Patent ID: 8767904

Claim:
A method for operating a pressurized water nuclear reactor comprising a core containing nuclear fuel assemblies comprising nuclear fuel rods, the method comprising: operating the nuclear reactor for successive cycles with, between each cycle, steps for replacing spent nuclear fuel assemblies with fresh nuclear fuel assemblies, including: operating the nuclear reactor for an initial cycle for starting the nuclear reactor, during which the core contains initial nuclear fuel assemblies, at least some of the initial nuclear fuel assemblies only comprising nuclear fuel rods, before irradiation, containing uranium oxide and not containing any plutonium oxide; then operating the nuclear reactor for transition cycles, at least some of the initial nuclear fuel assemblies being progressively replaced during the replacement steps preceding the transition cycles, with transition nuclear fuel assemblies or with plutonium-equilibrium nuclear fuel assemblies, the plutonium-equilibrium nuclear fuel assemblies only comprising, before irradiation, nuclear fuel rods exclusively based on uranium and plutonium mixed oxide, the nuclear fuel rods of each plutonium-equilibrium nuclear fuel assembly having a same nuclear fuel isotope composition and a same nominal total plutonium mass content; and then operating the nuclear reactor for at least one plutonium-equilibrium cycle during which the core only contains plutonium-equilibrium nuclear fuel assemblies.