In an uranium processing plant, a leak occurred at around 3:10 p.m. on an external 45 m³ tank containing uranyl nitrate (41.8 m³ of effluent containing nitric acid at 23 g/l of uranium). The leak occurred during a maintenance operation being performed by 3 people (involving the replacement of the heating pin in a thermowell of the tank). The tank’s thermowell would have broken. The stream of product, estimated at 2 or 3 m³, sprayed droplets into the face of an employee working nearby. The leak’s flow rate was quite high (30 m³/h).

The plant’s internal contingency plan was initiated, and the facility was secured. The intervention crew set up a deflector to channel the leak to the retention basin. A second agent was also sprayed with product while installing the deflector. The 37 m³ of effluent was confined within the retention basin, but 4.5 m³ was accidentally released, including 2 m³ dispersed via the stormwater network and recovered in isolated storm basins. Absorbents were spread abundantly outside the retention basin while contaminated absorbents were recovered and placed in drums.

The area was rinsed, and a vinyl cover was installed to prevent any transfer to the stormwater network. The contents of the retention basin were pumped out by an external company and then sent to nearby storage tanks for reuse. Radiation protection measures conducted on all personnel involved in the operation showed slight natural uranium contamination on the 3 workmen.

The preliminary risk analysis of the maintenance operation identified only one electrical risk leading to the issuance of a work permit. The 316L grade stainless steel tank, on which the accident occurred, had been in service for less than 10 years. It had not been inspected since then because it was not subject to the modernisation plan, although its construction code (CODRES) recommended quarterly monitoring and a detailed external inspection every 5 years.