From December 2011, reposting it today so that people won’t think that the March 2011 Fukushima Daiichi nuclear disaster is behind us.
“After 280 days of decaying, the 257 tons of lost corium from three of Fukushima’s reactors, which one assumes to have a burn rate of 14GWJ/t (14 kg fissioned per tonne), have produced a probable level of radioactivity of 180.37 million Curies, or 6.674E18 Becquerels (6673.6 PBq). […]
92.17% of this radioactivity is being emitted by fission products, and constitutes 28.07% of overall radiotoxicity. 7.83% of this radioactivity is made by activation products, and constitutes 71.93% of overall radiotoxicity. That is to say that here the radiotoxicity, which according to the eminently official ICRP’s dose factors equals 73.47 Billion potential lethal doses via inhalation and 15.53 Billion lethal doses via ingestion, results chiefly from the activation products, which by and large are alpha emitters.
On the other hand, the radioactivity in this case is produced primarily by fission products, which most often are beta (β− ) emitters. At the end of these 280 days of decaying, the radiation arises primarily from the following elements: Strontium 89 at 2.265%, Strontium 90 at 4.713%, Yttrium 90 at 4.713%, Yttrium 91 at 4.852%, …
…Yttrium 91 at 4.852%, Zirconium 95 at 8.067%, Ruthenium 106 at 9.297%, Caesium 134 at 4.737%, Cesium 137 at 6.209%, Barium 137 at 6.209%, Cerium 144 at 23.744%, Promethium 147 at 13.728%, Plutonium 241 at 5.505%, Cobalt 60 at 1.410%.
Consistent with the rate of decay of these 280 days, in 15 years the fuel will have lost 80.20% of its radioactivity, bringing it to 35.71 Curies – but its long-lived toxicity will be elevated by 13.35%, contrarily, to 83.28 Billion lethal doses. Without question, the overall radioactivity falls but the persistent radiotoxicity increases until 60 years or so later, it commences to decline ever-so slowly after 350 years! (This irrefutable augmentation of toxicity over time is largely due to the increase of Americium-241 – alpha – a daughter product far more toxic than its beta-emitting parent, Plutonium-241. Ultimately, it will take around 350 years for the radiotoxicity to return to its original level…”