In a report on the Fukushima accident, the Japanese government has recognized deficiencies in preparedness and responses. However, it insists that lessons will be learned from the accident.
|Tsunami defences proved to be inadequate at Fukushima Daiichi (Image: Tepco)
The government has prepared the report ahead of the International Atomic Energy Agency (IAEA) ministerial conference on nuclear safety scheduled to take place later this month. The report, it says, "is a preliminary accident report, and represents a summary of the evaluation of the accident and the lessons learned to date based on the facts gleaned about the situation so far."
After the huge earthquake and subsequent tsunami struck on the afternoon of 11 March, the nuclear accident "followed at an unprecedented scale and over a lengthy period," the government said. It added, "For Japan, the situation has become extremely severe since countermeasures to deal with the nuclear accident have had to be carried out along with dealing with the broader disaster caused by the earthquake and tsunami."
The magnitude 9 quake subjected the Fukushima Daiichi plant to forces much greater than the plant was designed to withstand. However, the six reactors at the plant, as well as the four units at the nearby Fukushima Daini plant, appeared to have survived the earthquake relatively unscathed. "Although damage to external power supply was caused by the earthquake, no damage caused by the earthquake to systems, equipment and devices important for nuclear reactor safety has been confirmed," the report said. "However, further investigation should be conducted as the detailed status remains unknown."
It was the subsequent huge tsunami, however, that inundated the plants and damaged power grids in the region that ultimately led to the loss of back-up power and cooling functions at the reactors and used fuel ponds.
The tsunamis that hit the Fukushima Daiichi plant were 14-15 metres high, the report said, "substantially exceeding the assumed height by the design of construction permit or subsequent evaluation ... The assumption on the frequency and height of tsunamis was insufficient, and therefore, measures against large-scale tsunamis were not adequately prepared."
"The recurrence of large-scale earthquakes is expected to be appropriately considered," the government said. "Moreover, residual risks are required to be considered. Compared with the design against earthquake, the design against tsunamis has been performed based on tsunami folklore and indelible traces of tsunami, not on the adequate consideration of the recurrence of large-scale earthquakes in relation to a safety goal to be attained."
The report noted several issues that made bringing the accident under control more difficult. These included the life of the emergency batteries on the site being short compared with the time required to restore an external power supply. The accident also occurred at more than one reactor at the same time. The close proximity of the reactors, with some facilities being shared between units, also complicated response efforts. The used fuel pools being situated above the reactors at the Fukushima Daiichi units also presented problems, as did contaminated water being able to flow from the reactor buildings into the turbine buildings. Furthermore, hydrogen explosions "aggravated the accident."
Some accident management measures taken at the plant in an effort to stop the accident reaching a 'severe' level, and to mitigate consequences in such a case, "turned out to be inadequate." The report noted, "Although some part of the measures functioned, such as alternative water injection from the fire extinguishing water system to the reactor, the rest did not fulfil their roles in various responses, including ensuring the power supplies and the reactor cooling function."
Lesson to be learned
"This accident led to a severe accident, shook the trust of the public, and warned those engaged in nuclear energy of their overconfidence in nuclear safety," the government said. "It is therefore important to learn lessons thoroughly from this accident." It added, "We consider it inevitable to carry out a fundamental review on nuclear safety measures in Japan based on these lessons. Some of them are specific to Japan."
With regards to Japan's current regulation of its nuclear industry, the report claimed, "It was not clear who has the primary responsibility for providing sufficient activities to ensure citizen's safety in an emergency. Also, we cannot deny that the existing organisations and structures made mobilization of capabilities difficult to promptly respond to such a large-scale nuclear accident." As a result, the government said that it would work towards making the nuclear regulator more independent by separating the Nuclear and Industrial Safety Agency (NISA) from the Ministry of Economy, Trade and Industry (METI), which promotes the use of nuclear energy. In addition, it will "review regulatory and administrative frameworks on nuclear safety and a structure of environment monitoring operation." It also stated, "We will be committed to reviewing and improving the legal structures on nuclear safety and nuclear emergency preparedness and related criteria and guidelines."
The government said that it is "taking very seriously the fact that the accident, triggered by a natural disaster of an earthquake and tsunami, became a severe accident due to such causes as the losses of power and cooling functions, and that consistent preparation for severe accidents were insufficient. In light of the lessons learned from the accident, Japan has recognised that a fundamental revision of its nuclear safety preparedness and response is inevitable." It noted, "It is necessary for Japan to conduct national discussions on the whole concept of nuclear power generation while disclosing actual costs of nuclear power generation including for securing safety."
"This nuclear accident has turned to be a major challenge for Japan, and Japan is now responding to the situation, with the relevant domestic organisations working together, and with support from many countries around the world," the report said. "Japan also takes it very seriously and with remorse that this accident has raised concerns around the world about the safety of nuclear power generation. And above all, Japan feels sincere regret for causing anxiety among the people all over the world about the safety of nuclear power facilities and the release of radioactive materials."
However, the government stated, "We are prepared to confront much difficulty towards restoration from the accident, and also confident that we will be able to overcome this accident by uniting the wisdom and efforts of not only Japan, but also the world."
The IAEA ministerial meeting is set to take place in Vienna between 20 and 24 June with the primary purpose of drawing on the lessons from the Fukushima accident in order to strengthen nuclear safety throughout the world.
Researched and written
by World Nuclear News