Why are the fuel rods in storage tank still hot & emitting?

Are these fuels rods emitting the radioactive Iodine, Cs, Te? Does it mean that fission still going on inside these rods? Why is Plutonium missing when other particles are being detected. I just read an article saying that japan is now sending the soil samples for checking plutonium in it - so they suspect it as a possibility. http://www3.nhk.or.jp/daily/english/27_21.html