Changes in the value of the control element assembly position signal (26, 28) are monitored over a preselected time period, and a determination is made whether these changes conform to a regular, predetermined pattern (S1), characteristic of normal control element assembly motion. If any change deviates (S2, S3) from the pattern by more than a permissible tolerance, a position invalidity signal is generated.
METHOD FOR DETECTING ABNORMAL GENERATION OF CORE CONTROL ELEMENT POSITION SIGNAL