Situation remains tense: 185 days after “Fukushima”


After a severe earthquake on 11 March 2011 extensive safety problems arose in diverse nuclear power plants on the East coast of Japan. Six months after the catastrophe Oeko-Institut has compiled key information on the sequence of events leading to the accident and the consequences of the catastrophe. Furthermore you can find links to bodies and institutions who continue to observe and assess the events.

What happened in Fukushima on 11 March 2011?

At 2.46 pm local time an earthquake measuring nine on the Richter scale hit the coast of Japan's largest island Honshu. A short time later the earthquake gave rise to a tsunami, with waves of up to approx. 38 meters high lashing the coast near Sendai. This natural catastrophe took the lives of thousands of Japanese citizens – and also led to the largest nuclear accident in Japan’s history.

Immediately the Fukushima reactors Daiichi and Daini and other nuclear power plants were automatically switched off as a result of the earthquake and tsunami. In order to keep the residual heat under control, the plants depend on an emergency or external power supply after the reactor has shut down. However, the emergency power supplies in the Daiichi plants malfunctioned due to the tsunami.

The huge destruction wrought in the area surrounding the plants and at the reactor site itself additionally also meant that the external electricity supply malfunctioned. A replacement power supply could not be procured and activated in time and a so-called “station blackout” occurred. As a result the electrical cooling systems, which are imperative for long-term residual heat removal, failed.

Explosions in the reactors

Without sufficient cooling the existing volumes of water in the Fukushima Daiichi plant evaporated until finally the fuel rods were no longer covered with water. Subsequently the temperature of the fuel assemblies rose dramatically. The fuel rod claddings and the steam reacted chemically and created huge quantities of hydrogen.

When there was an attempt to remove pressure from the reactor vessels, this hydrogen came into contact with oxygen, causing a series of explosions. These explosions wrought various degrees of destruction in the nuclear power plants. At the same time the fuel rods became so hot that core meltdown is assumed to have taken place in the first, second and third reactor.

Radioactivity released

With the pressure decreased through the blow down, large quantities of gaseous and vaporisable radioactive substances – in particular noble gases, iodine and caesium – escaped from the reactor vessel and entered the surrounding atmosphere. From 11 March 2011 onwards the Japanese government relocated all residents living within a two, then three kilometre radius of the nuclear power plants. On 12 March the evacuation zone was expanded step-by-step to a 20 kilometre radius.

A month later the authorities widened this zone again, this time to a 30 kilometre radius. High levels of radiation levels were recorded at the plant and beyond – including areas outside the relocation zone (predominantly to the north-west). Additional relocations are planned in these areas, although they will no longer occur in radius.

The highest radiation levels recorded at the reactor site so far – ten sieverts per second (Sv/h) – mean that workers would be very likely to receive a fatal dose of radiation within an hour, if exposed. Other areas surrounding the plant became so highly contaminated that it will not be possible to return to these areas for a long while.

On 12 April 2011 the Japanese authorities rated the Fukushima Daiichi nuclear disaster as a Level 7 event – that of a “Major accident”. Level 7 is the highest level on the INIS Scale used to describe the level of severity of nuclear events.

Current situation: still not under control

Cooling must continue for a long period of time at the damaged power plant in which the fuel rods are still generating heat in the reactor and in the fuel element storage pools. For now the pecialists at the plant have made the power supply and cooling system secure so that the immediate danger of large amounts of radioactive releases again seems to have been averted. However, there have been repeated technical problems with the cooling system, with the result that the situation is not under reliable control.

In the future TEPCO – the power plant operators – must also collect and safely store the radioactive material dispersed by the explosion both within the plants themselves and inside the plant’s premises. Large volumes of water contaminated with radioactive substances have to be stored and cleaned and the buildings must be covered. Only in this way can the situation inside the plant be stabilised in the long term and the radiation levels lowered for the workers involved in the clean-up operation.

Further information from Oeko-Institut

Presentation which summarises key information on the accidents in the Fukushima nuclear power plant (in German language)

Further information (on external websites)

German Federal Office for Radiation Protection (BfS) (in German language)

German Association for Plant and Reactor Safety (GRS) (in German language)

Information in English

Measured data from the TEPCO operators on the surrounding environment

News in brief and TV coverage from Japanese state television channel NHK

Japan’s Nuclear and Industrial Safety Agency NISA

Measured data and assessments of the Japanese Ministry of Education, Culture, Sports, Science and Technology (MEXT)

Report of the Japanese government on the accidents submitted to the International Atomic Energy Organisation (IAEA, Ministerial Conference on Nuclear Safety)

Info page of the International Atomic Energy Organisation IAEA

Report of IAEA’s Fact Finding Mission

Website of the Citizen Nuclear Information Center CNIC including many critical opinion pieces

Website of Japan’s NGO Greenaction including opinion pieces and discussion forums

Contact at Oeko-Institut

Dr. Christoph Pistner (on reactor safety)
Nuclear Engineering & Facility Safety
Oeko-Institut, Darmstadt office
Tel. +49-6151/8191-122

Stephan Kurth (on reactor safety)
Nuclear Engineering & Facility Safety
Oeko-Institut, Darmstadt office
Tel. +49-6151/8191-122

Christian Küppers (on radiation protection)
Deputy Head of Division
Nuclear Engineering & Facility Safety
Oeko-Institut, Darmstadt office
Tel. +49-6151/8191-122

Gerd Schmidt (on related environmental impacts)
Nuclear Engineering & Facility Safety
Oeko-Institut, Darmstadt office
Tel. +49-6151/8191-117