Due to increasing environmental requirements, oil must be prevented from leaking from a turbine rotor disk and reaching the medium circulating around the turbine. In Kaplan turbines comprising a hydraulic mechanism (6) for actuating the rotor disk blades (3), hydraulic liquid leaks from the servomotor (5) and is collected in the inner chamber of the rotor disk hub (2). The invention relates to a rotor disk (1) by which means said leakage liquid can be reliably and easily collected and guided out of the rotor disk (1). A collecting basin (8) is arranged-around the free end of the piston rod (7). The actuating movement of the servomotor (5) reduces and enlarges the pump volume (17), and hydraulic liquid is thus guided from the collecting basin (8) into the delivery pipe (11).