LES ACTIVITÉS NUCLÉAIRES : RAYONNEMENTS IONISANTS ET RISQUES POUR LA SANTÉ ET L’ENVIRONNEMENT Pre-stressed concrete wall Pre-stressed concrete wall Metal sealing liner Containment of 900 MWe reactors Containment of 1,300 MWe / 1,450 MWe reactors Containment of 1,600 MWe (EPR) reactors Reinforced concrete wall Annulus Pre-stressed concrete wall Reinforced concrete wall Annulus Metal sealing liner There are three containment model designs: ∙those of the 900 MWe reactors comprise a single pre-stressed concrete wall (concrete comprising steel tendons tensioned to compress the structure in order to increase its tensile strength). This wall provides mechanical pressure resistance and ensures the integrity of the structure in the event of an external hazard. Tightness is provided by a metal liner covering the entire internal face of the concrete wall; ∙those of the 1,300 and 1,450 MWe reactors has two walls: the inner pre-stressed concrete wall and the outer reinforced concrete wall. Leaktightness is provided by the inner wall and by a Ventilation System (EDE) which, between the two walls, collects and filters residual leaks from the inner wall before discharge. Resistance to external hazards is primarily provided by the outer wall; ∙that of the EPR reactor (see point 1.10). 1.7 The main auxiliary and safeguard systems In normal operating conditions, at power, or in reactor outage states, the auxiliary systems control nuclear reactions, remove heat from the primary system and residual heat from the fuel and provide containment of radioactive substances. They mainly comprise the reactor’s Chemical and Volumetric Control System (RCV) and the reactor’s Residual Heat Removal System (RRA). The role of the safeguard systems is to control and limit the consequences of incidents and accidents. This chiefly concerns the following systems: ∙the Safety Injection System (RIS), the role of which is to inject water into the primary system in the event of it leaking; ∙the reactor building Containment Spray System (EAS), the role of which is to reduce the temperature and thus the pressure in the containment, in the event of a major primary system leak; ∙the Steam Generators Auxiliary Feedwater System (ASG), which supplies water to the SGs if the normal feedwater system is lost, thus enabling heat to be removed from the primary system. This system is also used in normal operation during reactor outage or restart phases. After the Fukushima Daiichi NPP accident (Japan), the decision was taken to install a diversified water source, called the ultimate water source, which can be used in extreme situations to supply the SGs with water when the water reserves in the ASG system are empty and the various resupply solutions are no longer available. 1.8 The other systems important for safety The other main systems important for safety and required for reactor operation are: ∙the Component Cooling System (RRI) which cools a certain number of nuclear equipment items. This system functions in a closed loop between the auxiliary and safeguard systems; on the one hand and the systems carrying water from the river or sea (heatsink) on the other; ∙the Essential Service water System (SEC) which cools the RRI system with water from the river or sea (heatsink). This is a backup system comprising two redundant lines. In certain situations, each of its lines is capable of removing heat from the reactor to the heatsink; ∙the Reactor Cavity and Spent Fuel Pit Cooling and Treatment System (PTR), which in particular removes residual heat from the fuel elements stored in the fuel building pool; The design of the ultimate water source installed in the wake of the Fukushima Daiichi NPP accident, can also – in an extreme situation – inject water into the fuel building pool, if the PTR system and the water make-up systems are lost; ∙the ventilation systems, which ensure containment of radioactive substances by creating negative pressure in the rooms and by filtering discharges; ∙the fire-fighting water systems; ∙the I&C system, which processes the information received from all the sensors in the NPP. It uses transmission networks and sends orders to the actuators from the control room, through the programmable logic controllers or operator actions. Its main role with regard to reactor safety is to monitor reactivity, control the removal of residual heat to the heat sink and take part in the containment of radioactive substances; ∙the electrical systems, which comprise sources and electricity distribution. French nuclear power reactors have two external sources of electricity: the step-down transformer and the auxiliary transformer. In addition to these two external sources, there are two internal sources of electricity: diesel-powered emergency generators. In the event of a total loss of these external and internal sources each reactor has a backup diesel-generator set, known as the “Ultimate backup” (DUS), installed after the accident at the Fukushima Daiichi NPP, supplemented by an ultimate source, the nature of which varies depending on the plant in question. Depending on the plant, another generator set, consisting of a turbo-alternator, may be added to this equipment. Reactor containments ASNR Report on the state of nuclear safety and radiation protection in France in 2025 285 01 05 02 06 03 07 04 08 09 10 11 13 12 A / Z
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