Timeline of the Fukushima Daiichi nuclear disaster of caesium-137 by the Atmospheric Chemistry and Physics journal—an estimate about 42 percent of that released into the atmosphere in the Chernobyl explosion in 1986. Caesium-137 has a half-life of 30 years. TEPCO reports the completion of a cover for the reactor unit 1, which is 54 metres high, 47 metres wide and 42 metres deep. The cover has a built-in ventilation system that is supposed to filter radioactive material. Boric acid is injected into reactor number 2 after the discovery of xenon in its containment vessel. The presence of xenon may be an indication that a self-sustained fission reaction
Radiation effects from the Fukushima Daiichi nuclear disaster Ibaraki had been above regulatory limits between 16 and 21 March. On 26 March, IAEA reported that the values were now within legal limits. On 23 March, Tokyo drinking water exceeded the safe level for infants, prompting the government to distribute bottled water to families with infants. Measured levels were caused by iodine-131 (I-131) and were 103, 137 and 174 Bq/l. On 24 March, iodine-131 was detected in 12 of 47 prefectures, of which the level in Tochigi was the highest at 110 Bq/kg. Caesium-137 was detected in 6 prefectures but always below 10 Bq/kg. On 25 March, tap water