Method of detecting fuel assembly failure

Purpose: To shorten the time required for the failure detection of fuel assemblies thereby improve the plant operation efficiency and reduce the operator's exposure dose. Constitution: Channel water has been shipped so far to each of fuel assemblies in the prior art. According to the present invention, channel water of a plurality of fuel assemblies is shipped and sampled and mixed in a sample container. Then, the collected sample water is applied with chemical treatment and then subjected to radioactivity measurement. If sample water contains more than a predetermined amount of nuclear fission products as the result of the measurement, radiation measurement is conducted for the individual fuel assemblies to specify a failed fuel assembly. While on the other hand, if more than a predetermined amount of fission products are not detected in the mixed sample water, the processing is applied based on the judgement that there is no failure for a plurality of fuel assemblies, from which sampling has been made. This method enables to remarkably shorten the time required for the failure detection operation, as well as reduce the operator's radioactivity exposure dose. (Kawakami, Y.)