Natural convection heat transfer enhancement using cooling pipes in the heat generating debris bed

Abstract

The whole core meltdown scenario is considered as a beyond design basis accident with a probability of occurrence less than 10−6 per reactor year. To prevent and mitigate such a hypothetical severe accident, in fast breeder reactors, research has been focused on accommodating the destroyed core debris within the primary containment boundary. An in-vessel core catcher is provided to receive the fuel debris arising out of core meltdown and disperses it uniformly, thus enabling safe and adequate heat transfer by natural convection. The present study is focused on the thermal hydraulic analysis of in-vessel core catcher. A 3-D numerical analysis has been carried out in the lower plenum of the fast reactor. Turbulence is modeled using the standard k-ε turbulent model. The Boussinesq approximation is assumed for liquid sodium. The heat source is assumed to have spread on the heat shield plate and has a total volume of 5.12 m3 with inbuilt decay heat source. The mathematical model is validated with the available benchmark experimental results in the literature. The existing design of core catcher plate is modified by providing cooling pipes in the top collection plate with different configurations to assess the cooling capability of the debris by natural convection. The temperature and velocity contour are obtained to observe the flow field established above the heat source in the sodium pool. It has been found that new design of core catcher improves the natural circulation of sodium toward the center of CC and more than 50 °C temperature decrement is observed in upper heat shield plate.