Abnormality detector for pressure tube type reactor

In an abnormality detector for a pressure tube type reactor, means are disposed at two positions of a flow channel for measuring a physical amount of coolant flow rate. That is, a means is disposed to a lower shielding plug for measuring the momentum by utilizing mechanical deformation caused by increase/decrease of flow rate, and a signal line from the measuring means is led out of the pressure tube. The rate of coolants is measured based on the pressure difference between the two points of the flow channel, and a difference between a measured value and a preset reference value is calculated to judge the presence or absence of an abnormal event, then the position where the event occurs is detected and the kind of the abnormal event is judged. Further, a monitor is disposed for displaying the occurrence, position, and kind of the event. When the occurrence of the abnormal event is judged, a reactor is automatically controlled depending on the position and the kind of the event. When coolants in a subcooling state upon starting of the operation begin to continuously boil in the pressure tube, the result of the analysis how to change the coolant flow rate at the inlet is provided as a base. (N.H.)