The Shelter Object was constructed within 206 days. The accelerated time of its construction led to appearance of design flaws, in particular:
1. The bearing structures of the supporting walls (survived constructions of the Power Unit 4) and their junctions were significantly damaged, overloaded with the weight of the building structures that were dropped on them, and materials used during the accident elimination
2. Exposed reinforcing bars of the reinforced concrete structures and metal structures are corroded
3. The structures constructed after the accident are freely supported on the bearing structures without a physical connection and are retained without welded or bolted connections
Basic information Accident and its Elimination
The international competition of designs and technical solutions was announced in 1992 to transform the Shelter Object into an environmentally safe system, which was the first step towards the international cooperation.
Shelter Object’s design defects were described in 1995 in the report of the Alliance company and it contains the following conclusions:
1. The operating Shelter is unstable and seismically isn’t resistant. Urgent measures should be undertaken to stabilize it and delay is unacceptable
2. Due to the high radiation level and the actual state of existing structures long-term stabilization of the Shelter Object was considered as impossible. The state of the Shelter does not allow retrieving the radioactive materials
3. New protective encasement should be constructed to allow Unit 4 dismantling
4. The facility should be constructed for radioactive waste storage and management
5. Ukraine isn’t capable to provide financing for such a project without outside help
In June 1997, the G7 meeting accepted the "Shelter Implementation Plan" (hereinafter: SIP), developed under the assistance of the European Commission, Ukraine, United States and a team of international experts. This plan defined the basic concept, including a number of steps aimed at bringing the Shelter Object to an environmentally safe state.
Objectives of the Shelter Implementation Plan:
1. Reduce the Shelter Object collapse probability
2. Reduction of consequences in case of the collapse
3. Nuclear safety improvement
4. Improve the personnel and the environment safety
5. Develop a long-term strategy and investigate ways to transform the Shelter Object into an environmentally safe system
The Donor countries pledging conference took place November 20, 1997 in New York. These countries committed to allocate funds for this Plan implementation in a specially established Chornobyl Shelter Fund. The Fund administration was entrusted to the European Bank for Reconstruction and Development.
The Shelter Object transformation into an environmentally safe system is carried out in 3 stages::
1. Stabilization. Stabilization of the existing facility state and increase of its operational reliability
2. Preparation for transformation. Creation of additional protective barriers, in particular New Safe Confinement. This will provide the necessary conditions for the subsequent stages of transformation, as well as will protect the personnel, general public and environment. In addition, at this stage preparatory work is planned to develop a technology for Fuel Containing Masses retrieval from the Shelter Object and to create infrastructure for Radioactive Waste Management
3. Transformation. Fuel Containing Masses and Radioactive Waste retrieval from the Shelter object and their disposal. Shelter object decommissioning
SIP stabilization stage was implemented within 2004-2008.
The urgent stabilization measures were implemented during 4 years, which allowed strengthening the main most vulnerable Shelter Object's elements. At this stage the Shelter western wall was strengthened, the emergency slabs were stabilized, the Shelter northern zone, the southern zone roof and the western and eastern Mammoth Beam supports construction were reinforced, the light roof of the Shelter Object and the Ventilation stack of Units 3 and 4 were repaired.
These works allowed extending the Shelter Object lifetime for another 15 years.
The stage of preparation for the transformation stipulated the construction New Safe Confinement (hereinafter: NSC) — a protective structure, which includes a complex of technological equipment for FCM retrieval from the damaged 4th Power Unit, radioactive waste management and the safety assurance for the personnel, the general public and the environment.
Preparatory works for the NSC construction were started in 2005. In 2010 the site for the confinement construction was prepared.
Basic information: The project "New Safe Confinement Construction"
November 29, 2016 — the NSC Arch was installed in the design position above the Shelter Object.
© Video from YouTube channel PRIPYAT-film. See the video here.
In 2016, the Chornobyl NPP obtained a permission to operate the Shelter Object's Integrated Automated Monitoring System (IAMS).
The system is designed to perform automated monitoring of the Shelter Object's condition and improve the nuclear, radiation and general technical safety of this facility, including increase of emergency preparedness. The IAMS consists of a Nuclear Safety Monitoring System, Radiation monitoring system, system for building structures condition monitoring and seismic monitoring system.
Within the third stage of the transformation it is planned to retrieve the Fuel Containing Masses from the Shelter Object, to transfer them to the controlled state by storing them inside the protective barriers or by disposal in geological repositories for radioactive waste. The goal of this stage is to transfer the facility into an environmentally safe state.
The available level of knowledge is insufficient to identify the timeframe for the Stage 3 implementation. Priorities for the nearest future are the NSC commissioning and transition to dismantling of Shelter Object's unstable structures by 2023 — the final service life of the Shelter Object stabilized structures.