Acceptable Standard 

Format and Content for 

the Material Control and 

Accounting Plan Required 

for Low-Enriched Uranium 

Enrichment Facilities

Draft Report for Comment

Office of Nuclear Material Safety and Safeguards

NUREG-2158
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Acceptable Standard 

Format and Content for 

the Material Control and 

Accounting Plan Required 

for Low-Enriched Uranium 

Enrichment Facilities

Draft Report for Comment

Manuscript Completed: June 2013 

Date Published: September 2013

Office of Nuclear Material Safety and Safeguards

NUREG-2158
COMMENTS ON DRAFT REPORT

Any interested party may submit comments on this report for consideration by the NRC staff. 

Comments may be accompanied by additional relevant information or supporting data. Please 

specify the report number NUREG-2158 in your comments, and send them by the end of the 

comment period specified in the Federal Register notice announcing the availability of this 

report. 

Addresses: You may submit comments by any one of the following methods. Please include 

Docket ID NRC-2013-0195 in the subject line of your comments. Comments submitted in 

writing or in electronic form will be posted on the NRC website and on the Federal rulemaking 

website http://www.regulations.gov. 

Federal Rulemaking Website: Go to http://www.regulations.gov and search for documents 

filed under Docket ID NRC-2013-0195. Address questions about NRC dockets to Carol 

Gallagher at 301-287-3422 or by e-mail at Carol.Gallagher@nrc.gov.

Mail comments to: Cindy Bladey, Chief, Rules, Announcements, and Directives Branch 

(RADB), Division of Administrative Services, Office of Administration, Mail Stop: 3WFN-06-A44, 

U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001.

For any questions about the material in this report, please contact: Tom Pham, Senior 

Safeguards Analyst, at 301-287-9132 or by e-mail at Tom.Pham@nrc.gov.

Please be aware that any comments that you submit to the NRC will be considered a public 

record and entered into the Agencywide Documents Access and Management System 

(ADAMS). Do not provide information you would not want to be publicly available.
iii NUREG-2158

ABSTRACT

This guidance document updates NUREG/CR-5734, K/ITP-415, “Recommendations to the NRC 

on Acceptable Standard Format and Content for the Fundamental Nuclear Material Control 

(FNMC) Plan Required for Low-Enriched Uranium Enrichment Facilities,” issued 1991, and 

applies to uranium enrichment facilities licensed by the U.S. Nuclear Regulatory Commission 

(NRC) that are subject to Title 10 of the Code of Federal Regulations (10 CFR) 74.33, “Nuclear 

Material Control and Accounting for Uranium Enrichment Facilities Authorized To Produce 

Special Nuclear Material of Low Strategic Significance.” In 1991, the NRC added 10 CFR 74.33 

to the material control and accounting (MC&A) requirements of 10 CFR Part 74, “Material 

Control and Accounting of Special Nuclear Material.” As revised, this regulation applies to

NRC-licensed uranium enrichment facilities that are authorized to possess equipment capable 

of enriching uranium and to produce, possess, or use more than 350 grams of special nuclear 

material (SNM) of low strategic significance.

The 10 CFR 74.33 requirements are patterned after 10 CFR 74.31, “Nuclear Material Control 

and Accounting for Special Nuclear Material of Low Strategic Significance,” which applies to 

NRC licensees authorized to possess and use more than 350 grams of unencapsulated SNM of 

low strategic significance. Because enrichment facilities can produce SNM of moderate 

strategic significance and also strategic SNM, additional MC&A performance objectives and 

capabilities are required in 10 CFR 74.33 that are not required by 10 CFR 74.31. 

This NUREG provides a structure and information to facilitate licensee or applicant compliance 

with 10 CFR 74.33 on the preparation and implementation of MC&A plans and corresponding 

NRC review and inspection.

This document also provides guidance on the requirements of 10 CFR 74.3, “General 

Performance Objectives,” and 10 CFR 74.33, and describes methods that should be acceptable 

for compliance with the general performance objectives and program capabilities described in 

those sections. This includes guidance for implementing new requirements in 10 CFR 74.33 on

tamper-safing and designation of material balance areas and item control areas. It also 

includes guidance on commitments on general performance objectives and program

capabilities.

v NUREG-2158

CONTENTS

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

CONTENTS............................................................................................................................... v

ACRONYMS AND ABBREVIATIONS.......................................................................................ix

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

2. GENERAL PERFORMANCE OBJECTIVES, RELATED REQUIREMENTS, 

COMMITMENTS, AND ACCEPTANCE CRITERIA............................................................... 3

General Performance Objectives............................................................................................ 3

Commitments and Acceptance Criteria on General Performance Objectives.......................... 8

3. MANAGEMENT STRUCTURE ............................................................................................. 9

3.0 Regulatory Intent ............................................................................................................. 9

3.1 Corporate Organization ................................................................................................... 9

3.2 Plant or Site Organization................................................................................................ 9

3.3 Material Control and Accounting Organization................................................................. 9

3.3.1 Responsibilities and Authority ..................................................................................10

3.3.2 Material Control and Accounting Procedures ...........................................................10

3.4 Training and Qualification Requirements ........................................................................11

3.5 Material Control and Accounting Program Description....................................................11

3.6 Material Control Boundaries ...........................................................................................12

3.7 Commitments and Acceptance Criteria...........................................................................12

4. MEASUREMENTS...............................................................................................................15

4.0 Regulatory Intent ............................................................................................................15

4.1 Measurement Points.......................................................................................................15

4.2 Measurement Systems...................................................................................................15

4.2.1 Bulk Measurement Systems.....................................................................................16

4.2.2 Analytical Measurement Systems ............................................................................16

4.2.3 Nondestructive Assay Measurement Systems .........................................................16

4.2.4 Other Measurement Systems...................................................................................17

4.3 Measurement Uncertainties............................................................................................17

4.4 Measurement Procedures ..............................................................................................17

4.5 Commitments and Acceptance Criteria...........................................................................18

5. MEASUREMENT CONTROL SYSTEM ...............................................................................21

5.0 Regulatory Intent ............................................................................................................21

5.1 Organization and Management.......................................................................................21

5.1.1 Functional Relationships ..........................................................................................21

5.1.2 Procedures...............................................................................................................21

5.1.3 Contractor Program Audits and Reviews..................................................................22

5.2 Calibrations ....................................................................................................................22

5.3 Control Standards...........................................................................................................23

5.4 Replicate Sampling.........................................................................................................25

5.5 Control limits...................................................................................................................25

5.5.1 Measurement Control Data Analysis ........................................................................26
NUREG-2158 vi

5.5.2 Response Actions ....................................................................................................26

5.6 Commitments and Acceptance Criteria...........................................................................27

6. STATISTICS........................................................................................................................31

6.0 Regulatory Intent ............................................................................................................31

6.1 Determination of Measurement Uncertainties .................................................................31

6.2 Determination of Standard Error of the Inventory Difference...........................................32

6.3 Bias Corrections .............................................................................................................32

7. PHYSICAL INVENTORIES..................................................................................................35

7.0 Regulatory Intent ............................................................................................................35

7.1 General Description........................................................................................................35

7.2 Organization, Procedures, and Schedules......................................................................36

7.3 Typical Inventory Composition........................................................................................36

7.4 Description of Typical Item Strata ...................................................................................37

7.5 Conducting Dynamic Physical Inventories ......................................................................37

7.6 Conducting Static Physical Inventories ...........................................................................38

7.7 Inventory Difference Limits and Response Actions .........................................................40

7.8 Commitments and Acceptance Criteria...........................................................................41

8. PROGRAM FOR PREVENTING AND DETECTING UNAUTHORIZED PRODUCTION 

OF ENRICHED URANIUM ...................................................................................................45

8.0 Regulatory Intent ............................................................................................................45

8.1 Organization ...................................................................................................................45

8.2 General Description of Program .....................................................................................45

8.3 Data, Information, and Activities To Be Monitored ..........................................................47

8.4 Reporting and Documentation Requirements .................................................................49

8.5 Commitments and Acceptance Criteria...........................................................................49

9. ITEM CONTROL..................................................................................................................51

9.0 Regulatory Intent ............................................................................................................51

9.1 Organization ...................................................................................................................51

9.2 General Description........................................................................................................51

9.3 Item Identity Controls......................................................................................................52

9.4 Storage Controls.............................................................................................................52

9.5 Item Monitoring Methodology and Procedures................................................................52

9.6 Investigation and Resolution of Item Discrepancies........................................................53

9.7 Commitments and Acceptance Criteria...........................................................................53

10. SHIPPER-RECEIVER COMPARISONS ............................................................................55

10.0 Regulatory Intent ..........................................................................................................55

10.1 Receiving Procedures...................................................................................................55

10.2 Determination of Receiver’s Values ..............................................................................56

10.3 Evaluation of Shipper-Receiver Differences..................................................................56

10.4 Resolution of Significant Shipper-Receiver Differences ................................................56

10.5 Commitments and Acceptance Criteria.........................................................................56
vii NUREG-2158

11. ASSESSMENT AND REVIEW OF THE MATERIAL CONTROL AND 

 ACCOUNTING PROGRAM................................................................................................59

11.0 Regulatory Intent ..........................................................................................................59

11.1 General Description......................................................................................................59

11.2 Report of Findings and Recommendations ...................................................................60

11.3 Management Review and Response to Report Findings and Recommendations .........60

11.4 Commitments and Acceptance Criteria.........................................................................61

12. TAMPER-SAFING .............................................................................................................65

12.0 Regulatory Intent ..........................................................................................................65

12.1 Characteristics of Tamper-Safing Devices ....................................................................65

12.2 Use of Tamper-Safing Devices .....................................................................................66

12.3 Description of Tamper-Safing Records .........................................................................66

12.4 Commitments and Acceptance Criteria.........................................................................67

13. DESIGNATION OF MATERIAL BALANCE AREAS, ITEM CONTROL AREAS, 

 AND CUSTODIANS ...........................................................................................................69

13.0 Regulatory Intent ..........................................................................................................69

13.1 Material Control Boundaries .........................................................................................69

13.2 Custodians ...................................................................................................................69

13.3 Commitments and Acceptance Criteria.........................................................................69

14. RESOLVING INDICATIONS OF MISSING URANIUM AND OF UNAUTHORIZED 

 PRODUCTION OF ENRICHED URANIUM........................................................................71

14.0 Regulatory Intent ..........................................................................................................71

14.1 Methods and Procedures for Identifying Indicators .......................................................71

14.2 System and Procedures for Investigating and Resolving Indicators ..............................72

14.3 Response Actions for Unresolved Indicators ................................................................73

14.4 Documentation Requirements ......................................................................................74

14.5 Commitments and Acceptance Criteria.........................................................................74

15. INFORMATIONAL AID FOR ASSISTING IN THE INVESTIGATION AND 

 RECOVERY OF MISSING URANIUM OR ASSISTING IN THE INVESTIGATION 

 OF UNAUTHORIZED ENRICHMENT.................................................................................77

15.0 Regulatory Intent ..........................................................................................................77

15.1 Types of Information.....................................................................................................77

15.2 Information Indicating Possible Losses of Special Nuclear Material..............................77

15.3 Commitments and Acceptance Criteria.........................................................................79

16. RECORDKEEPING ...........................................................................................................81

16.0 Regulatory Intent ..........................................................................................................81

16.1 Description of Records .................................................................................................81

16.2 Program and Controls for Ensuring an Accurate and Reliable Record System .............82

16.3 Commitments and Acceptance Criteria.........................................................................83

17. GLOSSARY.......................................................................................................................85

18. REFERENCES ..................................................................................................................91

ix NUREG-2158

ACRONYMS AND ABBREVIATIONS

AEC Atomic Energy Commission

CFR Code of Federal Regulations

DOE U.S. Department of Energy

DQ detection quantity

DT detection threshold

DU depleted uranium

HEU high-enriched uranium

IAEA International Atomic Energy 

Agency

ICA item control area

ID inventory difference

LEU low-enriched uranium

MBA material balance area

MC&A material control and 

accounting

NDA nondestructive assay

NRC U.S. Nuclear Regulatory 

Commission 

RBIPI running book in-process 

inventory

SEID standard error of the 

inventory difference 

SM source material

SNM special nuclear material

SRD shipper-receiver difference

SWU separative work unit

TID tamper-indicating device

U uranium

UO2 uranium dioxide

U3O8 urano-uranic oxide

UF6 uranium hexafluoride

wt % weight percent

1 NUREG-2158

1. INTRODUCTION

The Atomic Energy Act of 1954, as amended, directed the U.S. Atomic Energy Commission 

(AEC) to regulate the receipt, manufacture, production, transfer, possession, use, import, and 

export of special nuclear material (SNM) to protect public health and safety and to provide for 

the common defense and security. The Energy Reorganization Act of 1974 transferred all the 

licensing and related functions of the AEC to the U.S. Nuclear Regulatory Commission (NRC). 

The principal requirements with respect to SNM licensing are in Title 10 of the Code of Federal 

Regulations (10 CFR) Part 70, “Special Nuclear Material,” and 10 CFR Part 74, “Material 

Control and Accounting [MC&A] of Special Nuclear Material.” Regulations in 10 CFR 70.22(b) 

specify that a full description of the applicant’s program for the control and accounting of such 

SNM must be contained in a license application to show how compliance with the graded MC&A 

requirements of 10 CFR Part 74, Subparts B–E, will be accomplished. This document 

describes the standard format and content suggested by the NRC for use in preparing MC&A 

plans for uranium (U) enrichment facilities authorized to produce, possess, or use a quantity 

greater than 350 grams of contained U-235 or SNM of low strategic significance. Facilities used 

to enrich uranium, because of the nature of the operations and the types of materials that will be 

on site, pose two unique problems addressed in the NRC’s regulations. First, because the 

equipment used to enrich uranium to authorized enrichment levels can also be used to produce 

higher enrichment levels, the NRC considers the possibility that this may be done through 

deliberate misuse of the equipment. Second, it is possible that undeclared source material (SM) 

or low-enriched U (LEU) feed could be introduced into the process equipment for unauthorized 

production of enriched uranium. Additional MC&A performance objectives are established in 

10 CFR 74.33(a) to protect against, detect, and respond to such possibilities. In general, the 

objectives are consistent with MC&A requirements for other NRC-licensed facilities authorized 

to possess and use more than 350 grams of SNM of low strategic significance.

This introduction describes the basis of the 10 general performance objectives of 10 CFR 74.3, 

“General Performance Objectives,” and 10 CFR 74.33(a) and the MC&A program features and 

capabilities needed to meet the objectives. Chapters 3–13 address the program capabilities

needed to maintain accurate, current, and reliable information on, and confirm the quantities 

and locations of, SM and SNM in the licensee’s possession. Chapters 14 and 15 address the 

program capabilities needed to promptly investigate and resolve anomalies indicating a possible 

loss or unauthorized production of SNM and provide information to aid in the investigation and 

recovery of missing SM or SNM or in the investigation of unauthorized enrichment. Chapter 16

addresses recordkeeping requirements. These chapters are intended to provide an outline for 

an acceptable MC&A plan for facilities authorized to hold SM and SNM of low strategic 

significance.

The acceptance criteria are for the use of applicants (or licensees) and NRC licensing 

reviewers. An application or proposed revisions that meet these criteria should be acceptable to 

the NRC staff. However, comprehensive criteria are included as examples, and each applicant 

or licensee should develop an MC&A program and plan that take into account the unique 

features of its particular operation. Where additional guidance is available on particular topics, 

an appropriate reference is included in the acceptance criteria section. Recommendations in 

this document provide guidance to applicants and licensees. This guidance may be used by 

licensees when making changes to their existing approved MC&A plans.

In preparing MC&A plans, applicants should keep in mind the capabilities specified in 

10 CFR 74.33, “Nuclear Material Control and Accounting for Uranium Enrichment Facilities 
NUREG-2158 2

Authorized To Produce Special Nuclear Material of Low Strategic Significance,” and the general 

performance objectives specified in 10 CFR 74.3. After accepting an MC&A plan and imposing 

it as a condition of license, the NRC will evaluate the adequacy of a licensee’s MC&A 

performance by inspecting for performance with commitments and practices described in the 

plan.

Because 10 CFR 74.3 and 10 CFR 74.33 are performance-oriented regulations, they do not 

contain a detailed set of technical specifications. With this flexibility, applicants and licensees 

have many alternatives with regard to how their overall MC&A program is designed, managed, 

and operated, which would permit a risk-informed, performance-based approach that focuses 

and, in turn, concentrates licensee resources on MC&A activities most important to safeguards. 

Accordingly, this document does not attempt to cover all possible methodologies that a licensee 

might use to meet the MC&A requirements. Instead, it provides examples of acceptable MC&A 

approaches that may be chosen. It is intended for use by applicants, licensees, and the NRC 

safeguards licensing reviewers. Acceptance criteria are not to be regarded as rigid, fixed 

standards; that is, a lower effectiveness of one capability relative to a particular aspect can be 

tolerated if there is a compensating system feature, or combination of features, that provides an 

overall effective safeguards system. In the final analysis, an NRC reviewer must make a 

judgment as to whether the applicant’s or licensee’s MC&A plan provides adequate assurance 

that regulatory requirements will be met. 

The contents of an MC&A plan are discussed in Chapters 3 through 16 below. The body of an 

approved MC&A plan will be made a condition of license in accordance with 10 CFR 70.32(c), 

and compliance with the MC&A plan’s commitments and pertinent procedures will be 

inspectable. Explanations and discussions appearing in the body of the plan should be 

sufficiently detailed and precise so that NRC licensing reviewers, NRC inspectors, and licensee 

personnel responsible for developing and implementing the MC&A plan have a clear and 

common understanding of what the plan requires.

The annex (or appendix) of an MC&A plan should provide supplementary and general 

information about the facility and the MC&A program (e.g., copies of blank record forms, site 

map, process diagrams, a sample standard error of the inventory difference (SEID) calculation). 

The annex will not be incorporated as a condition of license and will not be the basis for 

inspection. Thus, descriptions presented by the applicant or licensee to satisfy regulatory intent 

must be in the plan itself, rather than the annex, and must provide adequate detail so as not to 

be largely dependent on examples or supplementary information in the annex for proper 

understanding. As a result, procedures detailed in the annex may be changed without NRC 

approval or notification, provided that plan commitments and capabilities are not degraded. 

By using this standard format for preparing an MC&A plan, a licensee or applicant will minimize 

administrative problems associated with the submittal, review, and approval of the plan. 

Preparation of an MC&A plan with this standard format will assist the NRC in evaluating the plan 

and in standardizing the licensing and review process. However, the NRC does not require 

conformance with the standard format. An applicant may use a different format if it provides an 

equal level of completeness and detail.
3 NUREG-2158

2. GENERAL PERFORMANCE OBJECTIVES, RELATED 

REQUIREMENTS, COMMITMENTS, 

AND ACCEPTANCE CRITERIA

General Performance Objectives 

The general performance objectives for SNM that are to be addressed by the MC&A plan are 

set forth in 10 CFR 74.3, and the parallel performance objectives for source material are stated 

in 10 CFR 74.33(a). The basis on which each of the 10 general performance objectives were 

established is described in the following paragraphs of this section.

1. Maintain accurate, current, and reliable information on, and confirm the quantities 

and locations of SNM in the licensee’s possession.

2. Maintain accurate, current, and reliable information on, and confirm the quantities 

and locations of SM in the licensee’s possession.

The purpose of these two performance objectives is to verify the presence of all SNM and 

SM held by the licensee and to detect the occurrence of any significant loss, including 

possible theft or diversion. To maintain current information on all such SM and SNM,

licensees should have in place a program that provides timely, accurate, and reliable

information about the quantity and location of SNM and SM in their possession. Accurate 

information means that item quantities for both the element U and the isotope U-235 are 

based on measured values or on reliable information. Reliable information means that the 

quantity of SNM or SM in an item and the location of all items are known (except for items 

that have been created, transferred, or consumed within the past 8 hours) and that the 

location designations are specific enough to provide for the retrieval of the items in a prompt 

manner. Reliable information also means that the quantities and locations of all classes of 

material and items listed in the accounting records are, in fact, correct and verifiable.

The licensee or applicant should accurately account for all SNM and SM that is received and 

shipped. This should be accomplished by maintaining reliable records that are based on 

accurate measurements. When a shipment is received, the licensee should begin 

monitoring movement and location of the material within the facility using item control 

procedures (1) to monitor the location and integrity of items until they are processed and 

(2) to ensure that all SM and SNM quantities of record associated with receipts, shipments, 

discards, and ending inventory are based on measurements. Chapter 9 of this document 

contains recommendations on the item control program, and recommendations on 

measurements and measurement control programs are in Chapters 4 and 5, respectively. 

Monitoring the material in process may involve the use of process or material control data. 

To support this function, the licensee should maintain a detailed and accurate recordkeeping 

system for the generated data that provides knowledge of the material’s location on a timely 

basis. 

Once a year, at intervals not to exceed 370 calendar days, the licensee must conduct a total 

plant inventory in accordance with 10 CFR 74.33(c)(4) and be able to detect, with at least a 

90 percent power of detection, an actual loss or theft of a detection quantity (DQ) that may 

have occurred since the last yearly inventory. A DQ is a site-specific quantity of U-235, the 

magnitude of which is discussed in Chapter 6 of this document. 
NUREG-2158 4

In accordance with 10 CFR 74.33(c)(4), the licensee must verify the presence of all SNM 

and SM it holds under license, and this verification must be accomplished by (1) a dynamic 

(i.e., nonshutdown) physical inventory of the U and U-235 contained within the enrichment 

processing equipment and (2) a static physical inventory of all other U material that is not 

within the enrichment process system. Chapter 7 of this document contains 

recommendations on physical inventories. In summary, a total plant inventory involves the 

following: 

• verifying the presence, on a 100 percent basis, of all uniquely identified SNM and SM 

items listed in the accounting records

• measuring (by direct measurement or, if direct measurement is not feasible, by indirect 

measurement) all bulk SM and SNM quantities on hand (i.e., all SM and SNM not in 

item form) 

• measuring any items not previously measured 

• verifying the integrity of all encapsulated items and items affixed with tamper-indicating 

seals 

• measuring a sample of randomly selected unencapsulated and unsealed items, based 

on a statistical sampling plan, to verify the previously measured quantities of SNM or 

SM contained in the items 

The dynamic physical inventory of uranium in the enrichment process system must be 

performed at intervals not to exceed 65 calendar days, in accordance with 

10 CFR 74.33(c)(4)(i). This inventory provides a “snapshot” of the amount of material in 

process at a given time. The licensee is expected to strike a material balance around the 

processing equipment and any active feed, product, and tails containers (e.g., uranium

hexafluoride (UF6) cylinders in feed or withdrawal stations). This material balance could rely 

on indirect measurements and plant process parameters to estimate (1) the active material 

in the enrichment process, (2) the rate at which feed is being introduced to the process, 

(3) the rate at which product and tails are being removed from the process, and (4) the 

amount of process material deposited inside process equipment. The amount of material 

estimated to be inside the process equipment should be compared to the MC&A records to 

indicate whether a theft or unauthorized production may have occurred. The loss detection 

sensitivity associated with the bimonthly dynamic inventories should be sufficient to detect a 

DQ or greater loss or theft over a 12-month period with at least a 90 percent power of 

detection. Chapter 7 also provides recommendations on the conduct of these physical 

inventories.

3. Detect, respond to, and resolve any anomaly indicating a possible loss, theft, 

diversion, or misuse of SNM.

4. Detect, respond to, and resolve any anomaly indicating a possible loss, theft, 

diversion, or misuse of SM.

5. Permit rapid determination of whether an actual loss, theft, diversion, or misuse of 

SNM has occurred.

6. Permit rapid determination of whether an actual loss, theft, diversion, or misuse of 

SM has occurred.
5 NUREG-2158

The licensee or applicant should have a formalized program to detect, respond to, and 

resolve any anomaly indicating a possible loss of SM or SNM, including possible theft or 

diversion. Resolution of such indicators means that the licensee has made a determination 

that a theft or loss of SM or SNM has not occurred. A possible loss detected during a 

material balance closure must be investigated as required by 10 CFR 74.33(c)(6). 

Resolution of an anomaly depends on the type of indicator. Various types of anomalies at 

uranium enrichment plants can indicate a number of possible underlying scenarios

(e.g., from simple theft to isotopic substitution concealing diversion of product material). The 

investigation and resolution process should begin with a thorough review of the MC&A 

records to locate gross errors. These errors might include omissions of entire items, 

incorrect entries to computer programs or records, transcription errors, incorrect estimates of 

the amount of holdup in equipment, or calculational errors. A detailed examination of the 

MC&A records for each material type should identify gross errors. The next stage in the 

resolution process would be to isolate the process or storage area that appears to be 

causing the anomaly. Once this is accomplished, all of the information that contributed to 

the SM and SNM quantities for that location should be verified. 

If resolution still is not accomplished, the licensee should remeasure and sample material in 

the process or storage areas to verify quantities. If the investigation of an indicator results in 

a determination that an actual loss or theft has occurred, the loss or theft must be reported 

to the NRC under 10 CFR 74.11, “Reports of Loss or Theft or Attempted Theft or 

Unauthorized Production of Special Nuclear Material.” To achieve these objectives with 

regard to misuse of material, a licensee’s program should include monitoring process 

operations and personnel and process-related activities to detect the unauthorized 

production of enriched U. Timeliness is (1) an important aspect of protection and detection 

and (2) a function of the U-235 quantity and the enrichment level associated with the 

potential unauthorized production activity. 

The licensee should have a program for monitoring the isotopic composition of process 

material at credible product withdrawal points to provide high assurance of timely detection 

of unauthorized production of uranium. During cascade startup operations, transient isotopic 

assays of between 10 and 20 weight percent (wt %) U-235 may occur. These transients 

normally are less than 4 hours in duration. The higher assay material produced during the 

transient should remain in and not be withdrawn from the cascade. The licensee should 

perform additional monitoring when the enrichment process system is expected to undergo 

an assay transient. The monitoring program can use process control data and samples that 

can be validated and verified, or it can use duplicate measuring systems, if necessary. 

The enrichment technology installed may determine the extent of the monitoring program. 

For example, gaseous diffusion technology requires a limited program because of the 

difficulty in reconfiguring the equipment to produce higher enrichments in a short time; 

however, gas centrifuge technology will require a more extensive monitoring program 

because of the feasibility of reconfiguring the equipment to produce higher enrichments in a 

relatively short period. The program can use nondestructive assay (NDA) techniques with 

fixed or portable detectors or take samples to be analyzed for U-235 abundance. 

The possibility of misusing the equipment or plant for unauthorized production differs for 

each enrichment technology. Following are some sample scenarios for each of the main 

enrichment technology types. 
NUREG-2158 6

Centrifuge: This technology is sensitive to misuse because of the large number of machines 

deployed and the possibility of isolating individual cascades. Cascades could be temporarily 

isolated (e.g., valved off) from the building process piping and, with temporary piping and 

with covert feeding of process material, used to produce higher-than-licensed enrichments 

or to produce greater-than-recorded quantities. Other operating parameters in the licensed 

production line could be surreptitiously altered to mask the scenario. Surreptitious feeding of 

SM or SNM should be considered among the possible misuse scenarios. 

Gaseous Diffusion: This technology is more difficult to misuse than centrifuge; however, 

higher-than-licensed enrichments can be achieved by batching material repetitively through 

the same process equipment. Product from one pass could be refed and further enriched in 

a second or third pass through the cascade. However, establishing equilibrium status takes 

a relatively long time (i.e., weeks), and feeding the product from one pass would probably 

require use of autoclave equipment at the plant’s designated feed points. More credible 

misuse scenarios for this technology are (1) altering process parameters to produce more 

than an authorized amount of product at licensed enrichment levels (but with reduced tails 

enrichment values) and (2) producing more than an authorized amount of product by feeding 

more than the reported quantity of normal U. 

Laser Isotope Separation:

For all three technologies, the licensee should be able to detect the unauthorized 

introduction of any feed material and subsequent unauthorized production. Chapter 8

contains additional recommendations on the monitoring program.

The final design of a commercial plant has not been determined; 

therefore, misuse scenarios cannot be fully identified at this time. In general, however, 

expectations are that operating parameters may be changed to produce 

higher-than-licensed enrichments from natural U feed. Because of maintenance 

requirements, the process approximates a batch-processing system and, in this respect, is 

quite different from the centrifuge and gaseous diffusion processes, which are generally 

continuous. Unauthorized feed and the corresponding unreported product and tails are a 

credible possibility for misuse. 

The licensee should manage and maintain the MC&A program independent of the 

production or operations organization but should not exclude the use of process monitoring 

and production control data. 

Licensees or applicants are responsible for developing and following a formalized program 

designed to resolve indications of unauthorized production. Resolution of such an indicator 

means that the licensee has made a specific determination that the following have not 

occurred: (1) production of excess quantities of U enriched to less than 10 wt % U-235 and 

(2) enrichment of U to 10 wt % or more in U-235. The resolution process should include the 

investigation of all information contributing to the indication of unauthorized production. The 

licensee should determine the location of the indicators and isolate the process area or 

storage area to verify the indication. It should examine the instruments and measurement 

systems used for monitoring to determine if they are functioning properly and conduct

remeasurements as necessary. It should thoroughly examine the processing equipment to 

ensure that unauthorized modifications have not been made. The presence of U enriched to 

10 wt % or more in U-235 should be verified through remeasuring the material in question,

whether in item form or in process equipment. The material contained in the suspect 

container or enrichment process equipment should be measured by NDA or mass 

spectrometric analysis to determine the U-235 isotopic abundance. Chapter 14 contains 
7 NUREG-2158

additional information and recommendations on identifying, investigating, and resolving

indications of unauthorized production. 

If an investigation results in a licensee determination that unauthorized production has taken 

place, this finding must be reported to the NRC within 1 hour of such determination, under

10 CFR 74.11. 

7. Provide information to aid in the investigation and recovery of missing SNM in the 

event of an actual loss, theft, diversion, or other misuse.

8. Provide information to aid in the investigation and recovery of missing SM in the 

event of an actual loss, theft, diversion, or other misuse.

9. Provide information to aid in the investigation of any unauthorized production of 

U, including unauthorized production of U enriched to 10 percent or more in the 

isotope U-235. (For centrifuge enrichment facilities, this requirement does not 

apply to each cascade during its startup process, not to exceed the first 24 hours.)

If the NRC or other government agencies find it necessary to conduct an investigation 

relating to actual (or highly suspected) events of missing U or unauthorized enrichment, the 

licensee is to provide any information it believes relevant to (1) the recovery of material

involved in a loss, theft, or diversion and (2) the investigation of unauthorized enrichment 

activities; that is, the burden shall be on the licensee to provide all information that it 

recognizes as being relevant, rather than only providing information that the investigators 

are knowledgeable enough to request. Chapter 15 contains additional information and 

recommendations on providing information to aid in investigations. 

10. Control access to MC&A information that might assist adversaries to carry out 

acts of theft, diversion, misuse, or radiological sabotage involving SNM.

The purpose of this performance objective in 10 CFR 74.3(e) is to implement the practices 

and procedures needed to provide effective MC&A with respect to deterrence and detection 

of theft, diversion, misuse, or radiological sabotage involving SNM. Licensees should 

control access to MC&A information through access control, material contrainment, and 

material surveillance. Effective control systems should be multilayered, and redundant 

systems should be used to eliminate the consequence of a single-point failure.

The licensee should implement an effective quality assurance program that minimizes the 

possibility of potential failures for the MC&A program, and these control measures can 

contribute to deterrence of material loss, theft, diversion, or misuse by providing necessary 

checks and balances. Access control involving all movements of people and materials into 

and out of the material access areas should be carefully monitored and controlled. 

Adequate containment and surveillance measures should provide assurance that the 

integrity of nuclear material values is maintained.

The licensee should give primary attention to preventing errors or mistakes by MC&A 

personnel and violations of procedures, as well as compromising MC&A information and 

data. A system of balances and checks should be established to ensure data accuracy, and

this system should detect any instances of unauthorized access to data. Mistakes caused 

by inadequate training, accidents, improper equipment operation or maintenance, or any 

other unintentional actions, can cause the MC&A program to lose its effectiveness.
NUREG-2158 8

Commitments and Acceptance Criteria on General Performance Objectives

In its MC&A plan, the applicant or licensee should provide definitive commitments that adhere to 

the regulatory requirements and meet acceptance criteria with respect to these 10 general 

performance objectives and corresponding program capabilities. The MC&A plan should state 

these commitments. 

Chapters 3 through 5 and 7 through 16 of this document list the commitments and acceptance 

criteria.

The following chapters incorporate and expand on the performance objectives and on the 

MC&A program and plan capabilities specified in 10 CFR 74.3 and 10 CFR 74.33(c). The 

chapters are arranged in a format and sequence to provide licensees and applicants an outline 

for their required MC&A plans.
9 NUREG-2158

3. MANAGEMENT STRUCTURE

3.0 Regulatory Intent

The intent of 10 CFR 74.33(c)(1) is to require licensees to implement a management structure 

that permits effective functioning of the MC&A program and ensures that its performance will not 

be adversely affected by the plant management structure. Documentation, review and approval

of critical MC&A procedures, and assignment of the key functions to specific positions eliminate 

ambiguities about what is to be done by whom. The management structure is meant to 

separate key MC&A functions from each other to provide overchecks that increase MC&A 

program reliability and make the theft or diversion of SM or SNM less likely. It is also meant to 

free MC&A management personnel from conflicts of interest with other major functions, such as 

production.

3.1 Corporate Organization

The corporate structure should be described in detail, and all corporate organization positions 

that have responsibilities related to MC&A at the licensee’s site should be identified. A 

description of the corporate-level functions, responsibilities, and authorities for MC&A program 

oversight and assessments should be provided. At least one corporate official should have 

responsibilities for the control and accounting of all SM and SNM possessed by the licensee. 

3.2 Plant or Site Organization

A description of the site’s management structure emphasizing MC&A should be provided. By 

means of comprehensive organization charts, the site management structure should be shown.

As a minimum, the charts should indicate where the responsibility lies for the following 

functions: 

• overall MC&A program

• SM and SNM custodianship 

• receiving and shipping of SM and SNM 

• analytical laboratories 

• bulk and NDA measurements 

• sampling operations 

• measurement control system

• physical inventories 

• monitoring program to deter and to detect unauthorized enrichment activities

• onsite nuclear material handling operations 

A brief description should be provided for each site-level position, outside of the MC&A 

organization, that has responsibilities relating to MC&A activities (e.g., sampling, mass 

measurements, analytical measurements, and measurement control). For each position, the 

functions, responsibilities, and authorities should be clearly described. 

3.3 Material Control and Accounting Organization

An organizational chart and position-by-position description of the entire MC&A organization 

should be provided. An individual should be designated as the overall manager of the MC&A 

program. To ensure independence of action and objectivity of decision, the MC&A manager 

should either (1) report directly to the plant or site manager or (2) report to an individual who 

reports directly to the plant or site manager and who has no production responsibilities. 
NUREG-2158 10

3.3.1 Responsibilities and Authority 

A description that clearly indicates the responsibilities and authority of each supervisor and 

manager should be provided for the various functions within the MC&A organization. The 

description should indicate how the activities of one functional unit or individual serve as a 

control over, or checks on, the activities of other units or individuals. The MC&A plan should 

explain how coordination is achieved and maintained between the MC&A organization and other 

plant organizational groups that perform MC&A-related activities. A definitive statement should 

be made specifying that the MC&A manager will review and approve all written MC&A 

procedures, and any future revisions, both inside and outside of the MC&A organization, on

MC&A-related activities. In addition to the MC&A manager function, the functions to be 

addressed should include, as a minimum, the following:

• nuclear material accounting

• measurement control system

• item control system

• statistical applications

• monitoring program to detect unauthorized enrichment activities 

The discussion on statistics should identify those individuals responsible for such activities as 

calculation of the SEID, determination of active inventory, evaluation of shipper-receiver 

differences (SRDs), and determination of control limits. 

Whenever more than one key MC&A function is assigned to the same person, the MC&A plan 

should clearly describe the checks and balances that prevent the following: 

• performance of accounting or record control functions by individuals who also generate 

source data

• any individual from having sole authority to overcheck, evaluate, or audit information for 

which he or she is responsible 

3.3.2 Material Control and Accounting Procedures

Critical MC&A procedures to be described are those written procedures which, if not performed 

correctly, could result in a failure to achieve one or more of the performance objectives of 

10 CFR 74.3 and 10 CFR 74.33(a) and the program capabilities of 10 CFR 74.33(c). All critical 

MC&A procedures should be identified in the body of the MC&A plan. A licensee’s development 

of its critical MC&A procedures, and any changes later made to them, should involve technical 

review by cognizant licensee personnel, be approved by the line management directly affected, 

and also be approved by a level of management above the level responsible for executing the 

procedures. The MC&A plan should contain a definitive statement that the procedures will be 

followed. The set of critical MC&A procedures should, as a minimum, adequately address the 

following topics, regardless of which facility organizational group is responsible for the particular 

topic:

• accountability record system 

• sampling and measurements 

• measurement control system

• item control system
11 NUREG-2158

• static and dynamic physical inventories 

• investigation and resolution of loss indicators 

• investigation and resolution of indicators of unauthorized enrichment to 10 wt % or more 

in U-235 

• monitoring program to detect unauthorized production of U to enrichments less than 

10 wt % in U-235 

• determination of SEID, active inventory, and inventory difference 

• provision of information to aid in investigations 

• MC&A recordkeeping 

• independent assessment of the effectiveness of the MC&A program 

• tamper-safing

• designation of material balance areas (MBAs), item control areas (ICAs), and custodial 

responsibilities

3.4 Training and Qualification Requirements

This section of the MC&A plan should describe the training programs to be established and 

maintained to ensure qualified personnel and to provide for the continuing level of qualification 

with respect to personnel assigned responsibility for MC&A. Training procedures and 

qualification criteria should be discussed in definitive statements. Minimum qualification 

requirements should be stated for each key MC&A position.

3.5 Material Control and Accounting Program Description

The length of this section and its level of detail will depend on the information provided in the 

previous sections of this chapter. The overall MC&A organization should be described in a 

manner that explains how the 10 general performance objectives of 10 CFR 74.3 and 

10 CFR 74.33(a) and the capabilities of 10 CFR 74.33(c) will be effectively achieved. 

The individual who has responsibility for the following MC&A-related functions should be 

specified by title: 

• overall MC&A program management (with no major non-MC&A-related responsibilities) 

• measurements (noting that responsibility may be divided on the basis of type of 

measurements (e.g., analytical laboratory measurements, NDA measurements, bulk 

measurements, and sampling))

• measurement control and statistics 

• accountability records 

• item control 

• physical inventories 
NUREG-2158 12

• custodial responsibilities (e.g., SM and SNM storage and movement controls) 

• monitoring program for detecting unauthorized enrichment activities 

• investigation and resolution of indicators that suggest possible loss or possible 

unauthorized enrichment activities 

• receiving and shipping of SM and SNM 

• analytical laboratories 

• MC&A recordkeeping system and controls 

The MC&A program should include a description of the policies, instructions, procedures, 

duties, responsibilities, and delegation of authority in sufficient detail to demonstrate the 

separation or overchecks built into the MC&A program.

3.6 Material Control Boundaries

This section of the MC&A plan should describe how the licensee establishes various material 

control boundaries to minimize the occurrence of MC&A anomalies (e.g., inventory differences, 

missing items of SM or SNM, and potential theft or diversion of SM or SNM) and facilitate their 

resolution.

The MC&A plan should describe the establishment of MBAs and ICAs, because they are the 

basis for the control and accounting for all nuclear material in the facility. An MBA or ICA should 

correlate to physical or administrative boundaries and monitored locations. The MBA or ICA 

should be designed to limit losses to a specific area (i.e., the MBA should not be so large that it 

cannot localize inventory or process differences to a manageable level). Materials transferred 

into and out of an MBA or ICA must have quantitative measurements, as specified in the 

definitions of MBAs and ICAs in 10 CFR 74.4, “Definitions.”

The MC&A plan should describe roles and responsibilities of nuclear material custodians for 

MBAs and ICAs. The material custodian should have direct interaction with the MC&A 

organization and should be located within the physical operations area. Custodians who are 

responsible for more than one MBA or ICA should not be able to make material transfers 

between MBAs or ICAs under their direct control.

3.7 Commitments and Acceptance Criteria

In its MC&A plan, the applicant or licensee should provide definitive commitments that adhere to 

the regulatory requirements and meet acceptance criteria applicable to management structure. 

A finding that the licensee’s MC&A plan for management structure is acceptable and in 

accordance with 10 CFR 74.33(c)(1) will be based on, but not limited to, the following 

acceptance criteria:

• The authorship, approval authorizations, and effective dates of MC&A policies and 

procedures will be documented and will involve appropriate management and technical 

staff. All critical MC&A procedures, and any revisions thereto, are reviewed and 

approved before their implementation.

• The responsibilities and authorities for each position assigned a function having a 

significant impact on SM or SNM control and accounting (including all positions 
13 NUREG-2158

authorized to control SM or SNM movement, generate source data, define or implement 

measurement control requirements, and conduct data analysis) are clearly defined in a 

written position description that defines the responsibilities for that position.

• The qualifications and experience required for each position assigned an SM or SNM

control and accounting function will be sufficient to permit adequate performance of the 

duties required of that position.

• The descriptions (in the MC&A plan) of the management structure and assignment of 

duties and authorities show that those responsible for each MC&A function will have 

sufficient authority to perform the function in the intended manner.

• The MC&A organization is separate from the production organization and is also 

separate from organizations that generate source data, if practicable; otherwise, 

independence of the functions is attained by suitable controls and overchecks.

• The responsibility for MC&A program management is designated to an individual at an 

organizational level sufficient to ensure independence of action and objectivity of 

decisions.

• No two key MC&A functions are assigned to the same person unless adequate checks 

and balances are provided. As a consequence of this criterion: 

– individuals who generate source data, such as performing measurements or 

shipping and receiving activities, do not perform any accounting or record control 

functions unless suitable overchecks are provided to prevent falsification of both 

source data and accounting records, and

– no individual has the sole authority to overcheck, evaluate performance, or audit 

information for which he or she is responsible.

• The responsibility for each MC&A function is assigned to a specific position in the 

organization, and the organization is structured in a way that the key functions are 

separated or overcheck one another. The position descriptions are available in writing to 

the personnel affected.

• All current MC&A procedures are made easily accessible to all affected individuals and 

are maintained to show, for each procedure, (1) revision number, (2) date issued, 

(3) name of person preparing the procedure, and (4) name of person approving the 

procedure (as indicated by signature and date signed).

• Management policies are established, documented, and maintained to ensure that all 

MC&A procedures are adhered to, including measurement procedures used for 

accountability purposes.

15 NUREG-2158

4. MEASUREMENTS

4.0 Regulatory Intent

The intent of the 10 CFR 74.33(c)(2) measurement capability requirements is that licensees 

establish, maintain, and use a system of measurements to ensure that all quantities of SM and 

SNM (both element and fissile isotope) in their accounting records are based on reliable 

measurements. The measurement uncertainty associated with the values entered into the 

accounting records must be sufficiently small so as to ensure that the limit specified in 

10 CFR 74.33(c)(3), for the total MC&A measurement uncertainty (associated with a physical 

inventory material balance), is not exceeded. Except for sealed sources and samples, all SM 

and SNM receipts are to be measured for the purpose of performing shipper-receiver 

evaluations. In the absence of any significant SRDs, a licensee may book either its measured 

values or the shipper’s measured values. When recording shipper’s values (for SNM receipts), 

the measurement uncertainty associated with the values should be known and used in the 

determination of SEID. It is also intended that a licensee’s measurement program provide bias 

estimates to be used in correcting inventory difference values and SRDs for significant 

measurement biases. Chapters 5 and 6 discuss the estimation of measurement bias. 

4.1 Measurement Points

The MC&A plan should identify and describe each measurement that is used, either for 

accounting purposes or for a monitoring program, to detect an unauthorized activity. 

Measurements (1) establish the quantities in each custodial area, MBA, or ICA and in the facility 

as a whole, and (2) contribute to the desired capability to localize losses and generate and 

assess alarms. Typically, measurement points and sampling stations are selected to provide 

quantitative information about material flows and inventories that will permit detection and 

localization of any loss or diversion, or confirmation that no diversion has occurred. Essentially 

all nuclear material shipments and receipts to and from either diffusion or centrifuge enrichment 

plants involve UF6 in metal cylinders. Various non-UF6 materials are present at the plant as a 

result of process equipment maintenance, process vent gas trapping systems, routine 

equipment decontamination and cleaning activities, and laboratory operations. Typically, three 

functional types of MBAs and ICAs are present: (1) processing, (2) storage, and (3) receiving 

and shipping. Typical processing MBAs include (1) the cascade or isotope separations 

facilities, (2) decontamination and recovery areas, (3) laboratory, and (4) feed and product 

sampling and transfer areas. The identification and definition of measurement points for 

processing MBAs are necessary because of the physical, chemical, or isotopic changes of the 

nuclear materials that occur in them. Storage and receiving and shipping areas are 

typically ICAs. 

4.2 Measurement Systems

The MC&A plan should describe in detail each measurement system used for nuclear material 

accounting purposes. The principal elements and operations involved in the measurement 

system for MC&A at uranium enrichment plants include mass (or weight) or volume 

determination; sampling; chemical, nondestructive, and isotopic analyses; and process 

monitoring operations (for pressure, volume, temperature, and impurities) unique to the 

enrichment process operations. Each measurement system should also be defined or identified 

by its unique set of the following parameters: (1) measurement device or equipment used, 

(2) standards used for calibration, and (3) standards used for control. For analytical laboratory 

measurements, the following should also be identified: (1) sampling technique and equipment 

used, (2) sample aliquoting technique, and (3) sample pretreatment methodology. Chapter 5
NUREG-2158 16

describes elements of the measurement control system (e.g., standards traceable to a national 

system) used for validating and determining control limits, precision, and accuracy levels for 

each measurement element used for accountability. 

The MC&A plan should describe each measurement system associated with bulk, analytical, 

and NDA measurements, and should identify, where applicable, any other measurement 

systems used for accounting purposes that do not fall within these categories. These 

descriptions should provide sufficient information to demonstrate how the systems are used to 

ensure the ability to meet the precision and accuracy limits. The following sections provide 

examples of the types of information necessary for selected measurement systems.

4.2.1 Bulk Measurement Systems

For each weighing system, the applicant or licensee should specify the weighing device, the 

type of container(s) weighed, material within the containers being weighed, capacity of the 

weighing device (e.g., capacity not to exceed X kilograms), range to be used and sensitivity of 

the device(e.g., sensitivity is +/- Y grams), and the calibration frequency. 

For each volume measurement system, the MC&A plan should identify the vessel (e.g., tank, 

column); capacity of the vessel to which the measurement applies (e.g., capacity not to exceed 

X liters); the material being measured; the volume measuring device and instrumentation; the 

sensitivity of each device and system (e.g., sensitivity is +/- Y milliliters); the range of operation, 

or calibration, or both; and the calibration frequency.

4.2.2 Analytical Measurement Systems

For each analytical measurement system, the MC&A plan should specify the following: 

• type of material or chemical compound (e.g., UF6, U alloy, urano-uranic oxide (U3O8), 

uranyl nitrate solution) being sampled or measured

• sampling technique(s)

• sample handling (i.e., preanalysis sample storage and treatment) 

• analytical method used 

• characteristics measured (e.g., grams of U per gram sample, U-235 isotopic 

composition) 

• measurement interferences 

• expected measurement uncertainty 

• types of calibration standard(s) and calibration frequency

4.2.3 Nondestructive Assay Measurement Systems

For each NDA measurement system, the MC&A plan should identify the following:

• the NDA equipment package (i.e., type and size of detector and type of associated 

electronics and computer interface, as appropriate)

• the type of container measured 
17 NUREG-2158

• SM or SNM material type 

• attribute measured 

• measurement configuration (including source to detector distance) 

• calculational method 

• expected measurement uncertainties 

4.2.4 Other Measurement Systems

If applicable, the MC&A plan also should identify any other measurement systems used for 

accounting purposes that do not fall within the three categories covered by Sections 4.2.1. 

4.2.2, and 4.2.3. For example, the plan should identify the measurement systems used for 

determining the enrichment process system inventory.

4.3 Measurement Uncertainties

The expected measurement uncertainties of the described measurement systems should be 

provided. Variance components for calibration, sampling, random, and systematic error for 

each measurement system should be stated. The units in which the errors are expressed 

should be clearly identified.

4.4 Measurement Procedures

The licensee or applicant should make a definitive statement that an approved measurement 

procedures (i.e., methods) manual, or set of approved manuals, will be established and 

maintained. The organizational units that are responsible for the preparation, revision, and 

approval of measurement procedures should be stated. A definitive statement also should be 

made that a periodic review of the procedures will be conducted. 

The licensee or applicant should clearly state that a measurement procedure cannot be used for 

accountability purposes without documented approval. The overall MC&A manager and the 

manager of the organizational unit responsible for performing the measurement, as well as the 

measurement control program manager, should approve each procedure. 

The MC&A plan should provide a definitive statement that all SM and SNM quantities in the 

material accounting records will be based on measured values and measurement systems will 

be maintained for the measurement of all SM and SNM associated with the following: 

• additions to inventory (e.g., receipts) 

• removals from inventory (e.g., shipments and measured discards) 

• material on ending inventory 

For receipt of material, the licensee may use shipper’s measured values rather than its own 

measurements, provided that (1) a shipper-receiver comparison, based on attributes or 

confirmatory measurements, shows no significant SRD (as defined by 10 CFR 74.33(c)(7)), or 

(2) in the case of a significant difference between shipper and receiver, no significant difference 

exists between the shipper’s value and the umpire value used to resolve the difference, or 

(3) the material in question is exempted from shipper-receiver comparison requirements 

(e.g., sealed sources and samples). However, when booking shipper’s values, the shipper’s 

measurement uncertainty should be used in determining SEID. 
NUREG-2158 18

4.5 Commitments and Acceptance Criteria

In its MC&A plan, the applicant or licensee should provide definitive commitments that adhere to 

the regulatory requirements and meet acceptance criteria applicable to measurements. A 

finding that the licensee’s MC&A plan for ensuring that all quantities of SM or SNM are based 

on reliable measurements is acceptable and is in accordance with 10 CFR 74.33(c)(2), will be 

based on, but not limited to, the following acceptance criteria:

• A program of measurement procedures and methods is maintained for all SM and SNM 

receipts, removals, and inventory items, and all quantities of SM and SNM in the 

material accounting records are based on measured values.

• Measurement systems that are the key contributors to the total measurement standard 

error will be identified, and the list of such systems will be reviewed annually and 

updated as necessary so that these key measurement systems and their standard 

deviations will be monitored and controlled by the measurement control system.

• A basic description or summary of each key measurement system used to generate SM 

or SNM quantities for accountability purposes is provided. A measurement system is

defined as any instrument or device, or combination of devices, used to derive (1) an 

element concentration, (2) an isotope quantity, (3) a U-235 enrichment or isotopic 

distribution, (4) a bulk material mass (weight), or (5) a bulk material volume, and one that

can be characterized by its random and systematic error components.

• The set of key measurement systems, based on recent (or anticipated) measurement 

control data and modes of process operations, is expected to account for at least 

90 percent of the total measurement uncertainty contribution to the SEID.

• The recalibration frequency for each measurement system is compatible with its 

expected stability. Recalibrations for all measurement systems should be performed at 

frequencies compatible with widely established, or licensee demonstrated, stability for 

each particular system.

• All calibrations are made using primary standards or primary reference materials 

(certified and issued by the National Institute of Standards and Technology or the New 

Brunswick Laboratory, or an equivalent organization) or with reference standards 

traceable to primary standards. The standards used for calibrations need not be 

representative of the unknowns to be measured by the system unless it is to be 

regarded as a bias-free system that is calibrated during each time of use, in which case,

the calibration standards must be representative.

• When determining an SM or SNM quantity by weighing, sampling, and analyses, the net 

weight of material in each item within a uniform material batch (or lot), such as blended 

uranium dioxide (UO2) powder or sintered UO2 pellets, must be determined by direct 

mass measurement. However, the element and isotope concentrations for the batch 

need not be determined for each container but, instead, may be derived by sampling 

procedures, including either of the following:

– The MC&A plan can use an analysis of composite samples or measurements of 

representative items, objects, or samples selected by statistical sampling.
19 NUREG-2158

– Alternatively, the plan can use concentration or enrichment factors, or both,

determined from historical averages, controlled input specifications values, or 

empirical relationships where such values or relationships are periodically tested, 

their uncertainties or bounds have been determined to be within 2.00 percent of 

the factor value, and diversions with material substitution are improbable. 

However, heterogeneous materials, such as ammonium diuranate, may not be 

assigned common factors unless the quantities are small, such as less than 

500 grams of contained U-235 (per material type, per inventory period). The plan 

must justify any materials assigned common factors without batch-by-batch 

verification analyses.

21 NUREG-2158

5. MEASUREMENT CONTROL SYSTEM

5.0 Regulatory Intent

The intent of the measurement control requirements in 10 CFR 74.33(c)(3) is that measurement 

systems (as described in Chapter 4 of this document) used to establish SM or SNM

accountability quantities be controlled such that, in terms of a 95 percent confidence level, twice 

the standard error associated with a material balance total MC&A measurement uncertainty 

(for U-235) is less than the greater of 5,000 grams U-235 or 0.25 percent of the U-235 active 

inventory. It is also intended that bias estimates be used for adjusting inventory difference 

results and correcting shipper-receiver measurements for significant measurement biases.

5.1 Organization and Management

The licensee should describe the organization and management of the measurement control

system in sufficient detail to show how the measurement quality assurance function is assigned 

and how independence is maintained from the analytical laboratory and other units performing 

either sample taking or measurements. The measurement control system manager should be 

at a management level that is sufficiently high to ensure objectivity and independence of action. 

Thus, the measurement control system manager should either report directly to the overall 

MC&A manager or, if in a different organizational unit, be on the same level as the MC&A 

manager. 

The licensee’s measurement control system should be properly managed to ensure adequate 

calibration frequencies, sufficient control of biases, and sufficient measurement precision to 

achieve the capability required by 10 CFR 74.33(c)(3). 

5.1.1 Functional Relationships

The relationship and coordination among the measurement control system manager, the 

analytical laboratory, and other measurement performing groups should be clearly defined. 

Adequate assurance should be provided that the measurement control system manager has the 

authority to enforce all applicable measurement control requirements. 

5.1.2 Procedures

The measurement control system procedures should be established and maintained in a 

manual that is kept current and readily available. This manual should contain all the currently 

applicable written procedures pertaining to measurement control and measurement quality 

assurance. Responsibility for the preparation, revision, and approval of manual procedures 

should be specified. Individual measurement control procedures should have documented 

approval by the measurement control system manager. The procedures should address the 

following: 

• calibration frequencies and methods

• standards used for calibration (i.e., description and storage controls) 

• standards used for control (i.e., preparation or method of obtaining and traceability) 

• control standard measurements 

• replicate sampling and replicate measurements 
NUREG-2158 22

• verification of process control instrumentation through comparison with other process 

instruments 

• generation of control limits and control responses and collection of control data 

• recordkeeping controls and requirements 

5.1.3 Contractor Program Audits and Reviews

If an outside contractor or offsite laboratory provides measurement services, the review program 

used to monitor the offsite measurements must be described in accordance with 

10 CFR 74.33(c)(3)(iii). Such reviews are to ensure that the contractor or offsite laboratory has 

an acceptable measurement control program to the extent that use of the contractor’s 

measurements will not compromise the licensee’s ability to meet any measurement or 

measurement control requirement contained in either 10 CFR 74.33(c) or in its MC&A plan. The 

licensee should conduct an initial review of the contractor’s measurement control program

before it uses measurements performed by the contractor or offsite laboratory. 

All contractor or offsite laboratory assessment findings and recommendations should be 

documented and submitted to both the measurement control system manager and the overall 

MC&A manager within 30 calendar days of completion of the review. The two managers should 

agree on corrective actions that should be taken, based on their evaluation of the report, and 

should transmit these findings to the contractor or offsite laboratory in writing. The licensee 

should verify that the contractors or offsite laboratories have instituted the corrective actions 

before using their measurements. 

The persons who conduct a contractor review need not be employed by the licensee, but they 

should not be employed by, or be in any way associated with, the contractor or offsite 

laboratory, so that the independence of the conclusions may be maintained.

5.2 Calibrations

The MC&A plan should summarize the licensee’s calibration program and confirm that the 

licensee has written procedures covering the following topics: 

• calibration frequency for each measurement device or system 

• identification of the reference standards used for calibration of each measurement 

device or system 

• protection and control of standards used to calibrate measurement systems to maintain 

the validity of their certified or assigned values 

• the range of calibration for each measurement device or system and the minimum 

number of calibration runs (observations) needed to establish a calibration 

Unlike control standards, standards used for calibrating measurement systems need not be 

representative of the process material or items to be measured by the calibrated device or 

system. If practicable, the standard used during the calibration process should be subjected to 

all the steps involved in the measurement process that the process unknowns are subjected to 

(e.g., sample pretreatment), but this need not always be the case. It is the primary 

measurement device, not necessarily the entire measurement system, that needs to be 

calibrated, especially when the primary measurement device is common to two or more 
23 NUREG-2158

measurement systems. For example, the Davies & Gray titrimetric method is often used to 

analyze samples for U concentration of two or more different material types (e.g., UF6, U3O8 , 

and uranyl nitrate solutions). In this case, more than one measurement system is involved,

because different sampling and sample pretreatment methods and different control standards 

are used. The potassium dichromate titrant, however, is common to the systems; thus, the 

titrant is what is calibrated (or standardized) with a reference standard such as certified U3O8 or 

certified U metal. 

In the case of nonconsumable standards used to calibrate measurement systems (e.g., weight 

standards), the frequency of recertification of assigned values should be specified. The 

recertification frequency should be dependent on how often the standards are handled, the 

standard’s stability, and the adequacy of the controls used to maintain the integrity of the 

standards. Biennial recertifications of such standards are usually acceptable. 

The MC&A plan should contain a definitive statement that no SM or SNM accountability value 

will be based on a measurement that falls outside the range of calibration. The MC&A plan also 

should identify those measurement systems that are point calibrated. A point-calibrated 

measurement system is one in which the following are true: 

• The entire measurement system is calibrated with a standard or set of standards that 

are representative of the process unknowns that are measured by the system; that 

is, the representative calibration standard(s) undergoes all the measurement steps, 

and in the same manner, that the unknowns do. 

• One or more calibration standards are processed and measured along with each 

unknown or set of unknowns measured; that is, both the standard(s) and unknown(s) 

are measured during the same general time interval, with the same individual 

measuring both the standard(s) and unknown(s). 

• The measurement values assigned to the process unknowns are derived from the 

measurement response observed for the standard(s) that was measured along with 

the unknown(s). 

• The measurement response for each unknown must fall within plus or minus 

10 percent of the response for a standard measured at the same time as the 

unknown, or, as in the case of a low concentration unknown, the difference between 

the unknown’s response and the standard’s response should be less than four times 

the standard deviation associated with the standard’s response.

5.3 Control Standards

For those measurement systems that are not point calibrated, the licensee should establish 

and follow a defined method for the periodic measurement of control standards. Control 

standard measurements serve the dual purpose of (1) monitoring the stability of a previously 

determined calibration factor and (2) estimating the system bias over a period of time (e.g., an 

inventory period). The minimum total number of control standard measurements during the 

time period, as well as the typical frequency, should be specified for each measurement 

system. Generally speaking, for each measurement system, a minimum of two control 

standard measurements should be made during each week that the system is in use. For 

those systems that are used less than 8 weeks during a given material balance period, more 
NUREG-2158 24

than two control standard measurements per week of system use may be necessary to provide

the following: 

(1) a minimum of 12 control measurements for those systems used during the material 

balance period to measure material totaling less than 100 kilograms of U-235

(2) a minimum of 24 control measurements for those systems used to measure a total of 

100 or more kilograms of U-235

Key measurement systems for the current inventory period are any set of designated 

measurement systems (of the licensee’s choosing) which, based on the most recent previous 

period, account for at least 90 percent of the total measurement variance contribution to SEID. 

Within the set of key measurement systems should be included any system used to measure 

an SNM quantity (during an inventory period) greater than 25 percent of the active inventory, 

regardless of its contribution to SEID. The minimum number of control standard 

measurements for situations (1) and (2) above can be reduced to 8 and 16, respectively, for 

nonkey measurement systems that measure from 10 to 25 percent of the active inventory, 

and the minimum number of control standard measurements for situations (1) and (2) can be 

further reduced to 4 and 8, respectively, for those nonkey systems used to measure less than 

10 percent of the active inventory quantity.

Control standards should be representative of the process material or items being measured. 

To be representative, the standards need not always be identical to the process unknowns,

but any constituent of the process material, or any factor associated with a process item, that 

produces a bias effect on the measurement should be present to the same degree in the 

control standards. For scales used to weigh very large items, such as UF6 cylinders, the 

control standard weights should be artifact cylinders (i.e., both empty and full) of certified 

mass to avoid a bias effect caused by buoyancy or point loading.

For each measurement system that is not point calibrated, the control standards to be used for 

control standard measurements should be identified or described, or both. Along with material 

composition and matrix factors, biases also can be induced by changes in (among other things) 

temperature, humidity, line voltage, and background radiation. Biases can also be induced by 

operators or analysts. Therefore, the scheduling of control standard measurements should be 

based on the following considerations: 

• Does the variation between analysts or operators need to be considered and hence 

monitored? 

• Can environmental variables contribute to measurement bias? 

• Is bias likely to vary with respect to the time of day? 

• Is a particular bias likely to be long term, short term, or cyclic in nature? 

• Is bias a function of the process measurement values over the range of calibration 

(i.e., is the relative percent bias nonuniform over the range of calibration)? 

• What controls or procedures are needed to ensure that sampling or aliquoting of the 

control standard is representative of the sampling or aliquoting of the process material? 
25 NUREG-2158

• To estimate the bias for each measurement system, how much alike—in terms of 

chemical composition, U concentration, density, homogeneity, and impurity

content—should the control standards be, relative to the process unknowns?

5.4 Replicate Sampling

For systems involving sampling, duplicate measurements performed on single samples 

(or single items) and measurements of replicate samples are necessary to estimate the 

combined analytical and sampling random error. For nonsampling measurement systems,

such as NDA and weight measurement systems, the analytical variance component can be 

derived either from (1) replicate measurements performed on the process items or (2) the 

replicate data generated from the measurement of control standards. 

The licensee should ensure that replicate samples are independent of one another. The 

number of replicate samples measured for each analytical measurement system during an 

inventory period should be equal to at least one of the following: 

(1) 100 percent of the accountability batches sampled (when fewer than 15 batches) 

(2) the greater of 15 samples or 15 percent of the accountability batches sampled 

(3) 50 samples (when 15 percent of the batches is greater than 50) 

For nonkey analytical measurement systems, the minimum number of replicate samples to be 

measured during an inventory period should be equal to one of the following:

(4) 100 percent of the accountability batches sampled (when fewer than 8 batches)

(5) the greater of 8 samples or 10 percent of the accountability batches sampled

(6) 25 samples (when 10 percent of the batches is greater than 25)

For each measurement system involving sampling and analysis, the MC&A plan should indicate 

(1) how many samples are taken and measured for each accountability batch measurement and 

(2) how many analyses are performed on each accountability sample. If two or more samples 

are used and two analyses per sample are performed for each accountability batch 

measurement, replicate requirements are automatically met. If, however, one sample per batch 

is normally used for accountability purposes, the replicate program should include a periodic 

taking of a second (i.e., replicate) sample. Replicate or repeat measurements can be made on 

the same or similar production items. The scatter in the repeat measurements is used to 

estimate the random error variance using a statistical technique known as the one-way analysis 

of variance. (The NRC recommends the statistical methods described in NUREG/CR-4604, 

“Statistical Methods for Nuclear Material Management” (1988), for satisfying the statistical 

requirements of 10 CFR 74.33; see also Chapter 6 of this document.) Replication not only 

improves the precision of results obtained from the statistical analysis of the measurement data, 

it also can detect gross errors in the data.

5.5 Control limits

Both 0.05 (warning) and 0.001 (out-of-control) limits are to be established and used for both 

control standard and replicate measurements for those measurement systems used for nuclear 

material accountability. Out-of-control limits are also to be used for replicate measurements and 

measuring replicate samples. However, warning limits are optional for the replicate program. 
NUREG-2158 26

For point-calibrated systems, the assigned value of the standard(s) measured along with the 

unknown(s) is assumed to be valid. If the standard’s true value could change because of 

factors such as evaporation, moisture pickup, or oxidation, the value of the standard should be 

checked periodically. Therefore, control limits for the verification measurements associated with 

such standards should be established. This is especially true for those point-calibrated systems 

that use a single standard, or aliquots from a single standard, over any extended period of time. 

The warning and out-of-control limits are normally set by the licensee based on a tradeoff 

between (1) the cost of investigating and resolving incidents where limits are exceeded and 

(2) the cost of accepting measurements of poor quality. Warning limits set at the 0.05 level of 

significance and out-of-control limits set at the 0.001 level of significance are usually sufficient.

When a system generates a control measurement that falls beyond an out-of-control limit, the 

system should not be used for accounting purposes until it has been brought back into control 

(i.e., within the upper and lower warning limits). 

Control limits should be recalculated at a predetermined frequency and modified, if required. 

The MC&A plan should clearly explain how control limits are established and the frequency 

for redetermining them. 

5.5.1 Measurement Control Data Analysis

Measurement control data, such as control standard measurement results and the differences 

between measurement values of replicate pairs, should be plotted manually on graphs or 

entered into a computer data base to generate control charts. All control charts should be 

reviewed at least once every 2 weeks unless a measurement system was not used during that 

period. The review should assess the frequency of control data exceeding either the warning or 

the out-of-control limits and also evaluate for any significant trends. 

5.5.2 Response Actions

Either the analyst or the operator performing a control measurement or the supervisor should be

responsible for promptly reporting any control measurement that exceeds an out-of-control limit. 

Such reporting should be made to the measurement control system manager (or his or her 

designee), who should have the responsibility and authority to carry out the necessary response 

and corrective action. 

Minimum response and minimum corrective action requirements should be clearly defined. In 

addition, the measurement control manager (or his or her designee) should be responsible, and 

have the authority, for determining and executing additional response and corrective actions as 

deemed appropriate. 

The minimum response to a reported incident of a control measurement exceeding an out-ofcontrol limit should consist of the following: 

(1) verifying that the measurement system in question has been taken out of service with 

respect to accountability measurements 

(2) documenting the occurrence of the event 

(3) performing at least two additional control measurements 
27 NUREG-2158

(4) performing additional control measurements, if the results of Item (3) do not show the 

system to be back in control, using a different control standard or different replicate 

sample (as appropriate), or recalibrating the measurement system, or making any 

necessary system repairs 

(5) reviewing measurements performed on the system in question since the last in-control 

run to determine if there is a need to remeasure any items

For those measurement systems that make a significant contribution to the SEID, the response 

to an out-of-control condition should also include the remeasurement of any samples (or items) 

that were measured before the out-of-control condition but after the last within-control 

measurement. The validity of the previous measurements can be established without a 

complete remeasurement of all the samples (or items) involved, if remeasurement on a “last in, 

first out” basis is used; that is, the last sample (or item) measured before the out-of-control 

measurement should be the first to be remeasured, and continuing in reverse order until two 

consecutive remeasurements are found to be in agreement with their initial measurement at the 

95 percent confidence level. 

5.6 Commitments and Acceptance Criteria

In its MC&A plan, the applicant or licensee should provide definitive commitments that adhere to 

the regulatory requirements and meet acceptance criteria applicable to the measurement 

control system. A finding that the licensee’s MC&A plan for maintaining measurement quality 

and estimating measurement uncertainty values is acceptable and in accordance with 

10 CFR 74.33(c)(3) will be based on, but not limited to, the following acceptance criteria:

• The description of the measurement control program shows that the measurement 

systems that are the key contributors to the total measurement standard error will be 

routinely and adequately monitored for both bias and random error. The standard 

deviations of measurement systems are estimated from replicate data from 

measurements made in the same manner as made routinely on typical process samples 

and items. If standard deviations are based on replicated measurements of standards 

(for NDA or mass measurement systems), data is collected that demonstrate that the 

standard deviation estimates do not differ significantly from those based on replicated 

process item measurements. (NOTE: For analytical chemistry measurements, the 

combined analytical plus sampling random error must be derived from the measurement 

of replicate process samples, rather than based on multiple measurements of a 

standard.)

• All reasonable and probable sources of measurement error, such as the effects of 

sampling, instruments, environmental factors, and variability between operators or 

analysts are included in the estimates for standard deviations, either directly as 

experimental variables in an analysis of variance or by being included in the sample of 

measurement control data from which the standard deviations are determined. 

• Bias tests are made by measurements of representative control standards with assigned 

values that are traceable to national measurement systems. As reasonably achievable, 

the control standards should closely resemble the unknowns to which the measurement 

is applied, and the measurement procedures and conditions of measurement must 

closely resemble those of typical measurements made on process unknowns.
NUREG-2158 28

• A record of bias estimates for each key measurement system (not defined as a 

bias-free, point-in-time calibrated system), as derived from control standard 

measurements, is maintained. The basis for determining the timeframe associated with 

each significant bias should be provided (so that the quantity of measured SM or SNM to 

which that bias applies can be determined). Bias corrections (expressed as both grams 

element and grams isotope) are derived for each significant bias (based on the quantity 

of measured SM or SNM to which the bias applies). The MC&A plan must confirm that 

each significant bias is either applied as a correction to items listed in the accounting 

records (if the correction for an individual item is greater than the rounding error for that 

item) or included in the net bias correction to inventory difference (on line 7 of NRC 

Form 327).

• Schedules and frequencies of replicate and control standard measurements are 

designed so that the estimates of standard deviations and measurement biases will be 

based on measurement control data collected under the same measurement

circumstances and over the same time span as that of the SM or SNM accounting 

measurements to which the standard deviations and bias estimates will be applied. The 

standard deviation and bias of each key measurement system should be evaluated 

periodically. The frequency of such evaluations should typically be at least every 

4 months. When determining the average bias and standard deviation of a particular 

measurement system for an inventory period, pooling of data from previous 

determinations may be used only if statistical tests show that the standard deviations 

and biases from prior determinations do not differ significantly from those of the current 

period, and further, provided the pooled data do not include any data generated more 

than 24 months before the current determination of such bias or standard deviation.

• The effort expended by the licensee in monitoring and controlling the bias and standard 

deviations of each measurement system is shown to be consistent with its impact on 

inventory difference and the total measurement standard error. The number of degrees 

of freedom for estimating the measurement standard deviation may be graded according 

to its contribution to the total measurement standard error.

• Warning limits for a change in bias (for those systems that are not point-in-time 

calibrated, bias free) will be set at the 0.05 level of significance (or tighter), unless 

adequate justification for less stringent limits is provided. Warning limits are optional, 

however, for monitoring replicate data (for standard deviations). If a control datum 

exceeds this limit, the individual responsible for the measurement control system will be 

notified (this normally should occur within 72 hours), a data review will be initiated to find 

the cause, and corrective action will be taken when appropriate. Such reviews and 

corrective actions are completed and documented within 2 weeks.

• Unless adequate justification for less stringent limits is provided, out-of-control limits for 

both standard deviation and bias are set at the 0.001 level of significance for all key 

measurement systems, except that no bias control limits are needed for bias-free, pointin-time calibrated systems. If a control datum exceeds this limit, the system in question 

shall not be used for MC&A purposes until corrective action and resolution is completed 

and the system is back in control within the upper and lower boundaries of the warning 

limit. Likewise, any measurement values generated between the last within-control 

datum and the out-of-control datum shall not be used for MC&A purposes until their 

validity has been confirmed. Such confirmation can be accomplished by remeasurement 

of the involved items or samples on a “last in, first out” basis until two consecutive 
29 NUREG-2158

remeasurements are found to be in agreement with their initial measurement at the 

95 percent confidence level. It should be noted that other criteria for initiating corrective 

action relative to potentially out-of-control measurement systems may be accepted 

where it can be demonstrated that the licensee’s ability to meet the 0.25 percent of 

active inventory limit for total MC&A measurement uncertainty (as specified in 

10 CFR 74.33(c)(3)) will not be jeopardized.

• The approach used for bounding the total measurement standard error for a typical 

material balance period meets the following criteria:

- All reasonable and probable sources of measurement error affecting inventory 

difference are included.

- Any assumed measurement standard deviations are shown to be reasonable. 

They may be shown to be reasonable by comparison either to records of the 

licensee’s past performance data or to published measurement performance in 

similar applications.

• The calculation of the total measurement standard error is performed in accordance with 

a recognized error propagation method. Such methods have been published in

NUREG/CR-4604; TID-26298, “Statistical Methods in Nuclear Material Control” (1973);

and the International Atomic Energy Agency (IAEA) statistics handbook, “IAEA 

Safeguards Statistical Concepts and Techniques” (1989).

• The licensee will confirm that the accountability measurements provided by a contractor 

are controlled by a measurement control program and that the contractor’s 

measurement control program is adequate by conducting audit and assessment reviews 

of the contractor’s program at intervals not to exceed 24 months.

• The measurement systems have adequate calibration frequencies, sufficient control of 

biases, and sufficiently small standard deviations to achieve the requirements of 

10 CFR 74.33(c)(3). Measurement control is used both in-house and by any contractor 

used to ensure that the quality of the measurements is maintained on a level consistent 

with the regulatory requirements.

31 NUREG-2158

6. STATISTICS

6.0 Regulatory Intent

Proper use of statistics is important to ensure that the regulatory requirements in 10 CFR 74.33 

are met. An effective statistical program will ensure measurement systems perform within 

control limits, measurement uncertainties are calculated and propagated, the inventory 

difference (ID) and SEID are properly determined, and significant SRDs are identified. For 

example, 10 CFR 74.33(c)(4) requires licensees to calculate the ID and SEID for the material 

balance period terminated by each physical inventory. Proper use of statistics is important to 

correctly propagate the uncertainties from all measurements into an accurate SEID value.

6.1 Determination of Measurement Uncertainties

To achieve the objectives and capabilities of 10 CFR 74.3 and 10 CFR 74.33, each licensee or 

applicant should institute a statistical program that evaluates the MC&A data to ensure that 

(1) the measurement data are analyzed in a rigorous manner and (2) hypotheses concerning 

the status of the nuclear material possessed are appropriately tested. The NRC sponsored the 

development of a comprehensive reference that specifically addresses the statistical treatment 

of measurement control and accounting data. The statistical methods described in this 

reference, NUREG/CR-4604, as well as in TID-26298 and the IAEA statistics handbook, are 

recommended by the NRC for satisfying the statistical requirements of 10 CFR 74.33. 

The MC&A plan should do the following:

• Provide a detailed discussion of the procedures and methodologies for estimating 

measurement variance components.

• Discuss how biases are determined and how bias corrections are applied, including: 

- how often biases are estimated 

- how the effect of the bias on the measured quantity of material in the item is 

determined 

- when and how bias corrections to items are made 

- how their effect on inventory difference is determined 

- when and how bias corrections are applied to the ID 

• Describe the procedure and means for determining active inventory.

• Provide all relevant information on determining the SEID.

• Specify the DQ, which should not exceed 1.3 percent of the annual quantity of U-235 

introduced into the enrichment process, except when 1.3 percent of additions to process 

is less that 25 kilograms of U-235, in which case the DQ need not be less than 

25 kilograms of U-235.

• Specify the methodology for determining ID threshold values to be used to provide a 

90 percent power of detecting the loss of a DQ, as required by 10 CFR 74.33(c)(4).

(See Chapter 7 for additional information on ID limits and response actions.)
NUREG-2158 32

There should be a definitive statement in the MC&A plan for independent verification of the 

correctness of the SEID calculation for each total plant material balance. If the SEID value is 

calculated using a computer, the verification may involve two or more persons to check for 

correctness of the input data and to check the correctness of a sample calculation used to 

verify the computer program. 

6.2 Determination of Standard Error of the Inventory Difference

As defined in 10 CFR 74.4, the term “standard error of the inventory difference” means the 

standard deviation of an inventory difference that takes into account all measurement error 

contributions to the components of the ID. For strategic SNM facilities, nonmeasurement

contributors to the ID are not to be included in the SEID calculation. However, for facilities 

possessing only SNM of low strategic significance, the NRC allows licensees to take limited 

credit for nonmeasurement contributors. It is not really possible to quantify the 

nonmeasurement contribution to the uncertainty associated with an ID, but 10 CFR 74.33 

licensees are permitted to assume that the total nonmeasurement contribution to SEID equals 

the total measurement error contribution. When including only measurement uncertainty, SEID 

can be expressed as follows:

SEID =

where 

k = number of measurement systems 

= total grams U (or U-235) measured during inventory period by measurement 

system i 

= systematic error standard deviation for measurement system i 

= random error standard deviation for measurement system i 

n = number of batches (items) measured by measurement system i 

When taking the maximum allowable credit for nonmeasurement contribution (which assumes 

a 1:1 ratio of measurement to nonmeasurement contributions),

SEID = 

In theory, SEID provides the uncertainty, at the 67 percent confidence level, of the ID. 

The MC&A plan should provide all relevant information on determining the SEID. There should 

also be a commitment that at least two individuals independently verify the correctness of the 

SEID calculation for each total plant material balance. If the SEID value is calculated by a 

computer, the verification by two or more persons involves checking for the correctness of the 

input data used by the computer to calculate the SEID.

6.3 Bias Corrections

From a statistical perspective, biases that are not statistically significant (at the 95 percent 

confidence level) should never be applied as adjustments (corrections) to the accounting 

records. To obtain the best estimate of the true inventory difference value, such insignificant 
33 NUREG-2158

biases should be applied as a nonaccounting adjustment to the initially calculated ID (as 

obtained from the ID equation: ID = BI + A - R - EI). Such practice is not deemed necessary, 

however, for material balances pertaining to SNM of moderate strategic significance and is thus 

optional.

For biases that are statistically significant (at the 95 percent confidence level), it is common 

practice to adjust the accounting values for individual items if the bias effect on the item is more 

than the rounding error for that item, and if less than the rounding error, to apply the bias as a 

nonaccounting adjustment to the ID. Under a well-designed and well-managed measurement 

control system, bias corrections to the accounting records should seldom, if ever, be necessary 

under the above-mentioned approach. Although the effect on an individual item from a 

statistically significant bias should be negligible, the effect of that bias across hundreds or 

thousands of items (with SM or SNM values derived from the biased measurement system) 

could have a very significant impact on the ID value.

Nevertheless, in view of the very large quantity of SNM (of low strategic significance) that is of 

safeguards significance, the NRC acceptance criteria do not normally call for applying bias 

corrections to either the accounting records or as an adjustment to ID unless the effect of a 

single significant bias or the net sum of all significant biases is unusually large.

As a minimum, to meet the NRC acceptance criteria, a bias correction for a single key 

measurement system should be considered “significant,” and thus applied either as corrections 

to the accounting records or as an adjustment to the inventory difference, if (1) such bias is 

statistically significant at the 95 percent confidence level, and (2) either or both of the following 

are also

(A) Applying the correction would cause the ID to exceed its detection threshold (DT) value.

true:

(B) The bias is greater than 0.0100 percent relative and also affects the ID value by more 

than 1,000 grams U-235.

Additionally, the net algebraic sum (expressed as grams U-235) of all statistically significant 

(95 percent confidence level) biases, from key measurement systems not defined as bias free, 

that have not been applied as a correction or adjustment under condition A and/or B, above, is 

considered to be significant and is to be applied as a net adjustment to the ID if either or both of 

the following are true:

(C) Applying such correction would cause the ID to exceed its DT value.

(D) The net correction affects the ID value by more than 5.00 percent of the licensee’s DQ, 

or 10,000 grams U-235, whichever is larger.

35 NUREG-2158

7. PHYSICAL INVENTORIES

7.0 Regulatory Intent

The intent of 10 CFR 74.33(c)(4) is to require licensees to perform both dynamic 

(i.e., nonshutdown) inventories of the enrichment process system and static inventories of the 

balance of the plant so as to confirm that a loss or diversion of a safeguards-significant quantity 

of low strategic SNM has not occurred. Licensees are required by 10 CFR 74.33(c)(4) to 

conduct dynamic inventories at least every 65 calendar days and a static inventory at least 

every 370 calendar days. The principal method of confirming the presence of SM and SNM is

to perform a physical inventory and compare it to the book (record) inventory. If all SM and 

SNM is included, the expected difference between the book inventory and the physical inventory 

is zero plus or minus the measurement uncertainty associated with both the physical and book 

inventories. In any actual case, the size of the estimated ID depends on measurement errors, 

as well as various nonmeasurement contributors, such as recording errors, unmeasured losses, 

and unmeasured residual holdup, as discussed further in Section 7.1 (see Chapter 18, 

Glossary, for the definition of “residual holdup”). 

7.1 General Description

The applicant or licensee should provide a general description of how both dynamic 

(i.e., nonshutdown) inventories of the enrichment process system and static inventories of the 

balance of the plant will be planned, conducted, assessed, and reported. For enrichment 

facilities using laser isotopic separation technology, a total plant shutdown inventory may be 

required. 

The MC&A plan should contain a definitive statement that physical inventory functions and 

responsibilities will be reviewed comprehensively with the involved individuals before the start of 

each dynamic and static inventory. 

For static inventories, a book inventory listing, derived from the MC&A record system, should be 

generated just before the actual start of the inventory; such listing shall include all SM and SNM 

that the records indicate should be possessed by the licensee at the inventory cutoff time, 

except for material to be covered by the dynamic inventory that is to be conducted in

conjunction with the static inventory. 

For dynamic inventories, a book inventory quantity, to which the results of the dynamic physical 

inventory will be compared, is needed. One approach to estimate the in-process inventory is to 

use a “running book in-process inventory” (RBIPI) technique. The RBIPI is the quantity of U and 

U-235, calculated as follows: 

RBIPI = BI + CI -CO

where 

BI = beginning in-process inventory (i.e., inventory at the start of the current inventory 

period) as determined from the previous dynamic inventory 

CI = cumulative measured input to the enrichment process for the current dynamic 

inventory period. 

CO = cumulative measured output from the enrichment process for the current 

dynamic inventory period 
NUREG-2158 36

Hence, the inventory difference associated with a dynamic physical inventory is derived from 

the following equation: 

ID = RBIPI -El = (BI + CI) - (CO +EI)

where

El = ending in-process inventory as determined from the dynamic physical inventory.

For both static and dynamic physical inventories, the MC&A plan should contain sufficient 

information to show how the total in-process inventory for both U and U-235 is obtained. The 

means for measuring or estimating residual holdup should be addressed in detail, and the 

change or variation in such holdup from one inventory to the next should also be discussed. 

This information is important to ensure no SM or SNM held under license (except for waste 

materials assigned to holding accounts in accordance with the exceptions provided in 

10 CFR 74.33(c)(6) and U.S. Department of Energy (DOE)/NRC Form 741 instructions) will be 

omitted, and no quantity will be counted more than once.

The MC&A plan should also contain adequate commitments to ensure that each physical 

inventory will be organized and coordinated so that all involved persons are instructed in the use 

of uniform procedures for checking SM and SNM quantities and recording observations. The 

means for conducting the inventory should ensure that any SM or SNM held under license 

(except for waste materials as noted above) is properly inventoried.

The inventory difference and related information associated with each dynamic physical 

inventory are to be reported to the NRC, under 10 CFR 74.17(a), on NRC Form 327 as the 

results of a physical inventory associated with material code 89 (U in cascades). The inventory 

difference and related information associated with each static inventory are to be reported to the 

NRC on separate NRC Forms-327 for DOE/NRC material type codes 10, 20, and 81 

(i.e., depleted, enriched, and normal U, respectively). In addition to these submittals, the results 

of the plant-wide material balance, for total U element and total U-235 isotope (across all four 

material type codes), associated with each annual physical inventory must be reported on a 

separate NRC Form 327. 

7.2 Organization, Procedures, and Schedules

The MC&A plan should explain the makeup and duties of the typical physical inventory

organization for both dynamic and static inventories. The individual having responsibility for the 

coordination of the physical inventory effort should be identified by position title. The MC&A

plan also should indicate how the preparation and modification of inventory procedures are to 

be controlled. 

The MC&A plan should contain a definitive statement that specific inventory instructions will be 

prepared and issued for each dynamic and static inventory. 

7.3 Typical Inventory Composition

The typical expected in-process inventory within the enrichment equipment for both U and 

U-235 at the time of the dynamic physical inventory should be specified. Unlike other bulk 

nuclear material processing facilities, uranium enrichment facilities increase the strategic value 

of the U under complex dynamic operating conditions. For gas centrifuge and gaseous diffusion 

plants, the in-process inventory should be specified by accounting for UF6 gas, solid UF6, and 

residual holdup solids deposited within equipment.
37 NUREG-2158

A typical composition, by material type codes, of a static physical inventory should also be 

presented. The total inventory of UF6 cylinders should be accounted for by material type 

(i.e., tails, feed, and product). If cylinders or other containers of different sizes are used within 

any of the three UF6 categories, they should be treated as different item strata. 

Enrichment plants typically are divided into a number of MBAs and ICAs to reflect the functional 

activities as follows: 

Processing—This is an MBA in which occur (1) routine transfers of nuclear material from one 

container to another, (2) changes in isotopic or chemical assay, or (3) changes in chemical or 

physical form. Various measurements are required to define flows of materials through the 

process and to perform physical inventories so that periodic material balances can be 

completed for the MBA. Because these measurements have associated uncertainties, a 

processing MBA will normally have a nonzero inventory difference for each inventory. Of the 

total plant MBAs and ICAs, a relatively small number might be processing MBAs. Examples of 

operations are isotope separation (e.g., enrichment cascade facilities); decontamination and 

recovery; analytical laboratory; and material rebatching, blending, and sampling. Physical 

inventories for the enrichment process system and decontamination and recovery operations 

are the most complex and require the most coordination and careful timing.

Storage—These are ICAs in which all materials are sealed in containers with measured values 

and are being stored for future processing or shipment. Some minor sampling of containers can 

occur in a storage ICA. Because nuclear materials in a storage ICA are primarily accounted for 

on an item basis, a true storage ICA typically will have a zero inventory difference for each 

inventory period, when all items are accounted for and their integrity and previously documented 

measured values are confirmed. 

Receiving and shipping

7.4 Description of Typical Item Strata

—This term refers to an ICA from which materials are shipped or into 

which materials are received from off site. This ICA type will normally serve as an interim 

storage area and will see more activity (i.e., changes in current inventory) than the typical 

storage ICA. At some facilities, sampling and rebatching of items may occur in this ICA. 

The MC&A plan should describe the expected item population in terms of the following:

• type of item (i.e., stratum)

• expected range of the number of items within each stratum

• the average U and U-235 content of the items within each stratum

• the expected rate of item generation and consumption for each stratum

7.5 Conducting Dynamic Physical Inventories

A description of the dynamic inventory methodology, including cutoff and inventory minimization 

procedures, should be presented, and all measurements (including sampling) sufficient to meet 

the requirements of 10 CFR 74.33(c)(4) should be identified. 

Because of the size and complexity of a gaseous enrichment cascade system and the 

continuous dynamic operations, a detailed inventory notice should be prepared for each 

dynamic inventory. The notice should be issued to all involved parties and should contain 

instructions that define the timing and performance of various inventory steps and conditions 

under which the inventory is to be taken. Specific sampling points throughout the cascade and 
NUREG-2158 38

instructions on data submission to the accountability organization should be identified. The 

instructions should take into account the current cascade configuration (e.g., equipment 

offstream) and types of feed and withdrawal streams. The instructions should highlight any 

required deviation from normal inventory procedures contained in the plant’s operating 

procedures. The basic procedures for the cascade in-process inventory should (1) maintain the 

cascade in a steady-state operating condition for at least 24 hours before inventory time, 

(2) record the necessary process measurement data and collect process samples over a period 

of about 6 hours before inventory time, and (3) establish a complete feed and withdrawal 

system switchover to preinventoried containers at inventory time so that the amount of material 

in the active containers at the feed and withdrawal stations can be measured. 

Unless special circumstances require a change, the time for a routine inventory should be 

established (e.g., at 2400 hours) on the last day of the inventory period. For the gaseous 

enrichment processes, the dynamic gas-phase inventory requires recording gas pressure and 

temperature readings for equipment throughout the process system, quantities of UF6 contained 

in desublimers (i.e., cold traps) and chemical traps, and other measurements 

(e.g., concentration of impurity gases). Typically, many data points are collected during these 

operations for calculating the in-process inventory for input into established computer models 

and calculation programs. These programs incorporate fixed-cascade parameters, such as 

equipment volumes, compressor circuit balances, and gas law relationships. 

7.6 Conducting Static Physical Inventories

A description of the procedures and methodologies associated with performing static physical 

inventories should be provided in enough detail to demonstrate that valid inventories sufficient 

to meet the requirements of 10 CFR 74.33(c)(4) will be conducted. Such description should 

include a general outline of the following:

• organization and separation of functions 

• assignment of inventory teams and their training in the use of uniform practices 

• obtaining, verifying, and recording source data 

• control of inventory forms 

• assurance that item counts verify the presence of each item while preventing any item 

from being counted more than once 

• implementation of cutoff and material handling procedures for nonenrichment processes 

(e.g., scrap recovery) 

Decontamination and recovery also is a complex operation involving the disassembly and 

decontamination of failed pieces of process equipment, cleaning of UF6 cylinders, and recovery 

of U from various types of scrap materials. The basic inventory procedure should involve 

establishing a cutoff of movement of materials into the MBA and processing all materials to a 

measurable form, such as containers of solution or oxide. Except for the decontamination 

enclosure in which in-process solutions are mixed, sampled, and measured volumetrically, the 

inventory process should involve emptying and flushing process systems and piping, which 

then could be measured using NDA techniques to establish levels of residual holdup. 

The MC&A plan should describe special item storage and handling or tamper-indicating 

methods, which are used to ensure that the previously measured and recorded SM or SNM 
39 NUREG-2158

content values can be used for inventory purposes without remeasurements. In addition, the 

MC&A plan should describe how item identities are verified and how tampering with the 

contents of items will be detected or prevented. 

Items that are not encapsulated, affixed with tamper-indicating seals, or otherwise protected to 

ensure the validity of prior measurements, need special attention. The basis for determining 

which items are to be measured at physical inventory time and the justification of any proposed 

alternatives to the measurement of any SM and SNM included in the inventory should be 

presented. If statistical sampling is proposed as an alternative method to 100 percent 

verification, the MC&A plan should describe the sampling plan. Such description should 

include the following: 

• the method of segregating the types of items to be sampled (i.e., selected for 

remeasurement) 

• the procedure for calculating the sample size (i.e., the number of items) for each 

stratum 

• the parameter to be measured

• the quality of the measurement methods used to verify original measurement values 

• the procedure for reconciling discrepancies between original and remeasurement 

values and for scheduling additional tests and remeasurements 

• the basis for discarding an original SM or SNM value and replacing it with a 

remeasurement value 

One acceptable means for establishing the number of items (to be randomly selected for 

remeasurement) from a given stratum to give the required 90 percent power of detection of loss 

of a DQ is given by the following equation: 

n = N [1 − ]

where

n = number of items to be remeasured 

N = total number of items in a stratum 

x = maximum U-235 content per item (kilograms) 

g = DQ = detection quantity (kilograms − U-235) 

When using such a statistical sampling plan to confirm the validity of prior measurements, the 

remeasurement value obtained for each item (among the n items remeasured) must be 

compared to its original value. If the difference for a given item exceeds some predetermined 

limit (usually three times the standard deviation of the measurement, or, 3σ), that item is 

designated as a “defect.” To achieve the 90 percent power of detection capability for detecting 

the loss of a DQ, there must be at least a 90 percent probability that one or more “defects” will 

be encountered among the items remeasured across all involved stata if the actual loss of a DQ 

has occurred. If, across all strata, one or more defects are encountered, a second set of n 

randomly selected items (or all remaining items if n is equal to or greater than 0.5 N) from each 

stratum should be remeasured. If one or more defects are encountered (across all item stata) 
NUREG-2158 40

while performing any second round of remeasurements, all unsealed and unencapsulated items 

not yet remeasured are to be remeasured. Any item, regardless of whether there are any 

defects, whose remeasured value differs from its original measurement by more than two sigma 

(2σ) should have its accounting value revised to reflect its remeasured quantity.

The MC&A plan should also contain a definitive statement that all items on ending inventory that 

have not been previously measured will be measured for inventory purposes. 

The decision rationale for determining when the element and isotope factors for items, objects, 

or containers will be measured directly for inventory and when they may be based on other 

measurements should be presented in the MC&A plan. For example, if the U-235 contained in 

liquid waste batches is derived by applying an average enrichment factor to the measured U

element content, the rationale for such practice (as opposed to measuring each batch for both U

and U-235 content) should be discussed and the method for establishing the average 

enrichment factor should be described. 

If the content of items is established through prior measurements and those items are sealed 

with tamper-indicating devices or access to them is controlled, the SM or SNM quantity in those 

items may be based on those measured values. Otherwise, verification of SM or SNM content 

can be achieved by reweighing either (1) all items within a given stratum or (2) randomly 

selected items from the stratum based on a statistical sampling plan. A statistical sampling plan 

will not be acceptable if there is any likelihood of any significant change in the U concentration 

(or weight fraction) or in the U isotopic distribution, because of such factors as oxidation, 

change in moisture content, commingling with materials of different enrichments, or 

different compositions. 

7.7 Inventory Difference Limits and Response Actions

Each licensee should have a well-defined process for evaluating both dynamic and total plant 

IDs and taking action when IDs exceed certain predetermined thresholds. As a minimum, there 

should be three response levels for excessive IDs. The following would be an acceptable 

approach for three increasing levels of response actions with respect to static physical 

inventories:

Warning-level ID U-235 ID ≥ 1.7 (SEID) + 500 grams or U ID ≥ 1.7 (SEID) + 10 kg U 

Significant ID U or U-235 ID ≥ 3 (SEID)

problem

Major ID problem U-235 ID ≥ DQ -1.3 (SEID) 

For dynamic physical inventories, the following three response levels for excessive IDs would 

be acceptable: 

Warning-level ID U or U-235 ID ≥ 2 (SEID) 

Significant ID U or U-235 ID ≥ 3 (SEID)

problem 

Major ID problem U-235 ID ≥ DQ -1.3 (SEID) - (cumulative enrichment process 

system U-235 ID for past 10 months) 

All of the above limits are expressed in terms of absolute values of ID without regard for 

algebraic sign. The minimum response for a warning-level ID should be a documented licensee 

investigation conducted by the MC&A organization. Such an investigation should provide a 

conclusion for the probable cause of the excessive ID and give recommendations for avoiding 
41 NUREG-2158

recurrences. When a warning-level ID is positive, it should be regarded as being equivalent to 

an indicator of a possible loss that requires investigation and resolution (see Chapter 14).

For a significant ID problem, an extensive investigation by the licensee should be conducted. If 

a significant ID problem cannot be satisfactorily explained, a static or dynamic reinventory may 

be needed. 

For any unresolved ID determination that remains a major ID problem (without regard to 

algebraic sign), the licensee should conduct a plantwide reinventory and investigation. The 

NRC considers a positive ID large enough to be a major ID problem as a very serious 

condition. 

The MC&A plan should fully describe, in definitive statements, the minimum response actions 

for each ID action level.

7.8 Commitments and Acceptance Criteria

In its MC&A plan, the applicant or licensee should provide definitive commitments that adhere to 

the regulatory requirements and meet acceptance criteria applicable to the physical inventories. 

A finding that the licensee’s MC&A plan for conducting physical inventories is acceptable and in 

accordance with 10 CFR 74.33(c)(4), will be based on, but not limited to, the following 

acceptance criteria:

• An MC&A program will be maintained that is capable of confirming, at intervals not to 

exceed 370 days, the presence of all SM and SNM expected to be present (at a given 

time) based on accurate, current, and reliable information. The means for conducting 

the inventory must insure that no SM or SNM currently on hand will be omitted and no 

quantity will be counted more than once.

• Unless otherwise required by Facility Attachments that satisfy 10 CFR Part 75, 

“Safeguards on Nuclear Material—Implementation of US/IAEA Agreement,” total plant 

static physical inventories will be performed at least every 370 calendar days and will be 

used as the basis for reconciling and adjusting the book inventory, which is done within 

60 calendar days after the start of each physical inventory.

• Dynamic (nonshutdown) physical inventories of in-process (e.g., in the enrichment 

equipment) U and U-235 will be performed at least every 65 calendar days.

• For each physical inventory, inventory procedures are clearly written and are reviewed 

and approved by the individual responsible for conducting the physical inventory. The 

inventory procedures provide for confirming the presence of all items by direct 

observation and the presence, by direct measurement or an acceptable alternative, of all 

quantities of SM and SNM that are neither encapsulated nor tamper-safed.

• The individual responsible for conducting the physical inventory is either free from 

potential conflicts of interest or is overchecked sufficiently to prevent compromising the 

validity of the physical inventory.

• Each physical inventory listing will include all SM and SNM possessed on the inventory 

date, except for waste materials assigned to holding accounts (in accordance with the 

exception provided in 10 CFR 74.33(c)(6) and DOE/NRC Form 741 instructions). All 

such listed SM and SNM quantities are to be based on measurements for SM or SNM 

quantity.
NUREG-2158 42

• Within 60 calendar days after the start of each physical inventory, the inventory 

difference will be determined. Any inventory difference that is rejected by a statistical 

test that has a 90 percent power of detecting a discrepancy of a quantity of U-235 

established by the NRC on a site-specific basis will be reported to the appropriate NRC 

safeguards organizational units. 

• Discrepancies in the identity, quantity, or location of items, objects, or containers of SNM 

that are detected during a physical inventory will be corrected.

• Inventory difference values will be corrected for (1) accounting adjustments resulting 

from prior period activity and (2) significant biases that have not been previously taken 

into account. (NOTE: See the definition of significant bias in Chapter 6.)

• Adjustments made to reconcile the book inventory to the physical inventory are in 

accordance with standard accounting practices and are traceable and auditable in the 

MC&A records.

• Whenever a finalized U-235 ID (after applying any appropriate bias corrections and prior 

period adjustments) is greater than the U-235 DT and is not resolved within the 

60-calendar-day reconciliation period, all SM and SNM processing should be halted and 

a reinventory and investigation conducted. (NOTE: This applies to both positive and 

negative ID values.)

• The results of all physical inventories and of investigations and resolution actions 

following any excessive U-235 ID are recorded and auditable. An excessive ID is one 

(regardless of the algebraic sign) that exceeds both 3.00 times SEID and 9,000 grams 

U-235.

• The MC&A plan contains adequate commitments to ensure that each physical inventory 

will be organized and coordinated so that all involved persons are instructed in the use 

of uniform procedures for checking SM and SNM quantities and recording observations.

• The licensee may propose alternatives to remeasurement. The MC&A plan should 

describe the circumstances under which each proposed alternative may be used. The 

proposed alternatives to remeasurement should satisfy at least one of the following 

criteria:

- The SM or SNM content is verified by statistical sampling and measurement of 

representative items, objects, or samples of the material. The total overall 

sampling plan shall support the capability for detecting any loss in excess of the 

current DQ with 90 percent (or better) probability.

- The previous measurement results are accepted, because the items are stored in 

a controlled access enclosure that provides protection equivalent to 

tamper-safing.

- Residual holdup that remains after cleanout or draindown may be estimated, if 

the estimate is based on previously measured values, and it is periodically 

verified or validated.

- For material with SM or SNM content that has been previously measured, and 

there is no likelihood of any significant change in the U concentration (or weight 

fraction) or in the U enrichment caused by such factors as oxidation, change in 
43 NUREG-2158

moisture content, commingling with materials of different enrichment or different 

composition, the previously determined U and U-235 content may be accepted 

without verification of SM or SNM content, provided the gross weight or net 

weight, or both, of all items within the population is confirmed by (1) a 

100 percent reweighing of all such items or (2) reweighing an adequate number 

of randomly selected items (based on a statistical sampling plan) to provide a 

90 percent (or better) probability of detecting a loss equal to or greater than the 

current DQ.

- As an additional alternative to remeasurement (of unsealed SM or SNM) at 

physical inventory time, a program of routine process monitoring will be 

acceptable, when the combination of the process monitoring program and the 

inventory procedures will achieve the same level of loss detection capability as 

that provided by a physical inventory in which all unencapsulated items are either 

tamper-safed or remeasured.

- Any previously measured but unsealed (or unencapsulated) SM or SNM that is 

on hand at the time of the physical inventory, and which is to be introduced into 

subsequent processing steps before inventory reconciliation, should be 

remeasured or have its prior measurement value confirmed (by an acceptable 

alternative) before the subsequent processing is initiated.

• The DQ (in kilograms U-235) for any given inventory period will be no greater than 

1.30 percent of that period’s throughput for facilities involved in chemical processing 

(such as UF6 conversion, scrap recovery, oxidation or reduction processes), and no 

greater than 0.90 percent of throughput for facilities where material only undergoes 

physical changes (such as pressing UO2 powder into pellets or loading pellets into fuel 

rods), unless the 0.90 or 1.30 percent of throughput (as appropriate) is less than 

25 kilograms U-235, in which case the DQ need not be less than 25 kilograms. The 

U-235 throughput is defined as the greater of “additional to process” or “removals from 

process” during a 12-month inventory period.

• The information in the MC&A plan shows that the DT for an excessive ID will result in a 

90 percent (or better) probability of detecting a discrepancy (i.e., an apparent gain or 

loss) equal to or larger than the U-235 DQ for the inventory period in question. In 

general, a licensee may assume the ID distribution approximates a normal distribution, 

and therefore:

DT = DQ -1.30(SEID)

Acceptable methodology for calculating the measurement error contribution to the SEID 

by error propagation is found in NUREG-4604 TID-26298, and the IAEA statistics 

handbook. Special attention is given to inclusion of all applicable and measurable 

sources of error to avoid underestimating the SEID.

• In addition to the DT ID alarm limit (required by 10 CFR 74.33(c)(5)), there is at least one 

excessive ID warning level limit that, when exceeded, will require an investigative 

response action. The resources and level of effort to be committed to the investigation 

of an excessive ID will be proportional to the magnitude of the ID but will be sufficient to 

reassess the results of the physical inventory, the accounting records, and the 

measurement control program data; to confirm the relevant calculations and data 

analysis; and, when necessary, to carry out searches for unmeasured inventory, such as 
NUREG-2158 44

residual holdup and measured discards. Investigations are to be completed within 

60 days after initiating the inventory (except when additional time is granted by the NRC 

for extenuating circumstances). 
45 NUREG-2158

8. PROGRAM FOR PREVENTING AND DETECTING UNAUTHORIZED 

PRODUCTION OF ENRICHED URANIUM

8.0 Regulatory Intent

The intent of the 10 CFR 74.33(c)(5) detection program is to ensure that licensees establish an 

adequate detection program, independent of production, that provides assurance of detecting 

(1) the production of U to 10 percent or more of U-235, to the extent that SNM of moderate 

strategic significance, as defined in 10 CFR 74.4, could be produced in any 370-calendar-day 

period, (2) the production of U enriched to 20 percent or more of U-235, and (3) the 

unauthorized production of uranium of low strategic significance.

8.1 Organization

The licensee should identify the individual responsible for executing the program for detecting 

unauthorized production of enriched U. This individual need not be part of the MC&A 

organization but should be independent of the production organization. Other personnel who 

are assigned responsibilities in this program should also be independent of production 

supervision. This program should be well coordinated with both MC&A and production

management.

The overall organization, including the minimum staffing requirements and functions, should 

be in the MC&A plan. A definitive statement should be made that the program director will 

have the necessary authority to carry out all aspects of the program. 

8.2 General Description of Program

The overall design of this program should include an analysis of potentially credible means 

by which unauthorized production could occur; that is, for each conceivable and credible 

scenario for unauthorized production, a surveillance or an enrichment monitoring system for 

the timely detection of that scenario should exist. The analysis should be extensive and 

conducted by individuals having a thorough knowledge of the processing equipment and 

enrichment technology. All conceptual and credible scenarios for unauthorized production 

of U enriched to 10 wt % or more in U-235 by the employed enrichment technology should 

be identified. These scenarios should include cascade isolation, process system 

adjustments, batch recycle processing, cascade interconnections, and cascade 

reconfiguration (to increase the number of stages). 

The program should be capable of satisfying the following detection criteria as part of 

each bimonthly inventory cycle: 

• For any unauthorized production (from undeclared feed) of LEU within the cascade with 

an enrichment of less than 10 wt % U-235, detection should occur before the quantity of 

U-235 contained in such LEU amounts to 25 kilograms.

• For any unauthorized production of LEU within the cascade with an enrichment within 

the range of 10.00 to 19.99 wt % U-235, detection must occur before the quantity of 

U-235 contained in such LEU amounts to 10 kilograms. 

• For any unauthorized production within the cascade of high-enriched U (HEU)

(i.e., equal to or greater than 20 percent U-235), detection must occur before the 

quantity of U-235 contained in such HEU amounts to 1 kilogram. 
NUREG-2158 46

The MC&A plan should address the following aspects of the program that are aimed at 

protecting against and detecting unauthorized production of U of low strategic significance: 

• the type of surveillance, and its frequency, to be applied to the processing areas 

• the type of surveillance, and its frequency, to be applied to the process control room and 

other areas where operation of processing equipment can be controlled or modified 

remotely

• the type of surveillance, and its frequency, to be applied to potential feed and withdrawal 

areas 

• process monitoring activities (e.g., radiation monitoring and flow metering), other than 

process sampling, that could contribute to the detection of unauthorized production 

• use of TIDs on process valves and flanges 

• personnel access controls that limit the number of individuals who could gain access to 

the enrichment processing equipment or its control mechanisms 

• physical security controls, such as locked and alarmed doors and closed-circuit 

television monitors, that would detect unauthorized access to processing equipment 

or product material 

• production control activities that could contribute to the detection of unauthorized 

production 

• employee education and informant protection (e.g., whistle-blower protection rules) to 

increase the probability of detection and reporting of potential unauthorized activities 

by facility personnel 

• notification of appropriate MC&A personnel by operations organizations of the 

operating status of the enrichment process system, especially when a cascade is 

isolated from the process stream 

To address the unauthorized production of U enriched to 10 wt % or more U-235, the 

following types of measures should be considered: 

• process design features that preclude production of higher enrichments from being 

conducted simultaneously with normal (i.e., authorized) production 

• personnel access controls that limit the number of individuals who could gain access to 

the enrichment processing equipment or its control mechanisms 

• physical security controls, such as locked and alarmed doors and closed-circuit 

television monitors, that would detect unauthorized access to processing equipment or 

product material 

• process control systems that could detect unauthorized use of production equipment 

• production control systems that could detect unauthorized production of U enriched to

a level equal to or greater than 10 wt % U-235 
47 NUREG-2158

• technical safeguards systems (e.g., optical surveillance, tamper-indicating seals, 

radiation monitors, flow meters, and visual inspection procedures) that could detect 

unauthorized production of enriched U 

• nuclear material, minor isotope, and separative work unit (SWU) balances 

In describing the portion of the program aimed at protecting against and detecting production of 

U enriched to a level equal to or greater than 10 wt % U-235, the MC&A plan should address 

the following, in addition to the previously stated aspects for detecting unauthorized production: 

• location of the sampling ports, and frequency of sampling, to be used for monitoring 

product streams 

• the means for verifying the validity of process control measurements and laboratory 

enrichment measurements (i.e., describing how the falsification of process 

measurements would be detected) 

• the type of equipment or instrumentation (in addition to and independent from that used 

and controlled by production personnel) to be used for monitoring purposes

8.3 Data, Information, and Activities To Be Monitored

The licensee should identify the specific data, information, and activities to be monitored and 

should address the frequency of each specified monitoring activity and frequency of data 

evaluation. 

The means for independently assessing the authorized process enrichment parameters should

be shown. To accomplish this, the program should address verification of the following: 

• weighing, sampling, and isotopic assay of material introduced at the feed station(s) 

• weighing, sampling, and isotopic assay of material withdrawn at the product and tails 

withdrawal stations 

• sampling and isotopic assay of in-process material at randomly selected points 

• consistency of the quantity of U-235 determined to be in the product and tails with the 

quantity in feed 

• determination of the nuclear material, minor isotope, and SWU balances

Licensees or applicants should consider monitoring process parameters such as UF6 gas 

pressures, flow rates, enrichments, valve positions, cascade configuration and connections, and 

tracking of all potential UF6 containers in the process area. Verification of measurements also 

can be obtained by independent observations of measurement processes and by using NDA 

techniques to verify isotopic ratios and contents of containers. 

The overall design of the program should include analyses of all processing and product 

streams to determine where U isotopic measurements should be made and at what frequency 

they should be performed to prevent clandestine enrichment activities; that is, for each credible 

scenario for clandestine enrichment, a monitoring program for the timely detection of any 

implementation of that scenario should be implemented. Because the activity of most interest is 

whether unauthorized HEU is being produced, NDA measurement techniques for enrichment 
NUREG-2158 48

may be very practical. Either manual measurements using portable NDA instruments can be 

used or the instruments can be permanently affixed to the process equipment. In the former 

case, administrative controls should be used to prevent collusion of the measurement personnel 

with a potential clandestine perpetrator. In the latter case, frequent inspection and testing of the 

instruments should be performed to prevent tampering or disabling of the NDA measurement 

system. 

The scenario analysis performed should address each product stream, regardless of material 

type or composition, and be conducted by individuals having a thorough knowledge of the 

processing equipment and enrichment technology. Credible means for producing U at 

enrichment levels equal to or greater than 10 wt % U-235 should be identified. These 

approaches should include process system adjustments, batch recycle processing, cascade 

interconnections, and cascade reconfiguration (e.g., to increase the number of stages). 

The extensiveness and complexity of the monitoring program should be dependent on such 

factors as the following: 

• the minimum time required to produce HEU containing 1 kilogram of U-235 

• process design features that would prevent unauthorized enrichment from being 

conducted simultaneously with normal, authorized enrichment 

• personnel access controls that limit the number of individuals who could gain access to 

the enrichment processing equipment or its control mechanisms 

• physical security controls, such as locked and alarmed doors and closed-circuit 

television monitors, that would detect unauthorized access to enrichment equipment, 

feed or product material, or the enrichment production area 

• process control systems that would detect unauthorized use of enrichment equipment 

The MC&A plan should address such aspects as the following: 

• type and frequency of U isotopic measurements 

• type and frequency of NDA monitoring measurements 

• required accuracy of the isotopic measurements 

• administrative controls to be applied to all monitoring measurements 

The MC&A plan should show the means for independently verifying the authorized process 

enrichment parameters given in this section, identify the specific data that will be collected and

analyzed, and state the frequency of the measurements and of data evaluations. 

The following are some examples of technical measures that could satisfy the licensee’s 

responsibility for addressing unauthorized production and for providing auditability of the 

conclusion that unauthorized production has not occurred: 

• Installation of supplemental materials verification techniques, such as NDA 

measurements, process and cylinder sampling, flow measurements, cylinder 

weighings, and item verification, will assist in detecting missing material or out-ofbalance conditions. 
49 NUREG-2158

• Tamper-safing and additional containment and surveillance techniques on 

instrumentation could provide evidence of both unreported cascade reconfiguration 

and suspect feed or withdrawal in the cascade hall. 

• Potential containment and surveillance techniques include radiation measurement and 

surveillance instrumentation, personnel and vehicle portal monitors, package monitors, 

perimeter barrier sensor systems, optical surveillance instrumentation, automated keycontrol systems, and tamper-indicating seals. 

• Installation of in-line enrichment monitors and gas flow meters at the product 

withdrawal points could address most unauthorized production scenarios.

• Installation of material surveillance systems, such as weight sensors, heat sensors, 

video surveillance cameras, radiofrequency tags, or motion detectors, will provide 

useful and necessary information for assessing alarms and localizing unauthorized 

material removal and quantity or the form of missing materials.

8.4 Reporting and Documentation Requirements

The applicant or licensee should make a definitive statement defining the basis for declaring 

that there has been (1) unauthorized production of U to greater than 10 percent enrichment and 

(2) unauthorized production of LEU. 

Whenever systems indicate that unauthorized production of enriched U may have occurred or 

may be occurring, that determination becomes an “indicator” and subject to the investigation 

and resolution requirements of 10 CFR 74.33(c)(5). 

If actual unauthorized production of enriched U is discovered, that discovery must be reported to 

the NRC within 1 hour as required by 10 CFR 74.11. 

8.5 Commitments and Acceptance Criteria

In its MC&A plan, the licensee should provide definitive commitments that adhere to the 

regulatory requirements and meet acceptance criteria applicable to detecting unauthorized 

production of U to greater than 10 percent enrichment and unauthorized production of U of low 

strategic significance. A finding that the licensee’s MC&A plan for the detection program is 

acceptable and in accordance with 10 CFR 74.33(c)(5), will be based on, but not limited to, the 

following acceptance criteria:

• The detection program provides high assurance of detecting and resolving production 

of U enriched to 10 percent or more in the U-235 isotope, to the extent that SNM of 

moderate strategic significance could be produced within any 370-calendar-day period; 

production of U enriched to 20 percent or more in the U-235 isotope; and unauthorized 

production of U of low strategic significance.

• The overall design of the detection program includes an analysis of all potentially 

credible means by which unauthorized production could occur. For each credible 

scenario, there exists a surveillance or an enrichment monitoring system for the timely 

detection of that scenario.
NUREG-2158 50

• The program will detect misuse of plant or equipment to deliberately produce U at an 

enrichment level greater than permitted by license, or the production of a quantity of 

enriched U greater than reported to the NRC (e.g., by undeclared feed or by 

unrecorded lowering of the tails assay). Specifically: 

- Detection of the unauthorized production (from undeclared feed) of LEU within 

the cascade, with an enrichment of less than 10 wt % U-235, should occur before 

the quantity of U-235 contained in such LEU amounts to 25 kilograms.

- Detection of the unauthorized production of LEU within the cascade, with an 

enrichment in the range of 10.00 to 19.99 wt % U-235, must occur before the 

quantity of U-235 contained in such LEU amounts to 10 kilograms.

- Detection of the unauthorized production within the cascade of HEU (i.e., equal 

to or greater than 20 percent U-235) must occur before the quantity of U-235 

contained in such HEU amounts to 1 kilogram.

• The responsibilities and authorities for each position assigned a function having a 

significant impact on the program for detecting the unauthorized production of enriched 

U are clearly defined in a written position description that enumerates the 

responsibilities for that position.

• The qualifications and experience required for each position assigned functions 

associated with the program for detecting unauthorized production of enriched U will be 

sufficient to permit adequate performance of the duties required of that position.

• The descriptions in the MC&A plan of the duties and authorities show that those 

responsible for detecting the unauthorized production of enriched U will have sufficient 

authority to perform the function in the intended manner.

• The organization responsible for detecting the unauthorized production of enriched U is 

separate from the production organization and is also separate from organizations that 

generate source data, if practicable; otherwise, independence of the functions is 

attained by suitable controls and overchecks.

• Process and measurement data used for detecting unauthorized production of 

enriched U are independently verified.
51 NUREG-2158

9. ITEM CONTROL

9.0 Regulatory Intent

The intent of 10 CFR 74.33(c)(6) is to require licensees to establish, document, and maintain an

item control system to protect against unauthorized and unrecorded removal of items, or of 

material from items, and to enable timely location of items. Items, as defined in 10 CFR 74.4, 

means any discrete quantity or container of SM or SNM, not undergoing processing, having an

unique identity, and also having an assigned element and isotope quantity. Examples of items 

are known quantities of SM or SNM in well-defined and uniquely identified containment, such as 

cans, drums, and canisters, or fixed units such as fuel assemblies. Uncontainerized solid SNM, 

such as U metal ingots or buttons, are also items if they are uniquely identified. To promptly 

locate a given item, sufficient current information must be recorded.

9.1 Organization

The MC&A plan should identify, by position title, the individual responsible for overseeing the 

item control system. It should also identify the positions of those individuals who have 

significant item control system responsibilities. 

9.2 General Description

The licensee or applicant should state that the overall MC&A program maintains a record of all 

SM and SNM items, regardless of quantity or duration of existence. In addition, the item control 

system should provide current knowledge of the location, identity, and quantity of all SM and 

SNM contained in items that are not excepted from the item control requirements. As stated in 

10 CFR 74.33(c)(6), the following items are excepted from its requirements:

• containers of waste (designated for burial or incineration), and

• solution containers in which the U-235 concentration is less than 5.00 grams per liter.

All other items should be stored and handled in a manner that enables detection of, and 

provides protection against, unauthorized or unrecorded removals of SM and SNM. All items, 

whether or not they are subject to item control system coverage, should have a unique identity. 

For items subject to the item control system, the following are acceptable means for providing a 

unique identity: 

• a unique alpha-numeric identification on a tamper-indicating device (TID) applied to a 

container of SM or SNM 

• a unique alpha-numeric identification permanently inscribed, embossed, or stamped on 

the container or item itself 

• a uniquely prenumbered (or bar-coded) label applied to each item having good adhesive 

qualities, such that its removal from an item would prevent its reuse 

Location designations shown by the MC&A records need not be unique, but location 

designations should be specific enough so that any item may be located within 1 hour. Longer 

times may be acceptable but should be further justified in the MC&A plan. The MC&A record 

system should be controlled in such a manner that the record of an item’s existence cannot be 

destroyed or falsified without a high probability of detection. Each nonexempt item should be 

stored and handled in a manner that enables detection of, and provides protection against, 

unauthorized or unrecorded removals of SM and SNM. 
NUREG-2158 52

9.3 Item Identity Controls

The MC&A plan should describe the item records, showing how items are identified for each 

material type and each type of container. If the unique number on a TID is the basis for 

providing a unique item identity, the MC&A plan should do the following: 

• Describe the type of TID used.

• Describe how the TIDs are obtained and what measures are implemented to ensure that 

duplicate (counterfeit) TIDs are not manufactured.

• Describe how the TIDs are stored, controlled, issued, and accounted for.

• Describe how TID usage and disposal records are maintained and controlled.

The plan should provide similar information for other methods of unique item identity 

(e.g., labels).

9.4 Storage Controls

The MC&A plan should fully describe item storage areas and controls. In particular, controls 

that are used as the basis for ensuring the values of prior measurements, as opposed to 

remeasuring the item at inventory time, should be discussed in detail and the rationale for 

accepting prior measurements explained. Any controls used to ensure the validity of prior 

measurements should be equivalent to the protection provided by tamper-safing, which is 

defined by 10 CFR 74.4 as the use of devices on containers or vaults in a manner and at a time 

that ensures a clear indication of any violation of the integrity of previously made measurements 

of the SNM in the container or vault.

The MC&A plan should identify both administrative controls (e.g., custodian assignments and 

limiting authorized access to storage areas) and physical controls (e.g., locked and alarmed 

doors). 

9.5 Item Monitoring Methodology and Procedures

As part of the item control system, a licensee should maintain a system of item monitoring to do

the following:

• Verify that items shown in the MC&A records are actually stored and identified in the 

manner indicated in the records.

• Verify that generated items and changes in item locations are properly recorded in the 

MC&A record system in a timely manner.

• Detect, with high probability, any real loss of items, or U from items.

The item monitoring system should conduct the following activities at least, on a monthly 

basis: 

• For each item inventory stratum, compare the actual storage status to the recorded 

status of a sufficient sample of randomly selected items from the item control system

records.
53 NUREG-2158

• For each item inventory stratum, check the accuracy of the MC&A records for a sufficient 

sample of randomly selected items from each storage area.

• Check the accuracy of a sufficient sample of randomly selected production records of 

created and consumed items.

The actual frequency of the above activities, and the size of the random sample, should be a 

function of the expected discrepancy rate based on prior observations. The MC&A plan should 

specify minimum monitoring frequencies associated with each storage area, as well as

discrepancy rates that trigger more frequent monitoring frequencies, and should contain 

definitive commitments for resolving discrepancies. 

9.6 Investigation and Resolution of Item Discrepancies

The licensee or applicant should provide definitive statements of the procedures and controls 

that will ensure that all incidents involving missing or compromised items or falsified item 

records will be investigated. A compromised item is (1) one displaying evidence of tampering 

or (2) an unencapsulated and unsealed item assigned to a controlled, limited-access storage 

area that is found elsewhere. 

If any unsealed or unencapsulated item is located after having been determined to be missing, 

or if an item is found to be compromised, the contents should be reestablished by measurement 

(e.g., by NDA or by weighing, sampling, and analysis). The licensee should use the 

recommendations on resolution of indicators (Chapter 14 of this document) to resolve item 

discrepancies. 

9.7 Commitments and Acceptance Criteria

In its MC&A plan, the licensee should provide definitive commitments that adhere to the 

regulatory requirements and meet acceptance criteria applicable to maintaining current 

knowledge of items and detecting unauthorized removals. A finding that the licensee’s MC&A 

plan for the item control system is acceptable and in accordance with 10 CFR 74.33(c)(6) will be 

based on, but not limited to, the following acceptance criteria:

• The licensee’s item record system uniquely identifies items. The records include 

information on the chemical form, quantity of material (element and isotope), physical 

description, identification label or number, and location. The system provides 

reasonable assurance of detecting falsification or destruction of records of an item’s 

existence. 

• In its MC&A plan, a licensee may propose that certain groups of items that are 

produced, stored, processed, or otherwise handled together as a unit, such as a batch or 

sublot of material, may be uniquely identified and stored as a separate group under 

conditions such that group identity, composition, and quantity will be maintained 

constant.

• The record of the status of an item can be completed or updated in sufficient time to 

allow the licensee to meet the requirements for promptly locating an item.

• For items that will not be remeasured at inventory time, the item control procedures 

provide reasonable assurance that the SM or SNM contents stated in the records are 

valid and that unauthorized removal of SM or SNM from the item has not occurred. 
NUREG-2158 54

Remeasurement is not necessary, if the SM or SNM content of the item was measured 

previously and reasonable assurance is provided that the SM or SNM content has not 

subsequently changed.

• Items that are excepted from the 10 CFR 74.33(c)(6) item control requirements fall into 

one of the following categories:

− waste destined for burial or incineration

− solutions having less than a 5.00 grams U-235 per liter concentration

• A current accounting is maintained of the total quantity of SM or SNM contained in items 

that are exempted from item control. The accounts identify the quantities by material 

type category for both controlled and exempted items.

• For items that are subject to the 10 CFR 74.33(c)(6) item control requirements, a record 

system is maintained to provide knowledge of the current status of such items with 

respect to their identity, U and U-235 content, and stored location. For items subject to 

this commitment, the item control and records system can promptly locate and confirm 

the existence of any specific item or group of items upon demand. The item record 

system is secured in such a manner that the record of an item’s existence cannot be 

destroyed or falsified by a single individual without a very high probability of detection.

• Each item that is subject to the 10 CFR 74.33(c)(6) item control requirements will be

stored and handled in a manner that enables detection of, or provides protection against,

unauthorized or unrecorded removals of SM or SNM; otherwise, knowledge of the SM or 

SNM content is ensured by tamper-safing or maintaining the item as a sealed source 

(i.e., as encapsulated material).

• All incidents involving missing or compromised items or falsified item records are 

investigated. A compromised item is one for which there is evidence of tampering or 

that is found outside its assigned controlled access area.

• The contents of a compromised item or an unsealed, unencapsulated item located after 

it has been missing will be redetermined by measurements (i.e., by NDA or by weighing, 

sampling, and analysis).
55 NUREG-2158

10. SHIPPER-RECEIVER COMPARISONS

10.0 Regulatory Intent

The intent of 10 CFR 74.33(c)(7) is to require the licensee to conduct and document 

shipper-receiver comparisons for all SM and SNM receipts, on both an individual batch basis 

and total shipment basis, and to ensure that any SRD that is statistically significant and exceeds 

twice the estimated standard deviation of the difference estimator and 500 grams of U-235 is 

investigated and resolved.

10.1 Receiving Procedures

The first action to be taken on receipt of SM or SNM should be the verification of the number of 

items, the item identities, and the integrity of individual items and of TIDs. All SM and SNM 

shipments received from an external supplier are to be subject to shipper-receiver comparisons. 

Such comparisons involve measuring received material by the receiver, or by the receiver’s 

contractor (who is independent of the shipper), and comparing the receiver’s total receipt 

measurement for element and isotope to that of the shipper’s.

Previously, in approving MC&A plans, the NRC staff has recognized situations where the cost of 

conducting and documenting shipper-receiver comparisons outweighs the safety benefit of 

doing so and has accordingly granted relief in the form of exemptions, notwithstanding the 

10 CFR 74.33(c)(7) provision that the requirement applies to “all SM and SNM receipts.” The 

following are examples of situations in which such relief has been granted:

• shipments containing less than 500 grams of U-235;

• individual items containing less than 50 grams U-235;

• encapsulated items, the encapsulation integrity of which has not been compromised and 

which are to be retained by the licensee as encapsulated items;

• fuel assemblies and fuel rods previously shipped by the licensee that are being returned, 

provided that the original encapsulation has not been compromised;

• UF6 cylinders that are empty except for a heel quantity of UF6; and

• heterogeneous scrap that must be subject to dissolution before a meaningful 

accountability measurement can be obtained, noting that both shipper and receiver 

should agree to accept the “after dissolution plus residue@ measurements for accounting 

purposes.

Should licensees in the future seek similar relief from the 10 CFR 74.33(c)(7) requirements,

specific exemption requests will need to be submitted in accordance with 10 CFR 74.7, “Specific 

Exemptions.” The NRC will determine, on a case-by-case basis, whether granting such 

exemption requests is authorized by law and will not endanger life or property or the common 

defense and security, and whether such requests are otherwise in the public interest.

For any SM or SNM received, the licensee must provide all appropriate information on 

DOE/NRC Form 741 that accompanies the shipment, in accordance with 10 CFR 74.15, 

“Nuclear Material Transaction Reports.” (NOTE: See NUREG/BR-0006, “Instructions for 

Completing Nuclear Material Transaction Reports (DOE/NRC Forms 741 and 740M),” issued 

June 2008, for instructions and requirements for completing DOE/NRC Form 741.) 
NUREG-2158 56

10.2 Determination of Receiver’s Values

For normal and depleted UF6, the licensee may establish receiver’s values by (1) measuring the 

U-235 isotopic concentration (either by NDA or by sampling and analysis), (2) weighing each 

cylinder, and (3) using a nominal percent U factor. 

SNM receipts and any SM receipts not in the form of UF6 should be measured for total quantity, 

U concentration, and U-235 enrichment. 

10.3 Evaluation of Shipper-Receiver Differences

When shipper’s measurement uncertainty (or standard error) information is available, the 

following should define the estimated standard deviation of the difference estimator or combined 

measurement standard error: 

combined standard error = 

where

= shipper’s measurement standard error

= receiver’s measurement standard error

If the shipper’s measurement uncertainty values are not available, the receiver can assume that 

the shipper’s measurement uncertainty is equal to (but no greater than) its own uncertainty. In 

this situation (i.e., both shipper and receiver have the same measurement uncertainty), the 

following becomes the combined measurement standard error: 

combined standard error = = 1.414

Under 10 CFR 74.33(c)(7), the difference between the shipper’s value and the receiver’s value 

(i.e., the SRD), in terms of either (1) an individual container (for container batches) or a single 

batch or lot (when there is more than one container per batch), as appropriate, or (2) the total 

shipment, must be regarded as significant whenever the SRD exceeds both 500 grams of U-235 

and twice the combined standard error. If subject to 10 CFR Part 75 (international safeguards), 

an SRD in excess of both 500 grams U-235 and twice the combined standard error with respect 

to a single batch within the shipment must also be regarded as significant.

10.4 Resolution of Significant Shipper-Receiver Differences

The MC&A plan should describe the steps involved with the investigation of a significant SRD 

and discuss how such a difference is resolved. It should also present the criteria for defining a 

resolved SRD. Generally, the resolution of a significant SRD involves a referee (or umpire) 

measurement of a retainer sample(s) but not of the material weight. The resolution process 

should specify whose weight value is used in the resolution process if the shipper’s and 

receiver’s weights differ by more than one-half of the total combined standard error. 

10.5 Commitments and Acceptance Criteria

In its MC&A plan, the licensee should provide definitive commitments that adhere to the 

regulatory requirements and meet acceptance criteria applicable to shipper-receiver 

comparisons. A finding that the licensee’s MC&A plan for conducting SRD evaluations and 
57 NUREG-2158

resolving significant SRDs is acceptable and in accordance with 10 CFR 74.33(c)(7), will be 

based on, but not limited to, the following acceptance criteria:

• Each shipping container is inspected within 5 working days after receipt for loss or 

damage to the container or TIDs to determine if SM or SNM could have been removed. 

If the integrity of a container is questionable, the presence of all items that were 

packaged in the shipping container is confirmed within 24 hours of discovering the 

questionable integrity. Only acceptable tamper-safing methods will be used as 

described in Chapter 12 of this document and as agreed to with the receiver.

• Confirmatory measurements of scrap shipments are performed by the receiver to 

determine the amount of element and isotope within a time period consistent with the 

accountability needs of the shipper.

• The test for the significance of an SRD is based on statistical tests.

• The investigation procedure for significant SRDs is sufficiently comprehensive to ensure 

that the difference will be resolved. Comprehensiveness is sufficient if the licensee 

shows the capability to verify records, resample, perform remeasurements, establish 

liaison with the shipper, provide samples to a referee laboratory, and perform the 

statistical analysis needed to evaluate the measurements. Investigation and resolution 

should be completed within 90 days of material receipt.

• Measurements of the quantity of SM or SNM received in each shipment will be

performed and the SRD will be tested for statistical significance. The element and 

isotope content of SM or SNM shipped or received by the licensee is based on 

measurement systems subject to measurement control. Occurrences of significant 

SRDs in excess of 500 grams U-235 and missing items will be reported to the shipper

promptly. 

• Measurement results for shipments and receipts will be corrected for biases that are 

significant at the 0.05 level (i.e., for any bias that exceeds two times the standard error 

associated with a mean) and that affect individual items by more than their rounding 

error in terms of either U-235 or U content, or both.

• For SNM received, SRDs that are statistically significant and also greater than 

500 grams U-235, on a total shipment basis (and also on a batch basis, when subject to 

10 CFR Part 75), will be detected within 30 calendar days of receipt. 

• The documentation of shipments and receipts should be completed and transmitted 

within the timeframe specified in NUREG/BR-0006.

59 NUREG-2158

11. ASSESSMENT AND REVIEW OF THE MATERIAL CONTROL AND 

ACCOUNTING PROGRAM

11.0 Regulatory Intent

The intent of 10 CFR 74.33(c)(8) is to require independent assessments of the MC&A program.

Licensee management must periodically (at least every 24 months) review and assess the 

performance of the MC&A program, evaluate its effectiveness, and document management’s 

actions on prior assessment recommendations and any identified deficiencies. It is intended 

that the review be performed by knowledgeable, technically competent individuals free from 

conflicts of interest and that the deficiencies be brought to the attention of plant management so 

that they will be corrected. It should be emphasized that this review process is intended to be 

much more than a routine audit for compliance with existing procedures and commitments. 

Conclusions and recommendations relative to overall program effectiveness and to the 

adequacy of the MC&A program—including that of any contractor who performs SM and SNM 

measurements on the licensee’s behalf—must be made.

11.1 General Description

The capabilities, performance, and overall effectiveness of the licensee’s MC&A program should 

be independently reviewed and assessed at least every 24 months. The MC&A plan should 

describe the assessment and review program in terms of the following:

• maximum interval between assessments 

• selection procedures for the assessment team 

• number of team members to be selected 

• qualification and expertise of team members 

• independence of individual team members from the MC&A responsibilities and activities 

they will be reviewing and assessing 

• maximum elapsed time and minimum actual effort to be used for completion of the 

assessment and issuance of a final team report

The entire MC&A program generally should be reviewed and evaluated during each 

assessment. When this occurs, intervals between assessments can be as much as 24 calendar 

months. However, if individual assessments only cover part of the MC&A program, individual 

subsystems should be assessed at intervals no greater than 12 calendar months. Thus, the 

type of assessment (partial or total) and the maximum interval between assessments should be 

specified in the MC&A plan. “Interval” means the elapsed time between either the start or the 

termination of successive assessments. 

The responsibility and authority for the assessment program should lie at least one level higher 

in the licensee’s organizational structure than that of the MC&A manager. Such responsibility 

should include selecting the assessment team leader and initiating corrective actions. Team 

members may be selected from the facility staff or from outside, but an individual member 

should not participate in the assessment of the parts of the MC&A program for which that 

person has direct responsibility. Hence, the MC&A manager may not be a team member. Also, 

a given individual should not assess the parts of the program that are the responsibility of 
NUREG-2158 60

another team member if the other team member is assessing the given individual’s area. The 

leader of the assessment team should have no responsibility for managing any of the MC&A 

elements being assessed. 

The minimum number of individuals on any given assessment team should be dependent on the 

knowledge and expertise of the team relative to MC&A activities and their experience in 

conducting assessments. Personnel assigned to the assessment team should have a 

demonstrated understanding of the objectives and the requirements of the MC&A program and 

should have sufficient knowledge and experience to be able to judge the adequacy of the parts 

of the program they review. The team should have authority to investigate all aspects of the 

MC&A program and should be given access to all necessary information. 

To provide a meaningful and timely assessment, the review and evaluation process should not 

be protracted. The actual review and investigation activities should be completed in 30 calendar 

days, with an additional 15 calendar days allowed for completing and issuing a final team report. 

11.2 Report of Findings and Recommendations

The areas to be reviewed should encompass the entire MC&A program, and the level of detail 

of the reviews should be sufficient to ensure that the assessment team has adequate 

information to make reasoned judgments of the MC&A program effectiveness. The team report, 

as a minimum, should state findings on the following: 

• organizational effectiveness to manage and execute MC&A activities 

• management responsiveness to indications of losses of U and possible unauthorized 

enrichment activities 

• staff training and competency to carry out MC&A functions 

• reliability and accuracy of accountability measurements made on SM and SNM 

• effectiveness of the measurement control system in monitoring measurement systems

and its sufficiency to meet the requirements for controlling and estimating both bias and 

SEID 

• soundness of the material accounting records 

• effectiveness of the item control system to track and provide current knowledge of items 

• capability to promptly locate items and effectiveness in doing so 

• timeliness and effectiveness of SRD evaluations and resolution of excessive SRDs 

• soundness and effectiveness of the inventory-taking procedures 

• capability to confirm the presence of SM and SNM 

• capability to detect and resolve indications of unauthorized enrichment activities and the 

effectiveness of doing so 

• capability to detect and resolve indications of missing U 

On completion of each assessment, the findings and recommendations for corrective action, if 

any, should be documented. The written report should be distributed to the plant manager, the 

MC&A manager, and other managers affected by the assessment. 

11.3 Management Review and Response to Report Findings and Recommendations 

Management should review the assessment report and take the necessary actions to correct 

MC&A program deficiencies. The management review should be documented within 30 days 

following the submittal of the assessment team’s report, and it should include a schedule for the 

correction of deficiencies. Corrective actions, if any, that pertain to daily or weekly activities 

should be initiated promptly after the submittal of the final assessment report. 
61 NUREG-2158

The MC&A plan should address resolution and followup actions associated with concerns 

identified in the assessment report. The individuals responsible for resolving identified 

concerns, and the timeliness of such resolution, should be specified.

11.4 Commitments and Acceptance Criteria

In its MC&A plan, the licensee should provide definitive commitments that adhere to the 

regulatory requirements and meet acceptance criteria applicable to independent assessments 

of the MC&A program. A finding that the licensee’s MC&A plan for such assessments is 

acceptable and in accordance with 10 CFR 74.33(c)(8) will be based on, but not limited to, the 

following acceptance criteria:

• The capabilities and performance of the MC&A program will be reviewed and its 

effectiveness will be independently assessed at least every 24 months; that is, the 

nominal elapsed time from the completion of one review or assessment to the 

completion of the next will not exceed 24 calendar months.

• The periodic assessments will be comprehensive and sufficiently detailed to enable the 

assessment team to rate the MC&A program effectiveness, capability, and performance 

by comparison with the expected and required performance. The overall assessment 

objectives are to determine that the MC&A program, as designed and implemented, is 

continuing to meet the overall safeguards goals, and to identify weaknesses or 

deficiencies in the program design or performance that may need correcting.

• The areas to be reviewed encompass the entire MC&A program, and the level of detail 

of the reviews is sufficient to ensure that the assessment team has adequate information 

to make reasoned judgments of the MC&A program effectiveness, which includes the 

following:

− organizational effectiveness and management responsiveness to indicators of 

possible SM or SNM losses

− staff training and competency to carry out MC&A functions

− soundness of the material accounting records

− capability to promptly locate items

− timeliness and effectiveness of SRD evaluations and resolution of significant 

SRDs

− soundness of physical inventory procedures and practices

− effectiveness of the measurement control program to monitor key measurement 

systems, establish bias estimates and measurement uncertainties, and meet the 

requirements for controlling the total MC&A measurement uncertainty associated 

with ID

− capability to confirm the presence of SM and SNM

− capability to resolve indications of missing SM or SNM, as well as aid in any 

government-led investigation of missing SM or SNM, and provide information that 

would aid in the recovery of missing SM or SNM.
NUREG-2158 62

• Generally accepted auditing principles are used to check each type of record in which a 

representative sample (of a sufficient number) of randomly selected records is 

examined.

• Reviews and assessments are performed either by qualified individuals from outside or 

qualified individuals from inside the facility organization whose work assignments and 

positions within the organization will not impair their ability to make objective judgments 

of the MC&A program capabilities and performance. Personnel assigned to the 

assessment team will have an adequate understanding of the regulatory objectives and 

requirements of the MC&A program and will have sufficient knowledge and experience 

to be able to judge the adequacy of the parts of the program they are asked to review. 

The team will have authority to investigate any aspect of the MC&A program and will 

have access to all relevant information.

• An individual team member will not participate in the assessment of any part of the 

MC&A program for which he or she has direct responsibility. Also, an individual “A” will 

not assess any part of the program that is the responsibility of person “B” if person “B” is 

assessing an area under the responsibility of individual “A.”

• The entire MC&A program will be reviewed and evaluated during each single 

assessment (to be completed within an elapsed time that is short, relative to the time 

between changes in the MC&A program, and to demonstrate the ability to include any 

such changes made during the review or assessment). Conducting two or more 

assessments during a 24-month interval, in which only part of the MC&A program is 

covered in each, is not deemed acceptable; that is, reviewing a single component of the 

MC&A program at 24-month intervals is not very meaningful unless knowledge is 

obtained of how well the other components currently interact. Piecemeal review and

evaluation is permissible, however, if each subsystem is covered at 12-month (or fewer) 

intervals.

• The leader of the assessment team will have no responsibility for performing or 

managing the functions being assessed. The assessment team leader will have no 

responsibility for managing or performing any of the MC&A functions.

• The responsibility and authority for the assessment program and for initiating corrective 

actions will lie (1) at least one level higher in the organization than the MC&A manager 

or (2) at a level equal to that of the onsite plant manager.

• Each overall review and assessment will be conducted and completed in a timeframe 

that is short (e.g., a week), with respect to the time for changes that have occurred in the 

MC&A program, and will include any such changes made during the time the review and 

assessment is being conducted.

• The completion date for any review and assessment is defined as the date when the 

team submits its final written report (of findings and recommendations) to plant 

management. The start date is the first day in which one or more team members 

actually inspect records or interview MC&A personnel, and such start date will be 

documented.
63 NUREG-2158

• The results of the assessment and recommendations for corrective action, if any, will be 

documented and reported to the plant manager and other managers affected by the 

assessment. Management will review the assessment report and take the necessary 

actions to correct MC&A program deficiencies. Such corrective actions (if any) that 

apply to daily or weekly activities will be initiated within 40 calendar days following the 

submittal of the final report of the review and assessment.

• Management’s response to recommendations from the review and assessment, 

including any corrective actions ordered by management and the expected timeframe for 

completing such actions, will be documented within 30 calendar days following the 

submittal of the team’s report.

65 NUREG-2158

12. TAMPER-SAFING

12.0 Regulatory Intent

The intent of 10 CFR 74.33(c)(9) is to require licensees to maintain and follow tamper-safing 

procedures for SNM containers or vaults and control access to, and distribution of, unused seals 

and records. The intent of such procedures is to document the distribution, application, and 

destruction of TIDs, as well as the routine inventory of unused TIDs. Licensees are required to 

retain records for at least 3 years (or longer if specifically required by regulations external to 

10 CFR 74.33), thereby providing a means of assessing the performance of the tamper-safing 

program and inspecting for compliance with regulatory requirements.

12.1 Characteristics of Tamper-Safing Devices

Tamper-safing devices on containers or vaults are used to secure the integrity of SNM either 

when it is in transit or stored on site. The objective of TIDs is to ensure that no tampering or 

entry has occurred while the TID is on the container. Therefore, for MC&A purposes, the 

degree of confidence in the selection of a TID sealing system will vary depending on its unique 

characteristics and intended use.

When selecting TIDs, licensees should consider the following:

• intended use—the determination that the TID is appropriate for tamper-safing the 

container and withstanding the working environment (i.e., temperature, moisture, 

repeated handling)

• application—the relative ease or difficulty of physically applying the TID

• substitution—the ability of a TID to be destructively removed and replaced by new seals 

without detection

• removal and reapplication—the ability of a TID to be removed and reapplied without 

detection

• alteration of label data—the ability to alter recorded data on the TID without the 

alteration being apparent

• integrity verification—the degree of effort required to verify that the TID is intact or 

indicates tampering

The licensee should confirm manufacturer claims that the removal of a TID is not possible 

without detection by testing potential TIDs to see if they can be removed from the containers on 

which they are to be used. The licensee should confirm the results by using the manufacturer’s 

documented procedures and the samples used. The experiments should be documented, both 

with regard to what techniques were used to attempt to defeat the TID and observations as to 

the degree of success in defeating the TID. In lieu of testing by the licensee, similar tests 

conducted by an independent third party may be considered acceptable.
NUREG-2158 66

12.2 Use of Tamper-Safing Devices

The MC&A plan may allow the use of TIDs to do the following:

• They could ensure the long-term validity of measurement data. The application of a TID

to an item containing measured quantities of nuclear materials may allow the licensee to 

maintain the validity of the original measured value, thus eliminating or decreasing the 

need to remeasure the items to verify the nuclear material content.

• They could reduce the effort required to conduct physical inventories or item control 

activities. The application of a TID to a container housing multiple items may allow the 

licensee to maintain the validity of the container’s contents, thus minimizing the number 

of items requiring verification during a physical inventory or item control activity.

• They could provide assurance of integrity of intransit material. The application of a TID

to a shipping container may allow the licensee to maintain the validity of the shipping 

container’s contents and provide assurance that the integrity of the shipment has not 

been violated. To achieve this goal, the shipper should apply the TID(s) to the shipping 

container, verify the integrity of the TID(s) shortly before departure of the shipment, and 

provide the appropriate information (i.e., shipping container serial numbers, TID(s) 

type(s), and serial number(s)) to the receiver. Upon receipt of the shipment, the receiver 

should verify the shipping container serial numbers, TID(s) type(s), and serial number(s), 

and the integrity of the TID(s). Any discrepancies should be considered an MC&A 

anomaly and be addressed by the facility’s MC&A resolution program.

12.3 Description of Tamper-Safing Records

The tamper-safing system should identify all records, forms, reports, and standard operating 

procedures used throughout the system. Such records should include, but are not limited to, 

the following:

• receipt of purchased TIDs

• issuance of TIDs

• identification of the person applying the TIDs

• identification of the person who verifies the application of the TID

• identification of the container to which the TID(s) was(were) applied, including the TID(s) 

serial identification (if applicable)

• removal and destruction of TIDs

• routine inventory of unused and unissued TIDs

• identification of roles and responsibilities, including

- designation of the TID control officer(s)

- personnel approved to apply, verify, and destroy TIDs

• training of personnel in the application, verification, and destruction of TIDs
67 NUREG-2158

12.4 Commitments and Acceptance Criteria

The acceptability of a TID is based on an evaluation of the attributes of the device in relation to 

the time needed to defeat the tamper-indicating features. TIDs already deemed acceptable by 

the NRC include Type E, pressure-sensitive, tamper-evident wire seals; fiber optic seals; and 

steel padlocks. Other TIDs may be equally acceptable. Licensees proposing to use TIDs not 

currently approved by the NRC must provide the appropriate information, including references, 

to enable licensing reviewers to assess the adequacy of the proposed TID type.

In its MC&A plan, the licensee should provide definitive commitments that adhere to the 

regulatory requirements and meet acceptance criteria applicable to the use of TIDs. A finding 

that the licensee’s MC&A plan for tamper-safing is acceptable and in accordance with 

10 CFR 74.33(c)(9) will be based on, but not limited to, the following acceptance criteria:

• Only TIDs that are controlled and accounted for are used to maintain the validity of 

previously established SNM quantities associated with items.

• Written procedures are maintained to ensure that individuals authorized to handle TIDs 

are properly trained.

• Preferably a single individual, but no more than three individuals, none of whom have 

any responsibility for seal application or destruction, is (are) designated as the TID

control officer(s).

• TIDs are only applied and removed by individuals authorized for that purpose.

• Unused TIDs are controlled and inventoried. Unissued TIDs are stored in a locked 

container within a room that is locked when unoccupied or in an approved repository.

Blocks of TIDs issued to designated individuals are stored in a locked container within a 

room that is locked when unoccupied or in an approved repository.

• When TIDs are not in storage, they are in the possession of authorized individuals 

(i.e., the TID control officer or person responsible for applying the TID). As a rule, the 

number of available seals issued to these individuals should be limited to a single day’s 

use.

• The licensee has in its possession a commitment from the seal manufacturer that plates,

dies, and production residuals are controlled and protected.

• Upon removal, TIDs are destroyed (i.e., crimped, flattened, or otherwise rendered 

unusable) and properly disposed of.

• Records of TID application, verification, removal, and destruction are documented, and 

control measures are implemented to prevent alteration of records concerning 

containers protected by TIDs.

69 NUREG-2158

13. DESIGNATION OF MATERIAL BALANCE AREAS, ITEM 

CONTROL AREAS, AND CUSTODIANS

13.0 Regulatory Intent

The intent of 10 CFR 74.33(c)(10) is to ensure that the MBAs and ICAs designated by licensees 

will enable them to identify inventory differences and item locations on a scale smaller than that 

of the entire plant. Regulations in 10 CFR 74.33(c)(10) require licensees to designate MBAs 

and ICAs and assign custodial responsibilities for these areas, to provide internal controls to 

deter or detect any diversion or misuse of SNM at the licensee’s facility. 

13.1 Material Control Boundaries

The MC&A plan should describe how the licensee establishes various material control 

boundaries to minimize the occurrence of MC&A anomalies and facilitate their resolution. 

Examples of such anomalies are inventory differences, missing items of SNM, and potential 

theft or diversion of SNM.

Because MBAs and ICAs are important foundations for controlling and accounting for all SNM in 

a facility, the MC&A plan should describe the process for how their locations are chosen. An 

MBA or ICA should correlate to physical or administrative boundaries and monitored locations. 

The MBA or ICA should be designed to limit losses to a specific area (i.e., the MBA should not 

be so large that the licensee cannot localize inventory or process differences to a manageable 

level). Materials transferred into and out of an MBA or ICA must be subject to quantitative 

measurements, as specified in the definitions of MBAs and ICAs in 10 CFR 74.4.

13.2 Custodians

The MC&A plan should describe the roles and responsibilities of the custodians for MBAs and 

ICAs. Each custodian should have direct interaction with the MC&A organization, and such 

individuals should be located within the physical operations area. Custodians who are 

responsible for more than one MBA or ICA should not have the authority to make material 

transfers between MBAs or ICAs that are both under their direct control.

13.3 Commitments and Acceptance Criteria

In its MC&A plan, the licensee should provide definitive commitments that adhere to the 

regulatory requirements and meet the acceptance criteria applicable to the designation of 

MBAs, ICAs, and custodians. A finding that the licensee’s MC&A plan for designating MBAs, 

ICAs, and custodians is acceptable and in accordance with 10 CFR 74.33(c)(10) will be based 

on, but not limited to, the following acceptance criteria:

• MBAs and ICAs should have defined physical and administratively controlled areas that

allow for the physical and administrative control of nuclear materials such that the 

quantity of nuclear materials being moved into or out of the MBA is a 

measurement-based assigned value for element and isotope contents.

• MBAs and ICAs are established in such a way as to minimize the occurrence of MC&A 

anomalies and facilitate their resolution.

• MBA and ICA structures are properly documented and clearly described, including 

physical boundaries and categories of material in the individual MBA or ICA. 
NUREG-2158 70

• Custodial responsibilities are assigned for each designated MBA and ICA.

• Custodians responsible for more than one MBA or ICA are not authorized to transfer 

material between MBAs and ICAs under their control.
71 NUREG-2158

14. RESOLVING INDICATIONS OF MISSING URANIUM 

AND OF UNAUTHORIZED PRODUCTION OF 

ENRICHED URANIUM

14.0 Regulatory Intent

The intent of the general performance objectives in 10 CFR 74.3(b) and (c) and in 

10 CFR 74.33(a)(2) and (3) is that licensees be able to promptly investigate and resolve 

any indications of a possible loss, theft, diversion, or misuse of SM or SNM, whether 

arising from errors or deliberate actions. Additionally, uranium enrichment facilities are to 

have a system in place for detecting, investigating, and resolving any indications of 

unauthorized production of enriched uranium.

14.1 Methods and Procedures for Identifying Indicators

The MC&A plan should discuss the means by which the licensee will resolve indicators of the 

unauthorized production of enriched U, or indicators of missing material. The MC&A plan 

should enumerate all the potential indicators that can be postulated and develop resolution 

procedures for each. Any anomaly could potentially be an indicator of loss, theft, diversion, or 

misuse of SM or SNM. An anomaly is an unusual observable condition (such as excessive 

discrepancies, missing items, broken TIDs, or other possible indicators) that might result from 

theft, diversion, or other misuse of SM or SNM. The terms “indicator” and “anomaly” may be 

used interchangeably to describe a condition that may require further investigation to determine 

if an actual loss, theft, diversion, or misuse of SM or SNM occurred. The three generic types of 

indicators are as follows: 

(1) indications that SM or SNM is missing 

(2) indications that the enrichment equipment has been or is being used to produce 

undeclared U enriched to less than 10 wt % for unauthorized use or distribution 

(3) indications that the enrichment equipment has been or is being used to produce U

enriched to 10 wt % or more in U-235 

The licensee’s resolution program should address the possible indicators of missing U. The 

MC&A plan should enumerate all the potential indicators that can be postulated for indicator 

types (1) through (3) above and develop resolution procedures for each. 

The following are examples of possible indicators of missing U: 

• lack of agreement of dynamic or static inventories with the MC&A records 

• determination through the item control system that a specific item is not in its authorized 

location and its actual location is not immediately known 

• discovery that an item’s integrity or its TID was compromised 

• information from the process control system indicating potential loss of material from the 

process system (e.g., improper valve settings) 

• an allegation of theft or diversion 
NUREG-2158 72

The following are examples of possible indicators of unauthorized production of U enriched to 

less than 10 wt % U-235: 

• presence of unauthorized product, feed, or tails cylinders 

• SWU imbalances (e.g., reduced production capacity) 

• presence of tails at enrichments lower than the design range 

• presence of excess mass or amount of tails, or other ID 

• discovery of records tampering 

• discovery of unauthorized feed or withdrawal equipment or reset valve configurations to 

permit feeding and withdrawal 

• unauthorized operational activities in the enrichment process facilities 

• receipt of allegations 

The following are examples of possible indicators of unauthorized production of U enriched to 

10 wt % or greater in U-235: 

• any of the preceding items 

• any measurement from a stream monitoring program that indicates out-of-specification 

enrichment concentrations for any feed, product, or tails stream 

• unauthorized reconfiguration, isolation, or interconnection of enrichment equipment or 

changes in valve settings 

• equipment used for monitoring enrichment levels in product streams not functioning 

properly or compromised 

• an allegation that unauthorized production of U enriched to 10 wt % or more in U-235 

has occurred or is underway 

• radiation signatures or background radiation levels greater than normally expected 

14.2 System and Procedures for Investigating and Resolving Indicators

One or more MC&A procedures should address the system and practices for investigating and 

resolving indicators, because this topic pertains to four of the performance objectives of 

10 CFR 74.33(a). Thus, the licensee should have well-defined procedures for investigating

indicators of both (1) possible missing U and (2) possible unauthorized production activities. 

These procedures should include criteria for determining when an investigation of loss or 

unauthorized production indicators can be concluded. 

Resolving a loss or unauthorized production indicator means that the licensee has made a 

determination that loss, theft, or unauthorized production of U has not occurred and is not 

occurring. For each type of indicator, the licensee should develop detailed resolution

procedures and should describe or outline them in the MC&A plan. 

Any investigation of an indication of a loss or unauthorized production should provide, whenever 

possible, (1) an estimate of the quantity of SM and/or SNM involved, (2) the material type or 

physical form of the material, (3) the type of unauthorized activity detected, (4) the timeframe 

within which the loss or activity could have occurred, (5) the most probable cause(s), and 

(6) recommendations for preventing reoccurrence. 
73 NUREG-2158

For indications that loss or theft may have occurred, the resolution process should include 

(1) thoroughly checking the accountability records and source information, (2) locating the 

source of the problem, (3) isolating the exact reason for the problem within the area or

processing unit, (4) determining the amounts of SNM or SM involved, and (5) determining that 

the indication is or is not resolved. The resolution procedures should be prepared in such a 

manner that no individual who could have been responsible for the potential loss would also be 

responsible for its resolution. If an investigation of an indicator results in a conclusion that the 

indication is true, such conclusion must be reported to the NRC within 1 hour of its 

determination, under 10 CFR 74.11. The MC&A plan should specify the time allowed for 

resolution. In general, a time not exceeding 72 hours should be adequate.

For indications of unauthorized production of U enriched to less than 10 wt % U-235, the 

licensee should verify that the indicator is true, determine its cause, and conclude if 

unauthorized production has occurred or is occurring. If an investigation of an indicator results 

in a conclusion that the indication is true, such conclusion must be reported to the NRC within 

1 hour of its determination under 10 CFR 74.11. The MC&A plan should specify the time 

allowed for resolution. In general, a time not exceeding 72 hours should be adequate.

For indications of unauthorized production of enrichment of 10 wt % or greater in U-235, the 

resolution process should include investigation of all the information that contributed to the 

indication of such unauthorized production. On receipt of an indication that U enriched to 

10 wt % or more has been discovered, the licensee should immediately isolate the process area 

or storage area from which the indication came to verify the indication. The instruments and 

measurement systems used for monitoring should be examined to determine if they are 

functioning properly. A thorough examination of the processing equipment should be performed 

to ensure that unauthorized modifications were not made. The presence of U enriched to 

10 wt % or more in U-235 should be verified through remeasuring the material in question,

whether in item form or in process equipment. If this investigation determines that an indication 

of unauthorized production of enrichment of 10 wt % or more in U-235 is true, this condition is 

reportable under 10 CFR 74.11. The MC&A plan should specify the time allowed for resolution. 

In general, a time not exceeding 72 hours should be adequate. 

If the investigation conducted to resolve the indication does not observe the production of U

enriched to 10 wt % or more in U-235, further measures are needed before the licensee may 

conclude that the indicator is fully resolved. To protect against the relocation and concealment 

of the enriched U, a thorough investigation of the entire facility should be performed by 

individuals who are independent of the processing organization.

14.3 Response Actions for Unresolved Indicators

Actions in response to unresolved indicators should be clearly defined and should be on a 

graded scale appropriate to the level of potential safeguards significance. The responsibility 

and authority for initiating and executing response actions should also be defined. 

For indicators of missing U, the level of safeguards concern is related to such factors as the 

following: 

• whether the potential missing U is depleted, natural, or enriched 

• the potential quantity of U-235 involved 

• the material attractiveness (from the standpoint of its potential use in a nuclear explosive 
NUREG-2158 74

device) of the potential missing U relative to its composition or form (i.e., U metal, U308, 

uranyl nitrate solution, UF6, scrap, or waste) 

At LEU enrichment facilities, indicators of unauthorized production of U enrichment generally 

have a higher level of safeguards concern than indicators of missing U. The degree of concern 

for unauthorized production indicators is related to such factors as the following: 

• whether the indicator applies to unauthorized production in the planning stage, currently 

in progress, or already accomplished 

• whether the potentially produced material is low strategic SNM, moderately strategic 

SNM, or strategic SNM 

• the potential quantity of unauthorized material already produced

14.4 Documentation Requirements

The MC&A plan should identify all documentation requirements associated with the licensee’s 

program for reporting, investigating, and resolving missing U indicators and of unauthorized 

production indicators. The plan should also define the review and approval requirements and 

document custodial responsibility. As a minimum, documentation of the following should be 

included: 

• investigation procedures 

• resolution procedures 

• reporting of indicator to MC&A management, including date and time the indicator was 

reported, name of the individual who discovered the indicator, and a description of the 

indication 

• investigation findings and conclusion, including resolution status, date issued, name and 

signature of the principal investigator, and approval signature of the MC&A manager 

• reports made to the NRC for unresolved indicators and for indicators determined to be 

real, including date and time the report was made, method of communication, and name 

of the NRC individual contacted 

14.5 Commitments and Acceptance Criteria

In its MC&A plan, the licensee should provide definitive commitments that adhere to regulatory 

requirements and meet acceptance criteria applicable to investigating and resolving anomalies 

indicating possible missing SM or SNM or unauthorized production of enriched U. A finding that 

the licensee’s MC&A plan for resolving indications of loss, theft, diversion, or misuse of SM or 

SNM is acceptable and in accordance with 10 CFR 74.33(a)(2) and (3) will be based on, but not 

limited to, the following acceptable criteria:

• Adequate commitments are provided to ensure a high probability that any indicator of 

missing SM or SNM or misuse of SM or SNM will be (1) recognized as an indicator, 

(2) investigated, and (3) resolved.

• A prompt investigation will be conducted by the licensee for all indications of possible 

loss, theft, diversion, or misuse of SM or SNM.
75 NUREG-2158

• A cause or probable cause that is based on objective evidence will be assigned to each 

indication of possible loss that is investigated by the licensee.

• Investigation and resolution procedures will provide for adequate overchecks to ensure 

that no individual who could have been responsible for a possible loss or theft of SM or 

SNM would be the sole or primary individual responsible for resolving the indicator.

• No investigation relative to an indication of a loss or theft of SM or SNM exceeding the 

current DQ should be declared as completed but unresolved without first conducting a 

shutdown, cleanout inventory in which all unsealed SM or SNM is remeasured for 

element and isotope.

• The results of all investigations of alleged thefts, as well as any indications of a loss of 

SM or SNM that remains unresolved after 30 calendar days, will be reported by the 

licensee to the appropriate NRC MC&A licensing authority.

77 NUREG-2158

15. INFORMATIONAL AID FOR ASSISTING IN THE INVESTIGATION 

AND RECOVERY OF MISSING URANIUM OR ASSISTING IN 

THE INVESTIGATION OF UNAUTHORIZED ENRICHMENT

15.0 Regulatory Intent

The intent of the 10 CFR 74.3(d) and 10 CFR 74.33(a)(4) and (5) general performance 

objectives is for licensees to have ready and provide to investigators any information deemed 

relevant to the recovery of SM or SNM involved in a loss or theft or to investigating the 

unauthorized production of such material. The burden is on the licensee to provide (without 

being asked) all information that it recognizes as being relevant, as opposed to only providing 

information that the investigators are knowledgeable enough to request. This objective applies 

to investigations and recovery operations relating to actual (or highly suspected) events 

applying to missing SM or SNM, which would be conducted by the NRC or other government 

agencies, such as the Federal Bureau of Investigations. 

The 10 CFR 74.3(d) performance objective states that the licensee must be able to provide, in a 

timely manner, information to aid in the investigation and recovery of missing SNM in the event 

of an actual loss, theft, diversion, or misuse. The 10 CFR 74.33(a)(4) and (5) general 

performance objectives impose similar requirements for SM and for the unauthorized production 

of enriched U, respectively.

15.1 Types of Information

The following are the kinds of information that may aid the investigation and recovery effort: 

• data or observations that led the operator to determine that a loss or theft of U or 

unauthorized production may have occurred 

• data, observations, and assessments associated with attempts to resolve the indication 

of missing material or unauthorized production 

• the time period during which the material may have left the facility or when the 

unauthorized production occurred

• the path and means by which the material may have left the facility

15.2 Information Indicating Possible Losses of Special Nuclear Material

Information indicating that a loss of U may have occurred is provided by physical inventories, 

the item control system, and shipper-receiver comparisons (Chapters 7, 9, and 10, 

respectively). This information could include the following: 

• material accountability data records and reports 

• inventory records 

• inventory difference and propagation of error calculations 

• inventory reconciliation reports 

• indications of unrecorded or unauthorized removals of SM or SNM from storage or 

process locations 
NUREG-2158 78

• reports of apparent destruction or falsification of records of an item’s existence 

• records of broken TIDs or compromised item integrity 

• indications of unauthorized entry into SM and SNM storage areas 

• reports from monthly item status inspections 

• material receipt and log-in records 

• results from SRD evaluations 

• process monitoring and control records

Information indicating that unauthorized production may have occurred is provided by the 

program for preventing and detecting unauthorized production (Chapter 8). This information 

could include the following: 

• reports assessing potentially credible means for unauthorized enrichment 

• indications of unauthorized activities in enrichment process areas 

• indications of anomalous process configurations 

• indications of anomalous process conditions 

• indications of unauthorized entry into the enrichment process areas 

• indications of anomalous enrichment levels (e.g., process sample or radiation 

measurement data) 

• indications of anomalous feed, product, or tails quantities 

• indications of unauthorized feed or withdrawal locations or containers 

• anomalous production data (e.g., SWU imbalances) 

Information associated with resolving indications of missing U and of unauthorized production is 

discussed in Chapter 14. This information would include the following: 

• the type of unauthorized activity detected 

• the interval during which the loss or unauthorized production may have occurred 

• the amount of material and form of the material involved in the loss 

• estimates of the extent of unauthorized production 

• results of measures to validate indicators 

• results of extended measures to resolve indicators 

• results from special inventories (or reinventories) and tests performed 
79 NUREG-2158

• audit results of the SM and SNM accountability source data 

• assessments of measurement data and measurement controls 

• results from reviews of the MC&A program and status of corrective actions 

• history of indicator investigation and resolution activities 

• indicator investigation and resolution procedures and conclusions 

• probable cause of the loss 

• any abnormal events that may have contributed to or caused the loss 

• the names of the people who could have been responsible for the loss 

Much of the backup information necessary to assist in an investigation would be records 

maintained in the facility records system described in Chapter 16. 

15.3 Commitments and Acceptance Criteria

In its MC&A plan, the licensee should provide definitive commitments that adhere to regulatory 

requirements and meet acceptance criteria applicable to providing information to assist in the 

investigations and recovery of missing U or unauthorized production. A finding that the 

licensee’s MC&A plan for providing informational aid is acceptable and in accordance with 

10 CFR 74.3(d) and 10 CFR 74.33(a)(4) and (5) will be based on, but not limited to, the 

following acceptance criteria:

• Procedures are in place for the efficient and timely gathering of relevant information to

be provided to government investigators, so as to aid them in the investigation and 

recovery activities associated with missing SM or SNM or unauthorized enrichment

activities.

• Information will be provided to appropriate government authorities to aid in their 

investigation of indications or allegations of missing material and in the recovery of SM 

or SNM in the event of a loss that could include theft or diversion.

81 NUREG-2158

16. RECORDKEEPING

16.0 Regulatory Intent

The intent of 10 CFR 74.33(d) is to require the licensee to establish and maintain records that 

demonstrate that the general performance objectives of 10 CFR 74.3 and the 10 CFR 74.33(a)–

(c) requirements have been met. Records should include those documenting the following:

• receipt, shipment, disposal, and current inventory of SM or SNM held under license,

• quantities of SM or SNM added to and removed from process, and 

• shipper-receiver evaluations associated with SM or SNM receipts.

Records must be retained for at least 3 years (or longer if specifically required by regulations 

external to 10 CFR 74.33), thereby providing a means for assessing the performance of the 

MC&A program and inspecting for compliance with regulatory requirements. However, in 

accordance with 10 CFR 74.19(b), MC&A procedures (as documented in licensee records) must 

be retained until the Commission terminates the license.

16.1 Description of Records

The MC&A plan should identify all records, forms, reports, and standard operating procedures 

that must be retained for a minimum of 3 years, as required by 10 CFR 74.33(d). Such records 

should include, but are not limited to, the following: 

• documents that define changes in the MC&A management structure or changes in 

responsibilities relating to MC&A positions 

• procedures for any accountability-related measurement or sampling operation 

• forms used to record or to report measurement data and measurement results, including 

source data 

• forms and notebooks used to record calibration data associated with any accountability 

measurement system 

• forms and notebooks used to record quantities, volumes, and other data associated with 

the preparation of standards, both calibration and control, used in connection with 

accountability measurement systems 

• forms and official memoranda used to record or report measurement control program 

data, control limit calculations, and out-of-control investigations 

• forms listings and instructions associated with a physical inventory, both dynamic and 

static 

• forms and formal worksheets used in the calculation of SEID, ID, and active inventory 

values 

• ledgers, journals, and computer printout sheets associated with the accountability 

system 

• ledgers, journals, and computer printout sheets associated with the item control 

program, including seal usage and “attesting to” records 
NUREG-2158 82

• DOE/NRC Forms 741 and 742 and NRC Form 327

• forms, memoranda, and reports associated with identifying, investigating, and resolving

significant SRDs 

• loss indication and alleged theft investigation reports 

• investigation reports on indications of activities related to unauthorized production of 

enriched U

• investigation reports on excessive IDs 

• official reports containing the findings and recommendations of MC&A program

assessments and any letters or memoranda on response actions to assessment team 

recommendations 

• forms used for recording data associated with the monitoring program 

• monitoring program status or summary reports 

• records of training sessions, including date given, topics covered, name of instructor(s), 

and names and signatures of those attending 

• training, qualification, and requalification reports and records 

Examples of the more important MC&A forms should be provided in the MC&A plan annex or 

appendix. The retained records and reports should contain sufficient detail to enable NRC 

inspectors to determine that the licensee has met the requirements of 10 CFR 74.33(c) and the 

general performance objectives of 10 CFR 74.3 and 10 CFR 74.33(a). 

16.2 Program and Controls for Ensuring an Accurate and Reliable Record System

The MC&A plan should describe the controls used to ensure that records are highly accurate 

and reliable. The record system also should provide for easy traceability of all SM and SNM 

transactions from source data to final accounting records. 

The following topics should be addressed: 

• the auditing system or program to verify the correctness and completeness of records 

• the overchecks for preventing or detecting missing or falsified data and records 

• the plan for reconstructing lost or destroyed SM and SNM records 

• the access controls used to ensure that only authorized persons can update and correct 

records

• the protection and redundancy of the record system, such that any act of record 

alteration or destruction will not eliminate the ability to achieve the performance 

objectives of 10 CFR 74.3 and 10 CFR 74.33(a).
83 NUREG-2158

16.3 Commitments and Acceptance Criteria

In its MC&A plan, the licensee should provide definitive commitments that adhere to the 

regulatory requirements and meet acceptance criteria applicable to recordkeeping. A finding 

that the licensee’s MC&A plan for the recordkeeping system is acceptable and in accordance 

with 10 CFR 74.33(d) will be based on, but not limited to, the following acceptance criteria:

• Access to MC&A information will be controlled to provide deterrence and detection of 

theft, diversion, misuse, or radiological sabotage involving SNM.

• A record retention system is maintained for those records necessary to show that the 

MC&A system requirements of 10 CFR 74.33(d) have been met. Such records are 

retained for at least 3 years, unless a longer retention time is specified by 

10 CFR 74.15(b), by 10 CFR Part 75, or by a specific license condition. The records 

referred to in 10 CFR 75.22, “Accounting Records,” and 10 CFR 75.23, “Operating 

Records,” and generated during any period that the facility is under IAEA safeguards will 

be retained for at least 5 years. Records of the following will be maintained current and 

will be retained for at least 3 years:

- management structure, MC&A job descriptions, and MC&A policies and 

procedures;

- accounting source data records (data that normally consist of shipping and 

receiving forms, physical inventory forms, and the forms used for initially 

recording measurement and measurement control data);

- records of shipments and receipts and investigations of significant SRDs, plus 

the information used to resolve them;

- measurement data for receipts, shipments, discards, and inventory; 

- calibration of measurement systems, measurement control data, bias estimates, 

and the statistical analyses of the measurement control data;

- data used to demonstrate that the measurement system performance achieves 

the SEID limits required by 10 CFR 74.33(c);

- physical inventory listings and inventory work sheets;

- calculations of detection thresholds for excessive IDs of safeguards significance 

(i.e., any ID that exceeds three times SEID and specified minimal quantities);

- calculations of the standard error of the ID and information used to reconcile an 

excessive ID;

- reports of investigations and resolution of indications of loss of SM or SNM, or 

unauthorized production, and

- the results of independent assessments and management action taken to correct 

any deficiencies identified. 

• Sufficient protection and redundancy of the record system is provided so that an act of 

record alteration or destruction will not eliminate the ability to provide a complete and 

correct set of SM and SNM control and accounting information that could be used to 
NUREG-2158 84

confirm the presence of SM and SNM, resolve indications of missing material or 

unauthorized production, or aid in the investigation and recovery of missing material.

• All SM and SNM transactions from source data to final accounting records will be readily 

traceable.

• The source data will be retained in its original form until the physical inventory and any 

subsequent ID investigations have been completed. After this time, any readable 

facsimile is acceptable for the remainder of the required retention period. All other 

records may be retained as hard copy, microfiche, permanent computer-readable forms, 

or other permanently readable forms.

• The records will be retrievable and sufficiently complete and detailed to permit auditing 

all parts of the MC&A system and will be traceable back to original source data.

• The records of the data that are the basis of the calculated SEID will permit traceability 

to the sources of the variances because of calibrations, bias adjustments, and random 

effects in the measurements. These records may be summaries of calibrations, bias 

tests, and variance-monitoring data or control charts.

• The record system will have sufficient redundancy to enable reconstruction of lost or 

missing records, so that knowledge of the SM or SNM inventory is always available. 

The primary records, as contrasted with duplicate or backup records, will be provided 

security against computer failure, fire or water damage, vandalism, and access by 

unauthorized persons.

• All retained MC&A records are to be readily accessible to meet time restraints related to 

their use. In general, the record retention system should be able to retrieve records 

used for measurement control or accountability within 24 hours if the record was 

generated within the past 12 months, and within 7 calendar days if generated more than 

12 months ago. Physical inventory listings are to be available within 24 hours for the 

latest two physical inventories. Item control records are to be retrievable in time to 

satisfy the criteria in Section 9.7.

• Overchecks or other controls, including access controls for updating and correcting 

records, are provided so as to prevent or detect errors in the records that would affect 

inventory difference and item location.
85 NUREG-2158

17. GLOSSARY

The following terms are defined in the context of (1) their usage in this document or (2) how 

they should be used if contained in the material control and accounting (MC&A) plans 

submitted under Title 10 of the Code of Federal Regulations (10 CFR) 74.33, “Nuclear 

Material Control and Accounting for Uranium Enrichment Facilities Authorized To Produce 

Special Nuclear Material of Low Strategic Significance.”

ACTIVE INVENTORY—The sum of beginning inventory (BI), additions to inventory (A), 

removals from inventory (R), and ending inventory (El), after all common terms have been 

totally excluded. A common term is any source material (SM) or special nuclear material (SNM)

material value (or item) that appears in both BI and EI, or both BI and R, or both A and R, or 

both A and El, with both values derived from the same measurement (and thus, it does not 

contribute to the uncertainty associated with the current period inventory difference). The active 

inventory is used as an indicator of processing throughput or measurement activity, or both.

ADDITIONS TO INVENTORY (A)—Quantities of depleted uranium (U), SM, and SNM, by given 

material type code, added to a “plant” inventory and which, before such addition, were not part 

of the plant’s total possessed depleted U, SM, or SNM quantity for the material type code in 

question. For an enrichment facility conducting a bimonthly dynamic inventory, additions to 

inventory are typically “feeds” to the cascade or enrichment equipment.

ARTIFACT STANDARD—A container or item, of certified mass, having a size, shape, and mass 

that is representative of a particular type of process-related item or container (e.g., a U 

hexafluoride (UF6) cylinder). Weighing error caused by buoyancy is eliminated by the use of 

artifact standards for scale calibrations. 

ASSIGNED VALUE—A value for such entities as mass, volume, SM or SNM concentration, SM 

or SNM quantity, assigned to, for example, a standard weight or standard material, used for 

calibrating or controlling a measurement device or system. An assigned value may not 

necessarily be a certified value, but, nevertheless, it is the best estimate of the standard’s true 

value.

AUDITABILITY—The availability of evidence to U.S. Nuclear Regulatory Commission (NRC) 

inspectors demonstrating the validity of a licensee’s conclusion that unauthorized production 

has not taken place. 

AUTHORIZED LEVELS—The maximum U enrichment level (i.e., weight percent (wt %) U-235]

and the maximum quantity of U-235 (contained in enriched U) that can be possessed as 

specified by an issued NRC license.

BEGINNING INVENTORY—The total itemized quantity of depleted U, SM, or SNM of a given 

material type code possessed by a “plant” at the start of a material balance period (inventory 

period). The BI quantity for any given material balance period is (by definition) exactly equal to 

the ending inventory quantity for the immediately previous period.

BIAS (MEASUREMENT BIAS)—A constant, unidirectional component of error that affects all 

members of a measurement data set. Thus, a bias can be estimated from the deviation of the 

mean of several measurements of a representative standard from the reference value (or 

assigned value) of such standard. 
NUREG-2158 86

CALIBRATION—The process of determining the numerical relationship between the observed 

output of a measurement system and the actual value of the characteristic being measured, as 

based on primary or reference standards. 

CERTIFIED STANDARD—A standard weight, material, device, or instrument having an 

assigned value that is guaranteed to be within specified limits by a nationally or internationally 

recognized organization (e.g., bureau, laboratory) that issues or certifies standards.

CHECK STANDARD (BENCH STANDARD, WORKING STANDARD)—A standard, not 

necessarily traceable to a primary standard, that is used routinely (e.g., daily or weekly) to 

check (or verify) the reliability of, for example, a measurement device or instrument (including 

those of accountability measurement systems). Such standards are not, however, used for the 

actual calibration or control of accountability measurement systems.

COMBINED STANDARD ERROR—An error band derived from the respective standard error 

values associated with each of two measurements (usually independent of each other) 

performed on a given material quantity. For both measurement values (of the pair) to be 

regarded as being in agreement, they must not differ from each other by more than the 

calculated combined standard error, which is normally calculated by taking the square root of

the sum of squared individual standard errors. That is: 

combined S.E. = 

CONTROL STANDARD—A standard that (1) is representative of the process material being 

measured and (2) is itself measured periodically to monitor for and to estimate any bias 

associated with the measurements of the process material in question. A control standard must 

be traceable to a primary or reference standard.

DEPLETED URANIUM—Any U-bearing material with a U isotopic distribution can be 

characterized as being (1) less than 0.700 wt % in combined U-233 plus U-235, and (2) at least 

99.200 wt % U-238.

DETECTION QUANTITY (DQ)—A site-specific U-235 quantity for licensees subject to 

10 CFR 74.31, “Nuclear Material Control and Accounting for Special Nuclear Material of Low 

Strategic Significance,” or 10 CFR 74.33. The DQ is normally a function of annual throughput, 

but for low-throughput low-enriched U (LEU) facilities, the DQ need not be less than 

25 kilograms of U-235. The DQ also can be described as a goal quantity, the loss or theft of 

which must be detected with a 90 percent (or better) probability at the time of a physical 

inventory. 

DETECTION THRESHOLD (DT)—An inventory difference (ID) limit that will be exceeded (with 

90 percent or higher probability) by an ID resulting from the taking of a physical inventory 

whenever there has been an actual loss of a detection quantity. The DT is a function of both the 

DQ and the standard error of the inventory difference (SEID), as shown by the following 

equation: 

DT = DQ -1.3 (SEID)

ENDING INVENTORY (EI)—The total itemized quantity of depleted U, SM, or SNM of a given 

material type code possessed by a “plant” at the end of a material balance period, as 
87 NUREG-2158

determined by a physical inventory. The EI quantity for any given material balance period is (by 

definition) exactly equal to the beginning inventory quantity for the next period.

ENRICHED URANIUM—Any U-bearing material that does not qualify as natural or normal U, 

and that has a combined U-233 plus U-235 isotopic content of 0.725 wt % or higher, relative to 

the total U element content.

INVENTORY RECONCILIATION—The adjustment of the book record quantity of both element 

and fissile isotopes to reflect the results of a physical inventory. In the broad sense, inventory 

reconciliation also includes the activities of calculating (1) the ID for the material balance period 

in question, (2) the uncertainty (i.e., SEID) value associated with the ID, (3) the active inventory 

for the period, and (4) any bias adjustment or prior period adjustment associated with the ID 

value.

MATERIAL BALANCE PERIOD—The time span to which a material balance or physical 

inventory applies. 

MATERIAL TYPE CODES—Number codes for identifying basic material types with respect to 

SM, SNM, and byproduct materials. These codes are used by the Nuclear Materials 

Management and Safeguards System for tracking U.S.-owned and U.S.-possessed materials 

worldwide. For depleted U, SM, and SNM, eight material type codes have been assigned as 

follows: 

CODE MATERIAL TYPE CODE

10 Depleted U 81 Normal U

MATERIAL TYPE

20 Enriched U (*) 83 Plutonium-238(***)

50 Plutonium 88 Thorium

70 U-233 (**) 89 U in Cascades 

* For U.S. Department of Energy (DOE)/NRC Form 742, material code 20 has four subcodes to denote 

enrichment range: E1, E2, E3, and E4. For NRC Form 327, material code 20 has two subcodes: LEU 

and HEU.

** U materials should be regarded as material code 70 if the U-233 isotopic abundance is greater than 

(1) 10.00 wt % relative to total U elemental content or (2) both (a) the U-233 isotopic abundance is 

greater than the U-235 isotopic abundance and (b) the U-233 isotopic abundance exceeds 5.00 wt % 

relative to total elemental U content; otherwise, report as material code 10, 20, or 81, as appropriate.

*** Plutonium materials should be regarded as material code 83 if the plutonium-238 isotopic abundance 

is greater than 10.00 wt % relative to total plutonium elemental content; otherwise, report as material 

code 50. 

MEASURED DISCARD (MD)—A measured quantity of gaseous, liquid, or solid waste that is no 

longer possessed by a facility, or which has been transferred (accounting-wise) to a wasteholding-account using a DOE/NRC Form 741 transaction. 

MEASUREMENT CONTROL SYSTEM—A managed system for monitoring and controlling both 

accuracy and precision of depleted U, SM, and SNM accountability measurements. 

NATURAL URANIUM—Any U-bearing material with a U isotopic distribution that has not been 

altered from its naturally occurring state. Natural U is nominally 99.283 wt % U-238, 0.711 wt % 

U-235, and 0.006 wt % U-234. 
NUREG-2158 88

NORMAL URANIUM—Any U-bearing material having a U isotopic distribution that can be 

characterized as being (1) 0.700 wt % to 0.724 wt % in combined U-233 plus U-235 and (2) at 

least 99.200 wt % in U-238. (NOTE: All natural U having a U-235 isotopic abundance in the 

range of 0.700 wt % to 0.724 wt % is normal U, but not all normal U is natural U.)

POINT-CALIBRATED MEASUREMENT SYSTEM—A measurement system in which the 

measurement value assigned to an unknown measured by the system is derived from the 

response obtained from the measurement of a representative calibration standard(s) that was 

measured along with (i.e., at the same time as) the unknown. The standard(s) must undergo all 

the measurement steps (e.g., aliquoting, sample pretreatment), and in the same manner, as the 

unknown. Point-calibrated measurement systems can be regarded as bias free, provided that 

adequate controls are in place to ensure the validity of the standard’s assigned value.

PRIMARY STANDARD—Any device or material having a characteristic or parameter (such as 

mass, U concentration, U isotopic distribution) the value of which is certified (within a specified 

uncertainty) by, for example, a nationally or internationally recognized bureau or laboratory that 

issues or certifies standards. 

PRIOR PERIOD ADJUSTMENT—Any correction (i.e., adjustment) to an ID value because of a 

correction applied to a component of beginning inventory after the inventory period started. 

Such corrections may be because of resolution of a shipper-receiver difference on, for example,

material received during a prior inventory period or correction of a recording error. Because 

these types of corrections have nothing to do with current period losses or errors, and because 

the official beginning inventory value is not adjusted, an adjustment to the ID value (derived 

from the ID equation) is necessary to obtain an ID that reflects only current period activity. 

PROCESS MONITORING—A system of monitoring production data (e.g., flow rates, yields, 

densities) and of production control or quality control measurements (as opposed to 

accountability measurements) that could provide early (i.e., timely) detection of an anomaly that 

may indicate a significant loss or theft of SM or SNM or indicate unauthorized enrichment 

activities. 

RESIDUAL HOLDUP—Any SM or SNM that remains within the processing equipment (including 

ventilation filters and ductwork) after system draindown or cleanout, or both. If, at the time of 

physical inventory, the total quantity of residual holdup is significant, such holdup must be 

measured (or estimated on the basis of partial measurements and engineering calculations) and 

included in the physical inventory listing. The uncertainty associated with a total measured or 

estimated residual holdup quantity must be included in the calculation of the SEID.

RESOLUTION OF AN INDICATOR—A definitive determination (with auditable evidence) by the 

licensee that an indicated possible theft or unauthorized production of U has not occurred and is 

not occurring. 

RUNNING BOOK IN-PROCESS INVENTORY (RBIPI)—The dynamic inventory of a process 

system calculated by subtracting the cumulative measured outputs from the process system 

(CO) from the beginning inventory (BI) plus the cumulative measured inputs to the process 

system (CI). Mathematically, this can be expressed as: 

RBIPI = BI + CI − CO
89 NUREG-2158

SHIPPER-RECEIVER DIFFERENCE—The difference between what a sending facility 

(i.e., shipper) claims was contained in a shipment (of SM or SNM) and what the receiving facility 

claims was received, where both shipper’s and receiver’s values are based on measurement. 

STANDARD—See definitions for CERTIFIED STANDARD, CHECK STANDARD, CONTROL 

STANDARD, PRIMARY STANDARD, and STANDARD REFERENCE MATERIAL.

STANDARD DEVIATION—The random error (at the 67 percent confidence level) associated 

with a single value of a data set, which, in turn, is a measure (or indication) of the precision 

relating to a set of measurements (or set of data) applying to the same item or sample of 

material. Standard deviation is calculated as follows: 

standard deviation = S = 

where 

n = number of measurements performed

= the value obtained for the i th measurement for i = 1, 2, 3 ... n 

 ̄x = the average value for all n measurements 

STANDARD ERROR—The random error (at the 67 percent confidence level) associated with 

the average, or mean, value of a data set derived from repetitive determinations on the same 

item or sample. Mathematically, standard error is the standard deviation divided by the square 

root of the number of individual measurements used to derive the mean value. 

STANDARD REFERENCE MATERIAL—A material or substance that qualifies as a primary 

standard and the concentration of which, with respect to a nuclide or isotope, chemical element, 

or chemical compound, is certified within a specified uncertainty. 

SYSTEMATIC ERROR—A unidirectional error that affects all members of a data set. The terms 

“bias” and “systematic error” are often interchanged. However, any determined bias (i.e., a bias 

estimated from control standard measurements) has an uncertainty value associated with it. 

Thus, after correcting for any estimated bias, the uncertainty of that bias can be regarded as a 

systematic error. If an estimated bias is not applied as a correction, the combination of the bias 

plus its uncertainty should be regarded as the systematic error. 

UNAUTHORIZED PRODUCTION—Defined as (1) the misuse of plant or equipment to 

deliberately produce U at an enrichment level greater than permitted by license or (2) the 

production of a quantity of enriched U greater than reported to the NRC (e.g., by undeclared 

feed or by unrecorded lowering of the tails assay).

VERIFICATION MEASUREMENT—Defined as either (1) a nondestructive assay (NDA) 

measurement of an item conducted to verify that a previous NDA measurement value for 

isotope content of that item is still valid, (2) the reweighing and resampling of an item, batch, lot, 

or sublot, and performing chemical assays of the resample for element and isotope 

concentrations so as to verify a previously measured value for element and isotope content of 
NUREG-2158 90

the item (batch, lot, or sublot). Verification is achieved if the original and verification 

measurement values (for element and isotope quantities) agree within the range of 

measurement uncertainty (at the 95 percent confidence level).
91 NUREG-2158

18. REFERENCES

U.S. Code of Federal Regulations, Title 10, “Energy,” Part 74, “Material Control and Accounting 

of Special Nuclear Material.”

NUREG/CR-4604, “Statistical Methods for Nuclear Material Management,” U.S. Nuclear 

Regulatory Commission (NRC), December 1988.

NUREG/CR-0602, “Active Nondestructive Assay of Nuclear Materials,” U.S. Nuclear Regulatory 

Commission, January 1981.

NUREG/CR-2078, “Handbook of Nuclear Safeguards Measurement Methods,” U.S. Nuclear 

Regulatory Commission, September 1983.

NUREG/CR-5550, “Passive Nondestructive Assay of Nuclear Materials,” U.S. Nuclear 

Regulatory Commission, March 1991.

TID-26298, “Statistical Methods in Nuclear Material Control,” U.S. Atomic Energy Commission, 

1973.

NUREG/BR-0096, “Instructions and Guidance for Completing Physical Inventory Summary 

Reports” (NRC Form 327), U.S. Nuclear Regulatory Commission, October 1992.

NUREG/BR-0006, “Instructions for Completing Nuclear Material Transfer Reports”

(U.S. Department of Energy (DOE)/NRC Forms 741, 741A, and 740M), Revision 7, 

U.S. Nuclear Regulatory Commission, January 2009.

NUREG/BR-0007, “Instructions for the Preparation and Distribution of Material Status Reports”

(DOE/NRC Forms 742 and 742C), Revision 6, U.S. Nuclear Regulatory Commission, 

January 2009.

“IAEA Safeguards Statistical Concepts and Techniques,” 4th Revised Edition, International 

Atomic Energy Agency, Vienna, Austria, 1989.




UNITED STATES 

NUCLEAR REGULATORY COMMISSION

WASHINGTON, DC 20555-0001

--------------------

OFFICIAL BUSINESS
NUREG-2158

Draft

Acceptable Standard Format and Content for the Material Control and 

Accounting Plan Required for Low-Enriched Uranium Enrichment Facilities