JPS6120832B

PURPOSE:To prevent the scram from being caused by the drop-off of a control rod driving shaft due to a trouble, by providing in an optional position within the range of motion of a control rod driver a means for automatically operating a wrong scram preventer. CONSTITUTION:The electric wrong scram preventer comprises a scram lock-up casing 28 engaged with a latch push plate 13, scram lock-up claws 26 pivoted to support rods 27, and a grabbed annular projection 30 provided on the upper end of the control rod driving shaft 14. When an electromagnet 10 is energized, the grabbed annular projection is set in such a position that the scram can be locked up. Then, the scram lock-up casing 28 moves upward and the scram lock-up claws 26 hold the annular projection 30 of the control rod driving shaft 14 to prevent the shaft 14 from dropping off.