several hundred times it's normal operating power. and a big explosion right in the very center of the reactor where the fuel was. they have fragments of fuel. 150, 250 meters away from the plant and an enormous cloud release of radioactive material. we're 48 hours past when nuclear fission stopped here. a lot of the very worst of the radio activity will have died away we're several days away from safety. but i believe that the response has been proportionate and efficient. >> workers pouring sea water into the reactor to cool fuel rods. more than 50,000 people have been evacuated. 160 being tested for possible explosionure to radioactive material. cnn senior international correspondent matthew chance live with more on this story.