1. A method for analyzing at least one fuel rod comprising a stack of nuclear fuel, a rod comprising packed zones completely filled with fuel and intermediate zones partially full of fuel, the method being implemented by an analysis system comprising a gamma ray spectrometry device having a sensor and a spectrometry processing unit, the method comprising the following steps: measuring gamma ray radiation emitted by the nuclear fuel with the sensor of the gamma ray spectrometry device to acquire spectrometry measurements of said at least one fuel rod; acquiring a count profile with the spectrometry processing unit associated with a non-migrating isotope in said at least one fuel rod, a count profile being derived from the spectrometry measurements taken along the at least one rod for said non-migrating isotope with the sensor of the gamma ray spectrometry device; determining with the spectrometry processing unit a set of at least one indicator K_i to quantify a reduction in material at an intermediate zone of index i, the said indicator being deduced from the count profile; and detecting a change in geometry of said at least one fuel rod with the spectrometry processing unit by comparing the set of at least one indicator K_i against a set of at least one reference value RK indicative of the initial geometry of the nuclear fuel stack.