Japan raised the assessment of its nuclear crisis to the most severe rating Tuesday, on the same level as the Chernobyl disaster, the world's worst to date. Some answers to questions about the assessment and health and safety concerns:
Q. Has the situation at the Japanese nuclear power plant worsened?
A. No. The heaviest radiation leaks at the Fukushima Dai-ichi nuclear complex occurred in the first days after the March 11 earthquake-triggered tsunami crippled the plant's cooling systems. Workers are trying to lower temperatures in the overheated nuclear reactors, but still don't have full control. Problems persist, like the leak into the ocean plugged last week, but authorities say the radiation leaks are declining.
Q. If the situation's not getting worse, why did Japan raise its assessment of the crisis?
A. The decision was based on new assessments of radiation leaks since the crisis began, rather than on deteriorating conditions. The new data showed emissions exceeding the threshold for a "major accident," level 7 on a 1-to-7 scale set by the International Atomic Energy Agency. Only one accident has previously rated 7, the 1986 meltdown at the Chernobyl nuclear power plant.