The Great East Japan earthquake and tsunami

On 11 March 2011, the Great East-Japan earthquake struck approximately 72 km East of Oshika Peninsula. At magnitude 9.0, this was the largest earthquake ever recorded in Japan. The earthquake triggered a tsunami with an estimated height of 14 m at the site of the Fukushima Dai-ichi nuclear power plant (NPP).

The earthquake and resulting tsunami killed approximately 20,000 people, injured several thousand others and displaced hundreds of thousands. The disaster caused extensive damage and destruction to buildings and infrastructure in North Eastern Japan, including triggering the world’s worst nuclear disaster since Chernobyl in 1986.

Damage that occurred at the Fukushima Dai-ichi nuclear power plant

The Fukushima Dai-ichi NPP consisted of six reactor units. At the time of the earthquake, reactor units 1, 2 & 3 were in operation while reactor units 4, 5 & 6 were shut down for maintenance.

During the earthquake, the operating reactor units 1, 2 & 3 shut down automatically. External electrical power to the site was interrupted by the earthquake and the back-up diesel generators started up to provide continuity of electrical supply to emergency equipment, including the cooling systems. The cooling systems are essential for removing heat from the reactors, as the reactor fuel still generates heat from the decay of fission products even though the fission reaction has stopped.

The tsunami that resulted from the earthquake overwhelmed the site’s 6 m high sea defences, disabled the shared reactor heat exchangers and diesel generators, and broke the external connection to the power grid. These events led to an overheating of the reactor units 1, 2, & 3. In the hours and days that followed, several hydrogen explosions occurred and the reactor cores of units 1, 2 & 3 experienced partial to full meltdown, releasing radioactive material to the environment.

Release of radioactive material into the atmosphere led to the evacuation of the public out to a 20 to 30 km radius. For those remaining in affected areas, instructions to shelter in place (within dwellings) was given. These protective measures proved effective in limiting the radiation exposure to the public. During the emergency, workers were temporarily evacuated at various times when radiation levels made their work environment hazardous.

Decommissioning and remediation of the Fukushima Dai-ichi nuclear power plant site

Irreparable damage occurred to the reactor units as a result of the tsunami. The site is undergoing extensive decommissioning activities following the roadmap set out by the operator, Tokyo Electric Power Company (TEPCO) and the Japanese government, with remediation of the site expected to take decades.

Part of the remediation includes the removal of stored wastewater from the site.

Removal of stored wastewater from the site

On site, wastewater is generated from two main sources: 

  • water passing through the damaged reactors to assist with continued cooling of fuel debris
  • water ingress due to water passing through the site (for example due to heavy rainfall).

This water is considered wastewater as it is contaminated with various radionuclides. Wastewater is pumped into temporary storage tanks on site. It has been reported that the capacity of the tanks (1.37 million cubic meters) will be met by the end of 2022.

TEPCO and the Japanese Government, with assistance from the international community, have been planning for disposal of stored wastewater from the site. 

Prior to storage, the wastewater is treated using an Advanced Liquid Processing System (ALPS) to remove the majority of the radionuclide contamination. Prior to its release, it is likely that secondary ALPS will be employed to further reduce these levels. However, the ALPS equipment cannot remove the radionuclide Tritium as it is an unstable form of hydrogen and contains features almost identical to water with ordinary hydrogen, making it difficult to separate. The level of tritium in the treated water will further reduce by dilution to levels below operational limits.

In April 2021, TEPCO announced that the preferred method of release is to discharge the treated wastewater into the sea.

This would be undertaken under strict approval of their regulator, Nuclear Regulation Authority Japan, to ensure limits for discharge are not exceeded and that an extensive monitoring program is undertaken to ensure compliance. Releasing radionuclides into the sea is common practice and does not present health risks if radionuclide levels are kept within strict limits.

In their proposals, TEPCO has previously nominated a level of 1,500 Bq/L of Tritium in the water to be discharged into the sea. Discharges at this level are not expected to result in any health risks to people or the environment. To put this level of radioactivity into perspective, this is much lower than the international drinking water guideline level of 10,000 Bq/L. At this nominated level, it is predicted that the radiation exposure to the environment will be well below the screening level as outlined in ARPANSA’s Guide for Radiation Protection of the Environment (RPS G-1).

The proposal for disposal of wastewater has also been reviewed by the International Atomic Energy Agency (IAEA) who has concluded that this disposal option is feasible. Noting that there is not currently a feasible solution to remove tritium from water on this scale, the IAEA will provide further support into the ongoing monitoring and assessment to help ensure limits are adhered to and exposures to the population and environment are kept to levels which would not result in any health effects.

Impact on Japan

Health implications and restrictions

After the incident, there were wide scale evacuations in contaminated areas. In some areas, residents were allowed to return home because the radiation had decreased to acceptable levels. Other areas are expected to remain restricted for many years. The Japanese Government continues with decontamination efforts to enable most residents to permanently return to their homes.

The World Health Organization (WHO) and the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) have assessed the health impacts from the accident. The reports assessed a number of criteria, including possible radiation dose assessments and the lifetime risk of cancer. The assessment framework that was used in the reports was chosen to reduce the possibility of underestimation of the eventual health risks. The health risk assessment concludes that no discernible change in health risks from the Fukushima event is expected outside Japan. Within Japan, the Fukushima Health Management Survey (FHMS) was implemented following the accident to monitor the population for health effects. More recently, the UNSCEAR 2020 report on the levels and effect of radiation exposure due to the accident has been published. This report collates and analyses many studies since the accident, including the FHMS. The overall conclusion is that no adverse health effects among Japanese residents are directly attributable to the radiation exposure due to the accident, and that future effects are unlikely to be discernible.  

Travelling to Japan

It is safe to travel to Japan as radiation levels in most parts, including Tokyo, are within the normal range of background radiation. Entry to some areas close to the Fukushima Dai-ichi NPP is restricted due to elevated radiation levels. More detailed travel advice and a map showing the restricted areas is available on the Smart Traveller website.


Contamination of the food chain occurred in localised areas from radioactive material being deposited on the ground and released to the ocean, with levels varying geographically and with time. Measurements taken by the Japanese Government following the accident showed radioactive iodine and caesium levels in water and soil to be in excess of the regulatory guidance levels in certain areas of the Fukushima Prefecture and in some other areas within Japan. This led to the government restricting the distribution and consumption of food grown in these areas, and prohibiting fishing in the area close to the Fukushima Dai-ichi NPP.

The Japanese government reviewed their food safety regulations and established new limits on the allowable level of radioactivity in food. Extensive food testing has been undertaken in Japan since the accident, to ensure that the food produced in Japan continues to be safe for consumption.

Environmental contamination

Radioactive material from the Fukushima Dai-ichi NPP in the month following the accident was released into the atmosphere, ocean and deposited onto land.

The first release into the atmosphere occurred on 12 March 2011 and releases continued through April 2011. There was great variability in the rate of release, which was due to specific events, including hydrogen explosions, venting and leakage from the reactors and their containment systems. By April 2011, the releases were a thousand times less than during the first week.

Radioactive material entered the marine environment in a number of ways:

  • by direct releases of contaminated water that were both deliberate and accidental
  • from material that was released into the atmosphere that was dispersed and deposited over the ocean
  • from material that was deposited on land then washed into rivers and transported downstream to the ocean.

The deposition of the radioactivate material on land was concentrated in the 20 km zone northwest of the Fukushima Dai-ichi NPP. This zone formed part of the evacuation area. The radioactivity of the material that was deposited on the land within this zone has reduced dramatically since the accident due to the short half-lives of many of the radionuclides and the on-going decontamination activities of the Japanese government.

The Japanese Government operates and maintains an environmental radiation-monitoring program in the affected prefectures. Past and current results of the monitoring program can be found on the website of the Nuclear Regulation Authority. The Tokyo Electric Power Company (TEPCO) website contains further information and updates regarding projects on decommissioning and remediation at the Fukushima Dai-ichi site.

Impact on Australia

During and after the 2011 nuclear accident, ARPANSA undertook a range of measurements and studies to assess the impact of the accident on Australians in Japan and people and the environment in Australia. The report Assessment of the impact on Australia from the Fukushima Dai-ichi nuclear power plant accident was published in 2012. It provides a single point of reference for these assessments.

Testing and health implications

Australia undertook a range of testing and monitoring programs, all of which are discussed in detail in the technical report. Potential contamination from a number of sources coming from Japan were assessed, including food, cars, ship surfaces, ship ballast water and military helicopters. Contamination of the ocean and atmosphere was also assessed.

ARPANSA has assessed that the health impact from the Fukushima Dai-ichi NPP accident for people living in Australia is negligible.

The most important issue to address after the accident was the safety of Australian citizens in Japan. At the time, ARPANSA performed exposure assessments on individuals who were within an 80 km radius of the NPP. Monitoring of members of a family living 60 km north-west of the Fukushima Dai-ichi NPP during the accident showed that doses to the family were minimal. It was assessed that there were no health risks due to radiation exposure for anyone outside of that range.


In 2011, over 1,000 imported food samples from Japan were tested by ARPANSA and the Department of Agriculture, including noodles, rice, flour, fruit, vegetables, tea leaves and seafood (including edible seaweeds). No food samples tested by ARPANSA exceeded internationally accepted limits (set by Australia and many other countries following the accident). Some foods contained very low levels of contamination (less than 1% of the limit). Testing ceased in 2014 as all samples were found to be well below Australian guidelines.

The radionuclide contamination in Japan is well understood and measures are in place in Japan to control the sale and export of food. ARPANSA, the Department of Agriculture, and Food Standards Australia and New Zealand will continue to monitor the situation in Japan. More information on the food testing can be found in ARPANSA’s technical report 162.

Environmental contamination

In April 2011, radioactive xenon (133Xe) was detected by an air sampler in Darwin, however, it was at such low levels (a hundred million times lower than natural background radiation) that it had no health impact. Air samplers in Australia detected no other radioactive material from the accident.

To date, there has been no radiation from the Fukushima Dai-ichi NPP accident detected in Australian waters. Ongoing monitoring programs are in place to continue to monitor for the Fukushima signature, but it is expected that by the time it reaches Australian waters, the radioactive material will have been diluted to such low levels that it will be undetectable. More information on environmental monitoring can be found in the technical report 162.

Protecting Australians in the future

To ensure the safety of all Australians, Australia is participating in the International Atomic Energy Agency (IAEA) Marine Benchmark Study. This involves monitoring programs for fish and seawater, and the establishment of a regional database of radionuclide contamination of the marine environment in waters of the Asia-Pacific region. Of the fish tested so far, no radionuclide contamination attributed to the Fukushima Dai-ichi NPP accident has been found. See ARPANSA's Technical Report No. 172 for results of the fish testing program. Air sampling as part of the Comprehensive Nuclear-Test-Ban Treaty (CTBT) continues to monitor radiation levels around Australia.


Technical Report No. 172

Technical Report No. 162 

Short video on the UNSCEAR 2013 Report on the Fukushima-Daiichi nuclear power plant accident

The Fukushima Dai-ichi Accident

Nuclear Regulation Authority

Ministry of Education, Culture, Sports, Science and Technology


Mid-and-Long-Term Roadmap towards the Decommissioning of TEPCO's Fukushima Daiichi Nuclear Power Station Units 1-4 / METI Ministry of Economy, Trade and Industry  

The UNSCEAR 2020 Report

WHO Management of Radioactivity in Drinking Water