Fukushima: Ten Years On

Ten years ago, in the afternoon of 11 March 2011, a major earthquake measuring 9 on the Richter scale hit the east coast of Japan. The quake triggered a tsunami, with waves as high as 38 metres. The masses of water caused large-scale flooding and destroyed roads, the power supply and other infrastructure along Japan’s eastern seaboard.

What happened at Fukushima Daiichi?

The 2011 earthquake and tsunami also struck several nuclear power plants. Fukushima Daiichi sustained the worst damage, sparking a chain of events which led to core meltdown, major hydrogen explosions and massive releases of radiation.

The power plant site was inundated and large parts of the installations were destroyed. The reactors that were operating when the earthquake struck were automatically shut down immediately. With the earthquake causing widespread disruption to the national electricity grid, the plant was cut off from its external power supply. The tsunami caused the cooling water systems at all six Fukushima Daiichi reactors to malfunction. It also disabled the emergency electricity supply, which had been started automatically, to five out of six reactors; a station blackout occurred.

As a result, the electric pumps, which are imperative for long-term residual heat removal, failed. A replacement power supply could not be procured and activated in time. Without sufficient cooling, the water in the reactors steadily heated up and the volumes of water remaining in reactors 1-3 at the Fukushima Daiichi plant evaporated until finally the fuel rods were no longer covered with water. As a consequence, the temperature of the fuel assemblies rose dramatically.

The metal fuel rod claddings and the steam reacted chemically and produced large quantities of hydrogen. When there was an attempt to release pressure from the reactor vessels, high pressure pushed this hydrogen into the reactor buildings, where it came into contact with oxygen, causing a series of explosions. These explosions caused various degrees of destruction in the reactors. At the same time, the fuel rods became so hot that major damage to the reactor cores, including meltdown, occurred in the first, second and third reactor.

Detailed information can be found in an article by Dr Christian Pistner from the Oeko-Institut: Fukushima – Unfallablauf und wesentliche Ursachen, in the journal sicher ist sicher, 2013.

Who was responsible for the accident?

Fukushima Daiichi nuclear plant was not designed and had not been retrofitted to withstand an earthquake of this magnitude and its safety systems were not equipped to deal with such a massive tsunami or such high waves. As a result, no proper measures were in place to protect it from this type of earthquake-tsunami disaster.

The earthquake was the direct cause of the loss of the external power supply, while the tsunami disabled all the cooling systems and much of the plant’s own power supply.

Applicable reactor safety principles – such as storage of emergency diesel and batteries for the back-up power supply at physically separate locations – had not been properly implemented at the plant. Both the regulatory authorities and the plant operator lacked safety awareness and had failed to take appropriate safety measures at the site. They had ignored recent warnings about potential risks to the facility and had failed to implement international recommendations to improve safety. Instead, the operator – by his own admission – had sought to keep costs low and avoid any discussion of facility safety.

However, the Fukushima disaster has also clearly demonstrated that scenarios which are assumed to be impossible and are therefore excluded from contingency planning can nonetheless occur in reality.

Impacts on Japan’s energy policy

After the Fukushima disaster, Japan began a temporary shutdown of all its nuclear power plants to 2012. After a sweeping formal review, the Japanese government ordered on-site checks on safety standards at the nuclear power plants. To date, 21 of the 54 nuclear reactors in operation in Japan at the time of the accident have closed permanently. Of the remaining 33, nine reactors are back online (correct as at mid-2020); the future of the other 24 is still unclear.

The Japanese government has adopted new energy policy guidelines which reinstated nuclear power as part of the country’s energy mix. To what extent this will become reality remains to be seen, however. Although the construction of new nuclear power plants has been halted, Japan has not made an unequivocal commitment to a nuclear phase-out.

What still needs to be done to limit the damage?

Decommissioning the buildings and retrieving the fuel elements is a major project which is likely to take several decades. Experts predict that locating and safely recovering all the fuel debris from reactors 1, 2 and 3 will take 30-40 years. First, however, the reactor containment buildings will have to be cleared and decontaminated.

First of all, the fuel rods must be removed from the ponds. Work on retrieving the fuel from the damaged pressure vessels can then begin. The containment vessels must be repaired and flooded with water, both types of vessel must be opened, and the fuel must be packed securely and removed. There is intensive debate about the right way of proceeding. The fuel has partially melted and requires constant cooling, which poses major challenges for workers at the site. Radiation levels at the site remain very high, creating problems for repair and clean-up work. Although 10 years have passed since the core meltdown, the high levels of radiation in the installations mean that workers cannot enter the reactor containment buildings or can only do so for short periods.

Radiological effects of the disaster at the site and in the surrounding area

As before, the reactor pressure vessels, containment vessels and buildings – including, in some cases, the foundations – are wrecked and leaking, and radiation is still being released into the environment. In addition to the radiation from the reactor cores, large quantities of contaminated cooling water are still present at the site.

At affected locations around the plant, various decontamination measures have been carried out since 2012 with the aim of making some areas habitable again or further reducing radiation levels in those areas which are already occupied. These measures include spraying roof surfaces, removing topsoil to a depth of several centimetres, and collecting organic material.

This creates very large quantities of waste with low levels of contamination, for which temporary storage facilities have been set up in the Fukushima region. The long-term management of this waste is an issue which has yet to be resolved. Although these measures reduce local people’s exposure to radiation, it is doubtful whether they will be successful in the long term. In addition, wind or water can carry radioactive contamination from untreated into clean areas.

Fukushima province: two years after the accident

Further information