For 18 hours,  500 m³ of a solution containing 5 kg of uranium, 1121 kg of fluorine and 1332 kg of ammonium were emitted into the Tauran canal and then flowed into the Robine canal 3 km downstream. These substances originate from the hydrofluorination unit that transforms UO3 into UF4. This includes a heat exchanger for maintaining the temperature of the fluorinated effluents. The corrosion of this heat exchanger led to the mixing of vapours from the heating water and the fluorinated effluents. The daily analysis of the samples taken by the operator revealed that the thresholds laid down in the authorisation order had been greatly exceeded. 781 kg of fluorine and 962 kg of ammonium emitted (with thresholds of 5 and 230 kg/day respectively), followed by 340 kg of fluorine and 370 kg of ammonium on 24 August. The operator immediately shut the facility down. Additional measurements performed by the operator in the Tauran confirmed the fluorine content. The operator informed the authorities and the press.

The Inspectorate demanded that the operator perform a complete analysis of the effluent and environmental monitoring, compile a report on the accident and take measures to avoid a recurrence of the situation; 150 samples and 500 analyses of the levels of fluorine, ammonium, nitrate and uranium were taken during 7 days from the Tauran and the Robine canals. The peak of fluorine pollution was 15 mg/l in the Tauran and 0.97 mg/l at 02:00 on 25 August in the Robine (the threshold of potability is 1.5 mg/l). A low level of fish mortality was noted on 25 and 26 August. No change in pollutant content was revealed by the piezometers installed in the proximity of the Tauran. The level of the discharge fell back below the thresholds after 4 days.

According to the health services, the waters of the Tauran and Robine are not used for sensitive purposes (abstraction of drinking water, bathing); this together with the dilution of the effluent in the natural environment rule out the likelihood of any direct health issues for human populations. Since the level of the Robine was low, the Bages lagoon was not impacted.

The accident had several causes. The fluorinated effluents had been stored in a tank. In order to prevent their cooling from leading to crystallisation, circulation was maintained in an external heat exchanger containing a double-walled pipe dating from 1984. The effluents flowing into the interior pipe were heated by the steam injected between the two walls. At about 21:00 on 21 August, corrosion of a pipe inside the exchanger led to the appearance of several holes with a diameter of 1 mm and to the steam coming into contact with the effluents. The mixture was discharged into the condensate collector tank, the outlet valve of which was rapidly closed by the automatic control system, which had detected an excessively high level of conductivity. The contaminated condensates filled the tank to the point of overflowing before flowing into the retention basin. At 17:00 on 23 August, the operator detected the overflow and reopened the valve after misreading the display, believing that he had seen a value of 6 μS/cm (below the maximum threshold of 30 μS/cm), whereas the screen had changed scales, and was displaying 6mS/cm. The effluents flowed into two drainage ditches and then joined the Tauran. In the following 24 hours, the personnel switched off the site’s alarms and the ratemeter that had detected radiological activity in the discharge channel leading into the Tauran, without proceeding to dispel doubts [regarding the possibility of an accident having taken place]. Only the daily analysis of the waters of the canal made it possible to pinpoint the discharge.

Following the accident, the operator put in place a system of preventive monitoring of ageing and has reinforced the inspection of the dimensions of pipe fittings. The display no longer changes scale and gives a specific value in case of saturation. The manual valve on the condensate tank was removed, and an automatic valve was installed for the next tanks, as was an automatic shut-off for the emissions pumps in case of non-compliance. The verification of safety and environmental parameters became systematic each time new personnel take their duty, and accidental emissions are integrated into regular safety exercises. The director of the site presented a report to the Local Committee for Information and Consultation [French acronym: CLIC] on 14 September.