The Great East Japan Earthquake, followed by a massive tsunami, hits the Fukushima Daiichi nuclear power plant hard, causing its cooling system to fail.

Hydrogen explosions occur in the first and third reactors.

Hydrogen explosions occur in the second and fourth reactors.

The International Atomic Energy Agency (IAEA) gives the accident its highest rating of 7, the same as the Chernobyl accident.

Fukushima nuclear power plant confirms that around 300 tonnes of contaminated groundwater is flowing into the Pacific Ocean every day.

TEPCO (Tokyo Electric Power Company) proposes a basic strategy for dealing with nuclear wastewater, including freezing underground walls to prevent contaminated groundwater from flowing into the Pacific Ocean.

TEPCO states that the containers of nuclear effluent stored at the Fukushima plant are expected to be full around 2022.

The Japanese government says it plans to discharge treated nuclear wastewater into the Pacific Ocean.

Japan formally decides that it will begin discharging treated Fukushima nuclear wastewater into the sea in 2023.