TEPCO has revised the readings on the radioactivity levels at the Fukushima No. 1 nuclear plant well to 5 million becquerels of strontium per liter – both a record, and nearly five times higher than the original reading of 900,000 becquerels per liter. Strontium-90 is a radioactive isotope of strontium produced by nuclear fission with a half-life of 28.8 years. The ...