Review of Exemptions and 

General Licenses for Fissile 

Material in 10 CFR 71

Office of Nuclear Material Safety and Safeguards 

NUREG/CR-7239

ORNL/TM-2013/57
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Review of Exemptions and

General Licenses for Fissile 

Material in 10 CFR 71

Manuscript Completed: February 2017 

Date Published: January 2018

Prepared by: 

Douglas G. Bowen and Cecil V. Parks 

Oak Ridge National Laboratory 

Managed by UT-Battelle, LLC 

Oak Ridge, TN 37831-6170 

A. Barto, NRC Project Manager

NRC Job Code J5728

Office of Nuclear Material Safety and Safeguards 

NUREG/CR-7239

ORNL/TM-2013/57

iii

ABSTRACT

Title 10 of the United States (US) Code of Federal Regulations (CFR), Part 71, Packaging and 

Transportation of Radioactive Material, includes requirements for the transport of fissile material 

in packages. These regulations provide requirements for packages that are certified by the U.S. 

Nuclear Regulatory Commission (NRC) to transport fissile material. 10 CFR 71 also includes 

provisions for exemptions from classification as fissile material (10 CFR 71.15) and permits 

general licenses for limited quantities of fissile material and plutonium-beryllium special form 

sources (10 CFR 71.22 and 10 CFR 71.23, respectively). These provisions were extensively 

revised by the NRC as part of a broad rule-making effort in 2004. The exemption and general 

license provisions are used frequently for a wide-variety of fissile material shipping operations, 

and consignors must interpret the regulations for particular shipping situations. The purpose of 

this document is to provide explanatory information on the background, intent, and anticipated 

use of the provisions in an effort to assist fissile material licensees in their interpretation and 

application of the provisions such that criticality safety is ensured during transportation activities. 

A variety of examples are presented and discussed to illustrate how the regulations should be 

applied.

v 

TABLE OF CONTENTS

ABSTRACT..........................................................................................................................................iii

LIST OF FIGURES...............................................................................................................................vii

LIST OF TABLES................................................................................................................................. ix

ACKNOWLEDGMENTS...................................................................................................................... xi

ACRONYMS........................................................................................................................................xiii

1 INTRODUCTION.............................................................................................................................. 1

2 BACKGROUND DISCUSSION....................................................................................................... 3

2.1 Parameters Controlling Criticality Safety .................................................................................. 3

2.2 Packages Certified to Transport Fissile Material...................................................................... 4

2.3 Exemptions from Classification as Fissile Material................................................................... 5

2.4 General License Criteria............................................................................................................ 5

2.5 Packaging Requirements for Exemptions and General Licenses............................................ 6

3 RECENT HISTORY OF REGULATORY DEVELOPMENT ........................................................... 9

3.1 1997 NRC Emergency Rulemaking.......................................................................................... 9

3.2 Issuance of NUREG/CR-5342 (1998) ....................................................................................10

3.3 10 CFR 71 Final Rule (2004)..................................................................................................11

3.3.1 Exemptions from Classification as Fissile Material .....................................................11

3.3.2 General Licenses for Fissile Material...........................................................................12

3.3.3 Plutonium-Beryllium Special Form Material General Licenses...................................13

3.4 10 CFR 71 Final Rule (2015)..................................................................................................13

4 INTENT AND TECHNICAL BASIS ...............................................................................................15

4.1 Exemptions from Classification as Fissile Material................................................................. 15

4.1.1 10 CFR 71.15(a): Individual Package Containing 2 g or Less Fissile Material...........16

4.1.2 10 CFR 71.15(b): Package Containing 15 g or Less Fissile Material.........................17

4.1.3 10 CFR 71.15(c) Low Concentrations of Solid Fissile Material Comingled 

with Solid Nonfissile Material......................................................................................19

4.1.4 10 CFR 71.15(d): Uranium Enriched in 235U to a Maximum of 1 percent 

by Weight ....................................................................................................................23

4.1.5 10 CFR 71.15(e): Liquid Solutions of Uranyl Nitrate Enriched in 235U to 

a Maximum of 2 Percent.............................................................................................26

4.1.6 10 CFR 71.15(f): Packages Containing Plutonium with a Large Percentage of 

238Pu ............................................................................................................................28

4.2 General License: Fissile Material............................................................................................29

4.3 General License: Plutonium-Beryllium Special Form Material...............................................34

5 EXAMPLE PROBLEMS ................................................................................................................37

5.1 Fissile Material Exemption Examples .....................................................................................37

5.1.1 Small Samples .............................................................................................................37

5.1.2 Plutonium-Contaminated Glove Box ...........................................................................37

5.1.3 Uranium Contaminated Sludge ...................................................................................38

5.1.4 Uranium-Contaminated Graphite.................................................................................39

5.1.5 Soils Contaminated with Fissile Material.....................................................................40

5.1.6 Contaminated Uranium Alumina Trap Contents .........................................................40

5.1.7 Uranium-Contaminated Process Equipment...............................................................41
vi

5.1.8 Shipment of Multiple Drums.........................................................................................42

5.1.9 Uranium-Contaminated Oil ..........................................................................................43

5.1.10 Low-Enriched Uranium Waste.....................................................................................43

5.1.11 Uranium Metal Ingots...................................................................................................44

5.1.12 Uranyl Nitrate Solution from Spent Fuel Reprocessing ..............................................44

5.1.13 Uranyl Nitrate Solution Laboratory Experiments .........................................................45

5.1.14 Plutonium Oxalate Material..........................................................................................46

5.1.15 Plutonium-Contaminated Graphite Molds ...................................................................46

5.2 General License Criteria Examples ........................................................................................47

5.2.1 Uranyl Nitrate Solution Laboratory Experiments .........................................................47

5.2.2 Uranium-Graphite Waste.............................................................................................48

5.2.3 Uranium Metal Ingots...................................................................................................48

5.2.4 Sealed Sources for Gamma-Ray Measurements .......................................................49

5.2.5 Plutonium-Beryllium Sources.......................................................................................50

6 CONCLUSIONS AND FUTURE WORK .......................................................................................53

7 REFERENCES...............................................................................................................................55

APPENDIX A BRIEF HISTORY OF 10 CFR 71 AND IAEA REGULATIONS FOR SAFE 

TRANSPORT OF RADIOACTIVE MATERIAL.................................................. A-1

APPENDIX B DISCUSSION OF IAEA REGULATIONS ........................................................B-1
vii

LIST OF FIGURES

Figure 1 Spherical, Homogeneous Mixtures of 235U and Various Nonfissile 

Materials (30-cm Thick Water Reflection). ..................................................................19

Figure 2 Infinite Homogeneous Mixture of 235U Metal and Water with Aluminum 

Present as a Diluent....................................................................................................21

Figure 3 Infinite Homogeneous Mixture of 235U Metal and Water with a 

Diluent-to235U Ratio of 2000.......................................................................................22

Figure 4 Minimum Spherical Critical Masses as Functions of 235U Enrichment in 

Homogeneous and Heterogeneous Hydrogen-Moderated Systems 

(Ref. 21, Fig. 22). ........................................................................................................24

Figure 5 Arrays of U(0.995)-Metal Units Immersed in Water. ...................................................25

Figure 6 17 × 17 × 17 Array of U(0.995)-Metal Units Immersed in Water.................................26

Figure 7 kinf Calculated for UO2(NO3)2–H2O Mixtures (Ref. 24, Fig. 2)......................................27

Figure 8 Masses of Spheres of Homogeneous Water-Moderated 239Pu as 

Functions of 239Pu Density (Ref. 22, Fig. 10)...............................................................29

Figure 9 Illustration of the HEU Sealed Source in 10 CFR 71.22 Example 4 

(Figure Not to Scale). ..................................................................................................50

ix

LIST OF TABLES 

Table 1 Content in 10 CFR 71.15 “Exemption from the Classification as Fissile 

Material”..........................................................................................................................15

Table 2 Content in 10 CFR 71.22, “General License: Fissile Material”.....................................30

Table 3 10 CFR 71.22 Table 71–1—Mass Limits for General License Packages 

Containing Mixed Quantities of Fissile Material or 235U of Unknown 

Enrichment per 71.22(e)..............................................................................................31

Table 4 10 CFR 71.22 Table 71–2—Mass Limits for General License Packages 

Containing 235U of Known Enrichment per 71.22(e)....................................................31

Table 5 Content in 10 CFR 71.23 “General License: Plutonium-Beryllium Special Form 

Material” ......................................................................................................................35

Table 6 Isotopic Breakdown of Pu-Be Sources for 10 CFR 71.23 Example Problem..............51

xi

ACKNOWLEDGMENTS 

The authors would like to acknowledge the numerous sites throughout the U.S. Department of 

Energy (DOE) complex that provided perspective and feedback on the use of the regulations in 

10 CFR 71 to support the content in this report. D. M. Willaford of the DOE Oak Ridge Office 

provided invaluable assistance with respect to discussing the end-user and the regulator

perspective regarding the regulations. As the report was being developed the authors received 

invaluable direction and review by Andrew Barto of the U.S. Nuclear Regulatory Commission. The 

authors are also appreciative of the thorough technical reviews by C. M. Hopper, E. P. Elliott, 

B. Lee, E. Saylor, L. F. Gelder, and M. Conroy. The authors appreciate the technical editing by 

R. Raney. Kristin Ellestad provided administrative reviews of the document and final formatting. 

xiii

ACRONYMS

AEC U.S. Atomic Energy Commission

CFR Code of Federal Regulations

CSI Criticality Safety Index

DOE U.S. Department of Energy

DOT U.S. Department of Transportation

DU depleted uranium

HEU highly enriched uranium

IAEA International Atomic Energy Agency

ICC Interstate Commerce Commission

LLW low-level waste

NDA non-destructive assay

NRC U.S. Nuclear Regulatory Commission

ORNL Oak Ridge National Laboratory

QA quality assurance

1

1 INTRODUCTION

Title 10 of the United States Code of Federal Regulations (CFR), Part 71 (Ref. 1), Packaging and 

Transportation of Radioactive Material, includes requirements for the transport of fissile material in 

packages. These regulations require analyses for single packages and arrays of packages under 

10 CFR 71.55 and 71.59, respectively, to demonstrate the package remains subcritical. These 

analyses must consider normal conditions of transport defined in 10 CFR 71.71 and hypothetical 

accident conditions as defined in 10 CFR 71.73. These analyses are approved by the U.S. 

Nuclear Regulatory Commission (NRC), which issues a certificate of compliance for the fissile 

material package. 

The regulations also include provisions that allow for shipment of fissile material in packages that 

do not require NRC certification. These provisions include criteria for exemptions from 

classification as fissile material (10 CFR 71.15) and permit general licenses for limited quantities 

of fissile material and plutonium-beryllium special form sources (10 CFR 71.22 and 71.23, 

respectively).

The provisions in 10 CFR 71 were revised by the NRC in 2004 as part of a broad rulemaking 

effort that included extensive revision to the exemptions and general licenses for fissile material. 

The NRC has received many requests for interpretation of the exemptions from classification of 

fissile material and the general license provisions since the revisions were implemented. 

Consignors and shippers need to understand and correctly interpret and apply the regulations to 

ensure packages do not pose a criticality safety risk during transport. The consignor is responsible 

for verifying package contents and preparing a package for shipment under exclusive or nonexclusive use. The shipper is responsible for controlling the package consistent with the contents 

and the required shipping controls under exclusive or non-exclusive use. 

Packages that might pose a criticality safety risk are those containing fissile nuclides, defined by 

10 CFR 71 as 233U, 235U, 239Pu, and 241Pu or any combination of these radionuclides. According to 

10 CFR 71.4, Definitions, the definition of fissile material is meant to apply to the fissile nuclides 

themselves, not the bulk material containing fissile nuclides. The quantity of fissile material that 

presents a criticality safety risk depends upon the presence of other materials in the system that 

might absorb neutrons emitted from fission or moderate (slow) those neutrons to lower energies 

where the probability of them creating additional fission reactions is higher. Besides absorption 

and moderation of neutrons, other parameters that must be considered to ensure criticality safety 

are: the mass, concentration, or isotopic distribution of the fissile material and the system 

geometry and surrounding materials (reflectors) that might reflect neutrons back into the package. 

These parameters were carefully considered in developing the requirements for the exemptions 

from classification of fissile material and the requirements for general licenses for fissile material. 

Thus, the purpose of this document is to provide explanatory information on the background, 

intent, and anticipated use of the provisions in an effort to assist fissile material licensees in their 

interpretation and application of the provisions such that criticality safety is ensured during 

transportation activities. Numerous example problems are provided in this report to illustrate the 

intent of the regulations and how they are applied to realistic transportation scenarios.

The International Atomic Energy Agency (IAEA) also issues regulations for the safe transport of 

radioactive material (Ref. 2), including fissile material, and both the U.S. and IAEA regulations 

governing safe transport domestically and internationally have evolved significantly over the past 

50 years. 
2 

Appendix A provides a brief discussion about the history of 10 CFR 71 and IAEA regulations for 

the safe transport of fissile material. Appendix B provides additional information about the IAEA 

transportation regulations.
3

2 BACKGROUND DISCUSSION

The objective of the fissile material exemptions in 10 CFR 71.15 and fissile material general 

licenses in 10 CFR 71.22 and 71.23 is to facilitate the safe transport of low-risk (e.g., small 

quantities or low concentrations) fissile material by exempting shipments of these materials from 

the packaging requirements and the criticality safety assessments required for fissile material 

transportation, and to allow the shipments to take place without specific Commission approval. 

The lower amount of regulatory oversight is acceptable for these shipments because the 

exemptions are established to ensure safety under all credible transportation conditions. 

The exemption criteria in 10 CFR 71.15 provide criteria for the fissile material type, quantity, form, 

moderation, and mass concentration deemed adequate to ensure that there are no credible

means to achieve a critical condition for a package or accumulation of packages under normal 

conditions of transport or hypothetical accident conditions. The type and quantity of fissile material 

(e.g., 235U or 239Pu) are important because the mass required to achieve a critical condition (i.e., 

the critical mass) varies as a function of fissile nuclide. The critical mass for a fissile material can 

vary significantly when the fissile material is mixed with other types of material. Materials with a 

significant concentration of hydrogen or other moderating material (e.g., water, polyethylene) can 

thermalize neutrons in the system and significantly reduce the mass of fissile material necessary 

for criticality. Thus, the exemption criteria in 10 CFR 71.15 were established considering the 

potential for water to be present to an optimal extent; however, other moderators are also 

considered and limited as appropriate. 

The general license criteria in 10 CFR 71.22 (fissile material) and 71.23 (Pu-Be special form 

material) are intended for the shipment of small quantities of fissile material per package with 

accumulation control provided by an assigned criticality safety index (CSI) for each package. 

However, the general license provision requires that the fissile material be contained in a Type A 

package that meets U.S. Department of Transportation (DOT) requirements of 

49 CFR 173.417(a)1 applicable for “Authorized Fissile Material Packages,” to ensure the package 

withstands normal conditions of transport without dispersing fissile material.

2.1 Parameters Controlling Criticality Safety

Nuclear Criticality Safety is defined as the “Protection against the consequences of a criticality 

accident, preferably by prevention of the accident” (Ref. 3). Ensuring criticality safety can be a 

complex process because it depends upon the direct or indirect control of many nuclear 

parameters2

. The regulatory exemptions and general licenses for transport of fissile material 

establish criteria that, if followed, ensure that a package containing fissile radionuclides mixed with 

any type of material is incapable of inadvertent criticality during normal conditions of transport or 

hypothetical accident conditions. The NRC does not certify package designs or review shipments 

made in accordance with the criteria specified in 10 CFR 71 for exemption from fissile material 

classification or fissile material general licenses. To ensure that a transportation package 

1 This section of 49 CFR 173.417(a) provides the packaging requirements for fissile materials (less than A1 or A2

quantities). 

2 The nuclear parameters of interest to nuclear criticality safety are fissile mass, neutron absorption, fissile material 

geometry, and interaction between fissile material units, fissile concentration, neutron moderation, fissile nuclide 

enrichment, neutron reflection, and fissile material volume.
4 

containing fissile nuclides is incapable of inadvertent criticality (i.e., the package is subcritical3

), 

criteria for the principal parameters of concern to nuclear criticality safety must be specified. 

These parameters of concern are: (Ref. 4)

• Type, mass, and form of the fissile material;

• Moderator-to-fissile material ratio (degree of moderation);

• Amount and distribution of moderator and absorber materials;

• Package geometry – internal and external; and

• Reflector effectiveness.

Since the 10 CFR 71 exemptions and general licenses for fissile material do not require a 

criticality safety evaluation for the actual packaging that is used for transport, the content 

configuration that might be held in place by the packaging cannot be relied on for criticality safety 

control. The specification within the general licenses for use of a Type A package does provide 

assurance that the package geometry should remain intact during normal conditions of transport. 

However, in general, to establish the criteria for the exemptions and general licenses, the

parameters of concern for criticality safety were considered within the context of the hypothetical 

accident conditions of 10 CFR 71 and the ability of the consignor to confirm the contents of the 

package. The consignor should have knowledge of, or control over, the type, form, and mass of 

the fissile material; thus the specifications for these parameters were selected such that, when 

optimally configured and moderated, the package would remain in a subcritical condition at all 

times by assuming the worst-case abnormal conditions to account for any package alterations 

during shipment.

2.2 Packages Certified to Transport Fissile Material

Packages certified to transport fissile material are subject to rigorous criteria to ensure safety 

during transportation operations. Unless packages containing fissile material meet the exemption 

criteria in Part 71, Subpart B, “Exemptions,” or Part 71, Subpart C, “General Licenses,” they are 

subject to the requirements of Part 71, Subpart D, “Application for Package Approval,” which 

requires applicants to provide a thorough package description (10 CFR 71.33), safety evaluation 

(10 CFR 71.35), and description of the applicant’s quality assurance program (10 CFR 71.37). 

The packaging evaluation required by 10 CFR 71.35 includes provisions for the general 

requirements for individual packages containing fissile material and standards for arrays of such 

packages. These requirements are meant to ensure both individual packages and arrays of 

packages containing fissile material will be subcritical if subjected to normal conditions of transport 

and hypothetical accident conditions. Package accumulation on a conveyance is controlled by the 

CSI, which is defined in the regulations by 10 CFR 71.59(a) such that 2N packages will remain 

subcritical under hypothetical accident conditions and 5N packages will remain subcritical under 

normal conditions of transport. The number 50 divided by the limiting (lowest) N from the normal 

conditions of transport and hypothetical accident conditions array evaluations, rounded up to the 

 

3 A fissionable material system is considered to be subcritical if the system effective neutron multiplication factor, keff, is less 

than one. Ref. 3 defines the effective multiplication factor as the ratio of the total number of neutrons produced during a 

time interval to the total number of neutrons lost by absorption and leakage during the same time interval. This definition 

excludes neutrons produced by sources whose strengths are not a function of the fission rate.
5 

nearest tenth, is the CSI. The CSI limit on a conveyance is 50 for shipment under nonexclusive 

use, and 100 for an exclusive-use shipment.

As discussed in the introduction to 10 CFR 71.15, fissile material meeting the criteria in

10 CFR 71.15 are exempt from the classification as fissile material and from the rigorous

packaging standards in 10 CFR 71.55 and 71.59.

2.3 Exemptions from Classification as Fissile Material

The criteria for exemption from classification as fissile material are designed to maintain the fissile 

concentration, fissile mass, and/or fissile enrichment sufficiently low that accidental criticality is not

credible under normal conditions of transport or hypothetical accident conditions, as defined in 

10 CFR 71. Under normal conditions of transport, a single package could easily be shown to 

remain subcritical; however, the fissile exemptions also consider the accumulation of fissile mass

as a result of the commingling of multiple packages. Thus, the fissile mass or mass concentration 

must be sufficiently low, based on conservative assumptions, to assure a subcritical arrangement

for transport of individual or multiple packages. The exemption criteria are based on worst-case or

optimal conditions, including: unlimited accumulation; optimum moderation by water; presence of

low-neutron-absorbing moderators such as beryllium, graphite, or hydrogenous material enriched 

in deuterium; spherical geometry; and pure fissile content (i.e., 239Pu, 241Pu, 235U, or

233U, without

nonfissile uranium and plutonium nuclides). The bases for each of the exemption criteria will be

discussed later in this report. The exemption criteria also consider the rearrangement or

reconfiguration of fissile material during transport to ensure that all realistic and foreseen 

arrangements will remain in a subcritical state during the transport operations. The exemption 

criteria in 10 CFR 71.15 do not take credit for packaging materials or packing geometry since 

there are no packaging requirements listed with the provisions. Thus, reconfiguration of the 

contents during hypothetical accident conditions must be considered. The technical bases for the 

criteria to exempt material from classification as fissile material assumes limited preferential fissile 

material redistribution based on a risk-based assessment of normal conditions of transport and

hypothetical accident conditions.

2.4 General License Criteria 

A general license for fissile material applies to the shipment of a Type A quantity4 of radioactive 

material in a Type A package or fissile material in the form of plutonium-beryllium (Pu-Be) special

form sealed sources. The quantity of fissile material (235U, 233U, 239Pu and 241Pu) and moderating

materials, such as beryllium, graphite, or hydrogenous material enriched in deuterium is limited.

The quantity of fissile material in sealed special form5 source capsules (239Pu and 241Pu) is also 

limited to preclude criticality. A Type A package is required to prevent the loss or dispersal of the 

radioactive contents and to maintain its shielding properties for all normal conditions of 

4 Per the provisions in 10 CFR §71.4, “Definitions,” a Type A quantity means a quantity of radioactive material, the 

aggregate radioactivity of which does not exceed the A1 quantity for special form radioactive material, or A2, for normal 

form radioactive material, where A1 and A2 are given in Table A-1 of this part, or may be determined by procedures 

described in Appendix A to Part 71. A Type A package is assumed to meet normal conditions of transport as prescribed 

in 10 CFR 71. 

5 See 10 CFR 71.4, “Definitions,” for the definition of special form radioactive material.
6 

1. Changing climate conditions: humidity, temperature, pressure, solar heating, and

precipitation.

2. Dynamic and static mechanical effects: limited shock, repeated bumping, and vibration.

3. Compressive forces due to stacking or load movement.

The provisions in the general license criteria ensure that the fissile material configuration (fissile 

material mass mixed with other materials or Pu-Be sealed sources) present in a shipment will

remain below the mass needed to achieve criticality for water-reflected, water-moderated 

systems. The quantity of fissile material in a single package is limited to a CSI of 10 for the 

general license in 10 CFR 71.22. Packages containing Pu-Be special form material under the

general license of 10 CFR 71.23 are allowed to have a maximum CSI of 100. For the shipment of

multiple packages on a nonexclusive use conveyance, the CSI may be < 50. For the shipment of

multiple packages on an exclusive use conveyance, the CSI must be < 100, because more control

is required during the shipping process.

2.5 Packaging Requirements for Exemptions and General Licenses

The provisions of 10 CFR 71.15 provide exemptions from classification as fissile material and

eliminate the need for the fissile material to be shipped in packages subject to the provisions of

10 CFR 71.55, “General Requirements for Fissile Material Packages,” and 71.59, “Standards for

Arrays of Fissile Material Packages.” Radioactive material exempted from classification as fissile

material must, however, still meet the same requirements as nonfissile radioactive material. The 

packaging chosen for material exempted from fissile material classification must be consistent

with the type and amount of radioactive material present. The requirements in 10 CFR 71.15(a)–

(d) and (f), provide no specific packaging provisions. Uranyl nitrate solution shipped under

10 CFR 71.15(e) requires the liquid to be contained in at least a DOT Type A package.

The exemption in 10 CFR 71.15(a) requires that the mass of fissile material be limited to ≤2 g in

an individual package. There are no packaging requirements as long as the quantity of fissile 

material present does not exceed the radionuclide exemption values in Table A–2, “Exempt

Material Activity Concentrations and Exempt Consignment Activity Limits for Radionuclides.” If

the exemption values are exceeded for a particular radionuclide, a Type A package meeting the

DOT requirements of 49 CFR 173.417(a)6 would have to be used. A Type B package would be 

required if the fissile material or nonfissile radioactivity exceeds the A1 or A2 values. For

example, there are no packaging requirements for

235U with up to 2 g per package because the

A1 and A2 values are unlimited, whereas a Type B package would be required for shipping more 

than 0.435 g of 239Pu or 0.016 g of 241Pu because the Type A quantity limit has been exceeded 

(Ref. 6). The provisions in 10 CFR 71.15(b) and (c) are similar in that packaging requirements

are dictated by the total amount of fissile and nonfissile radioactive material in the package.

However, those provisions also contain limitations on lead, beryllium, graphite and hydrogenous

materials enriched in deuterium. 

6 49 CFR 173.417, titled, “Authorized Fissile Material Packages,” provides the packaging requirements for fissile material 

containing less than A1 or A2 quantities. 

transportation. As discussed in Ref. 5, a Type A package must withstand normal conditions of 

transport including: 
7 

For 10 CFR 71.15(e), the regulation states that liquid solutions of uranyl nitrate solutions must 

be contained within a DOT Type A package that meets the Type A standards in 71.43, “General 

Standards for All Packages.” This requirement was established to ensure the liquid solutions 

present in the package were protected from any adverse conditions that could affect nuclear 

criticality safety during transport operations (e.g., redistribution, dilution, low temperatures that 

could affect fissile concentration, or collection into an unfavorable geometry). The exemption 

provisions in 10 CFR 71.15(f) provide exemption limits for plutonium isotopes (e.g., total Pu 

mass less than 1000 g with less than 20% by mass being 239Pu or 241Pu). This provision allows 

a variety of nonfissile Pu isotopes (e.g., 238Pu heat sources) to be shipped without packaging 

requirements or criticality safety assessment. It is recognized that Pu quantities shipped under 

this exemption will likely exceed a Type A quantity and require shipment in a Type B package. 

The provisions of 10 CFR 71.22 and 71.23 both require the use of Type A packages. The fissile 

material is not required to be packaged in a container that meets the requirements of 10 CFR 71 

Subpart E and F. A Type A package must meet the DOT requirements of 49 CFR 173.417(a) 

and cannot contain more than a Type A quantity of nonfissile radioactive material based on the 

A1 and A2 values in Table A-1 of Part 71. Quantities of radioactive material greater than a Type 

A quantity will require a certified Type B package and cannot be shipped under a general 

license. Any Type A package required to ship fissile material with a general license must be 

able to withstand testing consistent with the normal conditions of transport such as a water 

spray test, 4 ft drop test, penetration test, and stacking test. Documentation of the package’s 

ability to withstand these conditions must be maintained to meet the requirements of 49 CFR 

173.415. The use of a Type A package for the general license provisions represents more 

control over the shipment than is typically required for the exemptions from classification as 

fissile material, and, thus, allows for somewhat higher fissile mass limits to be shipped with little 

or no NRC oversight.

9 

3 RECENT HISTORY OF REGULATORY DEVELOPMENT 

Since the inception of 10 CFR 71, provisions were included to allow exemption from classification 

as fissile material and fissile material general licenses. Prior to 1997, the following six exemptions 

from classification as fissile material were contained in 10 CFR 71.53: 

• packages with 15 g or less of fissile material;

• select homogeneous hydrogenous solutions or mixtures of fissile material with limits

specified on combinations of mass, 235U enrichment, hydrogen content, and/or solution

concentration;

• packages that can be demonstrated to have less than 5 g of fissile material in any 10 L

volume;

• packages containing uranium enriched in 235U to a maximum of 1 wt %;

• packages containing liquid solutions of uranyl nitrate enriched in uranium to a maximum of

2 wt % 235U; and

• packages with less than 1 kg of plutonium if the combined mass of

239Pu and 241Pu is less

than 20% of the total plutonium mass.

As will be discussed further in this report, the last three exemptions cited above are largely 

retained in the current provisions of 10 CFR 71.15(d), 10 CFR 71.15(e), and 10 CFR 71.15(f). The 

criteria for the first exemption were originally justified based on a maximum shipment of 250 

packages, with minimal consideration of hypothetical accident conditions. Criteria for the next two 

exemptions were specified with parameter values that ensured subcriticality under controlled 

conditions, but there was little consideration regarding how normal conditions of transport or 

hypothetical accident conditions might impact the as-loaded parameter values. These concerns, 

together with concerns regarding low neutron absorbing moderators, created extensive discussion 

at the IAEA in the decade prior to the issuance of the 1996 edition of the IAEA Regulations in 

which revisions to the exemptions were made to address the concerns.

The general licenses for fissile material prior to 1997 existed as four separate provisions: 

(1) limited quantity per package; (2) limited moderator per package; (3) limited quantity, controlled

shipment; and (4) limited moderator, controlled shipment. Both the general license provisions and

the exemptions from classification as fissile material have been significantly revised since the

10 CFR 71 versions that existed prior to 1997.The details of these revisions will be discussed in

the following sections.

3.1 1997 NRC Emergency Rulemaking

In September 1996, the NRC was notified by one of its licensees about use of the volume-based 

concentration criteria within the fissile material exemption provided at the time as 

10 CFR 71.53(d). This provision exempted the material from classification as fissile material 

provided there were less than 5 g of fissile radionuclides in a 10 L volume and the material was 

packaged such that this concentration was maintained during normal conditions of transport (Ref.

7). The licensee was planning to ship significant quantities of material containing enriched 

uranium and beryllium oxide (uranium-beryllium filter cake) that was the waste product of a 

process involving highly enriched uranium materials. Based on licensee calculations, (Ref. 8) the 

potential for criticality in a large volume system (e.g., greater than 2000 L) could be realized even 

with adherence to the volume concentration limits specified for exemption in 10 CFR 71.53(d). 

This potential for criticality was possible because the exemption limits at the time assumed that 

water is the most limiting moderator and reflector material that can be credibly present in a 
10

package. Although hydrogen, which is abundant in water, is the optimal moderator to obtain the 

minimum fissile mass that can achieve criticality, other moderators with absorption cross-sections 

smaller than hydrogen enable criticality with a lower mass concentration than that provided by 

hydrogen. Thus, the fissile mass to achieve criticality would be higher in a beryllium-moderated

system than in a hydrogen-moderated system. However, if the beryllium-moderated system is 

large enough, a critical configuration can be achieved with a fissile-to-moderator concentration 

that is lower than that for a hydrogen-moderated system. 

As determined by the licensee and by Oak Ridge National Laboratory (ORNL), (Ref. 4) other lowneutron-absorbing moderator materials such as beryllium, graphite, and heavy water (D2O) could 

be present in transportation packages, but their presence is expected to be far less frequent than 

water or other materials commonly used in the nuclear industry or found in the environment. 

Based on licensee calculations, the NRC declared 10 CFR 71.53 deficient (Ref. 9) and decided 

that the regulations should be changed to ensure that materials that have neutron absorption 

cross-sections less than that of water (e.g., beryllium, graphite and heavy water) were sufficiently 

limited to ensure subcriticality even for large volume systems. 

Also, the fissile material exemptions that existed at the time in 10 CFR 71.53 provided limits on 

the quantity of fissile materials that could be shipped in individual packages; however, the 

regulations did not limit the total amount of fissile material in a consignment or on a conveyance. 

There was a recognized concern for criticality safety given the possibility for accumulation of large 

numbers of packages in a consignment, even though the single package limits might be 

compliant. 

To address the concerns with (a) low neutron absorbing moderators, (b) moderators with 

hydrogen densities greater than water, and (c) uncontrolled mass accumulation, the NRC issued 

an emergency rulemaking in 1997 to revise 10 CFR 71 to be consistent with the fissile exception1

criteria developed by the IAEA (Ref. 10). This revision to 10 CFR 71 limited the quantity of 

beryllium, hydrogenous material enriched in deuterium, and graphite2 that could be present in 

packages that were to be shipped under a general license or handled as exempt from certification 

by the NRC to contain fissile material. The revised regulations allowed use of the exemptions or 

general licenses only when these moderating materials were not present in quantities exceeding 

0.1 percent of the fissile material mass (Ref. 11). In Ref. 10, accumulation of packages classified 

as exempt was addressed by providing limits on the fissile mass in a consignment and providing 

additional (lower) limits for systems where moderators with hydrogen density greater than water 

might exist. These limits on the fissile mass in a consignment were assumed by the IAEA to 

provide a conservative level of control from a criticality safety perspective during transportation. 

3.2 Issuance of NUREG/CR-5342 (1998)

The emergency rule issued by the NRC in 1997 resulted in numerous public concerns and 

comments because the rule was initially issued without a public comment period. Based on these 

issues and NRC staff concerns regarding potential deficiencies and inconsistencies in the 

regulations, the NRC decided to further assess the 10 CFR 71 provisions related to exemptions 

1 The IAEA uses the phrase “fissile material exception” in SSR-6 whereas the United States uses the phrase “fissile 

material exemption” in 10 CFR 71. 

2 Graphite has not been listed as a special moderator in IAEA SSR-6.
11

and general licenses for fissile material (Ref. 4). The NRC requested that ORNL assess the 1997 

revision of 10 CFR 71 with the following objectives in mind:

1. Document perceived deficiencies in the technical or licensing bases that might be averse

to maintaining adequate subcriticality under normal conditions of transport and

hypothetical accident conditions;

2. Identify areas where regulatory wording could cause confusion among licensees and

potentially lead to subsequent safety concerns;

3. Study and identify the practical aspects of transportation or licensing that could mitigate,

justify, or provide a historical basis for any identified potential deficiencies; and

4. Develop recommendations for revising the current regulations to minimize operational and

economic impacts on licensees while maintaining safe practices and correcting identified

deficiencies.

The assessment details and resulting recommendations can be found in Ref. 4. This report 

concluded that there were “no significant or immediate criticality safety hazards associated with 

the practical applications of the general licenses and exemptions. The reason for this conclusion 

is that the typical qualifying fissile material matrix in a general license or exempt consignment is 

relatively stable as a dry activated waste or in a nearly noncombustible form”. The report also 

noted that the consignment mass limits provided for the fissile material exemptions enhance the 

safety margin. However, the report concluded that consignors could misinterpret the fissile 

material exemption and general license requirements in the 1997 version of 10 CFR 71 and that 

the requirements could be applied inconsistently based on this misinterpretation. For example, 

limiting the fissile mass in a consignment did not appear to be effective considering some 

consignor’s misinterpretation of the regulations as only administrative requirements, maintaining 

the consignment mass limit but accumulating multiple consignments on a conveyance (Ref. 3). 

Further, the report provided recommendations aimed at clarifying and simplifying the regulations 

and enhancing the flexibility of use (e.g., suggestions that would allow removal of the consignment 

limit for certain exemptions) while still maintaining assurance of criticality safety (Ref. 4). The NRC 

considered the ORNL recommendations (Ref. 4) in the proposed revision to 10 CFR 71 issued in 

2002 (Ref. 12). The NRC allowed opportunities for the public to provide comments (Refs. 13-15) 

prior to the issuance of a final 10 CFR 71 rule that was effective in October 2004.

3.3 10 CFR 71 Final Rule (2004)

The final rule for a revision to 10 CFR 71 was effective on October 1, 2004 (Ref. 16). This rule 

revised the regulations to be generally more consistent with the 1996 revision of the IAEA 

regulations for the safe transport of radioactive material (Ref. 17). However, the exemptions from 

classification of fissile material are different than those found in Ref. 17. The final rule also 

considered changes in the exemption criteria for fissile material as a result of public comments 

that indicated some changes made during the 1997 emergency rulemaking were an economic 

burden for licensees with no gain in safety benefit. The intention behind the revised criteria was 

that they be practical for consignors to evaluate and be straightforward to implement. The criteria

were subject to a public comment period during the rulemaking process. 

3.3.1 Exemptions from Classification as Fissile Material

The existing six exemptions for fissile material were re-designated in the 2004 rulemaking as 

10 CFR 71.15, “Exemption from classification as fissile material,” under Subpart B, “Exemptions.” 

Criteria for three new exemptions were included in this revision: (a) 2 g of fissile material per 
12

package; (b) 15 g of fissile material with a mass ratio of nonfissile to fissile material of 200:1; and 

(c) fissile material with a mass ratio of nonfissile to fissile material of 2000:1, with a requirement 

that there may be no more than 180 g of fissile material distributed within any 360 kg of 

contiguous nonfissile material. These new provisions allowed for the presence of lead, beryllium, 

graphite, and hydrogenous material enriched in deuterium, provided these materials are not 

designated as solid nonfissile material mass for ratio determination. The exemption for 235U 

enriched up to 1 wt % was modified to replace the requirement for limiting heterogeneity and 

lattice arrangement within the package with a restriction on the quantities of beryllium, graphite, 

hydrogenous material enriched in deuterium of less than 5% of the uranium mass. The exemption 

for liquid solutions of uranyl nitrate was modified with the 2004 rulemaking to require the material 

be present in at least a DOT Type A package. Finally, the exemption for plutonium, 10 CFR 

71.15(f) (previously 10 CFR 71.53[e]), was modified slightly to note that the requirement is 

applicable to individual packages only. Exemptions that set criteria based on mass per unit 

volume had been used in previous versions of 10 CFR 71 but were removed from 10 CFR 71 

based on the recommendations in Ref. 4. 

3.3.2 General Licenses for Fissile Material

In the 2004 rulemaking, the previous general license requirements from 10 CFR 71.18, “General 

license: Fissile material, limited quantity per package,” 10 CFR 71.20, “General license: Fissile 

material, limited moderator per package,” 10 CFR 71.22, “General license: Fissile material, limited 

quantity, controlled shipment,” and 10 CFR 71.24, “General license: Fissile material, limited 

moderator, controlled shipment,” were simplified and combined under a single section, 

10 CFR 71.22, “General license: Fissile Material.” This section contains a formula to determine 

the CSI for each package based on the fissile material mass in the package. The CSI is limited to 

10 for any individual package, and the CSI formula is constructed to ensure that the fissile 

material mass on any conveyance is no more than half of the safe subcritical mass limit for a 

nonexclusive use shipment. 

This revised general license for fissile material includes a new requirement, 10 CFR 71.22(a), that 

directs licensees to ship fissile material under a general license in a Type A package to ensure the 

requirements of 49 CFR 173.417(a) are met. Prior versions of the regulations required only that the 

package contents are limited to no more than a Type A quantity of radioactive material, and did not 

contain packaging requirements. The revised regulation in 10 CFR 71.22(b) states that the general 

license provisions only apply to those licensees that have an NRC-approved quality assurance 

program that satisfies the requirements of 10 CFR 71, Subpart H, “Quality Assurance.” The general 

license criteria under 10 CFR 71.22(c)(1) and (c)(2) limit the package contents to no more than a 

Type A quantity of radioactive material and less than 500 total grams of beryllium, graphite, or 

hydrogenous materials enriched in deuterium. These criteria for beryllium, graphite, and deuteriumbased materials replace the earlier provision to limit them to 0.1% of the fissile material mass and 

should be more convenient from a licensee compliance perspective because the content quantities 

(e.g., fissile material and moderating material mass) are generally easier to determine.

The revised general license criteria under 10 CFR 71.22(d) provide the requirements for 

calculating the CSI of a package and limit the CSI for a shipment depending on whether the 

conveyance is exclusive use (CSI ≤ 100) or nonexclusive use (CSI ≤ 50). The CSI is calculated 

with the formula provided in 10 CFR 71.22(e)(1) along with the appropriate fissile material mass 

limits listed in Tables 71–1 and 71–2. Table 71–1 is a listing of mass limits for general license 

packages containing mixed quantities of fissile material (235U, 233U, 239Pu, and 241Pu) or 235U of 

unknown enrichment. The table provides separate mass limits for packages that might have fissile 

material mixed with moderating substances with hydrogen densities that are greater than that of 
13

water. Table 71–2 is a listing of mass limits for general license packages containing 235U of known 

enrichment, up to 24 wt %.

3.3.3 Plutonium-Beryllium Special Form Material General Licenses

A new provision was added to the 2004 revision of 10 CFR 71 for the shipment of Pu-Be specialform fissile material. This new provision consolidates general license provisions on the shipment 

of Pu-Be special form sources as contained in various portions (i.e., 10 CFR 71.18 and 

10 CFR 71.22) of the earlier regulations. The new provisions in 10 CFR 71.23 reduce the 

maximum quantity of fissile Pu-Be special form sources that can be shipped on a single 

conveyance through changes in the mass limits and calculation of the CSI (Ref. 15). As is the 

case for the fissile material general licenses, the revised regulations in 10 CFR 71.23 require 

licensees to have an NRC-approved quality assurance program that satisfies the requirements of 

10 CFR 71, Subpart H, “Quality Assurance.” The Pu-Be special form sources must be contained 

within a Type A package that meets the requirements of 49 CFR 173.417(a). These provisions 

require the package to contain no more than a Type A quantity of fissile material and less than 

1000 g of plutonium provided that 239Pu, 241Pu or any combination of these radionuclides 

constitutes less than 240 g of the total quantity of plutonium in the package. This general license 

applies to a package that is labeled with a CSI calculated using the formula of 10 CFR 71.23(e). 

The total CSI must be less than or equal to 50 for a non-exclusive use conveyance and less than 

or equal to 100 for an exclusive use conveyance. 

3.4 10 CFR 71 Final Rule (2015)

The 2004 rulemaking described above changed the provisions of 10 CFR 71.15(d) to remove the 

restriction that uranium enriched to 1 wt % or less in 235U must be distributed homogeneously and 

not form a lattice arrangement within the package. The terms homogeneity and lattice 

arrangement were not clearly defined, and a restriction on beryllium, graphite, and hydrogenous 

material enriched in deuterium would be sufficient to prevent criticality in all but a very large 

system that includes a repeating array of low-enriched uranium particles. These large systems 

were judged to be impractical for transport scenarios.

Subsequent to the 2004 rulemaking, DOE identified a planned shipment of large quantities of lowenriched fissile material that would qualify for the exemption at 10 CFR 71.15(d). Analyses 

performed by DOE indicated that large arrays (i.e., multiple conveyances) of heterogeneous 

uranium with enrichment of one percent by weight of 235U could exceed an effective multiplication 

factor (Ref. 3), keff, of 0.95 when optimally moderated by water. Because such a shipment, as 

analyzed, could both qualify for the fissile material exemption for low-enriched uranium and have a 

keff greater than 0.95, the NRC decided that additional restrictions on low-enriched fissile material 

shipped under the fissile material exemption at 10 CFR 71.15(d) were warranted to provide similar 

safety equivalence provided by certified packages per the criteria of 10 CFR 71.55 and 71.59.

The NRC has restored former lattice arrangement and homogeneous distribution provisions in the 

revised 10 CFR 71.15(d) exemption requirement (Ref. 18). The revised provision excludes from 

the exemption’s scope situations where fissile “lumps” or lattice arrangements of fissile material 

are present within the package. The 10 CFR 71.15(d) exemption language continues to exclude 

large quantities (less than 5% of the uranium mass) of low-absorbing moderators (beryllium, 

graphite, or hydrogenous material enriched in deuterium). These restrictions will preclude fissile 

material arrangements in packages that can potentially result in criticality at 235U enrichments less 

than 1 wt %.

15

4 INTENT AND TECHNICAL BASIS

The exemptions from classification as fissile material and general licenses for fissile material and

plutonium-beryllium special form sources are provided in the regulations without specifying the 

intent of the provision or the technical bases for the limitations in the provisions (e.g., fissionable 

material mass limits). The following sections provide this information to assist end users in 

effectively applying the fissile exemption and general license provisions.

4.1 Exemptions from Classification as Fissile Material

Fissile material is defined in 10 CFR 71.4 as the radionuclides 233U, 235U, 239Pu, and 241Pu, and

refers to the nuclides themselves, not material containing these nuclides. Unirradiated natural

uranium and depleted uranium, and natural uranium or depleted uranium that has been irradiated 

in thermal reactors only, are not included in this definition. Material that meets the definition of

fissile material but that also meets one of the six exemption criteria in 10 CFR 71.15 can be 

transported in packages that do not meet the fissile material transportation requirements of

10 CFR 71.55 or 71.59 for packages certified to contain fissile material. For purposes of ensuring

criticality safety, the exemptions consider that the material can be released from any packaging 

during transport, may reconfigure into a worst-case geometric arrangement, may combine with 

material from other transport vehicles, and may be subject to the fire and water immersion 

conditions assumed as part of the criticality safety assessment for package designs approved to 

transport fissile material. The exemptions are subject to all other requirements of 10 CFR 71

except as noted in the exemption criteria. 

Table 1 Content in 10 CFR 71.15 “Exemption from the Classification as Fissile Material” 

10 CFR 71.15 Exemption from Classification as Fissile Material

Fissile material meeting the requirements of at least one of the paragraphs (a) through (f) of this section are exempt 

from classification as fissile material and from the fissile material package standards of §§71.55 and 71.59, but are 

subject to all other requirements of this part, except as noted.

(a) Individual package containing 2 grams or less fissile material.

(b) Individual or bulk packaging containing 15 grams or less of fissile material provided the package has at

least 200 grams of solid nonfissile material for every gram of fissile material. Lead, beryllium, graphite, and

hydrogenous material enriched in deuterium may be present in the package but must not be included in

determining the required mass for solid nonfissile material.

(c)(1) Low concentrations of solid fissile material commingled with solid nonfissile material, provided that:

(i) There is at least 2000 grams of solid nonfissile material for every gram of fissile material, and

(ii) There is no more than 180 grams of fissile material distributed within 360 kg of contiguous

nonfissile material.

(c)(2) Lead, beryllium, graphite, and hydrogenous material enriched in deuterium may be present in the 

package but must not be included in determining the required mass of solid nonfissile material.

(d) Uranium enriched in uranium-235 to a maximum of 1 percent by weight, and with total plutonium and

uranium-233 content of up to 1 percent of the mass of uranium-235, provided that the mass of any beryllium,

graphite, and hydrogenous material enriched in deuterium constitutes less than 5 percent of the uranium

mass, and that the fissile material is distributed homogeneously and does not form a lattice arrangement

within the package.
16

(e) Liquid solutions of uranyl nitrate enriched in uranium-235 to a maximum of 2 percent by mass, with a total 

plutonium and uranium-233 content not exceeding 0.002 percent of the mass of uranium, and with a 

minimum nitrogen to uranium atomic ratio (N/U) of 2. The material must be contained in at least a DOT 

Type A package.

(f) Packages containing, individually, a total plutonium mass of not more than 1000 grams, of which not more 

than 20 percent by mass may consist of plutonium-239, plutonium-241, or any combination of these 

radionuclides.

The provisions for the exemption from classification as fissile material are currently present in the 

Code of Federal Regulations in two locations: 10 CFR 71.15 and 49 CFR 173.453. The intent and 

content of these regulations are identical. The current exemptions as taken from 10 CFR 71.15 

are listed in Table 1. 

The intent of including exemptions from classification as fissile material in the regulations is to 

reduce the burden and cost imposed for packages that contain quantities and concentrations of 

fissile material that are low risk in terms of potential for inadvertent criticality in transport. These 

packages can be shipped without a packaging assessment for criticality safety purposes and 

require little or no regulatory oversight. The exemption criteria in 10 CFR 71.15 provide limits on 

the fissile material type, quantity, form, moderation, and mass concentration under which there 

are no credible means to achieve a critical condition under normal conditions of transport or 

hypothetical accident conditions. Thus, the fissile exemption criteria in 10 CFR 71.15 limit the 

quantity of fissile material in a package while considering the presence of potential moderators. 

4.1.1 10 CFR 71.15(a): Individual Package Containing 2 g or Less Fissile Material

71.15(a) – Individual package containing 2 grams or less fissile material.

Exempting a small fissile material mass from classification as fissile material removes extensive 

regulatory and economic burden on what the NRC rulemaking process has deemed to be a low 

risk transportation activity. During the comment period after the NRC emergency rule was issued 

in 1997, there were nuclear industry concerns that, without a small mass exemption (there has 

previously been an exemption for 15 g of fissile material per package with no accumulation 

control), there would be a significant impact on commerce with respect to frequent shipments of 

very small quantities of fissile material such as environmental samples (Ref. 15). Individual 

packages containing less than 2 g of 233U, 235U, 239Pu, or 241Pu contain such a low quantity of 

fissile materials that the risk of accumulating the number and type of packages needed to present 

a potential criticality hazard was judged to be inconsequential (Refs. 15 and 16). 

Stated in Ref. 6, the intent of 10 CFR 71.15(a) is to limit a single package within a consignment to 

a de minimis value of two total grams of 233U, 235U, 239Pu, or 241Pu. This exemption does not limit 

the accumulation of 2 g packages because it was judged that shipment in sufficient numbers to 

pose a potential for criticality would be incredible based on practical and economic considerations. 

Unlimited quantities of 235U samples could be shipped without any package requirements as a 

result of the A1 and A2 values being unlimited (10 CFR 71, Table A-1). For other fissile nuclides, 

the samples would have to be shipped in a Type A package if the quantities of radioactive 

material exceed the exempted quantities. Furthermore, a Type B package is required if the 

quantity of radioactive material present exceeds the A1 or A2 values shown in Table A-1 (e.g., 

>0.435 g for 239Pu or >0.016 g for 241Pu for normal form material). 
17

The accumulation of a large number of these packages for this exemption does not appear to be 

credible, based on the number and volume of packages required to approach criticality. Ref. 15

discusses a series of calculations performed to determine the number of 1 L containers containing 

2 g of fissile material required to achieve criticality under optimal conditions [i.e., pure 235U (fully 

enriched uranium)], optimum moderation, optimum geometry (spherical units/cubic array), and full 

water reflected array. No packaging material is credited in these calculations. A cubic array of 

84,853 1 L packages was required at near-optimal moderation (hydrogen-to-uranium ratio of 

approximately 1200) for criticality to be possible. The size of the array in the calculation model 

was roughly 4.4 m (>14 ft) on a side. The results of these calculations demonstrate that it would 

be impractical or uneconomical to accumulate such a large number of such packages, especially 

considering that under realistic conditions (e.g., neutron absorption by package material and 

nonfissile uranium isotopes) a critical array would be much larger. Thus, the 2 g limit was added to 

the final rule issued in 2004. 

4.1.2 10 CFR 71.15(b): Package Containing 15 g or Less Fissile Material 

71.15(b) – Individual or bulk packaging containing 15 grams or less of fissile material 

provided the package has at least 200 grams of solid nonfissile material for every gram of 

fissile material. Lead, beryllium, graphite, and hydrogenous material enriched in deuterium 

may be present in the package but must not be included in determining the required mass 

for solid nonfissile material. 

The intent of this fissile material exemption is to allow up to 15 g of fissile material in a package 

that has at least 200 g of solid nonfissile material present per gram of fissile material. The 

distribution of small quantities of fissile material in a matrix of nonfissile material will ensure that 

accidental criticality is precluded. According to Ref. 16, the nonfissile mass can include the 

packaging mass. Common nonfissile materials include concrete, aluminum, steel, and other 

packaging or waste materials. Lead, beryllium, graphite and hydrogenous materials enriched in 

deuterium may be present, but cannot be counted as nonfissile material in complying with the 

1:200 mass ratio. The exemption was designed to allow industry to continue to use the 15 g limit 

historically used in the exemptions while addressing concerns related to package accumulation 

and low-absorbing non-hydrogenous moderators. 

This exemption requirement would allow for consignors to prepare a package to ship small 

quantities of fissile material in such a way that nuclear criticality safety concerns related to the 

accumulation of a large number of fissile material packages are precluded. Consignors can meet 

this exemption requirement based on using the mass quantities of fissile and solid nonfissile 

materials present to prepare packages instead of using volume-based concentration limits that are 

difficult to verify. The ratio of 200 g of nonfissile material (excluding select moderating and 

reflecting materials) for every gram of fissile material is judged to provide adequate assurance that 

the accumulation of large numbers of packages will remain subcritical. The reduction in density 

significantly increases the minimum critical mass and eliminating nonfissile mass credit for 

moderating or reflecting materials – lead, beryllium, graphite, and hydrogenous materials enriched 

in deuterium – will prevent critical concentrations of fissile material. The quantity of these nonhydrogenous moderating and reflector materials cannot be included in the nonfissile material 

quantity, although they can be present in the package. The mass of lead is also not allowed to be 

credited as a nonfissile material in the package because, as an abundant and high-density 

(11.4 g/cm3

) material with an extremely low neutron absorption cross section, the presence of lead 

may not provide sufficient dilution and density reduction if a large number of packages are 

accumulated. 
18

Ref. 16 states that many other nonfissile materials such as iron, generic steels, and concretes 

have sufficient neutron absorption for them to be considered as the nonfissile mass to mix with up 

to 15 grams of fissile material, in a mass ratio of at least 200:1, to ensure the overall system is 

subcritical. Aluminum is also a common nonfissile material included in a package design because 

of its material properties and availability (Ref. 16). However, aluminum has a smaller neutron 

absorption cross-section at thermal energies than hydrogen, which makes it more of a diluent to 

this fissile material system than a significant neutron absorber. A series of KENO V.a calculations 

using ENDF/B-VII neutron cross sections were performed to estimate the effective multiplication 

factor, keff, for a mixture of 235U metal and various nonfissile materials. The solid nonfissile 

materials considered include aluminum (Al), Regulatory concrete, Rocky Flats concrete, Oak

Ridge concrete, and carbon steel.

1 The calculations consider an initial, maximum, spherical 

volume of 584 m3 that is representative of the maximum available volume in five public highway 

transport vehicles, e.g., two tandem trailers pulled by a single tractor (Ref. 4). This volume was 

reduced in the calculations, as necessary, to determine the critical volume, and, subsequently, the 

number of 15 g 235U packages required for criticality (keff = 1.0). Two spherical configurations are 

considered in the calculations to directly determine the dilution effect of the keff on the quantity of 

nonfissile materials present in the mixture: a dry 235U metal-nonfissile mixture, and a flooded 

system that approximates an immersed package with the same 235U metal-nonfissile mixture. 

Both configurations consider a spherical 30 cm thick water reflector. As a starting point for an 

immersed package, the water-moderated system assumes an H/235U ratio of about 100, 

corresponding, approximately, to an optimally moderated system for an infinite 235U-water mixture. 

The nonfissile material is then added to the dry and optimally-moderated configurations to 

examine the diluent effect. The results for a nonfissile-to-fissile mass ratio of 200 are then used to 

estimate the number of 15 g 235U packages that will remain subcritical (keff < 1.0). 

The results in Fig. 1 illustrate the significant effect of adding nonfissile materials to 235U metal for 

both dry (unmoderated) and moderated configurations. It is clear from these results that only the 

carbon steel and 235U mixtures will remain subcritical for an unlimited number of 15 g 235U 

packages. For the rest of the nonfissile materials considered in these calculations, subcriticality 

can only be assured for a finite number of 15 g 235U packages. The number of packages that 

remain subcritical for the dry configuration is approximately 250, 850, 1100, and 500,000 for 

Regulatory concrete, Oak Ridge concrete, Rocky Flats concrete, and Aluminum, respectively. The 

number of 15 g 235U packages that remain subcritical for the moderated (immersed) configuration 

is approximately 600, 800, 1100, and 20,000 for Regulatory concrete, Oak Ridge Concrete, Rocky 

Flats concrete, and Aluminum, respectively. The Regulatory concrete results indicate the smallest 

number of 15 g 235U packages that remain subcritical for both dry and moderated configurations, 

but is a hypothetical concrete mixture. The Oak Ridge and Rocky Flats concrete mixtures, which 

are typical concrete mixtures, require additional 15 g 235U packages, 850 and 1100 for the dry 

configuration and 800 and 1100 for the moderated configuration, respectively, to achieve 

criticality. The Al results show much more Al can be added to 15 g 235

U packages as a diluent

than the concrete configurations. These extremely conservative calculations demonstrate a large 

number of packages can be combined and shipped safely with a 200 nonfissile-to-fissile mass 

 

1 NRC regulatory concrete, developed for the NRC, is a mixture (density is 2.3 g/cm3) comprised of 1.4 wt. % Fe, 1.0 wt. % H, 

3.4 wt. % Al, 4.4 wt. % Ca, 53.2 wt. % O, 33.7 wt. % Si, and 2.9 wt. % Na. Rocky Flats concrete is a mixture (density is 2.321 

g/cm3) comprised of 1.01 wt. % Fe, 0.75 wt. % H, 5.52 wt. % C, 0.02 wt. % N, 48.49 wt. % O, 0.63 wt. % Na, 1.25 wt. % Mg, 

2.17 wt. % Al, 15.5 wt. % Si, 0.19 wt. % S, 1.37 wt. % K, 23.0 wt. % Ca, and 0.1 wt. % Ti. Oak Ridge concrete is a mixture 

(density is 2.2994 g/cm3) comprised of 0.7784 wt. % Fe, 0.6187 wt. % H, 17.52 wt. % C, 41.02 wt. % O, 0.0271 wt. % Na, 

3.265 wt. % Mg, 1.083 wt. % Al, 3.448 wt. % Si, 0.1138 wt. % K, and 32.13 wt. % Ca. Carbon Steel (density is 7.8212 g/cm3) is 

comprised of 1.0 wt. % C and 99.0 wt. % Fe. Aluminum has a density of 2.702 g/cm3. These composition and density data are 

taken from Ref. 19. 
19 

ratio to dilute and to provide neutron absorption to the fissile material present. The calculations 

consider all the fissile and nonfissile material commingled in a single, spherical, package with a 

thick water reflector. Typical packages are assembled individually up to the 15 g 235U limit and, 

although there is neutron reflection present from packaging materials, adjacent packages and 

structure, the reflection is typically less than the tight-fitting, thick water reflected configurations 

assumed in the calculations. This significantly increases the mass required for criticality, even 

when multiple packages are commingled. Thus, the number of packages that would remain 

subcritical is realistically much greater than the values estimated from the conservative 

calculations summarized in Fig. 1. 

Figure 1 Spherical, Homogeneous Mixtures of 235U and Various Nonfissile Materials 

(30-cm Thick Water Reflection)

4.1.3 10 CFR 71.15(c) Low Concentrations of Solid Fissile Material Comingled with Solid 

Nonfissile Material 

71.15(c) – (1) Low concentrations of solid fissile material commingled with solid nonfissile 

material, provided that: 

(i) There is at least 2000 grams of solid nonfissile material for every gram of

fissile material, and

(ii) There is no more than 180 grams of fissile material distributed within

360 kg of contiguous nonfissile material.

(2) Lead, beryllium, graphite, and hydrogenous material enriched in

deuterium may be present in the package but must not be included in

determining the required mass of solid nonfissile material.

The intent of this fissile material exemption is to allow large volumes of waste material containing 

low concentrations of solid fissile material, commingled with a large amount of solid nonfissile 
20

material. The mass of solid nonfissile material required by the provision cannot include the mass 

of lead, beryllium, graphite, and hydrogenous material enriched in deuterium although these 

materials can be present in the package. The quantity of fissile material in this provision is not 

limited, but it must be commingled such that no more than 180 g is distributed within 360 kg 

(360,000 g) of solid nonfissile material. The intent is to have package contents that have an 

essentially homogeneous mixture of fissile and nonfissile material. According to the provision, the 

fissile material must be distributed within contiguous nonfissile material, which will ensure the 

fissile material will not form any heterogeneous arrangements within the waste matrix during 

normal conditions of transport and hypothetical accident conditions. 

This exemption could be applied to transporting large volumes of soil contaminated with fissile 

materials or uranium-contaminated alumina trap mix where the fissile material is essentially 

homogeneously distributed throughout the waste matrix, for example. This particular fissile 

material exemption would not apply to surface contaminated equipment or piping, for example, 

where the fissile material may exist in localized sections within the equipment or where the 

surface of the equipment is contaminated with fissile material because the fissile material is not 

commingled with the solid nonfissile material. 

This exemption requirement precludes nuclear criticality safety concerns by limiting the mass 

concentration and requiring a nearly uniform mixture of fissile and nonfissile materials. Lead, 

beryllium, graphite and hydrogenous material enriched in deuterium can be present in the 

package but not included in the determination of the nonfissile material present. The material 

should be well mixed and homogeneous. 

According to Ref. 15, the technical basis for the 2000:1 ratio of solid nonfissile material to fissile 

material in 10 CFR 71.15(c)(1) is that this concentration represents approximately 60% of the 

minimum critical fissile material concentration of 1.33 g 235U/L in a 1600-g-SiO2/L matrix. The 60% 

value is judged to be a reasonably conservative decrease in the minimum critical concentration to 

accommodate nonfissile materials other than SiO2. Calculations in Ref. 20 were performed to 

compare mixtures of fissile materials (e.g., 235U, 239Pu, and 233U) with various moderators: 

beryllium, graphite, deuterium, and SiO2. Based on the results of these calculations, SiO2 was 

chosen as the matrix of interest for deriving the fissile exemptions because it is judged to be the 

most representative and limiting matrix associated with the transport of waste material 

contaminated with small quantities of fissile materials, such as construction debris or 

contaminated soils (Ref. 20). SiO2 has a large abundance in nature and has a low tendency for 

absorbing neutrons, which is conservative from a criticality safety standpoint. Except for beryllium, 

graphite, and deuterium and pure forms of magnesium and bismuth, silicon or SiO2 is the most 

reactive diluent for fissile materials (Ref. 15). Furthermore, the density assumed for SiO2 (1.6 

g/cm3

) is representative of dry bulk mean world soil density (Ref. 20).

With respect to the fissile mass limitation of 180 g per 360 kg of solid nonfissile material, 

computations were performed for a 239Pu2 and SiO2-water matrix to determine the minimum 

critical mass under optimum conditions of moderation and reflection. According to the calculation 

results (Ref. 20) for these systems, the minimum critical mass of 239Pu in an SiO2-water matrix is 

approximately 920 g3

. Because of heterogeneity concerns, (i.e., lumps of fissile material in the 

2 These computations assume the ratio of 240Pu to 241Pu is greater than 1 and the 241Pu present in mixture is assumed to 

be 239Pu. This assumption would result in a bounding critical mass value for use in the derivation of a fissile material 

exemption value.

3 This critical mass value occurs at 0.01 g 239Pu/g SiO2 and 0.25 g H2O/g SiO2. 
21

nonfissile matrix), the 920 g minimum critical mass was reduced by a factor of five (to 180 g) to 

ensure subcriticality under normal conditions of transport and hypothetical accident conditions, 

where it is possible for some of the fissile material to redistribute in the matrix. Thus, to maintain 

the 2000:1 ratio of nonfissile to fissile material in the package requires 180 g of fissile material to 

be distributed within a minimum of 360,000 g (360 kg) of contiguous nonfissile material.

A series of KENO V.a calculations using ENDF/B-VII neutron cross sections were performed to 

estimate the infinite multiplication factor, kinf, for a mixture of 235U metal and aluminum to 

determine the effect of adding diluent to the system. The calculations with the diluent present are 

compared to a 235U metal-water system. kinf, the ratio of the number of neutrons resulting from 

fission in the current generation to the number absorbed in the preceding generation in a system 

of infinite size, does not consider neutron leakage because the size of the homogeneous 235U 

metal, water, and aluminum system is infinite. The kinf for a 235U metal-water system was first 

calculated to compare to the cases where the quantity of aluminum is increased in the U-water 

mixture (zero to 2000 grams of diluent per gram of 235U present). These calculations consider 

hydrogen-to235U (H/235U) ratios that range from a dry system (H/235U=10) to an over-moderated 

system (H/235U=4000) that corresponds to a much lower concentration than the limiting critical 

density for a 235U metal-water system (~12 g/L). The results in Fig. 2 indicate the kinf is less than 

1.0, regardless of the level of moderation, for a system with an Al-to235U ratio of 500 or greater. 

This indicates that aluminum is an effective diluent for this type of system.

Figure 2 Infinite Homogeneous Mixture of 235U Metal and Water with Aluminum Present

 as a Diluent

To expand on the aluminum, 235U, and water mixture analysis, the SCALE calculations were 

expanded to consider additional diluents of interest (beryllium [Be], graphite, bismuth [Bi], lead 

[Pb], magnesium oxide [MgO2], magnesium fluoride [MgF2], silicon oxide [SiO2], and hydrogenous 

materials enriched with deuterium) in place of the aluminum in the infinite homogeneous 235U and 

water system. As stated in 71.15(b), beryllium, graphite, hydrogenous materials enriched with 
22

deuterium, and lead are excluded as solid nonfissile material intended as a diluent. These are 

provided simply for comparison with the other results. The other diluents listed (MgO2, Bi, and

MgF2) are considered exotic in the sense that they have a very low probability of absorbing 

neutrons, but are not commonly available in large, pure quantities for use as a filler material in a 

package. Silicon oxide may be present in significant quantities as a constituent of soil (Ref. 20). 

Magnesium compounds are also not expected to be available as package filling material in large 

quantities, although magnesium fluoride, for example, may be present in the waste matrix itself 

rather than as a component of soil. 

The results, shown in Fig. 3, conclude that all diluents of interest considered in the calculations 

reduce the kinf for the system below that of a 235U metal-water system, regardless of the quantity of 

the diluent and moderation (water) present in the system. In other words, the 235U metal-water 

mixture is more reactive without the diluents present in the system. A key point is that the

configurations considered in the calculations do not represent realistic matrices commonly found 

in the industry. Systems are not infinite in extent nor optimally constructed. Realistic matrices of 

fissile and nonfissile materials will contain a wide variety of neutron absorbing materials or diluents 

in the system. The results in Fig. 3 demonstrate the kinf is less than 1.0 for the entire H/235U range

for aluminum, SiO2, and MgO2 but greater than 1.0 for those constituents that have a reduced 

tendency of absorbing neutrons from the system (D2O, Bi, MgF2, Graphite, Be, and Pb), which 

occurs in dry, low-moderated, systems. The results demonstrate the kinf is reduced below 1.0 as 

the H/235U ratio is greater than 100 for an Al-to 235U ratio of 2000 (Fig. 3). Again, MgO2, MgF2 and 

Bi are not expected in large quantities as a package filler material and the other diluents 

considered, deuterium, lead, beryllium and graphite, are excluded by the 10 CFR 71.15(c) as 

acceptable nonfissile material to mix with fissile material. 

Figure 3 Infinite Homogeneous Mixture of 235U Metal and Water with a Diluent-to235U

 Ratio of 2000
23

4.1.4 10 CFR 71.15(d): Uranium Enriched in 235U to a Maximum of 1 percent by Weight

71.15(d) – Uranium enriched in uranium-235 to a maximum of 1 percent by weight, and 

with total plutonium and uranium-233 content of up to 1 percent of the mass of 

uranium-235, provided that the mass of any beryllium, graphite, and hydrogenous material 

enriched in deuterium constitutes less than 5 percent of the uranium mass, and that the 

fissile material is distributed homogeneously and does not form a lattice arrangement 

within the package.

This fissile provision exempts low-enriched uranium from classification as fissile material 

assuming the uranium has a 235U enrichment of 1 wt % or less. To ensure subcriticality below this 

enrichment, the package must not contain plutonium or 233U content in excess of 1% of the 235U 

mass, and it must not contain low-neutron-absorbing moderator materials (beryllium, graphite, and 

hydrogenous material enriched in deuterium) with a mass greater than 5% of the 235U mass. The 

mass of 235U is unlimited in this provision; however, if 233U, plutonium, or low-absorbing 

moderators are present, the mass of the uranium must be known. For example, if 233U and 

beryllium are present in a package and the mass of uranium in the package is known to be 100 g, 

the 233U content is limited to 1 g, and the quantity of beryllium must be limited to 5 g or less in the 

waste matrix. The fissile material present must be essentially homogeneously distributed 

throughout the package since it is possible for heterogeneous configurations to be more reactive 

than homogeneous distributions of low-enriched fissile material. Small disparate volumes of 

heterogeneity may exist provided that a significant fraction of fissile material is homogeneous and 

mixed with nonfissile material. Heterogeneous effects in a package due to large fissile material 

lumps/particles or lattice arrangements of fissile material would only affect criticality safety for a 

lattice configuration over a large volume. Large quantities of fissile material (kilograms of 235U) and 

regions of heterogeneity on the order of a cubic meter in size are necessary before a system 

could adversely affect the validity of the 1 wt % 235U enrichment limit for this fissile exemption. 

Heterogeneous configurations of concern would consist of large, fixed, repeating arrays of 

separate fissile material lumps.

The technical basis of this fissile material exemption is based on experimental data for spherical 

homogeneous mixtures of 235U and water. Fig. 4 illustrates the results of experimental data for 

spherical homogeneous and heterogeneous systems of 235U and water (Ref. 21, Fig. 22). Both 

unreflected and water-reflected data are presented. The figure shows that for homogeneous 

unreflected and water-reflected systems, the critical limit (the limit below which criticality is not 

possible) for a homogeneous system is approximately 1 wt % 235U enrichment. The corresponding 

critical limit for a heterogeneous system is approximately 0.7 wt % 235U (i.e., natural uranium). 

Further, Fig. 4 indicates the critical masses for heterogeneous systems are smaller than the 

corresponding values for homogeneous systems when the enrichment values are below about 

10 wt % 235U. Since this fissile material exemption considers practical conditions during 

transportation operations, it was judged that geometric arrangements of such low-enriched fissile 

material shipped in commerce would not present a realistic challenge to criticality safety. 

Beryllium, graphite, and hydrogenous materials enriched in deuterium would have to be present in 

large quantities in order to provide conditions (low neutron absorbing moderator) with a potential 

for criticality; thus, these materials are excluded. 
24

Figure 4 Minimum Spherical Critical Masses as Functions of 235U Enrichment in 

Homogeneous and Heterogeneous Hydrogen-Moderated Systems 

(Ref. 21, Fig. 22) 

The exemption criterion requires the quantity of these low-neutron-absorbing moderators to be 

limited in the waste matrix to a maximum of 5% of the uranium mass. According to Ref. 15, 

calculations of infinite heterogeneous systems of uranium plates enriched to 1 wt % 235U and 

moderated with heavy water (D2O, the limiting special moderator) indicate that a moderator mass 

of at least 15% of the uranium mass is necessary to result in a critical configuration. Based on 

these calculation results, restricting the mass of the low-absorbing special moderators to 5% of 

the moderator mass will ensure that all types of heterogeneous systems are bounded from a 

criticality safety perspective. 

The intention of this requirement is that the waste matrix should stay essentially homogeneous 

and that significant heterogeneous lumps or volumes of lattice arrangements should be precluded 

because of the increased potential for criticality during transportation conditions. The effect of 

lumps or heterogeneities in a uranium-water system with an enrichment of 0.995 wt % 235U was 

studied using the KENO V.a sequence in the SCALE code system (Ref. 19). A series of keff

calculations with finite cubic arrangements of uranium metal units immersed in water was 

performed. The uranium metal array size and pitch4 was varied to determine the 235U mass and 

volume necessary to result in a keff of 1.0. The results are shown in Fig. 5. The results show that a 

4 The pitch was used to determine the H/X ratio in the unit cell modeled in Keno V.a based on the fissile unit dimensions 

and fissile unit edge-to-edge spacing.
25 

uranium metal unit diameter of approximately 5 cm at an edge-to-edge unit spacing of about 

0.37 cm (H/X |240) is required for a keff of 1.0. The uranium mass per unit is about 1,246 g U 

(12.4 g 235U at 0.995 wt % enrichment) and the volume is approximately 65.5 mL per unit. Fig. 5 

shows that 4,913 5 cm-diameter spherical uranium metal units (17×17×17 array) at theoretical 

density (19.05 g/cm3

) are necessary at an optimum pitch (H/235U) for a heterogeneous 

arrangement of lumps to result in a critical configuration immersed in water. The results for an 

infinite array of units at an optimum pitch are plotted alongside the other array results. The 

17×17×17 array was more closely examined to determine the optimum uranium unit size in the 

array. The results of this array in Fig. 6 show the fissile unit size is nearly optimized at a diameter 

of about 8 cm (50.8 g 235U per unit). Thus, uranium units larger and smaller than about 8 cm in 

diameter are less reactive in the modeled array configuration. 

Small volumes of heterogeneity may exist in a large shipment of fissile-contaminated waste that 

could be transported per this exemption, but it would not be credible for these shipments to exist 

as optimal arrangements of fissile material in heterogeneous lumps or arrangements that could 

achieve a critical state. Any heterogeneous regions of fissile material in this case would have a 

smaller effective density than would be present in an optimized configuration. Furthermore, the 

limitation on the uranium enrichment to less than 1.0 wt % 235U, the limitation on the presence of 

other fissile isotopes to less than 1.0% of the 235U mass, and the limitation on low neutron 

absorbing moderators to less than 5% of the 235U mass will ensure subcriticality under normal 

conditions of transport and hypothetical accident conditions. 

Figure 5 Arrays of U(0.995)-Metal Units Immersed in Water 
26

Figure 6 17 × 17 × 17 Array of U(0.995)-Metal Units Immersed in Water 

4.1.5 10 CFR 71.15(e): Liquid Solutions of Uranyl Nitrate Enriched in 235U to a Maximum of

2 Percent

71.15(e) – Liquid solutions of uranyl nitrate enriched in uranium-235 to a maximum of 

2 percent by mass, with a total plutonium and uranium-233 content not exceeding 

0.002 percent of the mass of uranium, and with a minimum nitrogen to uranium atomic 

ratio (N/U) of 2. The material must be contained in at least a DOT Type A package. 

The intent of this exemption is to allow shipment of uranyl nitrate solutions with uranium 

enrichments below 2 wt % 235U. An intended application of the exemption includes uranyl nitrate 

solutions created from spent fuel reprocessing activities. The solution must be contained within a 

Type A package to ensure that the solution material will not convert to oxide form, combine with 

fissile material from other packages, mix with water, or form into an unfavorable geometry during 

normal conditions of transport. The total mass of the 235U in the consignment is not controlled for 

criticality safety purposes; however, the mass of uranium in the uranyl nitrate solution is required 

to be known if there is plutonium or 233U present because the mass of plutonium and 233U is 

limited to 0.002% of the mass of uranium. For example, if there is 100 g of uranium in a package 

of uranyl nitrate solution, the 233U or plutonium content in the package cannot exceed 0.002 g. The 

ratio of atomic nitrogen to uranium (N/U) ratio must be greater than 2 to ensure a minimum level 

of neutron absorption by nitrogen is present in the fissile material package to prevent criticality. 

The technical basis of the fissile exemption for uranyl nitrate solutions [UO2(NO3)2 + 6H2O] is 

based on the critical enrichment limits and parasitic neutron absorption from nitrogen. The 
27 

subcritical enrichment limit for low-enriched UO2(NO3)2 solutions5

 with a thick water reflector is 

2.88 wt % 235U (Refs. 22 and 23) and shows that the kinf for a UO2(NO3)2–water system for 

1.95 wt % 235U enrichment and thick water reflection is less than 1.0, (Ref. 24) which means that 

criticality is not possible (Fig. 7). Furthermore, Ref. 3 provides the 235U subcritical enrichment limit 

for UO2(NO3)2 homogeneously mixed with water as 1.96 wt % 235U (assuming a margin of 0.02 in 

the keff). The exemption limit is set at 2 wt % enriched 235U, which is slightly larger than the 

uranium-water mixture limiting critical enrichment values. However, these limits provide a 

significant safety margin since the subcritical enrichment limit calculations assume optimum 

conditions (e.g., spherical geometry and thick, close-fitting water reflection). The fissile exemption 

also limits the quantity of other fissile nuclides to ensure that the enrichment limit for 235U is valid 

(i.e., quantities of Pu and 233U isotopes are inconsequential6

). 

The use of packages that meet Type A standards is sufficient to ensure that the uranyl nitrate 

solutions are protected from any adverse conditions encountered during normal conditions of 

transport that could affect nuclear criticality safety (e.g., loss of geometry). The exemption 

enrichment limit also accounts for the accumulation of 235U during hypothetical accident conditions 

that involve the loss of packaging during transport since an infinite system is considered. There is 

also a limitation on the minimum nitrogen-to-uranium atomic ratio (N/U) of 2. This requirement 

ensures that there is a minimum level of neutron absorption in nitrogen (a moderate thermal 

neutron absorber) to ensure the kinf is maintained less than 1.0. 

Figure 7 kinf Calculated for UO2(NO3)2–H2O Mixtures (Ref. 24, Fig. 2) 

5 These subcritical values are valid for uniform homogeneous aqueous solutions of UO2(NO3)2. The subcritical 

enrichment limit of 2.88 wt % 235U is the limit on 235U content of uranium in a saturated (2.5M) aqueous solution of 

UO2(NO3)2 to preserve subcriticality (Ref. 23). 

6 The NRC amended this fissile exemption requirement in 2004 with the limitation on total Pu and 233U (0.002% of 235U 

mass) to be consistent with international regulations. 
28

4.1.6 10 CFR 71.15(f): Packages Containing Plutonium with a Large Percentage of 238Pu

71.15(f) – Packages containing, individually, a total plutonium mass of not more than 1000 

grams, of which not more than 20 percent by mass may consist of plutonium-239, 

plutonium-241, or any combination of these radionuclides.

This provision allows for the exemption of individual fissile packages containing plutonium with a 

mass of 1000 g or less provided not more than 20% of the total plutonium mass contains the 

fissile nuclides 239Pu, 241Pu, or a combination of 239Pu and 241Pu. This fissile exemption does not 

constrain the mass of commingled nonfissile material or low-neutron-absorbing special 

moderating materials. This particular exemption requirement is not applicable for uranium that 

may have trace amounts of plutonium present, or for packages with other fissile material. This 

exemption is intended primarily for shipment of low-assay plutonium, such as heat sources, with a 

high percentage of 238Pu and a low percentage of fissile nuclides of plutonium. 

The radiological nature of plutonium would require the quantity of material allowed by this 

exemption to be shipped in a Type B package design certified by the NRC to maintain integrity 

under hypothetical accident conditions. However, this exemption would eliminate the need for a 

criticality safety assessment as required under 10 CFR 71.55 and 71.59. The amount of fissile 

plutonium nuclides (239Pu and 241Pu) allowed in such a shipment is 20% of the total plutonium 

mass, and the maximum fissile mass allowed would be 200 g in the limiting plutonium shipment of 

1,000 g. 

The technical basis for this exemption is that the presence of the nonfissile plutonium isotopes will 

provide significant parasitic neutron absorption and will eliminate the potential for criticality. Fig. 8

illustrates that 200 g of 239Pu corresponds to a keff of 0.8 under optimal conditions of pure 

materials, spherical geometry, and thick water reflector. Furthermore, the subcritical limits for 

239Pu and 241Pu are 450 and 200 g, respectively (Ref. 25). It is not likely that 241Pu would be 

present in greater quantities than 239Pu (Ref. 26); however, to ensure that criticality is precluded, 

the exemption limitation of 20% of the 1,000 g of total plutonium is bounded for 239Pu and 

combinations of 239Pu and 241Pu by the 200 g subcritical limit for 241Pu. Again, the presence of 

nonfissile plutonium isotopes would increase the safety margin by introducing a source of neutron 

absorption to the system. The mass required for criticality would tend to increase as a result. 
29

Figure 8 Masses of Spheres of Homogeneous Water-Moderated 239Pu as Functions of 239Pu 

 Density (Ref. 22, Fig. 10) 

4.2 General License: Fissile Material

The general license criteria in 10 CFR 71.22 (fissile material) are intended to allow NRC licensees 

to ship small quantities of fissile material in packages that have been assigned a CSI to ensure 

accumulation control for packages on a conveyance. 

The current general license language from 10 CFR 71.22 is listed in the tables below. Table 2 

provides the content of 10 CFR 71.22, “General license: fissile material.” Table 3 provides mass 

limits for general license packages containing mixed quantities of fissile material or 235U of 

unknown enrichment, and Table 4 provides mass limits for general license packages containing 

235U of known enrichment, which are needed to evaluate the equation in 71.22(e)(1). 
30

Table 2 Content in 10 CFR 71.22, “General license: Fissile material” 

71.22 General License: Fissile Material.

(a) A general license is issued to any licensee of the Commission to transport fissile material, or to deliver fissile

material to a carrier for transport, if the material is shipped in accordance with this section. The fissile material need

not be contained in a package, which meets the standards of subparts E and F of this part; however, the material

must be contained in a Type A package. The Type A package must also meet the DOT requirements of

49 CFR 173.417(a).

(b) The general license applies only to a licensee who has a quality assurance program approved by the Commission

as satisfying the provisions of subpart H of this part.

(c) The general license applies only when a package's contents:

(1) Contain no more than a Type A quantity of radioactive material; and

(2) Contain less than 500 total grams of beryllium, graphite, or hydrogenous material enriched in deuterium.

(d) The general license applies only to packages containing fissile material that are labeled with a CSI which:

(1) Has been determined in accordance with paragraph (e) of this section;

(2) Has a value less than or equal to 10; and

(3) For a shipment of multiple packages containing fissile material, the sum of the CSIs must be less than or

equal to 50 (for shipment on a nonexclusive use conveyance) and less than or equal to 100 (for shipment on an

exclusive use conveyance).

(e)

(1) The value for the CSI must be greater than or equal to the number calculated by the following equation:

(2) The calculated CSI must be rounded up to the first decimal place;

(3) The values of X, Y, and Z used in the CSI equation must be taken from Tables 71–17 or 71–28, as

appropriate;

(4) If Table 71–2 is used to obtain the value of X, then the values for the terms in the equation for uranium-233

and plutonium must be assumed to be zero; and

(5) Table 71–1 values for X, Y, and Z must be used to determine the CSI if:

(i) Uranium-233 is present in the package;

(ii) The mass of plutonium exceeds 1 percent of the mass of uranium-235;

(iii) The uranium is of unknown uranium-235 enrichment or greater than 24 weight percent enrichment; or

(iv) Substances having a moderating effectiveness (i.e., an average hydrogen density greater than H2O)

(e.g., certain hydrocarbon oils or plastics) are present in any form, except as polyethylene used for packing

or wrapping.

7 See Table 3 in this report.

8 See Table 4 in this report.
31

Table 3 10 CFR 71.22 Table 71–1—Mass Limits for General License Packages Containing 

Mixed Quantities of Fissile Material or 235U of Unknown Enrichment per 71.22(e)

Fissile material

Fissile material mass mixed with 

moderating substances having an 

average hydrogen density less than or 

equal to H2O (grams)

Fissile material mass mixed with 

moderating substances having an 

average hydrogen density greater 

than H2Oa (grams)

235U (X) 60 38

233U (Y) 43 27

239Pu or 241Pu (Z) 37 24

a When mixtures of moderating substances are present, the lower mass limits shall be used if more than 

15 percent of the moderating substance has an average hydrogen density greater than H2O.

Table 4 10 CFR 71.22 Table 71–2—Mass Limits for General License Packages Containing 

235U of Known Enrichment per 71.22(e)

Uranium enrichment in weight percent 

of 235U not exceeding

Fissile material mass 

of 235U (X) (grams)

24 60

20 63

15 67

11 72

10 76

9.5 78

9 81

8.5 82

8 85

7.5 88

7 90

6.5 93

6 97

5.5 102

5 108

4.5 114

4 120

3.5 132

3 150

2.5 180

2 246

1.5 408

1.35 480

1 1,020

0.92 1,800

The general license provisions are applicable to fissile materials in quantities and conditions that 

could potentially result in criticality if the provisions are not followed correctly. Therefore, the NRC 

requires that a licensee have a commission-approved quality assurance program to ensure that 

the general license criteria in this section are used appropriately and with the correct level of rigor 

for safety purposes. The general license criteria require that the user meet the requirements in 10 

CFR 71 Subpart H, “Quality Assurance,” (10 CFR 71.101-71.137) that apply to the design, 

purchase, fabrication, handling, shipping, storing, cleaning, assembly, inspection, testing, 
32

operation, maintenance, repair, and modification of components of the packaging that are 

important to safety (Ref. 1).

The technical bases for the general license mass limits used to calculate the CSI for packages are 

based on the subcritical mass values for the materials of interest. The first two provisions of 

10 CFR 71.22, 71.22(a), and 71.22(b), require the fissile material to be present in a Type A 

package meeting the requirements of 49 CFR 173.417(a), and the general license criteria are 

applicable to NRC licensees with an NRC-approved quality assurance program satisfying the 

provisions of 10 CFR 71 Subpart H. The packaging requirements for Type A packages are 

described in Sect. 2.5.

The general license criteria in 10 CFR 71.22 apply to fissile materials with Type A quantities of 

total radioactive material, mixed with limited quantities (less than 500 g) of beryllium, graphite, or 

hydrogenous material enriched in deuterium. Provisions 10 CFR 71.22(d)(1)-(3) apply to the 

calculation of a CSI for a package. The CSI is calculated using the formula provided in 

10 CFR 71.22(e)(1):

, 

where X, Y and Z represent the quantities of 235U, 233U, and Pu in the package, respectively. The 

value of the CSI for an individual package is limited to 10. The accumulation of multiple packages 

is controlled by limiting the CSI to less than or equal to 50 (for shipment on a nonexclusive use 

conveyance) or less than or equal to 100 (for shipment on an exclusive use conveyance). In a 

nonexclusive use conveyance, a CSI of 50 corresponds to a fissile mass of about 50% of the 

acceptable subcritical mass limit.

9 An exclusive-use conveyance with a CSI of 100 corresponds to 

the acceptable subcritical mass limit and requires additional control because of the larger quantity 

of fissile material that can be shipped.

The CSI for the package is calculated based on the fissile material contents in the package (233U, 

235U and/or Pu) and their corresponding mass limits, as specified in Tables 71–1 and 71–2. The 

fissile material mass limits are based upon the uranium enrichment and whether or not the fissile 

material is mixed with a moderating material with a hydrogen density less than or equal to water 

or with a hydrogen density greater than water. The mass limits in these tables were derived based 

on fissile material-water or fissile material-polyethylene systems, and they do not consider the 

presence of low-absorbing moderators. The CSI label is required to control the accumulation of 

packages on a conveyance (Ref. 6). To ensure that a conservative CSI is determined, the value of 

the CSI is rounded up to the first decimal place. As defined in 10 CFR 71.4, for an exclusive use 

conveyance, the conveyors and shippers must ensure that any loading or unloading is performed 

by personnel having radiological training and resources appropriate for safe handling of the 

consignment. Further, the consignor and shipper must issue specific instructions, in writing, for 

maintenance of exclusive use shipment controls, and include them with the shipping paper 

information provided to the shipper by the consignor. 

 

9 The acceptable subcritical mass limit is the limiting value assigned to the mass of fissionable material that results in a 

subcritical system under certain conditions. This mass limit is set by considering a bias and bias uncertainty of the 

calculation method used to determine the subcritical value.
33

Table 71–1 lists mass limits for general license packages containing mixed quantities of fissile 

material or 235U of unknown enrichment, which were generated based on fully enriched 235U. The 

first column of Table 71–1 applies for 233U, 235U or Pu systems that are mixed with moderating 

materials having an average hydrogen density less than or equal to water. The second column of 

Table 71–1 applies to these fissile nuclides when mixed with moderating materials having an 

average hydrogen density greater than water (e.g., hydrocarbon oils and high-density 

polyethylene). The mass limit data in the tables also require that if a package contains fissile 

materials mixed with both types of moderating materials that the lower mass limits (column 2 data) 

be used if more than 15% of the moderating substance has an average hydrogen density greater 

than water. Table 71–1 must be used if 233U is present in a package or if the mass of Pu in the 

package exceeds 1 percent of the mass of 235U. 

The fissile mass limits in Tables 71-1 were derived based on calculations10 performed in Ref. 4 to 

determine the acceptable subcritical mass limit of 235U, 233U, and 239Pu. The calculations 

considered water reflected and optimally moderated spheres of 235U, 233U, and 239Pu. For 

Table 71-1, column 1, the acceptable subcritical masses corresponding to a system keff of less 

than 0.95 for 235U, 233U, and 239Pu are 614 g, 437 g, and 379 g, respectively. For each fissile 

isotope, the acceptable subcritical mass limit was reduced by a factor of 10, corresponding to a 

package CSI of 10, and rounded down to the following values for 235U, 233U, and 239Pu: 60, 43, and 

37 g, respectively. The Table 71-1, column 2 data are applicable for fissile materials mixed with 

moderating substances having an average hydrogen density greater than water, such as 

polyethylene (not used for packing or wrapping materials) or hydrocarbon oils. The mass limits are 

lower for these waste matrices because these systems provide better moderation due to the 

greater hydrogen density in the matrix. According to Ref. 4, Table 3-1, the minimum critical mass 

of 235U homogeneously mixed with polyethylene is 527 g. The mass limit values in the second 

column of Table 71-1 were derived by reducing the column 1 values by the ratio of the minimum 

critical mass for a 235U/polyethylene system, 527 g, to the minimum critical mass for a 235U/water 

system, 820 g, which is equal to about 0.64 (for 235U, the 60 g limit becomes 60 × 0.64 or 38 g, for 

233U, the 43 g limit is 43 × 0.64 or 27 g, and for Pu, the 37 g limit is 37 × 0.64 or 24 g).

Table 71–2 lists mass limits for general license packages containing 235U of known enrichment up 

to 24 wt % 235U. If Table 71–2 is used to obtain a value of X in the CSI equation, then the values 

for the terms in the equation for 233U and Pu must be zero. The mass limits for known enrichments 

in Table 71-2 begin at 60 g at an enrichment of 24 wt % 235U. This corresponds to the subcritical 

(keff = 0.95) fissile material mass for fully enriched 235U (Ref. 4, Table 3-1), which is approximately 

600 g of 235U. This acceptable subcritical mass limit is divided by 10 to represent a package CSI 

limit of 10. The mass limit value for 0.92 wt % enrichment is 1,800 g (with a package CSI limit of 

10) and corresponds to a subcritical mass of 18,000 g 235U. These mass limit values were

increased by 150% from the pre-2004 general license criteria, based on recommendations in Ref.

4. Per 10 CFR 71.22(e)(2), the calculated CSI values must be rounded up to the first decimal

place; e.g., if a CSI were calculated to be 1.95, the actual value would be 2.0. Interpolating mass

limit values in the tables is not permitted. The licensee must use the mass corresponding to the

next highest enrichment value available in Table 71–2.

Above 24 wt % 235U enrichment, the mass limit is based on full enrichment (i.e., 100 wt % 235U). If 

Pu is present in the package with a mass that exceeds 1% of the mass of 235U, then the data in 

10 These criticality calculations were performed with the SCALE (Ref. 19) computer code system. Specifically, the 

minimum subcritical mass calculations were calculated with one-dimensional systems using the discrete ordinates 

transport theory code sequence CSAS1X using the 27-energy group library based on ENDF/B-IV data (Ref. 4). 
34

Table 71–1 must be used to ensure that the presence of any Pu in a package does not invalidate 

the mass limit data because 239Pu and 241Pu isotopes are more reactive than 235U in moderated 

systems. If any quantity of 233U is present in the package, then the data in Table 71–1 must be 

used because 233U is generally more reactive than 235U. The NRC recognizes that small quantities 

of 233U may be present along with 235U in some circumstances. Small quantities of 233U should not 

adversely impact nuclear criticality safety for a package. Determining the quantity of 233U that may 

be allowed may be addressed in a future rulemaking to 10 CFR 71.

Provision 10 CFR 71.22(c)(1) requires that each package contain no more than a Type A quantity, 

as specified in Table A-1, “A1 and A2 Values for Radionuclides.” This provision ensures that 

radiological limitations are maintained within each package. For example, the maximum 

radiological limits (A2 value) for 239Pu in Table A-1 can be used to calculate the maximum quantity 

of 239Pu allowed in a package, 0.435 g. The general license mass value from Table 71-1 is 39 g. 

Thus, this example illustrates that the radiological limitations (no more than a Type A quantity of 

radioactive in a Type A package) for the fissile nuclides will limit the quantity of fissile material 

present rather than the criticality safety limitations for some of the fissile isotopes of interest. The 

provisions preclude the use of a Type B package, which the NRC recognizes is inconsistent with 

the allowed plutonium mass values in Table 71-1. This issue may be addressed in a future 

rulemaking to 10 CFR 71. 

This provision also limits the quantity of low absorbing materials (beryllium, graphite, or 

hydrogenous materials enriched in deuterium) that can be present inside a package with fissile 

material to 500 g or less (total). The limitation on these low absorbing materials precludes forming 

a reflector that could be more effective than water around the optimally moderated system, which 

could reduce the subcritical mass for 235U, 233U, and 239Pu (Ref. 4).

4.3 General License: Plutonium-Beryllium Special Form Material

The general license criteria in 10 CFR 71.23 (Pu-Be special form material) is intended to allow 

NRC licensees to ship small quantities of fissile material in packages that have been assigned a 

CSI to ensure accumulation control for packages on a conveyance. The general license criterion 

in 10 CFR 71.23 applies to Pu-Be materials which meet the special form requirements of 

10 CFR 71.75, ensuring that the material itself will maintain its integrity and will not disperse 

during normal conditions of transport or under hypothetical accident conditions into an unfavorable 

geometry. Table 5 lists the content of 10 CFR 71.23, “General license: Plutonium-beryllium 

special form material.”

As stated in 10 CFR 71.23(b), the general licenses are applicable to licensees that have a quality 

assurance program approved by NRC. 10 CFR 71 Subpart H, “Quality Assurance,” 

(10 CFR 71.101-71.137) provides requirements for an acceptable quality assurance (QA) 

program to apply the general license criteria. This Subpart defines the QA requirements, 

organization, program, package design/procurement control, document control, test control, and 

other criteria relevant to ensuring the criteria in 10 CFR 71.23 can be applied by a licensee 

without NRC approval.

The general license criteria for Pu-Be special form materials are similar to those in the fissile 

material general license requirements with respect to having to calculate a CSI based on the 

quantity of fissile material present, specifically the quantities of the fissile isotopes 239Pu and 241Pu. 

For the general license to apply, the package containing Pu-Be special form sources cannot contain 

more than a Type A quantity of total radioactive material, and it is limited to 1,000 g plutonium with 

up to 240 g being the fissile isotopes 239Pu and/or 241Pu as required by 10 CFR 71.23(c). There are 
35

no provisions in 10 CFR 71.23 to limit the quantity of low neutron absorbing moderators because of 

the nature of the Pu-Be sources (small sealed capsules with a fixed geometry, and low mass limits). 

A CSI equation is provided in 10 CFR 71.23(e)(1) to allow the consignor to calculate the CSI for the 

package based on the mass of 239Pu and 241Pu in the package: 

CSI=10 �

grams of Pu 239 + grams of Pu 241

24 �.

Table 5 Content in 10 CFR 71.23 “General License: Plutonium-Beryllium Special Form 

Material” 

71.23 General License: Plutonium-beryllium special form material.

(a) A general license is issued to any licensee of the Commission to transport fissile material in the form of plutoniumberyllium (Pu-Be) special form sealed sources, or to deliver Pu-Be sealed sources to a carrier for transport, if the

material is shipped in accordance with this section. This material need not be contained in a package which meets the

standards of subparts E and F of this part; however, the material must be contained in a Type A package. The Type A

package must also meet the DOT requirements of 49 CFR 173.417(a).

(b) The general license applies only to a licensee who has a quality assurance program approved by the Commission

as satisfying the provisions of subpart H of this part.

(c) The general license applies only when a package’s contents:

(1) Contain no more than a Type A quantity of radioactive material; and

(2) Contain less than 1000 g of plutonium, provided that: plutonium-239, plutonium-241, or any combination

of these radionuclides, constitutes less than 240 g of the total quantity of plutonium in the package.

(d) The general license applies only to packages labeled with a CSI which:

(1) Has been determined in accordance with paragraph (e) of this section;

(2) Has a value less than or equal to 100; and

(3) For a shipment of multiple packages containing Pu-Be sealed sources, the sum of the CSIs must be less

than or equal to 50 (for shipment on a nonexclusive use conveyance) and less than or equal to 100 (for

shipment on an exclusive use conveyance).

(e)

(1) The value for the CSI must be greater than or equal to the number calculated by the following equation:

(2) The calculated CSI must be rounded up to the first decimal place.

This general license provision requires calculating the CSI for special form Pu-Be sources with the 

equation in 10 CFR 71.23(e)(1), which requires the consignor to know the quantity (grams) of total 

plutonium, including 239Pu and/or 241Pu, in the sources being packaged. The CSI limits for single 

and multiple packages containing fissile material based on the CSI equation and criteria in 

10 CFR 71.23(e) are meant to control the accumulation of fissile material in special form Pu-Be 

source packages on a conveyance (Ref. 6). For a single package, the CSI for these sources can 

be as high as 100. For shipment on a nonexclusive use conveyance, the CSI limit is smaller (50) 

and corresponds to half of the allowed 240 g mass limit for 239Pu, 241Pu, or mixtures of the two 

nuclides in the package. For shipment on an exclusive use conveyance, a higher CSI limit of 100 

is permitted due to the increased control on the shipment. A CSI limit of 100 corresponds to a total 

239Pu and 241Pu mass equal to the subcritical mass limit of 240 g. The general license criteria in 
36

10 CFR 71.23(d)(3) allow for a larger CSI for a single package (CSI = 100) than the general 

license criteria in 10 CFR 71.22(d)(2) (CSI = 10) because of the lower likelihood of special form 

fissile material escaping and reconfiguring into an unfavorable geometry during an exclusive use 

conveyance hypothetical accident.

The mass limits in 10 CFR 71.23(c) limit the quantity of plutonium in the Pu-Be special form 

sources to 1,000 g or less to ensure that there is sufficient criticality safety margin. This provision 

also requires that less than 240 g of the total plutonium quantity in the package is 239Pu, 241Pu, or 

a combination of 239Pu and 241Pu. To illustrate the difference between the fissile material 

exemption for Pu in 10 CFR 71.15(f) and the general license for special form Pu-Be sources, the 

240 g fissile Pu limit for 10 CFR 71.23 does not require a certain percentage of nonfissile material 

mixed with the fissile material (Pu), whereas 10 CFR 71.15(f) requires more than 80% of the Pu in 

the package to be nonfissile material. 

Provision 10 CFR 71.23(c)(1) requires that each package contain no more than a Type A quantity, 

as specified in Table A-1, “A1 and A2 Values for Radionuclides.” This provision ensures that 

radiological limitations are maintained within each package. For example, the maximum 

radiological limits (A1 value for special form material) for 239Pu and 241Pu in Table A-1 can be used 

to calculate the maximum quantity of these fissile nuclides allowed in a package, 4.35 kg and 

11 g, respectively. The Pu-Be general license allows for up to 1,000 g or less of Pu (up to 240 g 

total of 239Pu and 241Pu) to be present in a Type A package. Up to 760 g of other Pu isotopes is 

permitted in the package along with the fissile isotopes. The maximum radiological limits for 

special form material for each isotope (236Pu, 1.52 g; 237Pu, 0.045 g; 238Pu, 15.8 g; 242Pu, 69,230 g; 

and 244Pu, 61,111 g) can be present in the package along with the two fissile forms of Pu, up to 

the 1000 g limit. Thus, the consignor must ensure that no more than a Type A quantity of fissile 

material is present in a package but also that the package complies with the limitations of 

10 CFR 71.23. Also, the 10 CFR 71.23 provisions currently do not allow the use of Type B 

packages for shipping Pu-Be source materials. This issue may be addressed in a future 

rulemaking to 10 CFR 71. 

Provision 10 CFR 71.23(c)(2) limits the quantity of total plutonium present in the form of special 

form sources to 1,000 g or less. The fissile isotopes of plutonium, 239Pu and 241Pu, are those of 

significance to nuclear criticality safety. Thus, 239Pu, 241Pu, or combinations of these two isotopes 

are limited to 240 g or less of the total plutonium mass. For comparison, the acceptable subcritical 

mass limits of 239Pu and 241Pu are 370 g (Ref. 4) and 200 g (Ref. 26)respectively. The allowance 

for 240 g of fissile plutonium per package compared to the maximum general license allowance of 

37 g of fissile plutonium per package has been made because of the increased confidence that 

the fissile plutonium in the special form capsules would not escape during an accident and 

reconfigure into an unfavorable geometry (Ref. 16). Ref. 4 provides a technical basis for the 240 g 

239Pu + 241Pu mass limit in the package that is based on the acceptable subcritical mass of 379 g 

for 239Pu (keff = 0.95) for a thick water reflected fissile material-water moderated system. Using the 

same basis as the fissile material general licenses for moderators with a hydrogen density greater 

than water, the fissile Pu mass limit is equal to 64% of the critical mass value of 379 g and is 

rounded down to 240 g. The amount of fissile plutonium nuclides (239Pu and 241Pu) allowed in such 

a shipment is 24% of the total plutonium mass. Although typically limited in Pu-Be sources, the 

presence of the nonfissile plutonium isotopes will provide significant parasitic neutron absorption 

and will eliminate the potential for criticality.
37

5 EXAMPLE PROBLEMS

This section provides hypothetical examples for the fissile exemption provisions in 10 CFR 71.15 

and general license provisions 10 CFR 71.22 and 71.23. Each example problem was chosen based 

upon transportation scenarios that could illustrate how the provisions might be applied and justified. 

5.1 Fissile Material Exemption Examples

5.1.1 Small Samples

A variety of small samples that have contamination-level quantities of fissile material present are 

required to be shipped for disposition purposes. The fissile material samples present were 

generated from plutonium-bearing processes. These samples are contaminated metal, swipes, 

laundry, condensate from various fissile processes, environmental liquids, etc. The environmental 

samples contain fissile material at very low concentrations (milligrams or micrograms of fissile 

material per liter). The total measured fissile material mass plus two times the measurement 

uncertainty (total quantity of 239Pu and 241Pu) is significantly less than the 2 g fissile material 

exemption limit. Based on the measured quantity of fissile material present, these small samples 

can be shipped in an individual package within the 2 g exemption limit per individual package.

The 2 g fissile exemption in 10 CFR 71.15(a) was an obvious choice for this problem. This 

problem assumed that fissile mass was well known, but the content of the nonfissile materials 

present with the fissile material was not quantified. The need to quantify the amount of nonfissile 

material present along with the fissile material makes it difficult to comply with the requirements in 

10 CFR 71.15(b) or 10 CFR 71.15(c). The requirements of 10 CFR 71.15(d) and 71.15(e) also do 

not apply due to the presence of plutonium in the samples. The samples contain both 239Pu and 

241Pu with less than 200 g of 239Pu and 241Pu present; however, there is not enough information in 

the problem description to determine the quantity of nonfissile Pu present. Without knowing the 

quantity of nonfissile material present, the ratio of fissile Pu to nonfissile Pu cannot be calculated 

and compared to the 20% fissile Pu to nonfissile Pu limitation. These samples cannot be shipped 

using the requirements in 10 CFR 71.15(f). 

These samples can also be handled in greater quantities under the general license regulations in 

10 CFR 71.22 for licensees with an NRC-approved quality assurance program and no more than 

a Type A quantity of radioactive material in a Type A package. The need to quantify the amount of 

nonfissile material present along with the fissile material may make it difficult for a consignor to 

comply with the general license requirements to ship these sample materials under the fissile 

exemption provisions (10 CFR 71.15[b] and 71.15[c]).

5.1.2 Plutonium-Contaminated Glove Box

To support the decontamination and decommissioning of a plutonium processing facility, a glove 

box has been removed that contains 10 g of total Pu (including two times the measurement 

uncertainty) distributed uniformly on its interior surfaces. This is easily verified based on visual 

inspections of the interior surfaces. The glove box will be disassembled and packaged in a 

standard waste box for shipment to a waste repository. The glove box (mass of 300 kg) is made of 

stainless steel and contains no other moderating substances except a clear plastic cover held in 

place with duct tape. The total Pu mass can be assumed to be the fissile isotope 239Pu because it 

was used for weapons-grade plutonium processing operations. The quantity of 239Pu clearly 

meets the 15 g fissile material limit. The solid nonfissile mass of the glove box is 300 kg, which is 

much larger than required by the 200:1 ratio. The plastic bag mass is a negligible contribution to 
38

the nonfissile mass. Thus, the glove box can be shipped as fissile exempt material under 

71.15(b). 

Other fissile exemption regulations could have been applied to this example to determine if they 

could be used to ship the Pu-contaminated glove box. The exemption criteria from 

10 CFR 71.15(c) do not apply to this example problem. Because 71.15(c) states the exemption 

applies only when there is, essentially, a homogeneous mixture of fissile and nonfissile material 

(diluent), this provision cannot be applied to surface contaminated items since the fissile and 

nonfissile materials are not mixed together in a homogeneous matrix. 

The exemption regulation in 10 CFR 71.15(f) does not apply for this example problem. The 

contaminated glove box contains 10 g of total Pu based on physical measurements, which is

assumed to be 239Pu. There is no information provided on the content of nonfissile Pu that could 

also be present to calculate the ratio of fissile Pu to nonfissile Pu to compare to the limit provided 

in the exemption. Thus, the 71.15(f) provision cannot be applied to this example problem. 

The general license regulations in 10 CFR 71.22 can be considered for this example problem for 

licensees with an NRC-approved quality assurance program. In this case, there is a small quantity 

of plastic (negligible quantity) and a 300 kg stainless steel glove box present with 10 g of 239Pu. A 

Type A package is required by the general license provisions for the shipment, and there is no 

beryllium, graphite, or hydrogenous materials enriched in deuterium present. The general license 

provisions in 10 CFR 71.22 appear to be applicable to this problem; however, the use of a Type A 

package also involves radiological limitations based on the characteristics of the materials being 

shipped, in this case plutonium isotopes. The radiological limitations are provided in 10 CFR 71, 

Appendix A. Specifically, Table A-1 provides the A1 and A2 values for various radionuclides. The 

maximum mass of 239Pu permitted in a Type A package can be calculated by dividing the A2

value, 0.027 Ci, by the specific activity of 239Pu, 0.062 Ci/g. The quantity of 239Pu permitted in a

Type A package is 0.435 g, which is far less than the 10 g of total Pu needing to be shipped. 

Thus, the fissile material general license cannot be used to ship this material. 

5.1.3 Uranium Contaminated Sludge

Low-level waste (LLW) streams from various sites are contaminated with small concentrations of 

uranium. This LLW can be treated in a process to concentrate the wastes as sludge and place 

them into a 55 gal (208 L) drum that is filled with concrete for shipment to a disposal facility. 

Assume the density of the sludge is bounded by a value of 0.8 g/cm3 and the density of the 

concrete is 2.3 g/cm3

. The sludge and concrete are mixed together and the fissile material present 

is essentially homogeneously distributed in the sludge/concrete mixture. The only fissile isotope 

present is 235U, and there is no beryllium, graphite, or hydrogenous substances enriched in 

deuterium present in the package. The volume of the sludge is approximately 100 L, and the 

remainder of the drum volume, 108 L, is filled with concrete. This example considers 

235U-contaminated sludge with a concentration of 150 nCi/L, based on sampling results. The 

sampling error for the 235U data is ±50%. Based on the uncertainty in the sampling data, the total 

235U concentration in the sludge with two times the measurement uncertainty is equal to 300 nCi/L 

(150 nCi/L+ [2 × 0.50 × 150 nCi/L]). Based on the 235U concentration of 300 nCi/L, the specific 

activity for 235U, 2.2×10−6 Ci/g1

, and the sludge volume, 100 L, the total 235U mass can be 

calculated to be about 13.6 g ([300 nCi/L ÷ [109 nCi/Ci × 2.2x10−6 Ci/g] × 100 L). The total sludge 

mass is 80,000 g (100 L × 1,000 cm3

/L × 0.8 g/cm3), and the total concrete mass is 248,400 g 

 

1 The 235U Specific Activity is referenced from 10 CFR 71, Table A-1, “A1 and A2 Values for Radionuclides.”
39

([208 L – 100 L] × 1,000 cm3

/L × 2.3 g/cm3) for a total solid nonfissile mass of 328,400 g (80,000 g 

of sludge + 248,400 g of concrete). Thus, this waste stream can be transported as fissile exempt 

waste using the exemption in 10 CFR 71.15(b) because the total fissile material content is less 

than 15 g, and the total solid nonfissile content exceeds that required by the 200:1 ratio. If lead, 

beryllium, graphite, or hydrogenous substances enriched in deuterium were present in the LLW 

drum, it would be allowed, but the quantity of these moderating substances could not be counted 

toward the total quantity of solid nonfissile material. 

Other fissile exemption regulations could have been used to ship the uranium-contaminated 

sludge. The exemption criteria from 10 CFR 71.15(c) applies to this example as well. This 

example states that the material consists of low concentrations of solid fissile material 

commingled with solid nonfissile material. Based on the calculations above, there is more than 

24,000 g of nonfissile material for every gram of 235U present in the package, which meets the 

2,000-to-1 nonfissile -to-fissile ratio specified in 10 CFR 71.15(c)(1)(i). The fissile material is dilute, 

with 13.6 g of 235U distributed in about 328,400 g of nonfissile material, which is far less than the 

allowed fissile concentration of 180 g of 235U distributed within 360 kg of contiguous nonfissile 

material. 

The general license regulations in 10 CFR 71.22 can be applied to this problem for licensees with 

an NRC-approved quality assurance program as long as the material is shipped in a Type A 

package. Based on the information in the example problem, there is no beryllium, graphite, or 

hydrogenous materials enriched in deuterium present. The CSI can be calculated using the 

formula in 10 CFR 71.22(e)(1)-(5). The uranium enrichment is not provided in the example 

problem description, so the mass limits from Table 71-1 must be used. There are no moderating 

substances having an average hydrogen density greater than water present in the waste 

container, so the mass limits in column 1 in Table 71-1 can be used (60 g for 235U). The CSI for 

this example is 2.3 [CSI = 10 × (13.6 g of 235U ÷ 60 g of 235U)]. The calculated CSI for the package 

is less than 50, which qualifies the package to be shipped on a nonexclusive use conveyance.

5.1.4 Uranium-Contaminated Graphite

A large quantity of uranium-contaminated graphite has been discovered during decommissioning 

activities. The graphite was exposed to uranium during critical experiments in the past and NonDestructive Assay (NDA) measurements indicate that less than 10 g of 235U (including two times 

the measurement uncertainty) is present in a mass of graphite of approximately 2.5 kg consisting 

of “chunks” of graphite material. The uranium present is in the form of surface contamination. 

Based on the NDA measurement results and the mass of graphite present, a ratio of fissile 

material to nonfissile material present can be made. This ratio is calculated to be approximately 

1 g of 235U for 250 g of graphite present (10 g 235U ÷ 2500 g graphite). The uranium is diluted with 

graphite material such that the fissile-to-nonfissile ratio (1/250) is lesser than the ratio required by 

10 CFR 71.15(b) (1/200). However, the provision requires that the solid nonfissile materials not 

contain graphite, a low-absorbing moderating material. Thus, the graphite cannot be shipped as 

fissile exempt material. 

It is possible to use 10 CFR 71.15(c) to ship the uranium-contaminated graphite, provided 

nonfissile materials other than lead, beryllium, graphite, and hydrogenous material enriched in 

deuterium are present. These low neutron absorbing moderator and reflector materials cannot be 

included in the determination of the quantity of solid nonfissile material present. Thus, a solid 

nonfissile material (e.g., concrete or soil) can be added to the shipment in the required nonfissileto-fissile material ratio (2,000 g nonfissile material for every gram of fissile material) to be shipped 
40

as exempt from the requirements for fissile material, provided the material is mixed sufficiently to 

be considered commingled. 

With some redistribution and repackaging, the general license regulations in 10 CFR 71.22 can 

also be used for NRC licensees with an NRC-approved quality assurance program. The quantity 

of 235U present is compliant with the tabulated mass limits; however, the regulations only allow up 

to 500 g of graphite to be present in the shipment. The uranium-contaminated graphite can be 

shipped using this provision if less than 500 g graphite is present. Clearly, the quantity of 235U 

present would remain under the Table 71-1 mass limit. The material would have to be shipped in 

a Type A package.

5.1.5 Soils Contaminated with Fissile Material

A particular site has an area with 5 m3 (5,000,000 cm3

) of soil homogeneously contaminated with 

uranium from numerous past experiments. The experiments were known to use uranium with 

maximum enrichment of 3 wt % 235U. The soil density has been determined to be conservatively 

assessed as 1.33 g/cm3

, based on physical measurements of the medium textured soil present in 

the area. The quantity of uranium based on soil sample data is approximately 3 × 10−3

 g U/g soil 

(value represents the mean uranium value plus two times the measurement uncertainty). The total 

soil mass is approximately 6,650,000 g (5,000,000 cm3

 × 1.33 g/cm3), and, based on this quantity 

of soil, the quantity of uranium in the soil is about 19,950 g (6,650,000 g soil × 3 × 10−3

 g U/g soil). 

This corresponds to about 599 g of 235U contamination in the soil with uranium enriched to 3 wt % 

235U (19,950 g U × 0.03 g 235U/g U). To satisfy the exemption criteria of 10 CFR 71.15(c), there 

has to be at least 2,000 g of solid nonfissile material (soil in this case) per gram of 235U and no 

more than 180 g of 235U distributed within 360 kg of contiguous nonfissile material. The results of 

this example show that there is 6,650,000 g of soil mixed uniformly with 599 g of 235U, a ratio of 

11,102:1. This clearly meets the 2,000:1 ratio required by the exemption in addition to the 

concentration limit. Low neutron-absorbing moderators can be included in the package, but their 

mass cannot count toward the quantity of solid nonfissile material present. 

The provision of 10 CFR 71.15(b) is applicable assuming it is practical for the uraniumcontaminated soil to be broken into smaller shipments to comply with the 15 g fissile material 

mass limit and the required 200 g solid nonfissile material for each gram of fissile material ratio. 

This is likely to be an impractical option with respect to the quantity of contaminated soil needing 

to be shipped. 

The general license criteria in 10 CFR 71.22 can be used to ship the contaminated soil if the soil 

were significantly reduced in volume to comply with the shipping and packaging requirements. 

Each Type A package of uranium-contaminated soil would have to be measured for 235U content 

and would need to satisfy the Table 71-1 mass limits to generate a CSI for the package. This 

provision would tend to be impractical compared with the option to use 10 CFR 71.15(c) because 

control over the shipment would be required, including mass limits, packaging, and labeling 

requirements.

5.1.6 Contaminated Uranium Alumina Trap Contents

At a gaseous diffusion plant, a 55 gal drum (208 L) contains used alumina (Al2O3) trap mix 

(ρ = 0.8 g/cm3

) used to filter out UF6 from a particular gas stream. The UF6 reacts with the water 

loaded on the alumina to form uranyl fluoride dihydrate (UO2F22H2O). Grab sample results of the 

spent alumina trap mix material have verified that the uranium enrichment is less than 2.0 wt % 235U. 

These sampling results conservatively factor in two times the measurement uncertainties. 
41

Furthermore, the alumina was removed from a trap that had good gas flow, which ensures the 

alumina has a uniform quantity of uranium present throughout the trap (i.e., the mixture is 

homogeneous). This satisfies the 10 CFR 71.15(c) requirement that the fissile material is 

commingled with solid nonfissile material. Recent sampling data have confirmed previous sample 

results for the quantity of uranium present in the alumina and include two times the measurement 

uncertainty. There is approximately 8,000 g of uranium in the uranyl fluoride dihydrate present in the 

drum, which corresponds to about 160 g of 235U based on a uranium enrichment of 2.0 wt % 235U 

(8,000 g U × 0.02 g 235U/g U). Based on the density of the alumina (0.8 g/cm3

) and the volume of the 

55 gal drum (208 L), the total mass of alumina is 166,400 g (0.8 g/cm3

 × 208,000 cm3). To meet the 

exemption criteria in 10 CFR 71.15(c), there must be at least 2,000 g of solid nonfissile material per 

gram of fissile material. The nonfissile-to-fissile mass ratio for this example is 1,040:1, so the fissile 

exemption criterion cannot be met. For this exemption provision to be valid, based on the quantity of 

solid nonfissile material in the drum and the drum volume, less than about 83 g of 235U (4,160 g U) 

can be present to meet the dilution criteria. The uranium-contaminated alumina in the drum could be 

split into multiple drums, and fresh alumina or other nonfissile material could be added and mixed to 

reduce the ratio of fissile material to nonfissile material. 

The requirements in 10 CFR 71.15(b) could also be used to ship the uranium-contaminated 

alumina. Because the enrichment of the uranium contamination (2 wt % 235U) and the total 

quantity of uranium (8,000 g) are known, the alumina can be split into multiple packages to 

comply with the 15 g fissile mass limit. Assuming the uranium is homogeneously distributed 

throughout the alumina, this requires more than eleven packages with 728 g of uranium per 

package (14.5 g of 235U) to comply with the requirements. To increase the nonfissile-to-fissile 

mass ratio, at least 2,900 g of fresh or clean alumina, or other solid nonfissile material, would 

need to be added to the existing fissile material mixture.

The 10 CFR 71.22 general license regulations can be applied to this example to generate a 

package CSI limit based on the contents. Using these regulations would require the licensee to 

have an NRC-approved QA program and the shipment would have to be made in a Type A 

package. There are no special moderating materials present in the waste materials. The CSI can 

be calculated based on the 235U mass limits in Table 71-2 for an enrichment of 2 wt % 235U, 246 g 

235U. Assuming a Type A package can accept the volume of the contaminated alumina, the CSI 

for this package is 6.504 [CSI = 10 × (8,000 g uranium × 0.02 wt % 235U per gram of uranium 

÷ 246 g 235U)]. The final CSI, rounded up to the first decimal place is 6.6. Based on this CSI result, 

the package can be shipped with a CSI of less than 50, which qualifies the package to be shipped 

on a nonexclusive use conveyance. 

5.1.7 Uranium-Contaminated Process Equipment

Legacy equipment in a nuclear facility may contain fissile material in small quantities. For 

example, a converter from a gaseous diffusion plant may contain fissile material even following 

significant efforts to decontaminate the equipment non-destructively. Assume a converter from a 

gaseous diffusion plant processes uranium hexafluoride gas with uranium enrichment of 

1.75 wt % 235U. It is known that fissile material is present mainly as internal surface contamination. 

The interior portions cannot be visually inspected, and the equipment is known to contain less 

than 95 g of 235U, a value that contains at least two times the uncertainty of the NDA 

measurement. The site would like to ship this large item intact using fissile material exemption 

10 CFR 71.15(c) because it contains significantly more fissile material than allowed by 

10 CFR 71.15(a) and 71.15(b), and the 2,000:1 ratio of nonfissile material to fissile material is 

clearly met based on the quantity of 235U present and the large mass of the converter casing 

(nonfissile material). Based on operating experience, the consignor must assume that the fissile 
42

material present could redistribute during transportation operations, which is not consistent with 

the intent of 10 CFR 71.15(c) with respect to the fissile material being uniformly distributed within 

the nonfissile material, in this case the converter casing. Therefore, the converter cannot be 

shipped using the 10 CFR 71.15(c) fissile material exemption.

The size of the uranium-contaminated process equipment makes shipping options difficult. As 

discussed above, the fissile exemption regulations are not applicable to this situation. The general 

license requirements are an option; however, these requirements require an NRC-approved QA 

program and the use of a Type A package that meets the DOT requirements in 

49 CFR 173.417(a). If a Type A package can be designed or is available to ship the converter, the 

general license requirements can be used for the equipment. The uranium enrichment for this 

problem, 1.75 wt % 235U, is well within the enrichment data shown in Table 71-2, “Mass Limits for 

General License Packages Containing Uranium-235 of Known Enrichment per 71.22(e).” The CSI 

based on the 235U present, 95 g, and the mass limit for a 235U enrichment of 1.75 wt %, 246 g for 

2 wt % enrichment material (interpolation is not permitted and the next-highest enrichment value 

must be used), is 3.9 (CSI = 10 × [95 ÷ 246]). Based on this CSI result, and assuming the 

converter can be shipped in a Type A package, a single or multiple converters can be shipped 

with a CSI of less than 50, which qualifies the package to be shipped on a nonexclusive use 

conveyance.

5.1.8 Shipment of Multiple Drums

A temporary waste burial site that was used to bury metal drums of various kinds of wastes (e.g., 

uranium-contaminated piping, motors, tools, personnel protective equipment, etc.) has been 

exhumed for disposition to a permanent waste disposal site. During the excavation, operations 

personnel noticed that most of the metal drums had rusted sufficiently that the surrounding soil is 

suspected of being contaminated with radiological material, most of which is low-enriched 

uranium, greater than 1 wt % 235U enriched, based on historical records of the buried materials. 

The material was exhumed, including the contaminated soil, and repackaged into numerous steel 

drums with the fissile material carefully distributed throughout the nonfissile materials present. No 

lead, beryllium, graphite, or hydrogenous material enriched in deuterium was present in the 

loaded drums. Sample analysis results for the packaged drums indicate that all drums, except 

one, comply with the requirement in 10 CFR 71.15(c)(1) that there be at least 2,000 g of solid 

nonfissile material for every gram of fissile material present. The consignor noted that if all the 

drum ratio sample results were averaged together, all the drums would meet the 2,000:1 fissile 

material to nonfissile material ratio. However, the option to average the results of multiple drums 

to one result across multiple packages does not meet the intent of 10 CFR 71.15(c), which is that 

the material must be “commingled.” The outlier drum should be separated from the rest of the 

drums to allow the other compliant drums to be shipped under this exemption. 

The outlier drum could not be shipped as exempt from the definition of fissile material because the 

nonfissile-to-fissile material ratio was not greater than the 2,000-to-1 ratio required by 

10 CFR 71.15(c)(1). A simple option would be to repack the drum into two or more drums with a 

nonfissile diluent added and properly commingled such that it effectively reduces the nonfissile-tofissile ratio above the 2,000:1. The fissile exemption requirements in 10 CFR 71.15(b) could be 

applicable if less than 15 g of 235U were present along with greater than a 200:1 ratio of nonfissile 

material to fissile material, excluding lead, graphite, beryllium, or hydrogenous materials enriched 

in deuterium. The example problem does not provide sufficient information to determine whether 

or not 10 CFR 71.15(b) is applicable.
43

The general license requirements in 10 CFR 71.22 may be applicable to the outlier drum, 

depending upon the quantity of fissile material present and the characteristics of the nonfissile 

material in the drum. The general license requires an NRC-approved QA program and the use of 

a Type A package that meets the DOT requirements in 49 CFR 173.417(a).

5.1.9 Uranium-Contaminated Oil

This particular waste stream is prevalent in uranium enrichment operations where lubricating oils 

can become contaminated with uranium during operations. For this operation, the uranium is 

uniformly distributed throughout the oil based on the equipment in which the uranium and oil were 

mixed. The presence of uranium in hydrocarbon oil tends to significantly thicken the oil to the point 

that it will not flow freely, and operations personnel have to scoop the contaminated oil out of the 

equipment. The U-contaminated oil has been removed from the contaminated equipment and put 

into a 5.5 gal package for shipment to a disposal facility. This oil was sampled for enrichment but 

not for uranium mass. It is common for enrichment sample results to be reported with three times 

the measurement uncertainty at this particular site. For this case, the enrichment results for the oil 

are reported to be 0.92 wt % 235U meaning that the uranium present in the drum has been slightly 

enriched during diffusion plant operations. There is no 233U or Pu present, nor are low neutronabsorbing moderators such as lead, beryllium, graphite, or hydrogenous materials enriched in 

deuterium. Based on these results, the drum can be shipped as exempt from fissile classification 

based on the criteria in 10 CFR 71.15(d) because of the enrichment and distribution of the 

uranium in the drum. 

The 235U mass is not provided in the example problem although it could be estimated based on 

the viscosity of the oil and uranium mixture and historical sample results that consider uranium 

loading as a function of viscosity. However, this step is not required if the enrichment is known to 

be less than 1 wt % 235U. The 10 CFR 71.15(a) fissile exemption may apply to this situation, but it 

may be more difficult to demonstrate compliance with the regulation for these provisions. Because 

the oil and uranium mixture is not a solid material, the fissile exemptions in 10 CFR 71.15(b) and 

71.15(c) do not apply. The regulations for the general license in 10 CFR 71.22 could be applied to 

this example; however, it is far more practical and economical to use the fissile exemption in 

10 CFR 71.15(d) based on the information provided in the example problem.

5.1.10 Low-Enriched Uranium Waste

A waste process designed to chemically extract uranium from low-enriched solutions produces a 

filtrate that is solidified and ground into powder for storage. A package of this powder is to be 

shipped to another location and contains 400 g of 235U with an enrichment of 0.8 wt % 235U. 

Confirmatory samples show that there are 3.4 g of 233U and 0.4 g of 239Pu also present. These 

values include the sample analysis measurement uncertainty. The three fissile isotopes are 

distributed homogeneously in the powder. These quantities meet the exemption criteria in 10 CFR 

71.15(d) because the total mass of 233U and Pu (all assumed to be 239Pu) is less than 1% of the 

mass of 235U [(3.4 g of 233U + 0.4 g of 239Pu) ÷ (400 g of 235U) = 0.95%]. There were no moderating 

substances present in the waste material, so the criterion involving the presence of the low 

neutron-absorbing moderators is met.

The fissile exemption regulations in 10 CFR 71.15(c) may be applicable to this example if a 

nonfissile diluent was added in a sufficient quantity and comingled with the fissile material present 

([400 g of 235U + 3.4 g of 233U + 0.4 g of 239Pu] × 2000 g nonfissile per gram of fissile] = 807,600 g 

nonfissile) to meet the 2,000 g of nonfissile per gram of fissile material ratio. Furthermore, the 

distribution of fissile material in the nonfissile material must be assured to preclude more than 
44

180 g of fissile material per 360 kg of contiguous nonfissile material. The low-absorbing moderator 

materials cannot be included in the determination of the quantity of the nonfissile material present. 

The general license requirements in 10 CFR 71.22 may be used as well to ship the uranium 

powder with more rigorous justification and packaging requirements. Based on the information 

available in this situation, it is more economical and practical to use the fissile exemption criteria in 

10 CFR 71.15(d).

5.1.11 Uranium Metal Ingots

Uranium metal ingots with an enrichment of about 0.995 wt % 235U are produced as part of a 

fissionable material process. The metal ingots are cylindrical in shape, have a total uranium metal 

mass of 500 g (final density of about 18 g/cm3

) each, and have the diameter and height of 

approximately 3.3 cm (height-to-diameter ratio of 1.0). Sixty-four ingots are stored in a fixture 

made of stainless steel to preclude their rearrangement during shipping operations, and the 

individual ingots have an average edge-to-edge spacing of approximately 2 cm. The fixture has a 

configuration similar to a cubic array with four units in each dimension (4 × 4 × 4). The total 235U 

mass in the array of metal units is approximately 318 g (64 units × 500 g U/unit × 0.00995 g 

235U/g U). The consignor would like to transport this package as exempt from the classification as 

fissile based on 10 CFR 71.15(d), valid for fissile material with a uranium enrichment of less than 

1 wt % 235U. The uranium metal has been purified and does not contain any plutonium isotopes or 

233U, and there is no beryllium, graphite, or hydrogenous material enriched in deuterium present. 

The fissile exemption in 10 CFR 71.15(d) cannot be applied to fissile material in heterogeneous 

arrangements (i.e., a fixed, repeating array of fissile material lumps or distinct uranium metal 

units). It has been discussed previously that heterogeneous arrangement of low-enriched uranium 

can potentially be more reactive than homogeneous arrangements of the same material. Thus, 

these items cannot be shipped using 10 CFR 71.15(d). 

The fissile material exemptions do not apply to this situation based on the information provided. 

However, the 10 CFR 71.22 general license regulations appear to apply. The site would need an 

approved Type A package and an NRC-approved QA program. There are no requirements in the 

general license criteria regarding the homogeneity of the fissionable material being shipped. The 

general license requirements are applied to this example in Sect. 5.2.3. 

5.1.12 Uranyl Nitrate Solution from Spent Fuel Reprocessing

Uranyl nitrate solution that has been stored in 2 L bottles needs to be shipped to another site for 

research purposes. The facility is interested in using fissile exemption 10 CFR 71.15(e) for shipping 

these bottles. Each bottle contains 2 L of uranyl nitrate solution and no 233U is present in the 

solution. The solution has an enrichment of 1.5 wt % 235U based on sampling data that, with 

measurement uncertainties factored in, clearly satisfies the enrichment limitation of 2 wt % 235U or 

less for the exemption in 10 CFR 71.15(e). The uranyl nitrate solution being shipped was the 

product of spent fuel reprocessing and has very small concentrations of plutonium present. 

According to sampling data taken at the time the uranyl nitrate solution was produced, the quantity 

of Pu present is approximately 10 μg (measurement uncertainties included) and the Pu in the uranyl 

nitrate is expected to be uniformly distributed throughout all the uranyl nitrate solution stored in the 2

L bottles. The sampling records indicate that the N/U ratio is 3.7, which satisfies the exemption 

criterion for minimum N/U ratio. To ensure the limit on plutonium content, which must be less than 

0.002% of the mass of the total uranium present, the quantity of uranium in the 2 L bottle is 

determined from sampling data. According to the data logs, the uranium concentration is 200 g U/L 

(measurement uncertainty has already been factored into the concentration value). Thus, the 

uranium mass in the 2 L bottle of 400 g (200 g U/L × 2 L). Based on this uranium concentration, the 
45

maximum quantity of plutonium permitted in the 2 L bottle with uranyl nitrate solution is 0.008 g Pu 

(400 g U × 0.002%) and the total amount of Pu present in each 2 L bottle of solution is 

approximately 10 μg Pu (1 × 10−5

 g Pu). Multiple 2 L bottles of uranyl nitrate solution can be 

transported using 10 CFR 71.15(e) with these assumptions as long as the total amount of Pu in the 

Type A package is less than 0.008 g Pu. Based on the quantity of Pu in the 2 L bottle, 10 μg Pu 

(1 × 10−5

 g Pu), the requirements in 10 CFR 71.15(e) can be used to ship the uranyl nitrate solution, 

a single bottle of uranyl nitrate can be shipped as fissile exempt inside a Type A package. 

The only fissile material exemption specifically applicable to uranyl nitrate solutions is 

10 CFR 71.15(e). The general license regulations in 10 CFR 71.22 can be applied to this shipping 

scenario assuming the site has an NRC-approved QA program. These regulations also require 

the use of a Type A package. Beryllium, graphite, or hydrogenous materials enriched in deuterium 

are not present with the fissile material. Each 2 L bottle of uranyl nitrate solution contains 400 g of 

Uranium at a 235U enrichment of 1.5 wt. %. The total mass of 235U in each bottle is then (400 g U × 

0.015 g 235U per g U) about 6 g 235U. The quantity of Pu present (0.008 g of Pu) is less than 

1 wt % of the 235U mass present in each bottle (0.06 g of 235U), which allows use of mass limits for 

2 wt % 235U enrichment from Table 71-2 (408 g of 235U). The CSI, rounded up to the nearest tenth, 

is 0.1 for the uranyl nitrate (CSI = 10 × [6 g of 235U ÷ 408 g of 235U] = 0.0147), which is less than 

the single package CSI limit of 10. Single or multiple bottles of uranyl nitrate solution can be 

shipped up to the CSI limit of 50 for shipment on a nonexclusive use conveyance or the CSI limit 

of 100 for a shipment on an exclusive use conveyance. 

For this example, the provisions of 10 CFR 71.15(e) or 10 CFR 71.22 appear to be applicable to

the shipment of multiple 2 L bottles of uranyl nitrate solution in a single Type A package, 

assuming the radiological requirements are not exceeded.

5.1.13 Uranyl Nitrate Solution Laboratory Experiments

Uranyl nitrate solutions were used for various experiments at a site that processes uranium. The 

uranyl nitrate solutions are being shipped off-site to be converted to uranium oxide at another site. 

The solutions are stored in polyethylene 2 L bottles. Approximately 45 g of 235U in uranyl nitrate is

present in each bottle. The uranyl nitrate solution was generated from dissolving essentially pure 

uranium dioxide in nitric acid; thus, no other fissile isotopes are present. The solution was known 

to contain low-enriched uranium; however, sample and historical records had to be found to 

determine the enrichment of the solution. After this review was completed, the solution was 

determined to have an enrichment of 3.0 wt % 235U. Thus, the bottles of uranyl nitrate solution 

cannot be shipped as fissile exempt material per 10 CFR 71.15(e) because the enrichment limit is 

2.0 wt % 235U or less. 

The only fissile material exemption specifically applicable to uranyl nitrate solutions is 

10 CFR 71.15(e). The general license regulations in 10 CFR 71.22 can be applied to this shipping 

scenario assuming the site has an NRC-approved QA program. These regulations also require 

the use of a Type A package. There is no beryllium, graphite, or hydrogenous materials enriched 

in deuterium present with the fissile material. There is no 233U or Pu present, so the mass limits for 

3 wt % 235U enrichment from Table 71-2 (150 g of 235U) can be used. The CSI is calculated to be 

3.0 for the uranyl nitrate (CSI = 10 × [45 g of 235U ÷ 150 g of 235U]), which is less than the single 

package CSI limit of 10. Single or multiple bottles of uranyl nitrate solution can be shipped up to 

the CSI limit of 50 for shipment on a nonexclusive use conveyance.
46

5.1.14 Plutonium Oxalate Material

Nitric acid dissolution operations are performed at a plutonium processing facility to capture 

plutonium from scrap plutonium-contaminated items such as glass, graphite casting molds, 

incinerator ash, etc. The resulting plutonium solutions are passed through a column packed with 

anion-exchange resin to capture the plutonium in the solution. This plutonium is then precipitated 

out of the solution and passed through a filter. The filtrate is then dried under vacuum and placed 

into a sealed container and put into a vault for storage. This material is now in the form of 

plutonium oxalate, which can be converted to plutonium oxide by calcination at high temperature. 

The oxalate contains 150 g of weapons-grade plutonium that consists of 5 at. % 240Pu (5.02 wt % 

240Pu) and 95 at. % 239Pu (94.98 wt % 239Pu). No other plutonium isotopes are present in the 

plutonium oxalate. The quantity of 239Pu in the container is 142.5 g, which is significantly less than 

the maximum amount of fissile plutonium that could be shipped under 10 CFR 71.15(f); i.e., 200 g 

of fissile plutonium if the remainder up to the 1,000 g total is nonfissile plutonium. However, 10 

CFR 71.15(f) cannot be used for shipping the package of plutonium oxalate because the ratio of 

nonfissile plutonium (240Pu) to fissile plutonium (239Pu) does not exceed 80% (800 g nonfissile 

mass to 1000 g fissile mass). In this case, the ratio of 240Pu-to239Pu mass is much less than the 

required 80%; thus, the package of plutonium oxalate cannot be shipped individually under 

10 CFR 71.15(f). Furthermore, the quantity of 239Pu needing to be shipped in this example 

problem would require a Type B package because the quantity of 239Pu present would exceed a 

Type A quantity of radioactive material.

The other fissile exemption regulations in 10 CFR 71.15 do not apply to this example. The 

10 CFR 71.15(a) and 71.15(b) requirements are applicable for Pu systems; however, the quantity 

of Pu in this example exceeds the 10 CFR 71.15(a) and 71.15(b) mass limits 2 g and 15 g, 

respectively.

The general license regulations in 10 CFR 71.22 do not apply to this example problem. The 

quantity of 239Pu in this example, 142.5 g, exceeds the 239Pu mass limits in Table 71-1 (37 and 24 

for moderating substances having an average hydrogen density less than or equal to water or 

greater than water, respectively). For this example, the plutonium could be sub-divided amongst 

multiple containers; however, a Type B container would be required to comply with radiological 

requirements.

5.1.15 Plutonium-Contaminated Graphite Molds

There are fissile processes at some sites that use graphite molds to cast plutonium metal parts. 

After the plutonium metal in the mold cools, it is removed from the mold and the mold pieces are 

crushed and placed into containers. The molds from multiple casting operations are combined into 

a single container with a volume of 5 gal (about 18.9 L). Small quantities of plutonium remain in 

the molds. After the molds are crushed into a fine powder, the plutonium contamination is 

essentially homogeneously distributed in the graphite matrix. The 5 gal container holds the 

remains of 20 graphite molds that each contained approximately 4 g of 239Pu and 40 g of 240Pu of 

contamination (assume only 239Pu and 240Pu isotopes are present), based on a mass-balance 

after casting operations were completed. Thus, there is approximately 80 g of 239Pu and 800 g of 

240Pu present. In this case, there is less than 1000 g total of Pu present (880 g) with less than 20% 

of the total 239Pu (~9%). Thus, the plutonium-contaminated graphite molds can be shipped using 

the exemption in 10 CFR 71.15(f). This exemption applies to the quantities of fissile and nonfissile 

Pu isotopes present and does not restrict the presence of graphite with the fissile material.
47

The other fissile exemption regulations in 10 CFR 71.15 do not apply to this example. 

10 CFR 71.15(a) and 71.15(b) are applicable for Pu systems; however, the quantity of Pu in this 

example exceeds the 10 CFR 71.15(a) and 71.15(b) mass limits of 2 g and 15 g, respectively.

The general license regulations in 10 CFR 71.22 cannot be applied to this example problem. The 

quantity of 239Pu in this example, 80 g, exceeds the 239Pu mass limits in Table 71-1 (37 and 24 for 

moderating substances having an average hydrogen density less than or equal to water or greater 

than water, respectively). For this example, the plutonium could be sub-divided amongst multiple 

containers; however, a Type B container would be required to comply with radiological 

requirements.

5.2 General License Criteria Examples

5.2.1 Uranyl Nitrate Solution Laboratory Experiments

In Section 5.1.13, the example for 10 CFR 71.15(e) regarding uranyl nitrate solutions is 

reconsidered as an example to meet the general license requirements in 10 CFR 71.22. This 

example could not be used to demonstrate meeting the requirements of 10 CFR 71.15(e) 

because the enrichment of the 235U in the uranyl nitrate was too high, 3.0 wt % 235U. As previously 

stated, uranyl nitrate solutions were used for various experiments at a site that processes 

uranium. Some of these uranyl nitrate solutions are converted to uranium oxide at another facility. 

The solutions are stored in 2 L polyethylene bottles. Approximately 45 g of 235U of uranyl nitrate is 

present in each bottle. The uranyl nitrate solution was generated by dissolving essentially pure 

uranium dioxide in nitric acid; thus, no other fissile isotopes are present. The solution was known 

to contain low-enriched uranium; however, sample and historical records had to be found to 

determine the enrichment of the solution. After this review was completed, the solution was 

determined to have an enrichment of 3.0 wt % 235U, including measurement uncertainties. 

The contents will be contained within a Type A package, with no more than a Type A quantity of 

total radioactive material present. There is no beryllium, graphite, or hydrogenous material 

enriched in deuterium present in the package. Furthermore, the licensee that will ship the package 

has an NRC-approved QA program meeting 10 CFR 71 Subpart H. 

The CSI can be calculated by using the quantity of 235U present in the 2 L bottle of uranyl nitrate 

solution, 45 g. This mass quantity has already factored in uncertainties in the sampled data. The 

CSI equation with the mass of 235U and the mass limit referenced from Table 71-2 for uranium of 

known enrichment (3 wt % enriched in this case) is as follows: 

CSI=10 �

grams of U 235

X �

CSI=10 �

45 g

150 g� =3.0

The calculated CSI for the single package is less than the limit of 10. The package will be shipped 

on a nonexclusive use conveyance, which has a total CSI limit of 50 based on the CSI of the 

package. The consignor can ship up to 16 bottles if desired on the nonexclusive use conveyance.
48

5.2.2 Uranium-Graphite Waste

A particular fissile material operation generates wastes that contain a mixture of uranium, 

graphite, and other nonfissile solids after dissolution and precipitation operations. The enrichment 

of the uranium in the waste material is 20 wt % 235U. The solids are transferred to a 5 gal drum 

(18.9 L) and placed in a Type A package after the operations are completed. The solids have an 

average uranium concentration of about 7.5 g U/L. At 20 wt % 235U, the concentration of 235U is 

about 1.5 g 235U/L. The quantity of 235U in the 5 gal drum is about 28.4 g (1.5 g 235U/L × 18.9 L). 

Approximately 300 g of graphite (bulk density of 0.0159 g/cm3

) is present in the 5 gal drum. 

The contents will be contained within a Type A package, and no more than a Type A quantity of 

additional radioactive material is present in the container. Again, approximately 300 g of graphite 

is present inside the package and mixed with the fissile material, which is within the 500 g 

limitation. Furthermore, the licensee that will ship the package has an NRC-approved QA program 

as required by 10 CFR 71 Subpart H. 

The CSI can be calculated by using the quantity of 235U present in the 5 gal drum, 28.4 g, and the 

enrichment of the uranium, 20 wt % 235U. This mass quantity has already factored in two times the 

measurement uncertainties in the sampled data. The CSI equation, with the mass of 235U and the 

mass limit referenced from Table 71-2 for uranium of known enrichment, is as follows:

CSI=10 �

grams of U 235

X �

CSI=10 �

28.4 g

63 g � =4.507

The final CSI is 4.6, rounded up to the next decimal place. The calculated CSI for the single 

package is less than the limit of 10. The package will be shipped on a nonexclusive use 

conveyance which has a total CSI limit of 50. The consignor can ship multiple Type A packages if 

desired based on the calculated CSI. 

If a general license is not desired for shipping the drum of uranium graphite waste, the fissile 

exemption criteria in 10 CFR 71.15(c) can be used for this example if nonfissile diluent is added to 

the package to ensure a nonfissile-to-fissile mass ratio is greater than 2,000-to-1. This regulation 

allows graphite to be present in the package along with the fissile material and diluent material but 

the graphite cannot be used to determine the required mass of solid nonfissile material in the 

package. Because there is less than 30 g of 235U present in the package, the package will contain 

less than 180 g of fissile material distributed within the nonfissile matrix.

5.2.3 Uranium Metal Ingots

The uranium metal ingots from Sect. 5.1.11 cannot be shipped using the fissile material 

exemptions in 10 CFR 71.15. The consignor is now considering the requirements for a fissile 

material general license to ship the uranium metal ingots to another facility. As previously stated, 

the uranium metal units have an enrichment of about 0.995 wt % 235U, including measurement 

uncertainties. The metal ingots are cylindrical in shape, have a total uranium metal mass of 500 g 

each (final density of about 18 g/cm3

), and have a diameter and a height of approximately 3.3 cm 

(height-to-diameter ratio of 1.0). Sixty-four ingots are stored in a fixture made of stainless steel to 

preclude their rearrangement during shipping operations, and the individual ingots have an 
49

average edge-to-edge spacing of approximately 2 cm. The fixture has a configuration similar to a 

cubic array with four units in each dimension (4 × 4 × 4). The total 235U mass in the array of metal 

units is approximately 318 g (64 units × 500 g U/unit × 0.00995 g 235U/g U). The consignor has an 

NRC-approved QA program, and the consignor can ship the uranium fixture and units in a Type A 

package. The A1 and A2 values are unlimited for 235U and 238U, and there is no beryllium, graphite 

or hydrogenous materials enriched in deuterium present in the package. The consignor calculates 

the CSI based on the requirements in 71.22(e). The CSI equation from 71.22(e)(1) is used for the 

calculation. The 235U mass for the calculation is the total 235U present, 318 g, and the value of the 

X for 235U from Table 71-2 is 1,020 g (rounded up to an enrichment of 1 wt %).

CSI=10 �

grams of U-235

X �

CSI=10 �

318 g

1020 g� =3.12 (3.2)

The CSI calculation resulted in a CSI of 3.2 (rounded up to the first decimal place). The value of 

the CSI is less than 10, which is the CSI limit for a single package. If other fissile items are to be 

shipped using a fissile material general license, the sum of the CSIs must be less than or equal to 

50 for shipment on a nonexclusive use conveyance or less than or equal to 100 for an exclusive 

use conveyance. 

5.2.4 Sealed Sources for Gamma-Ray Measurements

A facility plans to ship a spherical sealed source containing depleted and highly enriched uranium 

(HEU) using the fissile material general license requirements in 10 CFR 71.22. The spherical source 

consists of four spherical shells with an HEU core. The core region contains a 53.76 g sphere of 

HEU (93 wt % 235U) metal with a density of 19.05 g/cm3 and a radius of approximately 0.86 cm. The 

shell around the core region is a 5.14-cm-thick spherical shell of aluminum metal (ρ = 2.7 g/cm3

), the 

third shell is a 2-cm-thick spherical shell of polyethylene (ρ = 0.92 g/cm3

), and the last shell is a 

0.5-cm-thick spherical shell of depleted uranium (ρ = 19.05 g/cm3

). The depleted uranium (DU) is 

0.3 wt % enriched 235

U. The sealed source is shown in Fig. 9. The consignor would need to consider 

the total 235U content present, as well as the mass of the polyethylene shell. Polyethylene has a 

larger hydrogen density than water; thus, the mass limits from Table 71-1, column 2, would apply 

(≤38 g of 235U). The total mass of 235U present can be calculated based on volume. The mass of the 

HEU core is 53.76 g, with an enrichment of 93 wt % 235U. The 235U mass in the core region is 50.0 g 

(53.76 g HEU × [0.93 g 235U ÷ gram HEU]). This exceeds the 235U mass limit for a fissile material 

general license, and 10 CFR 71.22 does not apply.

If the polyethylene shell were not present, or was replaced with a material with a hydrogen density 

less than that of water, the larger 235U mass limit would apply. In this case, the 235U mass in the 

core, 46.5 g, would be less than the mass limit in Table 71-1 for fissile material mixed or present 

with materials with a hydrogen density less than that of water. However, the calculation is not 

complete because the 235U content in the DU has not been factored into the 235U mass value. The 

DU is enriched to 0.3 wt % 235U. The volume of the DU shell is 427.8 cm3 (4π/3 × [router DU shell3

 – 

rinner DU shell3

] = 4π/3 × [(8.5 cm)3−(8 cm)3]), and the density is 19.05 g/cm3. The total 235U mass in 

the depleted uranium shell is the volume of the DU shell multiplied by the density of the material 

(19.05 g/cm3

) and the 235U enrichment (0.3 wt % 235U), which is equal to approximately 24.4 g 
50

235U. The total 235U in the sealed source is then the sum of the HEU core and the DU core, 74.4 g 

(50.0 g 235U in HEU + 24.4 g 235U in DU). Thus, even if the polyethylene shell was missing or 

replaced with another material, a fissile material general license could not be used to ship this 

sealed source.

Figure 9 Illustration of the HEU Sealed Source in 10 CFR 71.22 Example 4 (Figure Not to 

 Scale) 

5.2.5 Plutonium-Beryllium Sources 

Three plutonium-beryllium sources are to be shipped in a Type A package from one licensee to 

another to extract the plutonium from the sources for recycling purposes. The fissile content of the 

three sources is listed in Table 6. The licensee that will ship the package has an NRC-approved 

QA program as required by 10 CFR 71 Subpart H. 
51

Table 6 Isotopic Breakdown of Pu-Be Sources for 10 CFR 71.23 Example Problem 

Source Number Fissile Content (g) Total (g) 239Pu 241Pu

01-XYZ42 1.50 0.75 2.25

02-XYZ43 4.20 0.13 4.33

03-XYZ44 3.00 0.62 3.62

Total (grams) 8.70 1.50 10.20

Specific Activity (Ci/g) 6.20×10-2 1.0×102 –

Activity Present (Ci) 0.54 150.00 –

A1 Special Form Limit 270.00 1,100.00 –

The CSI can be calculated by using the total quantities for each fissile isotope, 8.7 g 239Pu and 

1.5 g 241Pu, from Table 6. These mass values have measurement uncertainties conservatively 

factored into them. 

The calculated CSI for the single package is less than the limit of 100. The package can be 

shipped on a nonexclusive use conveyance, which has a total CSI limit of 50. The consignor can 

ship up to 11 Type A packages if desired based on the results of the CSI calculation. To ensure 

the package meets the requirement in 10 CFR 71.23(c)(1) that it contain no more than a Type A 

quantity of radioactive material, the total activity is calculated based on the specific activity and 

A1/A2 values from 10 CFR 71, Table A-1, “A1 and A2 Values for Radionuclides.” The special form 

limits apply to the Pu-Be sources, which are sealed capsules that meet the definition for special 

form radioactive materials in 10 CFR 71.4. The specific activity, A1 values from Table A-1, and 

activities for 239Pu and 241Pu are provided in Table 6. The A1 special form limit is also provided in 

Table 6 to compare the activity result to the special form limit. The results in Table 6 show that the 

quantities of 239Pu and 241Pu present are within the A1 special form limits for a Type A package; 

thus, these Pu-Be sources can be shipped with the CSI limit of 4.3 in a Type A package.

Based on the quantities of fissile material present, 8.7 g of 239Pu and 1.5 g of 241Pu, it is possible to 

apply the fissile material exemptions, 10 CFR 71.15(f), to this problem only if there is greater than 

about 40.8 g of nonfissile plutonium (10.2 g 239Pu + 241Pu ÷ 0.2). The total amount of plutonium 

present is less than 1000 g (10.2 g–sum of 239Pu and 241Pu), which is required by 71.15(f), and 

less than 20% of the total plutonium present comprises fissile isotopes. However, there is no 

information in the example problem about the content of the nonfissile isotopes of plutonium 

present. Thus, the provisions of 10 CFR 71.15(f) cannot be applied to this situation. 

53

6 CONCLUSIONS AND FUTURE WORK

Title 10 of the United States (U.S.) Code of Federal Regulations (CFR), Part 71 (Ref. 26), 

Packaging and Transportation of Radioactive Material, contains requirements for exemption from 

classification as fissile material (10 CFR 71.15) and requirements for the general licenses for 

fissile material and plutonium-beryllium special form sources (10 CFR 71.22 and 71.23, 

respectively). The U.S. regulations in 10 CFR 71 have undergone significant evolution throughout 

the years. An overview of the history, technical basis, and intent of each of the fissile material 

exemptions and general licenses has been provided in this document, along with examples of 

their use, to assist fissile materials licensees and NRC review staff in understanding the 

requirements to transport fissile material. 

As this work was being completed, there were some potential opportunities for improvement 

compiled to improve the general licenses for fissile material in 10 CFR 71. Specifically, the 

provision for no 233U in 10 CFR 71.22(e)(5)(i) is overly restrictive given that small quantities of 233U 

may be present along with 235U in some circumstances, but those small quantities should not 

adversely impact nuclear criticality safety for a package. This issue could be resolved by 

modifying the provision to be similar to 10 CFR 71.22(e)(5)(ii), which limits plutonium to a mass 

percentage of the 235U. Additionally, there is a discrepancy between the limitation to a Type A 

quantity of radiological material in 10 CFR 71.22(c)(1) and the mass limits for plutonium in 

Table 71-1. The mass limits in this table are significantly larger than the Type A radiological limit of 

0.435 g 239Pu or 0.016 g 241Pu. There are no nuclear criticality safety issues with using a Type B 

package for the amount of fissile material in Table 71-1 provided the package is certified for the 

radiological content. Therefore, the NRC may consider revising the general license provisions to 

allow for shipment in a Type B package. These issues may be addressed in a future rulemaking 

to 10 CFR 71. 

The IAEA has regulations in SSR-6 that cover the packaging and transport of fissile material. 

These regulations have been historically similar to those in 10 CFR 71. With the 2012 Edition of 

the Regulations, the IAEA has significantly revised the approach used to provide exceptions for 

transport of fissile material in packages other than those certified for such transport (see 

Appendix B for more detailed information). These regulations are not consistent with the 

exemptions from classification as fissile material and fissile material general licenses in 

10 CFR 71. As in the past, the NRC will continue to monitor changes to the IAEA regulations and 

will seek compatibility wherever possible.

55

7 REFERENCES

1 Title 10 of the Code of Federal Regulations Part 71, Energy, Office of the Federal 

Register National Archives and Records Administration, February 18, 2016.

2 International Atomic Energy Agency, Safety Standards Series No. SSR-6, Regulations 

for the Safe Transport of Radioactive Material, 2009 Edition, International Atomic Energy 

Agency, Vienna, 2012.

3 ANSI/ANS-8.1-2014, “Nuclear Criticality Safety in Operations with Fissionable Material 

Outside Reactors,” American Nuclear Society, 2014.

4 C. V. Parks, C. M. Hopper, and J.L. Lichtenwalter, Assessment and Recommendations

for Fissile-Material Packaging Exemptions and General Licenses Within 10 CFR 71,

NUREG/CR-5342, (ORNL/TM-13607), U.S. Nuclear Regulatory Commission, Oak Ridge

National Laboratory, July 1998.

5 D. M. Willaford, Radioactive Materials Packaging and Transportation Primer, United

States Department of Energy, Oak Ridge Office, October 2011.

6 A. Barto, J. Smith, and C. V. Parks, “Bases for the General Licenses for Fissile Material

and Exemptions from Classification as Fissile Material in 10 CFR 71, ‘Packaging and

Transportation of Radioactive Material’,” Sixteenth International Symposium on the

Packaging and Transportation of Radioactive Materials, October 3-8, 2010, London,

United Kingdom.

7 Federal Register /, Vol. 62, No. 27, Monday, February 10, 1997 / Rules and Regulations 

10 CFR 71, Fissile Material Shipments and Exemptions.

8 Green, R. “Nuclear Criticality Safety Concerns Related to Transport of U-BEO Waste,” 

Trans. Am. Nucl. Soc., 76, pp. 256-257, Orlando, Fla., June 1-5, 1997.

9 NRC Information Notice 96-63. Potential Safety Issue Regarding the Shipment of Fissile

Material, U.S. Nuclear Regulatory Commission, Washington, D.C., December 5, 1996.

10 International Atomic Energy Agency, Safety Standards Series No. TS-R-1, Regulations 

for the Safe Transport of Radioactive Material, 1996 Edition (As Amended 2003), 

International Atomic Energy Agency, Vienna, 2003.

11 Title 10 of the Code of Federal Regulations Part 71, Energy, Office of the Federal 

Register National Archives and Records Administration, January 1, 1998.

12 Federal Register / Vol. 67, No. 83, Tuesday, April 30, 2002 / Compatibility with IAEA 

Transportation Safety Standards (TS-R-1) and Other Transportation Safety Amendments.

13 D. Hammer, K. Blake, L. Massar, S. Matheson, E. Piendak, Summary and Categorization

of Public Comments on the Major Revision of 10 CFR 71, U.S. Nuclear Regulatory 

Commission, NUREG/CR-6712, Apr. 2002.

14 Federal Register / Vol. 64, No. 207, Wednesday, October 27, 1999 / Fissile Material 

Shipments and Exemptions; Response to Comments and Request for Information.

15 International Atomic Energy Agency, “Consultant Services Meeting (CS-41) – 

Development of Exceptions from the Regulations for Transport Packages Containing 

Fissile Material – Discussion of Fissile Exemption Criteria Proposed by the United 

States,” Paris, France, March 15-17, 2004.
56

16 Federal Register / Vol. 69, No. 16, Monday, January 26, 2004 / Compatibility with IAEA 

Transportation Safety Standards (TS-R-1) and Other Transportation Safety Amendments.

17 International Atomic Energy Agency, Safety Standards Series No. TS-R-1, Regulations 

for the Safe Transport of Radioactive Material, 1996 Edition (As Amended 2003), 

International Atomic Energy Agency, Vienna, 2003.

18 Title 10 of the Code of Federal Regulations Part 71, Energy, Office of the Federal 

Register National Archives and Records Administration, June 12, 2015. 

19 SCALE: A Modular Code System for Performing Standardized Computer Analyses for 

Licensing Evaluation, ORNL/TM-2005/39, Version 6, Vols. I–III, January 2009. (Available 

from Radiation Safety Information Computational Center at Oak Ridge National

Laboratory as CCC-750.)

20 K. R. Elam, C. M. Hopper, C. V. Parks and T. E. Harris, Emplacement Considerations for 

Criticality Safety in Low-Level-Waste Disposal, ORNL/TM-13765, Oak Ridge National 

Laboratory, 2001.

21 N. L. Pruvost and H. C. Paxton, Critical Dimensions of Systems Containing 235U, 239Pu, 

and 233U, 1986 Revision, LA-10860-MS, Los Alamos National Laboratory (1986).

22 N. L. Pruvost and H. C. Paxton, Nuclear Criticality Safety Guide, LA-12808, Los Alamos 

National Laboratory (1996).

23 H. K. Clark, “Subcritical Limits for Uranium-235 Systems,” Nucl. Sci. Eng., 81, 351-378, 

(1982).

24 D. W. Magnuson, Calculated Limiting Critical Concentrations of Plutonium in Natural 

Uranium and Water, Oak Ridge National Laboratory, ORNL/TM-5443 (1976).

25 American National Standards Institute, American Nuclear Society, Nuclear Criticality 

Control of Special Actinide Elements, ANSI/ANS-8.15-1981(R2005).

26 Title 10 of the Code of Federal Regulations Part 71, Energy, Office of the Federal 

Register National Archives and Records Administration, January 1, 2012.
A-1

APPENDIX A 

BRIEF HISTORY OF 10 CFR 71 AND IAEA REGULATIONS 

FOR SAFE TRANSPORT OF RADIOACTIVE MATERIAL 

The early history of the regulations governing the transportation of fissile and other radioactive 

material has been previously discussed, in part, by Smith and Thomas (Ref. A1). Their paper 

provides chronological highlights of regulation development along with a brief discussion of the 

drivers of changes from 1936 to 1978. The brief history from that paper is provided below.

• United States post office issued an order banning “radium, thorium, or radioactive

substances, or any material containing radioactive substances” due to mail shipments of

radium occasionally fogging photographic film. Because of sensitive radiological detection

instrumentation and strict interpretations of this order by some (radiation could be detected

on or in most mail packages), an exemption was issued a few months later that allowed

limited quantities of radium paint to be shipped when properly packaged (1936).

• The National Cancer Institute convened a conference to consider the safe transport of

radium and resulted in criteria for the compatible transport of radium and film (1939).

• The Subcommittee on Shipment of Radioactive Substances of the Committee of Nuclear

Science of the Division of Mathematical and Physical Sciences of the National Research

Council developed a report (Ref. A2) that was a consistent and functional body of

regulations that provided some twenty years of safety transport of radioactive materials,

along with the bases behind them. These regulations introduced the concepts of exempt

quantities of fissile material, of low specific activity material and of the isolation of

radioactive materials and explosives that were transported together on rail cars (1951).

• The U.S. Atomic Energy Commission (AEC) adopted 10 CFR 71 regulations for the

protection of inadvertent criticality in the shipment of special nuclear materials (1958).

These regulations were replaced after a memorandum of understanding between the AEC

and the Interstate Commerce Commission (ICC) was written in 1966 that stated the

responsibility for regulation of carriers and consignors of radioactive materials belongs to

the ICC but with the AEC establishing packaging standards for fissile materials and large

quantities of radioactive material.

• The IAEA issued the first version of “Regulations for the Safe Transport of Radioactive

Materials1

,” which at this stage mainly consisted of recommendations and not regulations

(1961). This version of the regulations defined Fissile Classes I, II and III. Fissile I was

defined such that an unlimited number of undamaged packages would be subcritical in

any arrangement, or up to 250 would be subcritical in a damaged configuration. For

Fissile II packages, an acceptable number of packages from a criticality safety standpoint

was to be derived (five times the undamaged number of packages {NU} or two times the

damaged number of packages {ND} would be subcritical in a close-packed water-reflected

array configuration). The smaller of the two numbers (i.e., NU and ND) would be divided

into 50 to determine the minimum transport index for criticality safety purposes. The

aggregate of package transport indexes was limited to a value of 50 for a single shipment.

1This document is now designated SSR-6, “Regulations for the Safe Transport of Radioactive Materials.”
A-2 

It should be noted that the damaged package criteria were not added to the regulations 

until 1964. Fissile Class III shipments were those that required special arrangements for 

criticality safety control during transport and could have an aggregate of package minimum 

transport indexes no more than 100.

• The IAEA revised its regulations document (1964) with packaging test specifications and 

expanded the number of radiotoxicity groups to eight, and revised the document again 

(1967) to reduce the number of groups to seven and provided design principles for large 

radioactive source packages.

• The IAEA revised its regulations document again to eliminate the seven radiotoxicity 

groups and replaced them with two numerical limits, A1 and A2. Type A packages are 

limited to A1 curies in special form or A2 curies in normal form (1973). According to 

Ref. A3, A1 is defined as the maximum activity of special form radioactive material 

permitted in a Type A package, and A2 is defined as the maximum activity of radioactive 

material, other than special form material, Low Specific Activity2

, and Surface 

Contaminated Object3 material, permitted in a Type A package.

• The ICC regulations were superseded by regulations promulgated by the new Department 

of Transportation (DOT). The revised regulations were consistent with the 1967 version of 

the IAEA regulations. This led to two sets of criteria (A1/A2 for IAEA or Groups I through VII 

for the DOT) and many in the United States wanted to revise the DOT regulations to be 

consistent with the IAEA regulations; however, this was not done until 1983 when both the 

DOT and NRC adopted regulations that essentially conformed (certain minor exceptions 

and differences remained) with the 1973 IAEA requirements (Safety Series 6). 

Prior to 1996, fissile exemption and general license criteria in the regulations were based on 

criticality safety principles for fixed, well-known systems with common reflectors and moderators, 

such as water (Ref. A4). In 1996, the IAEA revised TS-R-1 regulations to limit the fissile mass per 

consignment4 and to restrict the presence of certain low-neutron-absorbing moderators5 (e.g., 

beryllium, carbon and deuterium).

 

2 Per Ref. A3, Low Specific Activity (LSA) material means radioactive material with limited specific activity which is 

nonfissile or is excepted under 10 CFR 71.15, and which satisfies the descriptions and limits set forth below.

3 Per Ref. A3, a Surface Contaminated Object (SCO) means a solid object that is not itself classed as radioactive 

material, but which has radioactive material distributed on any of its surfaces.

4 A consignment is defined in the regulations as any package or packages, or load of radioactive material, presented by 

a consignor for transport.

5 A “special” moderator is one that is effective in slowing down neutrons without the characteristic of absorbing neutrons 

that is a characteristic of hydrogen in water. In some conservative situations, the critical concentration and minimum 

critical mass of fissile material can be lower than similar configurations that contain water.
A-3

REFERENCES 

A1 D. R. Smith and J. T. Thomas, Review of the Bases for Regulations Governing the 

Transport of Fissile and Other Radioactive Material, LA-UR-78-1296, Fifth International 

Symposium on Packaging and Transportation of Radioactive Materials, May 7-12, 1978, 

Las Vegas, Nevada.

A2 R. D. Evans, Physical, Biological, and Administrative Problems Associated with the 

Transportation of Radioactive Substances, National Academy of Sciences, National 

Research Council, Washington, D.C., 1951.

A3 Title 10 of the Code of Federal Regulations Part 71, Energy, Office of the Federal Register 

National Archives and Records Administration, February 18, 2016.

A4 C. V. Parks, “Technical Basis for Proposed Fissile Exemption Criteria for Transport 

Packages, Presentation for the 14th International Symposium on the Packaging and 

Transportation of Radioactive Materials,” Berlin, Germany, Sept. 24, 2004.

B-1

APPENDIX B 

DISCUSSION OF IAEA REGULATIONS 

B.1 Background

The IAEA Regulations for the Safe Transport of Radioactive Material have, for over a 50-year

period, provided specific requirements for packages certified for transport of fissile material. With

the 2012 Edition of the Regulations (hereafter referred to as the 2012 Edition), the IAEA has

significantly revised the approach used to provide exceptions (the IAEA uses the term

“exceptions,” whereas in the United States the term “exemptions” is used) for transport of fissile 

material in packages other than those certified for such transport. Prior to the 1996 Edition of the 

Regulations (hereafter referred to as the 1996 Edition), the criteria for exception from transport in 

certified packages indicated criticality safety would be assured regardless of packaging and

without the need to control accumulations of packages or material. The adequacy of many of

these criteria was challenged, particularly with regard to unintended accumulation of material and

assurance of continued adherence to the criterion under accident conditions of transport. Thus,

with the introduction of the 1996 Edition, many of the exception criteria were constrained by an

imposed limit on the total mass of fissile material that could be shipped in a consignment.

Rather than resolve the discussion on exceptions for transport of fissile material, the 1996 Edition 

seemed to motivate further concerns, and by 2009 the IAEA had accumulated over 100 proposals

recommending changes to the criteria that allow exceptions from requirements to transport fissile 

material in certified packages. The 2012 Edition of the Regulations provides a significant

modification to the approach implemented for exceptions to the requirements for transport of

fissile material. This Appendix provides a simplified overview of the requirements for packages

certified for transport of fissile material and the categories of exceptions from these requirements

that are allowed in the 2012 Edition. 

B.2 Packages Certified for Transport of Fissile Material

Before discussing exceptions, it is beneficial to review the “standard” from which exceptions are 

allowed. Package designs certified for transport of fissile material must adhere to the

requirements and provisions specified in paragraphs 676-686 of the 2012 Edition of the 

Regulations. These paragraphs provide the expectations that an applicant must demonstrate 

relative to subcriticality of individual packages and arrays of packages under normal conditions of

transport and hypothetical accident conditions. Key requirements are:

1) “5 times N packages shall be subcritical for the arrangement and package conditions that

provide the maximum neutron multiplication” (keff) consistent with normal conditions of

transport, and

2) “2 times N packages shall be subcritical for the arrangement and package conditions that

provide the maximum neutron multiplication” under hypothetical accident conditions.

For each requirement, the “package conditions” must assume the range of specified contents for 

the package, and unknown values associated with the contents must be assumed such that the 
B-2

CSI = 50/N (1), 

where N is selected to be the smaller of the two values determined from the subcriticality

assessments for normal conditions of transport and hypothetical accident conditions.

The CSI value is included in the package certificate issued by the competent authority and is used 

to provide a means of control over the accumulation of packages during transport. For example, if

N = 5 for the purpose of determining the CSI per Eq. 1, then the CSI = 10 for the package. The 

CSI for a conveyance of packages must be limited to 50 unless the package is loaded,

transported, and unloaded by a single consignor under exclusive use (in which case a CSI up to 

100 is allowed subject to approval by the governing regulatory agency of the IAEA Member State).

Finally, packages certified by a competent authority will have an “F” as part of the type code on 

the certificate and must be shipped with a label that identifies the contents have been classified as

“FISSILE” consistent with shipping names and descriptions established by the United Nations.

The label also must include the CSI value consistent with the certificate issued by the regulatory

body of the IAEA Member State. 

B.3 Transport of Fissile Material in Packages Not Certified by the Regulatory

Agency

The IAEA Regulations provide the general expectation that all fissile material be transported so as 

to maintain subcriticality, but they also provide for exceptions that allow fissile material to be 

transported in packages not certified by the governing regulatory agency. Fundamentally, the 

IAEA provides two types of exceptions, where the fissile material is classified as “FISSILE” and 

subject to CSI control and exceptions where the fissile material is not classified as “FISSILE” and 

the transport is not subject to CSI control. 

The exceptions that require CSI control are very similar to those of the general licenses in 

10 CFR 71.22. The criticality safety during transport is assured largely on the fact that the 

respective mass of fissile material is controlled per the CSI to assure that 5N packages are 

subcritical under normal conditions of transport and 2N packages are subcritical under 

hypothetical accident conditions. The use of CSI control requires that each package must be 

classified as “FISSILE” and labeled with the proper CSI to control accumulation below the limiting 

safe mass values. 

The IAEA Regulations have a provision very similar to 10 CFR 71.15(f) whereby up to 1 kg of 

plutonium need not be shipped in a package certified for transport of fissile material provided not 

more than 20% of the plutonium mass consists of fissile nuclides of plutonium (e.g., 239Pu and 

241Pu). This historic exception has been included in the 2012 Edition, but with the new requirement 

that the package be classified as “FISSILE” and a CSI be provided on the package label to assure 

accumulation control. 

The second type of exception within the 2012 Edition are those where the fissile material is not 

classified as “FISSILE.” However, unlike the approach used for the exemptions of 

10 CFR 71.15(a)-(c), the 2012 Edition limits the quantity of fissile nuclides per package and 

combines that with a mass limit on the consignment. The mass of fissile material allowed per 

package is 2 g with a consignment limit of 15 g. For uranium with enrichments less than 5 wt % 

235U, 3.5 g per package is allowed, provided the consignment is limited to 45 g. Additionally, 

paragraph 417(e) allows shipment of up to 45 g fissile material, packaged or unpackaged, 

highest value of keff is obtained. Based on the assessment of these key requirements, the 

Criticality Safety Index (CSI) for each package is established to be 
B-3

provided the shipment is made under exclusive use (i.e., the conveyance is limited to 45 g fissile 

material). The exemptions of 10 CFR 71.15 (d)-(e) are also included within the 2012 Edition. 

B.4 Exception from Definition as Fissile Material

The 2012 Edition of the Regulations defines fissile material to be material containing fissile 

nuclides defined as 233U, 235U, 239Pu, and 241Pu. Excluded from the definition of fissile material is

natural uranium or depleted uranium that is unirradiated or that has been depleted in thermal

reactors only. With the 2012 Edition, the definition was expanded to exclude material with less

than 0.25 g of fissile nuclides. This exclusion was added in recognition that many materials have 

trace quantities of fissile nuclides and the intent of the Regulations is not to have such materials

governed under the requirements set forth for fissile material.

Douglas G. Bowen, Cecil V. Parks

Oak Ridge National Laboratory

Managed by UT-Battelle, LLC

Oak Ridge, TN 37831-6170

Division of Spent Fuel Management

Office of Nuclear Material Safety and Safeguards

U.S. Nuclear Regulatory Commission

Washington, DC 20555-0001

Title 10 of the United States (US) Code of Federal Regulations (CFR), Part 71, Packaging and 

Transportation of Radioactive Material, includes requirements for the transport of fissile material in 

packages. These regulations provide requirements for packages that are certified by the U.S. Nuclear 

Regulatory Commission (NRC) to transport fissile material. 10 CFR 71 also includes provisions for 

exemptions from classification as fissile material (10 CFR 71.15) and permits general licenses for limited 

quantities of fissile material and plutonium-beryllium special form sources (10 CFR 71.22 and 10 CFR 

71.23, respectively). These provisions were extensively revised by the NRC as part of a broad rule-making 

effort in 2004. The exemption and general license provisions are used frequently for a wide-variety of fissile 

material shipping operations, and consignors must interpret the regulations for particular shipping situations. 

The purpose of this document is to provide explanatory information on the background, intent, and 

anticipated use of the provisions in an effort to assist fissile material licensees in their interpretation and 

application of the provisions such that criticality safety is ensured during transportation activities. A variety of 

examples are presented and discussed to illustrate how the regulations should be applied.

Review of Exemptions and General Licenses for Fissile Material 

in 10 CFR 71

NUREG/CR-7239

January 2018

J5728

Technical

Fissile material 

Criticality safety 

Transportation 

Exemption 

General license



Review of Exemptions and General Licenses for Fissile Material in 10 CFR 71

NUREG/CR-7239 January 201

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