August are considered lethal for even brief human exposures, an exposure of 0.1 Sv being the normal accepted workplace exposure over 5 years and 8 Sv being a 100% lethal dose. Wednesday, 10 August Installation of the new, closed circulation cooling system is finished for all four damaged reactors (1–4), reactor 1 being the last. Previously, cooling was achieved with water injection by giant pump trucks. The water decontamination system is not working as well as expected, operating at roughly 66% of expected performance and suffering from numerous malfunctions. The system is necessary to decontaminate the large amount of radioactive water that remains on the site. September 2011 Thursday, 8 September The Japan Atomic Energy Agency calculates that a total of 15,000 terabecquerels of radiation has been released into the sea from the crippled Fukushima Daiichi power plant. Friday, 16 September Research indicates that the meltdown of reactor number 2 could have been avoided if water was injected to cool the reactor 4 hours earlier. Water injection was started at 8 pm on 14 March after the cooling system failed at 1 pm that day. The meltdown could have been avoided if injection had started by 4 pm. Wednesday, 21 September Typhoon Roke brings strong winds and up to 42 cm of rain to some areas of NE Japan. At the same time a magnitude 5.3 earthquake strikes just south of Fukushima. No significant problems are reported at the Fukushima Daiichi plant. Thursday, 29 September The measured core temperature falls below 100 degrees Celsius for all 3 damaged reactors with reactor number 2 finally achieving this status; reactors 1 and 3 had been below 100 degrees since August. Hydrogen is found at concentrations of 61 to 63 percent in pipes connected to the reactor 1 containment vessel. Plans are made to check for hydrogen in the pipes of all reactors and flush if necessary to prevent the possibility of another explosion. October 2011 Saturday, 8 October The Economist reports that high levels of radioactive particles, including plutonium have been found in an extended irregular zone that extends well outside the 30 km evacuation radius around the Fukushima Dai-ichi nuclear power plant. Monday, 31 October A French study by the Institute for Radiological Protection and Nuclear Safety revealed that the Fukushima nuclear disaster caused the biggest discharge of radioactive material into the ocean in history. The radioactive caesium that flowed into