The Chernobyl Nuclear Power Plant sarcophagus or Shelter Structure (Ukrainian: Об'єкт "Укриття", romanized: Ob'yekt "Ukryttya", Russian: Объект «Укрытие», romanized: Ob"yekt «Ukrytiye») is a massive steel and concrete structure covering the nuclear reactor number 4 building of the Chernobyl Nuclear Power Plant. Built in the aftermath of the 1986 Chernobyl disaster, the sarcophagus was designed to limit radioactive contamination of the environment by encasing the most dangerous area and protecting it from climate exposure. The sarcophagus locked in an estimated 200 tons of radioactive lava-like corium, 30 tons of highly contaminated dust and 16 tons of uranium and plutonium.
Structurally, the sarcophagus is largely supported by the damaged reactor building. By 1996, the structure had deteriorated to the point where numerous stabilization measures were required. Internal radiation levels were estimated to be as high as 10000 röntgens per hour in certain areas (normal background radiation in cities is usually around 20–50 microröntgens per hour, and a lethal dose is 500 röntgens over 5 hours). By 2017, the sarcophagus was surrounded by the New Safe Confinement structure, which is designed to protect the environment while the sarcophagus undergoes demolition and the nuclear cleanup continues. The reactor site is located within a large restricted area known as the Chernobyl Exclusion Zone.