The implementation of Sizewell B automatic control systems

The author describes a strategy for the implementation of closed loop control at Sizewell `B´ and the principles of the allocation of control functions to different computer control systems. It is shown that the station automatic control system (SACS) control loops are significant to safety and also have a direct effect on station output. Probabilistic safety assessment target reliabilities are derived making it essential to implement the SACS within the environment of the high integrity control system (HICS). Specific features of both the HICS design (redundant hardware) and SACS system design (redundant plant sensors and signal selection) are shown necessary to meet the calculated reliability targets