Chernobyl (2019) - Cleaning The Roofs Scene

HISTORY
This fire produced considerable updrafts for about nine days[5] before being finally contained on 4 May 1986.[6] The lofted plumes of fission products released into the atmosphere by the fire precipitated onto parts of the USSR and western Europe. The estimated radioactive inventory that was released during this very hot fire phase approximately equaled in magnitude the airborne fission products released in the initial destructive explosion.[7]

The total number of casualties, including deaths due to the Chernobyl disaster, remains a controversial and disputed issue.[8] During the accident, steam-blast effects caused two deaths within the facility: one immediately after the explosion, and the other compounded by a lethal dose of radiation. Over the coming days and weeks, 134 servicemen were hospitalized with acute radiation syndrome (ARS), of whom 28 firemen and employees died within months.[9] Additionally, approximately 14 radiation induced cancer deaths among this group of 134 hospitalized survivors were to follow within the next 10 years.[10] Among the wider population, an excess of 15 childhood thyroid cancer deaths were documented as of 2011.[11][12] Additional time and research is required to definitively determine the elevated relative risk of cancer among the surviving employees, those that were initially hospitalized with ARS, and the population at large.[13]

The Chernobyl accident is considered the most disastrous nuclear power plant accident in history, both in terms of cost and casualties. It is one of only two nuclear energy accidents classified as a level 7 event–the maximum classification—on the International Nuclear Event Scale, the other being the 2011 Fukushima disaster in Japan.[14] The struggle to safeguard against scenarios that were perceived as having the potential for greater catastrophe,[15] together with later decontamination efforts of the surroundings, ultimately involved over 500,000 liquidators, and cost an estimated 18 billion rubles.[16]

The remains of the No. 4 reactor building were enclosed in the Shelter Structure, a large cover whose purpose was to reduce the spread of remaining radioactive dust and debris from the wreckage, thus limiting radioactive contamination, and the protection of the site from further weathering. The structure was finished in December 1986, at a time when what was left of the reactor was entering the cold shutdown phase. The enclosure was not intended to be used as a radiation shield, but was built quickly as occupational safety for the crews of the other undamaged reactors at the power station, with No. 3 continuing to produce electricity until 2000.[17][18] An international team enclosed both the No. 4 reactor building and the original sarcophagus in a new, larger, state of the art covering—the Chernobyl New Safe Confinement—in 2017. The accident motivated safety upgrades on all remaining Soviet-designed RBMK reactors, the same type as reactor No. 4, of which 10 continue to power electric grids as of 2019.[19][20]

There have been several major accidents in graphite moderated reactors, with the Windscale fire and the Chernobyl disaster probably the best known.

In the Windscale fire, an untested annealing process for the graphite was used, and that contributed to the accident – however it was the uranium fuel rather than the graphite in the reactor that caught fire. The only graphite moderator damage was found to be localized around burning fuel elements.[1][2]

In the Chernobyl disaster the graphite was a contributing factor to the cause of the accident. Due to overheating from lack of adequate cooling the fuel rods began to deteriorate. After the SCRAM (AZ5) button was pressed to shut down the reactor, the control rods jammed in the middle of the core causing a positive loop since the nuclear fuel reacted to graphite. This is what has been dubbed the "final trigger" of events before the rupture. A graphite fire after the main event contributed to the spread of radioactive material. The massive power excursion in Chernobyl during a mishandled test led to the rupture of the reactor vessel and a series of steam explosions, which destroyed the reactor building. Now exposed to both air and the heat from the reactor core, the graphite moderator in the reactor core caught fire, and this fire sent a plume of highly radioactive fallout into the atmosphere and over an extensive geographical area.[3]

In addition, the French Saint-Laurent Nuclear Power Plant and the Spanish Vandellòs Nuclear Power Plant – both UNGG graphite-moderated natural uranium reactors – suffered major accidents. Particularly noteworthy is a partial core meltdown on 17. October 1969 and an heat excursion during graphite annealing on 13. March 1980 in Saint-Laurent, which were both classified as INES 4. The Vandellòs NPP was damaged on 19. October 1989, and a repair was considered not economic.