Understanding the accident of Fukushima Daiichi

Summary

On March 11, 2011, a massive earthquake and subsequent tsunami struck Japan, causing a nuclear disaster at the Fukushima Daiichi power plant. The event led to the meltdown of three reactors, hydrogen explosions, and the release of radioactive materials into the environment. The crisis was managed under extreme conditions, with workers battling to cool the reactors and prevent further contamination. The cleanup and decommissioning process is expected to last several decades, highlighting the long-term challenges of nuclear accidents.

Takeaways

• 🌏 A massive earthquake struck the Pacific coast of Honshu, Japan, on March 11th, causing widespread destruction and triggering a tsunami.
• 💧 The tsunami waves reached up to ten kilometers inland, leading to the death or disappearance of over 20,000 people and extensive damage to towns, ports, and land.
• 🔋 The Fukushima Daiichi nuclear power plant, located 250 km northeast of Tokyo, was severely affected by the disaster.
• ⚛️ Fukushima Daiichi has six boiling water reactors (BWRs), which differ from the pressurized water reactors by having a single system for feedwater and steam.
• 🚫 The earthquake caused the seismic sensors to trigger the insertion of control rods, stopping the fission reactions but leaving residual heat to be managed.
• 🛑 The tsunami disabled the emergency diesel generators, leading to a loss of core cooling in reactors 1, 2, and 3, which eventually led to meltdowns.
• 🔥 Hydrogen buildup due to the reaction of zirconium with steam led to explosions in the reactor buildings, further complicating the situation.
• 🌡️ The loss of cooling systems in the spent fuel storage pools posed a significant risk of radioactive release if not managed properly.
• 🌊 Seawater was injected into the reactor vessels as a last resort to cool and stabilize the corium, despite the long-term chemical issues it would cause.
• 🛠️ The crisis was managed by workers under extremely difficult conditions, who fought to cool the reactors and regain control of the plant.
• 🏗️ The long-term challenge involves spent fuel removal, radioactive waste management, and eventually decommissioning the site, a task expected to last several decades.

Q & A

What was the date and time of the powerful earthquake that struck the Pacific coast of Honshu, Japan?

The earthquake occurred on Friday, March the 11th at 2:46 p.m.

How did the tsunami impact the coastal areas of Japan after the earthquake?

The tsunami swept over the coast less than an hour after the earthquake, with waves going up to ten kilometers inland, resulting in over 20,000 people dead or missing and widespread destruction.

What is the Fukushima Daiichi nuclear power plant's location in relation to Tokyo?

The Fukushima Daiichi nuclear power plant is located 250 kilometers northeast of Tokyo.

How many reactors does the Fukushima Daiichi nuclear power plant have, and what type of reactors are they?

Fukushima Daiichi has six reactors, each commissioned during the 1970s, and they are boiling water reactors (BWRs).

What is the primary function of a boiling water reactor (BWR)?

In a BWR, the heat produced by fission reactions boils water, which then turns into steam to drive a turbine connected to a generator that produces electricity.

What is the process of dealing with residual heat in a nuclear reactor after shutdown?

Residual heat is the heat that continues to be produced even after the reactor is shut down. It is managed by keeping the fuel confined and cooled, which is a major safety issue.

What barriers are used to contain the fuel in a nuclear reactor?

The fuel is contained by multiple barriers: the fuel cladding made of zirconium alloy, the steel reactor vessel with cooling systems, and the containment building made of concrete with a leak-tight steel liner.

What happened to the Fukushima Daiichi reactors during the earthquake and tsunami?

The earthquake triggered the insertion of control rods, stopping fission reactions. The tsunami disabled the emergency diesel generators, leading to a loss of cooling for the reactors, which eventually resulted in core meltdowns in units 1, 2, and 3.

What is corium, and how did it form during the Fukushima Daiichi accident?

Corium is a molten mixture of nuclear fuel and reactor materials that formed when the fuel melted and mixed together at temperatures of around 2300 degrees Celsius during the meltdown.

What measures were taken to cool and stabilize the corium after the meltdown?

Seawater was injected into the reactor vessel to cool and stabilize the corium, despite the chemically active nature of salt.

What were the challenges faced by the workers during the initial crisis at Fukushima Daiichi?

The workers faced extremely difficult conditions, including being cut off from the rest of the world, without news from their families, no power supply, and the threat of radiation.

What is the current state of the Fukushima Daiichi nuclear power plant as of December 2011?

As of December 2011, the Japanese authorities officially declared that the nuclear power plant reached a cold shutdown state, where the cooling water remains liquid below 100 degrees Celsius and does not evaporate.

What are the long-term challenges for the decommissioning of the Fukushima Daiichi site?

The long-term challenges include removing the spent fuel from the pools for final storage, managing radioactive waste repositories, and eventually dismantling the site under the supervision of international experts, a task that is expected to last for several decades.