<Tr> <Th> Completed </Th> <Td> November 1986 </Td> </Tr> <Tr> <Th> Demolished </Th> <Td> To partially start in 2017 (estimated) </Td> </Tr> <P> The Chernobyl Nuclear Power Plant sarcophagus or Shelter Object (Ukrainian: Об'єкт "Укриття") is a massive steel and concrete structure covering the nuclear reactor No. 4 building of the Chernobyl Nuclear Power Plant . It was designed to limit radioactive contamination of the environment following the 1986 Chernobyl disaster, by encasing the most dangerous area and protecting it from climate exposure . It is located within a large restricted area known as the Chernobyl Exclusion Zone . The original Russian name is "Obyekt Ukrytiye" (Объект "Укрытие"), which means "sheltering" or "covering", as opposed to sarcophagus . The sarcophagus locked in 200 tons of radioactive corium, 30 tons of highly contaminated dust and 16 tons of uranium and plutonium . </P> <P> In 1996, it was deemed impossible to repair the inside of the sarcophagus as radiation levels were estimated to be as high as 10,000 röntgens per hour (normal background radiation in cities is usually around 20--50 microröntgens per hour, and a lethal dose is 500 röntgens over 5 hours). A decision to replace the sarcophagus with the New Safe Confinement was taken, and a project to reconstruct the enclosure has since been completed . </P>

Why do the ruins of the chernobyl disaster need to be covered