Numerical study of natural convection of water in a nuclear spent fuel pool

As nuclear energy continues to be used all around the world, spent nuclear fuel continues to be created. This spent fuel releases heat and radiations and must therefore be managed with care. It is usually stored in spent nuclear fuel pools, for a long time, in which the water acts as a shield against the radiations and as a coolant to evacuate the heat. In order to gain insight on those pools, this project aims at modelling the turbulent natural convection taking place inside the pool. Two numerical models are investigated. The first one considers the surface of the pool to be a fixed wall. This is a usual case study referred to as classical Rayleigh-Bénard convection. The second one is original and models the top of the pool as a free surface. Both cases are analyzed by means of a comparison of their respective Large Scale Circulation, of their statistical profiles and their flow re-orientations. It allows one to check similarities while also spotting differences induced by the free surface, a model that corresponds more to the reality of spent nuclear fuel pools. Differences in the temperature fields as well as a loss of symmetry of the velocity fields at the top of the pool are observed. One flow re-orientation is observed in both cases over a defined time-range but differences persist in their characteristics.