Taken from the book ‘Dark Pripyat‘, by Ric Wright & Fraser Blakemore
The disaster began during a systems test on Saturday 26th April 1986 at reactor number four of the Chernobyl nuclear power plant in the northern area of the Ukraine.
At 01.23 local time, there was a sudden power surge inside reactor four, in order to try to stem the extent of the surge an emergency shutdown was attempted. Due to a number of human failures and a flaw in the reactors RBMK control-rod design a more extensive spike in power output occurred, which led to a reactor vessel rupture and a series of explosions.
Within seconds of the original power surge, the emergency procedure was underway but the length or time required by the cooling water generators and the movement rate of the control-rods to achieve affective speeds and positions was too great. There was a massive build up of steam pressure within reactor four which ruptured the fuel channels and eventually the reactors 2000-tonne shield covering, the force of the explosion sent the shield cover 100ft into the air.
The remaining liquid coolant immediately turned to steam escaping the ruptured reactor which in turn released most of the nuclear material to the atmosphere.
The Chernobyl disaster went on to be the worlds worst nuclear disaster, the effects and fallout of the explosions at reactor number four reached as far as Sweden and the United Kingdom. At first, the Ukranian government denied that anything was wrong at the stricken power plant, fire fighters were not aware that this was anything other than a routine fire. It was only two days after the accident when radiation scanners at a power plant in Sweden were activated that the Ukranian officials admitted anything was wrong.
The worst of the debris was collected inside what was left of the reactor, much of it shovelled by the ‘Liquidators’ wearing heavy protective suits (dubbed ‘bio-robots’ by the military); these workers could only spend a maximum of 40 seconds at a time working on the rooftops of the surrounding buildings because of the extreme high doses of radiation given off by the blocks of graphite moderator and other debris.
The reactor itself was covered by bags of sand, lead and boric acid dropped from helicopters, some 5,000 metric tons of material were dropped during the week that followed the accident. At the time there was still fear that the reactor could re-enter a self-sustaining nuclear chain-reaction and explode again.
The initial ‘sarcophagus’ was the largest civil engineering task in history, involving a quarter of a million construction workers who all reached their official lifetime limit of radiation. By December 1986 a large concrete sarcophagus was erected to seal off the reactor and its contents.