The Fukushima Dai-ichi nuclear accident is a series of incidents, including four separate explosions, that took place at the Naraha nuclear power plant in Fukushima Prefecture, Japan, following the Tōhoku earthquake and tsunami on March 11. 2011. The Fukushima nuclear facility was a nuclear power plant to convert nuclear energy into electrical energy.
The accident was caused by an 8.9-degree earthquake near the northwest coast of Japan. Nuclear reactors 1, 2 and 3 stopped automatically at the time of the earthquake, while the remaining three reactors of the nuclear plant were already stopped for maintenance.
As a result of the earthquake there was a tsunami of 14 meters high. The tsunami flooded the six units, located on the seashore, damaging the power grid and emergency generators, preventing the operation of cooling systems.
After the earthquake the Fukushima reactors that were still working stopped automatically. To cool the reactors, in this type of nuclear power plants, electrical energy is needed, generally from the network, but because of the earthquake the electrical network did not work. Diesel engines started to operate to generate this electricity, but they also broke down at 3:41 p.m. when the tsunami hit. At this moment the cooling problems of the reactor core begin with the risk of melting the core. Later, the fusion of the core of the reactors 1, 2 and 3 would be confirmed.
Classification of the Fukushima nuclear accident
Level 7 of the INES scale is the same level at which the Chernobyl nuclear accident was classified, the highest possible. Although in the case of Chernobyl, the consequences were even worse than in the case of Fukushima.
First consequences of the tsunami at the Fukushima Daiichi nuclear power plant
As a result of the poor cooling of the reactors, the nuclear power plant suffered several explosions the day after the earthquake. In reactor 4, multiple fires were declared. In addition, in some plants spent fuel stored in pools of spent nuclear fuel, which still emitted large amounts of heat, began to overheat due to the evaporation of water from such pools.
Fear of leaks of nuclear radiation led authorities in Japan to evacuate first a radius of twenty kilometers around the plant. Later this radius was gradually extended up to 40km. Plant workers suffered exposure to nuclear radiation on several occasions and were temporarily evacuated at different times.
Chronology of the Fukushima nuclear accident
Events reported day after day at the Fukushima nuclear power plant after the earthquake.
Fukushima Friday, 11-3-2011
On March 11, 2011 an earthquake of 8.9 degrees on the Richter scale near the north east coast of Japan occurred at 2:46 pm (Japanese time). This earthquake reached the highest level in the history of Japan and was ranked as the fifth strongest earthquake in the entire planet since records have been recorded.
As a result of the earthquake there was a strong tsunami. A few hours after the earthquake, the first 10-meter waves reached the shores of Fukushima.
The safety systems of the nuclear power plants in the area were immediately activated: all the nuclear reactors in the region were stopped as foreseen in the design of these nuclear power plants for these situations.
Initially, a state of emergency was decreed in the 11 Japanese nuclear power plants in Miyagi, Fukushima and Ibaraki prefectures.
The following nuclear units were stopped:
- Onagawa nuclear power plant. Their three units were automatically stopped.
- Nuclear power plant of Fukushima Daiichi. Units 1, 2 and 3 were automatically stopped. Units 4, 5 and 6 were stopped for periodic maintenance.
- Fukushima Daini nuclear power plant. Their 4 units were automatically stopped.
- Tokai nuclear power plant. It had a single nuclear reactor that stopped automatically.
The cooling of the Fukushima Daiichi nuclear power plant required electrical power. For this, it had diesel electric generators (thermal motors for the generation of electricity) prepared to generate electric power if the power supply were cut off. However, initially there was no power supply and the diesel engines were damaged due to the flood after the tsunami. Therefore, instructions were given to evacuate residents within a 3km radius of the plant (about 2000 people).
Subsequently the supply of electrical power was solved, although at that time the pressure caused by the high temperatures in the nuclear reactor as a result of nuclear fission reactions was already very critical.
Fukushima Saturday, 12-3-2011
The Fukushima nuclear accident was classified as level 7 of the INES Scale by the International Atomic Energy Agency.
The radius around the nuclear power plant was extended to evacuate the population to 20km.
Fukushima Sunday, 13-3-2011
The number three reactor of Fukushima Daiichi suffered a hydrogen explosion.
Seawater was injected mixed with boric acid to the nuclear reactor with the intention of cooling it and having the integrity of the controlled containment enclosure.
In order to reduce the pressure in the Fukushima nuclear reactor, a controlled release of gases was carried out from the container of the external reactor (this action is called venting) as confirmed by the Japanese electricity company TEPCO.
Fukushima Monday, 03-14-2011
At this time, the Fukushima nuclear accident has already begun to provoke political reactions in other countries.
Angela Merkel, German Chancellor, confirmed the suspension for three months of the extension of the German nuclear power plants that allowed them to operate for longer than initially established.
Merkel considered that the supply of electricity in Germany will not be affected since the country was energetically eminently an electricity exporter.
Fukushima Tuesday 15-3-2011
During this night there was a new explosion at the Fukushima nuclear power plant, according to the Nuclear Safety Agency. The nuclear reactor affected was the number 4 reactor that was already stopped at the time of the earthquake. According to Tokyo Electric Power, the explosion caused a fire in the reactor.
During this day, the 50 workers who remained at the Fukushima facilities were evacuated trying to cool the reactor because of the high rate of radioactivity.
Fukushima Wednesday 16-3-2011
On Wednesday, workers evacuated from Fukushima returned to continue trying to lower the temperature of the reactor.
Due to the difficulty of using seawater to cool the reactor they tried to do it by launching it with an army helicopter. This action was also not feasible due to the high nuclear radiation in the area. Later it would try to do it with high pressure hoses that are used to disperse protesters.
The situation in the six reactors of the Japanese nuclear power plant was very serious: significant damage was observed in reactors 3 and 4. Reactor number 4 registered a new fire. In reactors 1 and 2 the nuclear fuel rods were also totally or partially damaged. Reactor 5, which was already off, the water level of the spent nuclear fuel pools continued to drop due to evaporation.
Fukushima Thursday 17-3-2011
On Thursday, army helicopters could fly over the Fukushima power station to pour seawater.
Due to the heat of the Fukushima power plant, the water from the nuclear fuel pools continued to evaporate. That is why it was necessary to fill-in.
The electric company Tepco, which owns the nuclear power plant, decided to send tankers with distilled water to fill the pools.
The pools are the first destination of spent fuel. When spent nuclear fuel is extracted from the reactor, it still generates too much heat and nuclear radiation to be able to transfer it to any nuclear waste management plant; You must first go through these pools to cool down and reduce your thermal energy levels.
The last resort was to install a 1km electric cable to operate the electric generators that would allow the cooling of the nuclear reactors.
Spokespeople for TEPCO and NISA denied that the spent fuel pool in unit 4 had been completely emptied, although efforts were still being made to improve their situation.
Fukushima Friday 18-3-2011
Japan decided to raise the emergency of the Fukushima nuclear power plant to level 5 at this time. The maximum level of the INES scale to classify the severity of a nuclear accident is 7. This meant that this nuclear accident would have far-reaching consequences and not of local scope as up to now.
The situation in Fukushima was stabilized. So that the state of the reactors did not get worse and the state of the spent nuclear fuel containment pools could be filled.
Work was still going on to re-establish the electric power in the nuclear reactors to be able to use the refrigeration systems themselves.
Fukushima Sunday 20-3-2011
Radioactive iodine was found in food products in the Fukushima prefecture, according to the International Atomic Energy Agency (IAEA). While the duration of radioactivity of iodine is short (about 8 days) it can be harmful to health.
What seemed obvious became official: The Japanese government announced that it would dismantle the Fukushima I nuclear power plant.
Fukushima Thursday 24-3-2011
Two workers at the Fukushima nuclear power plant were hospitalized after receiving high doses of nuclear radiation while continuing their work to carry power into reactor 3 to be able to use the cooling systems.
Fukushima Monday 28-3-2011
Finally, Tepco asked the French technicians for help to combat the nuclear crisis at the Fukushima power plant.
Plutonium was found at five points of the Fukushima nuclear power plant.
The Japanese government said it believed that the plutonium nuclear fuel rods could have been melted in the second Fukushima reactor when it came into contact with the water that was released to cool the reactor. This would explain the high rate of radiation found in the water.
Fukushima Tuesday 12-4-2011
The Japanese authorities raised the severity of the Fukushima nuclear accident from level 5 to level 7. The highest of the International Nuclear Accident Scale (INES scale). The same with which the Chernobyl nuclear accident was classified, the worst nuclear accident in the history of nuclear energy so far.
The reason for classifying the nuclear accident at level 7 was the emission of radioactivity abroad.
Although the Chernobyl accident and the Fukushima accident have the highest level of severity, at this time, the radioactive material released was estimated to be approximately 10% of that released in the Chernobyl accident.
In unit 1 of the Japanese nuclear power plant the pressure of the primary containment building was increased, compared to the values of the last days. Since April 6, nitrogen gas was being injected into the primary containment building of unit 1 to prevent hydrogen explosions from occurring. Nitrogen was also injected into the primary containment buildings of units 2 and 3.