In 1986, the Chernobyl nuclear reactor experienced a catastrophic accident and was encased in a sarcophagus. However, due to weathering and cracking, this structure needs to be replaced. Therefore, a new confinement structure is being built, which, due to the high radiation levels, will have to be slid across the old sarcophagus. This project will cost billions of dollars and the structure is expected to last a hundred years - although this is only a temporary solution. The half-life of uranium-238 is four and a half billion years, the same as the lifetime of the Earth. Therefore, in five billion years, only half of the uranium in the sarcophagus will have decayed away.