Device for protecting reactor-core upon control rod drop

Purpose: To enable rapid reactor core protecting operation such as control rod blocking and reactor trip by the easy and sure detection for the control rod drop. Constitution: An axial offset signal preparing device, an axial offset detecting device and a control rod drop judging device are connected to power range neutron detectors. The axial offset detecting device has a function of detecting V-shaped axial offset changes, in which both of the changes in the negative variation coefficient in excess of a setting value and the changes in the positive variation coefficient in excess of a setting value are resulted within a predetermined of time with respect to the axial offset on the basis of the axial offset signal inputted from the axial offset signal preparing device. Thus, the characteristic V-shaped changes in the axial offset of neutron fluxes accompanying the control rod drop can be detected thereby enabling to carry out rapid reactor core protecting operation such as the control rod blocking and the reactor trip. (Horiuchi, T.)