Caesium-137 alienation around the Chernobyl nuclear power plant. Together with caesium-134, iodine-131, and strontium-90, caesium-137 was among the isotopes distributed by the reactor explosion that constitute the greatest risk to health. The mean contamination of caesium-137 in Germany following the Chernobyl disaster was 2000 to 4000 Bq/m. This corresponds to a contamination of 1 mg/km of caesium-137, totaling about 500 grams deposited over all of Germany. In Scandinavia, some reindeer and sheep exceeded the Norwegian legal limit (3000 Bq/kg) 26 years after Chernobyl. As of 2016 the Chernobyl caesium-137 has decayed by half, but could have been locally concentrated by much
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