Two workers at ANSTO's new $168 million nuclear medicine plant at Lucas Heights are under observation after being exposed to an unsafe dose of radiation.
The Australian Nuclear Science and Technology Organisation (ANSTO) said early calculations were the exposure was equivalent to that of a conventional radiation therapy treatment.
The incident occurred on Friday last week at the new Australian Nuclear Medicine (ANM) plant, which was licensed in May by the independent regulator, ARPANSA.
"Last Friday morning, ANSTO ceased manufacturing Molybdenum-99 (Mo-99) after contamination was detected on the outside of a container holding 42 millilitres of Mo-99," an ANSTO spokesman said.
"Mo-99 is the parent isotope of Technetium-99m, which is used in hospitals and nuclear medicine centres to diagnose a variety of heart, lung, organ and muscular-skeletal conditions.
"Three ANSTO workers were attended to by radiation protection personnel, and initial indications are that two of these workers received a radiation dose above the statutory limit.
"An investigation commenced on Friday, and both the nuclear regulator, ARPANSA, and Comcare have been informed. An estimate of the radiation dose will be confirmed in coming weeks.
"Early calculations indicate that the radiation dose received by two of the workers involved in medicine processing, was equivalent to that of a conventional radiation therapy treatment.
"An occupational physician will continue to provide ongoing observation. All three workers involved are receiving ongoing support from ANSTO.
"Vital supplies of Molybdenum-99 nuclear medicine are currently being provided through alternative facilities at ANSTO, while the investigation is underway."
ANM began producing limited amounts of Molybdenum-99 in April. It received a license to ramp up to full production from ARPANSA in May.
"This is the most advanced and safest manufacturing facility for nuclear medicine on the planet today," ANSTO chief executive Dr Adi Paterson said at the time.
Molybdenum-99 is essential to the production of Technetium-99m, which is used in hospitals to diagnose a variety of health conditions including heart, lung, organ and muscular-skeletal conditions.
About 10,000 doses of Technetium-99m are used in Australia every week and the ANSTO spokesman said the organisation was working hard to ensure the shutdown has no impact on hospital patients.
Molybdenum-99 is being produced from another building on the Lucas Heights campus while the investigation takes place.
An ARPANSA spokesman said its inspectors had visited the site twice since the incident and it was waiting for ANSTO to provide a report.