A waste grinder and a method for maintenance of the grinder. In addition, the controller also controls the composition of the crude argon stream until an oxygen concentration of the crude argon stream reaches a selected value. , and a steam turbine plant having a rotor formed by the material, the invention provides a steam turbine plant including a very-high-pressure turbine of which steam inlet temperature is 675 to 725\xb0 C. A fuel injection flow rate at which fuel is injected into the exhaust stream by the fuel injector can be calculated based on the adaptive control model.