On March 11th 2011 a huge earthquake (14h46 local time) and the following tsunami (15h35 local time) caused the cooling of the reactors and the cooling of the spent fuel pools of the Fukushima Daiichi nuclear plants to fail. A non-stoppable nuclear disaster unveiled.
The release of radioactive material occurred through pressure relief, uncontrolled release of radioactive steam, fires, explosions and leakage and seepage of hundreds of thousands of litres of contaminated water.
Contrary to the Chernobyl disaster 30 years ago this disaster happened in multiple reactors at once – and it is still ongoing.
Chronology of the meltdowns
Immediately after the earthquake radio-active gases (xenon) are measured: the reactor is leaking. Within hours, the fuel – due to the failure of the cooling systems and the evaporation of cooling water – melts completely.
The molten nuclear fuel first accumulates at the bottom of the reactor pressure vessel. More and more holes are forming and the bottom melts. The steam of the evaporated water forms hydrogen and oxygen, a highly volatile mix which reacts with the zirconium alloy of the fuel rods. On March 12, at 15h25 local time, a hydrogen explosion tears the building apart.
In an attempt to solve the problem, 8000 litres of water are pumped into the reactor per hour, but it completely evaporates or runs away, through the wrecked vessel into the basement.
Also a complete meltdown. At 06h10 local time on March 14th an explosion and a leak occurred in the containment building. A plume of radioactive white steam is seen outside the buildings. More than 10.000 litre of water per hour are pumped into the reactor.
Months after the disaster it becomes crystal clear that the molten cores in the reactors 1, 2 and 3, lie as lava on the floors of the reactor buildings and that further meltdowns can only be prohibited by constantly, 24/7, pumping large amounts of water into the buildings.
This reactor also faces a full-meltdown due to loss of coolant. On March 14, at 11h01 local time, an enormous explosion disseminates large amounts of radioactive fission products. The wind distributes them mainly in a northwest direction.
There are strong scientific indications that a partial nuclear explosion of the nuclear fuel takes place at this moment in the spent fuel pool, caused primarily by an hydrogen explosion. This could explain the much bigger explosion than the one that took place in reactor 1. Until today the Japanese authorities have not released the data of the measurements that could shine a light on this issue (as one can identify specific isotopes that only occur in spent fuel).
This reactor was turned off for maintenance work at the time of the earthquake. But without cooling the pond, where 1331 spent fuel rods were stored, it also heated up, the cooling water evaporated and a hydrogen explosion occurred. At 06h12 local time the building disintegrated, the rooftop was blown away and the pond started to leak.
Up to 210.000 litres of water had to be injected every day to cool the pond – which is an open air basin without any protection. The water evaporated and leaked away.
In the years after the reactor building was more-or-less stabilised by an overarching structure and in December 2014 all fuel rods were recovered and transferred to a central interim storage facility.
At first the authorities used helicopters to throw water into the fuel pond. However, just as in Chernobyl, this failed. Then water cannons of the army and the fire brigades were used. More and more so-called concrete-pumps were added, first pumping seawater, and later fresh water into the boiling spent fuel ponds, to prevent the fuel rods from melting further.
The authorities then discover that at reactor 2 highly radioactive water is running uncontrolled from the reactor through a manhole into the ocean. The water has a radiation level of 1000 mSv per hour. One hour exposure to this amount is enough to develop severe radiation sickness.
The leak is stopped on April 6 but the water subsequently passes through several smaller leaks and keeps flowing into the Pacific.
To make room for even more highly radioactive water TEPCO decides to dump 11.500.000 litres of water – which contained 150 billion becquerels – from a central water treatment tank directly into the ocean.
Neighbouring countries such as South Korea and China strongly protest against this act of desperation, which is only a temporary measure as long as millions of litres of water have to be pumped into the highly contaminated buildings – and contaminated water keeps running out of those buildings into the ground and the ocean.
Remote-controlled robots are sent into the reactor. On April 26 they measure radioactivity up to 1120 mSv/hour. To illustrate: the limit for German workers in the nuclear industry is 20 mSv /year.
At the end of April TEPCO workers enter the destroyed reactor building and try to lower the radioactivity in the building by installing air filters. After reviewing the inspection instruments and the results of intensive measurements the conclusion is made that there was a total meltdown of the fuel, and that there are too many holes and leakages in the building and that it does not make any sense anymore to keep flooding the reactor.
Measurements by the Japanese government show that in the first six weeks of the disaster 42% of the total amount of caesium that was released at the Chernobyl disaster – is spread, together with the highest ever release of the radioactive noble gas xenon. After the explosions also radioactive strontium (up to 250 kilometres from the plants) and plutonium (up to 45 kilometres from the plants) are measured, in addition to iodine and caesium.
Levels of radioactivity at the site were reduced by collecting the highly radioactive debris. But values up to 10.000 mSv/h were still measured at the exhaust stack between reactor 1 and 2. All highly radioactive debris is stored temporarily on the grounds in the Fukushima prefecture.
The radioactive materials were first blown towards the Pacific by the wind. After the explosion of reactor 3 the wind direction changed and regions more to the northwest of the accident got contaminated. Particularly high levels of radiation are measured in the soil outside the 30-km (evacuation) zone. Large parts of Japan are contaminated for at least 300 years) with caesium, mainly in the northeast. Parts of this region will remain uninhabitable and unusable for agriculture.
After a few days the effects of the nuclear disaster could be seen worldwide, although of course extremely diluted: the global system of measure points registered radioactive iodine and caesium in the atmosphere.
The release of medium and highly radioactive contaminated water (directly and through the groundwater) into the Pacific has already resulted in measurable exposure of marine organisms: fishing of sand eels near the affected coast has been forbidden, but the radioactive particles are also spread and absorbed by algae, mussels, fish and crabs.
The area around the nuclear power plants contains highly contaminated solid. The map shows the cumulative load. As an example: the maximum accepted value of 1 millisievert per year (mSv/y) was exceeded 427 times in the village of Namie (until February 2015).
An area of 600 km² around the nuclear power plants were contaminated with about 600 kBq/m² -the limit for permanent resettlement by the Russian authorities after the Chernobyl disaster.
The Japanese government has decided to scrape off the top layer of soil (5 cm depth), in order to reduce the radiation exposure to a maximum of 1 mSv/y. This must be done in an area of 2000 square kilometres, therefore 100 million cubic meters of radioactive soil has to be removed – and safely stored.
Already on the second day of the disaster all people were evacuated from a 20-km radius around the nuclear power plants. On day 5 it was decided that everyone in the area between 20 and 30 kilometres around the plant were to stay inside. On March 25, a ‘voluntary evacuation’ of the zone up till 30 kilometre was advised.
Unfortunately most of the people were evacuated to regions north-west of Fukushima – the area with the highest contamination.
Around 164.000 people were evacuated from the area around the damaged reactors. Some of them were able to stay with relatives or in hotels, but by far most of them have – for several months – lived in major sports and exhibition halls, where they slept on the ground. In the meantime 72.000 container units have been built for the evacuees. Even about 5 years after the disaster 118.000 people are still evacuated – with a very unclear future.
Compared to the deaths caused by the natural disaster (earthquake and tsunami) the direct cases of deaths by the man-made reactor disaster in Fukushima have been very low.
During the explosion at reactor 1 four workers were injured, and at the explosion at reactor 3 eleven workers. One clean-up worker died of circulatory failure.
Of the tested workers nearly 2000 were found to be contaminated with a radiation dose above 100 mSv – a dose which causes radiation related diseases. Six workers were contaminated with doses from 309 mSv to 678 mSv.
The information policy of Tepco and the Japanese authorities were very similar to what we have seen from the Soviet authorities in the aftermath of the Chernobyl disaster. The true consequences of the Fukushima disaster are yet to be recognised.