35 years ago today – the sarcophagus was commissioned

35 years ago today – the sarcophagus was commissioned

The Acceptance Deed for maintaining the Chernobyl NPP preserved Unit 4 was signed on 30 November 1986. This document completed the construction of the Shelter Object and its operation started.

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The Shelter was constructed under the one-of-a-kind design unprecedented in the Soviet and world practices at that time. Decisions for some structures were taken and approved during the work process.

About 90,000 persons were involved into the Shelter construction. It was completed in very short time — 206 days.

The design of the sarcophagus started on 20 May 1986, 24 days after the disaster. Subsequent construction lasted for 206 days, from June to late November of the same year. Due to high radiation levels, it was impossible to directly screw down the nuts and bolts or apply any direct welding to the sarcophagus, so this work was done remotely where possible. The seams of the sarcophagus, however, could not be fully sealed.

The view before the New Safe Confinement was built

The entire construction process consisted of eight stages: clearing and concreting of territory around reactor unit 4, erection of initial reinforced 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 400000 m3 of concrete and 7,300 tonnes of metal framework were used during the erection of the sarcophagus. The building ultimately enclosed 740000 m3 of heavily contaminated debris inside, together with contaminated soil. On 11 October 1986 the Soviet Governmental Commission accepted a report entitled “Conclusion on Reliability and Durability of a Covering Constructions and Radiation Safety of Chernobyl NPP Unit 4 Reactor Compartment”. The sarcophagus has over 60 bore holes to allow observation of the interior of the core. In many places the structure was designed to have ventilation shafts to allow some convection inside. Filtration systems have been put in place so that no radioactive material will escape through these holes.

The structure is constructed on top of the ruins of the reactor building. The “Mammoth Beam” that supports the roof of the shelter rests partly on the structurally unsound west wall of the reactor building that was damaged by the accident. The western end of the shelter roof is supported by a wall at a point designated axis 50. This wall is reinforced concrete and was cracked by the accident.

The Designed Stabilisation Steel Structure is a yellow steel object that has been placed next to the wrecked reactor; it is 63 meters (207 ft) tall and has a series of cantilevers that extend through the western buttress wall, and is intended to stabilize the sarcophagus. This was done because if the wall of the reactor building or the roof of the shelter were to collapse, then large amounts of radioactive dust and particles would be released directly into the atmosphere, resulting in a large new release of radioactivity into the environment. In December 2006 the “Designed Stabilisation Steel Structure” (DSSS) was extended until 50% of the roof load (about 400 tons) was transferred from the axis 50 wall to the DSSS.

Designed Stabilisation Steel Structure and original Sarcophagus structure

A further threat to the shelter is the steel and concrete slab that formed the upper biological shield (UBS), situated above the reactor prior to the accident. This concrete slab was thrown upwards by the explosion in the reactor core and now rests at approximately 15° from vertical. The position of the upper bioshield is considered inherently unsafe, as only debris supports it in its nearly upright position. A collapse of the bioshield would further exacerbate the dust conditions in the shelter, possibly spreading some quantity of radioactive materials out of the shelter, and could damage the shelter itself. The UBS is a disk 17.7 meters in diameter, weighing 1000 tons. The shield is formally called Component E and nicknamed Elena. The twisted fuel bundles still attached to it are called Elena’s hair.

On 22 December 1988, Soviet scientists announced that the sarcophagus would only last 20–30 years before requiring restorative maintenance work. In 1998, with the help of the European Bank for Reconstruction and Development, a conservation programme was completed that included securing the roof beams from collapsing. Nonetheless, the rain-induced corrosion of supporting beams still threatens the sarcophagus’ integrity. 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.[5]

The Chernobyl New Safe Confinement, rolled into place in November 2016, allows for the dismantling of the sarcophagus and for radioactive material to be removed. The containment was expected to replace the existing sarcophagus in 2015. However, delays and a €100 million funding gap caused a yearlong delay, before being moved into place in November 2016.

As of 2020, the building is undergoing testing of its installed systems.

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