A method for operating a pressurized water nuclear reactor comprising a core containing nuclear fuel assemblies comprising nuclear fuel rods, the method comprising steps consisting of operating the nuclear reactor during successive cycles with between each cycle, steps for replacing spent nuclear fuel assemblies with fresh nuclear fuel assemblies, a method wherein: - the reactor is operated for at least one plutonium-equilibrium cycle during which the core contains plutonium-equilibrium nuclear fuel assemblies, the plutonium-equilibrium nuclear fuel assemblies comprising before irradiation nuclear fuel rods exclusively based on uranium and plutonium mixed oxide, and for each plutonium-equilibrium nuclear fuel assembly the nuclear fuel rods exclusively based on uranium and plutonium mixed oxide having the same isotope composition of nuclear fuel and the same nominal total plutonium mass content, and then - the reactor is operated for transition cycles, at least some of the plutonium-equilibrium nuclear fuel assemblies being progressively replaced, during the replacement steps preceding transition cycles, with: • zoned transition nuclear fuel assemblies, the zoned transition nuclear fuel assemblies each comprising: ▪ a central zone comprising nuclear fuel rods, which, before irradiation, contain uranium oxide but do not contain any plutonium oxide, and ▪ a peripheral zone extending along outer faces of the zoned transition nuclear fuel assembly, the peripheral zone only comprising before irradiation nuclear fuel rods exclusively based on uranium and plutonium mixed oxide, and then • uranium-equilibrium nuclear fuel assemblies, the uranium-equilibrium nuclear fuel assemblies only comprising before irradiation nuclear fuel rods which contain uranium oxide but do not contain any plutonium oxide, - the nuclear reactor is operated for at least one uranium-equilibrium cycle in which the core contains uranium-equilibrium nuclear fuel assemblies, the uranium-equilibrium nuclear fuel assemblies only comprising before irradiation nuclear fuel rods which contain uranium oxide but do not contain any plutonium oxide. - the reactor is operated for at least one plutonium-equilibrium cycle during which the core contains plutonium-equilibrium nuclear fuel assemblies, the plutonium-equilibrium nuclear fuel assemblies comprising before irradiation nuclear fuel rods exclusively based on uranium and plutonium mixed oxide, and for each plutonium-equilibrium nuclear fuel assembly the nuclear fuel rods exclusively based on uranium and plutonium mixed oxide having the same isotope composition of nuclear fuel and the same nominal total plutonium mass content, and then - the reactor is operated for transition cycles, at least some of the plutonium-equilibrium nuclear fuel assemblies being progressively replaced, during the replacement steps preceding transition cycles, with: • zoned transition nuclear fuel assemblies, the zoned transition nuclear fuel assemblies each comprising: ▪ a central zone comprising nuclear fuel rods, which, before irradiation, contain uranium oxide but do not contain any plutonium oxide, and ▪ a peripheral zone extending along outer faces of the zoned transition nuclear fuel assembly, the peripheral zone only comprising before irradiation nuclear fuel rods exclusively based on uranium and plutonium mixed oxide, and then • uranium-equilibrium nuclear fuel assemblies, the uranium-equilibrium nuclear fuel assemblies only comprising before irradiation nuclear fuel rods which contain uranium oxide but do not contain any plutonium oxide, • zoned transition nuclear fuel assemblies, the zoned transition nuclear fuel assemblies each comprising: ▪ a central zone comprising nuclear fuel rods, which, before irradiation, contain uranium oxide but do not contain any plutonium oxide, and ▪ a peripheral zone extending along outer faces of the zoned transition nuclear fuel assembly, the peripheral zone only comprising before irradiation nuclear fuel rods exclusively based on uranium and plutonium mixed oxide, and then ▪ a central zone comprising nuclear fuel rods, which, before irradiation, contain uranium oxide but do not contain any plutonium oxide, and ▪ a peripheral zone extending along outer faces of the zoned transition nuclear fuel assembly, the peripheral zone only comprising before irradiation nuclear fuel rods exclusively based on uranium and plutonium mixed oxide, and then • uranium-equilibrium nuclear fuel assemblies, the uranium-equilibrium nuclear fuel assemblies only comprising before irradiation nuclear fuel rods which contain uranium oxide but do not contain any plutonium oxide, - the nuclear reactor is operated for at least one uranium-equilibrium cycle in which the core contains uranium-equilibrium nuclear fuel assemblies, the uranium-equilibrium nuclear fuel assemblies only comprising before irradiation nuclear fuel rods which contain uranium oxide but do not contain any plutonium oxide.