Gas turbine plant

A gas turbine plant comprises an air compressor (8), a gas turbine (10) including at least one high temperature section, a driven equipment (11), which are operatively connected in series, a gas turbine combustor (9) arranged between the air compressor and the gas turbine, and a fuel system (12) for supplying a fuel to the gas turbine combustor. The gas turbine plant comprises further an air extraction closed circuit system (26; 35; 57) for said air compressor and a heat exchange section (16) provided for said air extraction closed circuit system for heating the fuel supplied to the gas turbine combustor from the fuel system (12). Said air extraction closed circuit system (35) is further provided with a valve opening control means (45) for detecting a fuel leak into the high pressure air by a fuel leak detector (45) provided for the heat exchange section and for closing a fuel valve (15) of the fuel system when a detection signal exceeds a predetermined value and also provided with an alarm device (47) for giving an alarm when the detection signal exceeds the predetermined value.