IAEAInternational Atomic Energy Agency

Categorization of Radioactive Sources

Day 8 – Lecture 7

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To understand categorization system of radioactive sources and its application in establishing the appropriate degree of regulatory control for activities relating to the safety and security of radioactive sources.

Objective

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• Objective and Scope

• Categorization system

• Implementation of the categorization system

Contents

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Part I: Objectives and scope of categorization

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• Provides a system for ranking of sources and practices in terms of their potential to cause harm to human health.

• Categorization supports international harmonization of controlling radioactive sources and their security.

• Code of Conduct on the Safety and Security of Radioactive Sources

• Guidance on the Import and Export of Radioactive Sources

Objectives of categorization of radioactive sources

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• Developing or refining national regulatory infrastructures;

• Developing national strategies for improving control over radioactive sources;

• Optimizing use resources by setting priorities for regulation;

• Optimizing security measures for radioactive sources;

• Emergency planning and response.

Applications of categorization

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Radioactive sealed sources

• Sources used in industry, medicine, agriculture, research and education;

• Sources within military or defence programmes, where appropriate in the national context;

Categorization is concerned with sealed sources, however, the method can also be used to unsealed sources.

Scope of the RS-G-1.9

RS-G-1.9 is NOT applicable to

Radiation generating devices (x-ray machines, accelerators)

Nuclear material Waste management of disused radioactive sources Packages of radioactive material in transport

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• A national categorization for establishing the appropriate degree of regulatory control should

• be based on a national inventory of practices and sources

• consider national circumstances and resources

• Take into account also practices and sources not covered by the RS-G-1.9:

• Use of unsealed sources

• Use of x-ray devices and accelerators

Application of the Categorization Guidance

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Part II: Categorization system

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The categorization is based on the concept of dangerous sources which are quantified in terms of D values.

The D value is the radionuclide-specific activity of a source which, if not under control, could cause severe deterministic health effects.

D values are used as normalizing factors to provide a reference for comparing risks.

Categorization System

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• An unshielded source (the D1 value)

• carried in the hand for one hour

• carried in a pocket for 10 hours

• being in a room for days to weeks

• Dispersal of a source by fire, explosion or human action (the D2 value)

• inhalation, ingestion and/or skin contamination

The lower value of D1 and D2 is used as the D value.

Exposure scenarios used in deriving the D values

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Radionuclide D (TBq)

Am-241 0.06

Co-60 0.03

Cs-137 0.1

Ir-192 0.08

Pu-238 0.06

Sr-90 1.0

Tc-99m 0.7

Examples of the D values

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Initial ranking of sources:The activity (A) of a source is divided by the corresponding radionuclide specific D value.

For commonly used sources the ratio A/D ranges from 106 to 10-6.

To obtain useful number of categories also other factors are considered:

• physical and chemical form• type of shielding• circumstances of use• accident case histories

Categorization System

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Five categories are introduced

Categorization System (cont)

Category Activity ratio (A/D)

1 A/D ≥ 1000

2 1000 > A/D ≥ 10

3 10 > A/D ≥ 1

4 1 > A/D ≥ 0.01

5 0.01 > A/D

and A > exempt

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• Examples

• Radioisotope thermoelectric generators (RTGs)

• Irradiators

• Teletherapy sources

• Fixed, multi-beam teletherapy (gamma-knife) sources

Category 1 Sources

A/D ≥ 1000

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Examples

• Industrial gamma radiography sources

• High/medium dose rate brachytherapy sources

Category 2 Sources

1000 > A/D ≥ 10

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Examples

• Fixed industrial gauges that incorporate high activity sources

• Well logging gauges

Category 3 Sources

10 > A/D ≥ 1

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Examples

• Low dose rate brachytherapy sources (except eye plagues and permanent implants)

• Industrial gauges that do not incorporate high activity sources

• Bone densitometers

• Static eliminators

Category 4 Sources

1 > A/D ≥ 0.01

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Examples• Low dose rate brachytherapy eye plagues and

permanent implant sources• X-ray fluorescence (XRF) devices• Electron capture devices• Mossbauer spectrometry sources• Positron emission tomography (PET) sources

Category 5 Sources

0.01 >A/D and A > exempt

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Summary of Categorization System

1000

10

1

0.01

exempt

Teletherapy sourcesIrradiators

Industrial gamma radiography sourcesHigh/medium dose rate brachytherapy sources

Industrial gauges with high activity sourcesWell logging gauges

Low dose rate brachytherapy sourcesIndustrial gauges with moderate/low activity sources

X-ray fluorescence (XRF) devicesElectron capture devices

1

2

3

4

5

Activity ratioA/D

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Part III: Implementation of the categorization system

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Regulatory measures

• A factor to be taken into account in a graded system for notification, registration and inspections.

• Assist in ensuring that allocation of resources to protection measures is commensurate with the degree of risk.

Use of the Categorization System

Security measures

• To optimize security measures for radioactive sources, including measures directed against their possible malicious misuse.

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National register of sources

• To optimize decisions regarding which sources should be included and what level of detail should be used in a national register of sources.

Use of the Categorization System (cont)

Import/export controls

• To optimize decisions regarding which sources should be subject to import and export controls, in meeting national and international standards.

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Labelling of high activity sources

• To guide decisions regarding which sources should be marked with an appropriate label warning of the radiation hazard.

Use of the Categorization System (cont)

Emergency preparedness and response

• To ensure that emergency preparedness plans and response to accidents are commensurate with the hazards posed by the source.

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Prioritization for regaining control over orphan sources

• To inform decisions relating to how efforts should be focused to regain control over orphan sources.

Use of the Categorization System (cont)

Communication with the public

• To provide a basis for explaining the relative hazard associated with events involving radioactive sources.

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The regulatory body should use the D and A/D values of the Safety Guide RS-G-1.9 to categorize the sources included in the national inventory of sources.

Situations where case by case considerations needed: • short half-life radionuclides• unsealed sources• aggregation of sources

Use of categorization

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In situations where several sources are in close proximity to each other, the regulatory body may wish to aggregate the activity in the sources to determine a situation based categorization for the purpose of regulatory control.

In addition to activity, also other factors may need to be considered because aggregations in different situations may have different safety implications.

Aggregation of sources

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Aggregation of sources

n n

i ni

D

AAggregateDA ,)(/

whereAi,n = activity of each individual source i of radionuclide nDn = D value of radionuclide n

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• The regulatory body should maintain a national register of radioactive sources;

• The register should contain, as a minimum, Category 1 and 2 sources, but preferably also Category 3 sources;

• The regulatory body should determine whether also Category 4 and 5 should be included;

National register of radioactive sources

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• The Code of Conduct on Safety and Security of Radioactive Sources provides general guidance for the import and export of Category 1 and 2 sources

• Import/Export guidance* provides specific procedures for the import and export authorization of Category 1 and 2 sources

Import and export of radioactive sources

* Guidance on the Import and Export of Radioactive Sources IAEA, Vienna (2012)

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The Safety Guide RS-G-1.9 provides also plain language descriptions of the categories for the purpose of public information.

In summary:

Communication with the public

Category Risk in being close to an source

1 Extremely dangerous

2 Very dangerous

3 Dangerous

4 Unlikely to be dangerous

5 Most unlikely to be dangerous

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• Categorization of Radioactive Sources, Safety Guide RS-G-1.9, IAEA, Vienna (2005).

• Code of Conduct on the Safety and Security of Radioactive Sources, IAEA, Vienna (2004).

• Guidance on the Import and Export of Radioactive Sources IAEA, Vienna (2012).

• Method for Developing Arrangements for Response to a Nuclear or Radiological Emergency: Updating IAEA-TECDOC-953, EPR-Method 2003, IAEA, Vienna (2003).

References

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A moisture/density gauge includes a 300 MBq Cs-137 source and a 1.48 GBq Am-Be source.

What is the appropriate category for such a device?

Exercise