A leak occurred on a 130 m³ tank of concentrated nitric acid (14N) in a unit manufacturing uranium tetrafluoride from uranium ores. This leak, with a flow rate estimated at between 10 and 20 l/h, was contained in the retention system connected to the tank. The emergency response operations included marking out the sector, spraying the area in order to contain the release of nitrous vapours and blocking the site entrances. No environmental impact was reported because all of the nitric acid contained in the leaky tank (112 t) was recovered and transferred to other storage capacities, and the acid contained in the retention system was treated in a waste treatment plant. No nitrous vapour was detected further than 10 m from the storage tank. Corrosion of an area at the base of the tank along a weld bead (old repair) had caused the leak. The tank was opened and a surface inspection was carried out to check the thickness of the base in particular. Repairs were carried out. The same inspections will be carried out on the site’s second nitric acid storage tank.