3D Reconstruction of Fukushima’s Nuclear Disaster

本站添加: 2026-05-31

[00:00:02]On March 11th, 2011, a tsunami triggered by a magnitude 9 earthquake struck a large part of Japan's northeastern coast, severely impacting the Fukushima Daiichi Nuclear Power Plant.

[00:00:13]The destruction and flooding of several critical facilities caused the explosion of four out of the six plant units, releasing large amounts of radioactive steam and contaminated gases outside.

[00:00:25]But to fully understand the elements involved and the sequence of events, we have conducted a profound technical analysis to determine how the facts occurred and to know what causes triggered the reactors' explosions.

[00:00:40]On March 11th, 2011, at 14:46, the northeastern coast of Japan suffered one of the most powerful earthquakes ever recorded, a magnitude 9 megathrust on the Richter scale, which shook the Tohoku region for almost 6 minutes.

[00:00:56]That day at the Fukushima Nuclear Power Plant, reactors number one, two, and three were operating at full capacity, while units four, five, and six were completely shut down for maintenance and nuclear refueling procedures.

[00:01:09]Each unit features a boiling water reactor.

[00:01:11]Within this specific type of reactor, water circulates directly through the core, boils inside the pressure vessel itself, and the generated steam drives the electric turbines.

[00:01:21]The containment of these reactors possessed a relatively compact design, featuring a toroidal structure partially filled with water, whose function was to condense steam in case of an accident, reducing pressure inside the primary containment.

[00:01:35]The problem was that the total volume of that containment was relatively small compared to subsequent designs. This implied that a rapid increase in temperature and pressure could completely saturate it within a few hours.

[00:01:47]The very instant that seismic vibrations commenced, the automated system successfully detected the ground acceleration and immediately executed an emergency shutdown procedure.

[00:01:58]All control rods were completely inserted into the active reactor cores to halt the nuclear chain reaction.

[00:02:04]However, even with the reactor shut down, the nuclear fuel continues producing energy due to radioactive decay heat.

[00:02:12]Right after the reactor shutdown, residual heat still amounted to approximately 7% of the total reactor power.

[00:02:18]That means tens of thermal megawatts accumulating inside the core, which if not continuously extracted, causes the fuel temperature to begin increasing in a gradual manner.

[00:02:29]During the first minutes following the earthquake, everything functioned as anticipated. The external electrical grid was lost almost immediately, but the emergency diesel generators started correctly and the cooling pumps continued operating.

[00:02:46]Approximately 50 [music] minutes following the earthquake, a series of waves exceeding 49 ft in height struck the station.

[00:02:52]The water overtopped the protective seawalls and penetrated deep [music] inside the turbine buildings and electrical rooms.

[00:02:59]Within a matter of minutes, the facility suffered a complete loss of electrical power supply.

[00:03:04]The diesel generators became flooded, the electrical switch gear was rendered useless, >> [music] >> and the cooling pumps stopped operating.

[00:03:11]The reactors were still producing residual decay heat, but practically every single system capable of extracting it had completely vanished at the exact same time.

[00:03:21]Unit 1 was the very first to enter a critical situation. It was also the oldest of the plant and featured a passive cooling loop known as the isolation condenser.

[00:03:30]Within this system, reactor steam escalated toward a heat exchanger where it condensed and returned to the reactor via gravity.

[00:03:37]In theory, it could function entirely without external electrical power, but the system depended on electrically actuated valves and on human operators who had to manually manage its operational behavior.

[00:03:50]Following the total loss of power, the system ceased to operate correctly, and for hours the operators believed that the reactor was still being cooled.

[00:03:57]Although in reality, the water level inside the pressure vessel was dropping rapidly.

[00:04:02]As the water continued to recede, the fuel rods composed of zirconium alloy cladding tubes began to become fully exposed. Nevertheless, zirconium possesses a critical property. At elevated temperatures, it reacts violently with water steam.

[00:04:18]That reaction began to release even more heat inside the reactor and generated massive quantities of hydrogen gas.

[00:04:24]When temperatures exceeded approximately 4,000° [music] F, the fuel began to melt and part of the core collapsed toward the bottom of the vessel, forming a mass known as corium, a radioactive mixture of molten fuel [music] and structural materials.

[00:04:38]At 15:36 on March 12th, unit 1 exploded due to the accumulation of hydrogen and oxygen inside the building, causing a detonation that completely tore away the roof and upper walls of the concrete structure.

[00:04:55]The next unit to exhibit serious complications was number 3.

[00:04:59]In this specific case, the reactor featured steam-driven pumps capable of injecting water even without external electrical power.

[00:05:07]For a period, these systems maintained the core relatively stable, but they presented the issue of being battery-powered. So, when the pressure and temperature of the suppression chamber began to rise, the system started to progressively degrade quite rapidly.

[00:05:20]The core began to melt during the early hours of March 13th, and operators attempted to inject water utilizing improvised firefighting pumps. But the internal pressure of the vessel was so high that water could not enter, requiring partial depressurization of the reactor to allow the injection, which released even more hydrogen and contaminated steam.

[00:05:40]At 11:01 on the morning of March 14th, the building of reactor 3 exploded, causing a significantly more violent detonation than that of unit 1. Debris was thrown hundreds of feet around the plant, and large metallic fragments fell upon adjacent facilities.

[00:05:55]Probably part of that violence was due to a greater accumulation of hydrogen and a different containment within the upper structure itself.

[00:06:03]Following the explosion of unit 3, unit 2 became the most complex problem of all.

[00:06:08]Although initially the cooling system resisted longer than in the other units, when the system finally ceased to function, the degradation occurred in an extremely rapid manner.

[00:06:17]The core began to become fully exposed, the temperature increased rapidly, and the zirconium started to react with the steam generating hydrogen gas.

[00:06:27]During the early hours of March 15th, the suppression chamber of reactor 3 exploded. Although it was not an external explosion like in the case of units 1 and 3.

[00:06:37]In the previous explosions, the reactors preserved part of their primary containment. Conversely, in unit number 2, a large part of the radioactive emissions ended up escaping directly from the damaged containment.

[00:06:53]Following the destruction and confusion generated by the previous explosions, unit 4 began to present a different problem.

[00:06:59]Although the reactor was shut down and had no fuel inside the core as it had been entirely transferred to the spent fuel pool. That pool contained over 1,300 assemblies and continued generating a considerable amount of residual decay heat.

[00:07:15]Furthermore, during the events in unit 3, a significant amount of hydrogen flowed through shared ventilation and gas treatment ducts into the unit 4 building, which combined with a total loss of electrical power ultimately created a critical situation.

[00:07:29]On March 15th, the building of unit 4 exploded, completely destroying the upper structure of the facility, and generating massive international dread regarding the actual condition of the pool.

[00:07:40]Firefighters began to inject seawater utilizing improvised pumping equipment and later military helicopters and water cannons were deployed to drop water directly over the fuel pools.

[00:07:52]Fortunately, with the passing of days, they managed to successfully re-establish a continuous water injection and stabilize the overall temperature of the pool.

[00:08:01]Units 5 and 6 were able to maintain sufficient cooling until reaching a cold shutdown state thanks to the fact that both units preserved a functional diesel generator situated in a higher and more protected area.

[00:08:17]During the months following the explosions, water injection was continuously maintained to keep the cores cooled and later on they began to introduce nitrogen gas into the containments to permanently prevent new hydrogen explosions.

[00:08:30]Finally, in December 2011, the Japanese government officially declared that the reactors had successfully reached a stable cold shutdown condition.

[00:08:40]The nuclear disaster at the Fukushima plant released large amounts of radioactive steam and contaminated gases containing elements such as iodine 131 >> [music] >> and cesium 137, two highly radioactive fission products that severely contaminated the environment. [music] Enormous quantities of water utilized to cool the molten reactor cores became heavily contaminated and a portion of it ended up [music] leaking into the sea.

[00:09:05]Although the emissions were considerably lower than those at Chernobyl, the accident forced the evacuation of over 100,000 people and left extensive areas uninhabitable for decades.

[00:09:16]Following the accident, practically the entire global nuclear industry thoroughly revised its safety protocols.

[00:09:23]Additional filtered venting systems were installed and passive autocatalytic hydrogen recombiners were added. Many emergency generators were relocated to elevated areas or protected against flooding and quick connections for mobile pumps and external electrical power sources were also developed.

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[00:09:52]Thank you very much for watching. I'll be reading your comments below and I'll see you in the next video.