ML23135A757

High Assay Low Enriched Uranium Transportation Packages Under 10 CFR Part 71 - U.S. NRC Research and Certification Activities ICNC2023 Paper Barto and Call

ML23135A757
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Issue date:	10/06/2023
From:	Andrew Barto, Michel Call NRC/NMSS/DFM/NARAB
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ICNC 2023 - The 12th International Conference on Nuclear Criticality Safety October 1st - 6th, 2023 in Sendai, Japan HIGH ASSAY LOW ENRICHED URANIUM TRANSPORTATION PACKAGES UNDER 10 CFR PART 71 - U.S. NRC RESEARCH AND CERTIFICATION ACTIVITIES Andrew B. Barto (1) *, Michel Call (1)

(1)

U.S. Nuclear Regulatory Commission, Washington, DC, 20555-001, USA Andrew.Barto@nrc.gov ABSTRACT Commercial Light Water Reactor (LWR) operators in the United States are pursuing Accident Tolerant LWR Fuel (ATF) designs which incorporate novel features. Non-LWR designers and fuel fabricators are pursuing reactor designs which use fuel with features that differ significantly from traditional LWR fuel.

In both cases, the fuel will rely on fuel enrichments in the 5 - 20 weight percent 235U range (wt%), which is known as High Assay Low Enriched Uranium (HALEU).

To meet industry needs for HALEU fuel, transportation package designers have begun seeking amendments to existing commercial fuel transportation package certificates of compliance and certificates of compliance for new package designs. These include packages for uranium oxide powder and pellets, fresh LWR fuel assemblies and rods, uranium hexafluoride, and tri-structural isotropic (TRISO) fuel.

The U.S. Nuclear Regulatory Commission (NRC) has engaged in efforts to prepare for and is active in reviews to certify packages to transport HALEU fuel. These efforts include sponsoring research to investigate the ability to satisfy subcriticality requirements with existing package designs and the adequacy of existing critical benchmark experiment data to support computer code validation.

This paper discusses that research and recently completed and ongoing NRC reviews of applications related to HALEU transportation. This discussion includes descriptions of the research and its outcome(s). It also notes the various approaches taken by applicants to demonstrate criticality safety of the package designs with HALEU contents. This paper will also discuss the NRC staffs confirmatory analyses, and any items of note associated with the reviews or designs.

KEYWORDS ICNC2023, Criticality safety, HALEU, Transportation Packages

1. INTRODUCTION United States Code of Federal Regulations (CFR), Title 10, Energy, Part 71, Packaging and Transportation of Radioactive Material, [1] includes requirements for the transport of fissile material in packages. Similar requirements for international transport of fissile material are contained in the International Atomic Energy Agencys (IAEA) Specific Safety Requirements No. SSR-6, Rev. 1, Regulations for the Safe Transport of Radioactive Material 1 (SSR-6) [2]. Applicants seek to meet these requirements while optimizing the authorized fissile contents through means that include packaging features such as fixed neutron absorbers and separation of fissile contents within the package cavity 1

Where citations of United States CFR Part 71 requirements are given in this paper, the equivalent or similar IAEA SSR-6 (Rev. 1) requirement is also shown in parentheses.

among others. To demonstrate that their package design meets the criticality safety requirements of 10 CFR Part 71, applicants for transportation package certificates of compliance (CoCs) perform criticality analyses using computer codes that must be benchmarked against laboratory critical experiments, consistent with the recommendations of ANSI/ANS 8.1, Nuclear Criticality Safety in Operations with Fissionable Material Outside Reactors, [3]. To do so, applicants rely on critical experiment data from sources such as the Nuclear Energy Agency International Handbook of Evaluated Criticality Safety Benchmark Experiments (ICSBEP Handbook) [4], which contains descriptions of laboratory critical experiments for over 5,000 critical configurations.

Commercial Light Water Reactor (LWR) operators in the United States are pursuing Accident Tolerant LWR Fuel (ATF) designs which incorporate novel features including new clad materials, cladding coatings, and fuel additives. Non-LWR designers and fuel fabricators are pursuing reactor designs which use fuel with features that differ significantly from traditional LWR fuel. In both cases, the fuel will rely on fuel enrichment in the 5 - 20 weight percent (wt%) 235U range, which is known as High Assay Low Enriched Uranium (HALEU). Prior to the start of efforts to pursue ATF and HALEU fuels, packaging designs for commercial fuel transportation have been designed to be subcritical for optimum LWR fuel contents at enrichments not exceeding 5 wt% 235U. Also, there are relatively few critical experiments in the HALEU enrichment range in the ICSBEP Handbook; most of the uranium experiments are focused on low enrichment (less than 5 weight percent uranium-235 (wt% 235U), or high enrichment (greater than 90 wt% 235U).

This paper will provide background information about the regulations that govern fissile material transportation, U.S. Nuclear Regulatory Commission (NRC) certification experience with higher enrichment uranium transportation packages, and recent NRC-sponsored research in HALEU transportation package design. This paper will also review the licensing actions related to HALEU transportation that the NRC has recently completed or are currently under review. This review will include a discussion of the various approaches taken by applicants to demonstrate criticality safety of the package designs with HALEU contents. It will also discuss the NRC staffs relevant confirmatory analyses, and any items of note associated with reviews or designs.

2. BACKGROUND 2.1 Regulations The primary criticality safety regulations for fissile material transportation packages in the U.S. are in 10 CFR 71.55 (Para 673, 680-682) for single packages, and 10 CFR 71.59 (Para 525, 526, 566(c), 567, 684-686) for package arrays. For single packages, applicants for CoCs for fissile material packages must demonstrate that the package is subcritical considering water leaking into the package containment system to the most reactive extent. This excludes uranium hexafluoride (UF6) packages meeting the conditions in 71.55(g) (Para 680(b)), including an enrichment of no more than 5 wt% 235U. Also, for single packages, applicants must demonstrate subcriticality with the package exposed to normal conditions of transport (NCT; defined in 10 CFR 71.71 (Para 719-724)) and hypothetical accident conditions (HAC; defined in 10 CFR 71.73 (Para 726-733)), per 10 CFR 71.55(d) (Para 682(b)) and 71.55(e) (Para 682(c)), respectively.

For package arrays, applicants must demonstrate subcriticality under NCT and HAC, per the requirements of 10 CFR 71.59(a) (Para 684-685). Under this requirement, applicants must determine a number of packages (N), such that five times N packages are subcritical under NCT, and two times N packages are subcritical under HAC. The lowest value of N from these two analyses are then used to determine the Criticality Safety Index (CSI), by dividing 50 by N, and rounding the resulting value up to the nearest decimal place, per the requirements of 10 CFR 71.59(b) (Para 686). The resulting CSI is used to control package accumulation on a conveyance (transport vehicle; large freight container; hold, compartment, or defined deck area of a vessel; or aircraft). Per 10 CFR 71.59(c) (Para 525, 526, 566(c),

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567), the sum of CSIs for packages on a conveyance are limited to 50 if shipped on a nonexclusive use conveyance, and 100 if shipped on an exclusive use conveyance.

Typically, the most challenging of these requirements to demonstrate compliance with has been consideration of potential water in-leakage for the single package under 10 CFR 71.55(b) (Para 680).

NRC staff anticipates that this will continue to be the case with HALEU packages. Although higher enriched uranium systems can approach criticality in lower moderation conditions in certain circumstances, consideration of full or close to full moderation by water in a transportation package is typically still the most reactive condition.

2.2 Previous certification experience for packages for higher enrichment contents Although demonstration of subcriticality can be more challenging for HALEU packages than for packages with uranium enriched to less than 5 wt% 235U, the NRC has a long history of certifying such packages. Packages certified for HALEU or higher enrichment have not typically been optimized for high capacity, as may be expected of package designs to support a hypothetical HALEU fuel cycle, and have typically included large margins of subcriticality to account for potential benchmarking limitations.

Nevertheless, both applicants and the NRC have a great deal of experience in certification of packages for HALEU or higher enrichments.

Three examples of such packages include the ATR FFSC (CoC No. 71-9330) [5], the ES-3100 (CoC 71-9315) [6], and the Versa-Pac (CoC 71-9342) [7]. While the ATR FFSC was designed for limited fuel forms (a single research reactor fuel element or loose fuel element fuel plates) and enrichments of either 20 wt% 235U or 94 wt% 235U, the other two packages were designed for multiple fuel forms and a range of enrichments up to 100 wt% 235U. Each package relies on different features to ensure subcriticality.

For the ATR FFSC, these features are spacing provided by the packaging as well as small array sizes (CSI = 4.0 and 25.0) [5]. For the ES-3100, these features are the spacing and neutron absorption provided by packaging components, contents mass limits, and, in some cases, array sizes (CSI = 0 - 3.2) [6]. For the Versa-Pac, these features include contents mass limits and content/packaging configurations (e.g.,

contents in pipes, limits on hydrogenous materials) while allowing relatively large package arrays (CSI

= 0.7 and 1.0) [7]. Benchmarking for these packages has included maintaining a large margin to the upper subcritical limit (USL) in instances with relatively few applicable critical experiments or determination of relatively low USLs or series of USLs based on a large selection of critical experiments needed to cover the broad range of contents (forms and enrichments).

These examples demonstrate that certification of packages for higher uranium enrichments, including the HALEU range, is not unusual, even long before the industry contemplated HALEU fuel cycles.

However, packages that are typical for a commercial power fuel cycle have been optimized to transport large quantities of low enriched uranium (LEU) fuel whereas packages are needed that are optimized to transport sufficiently large quantities of HALEU fuel for a commercial power fuel cycle that uses HALEU. Reviews by NRC to certify such packages for specific HALEU contents and non-LWR fuel forms, including new packages and modifications to existing packages are described later in this paper.

3. RECENT RESEARCH FOR HIGHER ENRICHMENT PACKAGE CONTENTS In anticipation of receiving applications for transportation CoCs for packages to transport HALEU fuel and fuel components, NRC sponsored research by Oak Ridge National Laboratory (ORNL) to evaluate several categories of fissile material transportation packages which could be amended to include higher enriched uranium contents in support of the front end of the fuel cycle. The focus of this research included providing an understanding of how existing packages perform with HALEU contents, insights into potential necessary limitations due to increased reactivity from higher enrichments, and indication as to whether sufficient applicable benchmark experiments can be identified for code validation. This research is documented in ORNL/TM-2020/1725, Assessment of Existing Transportation Packages for Use with HALEU [8].

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To accomplish these objectives, ORNL evaluated a representative package design from each of five categories of fissile materials that are commonly transported: 1) boiling water reactor (BWR) fresh fuel assemblies and rods, 2) pressurized water reactor (PWR) fresh fuel assemblies and rods, UF6, uranium metal and tri-structural isotropic (TRISO) particles, and uranium oxide (UO2) powder and pellets. The selected package designs for each category are shown in Table I.

Table I. Summary of analysis results for existing packages with HALEU fuel Fuel form category Package Model, Enrichments Changes Benchmark (CoC) evaluated, can ship (packaging, availability (ck)

(wt% 235U) contents, limits)

BWR fresh fuel Framatome, Inc. Assemblies; 5-9.8 Increased number many ( 0.9)

(assemblies and TN-B1 (71-9372) of assembly rods rods) [9] with Gd2O3, Reduced array size PWR fresh fuel Westinghouse Assemblies: 8 Assemblies: IFBA 2 many ( 0.9)

(assemblies and Electric Co., LLC Rods: 10 rods, reduced array rods) Traveller (71-9297) size, analysis

[10] margins Rods: none UF6 Orano NCS GmbH 5.8, 6.7, 9.5, 12.5 Reduced array size Very limited ( 0.8)

DN30 (71-9362)

[11]

Uranium metal and Orano TLI Versa- Up to 100 (current No evaluation done No evaluation done TRISO Pac: VP-55, VP- CoC; so, no 110 (71-9342) [7] analyses done)

UO2 powder, TN Americas, LLC Powder: 5-8, 10, 18 Reduced oxide Powder: many pellets CHT-OP-TU Pellets: 5-7, 16.5, vessel diameter, ( 0.9)

(71-9288) [12] 17 array size Pellets: many

( 0.9)

ORNL evaluated each package design for higher enrichment contents, from 5 wt% 235U up to 20 wt%

235 U. The report considered minimal design changes, including reduced mass per package, reduced package array size, increased absorber credit, and reduced safety analysis margin, and determined the maximum uranium enrichment that remained safely subcritical for each package type. For evaluation of applicable benchmark experiments, ORNL used a collection of 1,584 low-enriched and intermediate-enriched uranium critical experiments from the ICSBEP Handbook and the ORNL-maintained Verified, Archived Library of Inputs and Data (VALID) library [13]. ORNL used the SCALE [14] sensitivity and uncertainty tools, using the resulting similarity coefficient (ck), to determine candidate experiments for benchmarking of each packages analysis.

The results of these analyses are summarized in Table I. The results indicated that it is possible to increase enrichments for all package types to within the HALEU range, with different increased amounts for each package type. The sensitivity and uncertainty analyses indicated that numerous critical experiments were applicable for code validation at the enrichment ranges considered, for all package types except UF6. Note that the UF6 analysis did not consider water in-leakage as required by 10 CFR 71.55(b) (Para 680), which made the neutron spectrum for this analysis higher than the other package designs which did consider water in-leakage. It is expected that if UF6 package analyses were performed considering water in-leakage, the neutron spectrum would be more thermal, and more critical experiments would be applicable to this package type for code validation. Additionally, the NRC will 2

IFBA = Integral Fuel Burnable Absorber 4

Table II. Recent and current NRC reviews of transportation package applications for HALEU contents Package BU-D MAP-12,13 Traveller RAJ-II Versa-Pac OPTIMUS-L DN30-X VP-55, VP-110 CoC/CoCA D/4305/AF-96 71-9319 [17] 71-9380 [18] 71-9309 [19], [20] 71-9342 [21], [22] 71-9390 [23], [24] 71-9388 [25]

[15], [16]

Fuel form UO2 powder, PWR fresh fuel PWR fresh fuel BWR fresh fuel TRISO fuel TRISO fuel UF6 category pellets assemblies and assemblies and assemblies and rods rods rods Prior Approval CSI: 0.714 CSI: 2.8 CSI: 0.7, 1.0, 4.2 CSI: 1.0, 1.6 CSI: 0.7, 1.0 No currently CSI: 0.0 Contents: UO2, Contents: Contents: loose Contents: 10x10 Contents: approved fresh Contents:

any solid form, assemblies, rods, two assemblies/rods, multiple content fuel forms in 5 wt% 235U, 5 wt% 235U, 5 wt% 235U assembly groups, 5 wt% 235U categories, mass package contents 2,277 kg (5020 800 g (1.76 lb) 5 wt% 235U limits (incl. lb) UF6, 235 U HALEU) H/U ratio 0.088 Benchmark (DN30, 71-9362) experiments: [11]

many [7]

5 New Approvals, CSI: 0.71 CSI: 8.4, 25 CSI: 0.7, 2.5 CSI: 1.6 CSI: 0.7, 1.0, 1.4 CSI: 0.0 CSI: 0.0 Proposals Contents: UO2, Contents: new Contents: loose Contents: 10x10 Contents: Contents: TRISO Contents:

powder, 17x17 assembly, rods assemblies/rods, new/higher compacts, 10/20 wt% 235U, 10 wt% 235U, 8 wt% 235U ( 7 wt% 235U), 8 wt% 235U masses, 20 wt% 235U, 1,460/1,271 kg 650 g (1.43 lb) Benchmark new assembly Benchmark enrichments, 68 kg (150 lb) (3219/2802 lb) 235 U experiments: group experiments: content category U UF6, Benchmark many ( 6 wt% 235U) several Benchmark Benchmark H/U ratio 0.088 experiments: Package/other Benchmark Package/other experiments: experiments: Benchmark few changes: reduced experiments: changes: reduced many TBD experiments:

Package/other array size, require Several array size, more Package/other Package/other few - several changes: reduced Gd2O3 rods, Package/other Gd2O3 rods for changes: new changes: new Package/other contents mass analysis - most changes: reduced assemblies content category, basket Changes: neutron reactive Gd2O3 analysis basket (H-limited absorber system; rod pattern conservatisms for contents) ANSI N14.1 [26],

assemblies ASTM C996 [27]

not met Review Status Revalidation Approved Approved Under Review Approved Under Review Approved March 2022 Dec. 2021 April 2022 Sept. 2021, Nov. March 2023 2022

continue to look for and take advantage of opportunities to improve the benchmarking for package types for which there are not that many applicable critical experiments available for use.

4. CERTIFICATION OF TRANSPORTATION PACKAGES FOR HIGHER ENRICHMENT FUEL AND FUEL COMPONENTS To meet the needs of the industry for using HALEU fuel, transportation package designers have begun seeking amendments to existing transportation package CoCs and CoCs for new package designs under 10 CFR Part 71 by the NRC as well as revalidations of packages approved by other countries regulators.

Packages for which certification has been sought to transport HALEU include at least one package in each of the fuel form categories in Table I. Table II identifies each of these packages and provides some summary points about each one relevant to highlighting differences in the package or its analysis for fresh HALEU fuel contents versus fresh LEU fuel contents. With the exception of the BU-D package (D/4305/AF-96 (Rev. 10)) [15], all the packages have been or are being reviewed under 10 CFR Part

71. The BU-D package is a German-approved package that the NRC reviewed under IAEA SSR-6 and recommended (to the U.S. Department of Transportation, the U.S. competent authority) be revalidated

[16]. The table also gives a qualitative indication regarding the quantity of applicable benchmark experiments used in the application for HALEU fuel contents. Additionally, the information in the table gives some indication of the consistency of the changes for the package and benchmarking with the outcomes of ORNLs evaluations for packages for each fuel form category.

4.1 Packaging, contents, analysis A few interesting observations can be made from a look at the applications for the packages shown in Table II and the revised or new CoCs for those packages which have been approved. One observation is that most of the packages are already certified to transport LEU fuel in fuel forms for which approval is requested to transport HALEU fuel. The main exception is the OPTIMUS-L package, which currently does not include unirradiated, or fresh, fuel contents [23]. So, while it is a currently certified package, it is new in terms or unirradiated fuel transportation. The DN30-X is also a new package [25], though it is very similar to the DN30 package [11]. Thus, comparison is made between the DN30-X and the DN30 packages to identify differences between LEU and HALEU packaging and contents specifications and package analyses. Another observation is that, other than for the Versa-Pac in [21] and [22] where changes affected all contents (and the DN30-X for which UF6 is its only content [25]), applicants either requested HALEU enrichments for only a limited subset of their packages currently authorized contents or added a new content category or type specifically for HALEU.

Additionally, as would reasonably be expected, optimization of packages for HALEU fuel generally results in greater limitations on the amount of fuel that can be transported in a given shipment (larger CSI or smaller allowable mass per package). Exceptions to this are the loose fuel rod contents in the Traveller and RAJ-II packages for which the margins to the USLs for these contents are shown to more than compensate for the increases in keff due to the enrichment increases [18], [20]. It is unclear whether or not this pattern would be true for the OPTIMUS-L if it had unirradiated LEU contents as authorized contents, given the proposed uranium mass limits and CSI for 20 wt% 235U-enriched TRISO fuel.

Changes that applicants have proposed or introduced for their packages (for HALEU fuel versus LEU fuel) have been similar to or consistent with the changes that ORNL identified and considered in its evaluation for the packages for each fuel form category. These changes include reductions in allowed fuel mass, whether thats by a specific limit on the fuel mass or changes in packaging components which effectively reduce the fuel mass. For fuel assembly packages, this has included new or increased requirements for absorber rods that are part of the fuel assembly contents. Package array sizes have also been reduced. Margins have been used or reclaimed to alleviate or minimize the need for array size or other changes, as in the case of the fuel assemblies for the Traveller package for which structural and thermal analyses allowed changes to assumptions regarding fuel reconfiguration and melting of plastic packing materials in the criticality models for HAC [18].

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The Versa-Pac and DN30-X are of particular note. Although already authorized for contents at HALEU enrichments and so ORNL did not evaluate this package, the applicant introduced changes to this package as well, that can be considered as similar to those changes considered for the other evaluated packages. In the case of Versa-Pac, the changes, which included a new basket and a new content category that limited the mass of hydrogenous materials with the fuel contents, allowed increased masses in the package, though with some instances of reduced array size being necessary [21], [22]. The changes to the DN30-X were substantial [25], introducing a neutron absorber system in the interior of a 30B-like cylinder that is designated the 30B-X, with the system requirements varying for the two enrichments in this package. Also, though similar to the 30B cylinder, this packages 30B-X cylinders are not certified to ANSI N14.1 American National Standard for Nuclear Materials - Uranium Hexafluoride -

Packagings for Transport [26], these cylinders do not meet ANSI N14.1. The applicants approach is markedly different from the option that ORNL considered and evaluated for a UF6 package (a reduced package array size).

For some packages, the changes to the contents or packaging required changes to packages criticality analyses. Applicants had to confirm that the most packaging and contents parameters previously identified to be the most reactive still were the most reactive. Further, for HALEU fuel assemblies with requirements for absorber rods in the assemblies, the applicant had to identify the most reactive rod pattern in the assemblies. Also, for the DN30-X, the analysis had to consider changes to the internal neutron absorber system due to HAC (e.g., deformation, displacement) as well as internal water moderation for single package analyses since the enrichments exceed the criterion in 10 CFR 71.55(g)

(Para 680(b)) for excluding water moderation [25].

4.2 Benchmarking The NRCs reviews of the packages included evaluation of each applicants benchmark analysis and the resulting USL(s). The NRCs evaluation includes use of the guidance and recommendations in NUREG/CR-6361, Criticality Benchmark Guide for Light-Water-Reactor Fuel in Transportation and Storage Packages [28]. Typically, aspects of the applicants benchmark analysis that differ from this guidance receive additional NRC scrutiny. Additionally, for these HALEU applications, the NRC performed confirmatory benchmark evaluations, using the SCALE sensitivity and uncertainty tools to both independently evaluate the applicability of the applicants selected critical experiments and to make its own selection of applicable critical experiments. The NRC selected experiments which resulted in a high degree of similarity (ck 0.9) from which to calculate USLs, using appropriate statistical methods considering the normality or non-normality of the keff results for the experiments.

Evaluating each applicants benchmark analysis, in some instances the NRC observed instances of weaknesses and considerations to be aware of in experiment selection and benchmark analysis. These weaknesses are not unique to HALEU package analyses but can have implications for validation of those analyses. They included limited numbers of experiments, dissimilarities in characteristics of experiments versus the package, appropriate extrapolation methods when the package model is outside the area of applicability, checking for normality of the keff results for the experiments, and use of appropriate statistical (normal or non-parametric) methods to determine the USL(s). When applying the sensitivity and uncertainty tools method, confirming the use of the method and its results with some direct perturbation calculations became an additional important consideration and potential weakness. Despite identifying these weaknesses, the NRC was able to determine the acceptability of the applicants USL(s) based on other factors, among which was the NRCs confirmatory analyses resulting in similar USLs or indicating the applicants USL(s) to be conservative.

The numbers of critical experiments and the methods the applicants used to select them varied. The selection process either involved only traditional approaches (identification based on similarity of characteristics such as fuel form, composition, and non-fuel materials) or a combination of traditional approaches and use of the SCALE sensitivity and uncertainty tools. Table II includes a qualitative 7

indication of the quantity of critical experiments that were used in the application for each package. As indicated in Table I, the ORNL research indicated that, with the exception of the UF6 package, there are many critical experiments with a high degree of similarity available for HALEU fuel packages. While the number of experiments the applicant selected may have been less (as seen from Table II), the NRC confirmatory analysis did indicate and make use of a number of critical experiments that is consistent with the ORNL research. The NRC expects this will also be true for those packages with applications still under review.

The benchmark analysis for a couple packages is worth noting. The first is the Versa-Pac [21], [22]. To increase the number of experiments used in the benchmark analysis, in some instances the applicant used a lower degree of similarity (as low as ck 0.7), which is lower than the typical threshold and the threshold used by the NRC. While ORNL did not evaluate the availability of experiments to benchmark packages for TRISO fuel forms, the evaluations for other packages indicate many critical experiments with high similarity to this package type are likely available. Although the applicant had to use a lower similarity threshold for its analysis, this is likely a result of using the sensitivity and uncertainty tools on experiments the applicant had selected by traditional means versus as the means to evaluate all available experiments for similarity. Further, the staffs confirmatory analysis, which used the tools to assess available experiments indicates that there are a large number of highly similar and so applicable experiments for this package.

The other package is the DN30-X [25]. Since the package exceeds the enrichment criterion in 10 CFR 71.55(g) (Para 680(b)), the applicants single package analyses include optimum internal water moderation. However, the package array analyses do not include internal water moderation. Thus, the applicant did separate critical experiment selections and USL determinations for the single package and the array analyses. Similar to the ORNL research, which also did not include water moderation, the applicant identified relatively few experiments as being applicable to the package array analyses. The low USL and the margin between the maximum keff for the package arrays and the USL factored into the NRCs acceptance of the applicants benchmark analysis for the package arrays. On the other hand, the applicant identified several experiments as being applicable to the single package analyses. This outcome (though with a ck 0.8) is consistent with NRC expectations that more experiments would be applicable to UF6 packages with optimum water moderation.

5. CONCLUSIONS This paper provided background information about the regulations that govern fissile material transportation, U.S. Nuclear Regulatory Commission (NRC) certification experience with higher enrichment uranium transportation packages, and recent NRC-sponsored research in HALEU transportation package design. This paper also reviewed the licensing actions related to HALEU transportation that the NRC has recently completed or is currently reviewing. The research that NRC has sponsored on HALEU transportation packages indicates that they can accommodate higher enrichments, and that criticality analyses can be adequately benchmarked provided the maximum reactivity system is well moderated. NRCs long term and recent experience with certifying higher enrichment transportation packages is consistent with the outcomes of that research. The NRC expects that the research and this recent licensing experience will inform NRC reviews and ensure that the NRC can continue to effectively and efficiently certify HALEU packages to support ATF and non-LWR fuel cycles. Additionally, the NRC will continue to look for and take advantage of opportunities to improve the benchmarking for package types for which there are not that many applicable critical experiments available for use.

REFERENCES

[1] United States Code of Federal Regulations, Title 10, Energy, Part 71, Packaging and Transportation of Radioactive Material. 2016, Washington, DC, USA, U.S. Government Publishing Office, 2016.

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[2] International Atomic Energy Agency. Specific Safety Requirements No. SSR-6 (Rev. 1),

Regulations for the Safe Transport of Radioactive Material. 2018, Vienna, Austria, International Atomic Energy Agency, 2018.

[3] American Nuclear Society. Nuclear Criticality Safety in Operations with Fissionable Material Outside Reactors, ANSI/ANS 8.1. 2014(R2018), La Grange Park, IL, USA, American Nuclear Society, 2014.

[4] International Criticality Safety Benchmark Evaluation Project ICSBEP Handbook, NEA/NSC/DOC(95)03. Organisation for Economic Co-Operation and Development /Nuclear Energy Agency, 2021.

[5] U.S. Nuclear Regulatory Commission. Certificate of Compliance 71-9330. Revision 16, Washington, DC, USA, U.S. Nuclear Regulatory Commission, 2023. Agencywide Documents Access and Management System (ADAMS) Accession No. ML23033A521.

https://adamswebsearch2.nrc.gov/webSearch2/main.jsp?AccessionNumber=ML23033A521.

[6] U.S. Nuclear Regulatory Commission. Certificate of Compliance 71-9315. Revision 16, Washington, DC, USA, U.S. Nuclear Regulatory Commission, 2021. ADAMS Accession No. ML21005A250.

https://adamswebsearch2.nrc.gov/webSearch2/main.jsp?AccessionNumber=ML21005A250.

[7] U.S. Nuclear Regulatory Commission. Certificate of Compliance 71-9342. Revision 15, Washington, DC, USA, U.S. Nuclear Regulatory Commission, 2020. ADAMS Accession No. ML20139A033.

https://adamswebsearch2.nrc.gov/webSearch2/main.jsp?AccessionNumber=ML20139A033.

[8] Hall, R., Marshall, W. J., Wieselquist, W. A. Assessment of Existing Transportation Packages for Use with HALEU, ORNL/TM-2020/1725. Oak Ridge, Tennessee, USA, Oak Ridge National Laboratory, 2020.

[9] U.S. Nuclear Regulatory Commission. Certificate of Compliance 71-9372. Revision 2, Washington, DC, USA, U.S. Nuclear Regulatory Commission, 2019. ADAMS Accession No. ML19070A018.

https://adamswebsearch2.nrc.gov/webSearch2/main.jsp?AccessionNumber=ML19070A018.

[10] U.S. Nuclear Regulatory Commission. Certificate of Compliance 71-9297. Revision 11, Washington, DC, USA, U.S. Nuclear Regulatory Commission, 2019. ADAMS Accession No. ML19109A135.

https://adamswebsearch2.nrc.gov/webSearch2/main.jsp?AccessionNumber=ML19109A135.

[11] U.S. Nuclear Regulatory Commission. Certificate of Compliance 71-9362. Revision 2, Washington, DC, USA, U.S. Nuclear Regulatory Commission, 2019. ADAMS Accession No. ML19346E057.

https://adamswebsearch2.nrc.gov/webSearch2/main.jsp?AccessionNumber=ML19346E057.

[12] U.S. Nuclear Regulatory Commission. Certificate of Compliance 71-9288. Revision 11, Washington, DC, USA, U.S. Nuclear Regulatory Commission, 2018. ADAMS Accession No. ML18269A127.

https://adamswebsearch2.nrc.gov/webSearch2/main.jsp?AccessionNumber=ML18269A127.

[13] Marshall, W. J., Rearden, B. T. The SCALE Verified, Archived Library of Inputs and Data -

VALID. Topical Meeting held by the ANS Nuclear Criticality Safety Division (NCSD2013),

Criticality Safety in the Modern Era: Raising the Bar. Wilmington, NC, USA, 29 September - 3 October 2013, pp. 319-329.

[14] Rearden, B. T., Jessee, M. A. SCALE Code System. ORNL/TM-2005/39, Version 6.2.3, Oak Ridge, Tennessee, USA, Oak Ridge National Laboratory, 2018.

[15] Federal Office for the Safety of Nuclear Waste Management. Certificate of Approval D/4305/AF-

96. Revision 10, Berlin, Germany, Federal Office for the Safety of Nuclear Waste Management, 2019.

[16] U.S. Nuclear Regulatory Commission. Letter to U.S. Department of Transportation recommending revalidation for the Model No. BU-D Package. 3 March 2022. ADAMS Accession No. ML22062A499.

https://adamswebsearch2.nrc.gov/webSearch2/main.jsp?AccessionNumber=ML22062A499.

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[17] U.S. Nuclear Regulatory Commission. Certificate of Compliance 71-9319. Revision 13, Washington, DC, USA, U.S. Nuclear Regulatory Commission, 2021. ADAMS Accession No. ML21344A047.

https://adamswebsearch2.nrc.gov/webSearch2/main.jsp?AccessionNumber=ML21344A047.

[18] U.S. Nuclear Regulatory Commission. Certificate of Compliance 71-9380. Revision 1, Washington, DC, USA, U.S. Nuclear Regulatory Commission, 2022. ADAMS Accession No. ML22080A171.

https://adamswebsearch2.nrc.gov/webSearch2/main.jsp?AccessionNumber=ML22080A171.

[19] U.S. Nuclear Regulatory Commission. Certificate of Compliance 71-9309. Revision 12, Washington, DC, USA, U.S. Nuclear Regulatory Commission, 2022. ADAMS Accession No. ML19025A103.

https://adamswebsearch2.nrc.gov/webSearch2/main.jsp?AccessionNumber=ML19025A103.

[20] Global Nuclear Fuel - Americas, LLC. GNF-A Request for Revision and Renewal of Certificate of Compliance (CoC) USA/9309/B(U)F-96 for Model No. RAJ-II Package. 23 September 2022.

ADAMS Accession No. ML22266A187.

https://adamswebsearch2.nrc.gov/webSearch2/main.jsp?AccessionNumber=ML22266A187.

[21] U.S. Nuclear Regulatory Commission. Certificate of Compliance 71-9342. Revision 16, Washington, DC, USA, U.S. Nuclear Regulatory Commission, 2021. ADAMS Accession No.ML21236A208.

https://adamswebsearch2.nrc.gov/webSearch2/main.jsp?AccessionNumber=ML21236A208.

[22] U.S. Nuclear Regulatory Commission. Certificate of Compliance 71-9342. Revision 17, Washington, DC, USA, U.S. Nuclear Regulatory Commission, 2022. ADAMS Accession No. ML22280A141.

https://adamswebsearch2.nrc.gov/webSearch2/main.jsp?AccessionNumber=ML22280A141.

[23] U.S. Nuclear Regulatory Commission. Certificate of Compliance 71-9390. Revision 1, Washington, DC, USA, U.S. Nuclear Regulatory Commission, 2022. ADAMS Accession No. ML22020A169.

https://adamswebsearch2.nrc.gov/webSearch2/main.jsp?AccessionNumber=ML22020A169.

[24] NAC International. Request for a Revision to NAC OPTIMUS-L Transportation Package, Certificate of Compliance 71-9390. 2 November 2022. ADAMS Accession No. ML22306A108.

https://adamswebsearch2.nrc.gov/webSearch2/main.jsp?AccessionNumber=ML22306A108.

[25] U.S. Nuclear Regulatory Commission. Certificate of Compliance 71-9388. Revision 0, Washington, DC, USA, U.S. Nuclear Regulatory Commission, 2023. ADAMS Accession No. ML23083B977.

https://adamswebsearch2.nrc.gov/webSearch2/main.jsp?AccessionNumber=ML23083B977.

[26] American National Standards Institute, Inc. American National Standard for Nuclear Materials -

Uranium Hexafluoride - Packaging for Transport, ANSI N14.1. 2012, New York, NY, USA, American National Standards Institute, Inc., 2013.

[27] ASTM International. Standard Specification for Uranium Hexafluoride Enriched to Less Than 5

% 235U, C996. 2020, West Conshohocken, PA, USA, ASTM International, 2020.

[28] Lichtenwalter, J. J., Bowman, S. M., DeHart, M. D., Hopper, C. M. Criticality Benchmark Guide for Light-Water-Reactor Fuel in Transportation and Storage Packages, NUREG/CR-6361 (ORNL/TM-13211). Oak Ridge, Tennessee, USA, Oak Ridge National Laboratory, 1997.

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