inner portion of the disk. As a result of these temperature  gradients, thermal stresses are added to the rotational stresses.  Additionally, turbine blades are generally more susceptible to  operating damage than compressor blades due to the exposure  of high temperatures. There are various methods to relieve, at  least partially, the aforementioned stresses. One such method  is to bleed cooling air back onto the face of the disk. Another method of relieving the thermal stresses of the disk  is incidental to blade installation. A series of grooves or  notches, conforming to the blade root design, are broached  in the rim of the disk. These grooves allow attachment of  the turbine blades to the disk; at the same time, space is  provided by the notches for thermal expansion of the disk.  Sufficient clearance exists between the blade root and the  1-49 Figure 1-62. Impulse and reaction turbine blades. Impulse Turbine Reaction Turbine Rotor Rotor Stator Stator Rotor Rotor Moving buckets Fixed nozzle Rotating nozzle Steam pressure Steam pressure Steam velocity Steam velocity