High-level radioactive waste is residue left after uranium and plutonium are recovered from nuclear fuel used at nuclear power plants. It includes highly radioactive materials such as strontium, cesium and transuranic elements. The waste is extracted in liquid form and then mixed with glass to solidify it. The solid waste is then stored in a stainless steel tube that is 1.3m high and 40cm in diameter. The waste is very hot when placed in the tube, and it needs to be cooled for 30-50 years before it can be transferred to a permanent storage site several hundred meters underground. Filled tubes are being kept temporarily at a facility in Rokkasho, Aomori Prefecture, for cooling until a permanent storage site in Japan can be found.