cool the reactor. TEPCO workers turned off an emergency cooling system on reactor No. 3 for seven hours to try to switch to another system that was not working, allowing the reactor to overheat more quickly. 2012 19 January An attempt is made to view the state of the melted fuel in reactor 2 using a fibre-optic endoscope, however clear images of the water level and fuel location could not be obtained, probably due to the harsh environment inside the containment vessel. After radioactive water was discovered in a tunnel under reactor 2 on 18 December, the government directed TEPCO to survey the plant's underground facilities and check for more accumulation of radioactive water. TEPCO finds an additional 500 tons of water containing 16,200 Bq/cm3 of radioactive caesium in a pit near reactor 2, and 600 tons of 860 Bq/cm3 water near reactor 3. 22 February TEPCO begins pouring a 60-centimetre-thick layer of concrete over 70,000 square metres of the ocean seabed near the Fukushima Daiichi power plant in an effort to contain contaminated sediments. 27 March TEPCO measures atmospheric radiation at several points inside the containment vessel of reactor 2 for the first time, and reports values of 31.1 and 72.9 Sv/h. The utility states that radiation is too high for robots, endoscopes, and other devices to work properly. 5 April For the second time in 10 days highly radioactive wastewater is accidentally discharged into the sea. About 12 tons of wastewater leaks from a disconnected joint, a large portion of which flows into the sea through a drainage ditch. 5 May Japan's last remaining active nuclear reactor goes offline. Since the Fukushima Daiichi incident, nuclear reactors have not been allowed to restart after being shut down for maintenance or safety checks. One by one the number of active nuclear reactors has steadily decreased until the last of Japan's 54 nuclear reactors is finally taken offline. 22 May Japanese scientists report that the water depth inside the containment of unit 1 is only 40 cm; much lower than expected, and low enough to expose some fuel. From this observation, it is concluded that a 2 cm hole may exist in a pipe that is 40 cm from the bottom of the vessel. 24 May TEPCO releases new estimate of 900,000 terabecquerels for the total amount of radioactive material released from this facility into the environment. 5 July Japan once