ML22062A501

SER for Revalidation for the Model No. BU-D Package

ML22062A501
Person / Time
Site:	07103037
Issue date:	03/16/2022
From:	Storage and Transportation Licensing Branch
To:	US Dept of Transportation, Radioactive Materials Branch
Bernie White NMSS/DFM/STL 301-415-6577
Shared Package
ML22062A499	List: ML22062A500 ML22062A501
References
EPID L-2021-DOT-0008
Download: ML22062A501 (5)

Text

SAFETY EVALUATION REPORT Docket No. 71-3037 Model No. BU-D German Certificate of Package Approval No. D/4305/AF-96 Revision No. 10

SUMMARY

By letter December 1, 2021 (Agencywide Documents Access and Management System

[ADAMS] Accession No. ML21336A513), the U.S. Department of Transportation (DOT) requested the U.S. Nuclear Regulatory Commission (NRC) assistance in evaluating the Model No. BU-D package authorized by the German Certificate of Package Approval No.

D/4305/AF-96, Revision No. 10 and make a recommendation concerning the revalidation of the package for import and export use. The NRC reviewed the safety analysis report against the requirements in International Atomic Energy Agency (IAEA) Specific Safety Requirements, No. SSR-6, Regulations for the Safe Transport of Radioactive Material, (SSR-6), 2012 Edition.

In support of this request, the DOT provided the following documents for review with its letter dated December 1, 2021:

1. Orano Report No. 0007-BBR-2021-001, Container BU-D: Validation of Criticality Calculations and Results for Reduced Fissile Contents,

2. German Certificate of Package Approval No. D/4305/AF 96, Revision No. 10, and

3. Safety Report for the Container Type BU-D for the Transport of Uranium Compounds, dated May 2018.

The German certificate of package approval limits the weight of the contents to 90 kg, which NRC previously evaluated in 2001. Since the packaging has not changed, the only area of review affected by this request is criticality safety.

The NRC previously reviewed and recommended revalidation of German Certificate of Package Approval No. D/4305/AF 96, for this package on February 15, 2001 (ADAMS Accession No. ML010590503). Based upon our review, the statements and representations contained in the application, and for the reasons stated below, we recommend revalidation of German Certificate of Package Approval No. D/4305/AF 96, Revision No. 10 for the Model No. BU-D transport package.

1.0 GENERAL INFORMATION The BU-D is Type A fissile package consisting of an inner and outer steel drum with the volume between them filled with insulation for shipment of uranium compounds enriched up to a maximum of 10 weight percent (wt. percent) uranium-235 (235U).

Enclosure

1.1 Package Description 1.1.1 Packaging The outer drum is 213 liter volume which is 1.2 mm thick. The drum is closed by a clamping ring over a M12 screw and nut. The lid is sealed with an O-ring made of cellular rubber. The inner drum volume is 65 liters which is 1.2 mm thick, with a flange welded to the top. The inner drum is closed by a 5-mm-thick carbon steel lid. The lid is screwed to the drum body flange with twelve M10 screws und nuts. The gasket on the inner drum is ethylene propylene diene monomer. The volume between the inner and outer steel drums is filled with perlite concrete.

Containment is provided by the inner container with the lid and closure screws. The maximum weight of the packaging and contents is 260 kg.

Within the inner container, the contents are loaded into (up to 3) stackable pails made of stainless steel. A "distance frame" is positioned between the pails and the inner container to provide stability during transport. The pails have an inner diameter equal to or less than 285 mm.

1.1.2 Drawings The package is constructed in accordance with the drawings provided in Annex 3, Drawings of Container BU-D and Samples of Fuel Pails, to the May 2018 safety analysis report.

1.2 Contents The applicant requested increase enrichment from a maximum of 5 weight percent 235U to 10 weight percent 235U for uranium oxide powder only. No other changes were requested to the contents.

1.3 Criticality Safety Index The criticality safety index is 0.71.

6.0 CRITICALITY EVALUATION

The applicant provided a criticality safety analysis for the Model No. BU-D package with uranium oxide powder contents enriched up to 10.0 weight percent 235U, with a maximum of 650 grams of 235U per package. Staff previously revalidated this package for up to 800 grams of 235U in uranium compounds enriched up to 5.0 weight percent 235U. No package components have changed from the previous revalidation except the maximum 235U mass and maximum uranium enrichment.

The applicant performed criticality calculations for package arrays under normal and accident conditions of transport. The accident conditions array bounds the single package under normal and accident conditions of transport, as demonstrated in criticality analyses for the previous revalidation at lower enrichment. The staff finds that the single package system keff under all conditions will be less than that for the accident conditions array, given the small amount of per package fissile mass and the large number of packages shown to be subcritical in the array, and does not need to be explicitly evaluated. The applicant performed a criticality analysis of an array of packages under normal conditions of transport, without water in-leakage, demonstrating that the normal conditions array keff is much less than the limiting accident conditions array keff.

For the accident conditions array model, the applicant assumed that water could moderate the package contents to the most reactive extent. The applicant also assumed that the thermal test causes a total loss of water from the perlite concrete of the package. This is conservative, as it allows for greater neutron transport between packages, which increases system keff. The applicant assumed that the contents were uranium dioxide (UO2), as this form results in the highest system reactivity compared to other uranium oxides. The applicant assumed that the UO2 powder contents moderated with water formed a homogeneous mixture of water and UO2.

Although heterogeneous configurations of UO2 and water can be more reactive at low enrichment under certain conditions, the staff finds that a homogeneous arrangement is more conservative in this case, given the powder form of the contents and the fact that heterogenous effects are generally greater at lower enrichments than the 10.0 weight percent contents requested in this revalidation. The applicant also provides an analysis of a heterogeneous configuration based on the most reactive homogeneous configuration identified, showing that keff for the heterogeneous system is lower.

The normal and accident conditions array configurations considered by the applicant are shown in Figure 2 of the application. The applicant evaluated an array of 5N packages under normal conditions of transport, and 2N packages under accident conditions of transport, according to the requirements of SSR-6 paragraphs 684 and 685. For the accident conditions array, the applicant varied the water and UO2 density to find the most reactive moderation level for a 235U mass of 650 grams, with the results shown in Table 2 of the application. The most reactive keff plus two times the calculation Monte Carlo uncertainty (2) for the system was 0.922, which is less than the applicants calculated Upper Subcritical Limit (USL) of 0.938. The corresponding maximum keff for the normal conditions array was 0.8701. The array sizes evaluated by the applicant support the requested Criticality Safety Index of 0.71.

The staff reviewed the configurations modeled by the applicant for the package array analyses under normal and accident conditions of transport. The staff finds that the applicant has identified the most reactive credible condition of the package arrays, consistent with the condition of the package under normal and accident conditions of transport, and the chemical and physical form of the fissile and moderating contents.

The applicant benchmarked the computer code and cross section library used for all criticality analyses of the package against selected critical experiments that were similar to the application system. The applicant describes the benchmark critical experiments in Section 2.1 of the application and provides resulting calculated keff values in Table 1 of the application. The applicant also calculated energy of average lethargy causing fission (EALF) for each experiment, for comparison to the application system. Based on the plotted keff versus EALF shown in Figure 1 of the application, the applicant stated that the trend implied that the higher EALFs shown for the benchmark calculations would overpredict code bias for the EALF of the application system, which would be conservative.

The applicants benchmark analysis contained several deficiencies, when compared to U.S.

NRC guidance on code benchmarking contained in NUREG/CR-6361, Criticality Benchmark Guide for Light-Water-Reactor Fuel in Transportation and Storage Packages. These deficiencies include: 1) dissimilarities between critical experiments and the modeled system

2) application model is outside the range of applicability of the selected experiments for EALF, and no extrapolation method is applied to determine code bias outside the range. Despite these deficiencies, the staff finds the applicants benchmark analysis to be adequate in this case for the following reasons: 1) the applicants trending analysis indicates that the calculated USL is

conservative; 2) there is significant margin between the applicants maximum calculated keff and the USL (>0.015 in keff); 3) the applicant used a code (SCALE 6.1.2) that is a standard in the industry for performing criticality calculations, and it is unlikely that a code bias and bias uncertainty calculated for water moderated low-enriched UO2 powder in a package would be greater than the calculated margin of subcriticality; and 4) the staffs independent benchmark analysis (discussed below) demonstrated the applicability of the selected benchmark experiments and conservatism of the applicants calculated USL.

The staff performed confirmatory benchmarking calculations using the TSUNAMI sensitivity and uncertainty analysis sequence of the SCALE 6.2.4 code. First, the staff used TSUNAMI-IP to compare the application model with the applicants selected critical benchmark experiments.

For the critical experiments selected by the applicant, the staff determined that most experiments had a similarity index (ck) of greater than 0.9, and all experiments had a ck greater than 0.8. This indicates that the experiments selected by the applicant were similar to the application system, and therefore appropriate to use for benchmarking the criticality analysis.

The staff also independently selected experiments with high ck values compared to the package with the requested contents. The staff created sensitivity data files (SDFs) for the application model and used TSUNAMI to compare the SDFs with benchmark SDFs to determine ck values, and benchmark experiments with high similarity were then used to determine a USL. The staff independently identified 200 experiments that had ck values greater than 0.9, indicating that they are similar to the application system. Using keff values for these experiments, the staff determined an independent USL using four different statistical methods. The four independently calculated USL values were either larger than, or similar to, the applicants calculated USL, demonstrating that the applicants USL is appropriate for the criticality analysis.

The staff reviewed the CoC for the Model No. BU-D package, as well as the applicants initial assumptions, model configurations, analyses, and results in the SAR. The staff finds that the applicant has identified the most reactive configuration of the Model No. BU-D 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 IAEA SSR-6.

CONCLUSION Based on the statements and representations contained in the documents referenced above (see

SUMMARY

, above), the staff concludes that the Model No. BU-D package meets the requirements of IAEA Regulations for the Safe Transport of Radioactive Material, IAEA Safety Standards Series, No. IAEA SSR-6, 2012 edition.

Issued with letter to R. Boyle, U.S. Department of Transportation, dated .

March 16, 2022

ML22062A499; ML22062A501 OFFICE NMSS/DFM/STLB NMSS/DFM/STLB NMSS/DFM/NARAB NMSS/DFM/FFLB NAME BWhite BW SFigueroa SF ABarto AB MDiaz MD DATE Mar 11, 2022 Mar 11, 2022 Mar 14, 2022 Mar 16, 2022 OFFICE NMSS/DFM/STLB YDiaz-Sanabria NAME CJacobs for CJ DATE Mar 16, 2022