24, MPC-24E, MPC-24EF MPC-32, MPC-32F MPC-68, MPC-68F, MPC-68FF, MPC-68M, MPC-68MCBS (Note 3)
HI-TRAC MS (Note 2)
MPC-24, MPC-24E, MPC-24EF MPC-32, MPC-32F MPC-68, MPC-68F, MPC-68FF, MPC-68M, MPC-68MCBS (Note 3)
HI-STORM 100S HI-TRAC 100 MPC-24, MPC-24E, MPC-24EF MPC-32, MPC-32F MPC-68, MPC-68F, MPC-68FF, MPC-68M, MPC-68MCBS (Note 3)
HI-TRAC 100D MPC-24, MPC-24E, MPC-24EF MPC-32, MPC-32F MPC-68, MPC-68F, MPC-68FF, MPC-68M, MPC-68MCBS (Note 3)
HI-TRAC 100G MPC-24, MPC-24E, MPC-24EF MPC-32, MPC-32F MPC-68, MPC-68F, MPC-68FF, MPC-68M, MPC-68MCBS (Note 3)
HI-TRAC 125 MPC-24, MPC-24E, MPC-24EF MPC-32, MPC-32F MPC-68, MPC-68F, MPC-68FF, MPC-68M, MPC-68MCBS (Note 3)
HI-TRAC 125D MPC-24, MPC-24E, MPC-24EF MPC-32, MPC-32F MPC-68, MPC-68F, MPC-68FF, MPC-68M, MPC-68MCBS (Note 3)
HI-TRAC MS (Note 2)
MPC-24, MPC-24E, MPC-24EF MPC-32, MPC-32F MPC-68, MPC-68F, MPC-68FF, MPC-68M, MPC-68MCBS (Note 3)
HI-STORM 100S Version B (Note 5)
HI-TRAC 100 MPC-24, MPC-24E, MPC-24EF MPC-32, MPC-32F MPC-68, MPC-68F, MPC-68FF, MPC-68M, MPC-68MCBS (Note 3)
HI-TRAC 100D MPC-24, MPC-24E, MPC-24EF MPC-32, MPC-32F MPC-68, MPC-68F, MPC-68FF, MPC-68M, MPC-68MCBS (Note 3)
ATTACHMENT 3 TO HOLTEC LETTER 5014984 1 of 12
Table 1.0.4 (continued)
ALLOWABLE HI-STORM 100 OVERPACK AND MPC COMBINATIONS HOLTEC INTERNATIONAL COPYRIGHTED MATERIAL HI-STORM 100 FSAR Proposed Rev. 25a REPORT HI-2002444 1-43 Overpack HI-TRAC MPC MPC-32 MPC-68 HI-TRAC 125D MPC-24, MPC-24E MPC-32 MPC-68 HI-TRAC MS (Note 2)
MPC-24, MPC-24E MPC-32 MPC-68 Notes:
- 1) Information on HI-STORM 100U can be found in Supplement I.
- 2) Information on HI-STORM 100S Version E/E1, MPC-32M, MPC-32 Version 1, and MPC-68 Version 1 can be found in Supplement II.
- 3) Information on MPC-68M can be found in Supplement III.
- 4) Information on HI-STORM 100 UVH can be found in Supplement IV.
1)5)
This includes HI-STORM 100S Version B Type IS.
ATTACHMENT 3 TO HOLTEC LETTER 5014984 2 of 12
HOLTEC INTERNATIONAL COPYRIGHTED MATERIAL HI-STORM 100 FSAR Proposed Rev. 25a REPORT HI-2002444 2.II-4 2.II.0.4.2 Load Combinations and Applicable Codes Factored load combinations for ISFSI pad design are provided in NUREG-1536 [2.1.5]. The factored loads applicable to the pad design consist of dead weight of the cask, thermal gradient loads, impact loads arising from handling and accident events, external missiles, and bounding environmental phenomena (such as earthquakes, wind, tornado, and flood).
The factored load combinations presented in Table 3-1 of NUREG 1536 are reduced in number by eliminating loading types that are not germane or controlling in a HI-STORM ISFSI pad design. The applicable factored load combinations are as follows:
- a.
Definitions D =
Dead load plus effect of long-term settlement; L =Live load; T = Thermal load; E =DBE seismic load; Uc= Reinforced concrete available strength
- 5.
- b.
Load Combinations for the Concrete Pad Normal Events: Uc > 1.4 D + 1.7 L Off-Normal Events: Uc > 1.05 D + 1.275 (L+T)
Accident Events: Uc > D + L + T + E As an interfacing structure, the ISFSI pad and its underlying substrate must possess the structural strength to satisfy the above inequalities. As discussed in the main body of this FSAR, thermal gradient loads are generally small; therefore, the Off-Normal Event does not generally provide a governing load combination.
Table 2.II.0.1 provides a reference set of parameters for the ISFSI pad and its foundation that are used solely as input to the non-mechanistic tip-over analysis for the HI-STORM 100 Versions E and E1. Analyses in Chapter 3 show that this reference pad design does not violate the design criterion applicable to the non-mechanistic tip-over of the HI-STORM 100 storage system. The pad design may be customized to meet the requirements of a particular site without performing a site-specific tip-over analysis, provided that all ISFSI pad strength properties are less than or equal to the values in Table 2.II.0.1. Other ISFSI pad designs may be used provided the designs are reviewed by the Certificate Holder to ensure that impactive and impulsive loads under accident events such as non-mechanistic tip-over are less than the design basis limits when analyzed using the methodologies established in this FSAR.
Applicable sections of industry codes such as ACI 318-05, Building Code Requirements for Structural Concrete; ACI 360R-92, Design of Slabs on Grade; ACI 302.1R, Guide for Concrete Floor and Slab Construction; and ACI 224R-90, Control of Cracking in Concrete Structures may be used in the design, structural evaluation, and construction of the concrete pad. However, load combinations in ACI 318-05 are not applicable to the ISFSI pad structural evaluation and are replaced by the load combinations stated in this subsection.
2.II.0.4.3 Anchored Installation Because the HI-STORM 100 overpack has a thick outer shell welded to a thick Bottom Plate, it is straightforward to weld attachment lugs to the cask that serve to anchor it to ISFSI pad. The safety category for the ISFSI pad used to anchor the cask is raised to ITS-C if the cask is anchored to the pad.
Both the HI-STORM body and the anchor bolts (studs) are required to meet the stress limits of Section III, Subsection NF and Appendix F [2.II.9]. The applicable load combinations and allowable stress limits for the ATTACHMENT 3 TO HOLTEC LETTER 5014984 3 of 12
HOLTEC INTERNATIONAL COPYRIGHTED MATERIAL HI-STORM 100 FSAR Proposed Rev. 25a REPORT HI-2002444 2.II-6 Table 2.II.0.1 Reference Acceptable ISFSI Pad Data Design Parameters for Non-Mechanistic Tip-Over AnalysisHI-STORM 100S Versions E and E1 ItemDesign Parameter Minimum Permitted Parameter Value Concrete Thickness (inch) 3036 Concrete Pad Compressive Strength (at 28 days) (psi) 5,0006,000 Subgrade Effective Modulus of eElasticity (measured prior to ISFSI pad installation) of the subgrade (psi) 28,000 An acceptable method of defining the soil effective modulus of elasticity applicable to the drop and tipover analysis is provided in Table 13 of NUREG/CR-6608 with soil classification in accordance with ASTM-D2487 Standard Classification of Soils for Engineering Purposes (Unified Soil Classification System USCS) and density determination in accordance with ASTM-D1586 Standard Test Method for Penetration Test and Split/Barrel Sampling of Soils.
ATTACHMENT 3 TO HOLTEC LETTER 5014984 4 of 12
HOLTEC INTERNATIONAL COPYRIGHTED MATERIAL HI-STORM 100 FSAR Proposed Rev. 25a REPORT HI-2002444 2.III-1 SUPPLEMENT 2.III PRINCIPAL DESIGN CRITERIA FOR THE MPC-68M 2.III.0 OVERVIEW OF THE PRINCIPAL DESIGN CRITERIA A general description of the MPC-68M is provided in Supplement 1.III. This supplement specifies the loading conditions and associated design criteria applicable to the MPC-68M fuel basket. The loads, loading conditions, and design criteria presented in Chapter 2 are applicable to the HI-STORM 100 System using the MPC-68M unless otherwise specified in this supplement. The drawing package for the MPC-68M fuel basket is provided in Section 1.5. The safety classifications of Metamic-HT basket is ITS-A. The safety classification of shims in MPC-68M and MPC-68MCBS basket shims are ITS-A and NITS-B, respectively.
The design criteria pertaining to the HI-STORM overpack and the HI-TRAC transfer cask are completely unaffected by the incorporation of the MPC-68M. Likewise, the structural demands on the MPC Enclosure Vessel (whose design remains unchanged) are also unaffected. The design criteria in this supplement pertain to the loading conditions that bear upon the fuel baskets function and performance.
2.III.0.1 MPC-68M (Including MPC-68MCBS) Design Criteria
- i.
Structural The fuel basket is designed to meet both stress and deformation a more stringent displacement limits under accident conditions of loading (credible and non-mechanistic)mechanical loadings than those implicit in the stress limits of the ASME code (see Section 2.III.2). The basket shims are designed to remain below the yield limit of the selected aluminum alloy. If used, fuel basket welds are designed and fabricated in accordance with Supplement 9.III and the drawing package in Section 1.5. Fuel basket structural welds are designed to the minimum weld strength specified in the drawing package in Section 1.5. Fuel basket welds are not used for the CBS design variant of the MPC-68M.
Metamic-HT is a Holtec proprietary (non-ASME code) material. The critical characteristics and the attainment of the required critical characteristics through a comprehensive qualification process and production testing are discussed in Supplement 1.III with acceptance criteria established in Supplement 9.III.
All normal and off-normal conditions (including pressures) for the MPC-68M and MPC-68MCBS are the same as those described in Section 2.2. All loads on the HI-STORM 100 overpack and HI-TRAC transfer cask described in Section 2.2 remain applicable when using the MPC-68M and MPC-68MCBS.
The main acceptance criterion for the evaluation of accident conditions on the MPC-68M and MPC-68MCBS fuel baskets areis for the basket structure to maintain the fuel contents in a subcritical configuration. The structural design criteria for the MPC-68M and MPC-68MCBS baskets are the ATTACHMENT 3 TO HOLTEC LETTER 5014984 5 of 12
HOLTEC INTERNATIONAL COPYRIGHTED MATERIAL HI-STORM 100 FSAR Proposed Rev. 25a REPORT HI-2002444 2.III-2 same as those described in Subsection 2.II.2.6 for the MPC-32M and MPC-32MCBSprovided in Table 2.III.4.
The maximum primary membrane plus bending stress in the fuel basket panels, within the active fuel region, must be below 90% of the ultimate strength of Metamic-HT material, on a true stress basis, at the applicable temperature. This primary stress limit, which is adopted from subparagraph F-1341.2 of the ASME Code [2.II.9], is the key determinant of the baskets structural integrity under accident conditions. Notwithstanding the stress criterion, an additional deflection limit is imposed on the Metamic-HT fuel baskets to ensure their structural integrity and criticality safety, which is defined below.
The fuel basket material is subject to the requirements in Supplement 1.III and is designed to a specific (lateral) deformation limit of its walls under accident conditions of loading (credible and non-mechanistic). The basis for the lateral deflection limit,, in the active fuel region,, is provided in [2.III.6.1] as where is defined as the maximum average permanenttotal deflection sustained by the basket panels under the loading event and w is the nominal inside (width) dimension of the storage cell. Stated differently, is the maximum permanent deflection of a Metamic-HT panel averaged over the panel width, which is converted to a dimensionless parameter by dividing the average deflection by the unsupported panel width. The limiting value of is provided in Table 2.III.4, and it is also used conservatively to inform the criticality analysis model for the Metamic-HT fuel baskets, as described in Subsection 6.III.3. The portions of the fuel basket outside of the active fuel region are not subject to the deflection limit since they do not affect the reactivity control function of the Metamic-HT fuel basket. The height and relative position of the active fuel region with respect to the fuel baskets are dependent on the fuel assemblies being stored in the MPC-68M and MPC-68MCBS (see Table 2.1.10). The above deflection-based criterion has been used previously in the HI-STAR 180 Transportation Package [2.III.6.2] to qualify similar Metamic-HT fuel baskets.
ii.
Thermal The design and operation of the HI-STORM 100 System with the MPC-68M must meet the intent of the review guidance contained in ISG-11, Revision 3 [2.0.8] as described in Subsection 2.0.1.
All applicable material design temperature limits in Section 2.2 and 4.3 continue to apply to the MPC-68M. Temperature limits of MPC-68M fuel basket and basket shim materials are specified in Table 4.III.2.
The MPC-68M is designed for both uniform and regionalized fuel loading strategies as described in Subsection 2.0.1. The regions for the MPC-68M are given in Table 2.III.1. Additionally, four quarter-symmetric heat load patterns have been defined for MPC-68M as shown in Figures 2.III.1 through 2.III.4. The same temperature limits apply to these configurations. Alternative ATTACHMENT 3 TO HOLTEC LETTER 5014984 6 of 12
HOLTEC INTERNATIONAL COPYRIGHTED MATERIAL REPORT HI-2002444 Proposed Revision 25a 2.IV-1 CHAPTER 2.IV: PRINCIPAL DESIGN CRITERIA 2.IV.0 Introduction The principal design criteria for the HI-STORM 100 Version UVH canister storage system is unchanged in all respects except for those relating to its function related to limiting exposure of the overpack internal cavity to the external environment.
The Version UVH overpack does not have any open penetrations such as air vents in the classical design to permit ventilation of the ambient air and the Closure Lid is installed with a concentric gasket which inhibits the exchange of gas inside the cask with the ambient air. The Closure Lid is emplaced on the cask body with a set of large body bolts which are installed with a small axial clearance to allow any significant increase in internal gas pressure above the ambient pressure, to be relieved once it overcomes the counteracting lids weight. A simple force equilibrium shows that a pressure rise of 5 psi in the cask cavity is not possible to sustain even under the scenario of maximum density concrete installed in the casks lid. However, the structural evaluations are performed using a higher internal pressure.
The loadings associated with Version UVH must include internal pressure and external pressure which are not present in the ventilated cask. For all other Design Basis Loadings, Version UVH cask body is the same as the standard HI-STORM 100 cask body described in this FSAR. In this chapter, the Design pressures appropriate to Version UVH are defined and the overpack loadings are re-visited to ensure that the safety analyses presented in other chapters are comprehensive.
The ITS category of the Structures, Systems and Components (HI-STORM 100 UVH Overpack, MPCs, HI-TRACs) important-to-safety for the HI-STORM 100 UVH System are provided in the licensing drawings for the respective components as follow:
HI-STORM 100 UVH Overpack: Licensing Drawing in Section 1.IV.5 of the Supplement MPC-32M: Licensing Drawing in Section 1.II.5 of Supplement II of this FSAR MPC-68M: Licensing Drawing in Section 1.5 of Chapter 1 of this FSAR 2.IV.0.1 Principal Design Criteria for the ISFSI Pad Table 2.IV.0.1 provides a reference set of parameters for the ISFSI pad and its foundation that are used solely as input to the non-mechanistic tip-over analysis for the HI-STORM 100 Version UVH.
Analyses in Chapter 3 show that this reference pad design does not violate the design criterion applicable to the non-mechanistic tip-over of the HI-STORM 100 storage system. The pad design may be customized to meet the requirements of a particular site without performing a site-specific tip-over analysis, provided that all ISFSI pad strength properties are less than or equal to the values in Table 2.IV.0.1. Other ISFSI pad designs may be used provided the designs are reviewed by the Certificate Holder to ensure that impactive and impulsive loads under accident events such as non-mechanistic tip-over are less than the design basis limits when analyzed using the methodologies established in this FSAR.The principal design criteria for the ISFSI pad applicable for the Version ATTACHMENT 3 TO HOLTEC LETTER 5014984 7 of 12
HOLTEC INTERNATIONAL COPYRIGHTED MATERIAL REPORT HI-2002444 Proposed Revision 25a 2.IV-2 UVH cask remains unchanged from the main body of the FSAR with the exception of the requirements identified in Table 2.IV.0.1.
ATTACHMENT 3 TO HOLTEC LETTER 5014984 8 of 12
HOLTEC INTERNATIONAL COPYRIGHTED MATERIAL REPORT HI-2002444 Proposed Revision 25a 2.IV-3 Table 2.IV.0.1 Acceptable ISFSI Pad Requirements applicable Design Parameters for the HI-STORM 100 Version UVH system Design ParameterItem Allowable ParameterValue Concrete Thickness (inch) 30 Concrete Pad Compressive Strength1 (psi) 5,000 (maximum)
Subgrade Effective Modulus of Elasticity2 (measured prior to ISFSI pad installation) (psi) 28,000 Notes:
1 1 Compressive strength of concrete shall be determined based on 28-day break results, consistent with the guidance in NUREG-2215.
2 An acceptable method of defining the soil effective modulus of elasticity applicable to the drop and tipover analysis is provided in Table 13 of NUREG/CR-6608 with soil classification in accordance with ASTM-D2487 Standard Classification of Soils for Engineering Purposes (Unified Soil Classification System USCS) and density determination in accordance with ASTM-D1586 Standard Test Method for Penetration Test and Split/Barrel Sampling of Soils.
ATTACHMENT 3 TO HOLTEC LETTER 5014984 9 of 12
HOLTEC INTERNATIONAL COPYRIGHTED MATERIAL REPORT HI-2002444 Proposed Revision 25a 2.IV-15 Table 2.IV.2.1; Evaluation of the Mechanical Loadings for the Version UVH Storage Cask Applicable Loading Case from Table 2.2.14 Load Case Description Subsection in the main report where the loading is explained Safety Consideration and Conclusion 4
Moving Floodwaters Moving Floodwater with loaded HI-STORM on the pad 2.2.3.6 Determine the flood velocity that will not overturn the overpack. Because the weight of the loaded cask is slightly greater than the standard HI-STORM 100 overpack, due to removal of the vent openings, the resistance to overturning will be slightly greater.
Therefore, the admissible flood water velocity based on the standard overpack design is conservative.
4 Design Basis Earthquake (DBE)
Loaded HI-STORMs arrayed on the ISFSI pad subject to ISFSIs DBE 2.2.3.7 This case involves determining the maximum magnitude of the earthquake that meets the acceptance criteria of section 2.2.3.7. Because the outer diameter (OD) and height of the CG of Version UVH cask are essentially identical to the reference cask analyzed in Chapter 3, the discussion in Section 3.4.7 is applicable to Version UVH cask.
4 Strike by a Tornado-borne Missile A large, medium or small tornado missile strikes a loaded HI-STORM on the ISFSI pad or a loaded HI-TRAC 2.2.3.5 This criterion requires that the acceptance criteria of 2.2.3.5 be met. The intermediate and small Design Basis Tornado missiles are evidently satisfied by Version UVH because it is structurally identical to the standard HI-STORM 100 cask, except for the absence of vent penetrations which is a positive structural advantage for Version UVH. A stability analysis is performed for the large design basis missile.
4 Non-Mechanistic Tip-Over A loaded HI-STORM is assumed to tip over and strike the pad.
2.II.2.2 Version UVHs response to the tip-over event is analyzed in Chapter 3.IV to demonstrate that the acceptance criteria of 2.II.2.62 areis satisfied within the active fuel region of the fuel basket (applicable for both the MPC-32M and MPC-68M). The height and relative position of the active fuel region with respect to the fuel basket are dependent on the fuel assemblies being stored in the MPC, as the MPC height can be varied to accommodate different fuel types (see Table 3.IV.2.1).
4 Explosion The HI-STORM is exposed to an 2.2.3.10 Version UVHs response to an explosion event is analyzed in Chapter 3.IV to demonstrate that the overpack is capable of withstanding the resulting ATTACHMENT 3 TO HOLTEC LETTER 5014984 10 of 12
HOLTEC INTERNATIONAL COPYRIGHTED MATERIAL HI-STORM 100 FSAR Proposed Rev. 25a REPORT HI-2002444 6.II-22 6.II.3 MODEL SPECIFICATION 6.II.3.1 Description of Calculational Model Calculational models for the MPC-32M are generally the same as those described in Section 6.3 except for the different basket as noted below.
Figures 6.II.3-1 and 6.II.3-2 show representative cross sections of the criticality models for the MPC-32M basket. Figure 6.II.3-1 shows a single cell of the basket, while Figure 6.II.3-2 shows the entire MPC-32M basket. All calculations are performed with the bounding eccentric fuel positioning, where the fuel is placed closest to the center of the basket in each basket cell.
The basket shims of MPC-32M CBS basket is assumed as the same as that of the MPC-32M basket. This is considered acceptable and conservative since the amount of basket shims of MPC-32M CBS is less than the MPC-32M basket which may result in even higher neutron leakage.
To account for the potentially higher fuel density of higher enriched fuel, a conservative fuel stack density of 97.5% of the theoretical density (i.e. 10.96 g/cm3
- 97.5% = 10.686 g/cm3) is used in all analyses for the MPC-32M.
Variations of parameters, namely fuel density and temperature in the MPC-32M, were analyzed using CASMO5. The results are presented in Table 6.II.3.1 and show that the maximum fuel density and the minimum water temperature (corresponding to a maximum water density) are bounding. These conditions are therefore used in all further calculations.
The basket geometry can vary due to manufacturing tolerances and due to potential deflections of basket walls as the result of accident conditions. The basket tolerances are defined in [6.II.3.1]. The structural acceptance criterion for the basket during accident conditions is that the permanent deflection of the basket panels, defined as the maximum average across the width of any panel in the inner area of the basket (i.e. except for the panels on the periphery), is limited to a fraction of 0.005 (0.5%) of the panel width (see Chapter 23). Note that this criterion only applies to the axial section covering the active region of the fuel. Deformations outside the active region would be inconsequential from a criticality perspective, as those areas of the basket are conservatively omitted from the calculational models. Additionally, there are stress limits defined in Chapter 2. The analyses in Supplement 3.II demonstrate that permanent deformations of the basket walls during accident conditions are far below this limit. In the calculational model for the criticality analysesNevertheless, it is conservatively assumed that 2 adjacent cell walls in each cell are deflected to the maximum extent possible over their entire length and width, i.e. thatby reducing the cell ID is reduced by 0.5% of the cell width for every cell for MPC-32M and MPC-32M CBS cellsbaskets. This is considered sufficiently representative to model the maximum average deflection, since the condition is considered for all cells of the basket, and over the entire basket length, while the analyses in Chapter 3 show that, for the overwhelming majority of fuel basket cell walls, even the peak permanent deflection is less than the specified limit without averagingpermanent deflections as a result of accident conditions are only present in a few areas of the basket. Moreover, the permanent deflections due to a tipover event are mainly localized in the upper portion of the fuel basket, and they diminish significantly towards the bottom of the fuel basket where permanent deflections are mostly absent. This is also sufficient to allow excluding the panels on the basket periphery from the deflection criteria, since the lateral neutron loss in these areas would significantly reduce the impact of the deflections in those panels on reactivity, while large deflections in those panels are in fact prevented anyhow due to the stress limits. Overall, this modeling is therefore a conservative approach to model the basket from a criticality perspective, consistent with the limitations specified in Chapter 2. Further note that all evaluations considering potential deflections from accident conditions are still performed assuming a fully flooded MPC, while under such accident conditions the MPC would be internally dry. The calculated keff results (which do not include the bias, uncertainties, or ATTACHMENT 3 TO HOLTEC LETTER 5014984 11 of 12
HOLTEC INTERNATIONAL COPYRIGHTED MATERIAL HI-STORM 100 FSAR Proposed Rev. 25a REPORT HI-2002444 6.III-16 6.III.3 MODEL SPECIFICATION Calculational models for the MPC-68M are generally the same as those described in Section 6.3 except for the different basket as noted below.
Figures 6.III.3.1 and 6.III.3.2 show representative cross sections of the criticality models for the MPC-68M basket. Figure 6.III.3.1 shows a single cell of the basket, while Figure 6.III.3.2 shows the entire MPC-68M basket. All calculations are performed with eccentric fuel positioning, where the fuel is placed closest to the center of the basket in each basket cell. The wall thickness of the basket shims is modeled as 1 inch, while some of them are only 1/2 inch thick. This is conservative, since the model replaces water with aluminum, which reduces absorption and moderation outside of the basket.
To account for the potentially higher fuel density of higher enriched fuel, a conservative fuel stack density of 97.5% of the theoretical density (i.e. 10.96 g/cm3
- 97.5% = 10.686 g/cm3) is used in all analyses for the MPC-68M.
The basket geometry can vary due to manufacturing tolerances and due to potential deflections of basket walls as the result of accident conditions. The basket tolerances are defined on the drawings in Section 1.5. The structural acceptance criterion for the basket during accident conditions is that the permanent deflection of the basket panels, defined as the maximum average across the width of any panel in the inner area of the basket (i.e. except for the panels on the periphery), is limited to a fraction of 0.005 (0.5%) of the panel width (see Chapter 23). Note that this criterion only applies to the axial section covering the active region of the fuel. Deformations outside the active region would be inconsequential from a criticality perspective, as those areas of the basket are conservatively omitted from the calculational models. Additionally, there are stress limits defined in Chapter 2. The analyses in Supplement 3.III demonstrate that permanent deformations of the basket walls during accident conditions are far below this limit. In the calculational model for the criticality analysesNevertheless, it is conservatively assumed that 2 adjacent cell walls in each cell are deflected to the maximum extent possible over their entire length and width, i.e. thatby reducing the cell ID is reduced by 0.5% of the cell width, or 0.03 for every cell of the MPC-68M and MPC-68MCBS cellsbaskets. This is considered sufficiently representative to model the maximum average deflection, since the condition is considered for all cells of the basket, and over the entire basket length, while the analyses in Chapter 3 show that, for the overwhelming majority of fuel basket cell walls, even the peak permanent deflection is less than the specified limit without averaging. Moreover, the permanent deflections due to a tipover event are mainly localized in the upper portion of the fuel basket, and they diminish significantly towards the bottom of the fuel basket where permanent deflections are mostly absent permanent deflections as a result of accident conditions are only present in a few areas of the basket.
This is also sufficient to allow excluding the panels on the basket periphery from the deflection criteria, since the lateral neutron loss in these areas would significantly reduce the impact of the deflections in those panels on reactivity, while large deflections in those panels are in fact prevented anyhow due to the stress limits. Overall, this modeling is therefore a conservative approach to model the basket from a criticality perspective, consistent with the limitations specified in Chapter 2. Further note that all evaluations considering potential deflections from accident conditions are still performed assuming a fully flooded MPC, while under such accident conditions the MPC would be internally dry. Maximum keff results (including the bias, uncertainties, or calculational statistics), along with the selected dimensions, for a number of dimensional combinations are shown in Table 6.III.3.1 for ATTACHMENT 3 TO HOLTEC LETTER 5014984 12 of 12