ASN Report 2017

335 ASN report on the state of nuclear safety and radiation protection in France in 2017 Chapter 12  - EDF Nuclear Power Plants 1.5 Reactor containment building The PWR containment building has two functions: ཛྷ ཛྷ confine radioactive products likely to be dispersed in the event of an accident. The containments are therefore designed to withstand the pressures and temperatures that could result from the most severe reactor loss of coolant accident and offer sufficient leaktightness in such conditions; ཛྷ ཛྷ protect the reactor against external hazards. There are three containment model designs: ཛྷ ཛྷ Those of the 900 MWe reactors comprise a single pre- stressed concrete wall (concrete comprising tensioned steel tendons 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. ཛྷ ཛྷ The 1,300 MWe and 1,450 MWe reactor containments consist of two walls: an inner wall made of pre-stressed concrete and an outer wall made of reinforced concrete. Leaktightness is provided by the inner all and the ventilation system (EDE) which, in the annulus 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. ཛྷ ཛྷ The Flamanville EPR reactor containment consists of two concrete walls and a metal liner covering the entire internal face of the inner wall. 1.6 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 in outage states, as well as providing containment of radioactive substances. This chiefly involves the Chemical and Volume Control System (RCV) and the Residual Heat Removal System (RRA). The purpose of the safeguard systems is to control incidents and accidents and mitigate their consequences. This chiefly concerns the following systems: ཛྷ ཛྷ the Safety Injection System (RIS), the role of which is to inject water into the primary system in the event of its leaking; ཛྷ ཛྷ the reactor building Containment Spray System (EAS), the role of which is to reduce the pressure and temperature in the containment in the event of a major leak from the primary system; ཛྷ ཛྷ 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. 1.7 Other systems important for safety The other main systems or circuits important for safety and required for reactor operation are: ཛྷ ཛྷ 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; ཛྷ ཛྷ 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; ཛྷ ཛྷ the Reactor Cavity and Spent Fuel Pool Cooling and Treatment System (PTR), used notably to remove residual heat from fuel elements stored in the fuel building pool; Pre-stressed concrete wall Metal sealing liner 900 MWe reactor containments 1,300 MWe/ 1,450 MWe reactor containments 1,650 MWe reactor containments REACTOR containments Reinforced concrete wall Annulus Pre-stressed concrete wall Reinforced concrete wall Annulus Pre-stressed concrete wall Metal sealing liner