On April 26, 1986, reactor number 4 at the Chernobyl Nuclear Power Plant near Pripyat, Ukraine, suffered a meltdown and steam explosion. The accident, caused by reactor design flaws and human error, was the worst nuclear power plant disaster in history. Pripyat, a town of 50,000, was evacuated, along with neighboring areas, and today remains uninhabited as part of the Chernobyl Exclusion Zone.
The reactor's roof collapsed in the steam explosion, and radioactive substances and fission products were released into the atmosphere. To contain the reactor, a large concrete sarcophagus was built and put in place in December 1986. But the sarcophagus was only expected to last 30 years before decaying.
On November 29, 2016, the New Safe Containment was slid into place around the reactor. Primarily made of steel and concrete, the New Safe Containment is an arch-like structure, weighing 1944.25 tons and measuring 843 feet wide and 354 feet tall. An incredible feat of engineering, it is expected to contain the Chernobyl reactor for the next 100 years.