Abstract: The invention concerns a method and a device for evaluating the integrity of the nuclear fuel in a nuclear plant having a reactor (1) enclosing a reactor core formed by a number of fuel cladding members (2) arranged to enclose said nuclear fuel. The value of each of a number of parameters including activity data (4) of the off-gases from the reactor is determined. The value of each of a number of second parameters including chemical data and activity data of the liquid (5) flowing through the reactor is determined. The value of each of a number of operational parameters (6) including at least one of the reactor effects, control rod position, actual fuel type, flow of off-gases, and flow of the liquid flowing through the reactor is determined. The value of the first and second parameters are standardized (7, 8) in relation to the values of said operational parameters.