System for preventing erroneous operation of control rods

A system for preventing erroneous operation of control rods to be inserted in a nuclear reactor comprising:

• a control rod objective position setting means for producing an objective position setting signal indicating an objective position of a control rod selected to be driven;
• a control rod drive means for moving the selected control rod in the axial direction thereof in said nuclear reactor on the basis of said objective position setting signal;
• a control rod position detecting means for detecting a position of the selected control rod to produce a position signal;
• an operation means for obtaining a first absolute value representing a difference between said objective position setting signal and the position signal before movement of the selected control rod, and a second absolute value representing a differencce between said objective position setting signal and the position signal during movement of the selected control rod, for comparing said first absolute value with said second absolute value thereby to produce a movement blocking signal when said second absolute value exceeds said first absolute value, and for discriminating, after occurrence of said movement blocking signal, the direction of movement of the selected control rod necessary for approaching said second absolute value to said first absolute value to produce a rod block release signal and a return movement command signal;
• a control rod blocking means for stopping operation of said control rod drive means in response to said movement blocking signal and for establishing again an operative condition of said control rod drive means in response to said rod block release signal;
• and
• a return operation commanding means for causing said control rod drive means to operate whereby the selected control rod is accurately moved to said objective position thereof.