Conceptual design study of the actinide recycle reactor; Study of core structural with ductless fuel assemblies

Ogawa, Shinta; Hayafune, Hiroki; Tozawa, Katsuhiro; Ichimiya, Masakazu; Hayashi, Hideyuki; Mukaibo, Ryuichi

It is required enhanced core safety characteristics, recycle cost reduction, mitigation of risk to the environment and nuclear non proliferation for the fast reactor at the commercial use age of actinide recycle. The ductless fuel assembly, which has no wrapper tube, is promising for these requirements. In this study, the thermal hydraulic and mechanical characteristics of the ductless fuel core are evaluated for 600MWe MOX core with high burnup and long operating cycle length, and conceptual structure of the ductless fuel assembly core was established. The results of the study are summarized as follows; (1)Structural of Ductless Fuel Assembly. Conceptual design of components of the ductless fuel assembly, e.g. grid spacer, tie rod, upper shielding, lower nozzle and mechanical hold down spring, were performed and conceptual structure was established. Detail study of fuel pin bundle stiffness are required in the following design study. (2)Thermo-hydraulic Characteristics of Ductless Core and Ductless Fuel Assembly. The bypass flow rate strongly depends on the gap between core region and core barrel. For this bypass flow, it is found that thermal hydraulic feasibility is expected when the gaps between core region and core barrel are decreased(1mm). Since the core flow distribution is uniform, a coolant temperature distribution depend on the power distribution into core region. For fuel assembly, if the gaps between fuel assemblies are enlarged, the maximum sodium temperature increases (20C/mm), therefore a proper gap design are needed. (3)Mechanical Characteristics of Ductless Core. The seismic safety of ductless core, in which a mechanical hold down are used, is assured. To decrease the impact force at spacer grid, however, some considerations on the grid design is necessary to avoid buckling. (4)Thermohydraulic Safety Characteristics. The maximum sodium temperatures are roughly evaluation under the condition of natural circulation and coolant ...