A method for establishing a representative mapping of a power distribution within a nuclear reactor core, said mapping being established by means of sensors placed at least temporarily in the reactor core, which includes the different steps of: - equipping, at least temporarily, a first set of fuel assemblies of the nuclear reactor core with sensors of a first instrumentation system, known as a reference instrumentation system; - equipping, at least temporarily, a second set of fuel assemblies of the nuclear reactor core with sensors of a second instrumentation system; - performing a first partial set of activity measurements by means of the sensors of the reference system; - performing a second partial set of activity measurements by means of the sensors of the second instrumentation system; - converting the activity measurements of the second set of measurements into activity measurements associated with the reference instrumentation system, in order to obtain a set of converted measurements; - establishing, from the first partial set of activity measurements, from the set of converted measurements, from a complete theoretical distribution of the theoretical activities associated with a reference instrumentation system, and from a complete theoretical distribution of the theoretical activities associated with the second instrumentation system, for any instrumented point of the nuclear reactor core, a final set of activity experimental data of the reactor core, said set of data including only values related to the activities associated with the reference instrumentation system; - establishing, from the final set of experimental data and of theoretical data simulating a state of the reactor core at the time of performing the first set of measurements and the second set of measurements, the representative mapping of a power distribution within a nuclear reactor core. - equipping, at least temporarily, a first set of fuel assemblies of the nuclear reactor core with sensors of a first instrumentation system, known as a reference instrumentation system; - equipping, at least temporarily, a second set of fuel assemblies of the nuclear reactor core with sensors of a second instrumentation system; - performing a first partial set of activity measurements by means of the sensors of the reference system; - performing a second partial set of activity measurements by means of the sensors of the second instrumentation system; - converting the activity measurements of the second set of measurements into activity measurements associated with the reference instrumentation system, in order to obtain a set of converted measurements; - establishing, from the first partial set of activity measurements, from the set of converted measurements, from a complete theoretical distribution of the theoretical activities associated with a reference instrumentation system, and from a complete theoretical distribution of the theoretical activities associated with the second instrumentation system, for any instrumented point of the nuclear reactor core, a final set of activity experimental data of the reactor core, said set of data including only values related to the activities associated with the reference instrumentation system; - establishing, from the final set of experimental data and of theoretical data simulating a state of the reactor core at the time of performing the first set of measurements and the second set of measurements, the representative mapping of a power distribution within a nuclear reactor core.