Fukushima Daiichi Nuclear Power Plant
After the Chernobyl disaster, the atomic safety workmen used 1,800 metric tonnes of sand and clay cover the plant. This created a problem because they were thermal insulators and trapped heat inside. So first a non-evaporating coolant such as a liquid metal has to be put on it. After it has all cooled off a structure such as the Chernobyl Nuclear Power Plant 'sarcophagus tomb'.