The thermochemical state of UO 2 -based nuclear fuel is a key parameter for which experimental data are difficult to obtain. A new experimental procedure using in situ oxido-reduction indicators was applied to irradiated fuel, and we aim to use it with chromium-doped unirradiated UO 2 . Nevertheless, we had first to characterise the chemical state of the chromium precipitates in our sample before. Here, we present the method we used for statistical characterisation of these precipitates using several methods, amongst which Raman spectroscopy plays a major role. Moreover, the Raman spectra of the precipitates were interpreted as evidence of a uranium stabilised Cr 3 O 4 phase.