Abstract: Fuel performance during the operation of a nuclear power plant is a major constraint on operation management.If the performance and status of fuel rods is known before the shutdown,an appropriate fuel detection management policy can shorten the reactor outages.A diagnosis method for analyzing reactor coolant activity in order to determine the number,size and location of fuel clad failures is developed,and based on DAYA Bay nuclear power plant unit 1 cycle 2 operation data,a failure diagnosis for U1C2 fuel assembly has been carried out.It is showed that the diagnosis results are very similar to the results measured.