[en] After generation of scram signals, the operation state of a reactor scram means is monitored on real time. When a higher rank reactor scram means is not operated or operated incompletely, lower rank reactor scram means are automatically caused to operate successively. The operation state of a reactor cooling means is monitored on real time, and when a higher rank reactor cooling means is not operated or operated incompletely, lower rank reactor cooling means are automatically caused to operate subsequently. This can reliably provide reactor scram and reactor cooling upon occurrence of a scram accident. Then, such an event that the scram accident develops to a severer accident due to poor countermeasure at the initial stage of the accident can effectively be avoided. Further, the cooling state of the reactor is evaluated with reference to a knowledge base which stores the relation of a reactor water level and a ratio between a predetermined measuring information and a minimum limit thermal flux, thereby capable of recognizing the reactor cooling state in an extremely short period of time. (N.H.)

[en] The system of the present invention collectively recognizes a state of a nuclear reactor, on a real time, after occurrence of a scram accident and informs this state to an operator by a method capable of recognizing the state at a glance. Namely, a measuring means measures the state for each reactor portions after occurrence of the scram accident. A calculation means calculates a risk index showing a degree of danger of the reactor state based on predetermined measured information among individual information obtained by the measuring means. A display means displays the risk index calculated by the calculation means. In the system thus constituted, since the risk index is calculated/displayed by using only the predetermined measured information obtained by the measuring means, the operator can recognize the degree of danger of the reactor state collectively on real time at a glance. As a result, the operator can easily perform a countermeasure at an early stage, thereby enabling to effectively prevent the scram accident from developing to severe accidents. (I.S.)