Establishment of Thermal Mixing Behavior in Grid Plate of FBRs 1 & 2

The safety of a nuclear reactor should be ensured at all reactor operating conditions. During an unexpected transient in the secondary circuit, the inlet temperature of primary sodium into the grid plate (inlet plenum) through different inlet windows differentiates. In such cases, the mixing behavior of the flow inside the grid plate needs to be established in order to estimate the rise in central sub-assembly outlet temperature, which acts as an important alarming parameter. Toward this, a 3D thermal hydraulic analysis is carried out for the grid plate of FBRs 1 & 2 to establish and quantify the thermal mixing of primary sodium inside the grid plate. The differential inlet temperature of primary sodium, of 10 °C, during transient conditions is considered between two and four inlets, respectively in the present study. Based on the conservative analysis, thermal influence is observed in 120° in the vicinity of these pipes. Good mixing is observed at the outlet of central SA.