Hugh Pickens writes "Japanese nuclear experts are working to contain a partial meltdown at an earthquake-stricken nuclear power plant north of Tokyo, as fears grow that the death toll from Friday's massive quake and tsunami could reach the tens of thousands. A partial meltdown, experts said, would likely mean that some portion of the reactors' uranium fuel rods had cracked or warped from overheating, releasing radioactive particles into the reactors' containment vessels. Some of those particles would have escaped into the air outside when engineers vented steam from the vessels to relieve pressure building up inside. Adding to problems at the site, hydrogen was building up inside the Number Three reactor's outer building, threatening an explosion like the one that blew apart the Number One reactor building's roof and outer walls on Saturday. However, it remains unclear how far radiation has spread from the facility. Some local residents and health workers were diagnosed with radiation poisoning in precautionary tests, but they show no outward symptoms of distress. 'Even if you have a radiation release, although that's not a good thing, it's not automatically a harmful thing. It depends on what the level turns out to be,' says Steve Kerekes, a spokesman for the Nuclear Energy Institute, a US industry group, adding that a person exposed to the highest radiation levels measured at the Fukushima site would absorb in two to three hours the same amount of radiation that he would normally absorb in 12 months – a significant but not necessarily injurious amount, especially if exposure time was short."