SUPPRESSING DEVICE FOR NUCLEAR REACTOR SCRAM

PURPOSE:To suppress increment of neutron flux caused by pressure rise of a nuclear reactor, and reactor scram thereby by decreasing and controlling nuclear reactor output in case that of shutting off of a main steam pipe, such as shutting off of a main steam isolation valve, and the like. CONSTITUTION:For example, in case of shutting off of a main steam isolation valve 3a of a main steam piping 2a, main steam flow amount signal fa from a main steam flow meter 15a, is input to a selection circuit 21 of a pressure controlling device 20. Then, other two main steam flow amounts fb and fb under operation, which are close to normal value, are selectivly added together by an adder 22. The addition value is divided by two by the use of an averaging circuit 23 to obtain an average value, to be compared with the previous signal fa by means of a calculator 24a, to obtain deviation by inputting the comparison difference to a deviation value detection circuit 25a and finally to judge abnormality of the piping 2a. Output signal from the detection circuit 25a is generated, via an OR circuit 26, as insertion demand signal C of a selected control rod 14 at a nuclear reactor 1, and trip demand signal P1 and run-back demand signal P2 of a recirculation pump 12. In this way, by decreasing output of the reactor 1 and preventing pressure rise in the reactor 1, reactor 1 scram caused by neutron flux rise is well suppressed.