Process for automatic adjustment of soluble boron content in the cooling water of a PWR

The soluble boron content of the cooling water of a PWR is automatically controlled by vertical displacement of neutron absorbing control rods into the reactor core consisting of assemblies disposed vertically and side by side and a boron supply system and a dilution system for the water. The control rods comprise at least one control group. A system is associated with the reactor to determine the axial core power imbalance and the difference between this imbalance and a reference imbalance corresponding to minimum insertion of the control rods into the core and to xenon concentration equilibrium. The process involves predefining the respective operational ranges of the boron supply and dilution systems corresponding to the two values of two control parameters, i.e. a parameter characteristic of the position of the control group in the core and the power imbalance difference, taking into account the conditions of rector use and safety standards. The control parameters are determined continuously during reactor operation; the boron supply system or dilution system are stopped or actuated when the operation point goes over a limit of the operational range. The invention applies more particularly to reactors controlled in gray mode