Advice on radiation exposure from Japanese nuclear accident

Advice for Australians remaining in Japan on food and water precautions, the availability and use of potassium iodide tablets and on appropriate sheltering from radiation if required have been provided by Australia’s Chief Medical Officer and the Australian Radiation Protection and Nuclear Safety Agency (ARPANSA).

Extensive advice on these new topics of concern, together with information for people returning from Japan and for use by GPs is contained on the ARPANSA website and is updated regularly.

ARPANSA is closely following the safety issues surrounding the Fukushima Dai-ichi site and in particular the current status of the four reactor units and the spent fuel ponds at a number of the reactor units. The Japanese Government has upgraded the level of the nuclear incident from level 5 (“accident with wider consequences”) to level 7 (“major accident”) on the International Nuclear and Radiological Event Scale (INES). The upgrade is based on an assessment of cumulative radiation releases since the accident began and not due to any worsening of the situation at the Fukushima Dai-ichi site. The Japanese Government estimates that the total amount of radioactive material discharged into the air was approximately ten per cent of that of the accident at Chernobyl.

The ARPANSA modelling of airborne radioactive material released from Fukushima Dai-ichi predicted that during the 24 hours, for releases starting from Monday 9 May mid-morning, any plumes of airborne radioactive material would predominately be pushed north and east, mainly over Northern Japan. The modelling predicted that landfall is not likely to occur over Tokyo during this time.

For the following 24 hours, for releases starting from Tuesday 10 May mid-morning, changing weather systems would push any plumes of airborne radioactive material to the east and then south-west, over Southern Japan. Landfall in Tokyo may be expected during this time. The radiation levels from these plumes would be very low, with negligible consequences to health.

For the following 36 hours, for releases starting from Wednesday 11 May mid-morning, any plumes of airborne radioactive material would predominantly be pushed to the north-west, over Northern Japan. Landfall in Tokyo is not expected during this time.

Long-range modelling (up to 12 days) for releases during this time period show that the general plume behaviour includes movement over Russia and USA, as well as circulation over the North Pacific Ocean. The radiation levels from these plumes would be minimal and the health consequences negligible. Due to weather patterns either side of the equator, there will be minimal plume movement to the Southern Hemisphere.

ARPANSA maintains a number of air sampling stations around Australia for the purposes of monitoring under the Comprehensive Nuclear Test Ban Treaty (CTBT), including in Darwin. From early April to early May, trace amounts of Xenon-133 (Xe-133) have been detected in air samples collected at the Darwin CTBT radionuclide monitoring station. While detectable, the airborne contamination measured at Darwin is at insignificant levels.

These radiation levels are millions times lower than safe levels and will have negligible health impacts on the Australian public. The detection of Xe‑133 at Darwin is of no health significance for any person in Darwin or in Australia. This applies to all ages, including infants and young children. The presence of trace amounts of Xe‑133 in air in Darwin will have zero to negligible effect on the safety of Darwin food or water. ARPANSA’s assessment is that the detection of the Xe-133 in Darwin is consistent with a release of radioactive material from Japan. It should be noted that these levels are many thousands of times lower than detected in the US and Europe.

As a result of joint assessments of the situation in Japan, ARPANSA and the Department of Health and Ageing recommended, as a precautionary measure, that Australians within an 80 km zone from the Fukushima nuclear power plant move out of the area.

The US had made a similar recommendation in accordance with the standard guidelines of their Nuclear Regulatory Commission. Their guidelines would require a zone of 80 km (50 miles) around the Fukushima nuclear power plant.

Australians returning home from Japan are highly unlikely to be contaminated or exposed to significant radiation and will not require checks for radioactivity. However, if people wish to seek medical advice they should contact their local GP.

ARPANSA and the Chief Medical Officer advise that iodine tablets are only required when exposed to substantial radiation doses from radioactive iodine. There is no current need for those returning from Japan or those in Japan outside the Exclusion Zone to consider the use of potassium iodide tablets at this time.

Discussions continue with medical organisations and state and territory health authorities on these issues. Further information will continue to be provided by the Australian Government as the situation develops.