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
Windscale Piles There was a release to atmosphere of radioactive material that spread across the UK and Europe. The accident was rated a level 5 on the International Nuclear Event Scale. The chimney filters were credited with maintaining partial containment and thus minimising the radioactive content of the smoke that poured from the chimney during the fire. This included a large quantity of tritium, but it proved to be a negligible radiological hazard compared with the other radionuclides. The fire released an estimated of iodine-131, of caesium-137, of polonium-210 and of xenon-133. Iodine-131, which may lead to thyroid cancer, made the most