The V.I. Lenin Nuclear Power Station, known to the rest of the world as the Chernobyl Nuclear Power Plant, is 18 km northwest of the city of Chernobyl, 16 km from the border of Ukraine and Belarus and about 100 km north of Kiev. ​

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Construction of the plant began in 1970, with Reactor No. 1 commissioned in 1977. It was the third nuclear power station in the Soviet Union of the RBMK-type (after Leningrad and Kursk), and the first nuclear power plant on Ukrainian soil.

Chernobyl Power Plant before that fateful Saturday morning in 1986

​The completion of the first reactor in 1977 was followed by reactor No. 2 (1978), No. 3 (1981), and No. 4 (1983). Two more blocks, numbered 5 and 6, of more or less the same reactor design, were planned at a site roughly a kilometer's distance from the four older blocks. Reactor No. 5 was around 70 % complete at the time of block 4's accident and was scheduled to come online approximately six months later, on 7 November 1986. In the aftermath of the accident, the construction on reactors No.5 and No. 6 was suspended, and eventually cancelled in April 1989, just days before the third anniversary of the 1986 explosion. 

Reactor 4 covered by an aging sarcophagus

In the early hours of Saturday, 26th April, 1986 a safety test which simulated a station blackout power-failure and in which safety systems were deliberately turned off. A combination of inherent reactor design flaws and the reactor operators arranging the core in a manner contrary to the checklist for the test, eventually resulted in uncontrolled reaction conditions. Water flashed into steam generating a destructive steam explosion and a subsequent open-air graphite fire.This fire produced considerable updrafts for about nine days. These lofted plumes of fission products into the atmosphere. The estimated radioactive inventory that was released during this very hot fire phase approximately equalled in magnitude the airborne fission products released in the initial destructive explosion. Practically all of this radioactive material would then go on to fall-out/precipitate onto much of the surface of the western USSR and Europe.

The "New Safe Confinement" about to be rolled into place over the old sarcophagus.

A steel containment structure named the New Safe Confinement was built to replace the aging and hastily built sarcophagus that protected Reactor No. 4. Though the project's development was been delayed several times, construction officially began in September 2010.The New Safe Confinement was financed by an international fund managed by the European Bank for Reconstruction and Development (EBRD) was designed and built by the French-led consortium Novarka. Novarka built a giant arch-shaped structure out of steel, 270 m (886 ft) wide, 100 m (328 ft) high and 150 m (492 ft) long to cover the old crumbling concrete dome that had been in place for 30 years,

The casing will also meet the definition of a nuclear entombment device. On 14 November 2016, the arch began its expected five-day placement over the existing sarcophagus.However, it ended up taking fifteen days and was completed on 29 November 2016.

Despite all four reactors being decommissioned there are still several thousand people who work at the plant carrying out on-going waste management and site clearance tasks. Most of these workers come from Slavutych, the town built to replace Pripyat - a rail line connecting the two.

Chernobyl Nuclear Power Plant Links

World Nuclear Association - Very detailed WNA report on the accident in Reactor 4
Chernobyl Gallery - Superb collection of information and photographs
​Wikipedia - Wikipedia page on the Power Plant