Characterization and Categorization of
DSRS Inventory
Presenter Name
School of Drafting Regulations for Borehole Disposal of DSRS
2016
Vienna, Austria
IAEA
International Atomic Energy Agency
Outline of Presentation
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Presentation resources
Regulatory Framework for Cat I/2 SRS
Characterization of DSRS
Categorization of DSRS
Compare and Contrast
Summary
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Presentation Resources
• International Atomic Energy Agency, Management of
Disused Long Lived Sealed Radioactive Sources
(LLSRS), IAEA-TECDOC-1357., Vienna (2003).
• International Atomic Energy Agency, Code of
Conduct on the Safety and Security of Radioactive
Sources, IAEA, Vienna (2004).
• International Atomic Energy Agency, Categorization of
Radioactive Sources., Safety Guide No. RS-G-1.9,
Vienna (2005).
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Regulatory Framework
• Basis in national statues
• May be based upon IAEA documents
• Many countries have national regulations for controlling SRS in
higher activity categories.
• Protection of the public and the environment
• Examples of typical regulations governing
licensing:
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Public dose
Worker dose – conditioning/hot cell
Training
Isotope limits due to site safety assessment
Code of Conduct limits for SRS
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Definitions
Categorization – to provide a simple means
to rank (into categories) radioactive sources
with respect to their potential to cause harm to
human health. The rankings/categories
provide an internationally harmonized basis for
risk informed decision making.
Characterization – a list of physical, chemical
and radiological properties of the SRS.
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Characterization of DSRS’s
Minimum radiological properties needed:
•Isotope and radiation type
•Activity with manufacture date
•Status of source integrity (e.g., leaking?)
•Physical properties (e.g., size, shape)
•Source/device manufacturer
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Model number
Serial number
Design specs
•Traceability of source to documentation
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IAEA’s International Catalogue of Sealed Sources
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Characterization of DSRS’s
Additional helpful radiological properties:
• Isotope half-life, energy, & dose conversion
factors
• Neutron flux (for neutron sources)
Non-radiological parameters:
• Geometrical (e.g., long rods, spheres, strips)
• Chemical & physical form (solid, liquid, or gas)
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Liquid sources have a higher potential to leak
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Characterization of DSRS’s
Common classification of SRS is by type:
• Alpha
• Beta
• Gamma/X-ray
• Neutron sources
Rule of thumb is SRS emit more than one type of
radiation:
• Alpha decay has a gamma with it.
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Daughters are often beta emitters
• Beta conversion during absorption results in
Bremsstrahlung.
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Example of DSRS Characterization
Common SRS used in industry – Cs-137
Type of source: beta – gamma
Strength: variable (e.g., 3700 GBq) w/date
Physical property: solid salt in capsule
Chemical property: CsCl is common
Radiological half-life: 30.17 years
Energy: gamma energy is 0.662 MeV
Source integrity: leak check of shield date
Dose conversion factor: 4.6 E-9 Sv/Bq
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Categorization of DSRS’s
Purpose of categorizing DSRS is to provide an
internationally harmonized basis for risk informed
decision making.
System is based upon the concept of “dangerous
sources” as measured by “D” values.
Originally derived for emergency preparedness use
D value is the radionuclide specific activity which, if
not controlled, could cause severe deterministic
effects for a range of scenarios creating external
and/or internal exposures
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Categorization of DSRS’s
• For many isotopes, source strength can vary
over several orders of magnitude. D values serve
to normalize this range of activities for comparing
risk.
• A/D ratio is commonly used
• provide initial rankings,
• Rankings modified by other factors such as physical &
chemical form, type of shielding or containment,
supposed use, and accident case history,
• Other factors are subjective and largely based on
international consensus.
See Appendix I of SG No. RS-G-1.9
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Categorization of DSRS’s
• Categorization System has five categories
o Cat I is the most dangerous (fatal exposure in minutes)
o Cat 5 is the least dangerous (can exceed dose limits if
not controlled).
o Subdividing categories is NOT recommended as system
is not that precise and would lead to a loss of
international harmonization.
• RS-G-1.9 contains list of common sources.
o Can’t find your source in the listing, obtain D
factor for your isotope from table in 1.9
o Calculate A/D and compare to table.
o Other factors may tweak result.
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Categorization of DSRS’s
• Categorization System has five categories
• Cat 1 A/D≥1000
• RTG’s, teletherapy, gamma knifes
• Cat 2 1000>A/D≥10
• Industrial radiography, HD brachytherapy
• Cat 3 10>A/D≥1
• Fixed gages (high activity), well logging
• Cat 4 1>A/D≥0.01
• LD brachytherapy (except eye plagues and
permanent implants), industrial gages (low activity),
bone densitometers, static eliminators
• Cat 5 0.01>A/D and A> exempt
• XRF devices, electron capture, PET check sources,
LD brachytherapy eye plagues and permanent
implants
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Example of DSRS Categorization
Common SRS used in industry – Cs-137
D = 0.1 TBq
Cat 1 source (food irradiator) – 1.1 E5 TBq
A/D = 1.1 E6 (> 1000)
Cat 2 (brachytherapy) – .11 TBq
A/D = 1.1, but recommended Cat 2
Cat 3 (gage) – 0.19TBq >> A/D = 1.9
Cat 4 (fixed gage) – 0.0022 TBq >> A/D=0.022
Cat 5 (check source) – 7400 Bq >> A/D=7E-5
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Categorization of DSRS’s
• Operational considerations
o BSS and GSR-1 requirements to ensure safety and
security “commensurate” to the practice and
likelihood of exposures.
o Short half-life sources and unsealed sources
 Tc-99m and I-131 – Carefully choose “A” for A/D
o Aggregation – sources in close proximity per RB
 Sum isotopic activities, divide by isotope D , add A/D’s
 Cat III sources may end up with a Cat II quantity
o Other factors may dictate final category.
• Additional labeling of high activity sources
• National registry of at least Cat I or II sources
o Cat III sources can also be registered
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Categorization of DSRS’s
• Operational considerations
o Additional inspection protocols
o Constant monitoring/restricted access
o Coordination with local law enforcement
o Trustworthy individuals only allowed unrestricted
access
o Hardened source devices
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Compare and Contrast
Characterization vs. Categorization
• Similarities
• Activity is critical to both
• Protection of public is paramount
• Physical properties dictate handling
• Differences
• Physical and chemical properties
• License – safety requirements
• High activity sources – additional security
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Summary
• Characterization and Categorization are not
the same creature
• Characterization specifies the physical, chemical
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and radiological properties of the source.
Categorization specifies the degree of safety and
security needed to protect people from
deterministic effects.
With multiple sources within a facility (for storage
or conditioning), aggregation will be required.
Additional license conditions are required for Cat
1/2 sources.
Inspections review additional license conditions.
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IAEA
Thank you!
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