ML23345A096

Safety Evaluation Report for Revision No. 2 of the Certificate of Compliance

ML23345A096
Person / Time
Site:	OPTIMUS-L
Issue date:	12/14/2023
From:	Storage and Transportation Licensing Branch
To:	NAC International
Shared Package
ML23345A093	List: ML23345A094 ML23345A095 ML23345A096
References
EPID L-2022-LLA-0142, CoC No. 9390, Rev 2
Download: ML23345A096 (13)

Text

UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001

SAFETY EVALUATION REPORT Docket No. 71-9390 Model No. OPTIMUS - L Package Certificate of Compliance No. 9390 Revision No. 2

SUMMARY

By letter dated November 2, 2022 (Agencywide Documents Access and Management System Accession No. ML22306A109), NAC International (NAC or the applicant) submitted an amendment request to certificate of compliance (CoC) No. 9390 for the Model No. OPTIMUS-L package to include unirradiated TRI-structural ISOtropic (TRISO) fuel particle compacts (i.e.,

TRISO compact) as authorized contents.

On September 8, 2023, the applicant provided responses to staffs request for additional information (RAI) for the review of the Model No. OPTIMUS-L package, dated July 17, 2023. On September 26, 2023, staff communicated three outstanding issues, stemming from the review of the RAI responses, that needed resolution before CoC issuance and, on November 15, 2023, the applicant submitted a supplement to its RAI responses, including drawing changes associated with the supplemental responses (ML23320A201). The submittal also included a revised application The OPTImal Modular Universal Shipping Cask Safety Analysis Report, Revision No. 1, dated November 2023 which superseded all previous submittals. On December 11, 2023, the applicant submitted page changes to the application (ML23345A211).

The OPTImal Modular Universal Shipping Cask for Low activity contents (OPTIMUS-L) package is transported in a vertical orientation under exclusive use. The packaging consists of a Cask Containment Vessel (CCV), a CCV bottom support plate, and an Outer Packaging (OP) assembly. A Shield Insert Assembly (SIA) may be included inside the CCV for contents that require additional shielding. A GEO basket assembly, positioned inside the CCV cavity, is used to transport TRISO compacts contents; in this configuration, the CCV bottom support plate is not included.

Based on the statements and representations in the application, and the conditions listed in the CoC, the U.S. Nuclear Regulatory Commission (NRC) staff (the staff) concludes that the package meets the requirements of Title 10 of the Code of Federal Regulations (10 CFR) Part 71.

EVALUATION

1.0 GENERAL INFORMATION

The OPTIMUS-L packaging consists of a CCV, a CCV bottom support plate, an OP assembly, and SIAs.

Enclosure 2 The CCV bottom support plate is a free-standing coated carbon steel plate positioned at the bottom end of the CCV cavity below the contents. The CCV fits within the cavity of the OP. The packaging may also be configured with a SIA within the cavity of the CCV. However, the CCV bottom support plate is not used with the 1-inch (in.) SIA.

The CCV is the packaging containment system. It is a stainless-steel cylindrical vessel that includes a body weldment, bolted lid, bolted port cover, and elastomeric O ring seals. The CCV has an outer diameter of 34.5 (in.), which expands to 39.0 in. at the bolt flange and lid, and an overall height of approximately 51.4 in. The internal cavity of the CCV has a 32.5 in. diameter and is 47.0 in. high. The CCV cylindrical shell and bottom plate have the same thickness. The CCV lid is fastened to the CCV body by 1 in. diameter socket head cap screws (e.g., CCV closure bolts).

A GEO basket assembly is used to transport unirradiated TRISO fuel particle compact (i.e.,

TRISO compact) contents. In this configuration, the CCV bottom support plate is not included.

The GEO basket assembly is positioned inside the CCV cavity to support and maintain the geometry of the TRISO compact for criticality control under both normal conditions of transport and hypothetical accident conditions.

The nominal outer dimensions of the OPTIMUS-L packaging, excluding the lifting lugs and tiedown arms, is 49.0 in. by 70.0 in. high and the gross weight of the package, including the maximum CCV contents weight, is approximately 9,200 pounds (lbs..).

The packaging is constructed and assembled in accordance with the following NAC Drawing Nos.:

70000.14-L502, Rev 0P Packaging Assembly - OPTIMUS-L 70000.14-L510, Rev 0P CCV Assembly - OPTIMUS 70000.14-L511, Rev 0P CCV Body Weldment - OPTIMUS 70000.14-L512, Rev 0P CCV Lid - OPTIMUS 70000.14-L513, Rev 0P Port Cover - OPTIMUS 70000.14-L514, Rev 0P CCV Bottom Support Plate - OPTIMUS-L 70000.14-L540, Rev 0P Outer Packaging Assembly - OPTIMUS-L 70000.14-L541, Rev 1P Outer Packaging Base - OPTIMUS-L 70000.14-L542, Rev 1P Outer Packaging Lid - OPTIMUS-L 70000.14-L550, Rev 1P 1in. SIA - OPTIMUS 70000.14-L551, Rev 1P 21/4 in. SIA - OPTIMUS 70000.14-L553, Rev 0P 21/4 in. SIA Annular Spacer Plate - OPTIMUS-L 70000.14-L560, Rev 2P GEO Basket Assembly, OPTIMUS-L 70000.14-L561, Rev 1P GEO Basket Weldment, OPTIMUS-L

Drawings L550 and L551 were revised to be consistent with the response to RAIs for the OPTIMUS-H package (Docket No. 71-9392) currently undergoing review and a note was added to certify that all welding procedures and qualifications are in accordance with the American Society of Mechanical Engineers (ASME) section IX, while stating also the applicable ASME articles for weld examination and acceptance criteria.

The packaging contents now include TRISO fuel, formed from High Assay Low Enriched Uranium into cylindrical compacts through a coating and sintering process. TRISO compacts are solid right circular cylinders with an outside diameter ranging from 20 millimeters (mm) to 25

2 mm and a length (height) ranging from 23.4 mm to 27.4 mm. The TRISO compacts are unirradiated and shipped in the GEO basket assembly.

The maximum total weight of TRISO compacts per package is 581 lbs., and the maximum enrichment is 20 percent (%) U-235.

The maximum concentrations of contaminants are specified below:

Isotope Maximum Content

U-232 2.6 x 10-9 g/gU

U-234 1.00 x 10-2 g/gU

U-235 2.00 x 10-1 g/gU

U-238 Balance of Uranium

Np-237 3.85 x 10-6 g/gU

Pu-238 1.56 x 10-10 g/gU

Pu-239/Pu-240 4.29 x 10-8 g/gU

Fission Products 0.25 mCi/gU

Based on review of the statements and representations in the application, the staff concludes that the package design has been adequately described and evaluated, meeting the requirements of 10 CFR Part 71.

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 (packaging together with contents) and demonstrated that it meets the regulations in 10 CFR Part 71, Packaging and Transportation of Radioactive Material.

The NRC staff previously reviewed the application for the OPTIMUS -L package and issued CoC No. 9390. The staff reviewed and evaluated the proposed changes in the safety analysis report (SAR), Revision 22A, 23A and 23B which include the responses to the RAI. This section of the SER documents the staffs reviews, evaluations, and conclusions with respect to structural integrity of the amended transport package.

2.1 Description of the Amendment Request affecting the Structural Design

The original OPTIMUS-L package is designated as Type B(U)F and classified as a Category I package to transport Type B quantities of normal form transuranic waste and other contents listed in the previously issued certificate of compliance. The OPTIMUS-L package primarily

3 consists of a CCV, a CCV bottom support plate, and an OP assembly. The applicant requested in this amendment to permit transport of unirradiated TRISO fuel particle compact contents. The transport of this contents requires a new basket assembly identified as GEO basket assembly.

The GEO basket assembly is a free-standing structure 32.0 in. in diameter by 46.8 in. in height that is positioned in the CCV cavity to support and maintain the geometry of the TRISO compacts. It consists of an electroless nickel plated carbon steel basket weldment configured to accommodate two-hundred and forty (240) stainless steel fuel tubes with TRISO compact contents. The GEO basket weldment is a hexagonally shaped open top steel structure consisting of 24 triangular-shaped cells, each sized to hold 10 fuel tubes. The CCV bottom support plate and the SIA inside the CCV for additional shielding is not required when using the GEO basket assembly. The basket rests on the CCV base plate.

The applicant provided new licensing drawings 70000.14-L560 and 70000.14-L561 that depict the configuration of the GEO basket assembly and fuel tubes with dimensions, material designation, welding, and other details. In addition, the applicant revised the previously accepted OPTIMUS-L package drawings as follows:

a) revised general arrangement drawing 70000.14-L502 primarily to depict package configuration with the GEO basket assembly inside the CCV cavity for transportation of the unirradiated TRISO compacts;

b) revised CCV assembly drawings 70000.14-510 through 70000.14-513 primarily to provide an additional port in the CCV lid, add optional drain tube assembly and support details, add 1/2 (in.) deep recess in the CCV base plate; and add a note to permit alternate bolt material and torque requirement for the closure of the port covers; and

c) revised weld details on drawings 70000.14-L541 and 70000.14-L542 for the inner shell of the OP lid and the OP base assemblies. Specifically, the changes generalize the full penetration weld specification, removing specific weld bevel geometry requirements, to provide greater flexibility for welding the affected joints.

The overall design of the OPTIMUS-L package CCV and OP assemblies remain unchanged, except miscellaneous changes described above. The staff has reviewed the package structural design description and concludes that the contents of the application satisfy the requirements of 10 CFR 71.31 and 10 CFR 71.33.

2.2 Structural Evaluation of the Amendment Request

For this structural review, the staff focused primarily on any changes to the structural behavior of the package for the transport of the TRISO compacts content using GEO basket assembly and miscellaneous changes to other drawings that could have an impact on the OPTIMUS-L package design. Any changes in the configuration, material, weight, and structural integrity of the new basket assembly to maintain geometry of the payload under Normal Conditions of Transport (NCT) and Hypothetical Accident Condition (HAC) are evaluated.

2.3 Codes and Standards

Original Package

The material standards used for the original package comply with American Society for Testing

4 and Materials (ASTM) and American Society of Mechanical Engineers (ASME) section II, Part D. For simulation analyses, the applicant used LS-DYNA and used ANSYS to perform structural analyses. The applicant designed CCV and associated components in accordance with ASME Boiler and Pressure Vessel Code section III, Division 1, subsection NB, Class I Components.

The applicant designed the lifting attachments of the OPTIMUS-L package in accordance with the requirements of ANSI N14.6.

Amended Package

The applicant has maintained the same Type B(U)F designation and Category 1 classification for the amended package with the addition of TRISO Compacts. As a result, the codes and standards previously used for the original package components remain binding for the amended package. The applicant designed the new GEO basket assembly and fuel tubes in accordance with the applicable requirements of ASME Boiler and Pressure Vessel Code, section III, Division 1, subsection NG, Core Support Structures. The material standards used for the basket assembly and fuel tubes comply with ASTM and ASME section II, Part D.

The proposed codes and standards are acceptable to the staff, as they are properly applied and consistent with the safety classification and function of the package components.

2.4 Package Weight and Center of Gravity

The applicant summarized the nominal weight and center of gravity of the GEO basket assembly, TRISO compact contents, empty package, and loaded package (package gross weight) in table 2.12.5-2 of the SAR, Revision 22A. The nominal weight and center of gravity for the other major package components (CCV and OP) are reported in table 2.1-8 of the SAR. The reference point for the center of gravity is at the bottom of the OP base assembly, as shown in figure 2.1-2 of the SAR.

The staff found that the weight of the GEO basket assembly with its contents is 3270 lbs. which is less than 3500 lbs., the bounding weight (i.e. maximum combined weight of CCV contents, including waste content in a secondary container, CCV bottom support plate and/or optional SIA, and cribbing as required) accepted in the previous structural analyses and evaluations for the OPTIMUS-L package design, as provided in table 2.1.8 of the SAR.

The original OPTIMUS-L package design weight with the heaviest content is 9200 lbs. with a center of gravity located at 35.8 in. from the bottom of the OP base assembly. The amended package weight with the GEO basket assembly and TRISO compacts content is 8970 lbs. with a center of gravity (CG) located at 36.5 in. from the bottom of the OP base assembly. Thus, the amended package gross weight is bounded by the previously accepted package design for the transport of the waste contents, with a minor difference (0.7 in.) in CG location. Since there is no significant change to the configuration and material of the OP and the CCV assemblies, the staff does not expect any adverse impact to the dynamic characteristics of the package under the NCT and HAC free drop scenarios. As a result, the bounding NCT and HAC accelerations and the time histories determined from the previously accepted LS-DYNA impact analysis can be used for the analysis and evaluation of basket assembly and fuel tubes design.

2.5 Positive Closure

The applicant has revised CCV assembly drawings 70000.14-510 and 70000.14-512 to provide an additional port in the CCV lid and added a note on drawing 70000.14-510 to permit alternate

5 SA-320, Grade L7 or L43 alloy steel bolt in lieu of SA-193, Grade B8, Class 1 stainless steel bolt for the closure of the port covers. The staff reviewed the associated drawings and concluded that the additional port/closure detail is identical to the original port/closure detail.

The staff also reviewed mechanical properties of the alternate alloy steel bolt material in table 2.2-4 of the SAR, which significantly exceed those of the stainless-steel bolt material. Thus, there is no impact to the previously accepted package closure analysis described in the SAR section 2.4, and the package satisfies the requirements of 10 CFR 71.43(c) for positive closure.

2.6 Lifting and Tie-Down

The applicant describes lifting and handling of the package in calculation CN-16007-212, OPTIMUS-L Lifting and Tie-Down analysis, Rev. 1, and in SAR section 2.5. For the previously accepted design of the lifting and tie-down device, the OPTIMUS-L package design weight with the heaviest content is 9200 lbs. with a center of gravity located at 35.8 in. from the bottom of the OP base assembly. The package weight with the GEO basket assembly and TRISO compacts content is 8970 pounds with a CG located at 36.5 in. from the bottom of the OP base assembly. Based on this comparison and since the difference in vertical CG location is irrelevant to the lifting device design, the staff concludes that the previously accepted design of the lifting device bounds the package design for transport of the TRISO contents. The staff also concludes that the previously accepted design of the tie-down device bounds the package design for transport of the TRISO contents, because a minor difference (+0.7 in.) in vertical CG location is adequately compensated by the reduction in the package design weight.

2.7 Normal Conditions of Transport and Hypothetical Accident Conditions

2.7.1 GEO Basket Assembly & Fuel Tubes

The acceptance criteria used by the applicant for the GEO basket is to demonstrate that the basket maintain its structural integrity and maintain geometry of the fuel content during NCT and HAC. The applicant evaluated only heat and NCT and HAC free drop tests, as other tests are either remain bounded by the previously accepted design basis package or do not apply to this package with the TRISO compacts.

Heat

The TRISO compact contents are limited to fresh (unirradiated) fuel compacts, which do not produce any significant amount of decay heat. As such, temperatures are bounded by the maximum temperatures for the design basis conditions summarized in section 3.1.3 of the SAR Revision 22A. Also, TRISO compacts are not expected to generate any significant amount of gas and therefore the maximum internal CCV pressures summarized in section 3.1.4 are considered bounding for TRISO compact contents.

The applicant evaluated the differential thermal expansion between the GEO basket and CCV, conservatively assuming an upper-bound temperature of 400 degrees Fahrenheit (°F) and neglecting the thermal expansion of the CCV cavity. The results show that the differential thermal expansion of the basket in the nominal axial and radial directions within the CCV cavity is less than the nominal clearances available, so the basket can expand freely under NCT and HAC heat conditions. Based on the review of the results and conservatism in the analysis, this is acceptable to the staff.

6 Free Drop

The applicant performed detailed stress analyses of the GEO basket assembly using a combination of classical hand calculations and finite element analyses. Finite element analyses are performed using the ANSYS computer program described in SAR section 2.12.2.1.

The applicant used the ANSYS computer program to generate a three-dimensional finite element model of the GEO basket for the free side drop evaluation and determine its response to NCT and HAC in calculation 70000.14-2108, Revision 0. Bounding equivalent-static acceleration design loads are applied for controlling NCT and HAC free drop orientations.

The applicant performed an equivalent static analysis using the ANSYS code with a bounding acceleration determined from the previously accepted LS-DYNA impact analysis calculation CN-16007-214, Revision 1 and the dynamic load factors determined to capture dynamic response with the basket assembly in the analysis calculation 70000.14-2108, Revision 0. Post-processing within ANSYS is performed to determine linearized stresses at several locations within the basket. The results show that the minimum margin of safety available for the basket member under the NCT and HAC side drop is +0.01 and +0.06 respectively. The staff reviewed the calculated stresses in the basket assembly components and found that they are bounded by the allowable stresses per ASME Boiler and Pressure Vessel Code, section III, Division 1, subsection NG, and appendix F.

The applicant also performed the finite element analysis to evaluate the fuel tubes from the worst case radial compressive forces determined from the basket side drop analysis. The calculated stress intensities were compared to appropriate ASME code allowable stresses and the margins of safety were calculated. The resulting minimum margin of safety available for the tube membrane plus bending stress under the NCT and HAC is +0.20 and +0.57 respectively.

Therefore, the fuel tube satisfies the applicable allowable stress design criteria for the NCT and HAC side drop.

The applicant performed the end drop evaluation using classical hand calculations for the basket assembly, except the ANSYS computer program is used for the finite element analysis of the bottom plate. The stresses in the GEO basket weldment and the bottom plate are determined for the controlling end drop case. The results of the end free drop structural evaluation demonstrate that the GEO basket assembly and the bottom plate satisfies the applicable allowable stress design criteria. The staff reviewed the calculated stresses in the basket assembly components and fuel tubes and found that they are bounded by the allowable stresses per ASME Boiler and Pressure Vessel Code, section III, Division 1, subsection NG and appendix F. Also, considering the basket overall configuration, height and sturdiness of its primary elements, the staff does not expect buckling of the basket under the end drop scenario.

The staff reviewed the analytical model, analyses, and results of the analyses to conclude that the GEO basket assembly and fuel tubes designs support the package contents under NCT and HAC.

2.7.2 TRISO Compacts

The applicant demonstrated structural integrity of the TRISO compact contents under HAC free drop loads. This is demonstrated by determining the maximum axial compressive stress in the compact due to the HAC end drop and showing it to be less than the compressive strength of

7 the compact determined through mechanical testing. The maximum compressive stress in the compact when subject to the HAC end drop loads is 3800 psi, which is less than the allowable compressive strength of 7300 psi, as per section 7.4 of calculation 70000.14-2108, Revision 0, and section 2.12.5.5.1 of the SAR, Revision 22A.

For the NCT and HAC side drop, each compact is supported by the fuel tube along the full length. The applicant has calculated reduction of the inside diameter of the tubes from the applied compressive forces under NCT and HAC side drop. The maximum reduction in tube diameter when subject to the NCT and HAC side drop loads is 0.002 in. and 0.003 in.

respectively. Considering the minimum clearance available to the TRISO compact inside the fuel tube cavity, the staff concludes that the tube does not impinge on the TRISO compact contents residing within the fuel tube.

2.2.5.3OPTIMUS-L Package

The applicant revised weld details on drawings for the inner shell of the OP lid and the OP base assemblies. Specifically, the changes generalize the full penetration weld by removing specific weld bevel geometry requirements and allow the use of seal weld as an alternate weld configuration. The applicant stated that unlike the thicker outer shells and their full thickness weld connections including bolted flanges that form the exterior surfaces of the OP, the thin inner shells and their seal welds do not provide any significant structural function but serve as casing steel to facilitate pouring of the polyurethane foam cores of the OP base and lid. The staff concurs with this assessment considering the purpose and location of the OP inner shell connections.

As shown in section 2.2.2 of this SER, The OPTIMUS-L package gross weight with the GEO basket assembly and TRISO compacts is bounded by the previously accepted package design for the transport of the waste contents, with a minor difference (0.7 in.) in CG location. Since there is no significant change to the configuration and material of the OP and the CCV assemblies, the previously accepted evaluations, as provided in sections 2.6 and 2.7 of the SAR, remain bounding for the amended package under NCT and HAC.

2.3 Evaluation Findings

Based on review of the statements and representations in the SAR, the staff concludes that the performance of the OPTIMUS-L package while carrying TRISO compacts is adequately described and evaluated to demonstrate that the package continues to perform its original safety function and meets the structural integrity requirements of 10 CFR Part 71.

3.0 THERMAL EVALUATION

The objective of the amendment request was to verify that the changes related to the thermal performance of the OPTIMUS-L package (designated as Type B(U)F) transporting unirradiated TRISO fuel, in the form of TRISO compacts, were adequately described and evaluated under normal conditions of transport and hypothetical accident conditions to meet regulations, as required by 10 CFR Part 71. Regulations applicable to the thermal review include 10 CFR 71.31, 71.33, 71.35, 71.43, 71.51.

According to SAR sections 3 and 3.1.1, the unirradiated TRISO compact contents have no appreciable decay heat and are transported using the GEO basket assembly described in SAR section 1.2.1.5 within the CCV; the details of the CCV and other packaging components (e.g.,

8 Outer Packaging, Shield Insert Assembly) were analyzed in earlier OPTIMUS-L package certifications.

The SAR section 2.12.5.4.1 indicated that the thermal analysis of the TRISO compact content was represented by previous analyses with a near-zero decay heat load and stated that a package configured with the GEO basket has component temperatures that are bounded by the OPTIMUS-L design basis conditions. According to SAR section 3.5.3, the results of the near-zero decay heat thermal analyses indicated an NCT content temperature of approximately 160°F; likewise, SAR section 2.12.5.2.1 indicated that the NCT temperature range for the GEO basket is -40°F to 200°F. In addition, SAR section 2.12.5.4.1 and section 2.12.5.5 mentioned that structural analyses of the GEO basket assumed an upper bound temperature of 400°F, which is higher than the CCV peak temperature of 361°F of the HAC fire reported in SAR table 3.1-2 and section 2.7.4.1.

Finally, SAR section 2.12.5.4.1 noted that the maximum NCT and HAC internal CCV pressures reported in section 3.1.4 of earlier SAR revisions are bounding for the TRISO compact content; these pressures included a 100 psig maximum normal operating pressure and a 225 psig pressure used for HAC structural evaluations.

Based on review of the statements and representations in the application, the staff concludes that the amendment has not changed the previously reviewed OPTIMUS-L package thermal design; therefore, the package has been adequately described and evaluated and the package design meets the thermal requirements of 10 CFR Part 71.

4.0 CONTAINMENT EVALUATION

The objective of the amendment request was to verify that the changes to the containment performance of the OPTIMUS-L package (designated as Type B(U)F) transporting TRISO fuel were adequately described and evaluated under normal conditions of transport and hypothetical accident conditions to meet regulations, as required by 10 CFR Part 71. Regulations applicable to the containment review include 10 CFR 71.31, 71.33, 71.35, 71.43, and 71.51.

Containment-related changes to the amendment included the addition of unirradiated TRISO fuel as content in the form of TRISO compacts. The November 2023 RAI response supplement indicated that the TRISO fuel may originate from enriched slightly contaminated uranium with trace quantities of radionuclides, as listed in SAR section 1.2.2.3. As noted in SAR section 4.2 and section 4.3, the package is designed and tested to a leak tight containment criterion per ANSI N14.5.

There were no changes to the containment boundary design, which, according to SAR section 1.2.1.12, includes the CCV body weldment, bolted closure lid, bolted port cover, Viton lid O-ring seals, and Viton port cover O-ring seal. The SAR mentioned in section 2.12.5.4.1 and section 4.2.1 that the unirradiated TRISO does not have appreciable decay heat, does not off-gas, and that package temperatures and pressures remain bounded by the TRU waste contents analyzed in earlier amendments.

In addition, SAR section 1.2.2.3 and the November 2023 RAI response supplement indicated that non-metallic components included with the TRISO compact, such as spacers and adhesive-backed seals for material accountability, are not credited for any safety function during transport and must be evaluated for gas generation in accordance with SAR attachment 7.5-3 prior to shipment.

9 SAR sections 2.6 and 2.7 indicated that the integrity of the CCV containment boundary is maintained under NCT and HAC and, according to SAR sections 4.2.3 and 4.3.3, there is no loss or dispersal of radioactive contents. Further discussion of the TRISO compacts integrity after hypothetical accident conditions is provided in the structural chapter of this SER.

Based on review of the statements and representations in the application, the staff concludes that the amendment has not changed the previously reviewed OPTIMUS-L containment design; therefore, the package has been adequately described and evaluated and that the package design meets the containment requirements of 10 CFR Part 71.

6.0 CRITICALITY EVALUATION

The applicant requested to modify the CoC for the Model No. OPTIMUS-L package to include unirradiated TRISO fuel compacts containing uranium with uranium-235 (235U) enrichment up to 20 weight percent (wt.%) as allowable contents. The TRISO contents consist of right circular cylinders of TRISO coated fuel particles in a graphite matrix. The applicant is requesting up to 263 kilograms (kg) of TRISO compacts per package, with a maximum uranium content of 68 kg.

TRISO compacts are to be configured in the OPTIMUS-L cavity inside the steel GEO basket assembly pictured in figure 1.2-3 of the SAR.

The TRISO fuel material consists of coated UOC or UO2 fuel particles in a graphite matrix, with a material composition as described in table 6.9.3-5 of the SAR. The stainless and carbon steel properties of the basket materials are as described in tables 6.9.3-3 and 6.9.3-4 of the SAR, respectively. The applicant modeled the package under NCT and HAC neglecting the outer packaging. This allows closer spacing of adjacent packages in the array, and greater neutron communication between packages, and is therefore conservative. The applicant also only models the HAC package for the single package and array analyses, thereby using the most conservative packaging configuration for both the NCT and HAC analyses. The array analysis considered infinite arrays of packages.

The applicant considered optimum internal moderation by water for both the single package and array analyses, and optimum interstitial moderation and spacing between adjacent packages in the array. The applicant modeled the TRISO compacts at their maximum diameter, with no axial gap between compacts, in order to maximize uranium content. The applicant performed sensitivity studies to determine the most reactive configuration of fuel and basket, including variations in TRISO sphere and coating dimensions, UOC or UO2 fuel materials (including atom ratios of oxygen and carbon in UOC), fuel and graphite matrix densities, compact geometry, basket and tube geometry, and water density inside the basket, outside the basket, and outside the packaging.

The applicant reported the maximum calculated system keff for the single package analysis and package array analysis in table 6.9.1-1 of the SAR. All reported keff values are significantly below the applicants calculated Upper Subcritical Limit (USL), determined as discussed in section 6.8 of the SAR.

The staff reviewed the configurations modeled by the applicant for the single package and array analyses. The staff agrees that the applicant has identified the most reactive credible condition of the single package and arrays of packages, consistent with the condition of the package under NCT and HAC, and the chemical and physical form of the fissile and moderating contents.

10 For all calculations, the applicant used the MCNP6.2 computer code, with the continuous energy ENDF/B-VIII.0 cross section library. The applicant benchmarked their calculations against a series of critical experiments from the International Handbook of Evaluated Criticality Safety Benchmark Experiments and International Handbook of Evaluated Reactor Physics Benchmark Experiments, chosen to be as similar as possible to the OPTIMUS-L package with TRISO fuel contents.

The applicant calculated a USL for TRISO contents in the OPTIMUS-L package, using USL Method 1 from NUREG/CR-6361, Criticality Benchmark Guide for Light-Water-Reactor Fuel in Transportation and Storage Packages, as discussed in section 6.9.8 of the SAR. The applicant performed a trending analysis based on keff versus enrichment and energy of the average lethargy causing fission (EALF). Neither parameter resulted in a significant keff trend, but the EALF USL equation resulted in the lowest USL, which was conservatively chosen by the applicant to compare to system keff. The resulting USL is shown in table 6.9.8-1 of the SAR.

Although the applicants benchmark analysis included a relatively low number of applicable critical experiments, with some uncertainty in their applicability, the resulting system keff values are significantly below the calculated USL. Therefore, the staff agrees that the code and cross section library used by the applicant are appropriate for the analysis, and that the USL determined by the applicant is calculated appropriately given the large margin on system keff.

The staff performed confirmatory calculations using the SCALE 6.3.1 Monte Carlo radiation transport code, with the CSAS6 criticality sequence and the 252-group ENDF/B-VII.1 neutron cross section library. The staffs confirmatory analyses consisted of models of the single package and HAC array, with variation in fuel materials, moderation, and geometry. Using modeling assumptions similar to the applicants, the staffs independent evaluation resulted in keff values that were similar to, or bounded by, the applicants results.

The staff also performed confirmatory benchmarking calculations. The staff used the TSUNAMI sequence of the SCALE 6.3.1 code package, with the ENDF/B-VII.1 252-group cross section library, to independently select experiments with relatively high integral index (ck) values compared to the package with the requested contents. The staff used the USLSTATS code within the SCALE 6.3.1 package to independently determine a USL for the package evaluated with the SCALE 6.3.1 code and 252-group ENDF/B-VII.1 cross section library.

Using a larger set of critical experiments, the staff calculated a USL comparable to the applicants based on a ck trending analysis. Although this analysis was performed using a different version of the SCALE code and different set of critical experiments, this indicates that the USL calculated by the applicant is acceptable.

The staff reviewed the applicants requested changes to the CoC, initial assumptions, model configurations, analyses, and results. The staff finds that the applicant has identified the most reactive configuration of the Model No. OPTIMUS-L package with the requested contents, and that the criticality results are conservative. Therefore, the staff finds with reasonable assurance that the package, with the requested contents, will meet the criticality safety requirements of 10 CFR Part 71.

11 7.0 OPERATING PROCEDURES

The loading restrictions for the new authorized contents include the following:

- TRISO compacts shall be shipped in the GEO basket assembly.

- TRISO compacts shall not protrude above the top end of the GEO basket fuel tubes.

- TRISO compacts shall be shipped dry (i.e., no free liquids).

Non-metallic components such as spacers and/or adhesive-backed seals or labels may be included. However, these components must have an auto-ignition temperature of 300°F or higher and must be evaluated for gas generation in accordance with attachment 7.5-3 of the application prior to shipment.

CONDITIONS

Item No. 3.a has been updated to reflect the new address of NAC International.

Item No. 3.b has been updated to reference the last version of the application.

Condition No. 5(a)(2) has been modified to include the addition of the GEO basket assembly inside the CCV cavity to transport TRISO compact contents and specify that in that configuration, the CCV bottom support plate is not included.

Condition No. 5(a)(3) has been updated with new drawing revisions for the packaging.

Condition No. 5(b)(1)(vi) has been added to include the newly authorized TRISO contents, manufactured from slightly contaminated uranium with trace quantities limits as specified in the Table of the CoC.

Condition No. 5(b)(2)(viii) has been added to specify the maximum total weight and maximum enrichment of TRISO contents.

Condition No. 5(c) has been updated for the CSI of TRISO contents.

Condition No. 8 added that non-metallic components, such as spacers and/or adhesive-backed seals or labels, may be included with TRISO contents with an auto-ignition temperature of 300°F or higher and that they shall be evaluated for gas generation in accordance with attachment 7.5-3 of the application prior to shipment.

Condition No. 11 was rewritten as transport by air is authorized for packages, except those items specifically prohibited for air transport, e.g., fissile material, in lieu of Transport by air is not authorized.

Condition No. 14 allows the use of the previous certificate for approximately one year.

The expiration date of the certificate is not changed.

12 CONCLUSION

Based on the statements and representations in the application, the staff finds that these changes do not affect the ability of the package to meet the requirements of 10 CFR Part 71.

Issued with CoC No. 9390, Revision No. 2.

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