Natural Heat Convective Coefficient Measurements Around a Large-Diameter Cylindrical Surface Equipped with Axial Fins

Used nuclear fuel transportation casks are subjected to a permanent heat load that must be released in the air by passive dissipation as natural convection and infrared radiation. Because of the large size of the cask, natural convection operates in nonisothermal conditions at very high Rayleigh numbers where few experimental works exist and where computational fluid dynamics codes are often not representative. Thermal tests are then needed to estimate and check thermal designs. This work is a starting point of a research and development program that aims to improve the knowledge of natural convective heat transfer around casks, to explain the effect of a design parameter such as fins, and finally to propose and check improved solutions. In this work, we present the qualification of a mock-up that has been set up to measure the local heat convective coefficient of a fin-equipped cask in transport conditions. The geometry concerns short axial fins that are widely used on transportation/storage casks. The first results show a large variation of the heat convective coefficient along the cask from a constant low level at the bottom and then a linearly increasing level leading to a maximum value close to the top that is strongly temperature dependent.