Chernobyl Sarcophagus

Definition and names

The Chernobyl Sarcophagus is the steel-and-concrete structure built over the reactor No. 4 that exploded on 26 April 1986. Its official designation was the Object Shelter (Объект «Укрытие»), meaning a sheltering or covering object; 'sarcophagus' was never the official name but a widely used nickname. The structure was meant to isolate the destroyed unit from the environment and reduce the dispersal of radioactive dust and aerosols, sealing an estimated 200 tonnes of corium, 30 tonnes of highly contaminated dust and 16 tonnes of uranium and plutonium. Up to an estimated 95 per cent of the original radioactive inventory of reactor No. 4 is believed to remain inside the ruins of the reactor building.

Construction

Design began on 20 May 1986, 24 days after the disaster, and construction lasted 206 days, from June to late November 1986. Radiation at the site made direct bolting and welding impossible, so work was done remotely where possible, and the seams could not be fully sealed. Building proceeded in eight stages: clearing and concreting the ground around unit 4; reinforced concrete perimeter protective walls; separation walls between units 3 and 4; a cascade wall; covering the turbine hall; a high-rise buttress wall; supports and a covering for the reactor compartment; and a ventilation system. The Russian-language source records 400,000 cubic metres of concrete mix and 7,000 tonnes of metal structures, and states that 90,000 people were employed in building the shelter in the shortest time, 206 days. The English-language source gives 7,300 tonnes of metal framework and says the structure enclosed 740,000 cubic metres of heavily contaminated debris together with contaminated soil. V. A. Kurnosov was the author and technical project lead, V. G. Asmolov the scientific lead and V. I. Rudakov the installation works lead. The sarcophagus was formally accepted on 11 October 1986, when the Soviet Governmental Commission received a report on the reliability and durability of the covering structures and the radiation safety of the unit 4 reactor compartment. Its projected service life at construction was 20 to 40 years.

Deterioration and reinforcement

Internal radiation levels in some areas were estimated as high as 10,000 röntgens per hour, against a normal urban background of about 20 to 50 microröntgens per hour and a lethal dose of 500 röntgens over five hours. A structure built under those conditions did not last. By 1996 it had deteriorated to the point where numerous stabilisation measures were required; Russian-metal strengthening structures (МКУ) were begun in 1996 and completed in 2007. In 1998, with help from the European Bank for Reconstruction and Development, a conservation programme was completed that secured the roof beams from collapsing, but rain-induced corrosion of supporting beams continued to threaten the structure, with water leaking through roof holes, becoming contaminated and seeping into the soil. In February 2013 a 600-square-metre portion of the roof and wall adjacent to the covered turbine hall collapsed into the entombed turbine hall; no other part of the shelter or the New Safe Confinement was affected and no radiation variance was detected. A 63-metre-tall yellow Designed Stabilisation Steel Structure (DSSS) with cantilevers through the western buttress wall stands next to the wrecked reactor to prevent wall or roof collapse, and in December 2006 it was extended until 50 per cent of the roof load, about 400 long tons, was transferred from the axis 50 wall to it.

Replacement and current state

One structure of particular concern is the upper biological shield, thrown upward by the explosion. Formally called Scheme E and nicknamed Elena, the 17.7-metre-diameter, 1,000-ton disk rests about 15 degrees from vertical, supported only by debris, and its collapse would exacerbate dust conditions. The sarcophagus was never intended as a permanent containment structure; it was an emergency measure built under severe time constraints while the three remaining reactors could be restored to service. From 14 November 2016 the New Safe Confinement was pushed on Teflon pads by laser-guided hydraulic pistons over 15 days, reaching its final location on 29 November 2016, and it was formally put into operation on 10 July 2019. The arch has a 260 by 165 metre base, is 110 metres high and weighs 36,200 tonnes; it was designed to protect the environment while the sarcophagus is dismantled and to confine the radioactive remains for 100 years. The current deadline to dismantle the sarcophagus is 31 October 2029. On the night of 14 February 2025, the Russian-language source records, the structure housing the sarcophagus was struck by a drone that made a hole about six metres in diameter.

Distinctions and relations

The sarcophagus is distinct from the wider recovery effort. It was the emergency measure over unit 4, while the liquidator mobilisation was far broader: about 200,000 people from across the USSR took part in recovery and clean-up in 1986-1987, averaging around 100 mSv, and the number later swelled to over 600,000, most receiving only low doses. The 90,000 figure cited for construction should be read apart from that wider mobilisation. The sarcophagus also differs in purpose from a reactor containment building: the term 'confinement' in the New Safe Confinement distinguishes the confinement of solid radioactive waste from the containment of radioactive gases typical of reactor containment buildings. The entry connects directly to the Chernobyl disaster topic.