Method of detecting fuel failures

Purpose: To improve the detection accuracy for the presence or absence of nuclear fission products. Method: The top end of an optional fuel assembly in a reactor vessel is covered with a cap formed with an air pipe and a sampling pipe. Then, air is sealed through the air pipe to interrupt the flow of the coolants from below to above within the fuel assembly and this state is maintained for a certain period of time. Then, the total amount of the coolants stagnating in the fuel assembly is sampled from the sampling tube in which a portion of them is collected in a sampling vessel and the remaining portion is flown back through a by-pass to the reactor vessel. Since the coolants at each of the positions in the fuel assembly are sampled portionwise homogenously, nuclear fission products deviated locally can also be collected surely. Furthermore, the required amount of sampling may be relatively small and the operation can be facilitated. (Sekiya, K.)