Fundamental study on design margin for fast reactor plant with seismic isolation system

A sodium-cooled fast reactor plant uses liquid metal sodium as a coolant. Sodium has a high boiling point and excellent heat transfer capabilities. These properties allow the reactor to operate at low pressure. However, thermal fatigue occurs due to repeated thermal expansion and contraction within the creep temperature range. Accordingly, the fast reactor’s components and piping are designed with thin walls. Seismic isolation systems are used to reduce the seismic loads acting on components. Seismic isolation systems are used to reduce the seismic loads acting on components. Research and development of seismic design methods is progressing. Applying seismic isolation to nuclear power plants requires clarifying the design margin approach for equipment in fast reactor plants and seismic isolation devices. Here, the design margin refers to the margin relative to the design criteria for components or seismic isolation systems, i.e. the ratio of seismic response to the design criteria for the design basis ground motion, The design margin should be set to a value equal to or greater than the safety margin. Here, the safety margin is defined as the minimum margin specified in regulatory requirements and standards. This report proposes an approach for determining design margins for fast reactor plants with the horizontal seismic isolation system. We conducted the seismic response analysis of the reactor building and created the fragility curve with buckling evaluation of the reactor vessel. Based on these results, an approach for determining design margins of the components and the horizontal seismic isolation system was investigated.