A fast piezoelectric tuner has been proposed for dynamic Lorentz force compensation for the TESLA linear collider [1]. Initial experiments with the tuner have demonstrated the successful control of the cavity resonance during pulsed operation at high gradients. So far no extensive experience exists for piezos actuators operated in pulsed operation at cryogenic temperatures in presence of radiation. A series of tests has been initiated at DESY to demonstrate that piezo elements are adequate for TESLA operation in terms of gradient as well as lifetime. The paper addresses various issues including coupling to mechanical resonances, and lifetime testing exposing the piezos to gamma radiation.