ML26050A071

Letter to H. Baldner Re Certificate of Compliance No. 9225, Revision No. 78, for the Model No. NAC Lwt Package

ML26050A071
Person / Time
Site:	07109225
Issue date:	03/13/2026
From:	Yoira Diaz-Sanabria Storage and Transportation Licensing Branch
To:	Baldner H NAC International
References
EPID L-2025-LLA-0108, 20260219-40008
Download: ML26050A071 (0)

Text

UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 Heath Baldner, Director, Licensing, Engineering NAC International, Inc.

Atlanta Corporate Headquarters 2 Sun Court, Suite 220 Peachtree Corners, GA 30092

SUBJECT:

REVISION 78 OF CERTIFICATE OF COMPLIANCE NO. 9225 FOR THE MODEL NO. NAC INTERNATIONAL, INC.-LEGAL WEIGHT TRUCK PACKAGE

Dear Heath Baldner:

By letters dated June 26, 2025, and July 7, 2025 (Agencywide Documents Access and Management System [ADAMS] Accession Nos. ML25178C679 and ML25189A260, respectively) as supplemented on January 23, 2026, and February 9, 2026 (ADAMS Accession Nos. ML26023A079 and ML26040A328, respectively), NAC International applied for an amendment to Certificate of Compliance (CoC) No. 9225 for the Model No. NAC-Legal Weight Truck (LWT) package.

The approval constitutes authority to use the package for shipment of radioactive material and for the package to be shipped in accordance with the provisions of Title 10 of the Code of Federal Regulations (10 CFR) Section 71.17, General License: NRC-Approved Package and 49 CFR 173.471.

In accordance with 10 CFR 2.390, Public inspections, exemptions, requests for withholding, a copy of this letter will be available electronically for public inspection in the U.S. Nuclear Regulatory Commissions (NRC) Public Document Room (PDR) or from the Publicly Available Records component of the NRCs ADAMS. ADAMS is accessible from the NRC website at http://www.nrc.gov/reading-rm/adams.html. The PDR is open by appointment. To make an appointment to visit the PDR, please send an email to PDR.Resource@nrc.gov or call 1-800-397-4209 or 301-415-4737, between 8 a.m. and 4 p.m. eastern time (ET), Monday through Friday, except Federal holidays.

March 13, 2026

H. Baldner 2

If you have any questions regarding this CoC, please contact Nishka Devaser of my staff at 301-415-5196.

Sincerely, Yoira Diaz-Sanabria, Chief Storage and Transportation Licensing Branch Division of Fuel Management Office of Nuclear Material Safety and Safeguards Docket No. 71-9225 EPID No. L-2025-LLA-0108

Enclosures:

1.

CoC No. 9225, Rev. No. 78 2.

Safety Evaluation Report cc w/encls.1 & 2:

L. Falat, DOT c/o R. Vierling J. Shenk, DOE c/o L.F. Gelder Signed by Diaz-Sanabria, Yoira on 03/13/26

H. Baldner 3

SUBJECT:

REVISION 78 OF CERTIFICATE OF COMPLIANCE NO. 9225 FOR THE MODEL NO. NAC INTERNATIONAL, INC.-LEGAL WEIGHT TRUCK PACKAGE DATED: March 13, 2026 DISTRIBUTION:

DFM r/f SHelton, NMSS EEve, RI LMcKown, RII DHills, RIII NGreene, RIV Closes EPID No. L-2025-LLA-0108 ADAMS Accession Nos. PKG: ML26050A065, Main and Encl 2: ML26050A071, Encl 1: ML26050A070, econcurrence: 20260219-40008 UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 SAFETY EVALUATION REPORT Docket No. 71-9225 Model No. NAC-LWT Package Certificate of Compliance No. 9225 Revision No. 78

SUMMARY

By letters dated June 26, 2025, and July 7, 2025 (Agencywide Documents Access and Management System [ADAMS] Accession Nos. ML25178C679 and ML25189A260, respectively) as supplemented on January 23, 2026, and February 9, 2026 (ML26023A079 and ML26040A328, respectively), NAC International Inc. (NAC or the applicant) applied for an amendment to Certificate of Compliance (CoC) No. 9225 for the Model No. NAC-Legal Weight Truck (LWT) package. The U.S. Nuclear Regulatory Commission (NRC) staff reviewed the amendment requests using guidance in NUREG-2216, Standard Review Plan for Transportation Packages for Spent Fuel and Radioactive Material, dated August 2020 (ML20234A651).

Following staff review of the associated safety analysis reports (SAR), the staff finds that the requested changes do not affect the ability of the package to meet the requirements of Title 10 of the Code of Federal Regulations (10 CFR) Part 71, Packaging and Transportation of Radioactive Material.

EVALUATION 1.0 GENERAL INFORMATION 1.1 Packaging Description The NAC-LWT is a Type B(U)F-96 radioactive material transportation packaging design. It is authorized to transport several types of contents, including light-water reactor spent fuel, research reactor spent fuel, and high enriched uranyl nitrate liquid in containers specifically designed for the liquid. The NAC-LWT package may be shipped by truck, boat, or railcar and depending on the content, within an international shipping organization container.

In its application dated June 26, 2025 (ML25178C679), as part of the corrective actions to an adjoined 10 CFR 71.95 report, the applicant updated the SAR analyses to demonstrate that only two impact limiter attachment lugs (per impact limiter) are required to perform impact limiter safety functions described in SAR subsection 2.6.7.4.7 under normal and accident conditions of transport.

In its application dated July 7, 2025 (ML25189A260), the applicant requested to introduce an alternative to the WESF basket assembly, a new UCS basket assembly, used to position WESF capsules within the NAC-LWT transport cask cavity. As stated in the SAR and shown on submitted drawings, the UCS basket assembly is made up of a pressurized-water reactor

2 (PWR) fuel basket and a new UCS basket insert. The UCS basket assembly contains the three UCS assemblies with WESF fuel capsules, or a combination of UCS assemblies with capsules and capsule spacers, UCS spacer assemblies, and a lid spacer. Like the WESF basket assembly, up to 18 WESF capsules can be loaded in the UCS basket assembly. The NAC-LWT transport package and other associated components remain unchanged.

1.2 Drawings The applicant has added the following new drawings:

315-40-198 Rev 0P, LWT Transport Cask, Shipping Configuration, UCS, Zeno 315-40-199 Rev 0P, UCS Basket Assembly, Zeno 315-40-200 Rev 1P, LWT Lid Spacer, UCS, Zeno 315-40-201 Rev 0P, Universal Capsule Sleeve (UCS) Assembly 315-40-202 Rev 1P, UCS and Capsules Spacers Assemblies 2.0 STRUCTURAL EVALUATION The objective of the structural evaluation is to verify that the applicant has adequately evaluated the structural performance of the package and demonstrated that it meets the regulations in 10 CFR Part 71, Packaging and Transportation of Radioactive Material.

The NRC staff reviewed and evaluated the proposed changes primarily in safety analysis report (SAR) section 2.0, revision 25A (ML25189A263), revision 25B (ML25178C680), and revision 26A (ML26023A081) and supporting calculations. This section of the safety evaluation report documents the NRC staffs reviews, evaluations, and conclusions with respect to structural safety aspects of the amended transport package.

2.1 Description of Structural Design Change Change No. 1 - Universal Capsule Sleeve (UCS) Basket Assembly (ML25189A260)

The NAC-LWT is a Type B fissile material transport package, previously licensed to transport Strontium Fluoride (SrF2) fuel material as one of the approved contents. There are two varieties of the SrF2 fuel: Waste Encapsulation and Storage Facility (WESF) capsules and BUP-500 capsules. The transport of WESF capsules was previously approved using WESF basket assembly to position the contents within the NAC-LWT transport cask cavity.

In this amendment, the applicant requested to introduce an alternative to the WESF basket assembly, a new UCS basket assembly, used to position WESF capsules within the NAC-LWT transport cask cavity. As stated in the SAR and shown on submitted drawings, the UCS basket assembly is made up of a PWR fuel basket and a new UCS basket insert. The UCS basket assembly contains the three UCS assemblies with WESF fuel capsules, or a combination of UCS assemblies with capsules and capsule spacers, UCS spacer assemblies, and a lid spacer.

Like the WESF basket assembly, up to 18 WESF capsules can be loaded in the UCS basket assembly. The NAC-LWT transport package and other associated components remain unchanged.

3 Change No. 2 - Impact Limiter Attachment to the Cask Body (ML25178C679)

As part of the corrective actions to the 10 CFR 71.95 report dated June 26, 2025, the applicant updated the SAR analyses to demonstrate that only two impact limiter attachment lugs (per impact limiter) are required to perform impact limiter safety functions described in SAR subsection 2.6.7.4.7 under normal and accident conditions of transport (NCT). These changes also include the analyses for the increased pinhole diameter of the impact limiter attachment lugs to 1.23 inch from 0.53 inch in the updated analyses to account for expected wear from NCT.

2.2 Structural Evaluation under Normal Conditions of Transport and Hypothetical Accident Conditions Change No. 1 - UCS Basket Assembly The applicant analyzed and evaluated the UCS basket assembly components (i.e., PWR fuel basket, UCS basket insert, UCS assemblies, UCS and capsule spacers, LWT lid spacer) under the NCT and Hypothetical Accident Conditions (HAC) in SAR sections 2.6.12.17.3 and 2.7.7.19.3, respectively. Each component design was evaluated for side drop and end drop orientations which represent the two limiting cases.

The evaluations indicated that the UCS basket and components within are supported along their lengths in bearing on the supporting components during the side drop, and all structural loads are ultimately transmitted to the shipping cask structure of the transport package. The results of the end drop evaluations demonstrated that the UCS assembly components (i.e., UCS, UCS and capsule spacers) and LWT lid spacer do not buckle under the loads in the end drop orientation. The NRC staff reviewed the calculated stresses in the UCS assembly components and LWT lid spacer and found that they are bound by the allowable stresses per American Society of Mechanical Engineers, Boiler and Pressure Vessel Code,Section III, Division 1, Sub-section NG and Appendix F, 1995 Edition with 1997 Addenda.

The NRC staff finds that the weight of a UCS basket assembly with its contents and spacers for the WESF contents is less than 4000 pounds, which was the bounding weight (for the PWR fuel basket assembly with its content) accepted in the previous structural analyses and evaluations, as provided in SAR table 2.2.1-1. Since there is no design change to the basket material and configuration, the previously accepted PWR fuel basket evaluations, as provided in SAR sections 2.6.12.3 and 2.7.7.3, remain bounding for WESF capsules transport using a UCS basket within the LWT cask under the NCT and HAC. Thus, the NRC staff concludes that UCS basket assembly components design adequately supports the package contents under the NCT and HAC.

The NAC-LWT package shipping weight with the WESF load and using a UCS basket assembly is less than the package shipment design weight of 52,000 pounds as provided in SAR table 2.2.1-2, and evaluated in SAR sections 2.6 and 2.7 previously. Also, the transport package design has not changed and therefore its structural performance remains bounding for the WESF payload transport using a UCS basket assembly under NCT and HAC. As a result, the NRC staff conclude that the amended package will continue to meet all applicable requirements of 10 CFR 71.55 when evaluated under the conditions identified in 10 CFR 71.71 and 71.73.

Change No. 2 - Impact Limiter Attachment to the Cask Body The applicant analyzed the LWT impact limiter attachment components (impact limiter attachment lug, cask body lug, and Ball-Lok pin) to show that the limiter will remain attached to

4 the cask body under NCT and HAC free drop events to perform its required function. For the impact limiter attachment lug, the applicant also analyzed the increased diameter of the pinhole to 1.23 inch to account for expected wear under NCT.

The SAR subsection 2.6.7.4.7, Impact Limiter Attachment Analysis, provides the results of the stress analyses of the LWT impact limiter attachment components. The methodology (i.e., use of the classical engineering equations with hand calculations) is same as the one used for the previous analyses, which was previously reviewed and accepted by the NRC staff.

The NRC staff reviewed the applicants stress analyses and found that the calculated margin of safety (MS) shown in the SAR subsection 2.6.7.4.7 is positive (greater than zero) indicating that the induced stresses in the impact limiter attachment components are smaller than the allowable stresses under NCT and HAC, where the MS is defined as the factor of safety (FS, a ratio of allowable stress/ induced stress) minus one (MS = FS -1.0). Therefore, the NRC staff finds that the impact limiters remain attached to the cask body to perform its required safety function and only two impact limiter attachment lugs per impact limiter are required. The NRC staff also finds that the increased diameter of the pinhole up to 1.23 inches from 0.53 inches is acceptable.

2.3 Evaluation Findings

Based on the review of the statements and representations in the SAR, the NRC staff concludes that the performance of the NAC-LWT package while carrying WESF contents using UCS basket assembly and changes to the impact limiter lug attachment analyses is adequately described and evaluated to demonstrate that the package continues to perform its original safety function and meets the applicable requirements of 10 CFR Part 71.

F2-1 The NRC staff has reviewed the package structural design description and concludes that the contents of the application satisfy the requirements of 10 CFR 71.31(a)(1) and (a)(2) as well as 10 CFR 71.33(a) and (b).

F2-2 The NRC staff reviewed the structural performance of the packaging under the NCT required by 10 CFR 71.71 and concludes that there will be no substantial reduction in the effectiveness of the packaging that would prevent it from satisfying the requirements of 10 CFR 71.51(a)(1) for a Type B package and 10 CFR 71.55(d)(2) for a fissile material package.

F2-3 The NRC staff reviewed the structural performance of the packaging under the HAC required by 10 CFR 71.73 and concludes that the packaging has adequate structural integrity to satisfy the subcriticality, containment, and shielding requirements of 10 CFR 71.51(a)(2) for a Type B package and 10 CFR 71.55(e) for a fissile material package.

3.0 THERMAL EVALUATION The objective of this amendment review was to verify that the changes related to the thermal performance of the NAC-LWT package (designated as Type B(U)F) transporting WESF capsules (containing solid SrF2 salt, per SAR table 1.2-19), within the UCS configuration were adequately described and evaluated under normal conditions of transport and hypothetical accident conditions to meet regulations, as required by 10 CFR Part 71.

The thermal-related change associated with this amendment was the addition of a newly designed UCS assembly to transport WESF capsules within the Cask Containment Vessel

5 (CCV) containment boundary. It is noted that details of WESF capsules transported in the previously reviewed WESF capsule container assembly were provided in an earlier amendment. Section 3.1 of the application indicated that the WESF capsules within the UCS continue to have a total maximum decay heat of 2.4 kW.

3.1 Description of Package Section 1.1 of the application stated that UCS assemblies are loaded in the UCS basket assembly, which consists of a UCS insert assembly within a PWR basket. Staff notes the PWR basket was previously analyzed in an earlier amendment to hold the WESF capsule container assembly. The UCS basket assembly is loaded with a maximum of three UCS assemblies. A UCS assembly is filled with WESF capsules or capsule spacers that maintain the position of a WESF capsule within the UCS assembly. SAR table 1.1-1 stated that the UCS assembly is a stainless-steel cylindrical container that holds up to six WESF capsules in two elevations with each elevation holding three capsules. Section 1.2.3 noted that there is a maximum of 18 WESF capsules in three UCS assemblies (i.e., up to six capsules per UCS assembly) in the UCS basket assembly with a maximum of 0.8 kW per UCS, with each elevation in the UCS limited to 0.4 kW. Section 3.1 stated that the horizontal NAC-LWT package transporting the WESF/SrF2 capsules is enclosed within an ISO container. This indicates that the ISO container, which acts as a thermal barrier that is offset from the package surface and therefore, would meet 10 CFR 71.43(g), considering that the package is currently certified to transport other radioactive material (e.g., PWR assembly) up to 2.5 kW, according to SAR table 5.1.1-3.

Staff notes that the details of other packaging components (e.g., CCV, PWR fuel assembly, WESF capsule container assembly) were evaluated in previous NAC-LWT package amendments.

3.2 Thermal Analyses under NCT and HAC Thermal calculation document 50088.02-3010 Rev. 0 Thermal Evaluation of UCS with SrF2 Loaded in NAC-LWT Cask and section 3.4.1.22 of the application discussed the thermal analyses for determining package temperatures during NCT and the fire HAC when transporting WESF capsules within the UCS configuration. Staff notes that the conservative assumptions discussed in the thermal calculation document and in sections 3.4.1.22 and 3.5.1.3 of the application would result in calculated component temperatures higher than using more realistic assumptions. The NCT calculation and analysis used the ANSYS (Revision 16.2) finite element thermal code and were similar to the WESF capsule container assembly analyses discussed in previous SAR versions. For example, the three-dimensional 180-degree symmetric model of the horizontal package was composed of ANSYS elements to model conduction, convection, and radiation. According to section 3.4.1.22 of the application and section 6.2 of the thermal calculation document, the NCT model included a volume of air representing the space between the package and an ISO container, which was modeled by applying thermal properties of its carbon steel plates to the ANSYS SHELL131 elements at the air volumes boundary. SAR figure 1.2.3-23 indicated that an air gap was modeled between inner and outer capsules. The package interior was backfilled with helium and, therefore, section 3.4.1.22 noted that the model included five helium gaps between the following adjacent components: outer capsule and UCS insert, UCS insert and UCS shell, UCS shell and PWR basket insert, PWR basket insert and PWR basket, PWR basket and cask inner shell. Staff notes that although SAR section 3.4.1.22 indicated that the basket components in the model are shifted down to simulate the casks horizontal orientation during transport, the response to RAI 3-1 (submitted January 2026) stated that the WESF UCS model has uniform gaps through the cross-section, while the WESF

6 capsule container configuration has more realistic non-uniform gaps in which the basket contents are shifted down in the direction of gravity, reducing the gaps at the bottom.

The NCT and fire HAC thermal analyses were based on the packages 2.4 kW decay heat.

Therefore, section 6.3, figure 6.3-5, and figure 7.1 of the thermal calculation indicated that the 1.2 kW decay heat was modeled by six half-symmetric WESF capsules (therefore, 200 W for each modeled half-capsule) within the UCS basket assembly. Section 6.3 of the thermal calculation and the response to RAI 3-1 (submitted January 2026) noted that the WESF capsules decay heat (the bounding Type 1 WESF capsule, per section 3.4.1.22) was applied as a volumetric heat generation source of approximately 27.47 Btu/hr-in3, such that the total package decay heat for the half-symmetric model was 1.2 kW.

Thermal properties (e.g., thermal conductivity, density, specific heat, emissivity) of package materials (e.g., 304 stainless steel, lead, helium, air, neutron absorber liquid) were provided in section 3.4.1.22 of the application and the thermal calculation document and were similar to those listed in the earlier WESF content amendment, although the RAI 3-1 response (submitted January 2026) noted that the SrF2 thermal conductivity values were lower. Section 6.2 of the calculation document noted that effective properties of the liquid filled neutron shield tank and expansion tank were calculated based on the previously submitted methodology found in section 3.2.3 of the safety analysis report (denoted as reference 4 in the calculation document).

Similarly, section 6.3 of the calculation document noted that the conduction and radiation heat transfer across many of the gaps in the basket and UCS zones were modeled as a modified conductivity using the methodology from the TRIGA-content thermal evaluations in the NAC-LWT SAR.

Section 3.4.1.22 of the application stated that the hot NCT condition assumed 100°F ambient conditions with insolation. The insolation values and convection heat transfer coefficient equations applied as boundary conditions were found in section 3.4.1.22 of the application and section 4 of the thermal calculation document and were the same as those listed in an earlier amendment. The cold NCT condition assumed a -40°C ambient temperature without insolation.

Staff notes that section 3.3 of the application indicated that package components (e.g., O-rings, gamma shield, neutron shield) had a safe operating temperature range that included -40°C.

Staff notes that the above-mentioned ambient conditions are consistent with 10 CFR 71.71.

Temperature results from the NCT thermal analysis were presented in table 3.4-29 of the application, which showed that content and package component temperatures were below the allowable temperatures reported in section 3.4.1.22 of the application. In addition, staff notes that the package component temperatures (e.g., O-rings) were bounded by the component temperatures reported in table 3.4-10 of the application for PWR content reported in earlier amendments.

Section 7.1.23 of the application indicated that the package is backfilled with helium to 1 atmosphere (absolute) during the loading procedures vacuum drying process. Specifically, step 30 of the loading procedure in section 7.1.23 includes a helium purge in order to establish the helium atmosphere prior to vacuum conditions. The RAI 3-3 response (submitted January 2026) noted that the thermal conductivity of helium at the vacuum condition results in gas thermal conductivity that is comparable to values during NCT conditions and thus is higher than a corresponding air thermal conductivity.

Section 3.4.1.22 of the application and the RAI 3-1 response (submitted January 2026) noted that the current amendments UCS model included a number of thermally conservative aspects that increased the models thermal resistance, including modeling uniform gaps and the use of

7 lower SrF2 thermal conductivity values. These model aspects contributed to higher content (i.e.,

salt interface) and aluminum insert/basket NCT temperatures when compared with the previously reviewed SrF2 thermal models that did not incorporate the conservative features, as indicated in SAR table 3.4-29 and the RAI 3-1 response (submitted January 2026). For example, at hot NCT, the WESF UCS salt interface temperature and aluminum basket/insert temperature were 118°F and 53°F higher, respectively, than the previously reviewed WESF container configurations salt interface and aluminum insert temperatures. These temperature differences were relatively large, considering that the WESF UCS design and the earlier WESF container design had the same decay heat (2.4 kW) and similar aluminum basket designs, as noted in the RAI 3-1 response (submitted January 2026). The differences in the two WESF models results also were relatively large considering that a comparison of the salt interface and aluminum insert temperatures between the BUP-500 configuration model and WESF container configuration model showed temperature differences of 30°F and 7°F, respectively. It is noted that similar temperatures occurred even though the BUP-500 design had a smaller decay heat (2.2 kW) than the WESF container configuration decay heat (2.4 kW) and had a different internal support structure (e.g., presence of a strength member).

Although the application described the NCT numerical thermal analysis (i.e., ANSYS) based on the WESF UCS structure, a fire HAC numerical thermal analysis of that model was not performed. Rather, considering the similar thermal HAC temperatures mentioned above between the two previously reviewed BUP-500 configuration and the WESF container configuration, section 3.5.3.20 of the application noted that each HAC temperature of the WESF UCS salt interface and aluminum insert/basket was estimated by adding the WESF UCS NCT component temperature (i.e., the salt interface or aluminum insert using the NCT thermal model with conservative assumptions) to the component temperature difference of the earlier WESF container configurations numerically calculated HAC temperature and NCT temperature. Based on that calculation, table 3.5-7 of the application noted a salt interface temperature and aluminum insert/basket temperature that were 551°F and 58°F, respectively, below their allowable values. Staff notes that the calculation of determining the WESF UCS HAC component temperatures was similar to that found in SAR section 3.5.3.9 of an earlier amendment for determining the thermal HAC temperatures of the weldment and damaged PWR and BWR fuel in a rod holder by using the difference in HAC and NCT temperatures from an earlier analysis (section 3.3.5.3.5 of the application) of the weldment and (undamaged) PWR and BWR high burnup fuel contents in a rod holder design.

Staff notes that, unlike the previously reviewed BUP-500 and WESF container configurations with their respective transient ANSYS thermal HAC models, the applicants methodology for calculating the WESF UCS component HAC temperatures does not consider the important relation of content decay heat and thermal mass during the heat-up and cooldown phases of the fire hypothetical accident condition. Although the results for the current conditions studied (e.g., content basket design, decay heat, thermal mass) have shown component temperature margins of 551°F (salt interface) and 58°F (aluminum insert/basket) within allowable values, relative to the 30°F (salt interface) and 7°F (aluminum insert) temperature differences between the BUF-500 and WESC container configuration designs that underwent numerical HAC fire analyses, it has not been demonstrated that the non-numerical SAR method will guarantee bounding values for future WESF USC design changes and operating conditions.

Finally, the response to RAI 3-2 (submitted January 2026) indicated that the maximum LWT cavity gas pressures during NCT and fire HAC for the UCS configuration were less than their respective 50 psig and 168 psig allowable pressures (i.e., structurally analyzed in section 2.6.1.2.2 and section 2.7.3 during NCT and HAC).

8

3.3 Evaluation Findings

Based on the staffs review of the statements and representations in the application, the staff finds that the addition of SrF2 capsules in the UCS configuration as contents to the NAC-LWT package has been adequately described and evaluated and that the staff has reasonable assurance that the thermal performance of the package design meets the thermal requirements of 10 CFR Part 71. The staff makes the following findings:

F3-1 The staff has reviewed the package description and evaluation and concludes that they satisfy the thermal requirements of 10 CFR Part 71.

F3-2 The staff has reviewed the material properties and component specifications used in the thermal evaluation and concludes that they are sufficient to provide a basis for evaluation of the package against the thermal requirements of 10 CFR Part 71.

F3-3 The staff has reviewed the methods used in the numerical thermal evaluation and concludes that they are described in sufficient detail to permit an independent review of the package thermal design.

F3-4 The staff has reviewed the package as it will be prepared for shipment and concludes that 10 CFR 71.43(g) for packages transported by exclusive-use vehicle would be satisfied.

F3-5 The staff has reviewed the package design, construction, and preparations for shipment and concludes that the package material and component temperatures will not extend beyond the specified allowable limits during NCT consistent with the tests specified in 10 CFR 71.71.

F3-6 The staff has reviewed the package design, construction, and preparations for shipment and concludes that the package material and component temperatures will not exceed the specified allowable short-term limits during HAC consistent with the tests specified in 10 CFR 71.73.

4.0 CONTAINMENT EVALUATION The applicant did not propose any changes that affect the staffs containment evaluation provided previous SERs supporting CoC No. 9225. Therefore, the staff determined that a new evaluation was not required.

5.0 SHIELDING EVALUATION 5.1 Review Objective The purpose of this evaluation is to assess the applicants request to revise CoC No. 9225 for the NAC-LWT cask. Specifically, the revision seeks to expand the definition of the WESF strontium fluoride (SrF) capsules to confirm that their design continues to meet the external radiation requirements outlined in 10 CFR Part 71, Packaging and Transportation of Radioactive Materials.

The applicant has proposed Revision 76 to CoC No. 9225 to include additional design details for the WESF SrF capsules previously authorized for transport. This revision introduces a new basket configuration, along with updated assemblies and axial spacers, which are necessary to

9 properly position the capsules within the NAC-LWT transport cask. These components are detailed in the following engineering drawings: 315-40-198, 315-40-199, 315-40-200, 315 201, and 315-40-202.

5.1.1 Description of the Shielding Design 5.1.1.1 Shielding Design Features Section 5.3.27 of the application analyzes a payload consisting of three Universal Capsule Sleeve (UCS) assemblies, each containing six WESF SrF capsules. This UCS payload features a specialized basket configuration designed to be positioned within the standard PWR basket of the NAC-LWT cask. The evaluation considers the maximum strontium-90 activity of the payload, which is translated into a corresponding gamma energy spectrum for modeling in MCNP, Version 6.2 (MCNP 6.2) computer code. MCNP is a versatile tool used in various applications like radiation protection. Design basis material properties are detailed in table 5.1.1-1 of the application, while source term data used in the dose rates calculations are provided in table 5.1.1-3 of the application.

5.1.1.2 Summary tables of maximum external radiation levels Dose rates under both normal and accident conditions are presented in table 5.3.27-2 of the application. These results are further evaluated against regulatory dose rate limits in table 5.3.27-3 of the application. The analysis confirms that a payload consisting of three UCS assemblies, each containing up to six WESF SrF capsules, complies with the requirements of 10 CFR 71.47 and 10 CFR 71.51 for exclusive use shipments. Dose rate profiles for the maximum exposure scenarios are illustrated in figures 5.3.27-3 and 5.3.27-4 of the application.

5.2 Radioactive Materials and Source Terms Consistent with the methodology outlined in section 5.3.25 of the application, the applicant uses ORIGEN module within SCALE 6.2.4 to simulate the decay of 2 curies of strontium-90 (Sr) over one half-life (28.79 years), resulting in an equivalent gamma source term of 1 curie.

The resulting gamma source spectrum is provided in table 5.3.25-1 of the application. A bounding activity level has been evaluated and is summarized in section 5.3.27. The total activity per capsule of Sr-90 is 59,000 curies. Based on this activity, the gamma source term used in the MCNP tally is 3.6899 x 10¹ photons per second.

5.3 Shielding Model and Model Specifications 5.3.1 Configuration of Source and Shielding The basket and cask are modeled in accordance with the license drawings specified in section 5.1 of this SER. The applicant takes no credit for the shielding effects of the baskets upper and lower fittings or the basket/lid spacers. The cask lid spacer ensures that the UCS assemblies remain below the elevation of the radial lead shield taper in the NAC-LWT cask. Accordingly, UCS assemblies are positioned at the bottom of the LWT cavity for radial and bottom axial MCNP tallies. For top axial tallies, the UCS assemblies are shifted upward by the full length of the lid spacer to represent their maximum axial extent. All elevations in the three-dimensional MCNP combinatorial geometry are referenced from the center bottom of the NAC-LWT cask cavity. Material compositions used in the model are detailed in section 5.3.25 of the application.

An illustration of the WESF capsules is provided in figure 5.3.25-2 of the application, and a

10 three-dimensional NAC-LWT MCNP model is shown in figure 5.3.27-1 of the application.

Capsule dimensions critical to dose rate calculations are listed in table 5.3.25-4 of the application. Lastly, UCS and basket dimensions relevant to the model and dose rate results are listed in table 5.3.27-1 of the application.

The staff reviewed the drawings provided in the application to assess the applicants shielding models. They verified that the dimensions and material properties of the contentsincluding any radioactive sourcesand the packaging components used in the shielding models are consistent with the specifications outlined in the package drawings and the contents descriptions presented in the General Information section of the application.

5.3.2 Material specifications:

The applicant provides a discussion of the material properties used in the dose rate evaluations in section 5.3.27 of the application. Key components of the package include the USC body, constructed from stainless steel 316; heat shunts, made of aluminum; and the basket and insert, which are also fabricated from aluminum.

5.4 Shielding Evaluation The shielding evaluation was conducted using MCNP 6.2, employing a continuous-energy Monte Carlo method. The staff found the use of this method acceptable since MCNP (Monte Carlo N-Particle) is a continuous-energy Monte Carlo radiation transport code that uses detailed geometry of the models and high-quality nuclear data to simulate the behavior of various particles, including neutrons, photons, and electrons, over a broad range of energies. The MCNP shielding model incorporates source terms to estimate dose rate profiles at various distances from the side, top, and bottom of the cask under both normal and accident conditions.

To enhance computational efficiency, the applicant used a Monte Carlo-based weight window generator to accelerate code convergence. The weight window method was developed to increase sampling in important regions and to control particle weights. Upper and lower weight bounds are assigned to each region of phase space. Particles with weights above the bounds are split so that there are more particles and their weights are within the window bounds. The adequacy of the weight window and overall problem convergence was verified through MCNPs ten standard statistical checks. Additionally, radial or axial biasing was applied based on the location of the dose rate being evaluated.

5.4.1 Fluence-rate-to-radiation-level Conversion Factors The applicant uses ANSI/ANS 6.1.1-1977 flux-to-dose rate conversion factors in the MCNP analysis. The ANSI/ANS gamma dose conversion factors are shown in table 5.3.25-5 of the application.

5.5 Evaluation Findings

F5-1 The staff has reviewed the application and finds that it adequately describes the package contents and design features that affect shielding, in compliance with 10 CFR 71.31(a)(1), 71.33(a), and 71.33(b). The application also provides an evaluation of the packages shielding performance consistent with 10 CFR 71.31(a)(2), 71.31(b), 71.35(a),

and 71.41(a). The descriptions of the packaging and contents are sufficient to support a thorough evaluation of shielding performance. The analysis is both appropriate and bounding for the described packaging and contents.

11 F5-2 The staff finds that the application demonstrates the package is designed such that, under the evaluations specified in 10 CFR 71.71 (NCT), and in compliance with 10 CFR 71.43(f) and 10 CFR 71.51(a)(1), external radiation levels do not significantly increase.

F5-3 The application demonstrates that, under NCT as specified in 10 CFR 71.71, external radiation levels remain within the limits established in 10 CFR 71.47(a) for nonexclusive-use shipments and 10 CFR 71.47(b) for exclusive-use shipments, as applicable.

F5-4 Under the hypothetical accident conditions (HAC) specified in 10 CFR 71.73, the application demonstrates that external radiation levels do not exceed the limits defined in 10 CFR 71.51(a)(2).

F5-5 The application identifies the codes and standards used in the shielding design and analyses, in compliance with 10 CFR 71.31(c).

F5-6 The application includes descriptions of operations, acceptance tests, and maintenance programs that ensure the package will be fabricated, operated, and maintained in accordance with the shielding requirements of 10 CFR Part 71.

5.6 Conclusion Based on its review of the information and representations provided in the application, along with independent confirmatory calculations, the staff has reasonable assurance that the proposed package design and contents meet the shielding requirements and radiation level limits specified in 10 CFR Part 71. In reaching this conclusion, the staff considered the applicable regulations, relevant regulatory guides, recognized codes and standards, and accepted engineering practices.

6.0 CRITICALITY EVALUATION

An update to the criticality evaluation was not needed for this amendment request. Sr-90 is not fissile, and no changes were made to the other fissile contents of the package.

7.0 MATERIALS EVALUATION The purpose of the staffs materials evaluation is to assess whether the applicant adequately described and evaluated the materials used in the construction of the NAC-LWT package to ensure that the package meets the requirements of 10 CFR Part 71. The staffs review addressed materials for the new and updated components of the NAC-LWT package for transporting DOE WESF SrF2 capsules. The application includes the following changes to the design, construction, and associated safety analyses of NAC-LWT packaging components.

Modifications to a previously approved design of the internal basket assembly to accommodate new UCS assemblies and associated spacers for transporting WESF SrF2 capsules. These modifications include updates to the structural, thermal, and shielding analyses to ensure adequate structural performance, heat transfer, and radiation shielding performance for the new shipping configuration of SrF2 contents for NCT and HAC.

Changes to the analyzed dimensions of the impact limiter attachment brackets to accommodate potential wear and a new maintenance requirement to visually inspect these attachment brackets for excessive wear.

12 The first set of proposed changes are a modification to a previous approved NAC-LWT package configuration for transporting radioactive SrF2 contents. The NAC-LWT package was approved by the NRC in June 2023 (ML23158A139) for transporting radioactive SrF2 in WESF capsules or in BUP-500 capsules. The proposed modification expands on the scope of WESF capsule configurations that are allowed for transport using the NAC-LWT package through the addition of UCS assemblies for housing the WESF capsules inside the NAC-LWT transport cask. The second proposed change is described in the application as an interim corrective measure to ensure that the impact limiter attachment brackets will function as designed (i.e., ensure that impact limiters remain attached to the NAC-LWT transport cask) for normal and accident conditions of transport considering that wear was observed in these items during post-shipment inspection of NAC-LWT packaging components. Since the second change does not alter the physical design or construction of any packaging components, and it does not affect material properties, the staffs materials evaluation covers only the first set of changes.

7.1 Drawings, Codes, and Standards New or updated components for the NAC-LWT packaging include the new UCS assemblies, a modified basket assembly and LWT lid spacer to accommodate the new UCS assemblies, and new UCS and WESF capsule spacer assemblies. The package application and the licensing drawings show that the modified basket assembly is comprised of the existing NAC-LWT PWR fuel basket and a modified basket insert assembly to interface with the UCS assemblies. The staff noted that these components are constructed from materials that are generally the same as or similar to those approved for the construction of internal components for the previous approved NAC-LWT package for transporting WESF SrF2 capsules. Specifically, the modified basket insert assembly is constructed of austenitic stainless steel and precipitation hardened aluminum alloy. The UCS assemblies are constructed from welded austenitic stainless steel and include an aluminum shell insert. The modified LWT lid spacer and new UCS and WESF capsule spacer assemblies are entirely constructed from welded austenitic stainless steel. The staff confirmed that the licensing drawings include adequate standard material product specifications and alloy grades for all new and updated components. The staff reviewed the material specifications and confirmed that they are suitable for use in the construction of these components since the required properties and performance characteristics of these materials are adequately assured in accordance with the requirements of the applicable material specifications.

The staff also verified that the drawings adequately depict the design of the welded joints and associated nondestructive examination (NDE) methods for the new and updated components using standard symbols that are consistent with American Welding Society standard AWS A2.4:2020, Standard Symbols for Welding, Brazing, and Nondestructive Examination. The staff confirmed that the drawings include a requirement that welding procedures and qualifications shall be in accordance with ASME Boiler and Pressure Vessel Code,Section IX welding qualification standards. The staff also confirmed that the drawings specify suitable weld NDE methods and associated code requirements and acceptance criteria to ensure that the welds are free of unacceptable fabrication defects that could adversely affect their structural integrity.

Based on the above considerations, the staff determined that the applicants licensing drawings and the use of codes and standards for materials, fabrication, and NDE of the new and updated NAC-LWT components are acceptable.

13 7.2 Mechanical and Thermal Properties of Materials The staff reviewed the mechanical properties reported in the application for the new components, including the yield stress and ultimate tensile strength, and confirmed the properties are consist with those specified in the ASME Code,Section II, Part D for the applicable material specifications. The staff also noted that the application reports mechanical properties at elevated temperatures that conservatively bound the highest analyzed temperature for normal conditions of transport. The staff identified that the new and updated component materials are not susceptible to brittle fracture since they are austenitic stainless steel and aluminum that have adequate ductility at the lowest service temperature. Therefore, the staff determined that the mechanical properties of the packaging materials are acceptable for use in the structural evaluation of the package.

The staff reviewed the thermal properties reported in the application for the new components, including the thermal conductivity and specific heat capacity, and confirmed the properties are consistent with those specified in the ASME Code,Section II, Part D for the applicable materials. The staff also confirmed that a loss of strength due to thermal aging is not a concern for the precipitation hardened aluminum alloy used in the new components since the maximum service temperature for normal conditions of transport is less than the threshold temperature at which adverse thermal aging of precipitation hardened aluminum is a concern. Therefore, the staff determined that the thermal properties of the packaging materials are acceptable for use in the thermal evaluation of the package.

7.3 Package Contents and Chemical / Galvanic Reactions The relevant package contents consists of radioactive SrF2 sealed inside stainless steel and nickel alloy capsules that have been stored at the DOE WESF, referred to in the application as WESF capsules. These contents were previously approved for transport in the NAC-LWT package using WESF capsule container assemblies. With respect to potential chemical and galvanic reactions between packaging components and between packaging components and package contents, the staff verified that the new and updated components of the packaging are constructed of the same types of materials (austenitic stainless steels and aluminum) that were previously approved, and they do not introduce any new potential for chemical and galvanic reactions inside the package. Further, the staff confirmed that the alloy grades specified for the new and updated components of the packaging are generally not susceptible to corrosion, including galvanic effects, in the dry helium environment in the package cavity. Therefore, the staff determined that the application adequately demonstrates that there are no significant chemical or galvanic reactions that could result in significant corrosion of the structural components inside the package.

7.4 Radiation Shielding and Criticality The application does not specify any changes to dedicated radiation shielding materials and compounds, including the lead gamma shield and the liquid neutron shield, which is credited in the gamma shielding analyses1. The staff confirmed that there are no changes to the service environment that could adversely affect the performance of these radiation shielding materials.

The staff also confirmed that the updated radiation shielding analyses incorporate valid material properties, including density and material composition, for all new structural components credited for radiation shielding. Since the WESF SrF2 capsules are non-fissile radioactive 1 The application notes that there is no neutron source associated with the SrF2 contents; however, since the liquid neutron shield tank is to be kept filled, its gamma shielding properties are credited in the shielding analyses.

14 byproduct material, there is no potential for criticality, and accordingly, the existing criticality safety analyses (which are performed for separate fissile categories of authorized contents) are not affected by the proposed changes. Therefore, the staff determined that the application is acceptable with respect to component materials that are used for radiation shielding.

7.5 Evaluation Findings

F7.1 The staff has reviewed the package and concludes that the applicant has met the requirements of 10 CFR 71.33. The applicant described the materials used in the transportation package in sufficient detail to support the staffs evaluation.

F7.2 The staff has reviewed the package and concludes that the applicant has met the requirements of 10 CFR 71.31(c). The applicant identified the applicable codes and standards for the design, fabrication, testing, and maintenance of the package and, in the absence of codes and standards, has adequately described controls for material qualification and fabrication.

F7.3 The staff has reviewed the package and concludes that the applicant has met the requirements of 10 CFR 71.43(f) and 10 CFR 71.51(a). The applicant demonstrated effective materials performance of packaging components under normal conditions of transport and HAC.

F7.4 The staff has reviewed the package and concludes that the applicant has met the requirements of 10 CFR 71.43(d), 10 CFR 71.85(a), and 10 CFR 71.87(b). The applicant has demonstrated that there will be no significant corrosion, chemical reactions, or radiation effects that could impair the effectiveness of the packaging. In addition, the package will be inspected before each shipment to verify its condition.

F7.5 The staff has reviewed the package and concludes that the applicant has met the requirements of 10 CFR 71.43(f) for Type B packages. The applicant has demonstrated that the package will be designed and constructed such that there will be no loss or dispersal of radioactive contents, no significant increase in external surface radiation levels, and no substantial reduction in the effectiveness of the packaging under the tests for normal conditions of transport.

Based on review of the statements and representations in the application, the NRC staff concludes that the materials used in the transportation package design have been adequately described and evaluated and that the package meets the requirements of 10 CFR Part 71.

8.0 PACKAGE OPERATIONS EVALUATION The purpose of the package operations evaluation is to verify that the proposed changes to the operating controls and procedures of the transport package continue to meet the requirements of 10 CFR Part 71. The objective of the staffs review of the package operations is to verify that the NAC-LWT cask package operational controls and procedures present acceptable operating sequences, guidance, and generic procedures to ensure that the package is operated in a safe and reliable manner under NCT and HAC pursuant to the provisions of 10 CFR Part 71. The operations covered in SAR chapter 7 Revision 25A include the preparation for dry loading a packaging, the loading of the contents, and the preparation for shipment of a package.

The SAR chapter 7 provides procedures for package loading, unloading, and preparation of the empty package for transport. SAR revised section 7.1.20 operating procedures to include

15 Capsules Container Assembly into the NAC-LWT cask, but no major changes. The applicant added new section 7.1.23 that describes the procedure for the dry loading of WESF capsules in the in Universal Capsule Sleeve (UCS) Assembly into the NAC-LWT Cask package. The basket UCS consists of UCSs loaded in the UCS basket assembly, which consists of a PWR basket assembly and UCS insert assembly. The UCS basket assembly is loaded with a maximum of three UCSs or one or more UCSs with up to two UCS spacer assemblies. Within each UCS, up to six capsule spacers may be used. Capsule spacers shall be placed in empty UCS locations above or below a WESF capsule, as needed to maximum position of the WESF capsule. The UCS LWT lid spacer may be used when the uppermost layer of the uppermost UCS is loaded with WESF capsules.

In SAR section 7.1.23, the applicant describes the dry loading-related preparations, package loading sequences, and inspections of the package for transportation of the NAC-LWT with WESF capsules in a UCS, such as those performed to ensure the package is not damaged and that radiation and surface contamination levels are within allowable regulatory limits. The applicant states that the maximum decay heat load of the WESF capsule is per shipment or a maximum combined heat load 2400 Watts. Prior to loading and release for transport, the user shall verify the identified NAC-LWT cask and associated lift yokes are withing the allowable annual maintenance period specified in the package content meets the CoC.

8.1 Evaluation Findings

The staff reviewed the Operating Procedures for Dry Loading of WESF Capsules in the UCS into the NAC-LWT Cask described in SAR chapter 7 to verify that the package will be operated in a manner that is consistent with its design evaluation. Based on its evaluation, the staff concludes that the combination of the engineered safety features and the operating procedures provide adequate measures and reasonable assurance for safe operation of the proposed dry loading of WESF capsules in the UCS into the NAC-LWT cask package in accordance with 10 CFR Part 71.

Further, the CoC is conditioned that the package must be prepared for shipment and operated in accordance with the Operating Procedures specified in SAR chapter 7.

F8-1 The NRC staff has reviewed the description of the operating procedures and finds that the package will be prepared, loaded, transported, received, and unloaded in a manner consistent with its design and evaluation for approval.

CONDITIONS The following changes have been made to the certificate:

Condition No. 5(a)(3), Drawings, was updated to incorporate the new drawings associated with the addition of the UCS assemblies.

Condition No. 5(b)(2)(xxiv) was updated to incorporate the details of the UCS assemblies.

Condition No. 19 was added to reduce the number of required impact limiter lugs required during transport.

Condition Nos. 20 - 23 were renumbered after adding Condition No. 19.

16 Condition No. 21 was updated to include authorizing the use of revisions 76 and 77 of the certificate for one year.

The references section has been updated to include the current applications as supplements.

CONCLUSION Based on the statements and representations in the applications, as supplemented, and the conditions listed above, the staff concludes that the Model No. NAC-LWT package design has been adequately described and evaluated, and that these changes do not affect the ability of the package to meet the requirements of 10 CFR Part 71.

Issued with CoC No. 9225, Revision No. 78.