【Live Footagek】Real-time Monitoring of the Decommissioning Work at Fukushima Daiichi Nuclear Power Plant

The Long Battle Since 3.11: The Fukushima Daiichi Nuclear Power Plant Accident and the Path to Decommissioning

On March 11, 2011, the Great East Japan Earthquake and the subsequent tsunami caused a severe nuclear accident at the Fukushima Daiichi Nuclear Power Plant. This accident became the most serious nuclear disaster since the Chernobyl disaster in 1986. About 50 minutes after the earthquake, the plant was hit by a massive tsunami, damaging the power and equipment necessary for cooling the reactors. The fuel inside the reactors melted, causing hydrogen explosions and releasing radioactive materials into the atmosphere, soil, and ocean. As a result, some areas in Fukushima Prefecture were designated as evacuation zones, and return-restricted areas were established. Currently, decommissioning work is ongoing, with completion expected between 2041 and 2051.

【Recorded Footage】Tsunami Strikes Fukushima Daiichi Nuclear Power Plant (March 11, 2011)

【Recorded Footage】 Explosion at Fukushima Daiichi Nuclear Power Plant

【Live Footage】Restoration Work at Fukushima Daiichi Nuclear Power Plant

⇒Live Footage of Units 1 and 4 at Fukushima Daiichi Nuclear Power Plant by TEPCO

⇒Latest LIVE Footage of Flounder Being Raised in Treated Water Discharged from Fukushima Daiichi Nuclear Power Plant

【Timeline】 Hydrogen Explosion at Unit 1 of Fukushima Daiichi Nuclear Power Plant

Earthquake Occurrence ~ Emergency Shutdown
At 14:46 on March 11, 2011, the Great East Japan Earthquake occurred. Unit 1 automatically shut down as designed, with control rods inserted simultaneously with the earthquake.

Tsunami Arrival ~ Total Power Loss
The earthquake caused a loss of external power. Emergency diesel generators automatically started, and the emergency condenser began cooling the reactor core. About 50 minutes later, the tsunami struck. The emergency diesel generators, batteries, and power distribution panels were flooded, resulting in a total power loss. Consequently, all cooling functions, including the emergency condenser and high-pressure injection systems, were lost. Monitoring and measurement functions were also lost, making it impossible to confirm the reactor’s status.

Core Damage ~ Hydrogen Explosion
About four hours after the power loss, the cooling function stopped, causing the water in the pressure vessel to continue evaporating, exposing the fuel rods above the water surface. Core damage began. The exposed fuel rods’ temperature rose, reacting with steam to produce a large amount of hydrogen. The hydrogen leaked from the damaged containment vessel into the reactor building, accumulating at the top. At 15:36 on March 12, the hydrogen ignited for some reason, causing a hydrogen explosion.

Melted Core Drop
The melted core penetrated the bottom of the pressure vessel, eroding the concrete floor of the containment vessel.

Cause of the Accident
The primary cause was flooding due to the tsunami. The tsunami, far exceeding expectations, flooded the power and cooling equipment, leading to a loss of function, which was the fundamental cause of the accident. Particularly, the low position of the emergency diesel generators and insufficient tsunami countermeasures led to the total power loss. Additionally, measures to prevent hydrogen explosions were inadequate, and the explosion damaged the building, making subsequent responses difficult.

【Timeline】 Release of Radioactive Materials from Unit 2 of Fukushima Daiichi Nuclear Power Plant

Earthquake Occurrence ~ Emergency Shutdown
At 14:46 on March 11, 2011, the Great East Japan Earthquake occurred. Unit 2 automatically shut down as designed, with control rods inserted simultaneously with the earthquake.

Tsunami Arrival ~ Power Loss
The earthquake caused a loss of external power. Emergency diesel generators automatically started, and the reactor isolation cooling system also started. About 50 minutes later, the tsunami struck. The emergency diesel generators, batteries, and power distribution panels were flooded, resulting in a total power loss. However, the reactor isolation cooling system, which had been operating before the tsunami, maintained its function and continued injecting water for about three days.

Reactor Isolation Cooling System Shutdown ~ Core Damage
On March 14, the reactor isolation cooling system stopped. After the power loss, a power car was connected to the power distribution panel that had escaped flooding, and preparations for water injection with other cooling systems were underway. However, cables were damaged by the hydrogen explosion at Unit 1 (March 12), making the power car unusable. Additionally, the hydrogen explosion at Unit 3 (March 14) damaged the prepared fire trucks and hoses, making them unusable. After the reactor isolation cooling system stopped, depressurization was attempted to switch to the low-pressure injection system, but it took time, and during that time, the water level in the pressure vessel dropped, causing core damage. Hydrogen was also generated simultaneously.

Avoidance of Hydrogen Explosion and Release of Radioactive Materials Due to damage to the pressure vessel and containment vessel after core damage, hydrogen and radioactive materials leaked into the reactor building. However, at Unit 2, the panels on the upper side of the reactor building were opened by the impact of the hydrogen explosion at Unit 1, allowing hydrogen to be vented outside, avoiding an explosion in the reactor building. On the other hand, due to the failure of the vent (operation to lower the pressure inside the containment vessel), gas containing radioactive materials leaked directly from the containment vessel, and it is estimated that the most radioactive materials were released among Units 1 to 3.

Cause of the Accident
The primary cause was flooding due to the tsunami. The tsunami, exceeding expectations, flooded the power and cooling equipment, leading to a loss of function. Although the reactor isolation cooling system functioned for about three days, the delay in power restoration led to core damage. The hydrogen explosions at Units 1 and 3 also delayed the response to Unit 2, contributing to the expansion of the damage.

【Timeline】 Hydrogen Explosion at Unit 3 of Fukushima Daiichi Nuclear Power Plant

Earthquake Occurrence ~ Emergency Shutdown
At 14:46 on March 11, 2011, the Great East Japan Earthquake occurred. Unit 3 automatically shut down as designed, with control rods inserted simultaneously with the earthquake.

Tsunami Arrival ~ AC Power Loss
The earthquake caused a loss of external power. Emergency diesel generators automatically started, and the reactor isolation cooling system also started. About 50 minutes later, the tsunami struck. The emergency diesel generators were flooded, resulting in a total loss of AC power. However, the DC power equipment was installed at a higher position than Units 1 and 2, avoiding flooding and maintaining function. Consequently, the reactor isolation cooling system and high-pressure injection system continued to operate. Monitoring of the reactor’s status with instruments also continued.

High-Pressure Injection System Shutdown
About a day and a half later, the high-pressure injection system was stopped to switch to the low-pressure injection system. However, the depressurization operation took time, and during that time, the water level in the pressure vessel dropped, causing core damage. Hydrogen was also generated simultaneously.

Hydrogen Explosion After confirming depressurization, water injection with fire trucks was started, but a hydrogen explosion occurred in the reactor building at 11:01 on March 14 due to hydrogen leaked from the containment vessel.

Cause of the Accident The primary cause was flooding due to the tsunami. The flooding of the emergency diesel generators and the loss of AC power were the starting points of the accident. Although DC power was secured, unlike Units 1 and 2, the delay in the depressurization operation after stopping the high-pressure injection system led to core damage.

【Timeline】Hydrogen Explosion at Unit 4 of Fukushima Daiichi Nuclear Power Plant

At the time of the earthquake, Unit 4 was undergoing regular inspection and was not in operation, with all the fuel removed to the spent fuel pool. The total power loss due to the tsunami also resulted in the loss of cooling and water injection functions for the spent fuel pool, raising concerns about the water level dropping due to evaporation. Additionally, at 4:08 AM on March 14, it was confirmed that the water temperature in the spent fuel pool was 84 degrees, and it was predicted that the water level would drop to the top of the fuel by late March. Therefore, it was confirmed that there was some time to respond, but around 6:14 AM on March 15, a hydrogen explosion occurred in the reactor building of Unit 4. The cause is presumed to be the inflow of vent gas containing hydrogen from Unit 3 through the exhaust pipe during the containment vessel venting.