The long-term damage from an accident at the Chernobyl nuclear power plant more than 30 years ago is still unknown. When explosions ripped through the reactor in rural Ukraine, then part of the Soviet Union, they spewed huge amounts of radioactive material into the atmosphere and caused the worst nuclear disaster in history. About 10,000 people have died or will die because of their exposure to radiation, and experts worry about the children born to parents who were living near the disaster area. With international help, Ukraine has enclosed the damaged reactor, giving scientists time to...