The Fukushima accident was caused by the loss of power, and situations started calming down with the return of power. It was during this time without power that core meltdown, hydrogen explosion and radiation release, all disasters that tremendously startled the world, took place. People evacuated from areas with possible radiation impact, around this time as well.

With the installation of temporary power sources on March 20, light returned to the site. With it, vitality was brought to on-site work and situations at the station gradually gained stability. Boiling inside the containment vessel came to a halt with the operation of the condensate injection line in June, which greatly reduced the amount of released radiation. The amount of Cesium released recorded 800 trillion Bq/h right after the accident, but it has now dropped to 10 million Bq/h, or nearly 1/100 millionth the highest value.

The situation subsided thanks to the return of power. Electricity is an inevitable prerequisite to any action in modern society. The Fukushima accident is a perfect example that shows both the preciousness of electricity and the horrors that may occur without it. On June 8, Prime Minister Noda appeared on TV regarding the restarting of Ohi Nuclear Power Station, where he clearly stated that nuclear power is necessary to protect the livelihoods of the people of Japan. The decision of the restart seems to be common sense, but his statement was one that took courage considering greater opposition to nuclear power these days. I personally wish to praise and commend the Prime Minister for his action. This action would save Japan.

Changing the subject slightly, not many people know that some safety equipment continued operating after the disaster, even without power. This allowed for continued core cooling at Units 2 and 3 for a certain amount of time. The main actor here is RCIC mentioned in the title of this article, and the differences in its operation came out as the difference in the time of explosions.

RCIC is safety equipment that injects the core with water stored inside the containment vessel, using a steam turbine-driven pump. The steam which drives the pump is generated by the energy of radioactivity (decay heat) inside the core. This enables core cooling even with the loss of power, just as it had been observed during the Fukushima Accident. The idea of driving the pump with decay heat, which would melt the core if left unattended, turns a possible negative into a positive, and thus, it is used in the design for the eight hours required for normal power restoration. Since this design is used almost worldwide, it could be argued that the ten days of power loss after the Fukushima accident was an unexpected event caused by the whole world.

RCIC was manually activated at Unit 2 immediately before the loss of D/C power due to tsunami, which continued operating after power was lost. It fought on for three days without any control. Looking at the retrieved data, it can be judged that the turbine was driven with poor-quality steam mixed with water to continue core cooling. Whether the turbine stopped due to turbine blade damage or steam pressure dropping remains a matter of speculation.

At Unit 3, on the other hand, D/C power fortunately survived the tsunami. This allowed RCIC to continue operating normally even after the tsunami. However, its operation time was limited by its battery life, and it eventually shut down after about one day. Unit 3 later experienced a core meltdown, leading to its explosion.

To elaborate further, Unit 3 could have avoided a core meltdown if the battery capacity was larger. The turbine at Unit 2 continued operating on its own for three days without any electrical control. The safety equipment at the station operated far beyond expectations. If power had been restored within 8 hours, as initially planned, the two reactors could have avoided their disasters.

This fact should be thoroughly recognized. Safety equipment operated as designed and performed beyond expectation in the Fukushima accident. We can be confident of the current safety equipment we have, and the current safety equipment policies are not to be blamed on.

However, even the best equipment will stop working without replenishment. The island defense forces at Attu, Saipan and Iwo Jima during World War II lost because they were out of supplies. It was not because the soldiers were weak. In the same way, the fact that power was lost for ten days turned tsunami damages into disasters. This point must be reviewed.

Considering the above, future improvements for nuclear safety rest upon expecting unexpected events that go beyond the design by training personnel and having preparation of supplies so that emergency response actions can be taken to mitigate the scale of the disaster.

Supply preparation should not be regulated by a single guideline, as siting characteristics differ by station. Instead, preparations should be made according to station characteristics, and every effort should be made in Japan as a whole.