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DEFENCE IN DEPTH
Defence in depth: sources

MULTIPLE SOURCES / PACKAGES

 

Events don’t always involve a single isotope source of known activity.

The next few slides deal with situations where the

event involves
multiple sources
and/or
unknown activity

The first involves multiple sources or packages involved and the guidance here explains the approach for rating.

If the reduction in safety provisions can only affect a single item,
e.g. inadequate labelling of one transport package

Use the inventory of the single item

If the reduction in the safety requirements has the potential to affect all the items
e.g. a fire

Use the total inventory of all the items

Appendix III gives the methodology for calculating aggregate D values

Appendix III.3.
CALCULATION OF AGGREGATE VALUES

Where a number of radioactive sources or transport packages are relevant, an aggregate D value should be calculated. Based on the guidance in Categorization of Radioactive Sources* and Regulations for the Safe Transport of Radioactive Material**, the aggregate value is calculated as:

1/D = ∑fi /Di

where D is the aggregate value of D, fi is the fraction of isotope i, and Di is the D value for isotope i, or

A/D = Ai /Di

where A is the total activity and Ai is the activity of the isotope.

* INTERNATIONAL ATOMIC ENERGY AGENCY, Categorization of Radioactive Sources, IAEA Safety Standards Series No. RS-G-1.9, IAEA, Vienna (2005)

** INTERNATIONAL ATOMIC ENERGY AGENCY, Regulations for the Safe Transport of Radioactive Material 2005 Edition, IAEA Safety Standards Series No. TS-R-1, IAEA, Vienna (2005)