Security of Radioactive Sources in Radiation Facilities

3. SECURITY LEVELS BASED ON CATEGORISATION OF
SOURCES
3.1 Purpose of Categorising Sources
Radioactive sources with a wide range of radiation intensity are used in a
variety of authorised applications in medical, industrial and research
institutions. Sources with high activity, if not managed safely and securely,
could cause severe deterministic effects to individuals in a short period of
time. The categorisation provides an internationally harmonised basis for
risk informed decision making. The categorisation is not relevant to radiation
generating devices such as X-ray machines and particle accelerators. There
are also certain situations where the categorisation is not applicable because
of factors such as specific activity, chemical properties and half-life. For
example, at a waste management facility for the disposal of disused sources,
the security requirements would be different from what was required when
the sources were originally in use. The categorisation described in this safety
guide essentially reflects the system of categorisation of sources devised by
the International Atomic Energy Agency (IAEA) [6].
3.2 Basis of Categorisation
When the activity of a source is high enough to deliver a radiation dose
which would result in severe deterministic effects in the exposed individual,
the source is considered as a ‘dangerous source’. The activity of a source,
which can deliver this dose, is termed its ‘D value’. Both external and internal
exposures are therefore considered in the derivation of D values. The criteria
for the derivation of D values are given in Appendix-I. Based on the D
values thus derived, sources are divided into five categories [6]. The
commonly used sources and their respective categories are listed in
Appendix-II.
3.3 Graded Approach to Security
Based on the vulnerability analysis for a specific source, an assessment can
be made of the level of risk involved. This risk level would determine the
security measures required to protect the source. The higher the risk, the
more capabile security systems are required. This ‘level’ of capability can be
expressed in terms of the ‘performance objectives’ of the security system.
While the range of possible specific security measures could be quite wide,
they can be described by their capability to deter, to detect and to delay
unauthorised access or acquisition. This graded approach will ensure that the
level of security measures in place is commensurate with the potential
consequence associated with the possible breach of security with respect to
that source.
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