Chernobyl disaster shelter maintenance. Workers inside the Object Shelter of reactor number four 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 and a 30km exclusion zone was created. A concrete sarcophagus, the Object Shelter, was built to contain the radioactive materials, but within the restricted area the radiation is still lethal to humans. However, up to 120 people work in shifts inside the shelter, performing maintenance and consolidation works.