Chernobyl Nuclear Power Plant

Radiation background in the Administrative building area is in average 65 microrentgens per hour, in the Shelter object's Observation pavilion area - 1,08 myllyrentgens per hour.
Controllable parameters of the Shelter object are within the limits established by Operational Regulations. According to monitoring systems data the maximal value of gamma - radiation rate inside the object has made 3403 Rontgens per hour, temperature near to Fuel Containing Materials is +29 degrees on Celsius. Exceeding of control levels of Shelter object condition parameters is not fixed.

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Construction

In the middle of May, 1986 the Governmental Commission has made a Decision on long-term conservation of destroyed Unit 4.

Realization of this task was complicated by extremely high gamma - radiation fields, absence of reliable information on a level of destruction and on Unit 4 constructions condition, absence of similar accidents liquidation experience in global practice.
The task for the works performance connected to ChNPP Unit 4 conservation, was established by the Decision of SU CP Central Committee and USSR Council of Ministers dated June, 5, 1986 ¹ 663-194. Functions of the General contractor on this activity implementation were entrusted to the USSR Machine-Building Ministry. The object has received the name “Shelter of ChNPP Unit 4”. All-Union Research and Design institute of power technologies (VNIPIET) has been appointed the General Designer of works. Sketch design developed by VNIPIET experts under professor I.Kurnosov leadership has been taken as a basis for future "sarcophagus". The design was elaborated and changed during construction. Kurchatov Nuclear Energy Institute was the scientific manager of works.

Designing of Shelter started on May, 20, 1986. Construction continued 206 days and nights from June till November, 1986. About 90 thousand builders participated in it. During 1986 - 1987 about 200 thousand persons worked in Chernobyl area.

Process of Shelter construction can be subdivided on three stages.

The first stage since May, 20 till July, 15, 1986 was characterized by high levels of exposure rate and uncertainty of radiation fields structure. The main works, carried out during this period, consisted in manufacturing of the Shelter object constructions and elements, protecting workplaces against main sources of radiation, in these sources removal or decontamination. In such way the space for the major civil works deployment have been prepared. Concrete mixing plant, transport communications have been constructed, the railway junction has been enlarged, the social infrastructure has been developed, large-scale constructions have been produced, etc.

During the second stage from July, 16 till September, 15, 1986 the basic scope of civil work, assured necessary strength and radiation-protective properties of the Shelter object achievement has been executed. Man-hours of builders were maximal, and relative dose rates were in order lower, than at the first stage.
The third stage, during the period from September, 16 till November, 30, 1986, was characterized by constructing-and-mounting works termination.

Works sequence during "sarcophagus" construction.
1. Clearing and concreting of a territory around Unit 4.
2. Construction of protective (pioneer) walls along perimeter.
3. Construction of separation walls between Units 3 and 4.
4. Cascade wall construction.
5. Turbine Hall covering.
6. High-rise counterforce wall mounting.
7. Erection of supports and installation of a reactor compartment covering.
8. Installation of ventilation system and monitoring and measuring communications and devices.
During "sarcophagus" construction it has been placed more than 400 thousand cubic meters of concrete and 7000 tons of metal constructions has been mounted. During Shelter construction partitions and walls, separated destroyed Unit 4 from Unit 3 have been erected. Along the destroyed Unit perimeter firstly ferro-concrete "pioneer" protective walls have been erected for safety ensuring during the subsequent civil and erection works performance. Northern cascade wall has been executed from concrete as ledges in height about 12 meters. The shuttering of ledges was made of metal panels. Each subsequent ledge was carried out as closely as possible to the destroyed Unit. Worn and damaged steal constructions and containers with highly active wastes were enclosed inside ledges. A wall closed the remained western wall from the outside with buttresses in height up to 50 meters. 27 pipes with diameter of 1200 mm were used for Central Hall covering formation. Simultaneously with Shelter construction large scope of works on territory decontamination around object has been performed. Decontamination of a territory and roof has ensured fast exposure rate (ER) reduction outside of its premises.
New constructions have been built according to construction norms and rules, but term of their use is limited by periodic survey and corrosion-resistant coating renewal impossibility.
In October, 11, 1986 the Governmental Commission accepted “Conclusion on reliability and durability of a covering constructions, and radiation safety of Chernobyl NPP Unit 4 reactor compartment”. Concerning facility life time in the document it was stated: “In connection with that the shelter of reactor compartment is constructed on the destroyed constructions and in high radiation conditions, and taking into account complexity of constructions installation and control of their position, we have no a possibility to obtain the reliable data on their bearing strength”.
In the same document it is mentioned: “Taking into account low corrosion rate in operating conditions of constructions with protective coatings their life time can be ensured: for pipes 30-40 years, for beams - 30 years”.

On November, 30, 1986 State Acceptance Committee accepted for maintenance conserved Unit 4 of Chernobyl NPP.