Fukushima Daiichi Accident FAQ

What actually happened at Fukushima Daiichi?

On 11 March 2011, the strongest earthquake ever recorded in Japan shook the country for six minutes. The earthquake and the ensuing tsunami resulted in the death of 19,729 people (with 2559 still missing) and devastated communities up and down the country. Reactors close to the earthquake, including those operating at Fukushima Daiichi, shut down as designed.

However, due to insufficient sea defences, the Fukushima Daiichi plant’s backup generators, which were meant to pump cooling water through the reactor, were destroyed by the 15-metre tsunami. As a result, the cores of units 1-3 largely melted over the following three days, and the accumulation of hydrogen produced by the reaction of the hot fuel cladding with water resulted in several hydrogen explosions in units 1, 2 and 4, as well as the release of nuclear material into the surrounding environment.

Since then, efforts have been underway to decommission the damaged reactor buildings (alongside units 5 and 6, which were also closed after the accident), a process which is going to take 30-40 years.

What are the health effects of the accident?

The radiation doses to which the general public were exposed during and after the accident were very low. The United Nations Scientific Committee on the Effects of Atomic Radiation concluded in 2013 (and reaffirmed in 2015) that “no radiation-related deaths or acute diseases have been observed among the workers and general public exposed to radiation from the accident” and that “no discernible increased incidence of radiation-related health effects are expected among exposed members of the public or their descendants.”

More than 160,000 people were evacuated following the tsunami and the nuclear accident, of which about 41,000 have not been able to return home yet. These evacuations were in many places rushed and had a near-immediate toll among the frail elderly and those requiring care in hospitals. As of September 2020, 2313 indirect disaster-related deaths among evacuees from Fukushima Prefecture had been identified.  

Just as following the Chernobyl accident, the main health effects of the Fukushima Daiichi accident have not been caused by radiation, but rather caused by the countermeasures, and psychosocial aspects. It has been established that there has been a dramatic increase in depression, PTSD, substance abuse, and suicides, driven partially by the evacuations, partially by stigmatisation, and partially by an amplified perception of radiation risks which goes far beyond the scientific evidence.  

What are the lessons learned? Can we prevent this from happening again in the same circumstances?

A number of lessons were learned from the accident.

From a design viewpoint, it was clear that the decision to place backup generators in the basement was incorrect, as they were flooded by the tsunami. Placing them higher up, as is the case at other Japanese power plants, would have prevented this. Equally, the sea walls at Fukushima Daiichi were insufficient, with historical evidence suggesting previous tsunamis had been higher than the existing sea walls.

In response to the accident, governments, regulators and nuclear operators around the world carried out ‘stress tests’ on their plants to explore how they could minimize the risk of similar accidents happening. Existing units have been hardened against extreme external events. New reactor designs have incorporated these systems and emergency response regulations have introduced the lessons learned from the event.

In addition, there have been global efforts to move to a more systematic and holistic approach to safety, with more effective coordination between regulatory authorities, government and industry. There has also been more emphasis on the importance of cultural aspects in organizational and safety culture.

There has also been a considerable debate about the decision to evacuate and subsequently relocate people following the accident. The unduly rushed evacuations caused a near-immediate death toll among vulnerable patients, and more than 2300 indirect disaster-related deaths have been recognized. A study by Waddington and colleagues published in 2017 which looked at the long-term evacuations concluded that “…no relocation was justified on scientific and economic grounds after the accident at Fukushima Daiichi”.

However, it is important to acknowledge that there was considerable uncertainty in the early phases of the accident and the actions taken by the Japanese government should be viewed in that light. When facing future scenarios concerning public health and safety, whatever the event, it is important that authorities take an all-hazards approach. Actions taken to mitigate against a situation should not result in worse impacts than the original events. It is crucial that the decision of whether to evacuate takes into account the very real dangers associated with evacuations, that evacuations remain a matter of last resort, and that people are allowed to return home much faster than following the Fukushima Daiichi accident.   

What’s the deal with the water that is being stored at Fukushima Daiichi?

A large volume of contaminated water was generated during the accident and additional water has become contaminated and accumulated as water became in contact with radioactive material or reactor fuel debris. This contaminated water comes from the continuous and ongoing cooling of the damaged reactors, as well as groundwater and rainfall flowing into the plant buildings. Processes to clean the contaminated water have been implemented that have been very effective in removing nearly all the radioactivity, with the exception of tritium. Tritium, which is a slightly radioactive type of hydrogen, cannot be removed as it is part of the water molecules. However, the concentrations of tritium are far below those resulting in any harm to humans, animals or the environment.

As of March 2020, there are more than 1.2 million tonnes of treated water stored in some 1000 tanks at the site.

By the summer of 2022, the capacity for storing treated water will be reached. Two options for the safe disposal of this water have been proposed: either releasing it slowly into the sea (which is the international best practice) or releasing it as water vapour. The radiation doses of either options would be well below background radiation levels, and thus would pose no risk of harm to humans, animals or the environment. The UN’s International Atomic Energy Agency supports both options, and it is now up to the Japanese government to decide which option they prefer.


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