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DEFENCE IN DEPTH
Defence in depth: sources

WORKED EXAMPLE: MISSING SOURCE FROM A HOSPITAL

 

Summary:

  • Missing 100 TBq 60Co Source
  • Found on open land
  • No shielding but source intact

Scenario

A source inventory check at a hospital that had been closed for some time, revealed that a teletherapy head containing a 100 TBq 60Co source was missing. The unit had been stored in a dedicated facility, but an inventory check had not been carried out for several weeks. It was suspected that the unit had been taken out of the hospital by unauthorized persons. A search was carried out and one day later, the source was located on open land two kilometers away. The unit had been dismantled and the source was unshielded, but not breached. It was recovered by the national authorities.

INES procedure (click the highlighted flowchart items to follow the procedure)

Figure 8, page 149 of the Manual

Calculate A/D and determine category

Here is the calculation for the category:

3.E-02 = 0.03
100(60Co)/0.03 = 3333.33

Check the category and maximum defence in depth rating here

A/D ratio

Source category

Rating for maximum
potential consequences

Maximum rating under
defence-in-depth

0.01 ≤ A/D < 1

4

1 ≤ A/D < 10

3

10 ≤ A/D < 1000

2

1000 ≤ A/D

1

 

Return to flowchart

Answer

Here is the rating for a Category 1 source, which has been lost.

The missing source from a hospital was rated at Level 3.