According to the method, either CO2-free air or pure nitrogen N2 is pumped into the cooling circuit selectively depending on system parameters. To this end, the method ensures that the air injection rate is high enough that, under normal conditions, the hydrogen concentration in the tank and in the riser remains below 2% H2. On air injection, the oxygen O2 (>2 ppm) in the cooling water reacts with the copper in the cooling ducts and a layer of copper oxide forms on the inner walls of said ducts. No reaction is triggered by the injection of nitrogen N2. The CO2 content in the injection air and, at the same time, also the H2 content in the exhaust air are continuously measured and monitored, and an alarm is triggered if adjustable limit values are exceeded. The equipment for performing the method comprises an electronic control unit (65) with an input field and display as a control box, and a pump and a pipe circuit for drawing air in from the riser. The control unit (65) can evaluate all the measured data from the sensors and analysers connected to the pipe and can at least check the CO2 content in the supply air and the H2 content in the riser (13) and display the hydrogen leakage.