AUDIT REPORT

REDACTED FOR PUBLIC RELEASE

Audit of NRC’s Oversight of Irradiator Security

OIG-10-A-17 September 2, 2010

All publicly available OIG reports (including this report) are accessible through

NRC’s Web site at: 

http:/www.nrc.gov/reading-rm/doc-collections/insp-gen/
OFFICIAL USE ONLY – SECURITY RELATED INFORMATION

UNITED STATES

NUCLEAR REGULATORY COMMISSION

WASHINGTON, D.C. 20555-0001

OFFICE OF THE

INSPECTOR GENERAL

OFFICIAL USE ONLY – SECURITY RELATED INFORMATION

September 2, 2010

MEMORANDUM TO: R. William Borchardt

Executive Director for Operations

FROM: Stephen D. Dingbaum /RA/

Assistant Inspector General for Audits

SUBJECT: AUDIT OF NRC’S OVERSIGHT OF IRRADIATOR 

SECURITY (OIG-10-A-17)

Attached is the Office of the Inspector General’s (OIG) audit report titled, Audit of NRC’s

Oversight of Irradiator Security.

The report presents the results of the subject audit. Agency comments provided at the 

August 2, 2010, exit conference have been incorporated, as appropriate, into this 

report.

Please provide information on actions taken or planned on each of the 

recommendations within 30 days of the date of this memorandum. Actions taken or 

planned are subject to OIG followup as stated in Management Directive 6.1.

We appreciate the cooperation extended to us by members of your staff during the 

audit. If you have any questions or comments about our report, please contact me at 

415-5915 or Beth Serepca, Team Leader, Security and Information Management Audit 

Team, at 415-5911.

Attachment: As stated 
Audit of NRC’s Oversight of Irradiator Security

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EXECUTIVE SUMMARY 

BACKGROUND

Irradiators are devices that expose products, such as food and medical 

supplies, to radiation for sterilization and other purposes. Radiation is 

achieved by the exposure to high-risk radioactive materials, such as 

Cobalt-60 and Cesium-137. Commercial firms, as well as State-run 

organizations such as hospitals and universities, operate irradiators and 

are licensed to possess the radioactive materials used in these devices. 

The U.S. Nuclear Regulatory Commission (NRC) and NRC “Agreement 

States” regulate the safe and secure use of these irradiators and other 

radioactive materials. NRC’s Office of Federal and State Materials and 

Environmental Management Programs develops and implements rules 

and guidance for the safe and secure use of source, byproduct, and 

special nuclear material in industrial, medical, academic, and commercial 

activities, including irradiators. 

In the changed threat environment since the terrorist attacks of 

September 11, 2001, NRC determined that certain licensed material 

should be subject to enhanced security requirements and issued several 

orders to address the security of radioactive materials.

PURPOSE

The purpose of this audit was to determine the adequacy of NRC’s 

oversight of industrial irradiator security. Due to the scope of the security 

orders and NRC’s efforts to combine these security orders into one 

section of the Code of Federal Regulations, the audit findings and 

recommendations expand beyond irradiators to address the radioactive 

materials security program as a whole. See Appendix A for information on 

the audit scope and methodology.

RESULTS IN BRIEF

While NRC has worked to increase security of irradiators and other 

radiological materials of concern, enhancements in the materials security 

program are needed to better ensure the security of these materials. 
Audit of NRC’s Oversight of Irradiator Security

ii

Specifically, NRC needs to (1) establish security inspection frequencies 

based on a risk-informed approach, (2) enhance access authorization 

controls of individuals with unescorted access to materials of concern, and 

(3) fully develop the security training program for materials inspectors.

Security Inspection Frequency

The frequency of materials security inspections should be based on a riskinformed process that takes into account the security risk associated with 

the material. Currently, security inspections are based on a licensee’s 

safety inspection schedule rather than the risk that the material will be 

stolen or exploited for malevolent purposes. The frequency of the security 

inspections is not risk-informed because the frequencies established in 

Inspection Manual Chapter 2800 do not consider current security risks. 

Without a risk-informed approach to the security inspection program, 

radioactive materials could be at an increased vulnerability to theft or 

sabotage. 

Access Authorization Controls

OFFICIAL USE ONLY – PARAGRAPH HAS BEEN REDACTED FOR 

PUBLIC RELEASE

Security Training Program

NRC materials inspectors should be provided the tools and training 

necessary to make risk-informed decisions to address security, health and 

safety, and environmental aspects of licensee compliance. While these 

inspectors receive initial training on the security requirements for material 

licensees, they do not receive any refresher training to address the 

security aspects of their jobs. Although NRC has acknowledged the need 
Audit of NRC’s Oversight of Irradiator Security

iii

to incorporate security training into the inspector qualification program, the 

development of a security refresher course has not been a priority. 

Without formalized refresher training, NRC might not be able to ensure 

licensees are adequately protecting materials of concern.

RECOMMENDATIONS

This report makes recommendations to improve the agency’s radioactive 

materials security program. A consolidated list of these recommendations 

appears in Section IV of this report.

AGENCY COMMENTS

At an exit conference on August 2, 2010, agency management stated their 

general agreement with the findings and recommendations in this report. 

Agency management also provided supplemental information that has 

been incorporated into this report as appropriate. As a result, the agency 

opted not to provide formal comments for inclusion in this report.
Audit of NRC’s Oversight of Irradiator Security

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ABBREVIATIONS AND ACRONYMS

FSME Office of Federal and State Materials and Environmental 

Management Programs

IAEA International Atomic Energy Agency

NRC U.S. Nuclear Regulatory Commission

OIG Office of the Inspector General
Audit of NRC’s Oversight of Irradiator Security

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TABLE OF CONTENTS

EXECUTIVE SUMMARY ........................................................................ i

ABBREVIATIONS AND ACRONYMS................................................... iv

I. BACKGROUND..............................................................................1

II. PURPOSE......................................................................................4

III. FINDINGS ......................................................................................5

A. REEVALUATION OF SECURITY INSPECTION 

FREQUENCY IS NEEDED ................................................5

B. PROCESS TO REGULARLY CHECK INDIVIDUALS 

WITH UNESCORTED ACCESS TO MATERIALS OF 

CONCERN IS NEEDED.....................................................9

C. FORMAL MATERIALS SECURITY REFRESHER

TRAINING PROGRAM IS NEEDED ................................12

IV. CONSOLIDATED LIST OF RECOMMENDATIONS ....................15

V. AGENCY COMMENTS.................................................................15

APPENDIXES

A. SCOPE AND METHODOLOGY.....................................................16

B. CATEGORY 1 AND CATEGORY 2 QUANTITIES 

OF CONCERN ...............................................................................18
Audit of NRC’s Oversight of Irradiator Security

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I. BACKGROUND

Irradiators are devices that expose products, such as food and medical 

supplies, to radiation for sterilization and other purposes. Radiation is 

achieved by the exposure to high-risk radioactive materials, such as 

Cobalt-60 and Cesium-137. Commercial firms, as well as State-run 

organizations such as hospitals and universities, operate irradiators and 

are licensed to possess the radioactive materials used in these devices. 

Figure 1: Illustration of Large Irradiator

Source: NRC Public Web Site.
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Figure 2: 

Small Irradiator The U.S. Nuclear Regulatory Commission (NRC) and NRC 

“Agreement States”1regulate the safe and secure use of 

these irradiators and other radioactive materials. NRC’s

Office of Federal and State Materials and Environmental

Management Programs (FSME) develops and implements 

rules and guidance for the safe and secure use of source, 

byproduct, and special nuclear material in industrial, 

medical, academic, and commercial activities, including 

irradiators. Inspections to ensure compliance with these 

regulations are conducted by approximately 46 NRC

materials inspectors and numerous inspectors within the 37 

Agreement States. Nationwide, there are approximately 50

licensees that operate about 50 large irradiators that contain 

more than 10,000 curies of Cobalt-60. (See Figure 1 for an 

illustration of a large irradiator.) Additionally, there are 

approximately 590 licensees that operate about 1,100 

smaller type irradiators that use lesser quantities of 

radioactive materials. (See Figure 2 for a picture of a 

smaller type irradiator.) 

Materials Inspection Program

NRC materials inspectors based in NRC’s regional offices2are 

responsible for ensuring licensee compliance with regulatory safety and 

security requirements. NRC Inspection Manual Chapter 2800, “Materials 

Inspection Program,” outlines NRC’s materials inspection program policy. 

This manual chapter establishes frequencies for routine inspections of all 

licensees, details when poor performance requires increased inspection 

oversight, and addresses other areas of materials oversight. NRC 

Inspection Manual Chapter 1246, “Formal Qualification Programs in the 

Nuclear Material Safety and Safeguards Program Area,” defines training 

and qualification requirements for personnel working within the nuclear 

materials inspection program.

 

1

An Agreement State is a State that has assumed regulatory responsibility over certain byproduct, 

source, and small quantities of special nuclear material through an agreement with NRC. As of June 

2010, 37 States had signed formal agreements with NRC.

2

These NRC inspectors are located at NRC Regions I, III, and IV. Region II facilities are inspected by 

Region I personnel.
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History of NRC’s Materials Security Oversight

NRC regulations provide requirements for the safe use, transport, and 

control of licensed radioactive material. A licensee’s loss of control over 

high-risk radioactive material, whether inadvertent or through a deliberate 

act, has the potential to result in significant harm to public health and 

safety, the environment, and cause significant economic loss. 

In the changed threat environment since the terrorist attacks of 

September 11, 2001, NRC determined that certain licensed material 

should be subject to enhanced security requirements.3 In developing the 

enhanced security measures, NRC performed vulnerability assessments 

to identify gaps or vulnerabilities in security, and the effectiveness and 

cost of certain physical protection enhancements at various licensed 

facilities. The vulnerability assessment results were used to develop

security orders that were issued to licensees based on the relative risk 

and quantity of material possessed by the licensee. 

These security orders specifically address the security of radioactive 

material possessed in quantities greater than or equal to Category 1 and 

Category 2 quantities (referred to as “materials of concern” throughout this 

report).4 Both large and small irradiators contain radioactive materials 

within the Category 1 and Category 2 quantity thresholds. In June 2003,

NRC issued Safeguards Order EA-02-249 to large irradiator licensees that 

possessed more than 10,000 curies of radioactive material. In November 

2005, NRC issued Increased Control Order EA-05-090 to smaller 

irradiator licensees and other licensees authorized to possess Category 1 

and Category 2 quantities of radioactive material.

The Energy Policy Act of 2005 authorized NRC to require all individuals

who are permitted unescorted access to “significant” radioactive material 

to be fingerprinted and undergo a Federal Bureau of Investigation criminal 

 

3 NRC adopted the International Atomic Energy Agency (IAEA) “Code of Conduct on the Safety and 

Security of Radioactive Sources” (Code of Conduct) categorization system for radioactive materials. 

Specifically, the IAEA characterizes Category 1 and Category 2 as quantities of radiological materials that 

are deemed to be attractive targets for malevolent use and pose the greatest risk to people and the 

environment if not safely managed or securely protected. (See Appendix B for information on these 

materials and associated thresholds).

4

As of May 2010, there were approximately 1,400 licensees in these two categories.
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history records check. NRC determined that Category 1 and Category 2 

quantities of radioactive material are “significant,” and by December 2007, 

had issued responsive orders to all licensees possessing Category 1 or 

Category 2 quantities of radioactive material.

In May 2010, NRC proposed adding a new Part 37 to NRC’s regulations in 

Title 10 of the U.S. Code of Federal Regulations to impose security 

requirements for the use of Category 1 and Category 2 quantities of 

radioactive material. The proposed requirements would codify and 

expand upon the previously issued security orders.

II. PURPOSE

The purpose of this audit was to determine the adequacy of NRC’s 

oversight of industrial irradiator security. Due to the scope of the security 

orders and NRC’s efforts to combine these security orders into one 

section of the Code of Federal Regulations, the audit findings and 

recommendations expand beyond irradiators to address the radioactive 

materials security program as a whole. See Appendix A for information on 

the audit scope and methodology.
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III. FINDINGS

While NRC has worked to increase security of irradiators and other 

radiological materials of concern, enhancements in the materials security 

program are needed to better ensure the security of these materials. 

Specifically, NRC needs to (1) establish security inspection frequencies 

based on a risk-informed approach, (2) enhance access authorization 

controls of individuals with unescorted access to materials of concern, and 

(3) fully develop the security training program for materials inspectors.

A. Reevaluation of Security Inspection Frequency Is Needed

The frequency of materials security inspections should be based on a riskinformed process that takes into account the security risk associated with 

the material. Currently, security inspections are based on a licensee’s 

safety inspection schedule rather than the risk that the material will be 

stolen or exploited for malevolent purposes. The frequency of the security

inspections is not risk-informed because the frequencies established in 

Inspection Manual Chapter 2800 do not consider current security risks. 

Without a risk-informed approach to the security inspection program, 

radioactive materials could be at an increased vulnerability to theft or 

sabotage.

Risk-Informed Process

The frequency of materials security inspections should be based on a riskinformed process that takes into account the security risk associated with 

the material. In 1999, the Commission defined its expectations for riskinformed and performance-based regulation. This process is an approach 

in which risk insights, engineering analysis, and performance history are 

used to guide the inspection program. NRC defines risk by asking three 

questions: (1) What can go wrong? (2) How likely is it to happen? and (3) 

What are the consequences? 
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Frequency of Security Inspections Based on Safety Inspection 

Schedule

Currently, NRC bases security inspections on a licensee’s safety 

inspection schedule rather than the risk that the material will be stolen or 

exploited for malevolent purposes. When Safeguards Order EA-02-249

was issued in June 2003, initial security inspections were completed within 

a year; however, there was no established frequency as to how often 

subsequent inspections should be conducted to verify licensee 

compliance with this order. After many discussions to try to determine the 

frequency, FSME, the program owner, decided to use the established 

frequency for safety inspections as previously outlined in Inspection 

Manual Chapter 2800.

5

 Specifically, “priority codes” are assigned to a 

particular radioactive material license (e.g., panoramic/large irradiator,

self-shielded/small irradiator) based on safety risk. The priority code (i.e., 

1, 2, 3, or 5) is the interval, expressed in years, between routine 

inspections. The priority represents the relative risk of radiation hazard for 

the type of use. Priority Code 1 presents the greatest risk to the health 

and safety of workers, members of the public, and the environment. 

Priority Code 5 presents the least potential risk.

Established Frequency Does Not Include Current Security Risk

The current security inspection frequency is not based on a risk-informed 

approach because the frequencies established by Inspection Manual 

Chapter 2800 do not consider current security risks. According to FSME 

management, NRC used risks to safety, security, and the environment 

when establishing the priority codes; however, FSME established the 

codes prior to 2001 when security threats were viewed differently 

compared to today. 

Prior to September 11, 2001, NRC license requirements focused on 

worker and public safety and preventing inadvertent or accidental 

exposure to radioactive materials. According to NRC, these requirements

also indirectly provided materials security. Specifically, by protecting 

workers and the public from inappropriate exposure through safety 

 

5

In November 2005, Increased Control Order EA-05-090 was issued with guidance to conduct 

inspections at the frequency established in Manual Chapter 2800.
Audit of NRC’s Oversight of Irradiator Security

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requirements, licensees implemented controls that also provided 

additional security protection to materials. However, as noted in the 

Background section of this report, the events of September 11 prompted 

NRC to reevaluate its requirements and the protections needed to prevent 

a terrorist from obtaining materials of concern. While NRC subsequently 

issued a number of security orders to impose additional controls, the 

agency did not update its inspection frequency requirements to 

incorporate increased security risks to materials. 

Furthermore, in 2007, NRC chartered an independent external review 

panel to identify vulnerabilities in the NRC’s materials licensing program 

and to validate the agency’s ongoing radioactive materials security efforts. 

The panel’s March 2008 report stated that fully integrating security with 

health, safety, and environmental protection when regulating radioactive 

material would require a culture change at NRC and in the Agreement 

States. The report further stated that:

Security starts with identifying an appropriate level of 

protection based on the type, form, and quantity of 

radioactive material. The processes currently used to 

make risk-informed decisions for health, safety, and 

environmental protection are identical to those used 

to determine risk as it applies to security. The 

strategies for responding to security threats are 

different from the strategies for responding the [sic] 

health, safety, and environmental concerns in that 

they must consider malevolent action.

FSME plans to conduct a pilot inspection program for security inspections 

to help determine the appropriate inspection frequency. However, this 

pilot program is in its infancy and FSME has yet to define how it will 

evaluate the inspection frequency and the methodology for this review. 

The FSME Office Director supports an initiative to reevaluate the materials 

inspection program taking a risk-informed approach that integrates both 

safety and security.

Without a risk-informed approach to the security inspection program, 

radioactive materials could be at an increased vulnerability to theft or 

sabotage. NRC conducts inspections to ensure licensees are following 
Audit of NRC’s Oversight of Irradiator Security

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the security requirements, and by taking a risk-informed approach to 

security inspections, NRC can enhance the protection for materials of 

concern.

Recommendation

The Office of the Inspector General (OIG) recommends that the Executive 

Director for Operations:

1. Reevaluate and determine the frequency of security inspections 

based on a risk-informed approach.
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B. Process To Regularly Check Individuals With Unescorted Access to 

Materials of Concern Is Needed

OFFICIAL USE ONLY – SECTION HAS BEEN REDACTED FOR 

PUBLIC RELEASE
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OFFICIAL USE ONLY – SECTION HAS BEEN REDACTED FOR 

PUBLIC RELEASE
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OFFICIAL USE ONLY – SECTION HAS BEEN REDACTED FOR 

PUBLIC RELEASE

Recommendation

OIG recommends that the Executive Director for Operations:

2. OFFICIAL USE ONLY – RECOMMENDATION HAS BEEN 

REDACTED FOR PUBLIC RELEASE
Audit of NRC’s Oversight of Irradiator Security

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C. Formal Materials Security Refresher Training Program Is Needed

NRC materials inspectors should be provided the tools and training 

necessary to make risk-informed decisions to address security, health and 

safety, and environmental aspects of licensee compliance. While these 

inspectors receive initial training on the security requirements for material 

licensees, they do not receive any refresher training to address the 

security aspects of their jobs. Although NRC has acknowledged the need 

to incorporate security training into the inspector qualification program, the 

development of a security refresher course has not been a priority. 

Without formalized refresher training, NRC might not be able to ensure 

licensees are adequately protecting materials of concern.

Security Training Requirements

NRC materials inspectors should be provided the tools and training 

necessary to make risk-informed decisions to address security, health and 

safety, and environmental aspects of licensee compliance. Specifically, 

initial and refresher security training should be provided to all personnel 

involved in the security oversight of materials licensees. 

No Formal Security Refresher Training

While materials inspectors receive initial training on the materials security 

requirements, they do not receive formal refresher training to address the 

security aspects of their jobs. When NRC issued Safeguards Order 

EA-02-249 to large irradiator licensees, the Commission designed and 

implemented a training course at Sandia National Labs to provide 

instruction on a methodology to evaluate physical protection systems 

associated with the security order. Subsequently, when NRC issued 

Increased Control Order EA-05-090 to the small irradiator licensees, the 

training course was modified to focus on the security controls of this order 

as well. Although Inspection Manual Chapter 1246 does not discuss 

specific security training requirements, NRC materials inspectors generally 

take this initial security training course at Sandia National Labs prior to 

conducting security inspections. However, in the 7 years since NRC 

introduced the security orders, it has neither provided nor required 

additional formal security training courses for the materials inspectors. 
Audit of NRC’s Oversight of Irradiator Security

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Since there is not a formal refresher training course, some regions and 

Agreement States have developed their own methods of communicating 

information and lessons learned on security aspects. These courses help 

ensure consistency within the region or the State; however, without FSME 

involvement, there are no assurances that these self-developed refresher 

courses meet the intent of the program office.

The regional inspectors conducting materials security inspections have 

health physics backgrounds, and in-depth security reviews only became 

part of their job function after the introduction of the security orders. 

Inspectors interviewed expressed the need for refresher training. OIG 

interviewed 22 regional-based employees involved with the materials 

security program. Of these 22 employees, 16 expressed the need to have 

security refresher training. For example, one inspector stated that 

refresher training would be helpful since security inspections are not done 

all the time and it is important to be fresh on the inspection procedures 

before conducting inspections. Another inspector expressed a desire for 

refresher training to help ensure consistency between regions and to allow 

lessons learned to be shared across the materials inspector community.

Development of Security Refresher Training Is Not a Priority

While NRC has acknowledged the need to incorporate security training 

into the inspector qualification program, the development of a security 

refresher course has not been a priority. However, FSME has recently 

established a working group to revise Inspection Manual Chapter 1246. 

As part of this review, the group will look to make necessary changes to 

the training program to provide inspection personnel with the tools and 

training necessary to make risk-informed decisions that address security 

aspects, as well as health and safety aspects, and to foster a security 

culture. The group began meeting in April 2010 and the working group 

charter was approved in July 2010.

Additionally, FSME has worked to provide tools for inspectors and others 

involved with increased security to discuss concerns and lessons learned. 

For example, FSME created the Increased Controls Toolbox as a method 

of sharing updated information and clarification about the Increased 

Control Order. Individuals can also use this Web portal to ask specific 

questions to other toolbox members.
Audit of NRC’s Oversight of Irradiator Security

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Without formalized refresher training, NRC might not be able to ensure 

licensees are adequately protecting materials of concern. Specifically, 

inspectors might not be able to conduct adequate security inspections 

because they may not have a full understanding of the ever-changing 

security environment and threats. As materials inspectors continue to 

perform inspections, it is critical that they are knowledgeable in all aspects 

of security relating to materials of concern, and that NRC implements 

security refresher training in the near future. 

Recommendation

OIG recommends that the Executive Director for Operations:

3. Develop and offer periodic refresher training for all individuals 

involved in the materials security program.
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IV. CONSOLIDATED LIST OF RECOMMENDATIONS

OIG recommends that the Executive Director for Operations:

1. Reevaluate and determine the frequency of security inspections based 

on a risk-informed approach.

2. OFFICIAL USE ONLY – RECOMMENDATION HAS BEEN 

REDACTED FOR PUBLIC RELEASE

3. Develop and offer periodic refresher training for all individuals involved 

in the materials security program.

V. AGENCY COMMENTS

At an exit conference on August 2, 2010, agency management stated their 

general agreement with the findings and recommendations in this report. 

Agency management also provided supplemental information that has 

been incorporated into this report as appropriate. As a result, the agency 

opted not to provide formal comments for inclusion in this report.
Audit of NRC’s Oversight of Irradiator Security

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Appendix A

SCOPE AND METHODOLOGY

Auditors evaluated the adequacy of NRC’s oversight of industrial irradiator 

security. However, due to the scope of the security orders and NRC’s 

efforts to combine these security orders into one section of the Code of 

Federal Regulations, the audit findings and recommendations expand 

beyond irradiators to address the radioactive materials security program 

as a whole.

The audit team reviewed relevant criteria, including Safeguards Order EA08-033, Compensatory Measures For Panoramic And Underwater 

Irradiator Licensees, and Increased Controls Order EA-05-090, Increased 

Controls For Licensees That Possess Sources Containing Radioactive 

Material Quantities Of Concern. Additionally, auditors reviewed NRC 

policies, including Inspection Manual Chapter 1246, “Formal Qualification 

Programs in the Nuclear Material Safety and Safeguards Program Area,” 

and Inspection Manual Chapter 2800, “Materials Inspection Program.” 

At headquarters in Rockville, MD, auditors interviewed NRC staff and 

management from FSME and the Office of Nuclear Security and Incident 

Response to gain an understanding of their roles and responsibilities in 

the oversight of industrial irradiator security. Auditors also traveled to and 

interviewed NRC staff and management located in Region I (King of 

Prussia, PA), Region III (Lisle, IL), and Region IV (Arlington, TX) and 

Agreement State officials on their roles and involvement in the oversight 

program. 

We conducted this performance audit from January 2010 through June 

2010, in accordance with generally accepted Government auditing 

standards. Those standards require that the audit is planned and 

performed with the objective of obtaining sufficient, appropriate evidence 

to provide a reasonable basis for any findings and conclusions based on 

the stated audit objective. OIG believes that the evidence obtained 

provides a reasonable basis for the report findings and conclusions based 

on the audit objective. Internal controls related to the audit objective were 

reviewed and analyzed. Throughout the audit, auditors were aware of the 
Audit of NRC’s Oversight of Irradiator Security

17

possibility or existence of fraud, waste, or misuse in the program. The 

work was conducted by Beth Serepca, Team Leader; Rebecca Underhill, 

Audit Manager; Gail Butler, Management Analyst; Michael Blair, 

Management Analyst; and Kevin Nietmann, Senior Technical Advisor. 
Audit of NRC’s Oversight of Irradiator Security

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Appendix B

CATEGORY 1 AND CATEGORY 2 QUANTITIES OF CONCERN

The IAEA “Code of Conduct on the Safety and Security of Radioactive 

Sources” (Code of Conduct) contains a categorization system for 

radiological sources to allow controls to be applied commensurate with the 

radiological risks. The Code of Conduct identified 16 radioactive materials 

that could pose a serious threat to people and the environment and 

furthermore, identified the different quantities or “thresholds” of materials 

that could be useful to a terrorist (i.e., Category 1 and Category 2). Table 

A identifies these materials and the associated thresholds. NRC adopted 

the IAEA Code of Conduct Category 1 and Category 2 threshold quantities 

to provide consistency between domestic and international efforts for 

security of radioactive materials that are deemed to be attractive targets 

for malevolent use. 

Table A. Radionuclides of Concern

Radioactive Material

Category 1 Threshold Category 2 Threshold

Terabecquerels Curies Terabecquerels Curies

Americium-241 60 1,620 0.6 16.2

Americium-241/Beryllium 60 1,620 0.6 16.2

Californium-252 20 540 0.2 5.40

Curium-244 50 1,350 0.5 13.5

Cobalt-60 30 810 0.3 8.10

Cesium-137 100 2,700 1 27.0

Gadolinium-153 1000 27,000 10.0 270

Iridium-192 80 2,160 0.8 21.6

Plutonium-238 60 1,620 0.6 16.2

Plutonium-239/Beryllium 60 1,620 0.6 16.2

Promethium-147 40,000 1,080,000 400 10,800

Radium-226 40 1,080 0.4 10.8

Selenium-75 200 5,400 2.0 54.0

Strontium-90 (Yttrium-90) 1,000 27,000 10.0 270

Thulium-170 20,000 540,000 200 5,400

Ytterbium-169 300 8,100 3 81.0