The Decaying Sarcophagus of Chernobyl

The Chernobyl Nuclear Power Plant sarcophagus or stone coffin is a massive concreteenvelope surrounding the nuclear reactor unit 4 of the Chernobyl Nuclear Power Plant. It is designed to halt the release of radiation into the atmosphere following the Chernobyl disasteron April 26, 1986 and encase the most dangerous area.^[1][2] The official Russian name is No 4. ukrytiye which means housing or covering as opposed to sarcophagus.^[2] The sarcophagus locked in 200 tons of radioactive corium, 30 tons of highly contaminated dust and 16 tons of uranium and plutonium.^[1] In 1996 it was deemed impossible to repair the inside of the sarcophagus as radiation levels were estimated to be as high as 10,000röntgens per hour (normal background radiation in cities is usually around 20-50 microröntgens per hour).^[3]

The designing of the sarcophagus started on May, 20, 1986. Subsequent construction lasted for 206 days, from June to late November of the same year.^[2] The first task before construction started was to build a cooling slab under the reactor to prevent the hot nuclear fuel from burning a hole in the base. Coal minerswere called up to dig the necessary tunnel below the reactor and by June 24, 1986 four hundred coal miners had dug the 168 metre (551 ft) long tunnel.^[4] When the building became overly radioactive it became impossible to directly screw down the nuts and bolts or apply any direct welding to the sarcophagus, so this work was done by robots.^[1] The seams of the sarcophagus, however, were not properly sealed. The entire construction process consisted of eight stages: clearing and concreting of territory around reactor unit 4, erection of initial ferro-concrete protective walls around the perimeter, construction of separation walls between units 3 and 4, cascade wall construction, covering of the turbine hall, mounting of a high-rise buttress wall, erection of supports and installation of a reactor compartment covering and finally the installation of a ventilation system.

More than 400,000 m³ of concrete and 7,300 tonnes of metal framework were used during the erection of the sarcophagus.^[2] The building ultimately enclosed 740,000 m³ of heavily contaminated debris inside,^[1] together with contaminated soil.^[4] On October 11, 1986 the SovietGovernmental Commission accepted "Conclusion on Reliability and Durability of a Covering Constructions and Radiation Safety of Chernobyl NPP Unit 4 Reactor Compartment".^[5] The sarcophagus has over 60 bore holes to allow observation of the interior of the core.^[6] In many places the structure was designed to have ventilation shafts to allow some convection inside.^[6] Filtration systems have been put in place so that no radioactive material will escape through these holes.^[6]

On December 22, 1988 Soviet scientists announced that the sarcophagus would only last 20—30 years before it needed repairing. In 1998, with the help of the European Bank for Reconstruction and Development, a conservation programme was completed which included securing the roof beams from collapsing. Nonetheless the rain-induced corrosion of supporting beams still threatens the sarcophagus's integrity.^[4] It was revealed that the water is leaking through the sarcophagus via holes in its roof, becoming radioactively contaminated, and then seeping through the reactor's floor into the soil.^[4] In 2013 the New Safe Confinement is expected to replace the existing sarcophagus. The new containment device will allow the sarcophagus to be dismantled and radioactive material to be removed.^[7]

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