Even before the explosion on Saturday, officials said they had detected radioactive cesium, which is created when uranium fuel is split, an indication that some of the nuclear fuel in the reactor was already damaged. 1 reactor at the plant, rather than inside the reactor itself. An explosion occurred at the 40-year-old Daichi 1 reactor as plant operator Tokyo Electric Power Co (Tepco) tried to reduce pressure in the core after the total loss of power needed to keep water circulating to prevent it from overheating.  VIENNA Radiation leaked from Japan's quake-stricken Fukushima Daiichi nuclear plant on Saturday after a blast blew its roof off. View all New York Times newsletters. Photo 
 
 Those releases apparently did not prevent the buildup of hydrogen inside the plant, which ignited and exploded Saturday afternoon, government officials said.
– If it's been tough to gauge how much risk is posed by Japan's damaged nuclear plants, it's because officials have given what the New York Times describes as "confusing accounts" of exactly what's going on. Safety officials say the explosion at the Fukushima Dai-ichi plant destroyed walls of the building where the reactor is located, but not the metal housing enclosing the reactor, notes AP. The blast released radioactive material, but officials say the amounts are so small the public isn't endangered. Nevertheless, they widened the evacuation zone, warned people to stay inside, and prepared to distribute iodine tablets. Reuters rounds up assessments of experts, but the bottom line seems to be that more information is needed. "We don't know enough about what the status of the fuel is in the reactor core," says one. "The issue is whether the core is uncovered, whether the fuel is breaking up or being damaged, or whether the fuel is melting." The Washington Post talks to one doctor who arrived from Germany to provide relief, but is curtailing plans to go too far north. "I'd rather be working with a pocket knife in Haiti than worrying about the danger of a radioactive cloud."