Safety systems of NPPs with VVER–1200 / VVER-TOI
The inner containment is a cylindrical structure made of prestressed reinforced concrete. The inner surface is covered with a welded carbon steel lining to ensure tightness. The outer containment is a cylindrical structure made of reinforced concrete with a hemispherical dome.
Passive heat removal system via steam generators (PHRS HG)
Designed for long-term removal of residual heat of the core to the final absorber through the secondary collant circuit in case of beyond-design accidents. The system duplicates the corresponding active heat removal system if it is not possible to operate it. Functioning of the system is based on the natural circulation of the coolant of the secondary circuit in the pipelines of the system. Steam coming from the steam generator condenses in the air heat exchangers transferring heat to the atmospheric air due to the occurrence of thermal traction.
System for removal of hydrogen from containment
It consists of two independent subsystems: a hydrogen removal system and a system for monitoring concentration of hydrogen under containment. Ensures during design-based accidents maintenance of concentration of hydrogen in a mixture with water vapor and air below the limits of flame propagation under containment (design-based accidents), as well as at levels that exclude detonation and development of combustion in large volumes (beyond-design accidents).
Containment passive heat removal system (CPHRS)
The system is designed for long-term heat removal from containment in case of beyond-design accidents. Provides reduction and maintenance within the specified design limits of the pressure inside the containment and the removal of heat to the final absorber, released under the containment.
Hydraulic tanks of the 1st stage and the 2nd stage
The system is designed for emergency cooling of the core in case of accidents with leaks of the primary coolant. Borinated water is supplied to the reactor core under the influence of the nitrogen cushion pressure with a decrease in the reactor pressure below 5.9 MPa. Duration of operation of hydraulic tanks of the 1st stage is approximately 3 minutes. The pipelines of the system are equipped with shut-off valves that reliably protect the reactor plant from nitrogen ingress into the primary circuit.
Designed for long-term passive recharge of reactor when the core is cooled in a boiling water reactor. Water supply to the reactor is carried out with a stepwise change in the flow rate in accordance with the decline in residual heat. Shut-off valves on the pipelines open when the pressure in the primary coolant circuit is reduced to 1.9 MPa. The system is activated during the operation of the hydraulic tank system of the primary coolant circuit, thus ensuring continuous inflow and cooling of the core.
Core melt localization device
One of the technical means specifically designed for the management of severe beyond-design accidents at the off-vessel stage. In the "melt trap", the materials of the core, internals and reactor vessel are received, placed and cooled down until complete crystallization.
Emergency and planned cooldown system of the primary coolant circuit
Designed to cool down the reactor plant in all operating modes of the unit. Removes residual heat release from the fuel located in the reactor and in the cooling pond, and also partially replenishes the supply of coolant in the reactor in case of accidents with loss of tightness of the primary coolant circuit. Primary coolant and coolant of cooling pond is cooled in a special heat exchanger that is part of the system. Eventually, the heat is transferred to the atmospheric air in the splash pools. Pipeline fittings prevent the release of radioactive substances into the environment, even if they are destroyed.