PURPOSE: To achieve a higher accuracy of diagnosis, by performing a diagnosis from a working pattern of a comparator which is generated when a control rod controlling system fails to minimize the possibility of erroneously diagnosing the control rod controlling system to break down when it does not.
CONSTITUTION: In case a control rod is inserted due to a trouble in a control end outside a control rod controlling system 20, an output thereof 20 coincides with an output of a simulation circuit 22. So, outputs of comparators 32 and 34 both turn to '0' and hence, outputs of AND circuits 46 and 50 go to '0', which eliminates the possibility that the control rod controlling system may be erroneously diagnosed to break down due to a trouble factor in a sector other than the control rod controlling system. In case the simulation circuit 22 fails, either of the comparator 32 or 34 outputs '1'. But as there is no abnormality in signals T, F and P, comparators 36, 38, 40 and 42 all output '0' and thus, the AND circuits 46 and 50 both output '0' thereby eliminating the judgement that the control rod controlling system breaks down.
NATSUME AKINORI
TERANISHI SUSUMU
NAKAO TADASHI
