System for monitoring the shut-down margin of a reactor

Object: To monitor whether the operation of a reactor can be safely stopped if for some reason a given rod should be incapable of being inserted into a reactor core. Structure: Detection signals representing neutron flux distribution around a specified control rod in the reactor, reactor core flow rate, reactor core outlet temperature and so forth are fed into a performance calculating means for calculating nuclear characteristics of a fuel assembly only in the vicinity of a specified control rod at the time of reactor shut-down. The results of calculation are then fed to a reactor shut-down safety margin evaluating means, whereby the specified control rod is withdrawn from the reactor core while the reactivity of the reactor with all the other control rods inserted in the reactor core is estimated. In this way, the reactor shut-down safety margin with respect to the specified control rod is obtained and indicated by display means. (Kamimura, M.)