Method and system for controlling the introduction of gas into a coolant, and nuclear reactor installation

Disclosed are a method and system for controlling the introduction of gas into a coolant of a nuclear reactor installation. The method includes the following steps: feeding gas, intended for being introduced into a coolant, from a gas system into a space above a coolant; introducing the gas into the coolant; removing gas from the space above the coolant into the gas system. Technical result: preventing the reuse of contaminated gas.