What Happened to Fukushima Daiichi Nuclear Power Plant?

The Fukushima Daiichi Nuclear Power Plant, located in Ōkuma, Fukushima Prefecture, Japan, became the site of the world's most severe nuclear accident since Chernobyl on March 11, 2011. A magnitude 9.0 earthquake struck off the coast of Honshu Island, automatically shutting down reactors 1, 2, and 3. Approximately an hour later, a devastating 15-meter tsunami breached the plant's 5.7-meter seawall, inundating the site and disabling critical backup diesel generators and cooling systems. This led to a complete loss of AC power in five of the six reactors and subsequently DC power in Unit 1, preventing the circulation of cooling water to the intensely hot reactor cores.

The failure of the cooling systems resulted in core meltdowns in Units 1, 2, and 3, followed by hydrogen explosions in the reactor buildings of Units 1, 3, and 4 (Unit 4 was offline but suffered damage due to hydrogen backflow from Unit 3). These events caused significant releases of radioactive materials into the environment, leading to widespread evacuations and the declaration of a Level 7 'Severe Accident' on the International Nuclear and Radiological Event Scale (INES) on April 12, 2011. The immediate consequences included extensive environmental contamination of land and sea, mass displacement of residents, and a profound shift in Japan's energy policy away from nuclear power.

Key turning points in the aftermath included achieving a 'cold shutdown' state for the damaged reactors by December 2011, signifying stable cooling. Subsequently, the focus shifted to the long-term decommissioning roadmap, a process projected to take 30 to 40 years from the cold shutdown, aiming for completion by around 2051. A major challenge has been the accumulation of contaminated water, a mixture of cooling water, groundwater, and rainwater that has come into contact with melted fuel debris. This water is treated using the Advanced Liquid Processing System (ALPS) to remove most radionuclides, with the exception of tritium.

As of March 2026, the decommissioning efforts continue to face unprecedented technical challenges. The most prominent ongoing activity is the controlled release of ALPS-treated water into the Pacific Ocean, which began in August 2023. TEPCO completed its 17th round of discharge by December 2025, with a cumulative volume of approximately 133,000 tons. For fiscal year 2025 (ending March 2026), TEPCO planned seven rounds of discharge, and for fiscal year 2026 (April 2026-March 2027), it plans to increase the discharge to 62,400 tons over eight rounds. The International Atomic Energy Agency (IAEA) maintains a continuous presence at the site, monitoring the water discharge and consistently confirming that it meets international safety standards, with tritium levels well below regulatory limits.

The removal of melted fuel debris from the reactor containment vessels remains the most complex and dangerous task. While trial debris retrieval from Unit 2 began in September 2024, the full-scale removal from Unit 3, initially targeted for the early 2030s, has been delayed to at least 2037 due to the extreme radiation levels and technical difficulties. In February 2026, TEPCO unveiled a new 22-meter snake-like robot arm designed for inspecting and retrieving debris, with a third trial operation planned for later in the year. Concurrently, TEPCO is demolishing emptied treated water tanks to create space for new decommissioning facilities, including those for storing retrieved fuel debris. Preparatory work for fuel removal from Unit 1, including the completion of a large cover in January 2026, is underway, with fuel removal planned for fiscal years 2027-2028. Adding to the scientific intrigue, a February 2026 report indicated the discovery of active, seemingly 'normal' marine bacteria thriving in highly radioactive water within the plant's contaminated basements.