The temperature of the reactor coolant in the cold leg is compensated by a lead-lag circuit, and is then compared with the cold leg reference temperature which is a function of station load. The error signal is then added to the difference between the reactor power and the total turbine power to form an error signal; this then passes to the principal programmer whose main role is to introduce a dead band within which all the dump valves remain closed.

The signal from the principal programmer is di­vided between two individual programmers, one tor each turbine-generator unit, according to the propor­tion of the total loss of load which has been rejected bv each unit. The signals from the indmdual pro­grammers are then used to modulate the sequential openina of the three banks of dump saUes propor — — ional to the partial error signals. Each bank of dump — ibes can be modulated tuily open or closed within 20 seconds.

Each dump vale also has associated with it a trip open setpoint. The valve is tripped to its fully open position when the error signal from the individual proarammer exceeds the trip open setpoint, the valves beins able to move from the fully closed to the fully open position within 3 seconds. The dump valves are subsequently modulated dosed as the reactor control svstem reduces the reactor coolant temperature and the error signal falls below the dead band of the load rejection controller.