How does a pressurised water reactor work?
In a Pressurised Water Reactor (PWR) like the EPR™ reactor, ordinary (light) water is utilized to remove the heat produced inside the reactor core by nuclear fission. This water also slows down (or moderates) neutrons (constituents of atom nuclei that are released in the nuclear fission process).
Slowing down neutrons is necessary to sustain the nuclear chain reaction (neutrons have to be moderated to be able to break down the fissile atom nuclei).
The heat produced inside the reactor core is transferred to the turbine through the steam generators. Only heat is exchanged between the reactor cooling circuit (primary circuit) and the steam circuit used to feed the turbine (secondary circuit). No exchange of cooling water takes place.
The primary water is pumped through the reactor core and the primary side of the steam generators, in four parallel closed loops, by coolant pumps powered by electric motors.
Each loop is equipped with a steam generator and a coolant pump. The reactor operating pressure and temperature are such that the cooling water does not evaporate and remains in the liquid state, which increases its cooling effectiveness.
A pressuriser connected to one of the coolant loops is used to control the pressure in the primary circuit.
Feedwater entering the secondary side of the steam generators absorbs the heat transferred from the primary side and evaporates to produce saturated steam. The steam is dried in the steam generators then delivered to the turbine.
After exiting the turbine, the steam is condensed and returns as feedwater to the steam generators.
The generator, driven by the turbine, generates electricity.