For more information please get in touch with ARPANSA
- Phone Number+61 3 9433 2211
- Fax Number+61 3 9432 1835
- email ARPANSA
Date: 21 August 2013
FUKUSHIMA DAI-ICHI NUCLEAR POWER ACCIDENT
Following the Great East-Japan, or Tohoku earthquake and tsunami on 11 March 2011, a series of engineering design and equipment failures caused severe damage to four of the reactors at the Fukushima Dai-ichi Nuclear Power Plant (NPP), resulting in significant releases of radioactive materials into the environment. It is the largest nuclear accident since the Chernobyl accident of 1986.
The Fukushima Dai-ichi NPP, operated by the Tokyo Electric Power Company (TEPCO), is situated in the Fukushima Prefecture on the eastern coast of the main Japanese island of Honshu about 200 km north of Tokyo, and comprises six boiling water reactors (BWR). At the time of the earthquake, three of the reactors (Units 1 to 3) were in operation, Unit 4 had been de-fuelled and Units 5 and 6 were in cold shutdown for planned maintenance.
What happened during the Tohoku earthquake and tsunami?
Units 1, 2 and 3 shut down automatically during the earthquake. The 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. These systems are essential in removing heat from the reactors, as the reactor fuel is still generating heat from the decay of fission products - although the fission itself has stopped.
The tsunami resulting from the earthquake, estimated at a height of 14 m at the Fukushima Dai-ichi NPP, overwhelmed the site’s 6 m high sea defenses, disabling the shared heat exchangers and diesel generators and breaking the connection to the power grid. With external assistance hindered by flooding, debris and earthquake damage, these serious events led to overheating of the reactors. In the hours and days that followed, the reactor cores of Units 1, 2 and 3 experienced significant to full meltdown. In the June 2011 Report of the Japanese Government to the IAEA Ministerial Conference on Nuclear Safety it was confirmed that fuel had melted in Units 1, 2 and 3. From the analysis of updated information and temperature data it was established that the insufficient maintenance of the reactor water level in the fuel region had caused the cores to melt, and that the melted fuel had moved to the base of the reactor pressure vessels in the early days of the emergency.
Technical information provided by TEPCO can be accessed on https://fdada.info/Top of Page
As the operators struggled to cool and shut down the reactors, courageously and under very difficult circumstances, several hydrogen explosions occurred in the containment vessel. Release of radioactive material into the atmosphere led to evacuation of the public out to a 20 to 30 km radius. For those remaining in affected areas, instructions to shelter in dwellings were given. These protective measures, whilst insufficiently guided by assessment data at the time, 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 unacceptably hazardous.
How much radioactive material was released?
During the emergency radioactive material was released into the atmosphere and ocean waters. Measurements taken by the Japanese government showed radioactive iodine and caesium levels in excess of regulatory limits in certain areas of Fukushima and around the country, leading the government to restrict the distribution and consumption of food grown in these areas. Further details of past and current restrictions, and results of food sampling, can be found on the website of the Japanese Ministry of Health, Labour and Welfare.
Estimates made by the Japanese authorities indicate that the release of radioactive iodine, which in the early phase of the accident was a cause for major concern, was approximately one-tenth of the radioactive iodine release from the Chernobyl accident. One year on, the levels of radioactive iodine had declined to insignificant levels. The quantity of radioactive caesium released was about one-fifth of the corresponding release from the Chernobyl accident. Radioactive cesium released from the Fukushima Dai-ichi reactors will slowly reduce in the environment over decades (e.g. cesium-137 levels will halve in approximately 30 years).
In June 2013, the operator of the Fukushima Dai-ichi site announced that water contaminated with radioactive material has continued to leak into the Pacific Ocean since the accident. TEPCO estimates that approximately 400 tonnes of groundwater flows into the station building basement per day. This water becomes contaminated when it mixes with highly irradiated water used to cool melted fuel. The continuous leak into the ocean has resulted from the inability to manage ground water inflow and the partial failure of the engineering barrier between the reactor buildings and the sea. TEPCO and the Japanese Government have been working since May 2013 on a proposal to prevent groundwater from leaking into the reactor buildings.
The Japanese government operate and maintain a seawater monitoring program offshore in the affected Prefectures. Past and current results of the monitoring programs can be found on the website of Nuclear Regulation Authority.
A comparison to the Chernobyl accident
The Fukushima and Chernobyl accident both released significant amounts of radioactive material. However, the accidents and the extent of the radioactive releases are different. During the Chernobyl accident, the reactor core was instantaneously destroyed, resulting in a graphite fire that burnt for 10 days releasing large amounts of radioactive material into the atmosphere. Some of the workers who dealt with the emergency lost their lives due to acute radiation effects (commonly referred to as acute radiation syndrome (ARS)). This material affected not only the areas close to the accident, but also affected many other countries in Europe. Exposure to radioactive iodine, mainly in food, led to increased thyroid cancer in children living in the affected area. The United Nations Scientific Committee on the Effects of Atomic Radiation has published a series of reports on the health effects of the Chernobyl accident.
The radioactive releases from the Fukushima Dai-ichi NPP accident have significantly contaminated areas in the Fukushima and surrounding Prefectures, but the radiation levels in other parts of Japan and in countries outside Japan were low and are of minimal health consequence. There were no worker deaths attributed to direct radiation exposures, nor any cases of acute radiation syndrome, but at least six workers exceeded lifetime legal occupational limits for radiation. Exposure to the public from radioactive iodine occurred but protective measures limited this exposure.Top of Page
Long-term health studies
Many long-term assessments and studies are planned to assess the health effects of the Fukushima Dai-ichi NPP accident. Long-term epidemiologic studies are important because there is a need to better understand the health consequences of long-term exposure to radiation at low levels.
The World Health Organization (WHO) has estimated the radiation doses received by members of the public utilising data collected in the first six months after the Fukushima Dai-ichi NPP accident. In May 2012 the WHO published their report Preliminary Dose Estimation from the Nuclear Accident after the 2011 Great East Japan Earthquake and Tsunami. This report provides information on the estimated radiation exposure of populations in Japan and the rest of the world in the first year following the accident. Based on this preliminary dose estimation the WHO subsequently conducted a Health Risk Assessment to give an indication at a global level of the potential health consequences of exposure of people to radiation as a result of the accident. The WHO released their second report, Health Risk Assessment from the nuclear accident after the 2011 Great East Japan Earthquake and Tsunami based on a preliminary dose estimate in February 2013. A key finding of this report was that no significant increase in health risk is expected from the Fukushima event for people in most of Japan (i.e. outside of the most affected areas), in neighbouring countries and for the rest of the world.
For certain groups in the most affected locations in Fukushima Prefecture the report estimates that the additional lifetime risk, above baseline cancer rates, for the development of solid cancers, breast cancer and leukaemia range from four to seven per cent. In these affected locations a much larger increase of 70% in the additional lifetime risk was estimated for thyroid cancer in females exposed as infants. For this group, this equates to an increase in thyroid cancer incidence of an additional 52 per 10,000, above the baseline rate of 77 per 10,000.
For emergency workers at the Fukushima Daiichi nuclear power station, the report estimates a small increase in the lifetime risks for leukaemia, thyroid cancer and other solid cancer. An increased risk of non-cancer thyroid disorders for those workers exposed to high levels of radioactive iodine is also anticipated.
The United Nations Scientific Committee on the Effects of Atomic Radiation has commenced an assessment of the levels and effects of radiation exposure due to the Fukushima Dai-ichi NPP accident. This study will evaluate information on the levels of radiation exposure due to the accident, and the associated effects and risk to human health (both public and workers) and effects on the environment. It will use data for the first year and for some data subsets beyond the first year. In addition to the public and worker exposure and health impact, it will also consider the effects of evacuation as well as provide a brief account on exposure in the natural environment. The draft UNSCEAR Fukushima Report was discussed by the UNSCEAR Scientific Committee at its May 2013 meeting and is expected to be made publically available late in 2013.
The Fukushima Prefecture government has initiated activities for a long-term health study (PDF 4.7 mb) of all its residents. The study is planned to include surveys on demographics, health conditions and geographic location to estimate the cumulative radiation dose exposure and make predictions of the impact on health over the coming decades. Top of Page
Independent assessment of the accident
Interim reports have been published by the Japanese Government's Investigation Committee on the Accident at Fukushima Nuclear Power Stations, the Fukushima Nuclear Accident Independent Investigation Commission (PDF 1.4 mb) and by the Rebuild Japan Initiative Foundation’s Independent Investigation Commission on the Fukushima Dai-ichi Nuclear Accident. Both reports were critical of the Japanese Government’s handling of the Fukushima crisis, including information dissemination.
A global safety plan which seeks to draw on the lessons learned from the Fukushima Dai-ichi Nuclear Power Plant accident was approved by the International Atomic Energy Agency’s Board of Governors on 13 September 2011 and endorsed by all 151 Member States at its General Conference.
The 12-point action plan is aimed to promote nuclear safety controls in the world's operating and planned power reactors, to improve standards and independence of supervisory authorities and to strengthen emergency preparedness and radiation protection of people and the environment worldwide. The IAEA will oversee the implementation of the action plan and ensure proper coordination among all stakeholders. Progress in implementing the actions can be viewed via the IAEA’s Nuclear Safety Action Plan Dashboard.
Japan's Roadmap to Recovery
The national recovery plan published on 25 June 2011 by the Japanese Government represented an important post-disaster point, with a transition from an emergency response phase to a primarily recovery phase. During December 2011, cold shutdown of all reactors was achieved limiting the potential for any significant release of radioactive material into the environment into the future. The recovery phase has now entered the mid to long term phase that will see complete fuel removal and disposal achieved within 40 years.
Concern has been expressed internationally over the safety of the spent fuel pool of reactor 4 (SPF4). Defuelling of SPF4 is planned to commence late 2013. The structural integrity of the pool is being regularly monitored and the supporting structures in the badly damaged reactor building have been reinforced. The strength of the concrete of SPF4 is estimated to exceed original design criteria. Furthermore, the reactor building of Unit 4 has been dismantled to Level 5 which is the top level of both containment and SPF4. This has removed more than 4,000 tonnes of building material from the top levels of the reactor building, thus rendering the structures underneath less vulnerable to any new earthquake. SPF4 is considered to be able to withstand an earthquake of similar strength as the one that occurred on 11 March 2011.
What does it mean for Australia?
While the releases of radioactive material from the Fukushima Dai-ichi NPP accident resulted in the detection of small amounts of radioactivity in both hemispheres, there are no health concerns for people living in Australia. Following environmental monitoring and testing of people, wildlife, shipping, aircraft and imported food and vehicles, ARPANSA published the technical report Assessment of the impact on Australia from the Fukushima Dai-ichi nuclear power plant accident in October 2012. This report summarises ARPANSA's assessment of the impact of the releases of radioactive materials from the Fukushima Dai-ichi NPP on Australia's people and environment. ARPANSA will continue testing food imported from Japan and monitoring the ocean and atmosphere in Australia for radioactive materials in order to provide accurate and current advice to the Australian Government and the public.
Australia is also supporting a number of international programs to assess the impact of the Fukushima Dai‑ichi NPP accident on people and the environment.Top of Page
Japanese document links
|The Fukushima Nuclear Accident Independent Investigation Commission (PDF 1.4 mb)||The National Diet of Japan, The Fukushima Nuclear Accident Independent Investigation Commission
|Final Report||Japanese Governments Investigation Committee on the Accident at Fukushima Nuclear Power Stations||2012 July|
|Road to Recovery Update (PDF 4.7 mb)||Prime Minister of Japan and His Cabinet||2012 March|
|Research Investigation Report||Rebuild Japan Initiative Foundation's Independent Investigation Commission on the Fukushima Daiichi Nuclear Accident Nuclear Accident (in Japanese; English version to be published)||
||Japanese Governments Investigation Committee on the Accident at Fukushima Nuclear Power Stations||2011 December|
|Additional Report of Japanese Government (PDF 4.7 mb)||Additional Report of Japanese Government to IAEA - Accident at TEPCO's Fukushima Nuclear Power Stations||
|Report of Japanese Government||Report of Japanese Government to IAEA Ministerial Conference on Nuclear Safety - Accident at TEPCO's Fukushima Nuclear Power Stations||
International document links
|Health Risk Assessment from the nuclear accident after the 2011 Great East Japan Earthquake and Tsunami based on a preliminary dose estimation||
World Health Organization
|Preliminary dose estimation from the nuclear accident after the 2011 Great East Japan earthquake and tsunami||
World Health Organization
|Fukushima, one year later||
Institut de Radioprotection et de Surete Nucleaire
|Lessons from Fukushima (PDF 2.5 mb)||Greenpeace||2012 February|
|IAEA Action Plan on Nuclear Safety (PDF 218 kb)||International Atomic Energy Agency||2011 September|
|International Fact-Finding Mission Preliminary Summary (PDF 36 kb)||International Atomic Energy Agency||2011 June|
For media queries please contact: