One of the reactors at Japan's crippled nuclear power plant will be covered in a giant tent. Officials hope the covering will keep radioactive material from spreading and keep rainwater from seeping in. Workers had been unable to erect the tent until now because of dangerous levels of radiation. Construction for the tent began this week and is scheduled for completion by the end of the September. If the tent is successful, similar coverings will be put over the other reactors at the plant.