Abstract: Device for cleaning the instrumentation guide tubes (5) of a pressurized-water nuclear reactor, comprising a pump (18) for injecting demineralized water under pressure into the tubes (5) and an assembly (15, 20, 21, 22) for recovering the radioactive waste. The assembly (15) can take up a position above each of the passages (7) located in the vessel bottom (2) and through which the guide tubes (5) open into the vessel (1). The assembly is put in place at the end of each of the passages (7) in succession, without the need to remove the lower internal equipment (9, 40) of the reactor. All operations are controlled from the platform (17) of the reactor fuelling machine. The invention is used for the maintenance of pressurized-water nuclear reactors during refuelling .