30.06.2020

Chernobyl vent pipe dismantling

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How and why did the dismantling of the ventilation pipe of the second unit of the Chernobyl NPP

 

In 2013, the Chernobyl NPP began unique work on the removal (dismantling) of the ventilation pipe of the second stage of the nuclear power plant. This is perhaps the most dangerous and responsible work at the Shelter, which was carried out after the construction of this protective structure in 1986, which covered the destroyed reactor of the 4th unit. The uniqueness of this work lies in the fact that the VT-2 has a complex structure, the surfaces of the VT-2 elements have high levels of radiation pollution, personnel access to the VT-2 structures, which is located 75 meters above the ground, is quite problematic. When removing the VT-2, special attention was required to the process of dismantling the elements (individual blocks of the ventilation pipe), since the crane's arrow will be above the nuclear and radiation-hazardous object, which is the Shelter.


In this regard, the VT-2 removal project can be considered one of the most critical stages of work performed in the post-accident period at the Chernobyl NPP site. By the way, it is worth mentioning that VT-2 is a certain symbol of the Chernobyl nuclear power plant and its disappearance led to a significant change in the familiar, well-established appearance of the Shelter object and the entire Chernobyl nuclear power plant. The Shelter with VT-2 is an unofficial symbol, a recognizable sign of the Chernobyl tragedy, which is familiar to most people, both in Ukraine and abroad.


Removal of VT-2 is a necessary measure, which is associated with the end of its useful life. The life of the VT-2 is 30 years and expired in 2010. In addition, the location of the VT-2 prevents the installation of the Arch. Therefore, the ventilation pipe had to be removed before it would be necessary to install the Arch in the position required by the design of this new protective structure.


VT-2 was intended for the organized release of air from the ventilation systems of the II stage of the Chernobyl nuclear power plant (3rd and 4th power units) and storage of liquid and solid radioactive waste. After the accident at the 4th block and the construction of the Shelter object, the ventilation pipe provided an organized release of radioactive aerosols from the 3rd block of the Chernobyl NPP and the Shelter object. The ventilation pipe of the Chernobyl Phase II was built in 1980. The installation of the pipe was carried out in stages, with the help of several cranes installed directly at different elevations of the nuclear block under construction. Each element was supplied separately to a certain mark, from where it was transferred to the upper marks by another crane installed above.

 

VT-2 was almost at the epicenter of the explosion of the Chernobyl reactor No. 4 in 1986, which led to damage to the supporting structures of the VT-2 and to intense contamination of the VT-2 elements with radioactive substances. Some elements of the supporting structures were damaged. According to the Ministry of Emergencies of Ukraine, defects on the VT-2 were detected after examining the elements and components that make up the frame of the supporting structures. After examination, about thirty defects were identified. Specialists point out that such defects were breaks in structural elements, loss of stability of VT-2 elements, and facts of significant corrosion of some elements were established. In 1998, support structures were repaired. Repair work was carried out with the financial support of foreign states - the USA and Canada.


When organizing VT-2 repair work, highly active sources (fragments of the destroyed reactor) were discovered at service sites. To ensure the radiation safety of the personnel involved in the VT-2 repair work, these “hot spots” were shielded and covered with lead plates.


To perform the removal of VT-2, a special Contractor was selected. As a result of the tender, Ukrtransbud was selected with which a special contract was concluded. Judging by the company’s website, the contract SIP09-1-003 was signed on April 27, 2012 “Designing dismantling, field supervision of dismantling and dismantling the ventilation pipe of the second stage of the Chernobyl nuclear power plant”. The removal of VT-2 was funded by the European Bank for Reconstruction and Development.

 

VT-2 removal was carried out by cutting the pipe and supporting structures into seven elements, which were removed from top to bottom in whole blocks. For cutting metal structures, it was customary to use a gas cutter. The removal of the cut-off parts of the VT-2 was carried out using a special crane. By the way, this is one of the most powerful modern self-propelled crawler cranes - DEMAG SS-8800-1. Technical characteristics of the DEMAG SS-8800-1 crane are also outstanding - the carrying capacity is 1600 tons. The length of the main boom of the crane is 156 meters, the length of the additional boom is 108 m. Control over the control of the crane (monitoring the load, hook, etc.) is carried out using a camera system.


At the time of VT-2 removal, the radiation background on the structures was about 100 - 300 mR / h. More visual information on the radiation situation on the VT-2 structures is presented in the figure.


Each dismantled VT-2 unit after dismantling underwent a radiation survey. According to the results of the assessment, it was determined that all fragments of VT-2 are highly radioactive elements. Today, the legendary disassembled pipe of 3-4 units is located in the engine room of the second unit.

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