Japan's nuclear crisis seems to be getting worse, as officials say they think partial meltdowns have occurred at two reactors damaged by the earthquake and tsunami, and four others experienced serious cooling problems. They also said they were bracing for a second explosion, similar to the one that happened at the No. 1 reactor at Fukushima Daiichi Saturday when they vented hydrogen from the overheating plant, as they try to release pressure at the second failing reactor. The Japanese Nuclear and Industrial Safety Agency said as many as 160 people may have been exposed to radiation around the plant, and the Japanese news media said three workers at the station were suffering from radiation sickness. Though officials insist that the radiation leaks were small and didn't pose a major health risk, they did distribute iodine tablets to keep the thyroid gland from being exposed to radiation.