Specific Features of BN-1200 Core in Case of Use of Nitride or MOX Fuel

The BN-1200 reactor core has been developed for the options using the well-mastered MOX fuel and the advanced nitride fuel. Among the features of both the MOX fuel core and nitride fuel core, it should be noted that the core has a reduced power density compared with BN-600 and BN-800, the flattened configuration with the upper sodium plenum and the upper absorber shield of natural boron carbide, as well as the fuel of one enrichment (plutonium content) is used in all fuel subassemblies (FSAs). Because of the difference in the neutronic characteristics of the nitride and MOX fuels, the above-mentioned core options have certain differences in their designs: - For the MOX-fuel core the configuration with an axial breeding interlayer is applied in order to reduce the burnup reactivity loss and to ensure a 1-year operating cycle length. An additional advantage of such core configuration is that the damage dose accumulation rate is reduced. - When the nitride fuel is used, the plutonium breeding ratio in the core is self-sufficient to completely supply the reactor with plutonium in closed fuel cycle, and unlike the MOX fuel core the nitride fuel core does not have the axial and radial blankets. To minimize the reactor reactivity margin and to enhance power distribution, the peripheral FSAs use fuel pins of larger diameter (10.5 mm). (author)