Chernobyl reactor 3 control room. Worker pointing at the two buttons used to initiate the shutdown of reactor number 3 at the Chernobyl nuclear power station, Ukraine. On 26th April 1986, reactor number 4 went out of control, leading to meltdown and an explosion. Around 1000 square kilometres of land were directly contaminated by radioactive fall-out. A concrete sarcophagus was built to contain the radioactive materials, but within the restricted area the radiation is still lethal to humans. After the explosion at reactor four, the remaining three reactors at the power plant continued to operate. In 1991, reactor two suffered a major fire, and was subsequently decommissioned. In November 1996, reactor one was shut down, followed by reactor three on 15th December 2000.