Search and recovery The initial search comprised major transport points such as a mine site , loading area and transfer yards using a combination of industry and State resources , and some targeted searching based on public information . Specialised instrumentation and teams were sourced from Commonwealth agencies ( Australia ' s Nuclear Science and Technology Organisation , ( ANSTO ), the Australian Radiation Protection and Nuclear Safety Agency ( ARPANSA ) and Australian Government Defence ). Larger and more sensitive detectors enabled the speed of search to be greatly increased .
The source , containing caesium-137 , measured 6mm in diameter and 8mm tall – similar to the size of the clicker on a ball point pen .
A week after notification of the loss of the source it was found approximately 2 m from the edge of a road in a remote area of the Australian outback . It had travelled approximately 100 miles ( 161 km ) from the point of origin . It remained fully intact with no release of material from the double encapsulation . Dose estimates indicate no individual is likely to have received a radiological exposure even a small fraction of the public dose limit or the annual exposure to natural background radiation .
Root cause and lessons learned The primary cause of failure was that the ( relatively new ) design of the gauge was susceptible to vibration , allowing bolts to come undone and the gauge to shake itself apart . Secondary causes
Radiation Protection Today Autumn 2024 included poor quality control , lack of antivibration controls , use of wrong bolts during repair , and packaging as per a new gauge . Following the loss and recovery of the source , areas for improvement in State , Commonwealth and international guidance and regulations were identified . These include :
• More consideration of vibration as a potential cause for loss of containment in design , testing , licensing , installation , and periodic maintenance
• Quality control in manufacture , as per design and approval documentation
• Testing of gauges for vibration of the whole gauge in the direction of maximum load
• Consider making a requirement for checking that the source remains in place ( such as comparing the pre and post Transport Index ) upon receipt of the item , to identify whether there is any damage either before or during transport .
Conclusion The loss of a source capsule from an industrial radiation gauge is extremely unusual , and loss during transport is even more uncommon . The loss of the source capsule in January 2023 created significant public , media and Government concern . Due to excellent cooperation between State and Commonwealth agencies , the source was found . Radiological exposure to all individuals was extremely low ( well below the public dose limit ) and the source encapsulation was intact , ensuring no distribution of radioactivity to the environment . Poor design and vibration were the primary contributors to the failure of the gauge , and allowed the source capsule to escape from the overpack during transport . A number of key learnings arise from the incident , and these have been or are in the process of being implemented . There are deeper learnings for the regulations for radioactive transport and gauge design and manufacture . Rio Tinto was investigated by the appropriate regulatory authority and deemed to have performed appropriately throughout the incident ( no breaches ).
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