In the 2009 Andra repository concept, Intermediate Level Long Lived Wastes are stored in several 100-m-long storage cells. Concrete over-packs are stacked in piles before being emplaced by row. The large sections opened in the slab floor to enable emplacement by the conveyor could have a major effect on the temperature distribution in the storage cell. The aim of the study is to assess the ability of the ventilation to regulate temperatures along the cell. We focus on the period before closure, when the ventilation rate is at a minimum. The issue has been addressed by undertaking numerical simulations. A specific modelling approach based on head-loss correlations has been used to calculate the distributions of temperature and air velocity at a decimetre scale along the storage cell. The heat transfer and the air flow problems have been solved on a 3D mesh representing 225 rows of waste packages, the concrete walls and the surrounding rock. Different scenarios have been considered about the air flow rate, the heat release and the closure of the conveyor sections at several locations. Results have been analysed in terms of flow patterns, temperature distributions and thermal gradients in air and in concrete.