This paper presents the results of experimental and computer analyses of seismic margin capacity and operability under abnormal vibration of PWR (WWER) Control Rod Drive System (CRDS). A special PC computer program “SEISM-2000” for non-linear dynamic analysis of CRDS has been developed and verified regarding to shaking table experiment of the CRDS ¼ scale model. The result of experiment and analysis show high sensitivity of the PWR CRDS operability to seismic and vibration loading.