I−2. STAGE 1: STABILIZATION
Measures were carried out during this stage (1998–2008) to improve durability, reliability and efficiency of existing and newly created structures and systems (construction, control, dust suppression, emergency) needed for the maintenance or improvement of the existing safety level at the facility.
The objective of stabilization was to reduce the risk of structural collapse of the shelter prior to construction of the new safety confinement (NSC) planned for completion in the longer term. Implementation of stabilization measures allowed improvement of the safety level of the shelter until 2023. In the future, the problem of unstable shelter structures will be resolved by dismantling or reinforcing the inside of the NSC.
I−3. STAGE 2: CREATION OF PROTECTIVE BARRIERS
The construction of the NSC (2008–2016) was to achieve the following objectives:
(a) Ensure personnel, public and environmental protection from nuclear and radiation hazards associated with the existing shelter;
(b) Create the necessary conditions for performing practical activities aimed at transforming the shelter into an ecologically safe system, including retrieval of residues of nuclear fuel and fuel containing material (FCM), radioactive waste management and dealing with unstable shelter constructions requiring dismantling or reinforcement.
The NSC is a protective structure that includes technological equipment for retrieval of fuel containing material from Unit 4 and equipment for radioactive waste management. Other systems are intended for transforming this unit into an ecologically safe system providing safety and environmental assurance for both operating personnel and the public.
The design, construction and commissioning of the NSC was performed by the International Consortium, NOVARKA, consisting of two French companies: VINCI Construction Grands Projects, and Bouygues Travaux Publics. Installation of NSC into the final position was completed in December 2016 as illustrated in Fig. I–3.
According to the design, the NSC includes the following:
FIG. I−2. A general view of the shelter or sarcophagus. (Courtesy of Chernobyl NPP, Ukraine.) FIG. I−3. NSC in the final position over the Unit 4. (Courtesy of Chernobyl NPP, Ukraine.)
— A main building, consisting of an arch structure that spans in the north–south direction 257.44 m, 108.39 m high, 150 m long. Additionally, there are foundations, eastern and western end walls, and necessary support systems.
— A technological building, including decontamination, fragmentation and packaging facilities, sanitary locks, workshops and other technological facilities.
— Auxiliary facilities.
An integrated management system was created for the NSC to ensure nuclear, radiation and industrial safety and its effective operation with a minimum quantity of operating personnel. It consists of the following systems:
(a) Radiation safety monitoring system.
(b) Seismicity monitoring system.
(c) Building construction condition monitoring system.
(d) Operations support systems: Ventilation system, water supply system, sewerage system (including liquid radioactive waste management), power supply system.
(e) Technological systems for radioactive waste and FCM management.
Fire safety and security systems are created and communication and television networks are provided. Crane equipment was installed to ensure dismantling of Unit 4 unstable structures. The main functions of the NSC are the following:
(1) Limit the radiation impact on the population, personnel and the environment within the established boundaries, both during normal operation of the shelter object and in the case of disturbances to normal operations (i.e. emergencies and accidents, including accidents during the dismantling of unstable structures, FCM and radioactive waste management operations);
(2) Limit the spread of ionizing radiation and radioactive substances present inside the shelter object;
(3) Provide technological support, including the creation of conditions for dismantling the unstable structures, the future retrieval of FCM and radioactive waste, accumulated water removal, and ensuring the implementation of control and maintenance measures in the shelter and at its industrial site;
(4) Monitoring of all shelter condition parameters and technological process controls;
(5) Physical protection, including the prevention of unauthorized access to FCM and radioactive waste and maintenance of safeguards for nuclear materials.
FIG. I−2. A general view of the shelter or sarcophagus. (Courtesy of Chernobyl NPP, Ukraine.) FIG. I−3. NSC in the final position over the Unit 4. (Courtesy of Chernobyl NPP, Ukraine.)
NSC construction is intended to allow the following to be achieved by providing an increase in the durability of the containment system:
(a) To improve the radiation safety level; the integrity of NSC construction restricts radiation impact on the population, personnel and the environment within the planned period of operation of 100 years.
(b) To reduce the probability of accidental collapse during the dismantling of unstable structures.
(c) To reduce the impact of emergency collapse from the load-bearing structures and monitoring systems inside the NSC.
(d) To improve the nuclear safety of the shelter by elimination of atmospheric moisture penetration into FCM, hence significantly reducing the risk of a self-sustaining chain reaction.
I−4. STAGE 3: TRANSFORMATION INTO THE ECOLOGICALLY SAFE SYSTEM
Within the third stage, according to the strategy, it is planned to remove FCM from the shelter, and to transform them into a controlled state by providing storage within the protective barriers and/or disposal in geological radioactive waste disposal facilities. All FCM will be sorted according to activity level, compacted and transferred in safe condition before storage (high level and nuclear hazardous radioactive material). FCM accounting should be in accordance with current legislation (see the tentative schedule in Fig. I–4).
After FCM retrieval from the shelter object, it will be possible to implement the final stage of the life cycle (i.e. decommissioning). At the decommissioning stage of the shelter, long term risks to people and to the environment will be eliminated. The decommissioning strategy will be chosen in accordance with the available technical and financial resources available for transformation into an ecologically safe end state.
FIG. I−4. Tentative schedule of implementation strategies for shelter object transformations.