Why was the Fukushima nuclear accident (loss of all power and core meltdown) not prevented? -March 2011

Why was the Fukushima nuclear accident (loss of all power and core meltdown) not prevented? -March 2011


The Fukushima Daiichi Nuclear Power Plant accident was triggered by the Tohoku earthquake and subsequent tsunami that occurred on March 11, 2011. After the earthquake, the reactors automatically shut down and the fission reaction stopped, but the core remained hot and required continuous cooling. However, the tsunami that struck shortly thereafter inundated the emergency power supply facilities and the power plant was in a serious condition of total power loss (station blackout). As a result, the cooling function was completely lost and the temperature inside the reactor rose dramatically. The fuel rods melted, resulting in a core meltdown.

In addition, the metallic zirconium used as fuel coating material underwent a chemical reaction with water at high temperatures, generating hydrogen, which filled the reactor buildings and caused a series of hydrogen explosions in Units 1, 3, and 4. This caused a large amount of radioactive materials to be released into the environment, resulting in serious damage to the surrounding areas.

The accident was caused by technological underestimation of natural disasters and institutional deficiencies. The plant's design neglected past tsunamis and assumed a maximum tsunami height of only 5.7 meters, which led to increased damage. In addition, the power plant itself was an outdated design from the 1970s, and its multiple layers of protection (layered protection) against tsunamis and earthquakes were inadequate. Furthermore, there was confusion in the initial response to the accident, which led to delays in the release of information and evacuation, and other factors that contributed to the worsening of the damage.

The nuclear regulatory system at the time was also problematic. The Nuclear and Industrial Safety Agency (NISA), which was in charge of safety regulations, was under the control of the Ministry of Economy, Trade, and Industry (METI), the parent body that promoted nuclear power, and as a result, its independence as a regulatory agency was not ensured and risks were not strictly monitored. It is believed that these deficiencies in the regulatory system contributed to the magnitude of the accident, and it has been strongly criticized as a "man-made disaster.

This accident was the most serious nuclear disaster in Japan's history, caused by a combination of overconfidence in the threat of natural disasters and human institutional vulnerability. Since then, it has triggered a general review of nuclear power safety, multiple protection, crisis management, and evacuation planning. It is a symbolic event that shows how important it is to be humble toward nature and rigorous in institutional design.