The PUREX process has been designed for the reprocessing of spent nuclear fuel to separate uranium and plutonium from the fission products. Following the dissolution of the irradiated fuel in aqueous nitric acid, uranium and plutonium are transferred to an organic phase by intensive mixing with an organic solvent extraction (tributyl phosphate in kerosene), while fission products remain in the aqueous nitric phase. The degradation products of TBP by hydrolysis can react with nitric acid through very exothermic chemical reactions that can lead to a rapid increase of temperature in the reprocessing vessels. In the worse cases, the in-cell solvent fire is considered to be an important postulated accident even if its probability is low. In such cases plutonium is released in volatile forms such as PuO₂, PuO₃ or PuO₂(OH)₂. Our theoretical study focusses on the thermodynamics properties of those molecules, in particular the former two species for which large experimental uncertainties remain.