Dome above the Sarcophagus

 

Early August 2014 the first stage of the second lift of the arch western section was completed. The second lift consists of two stages. The first one is lifting three arch segments to 33 meters: crane girders for the primary crane system and steel structures of the western end wall. The second stage is lowering to 1 meter with a transfer of load to locking gear. This operation was performed upon installation of two more arch segments. The second stage was accomplished at the end of August 2014.

At the first lift stage the arch weighs 8,352 tons. After the second lift stage its weight will be 10,594 tons.

It is to be recalled that the first lift of the arch western section to 22 meters took place this April and the last lift – the third one – is scheduled for the end of 2014 (also to 22 meters).

Eastern part of the arch is now in the waiting area. Its 12,852-ton steelwork has been installed, and mounting of external and internal shells is still in progress.

As soon as steel structures of the arch western section are in place, the second stage of handling will start. It will include moving the arch eastern section to 25 meters in the reverse direction and mating it with the western section. The third stage of handling the whole arch will move it to 330 meters into operating position.

Relocation works are carried out by a subcontractor of Novarka – the Dutch MAMMOET with unique own-produced equipment. A total of 112 heavy-duty jacks placed along the Arch perimeter on the northern and southern sides are used for relocation.

The arch structure, weight of which now equals 12.6 thousand tons, is moved at a speed of 10 meters per hour. Maximum speed that can be reached when handling this structure – is 11.5 meters per hour.

As underlined by Pyotr Britan, PMT lead project and program engineer, these works are unique because this is the first time handling of such massive and bulky structures takes place.

You may recall that the existing protective structure built right after the accident and popularly known under the name “sarcophagus” is far from ideal. It has never been air-proof, and its condition is deteriorating in the course of time. Concerned Europe finally allocated the funds and chose the project of a new shelter. The engineers faced a difficult task. Main conditions: to build a hermetic dome above the reactor allowing consequent demounting of the “sarcophagus” and removal of reactor debris, inside the new dome; ensure complete safety of the builders.

In other words, it was necessary to construct a gigantic structure enclosing the most hazardous facility in the world and at the same time protect the builders from exposure. Radiation level around the fourth reactor is exponentially growing depending on the above ground level…

Novarka Consortium designed a unique solution – to build the dome off-site step by step and then just pull it over the sarcophagus. With a total height of the structure being 110 meters the workers will never have to climb higher than 30 meters.

The first stage enabled to prepare a site 600 meters away from the existing sarcophagus end face. Digging was reduced to a minimum to minimize generation of polluted waste (soil). The entire area was covered with 1 meter of clean soil. New roads were laid and associated facilities provided for. Concrete was poured over all possible areas to avoid unnecessary dusting.

Rails for moving the dome were then set up. Huge hydraulic jacks capable of lifting a structure to 30 meters were placed on the foundations reinforced for this purpose. Upper dome sections are put between the jacks. They are connected to each other making the single dome section – 70 meters long, half the length of the whole structure.

Further sections – “legs” are then hinged to the edges of this structure. When the jacks simultaneously lift the entire structure, legs lower into working position. They are fixed and connected to each other and the given structure. This process is repeated several times until the full size of the dome (in height) is available.

Whenever possible, electric cables, ventilation, utilities, and the rest of auxiliary equipment are mounted on the section before the final assembly starts.

The whole structure – half the new shelter – is taken aside, and the process is repeated for the second half. Blind wall is hung on the second half on the far side from the reactor.

After that the two halves connect. The entire structure travels on custom-designed teflon pads. When the dome is ready, it is pulled over the fourth block and teflon pads are removed. All gaps of the dome edges are sealed.

The new dome is designed for 100 years of operation. To prevent steel corrosion huge air conditioners keeping the air humidity at 40 percent are installed inside. The structure also accommodates an overhead crane and leaves much space for large equipment maneuvers inside. All this will allow full demounting, removal and burial of the concrete “sarcophagus”, remnants of the reactor and nuclear fuel accumulated under it. That is, if the money is allocated…