ASN Report 2018

EDF uses two types of fuels in its Pressurised Water Reactors (PWR): ∙ ∙ uranium oxide based fuels (UO 2 ) with uranium-235 enrichment to a maximum of 4.5% by mass. These fuels are fabricated in several French and foreign plants, by Framatome and Westinghouse; ∙ ∙ fuels consisting of a Mixture of depleted uranium oxides and plutonium (MOX). The MOX fuel is produced by the Orano Melox plant. The maximum authorised plutonium content is currently limited to 9.08% (average per fuel assembly) and provides an energy performance equivalent to UO 2 fuel enriched to 3.7% with uranium-235. This fuel can be used in the twenty-eight 900 MWe reactors for which the Creation Authorisation Decrees (DAC) provide for the use of plutonium fuel. EDF has standardised how the fuel is used in its reactors, referred to as “fuel management”. Fuel management, which concerns similar reactors, is more particularly characterised by: ∙ ∙ the nature of the fuel used and its initial fissile content; ∙ ∙ the maximum degree of fuel depletion at removal from the reactor, characterising the quantity of energy extracted per tonne of material (expressed in gigawatt days per tonne – GWd/t); ∙ ∙ the duration of a reactor operating cycle; ∙ ∙ the number of new fuel assemblies loaded at each reactor refuelling outage (generally 1/3 or 1/4 of the total number of assemblies); ∙ ∙ the reactor operating mode (at constant power or by varying the power to match demand), which determines the loads to which the fuel is subjected. 1.3  ̶  Primary system and secondary systems The primary system and the secondary systems transport the energy given off by the core in the form of heat to a turbo- generator set which produces electricity. The primary system consists of cooling loops, of which there are three for a 900 megawatt (MWe) reactor and four for the 1,300 MWe, 1,450 MWe or 1,650 MWe EPR type reactors. The role of the primary system is to extract the heat given off in the core by circulating pressurised water, referred to as the primary coolant or reactor coolant. Each loop, connected to the reactor vessel containing the core, comprises a circulating pump (known as the primary or reactor coolant pump) and a Steam Generator (SG). The primary water, heated to more than 300°C, is kept at a pressure of 155 bar by the pressuriser, to prevent it from boiling. The entire primary system is located inside the containment. The water in the primary system transfers its heat to the water in the secondary systems in the steam generators. The steam generators are heat exchangers that contain 3,500 to 5,600 tubes, depending on the model, through which the reactor coolant circulates. These tubes are immersed in the water of the secondary system and boil it, without ever coming into contact with the primary water. Each secondary system principally consists of a closed loop through which water runs in liquid form in one part and as steam in the other part. The steam produced in the steam generators is partly expanded in a high-pressure turbine and then passes through moisture separators before final expansion in the low-pressure turbines, from which it is then routed to the condenser. The condensed water is then sent back to the steam generators by the condensate extraction pumps and the feedwater pumps, after passing through the reheaters. 1.4  ̶  The secondary system cooling system The function of the secondary system cooling system is to condense the steam exiting the turbine. This is achieved by a condenser comprising a heat exchanger containing thousands of tubes through which cold water from outside (sea or river) circulates. When the steam comes into contact with the tubes it condenses and can be returned in liquid form to the steam A steam generator and a main primary system of a 1,300 MWe reactor Steam discharge Moisture separators Feedwater ring Bundle wrapper Tube bundle Tube support platev Channel head Primary pumps Core instrumentation Control rod drive mechanisms Steam generator Reactor core Reactor vessel Vessel head Pressurizer 278  ASN report on the state of nuclear safety and radiation protection in France in 2018 10 – EDF NUCLEAR POWER PLANTS