PARIS (Reuters) - France's nuclear safety authority (ASN) said on Thursday it had provisionally classified a leak of liquid containing uranium on a site in southeastern France earlier this week at level one of the INES nuclear scale.
The International Nuclear Event Scale (INES), used to measure the potential danger of incidents at nuclear installation, has seven levels, the lowest of which is zero.
"The ASN has provisionally classified this event at the level one on the INES scale," the ASN said in a statement.
Areva said late on Tuesday that 30 cubic meters of liquid containing uranium, which was not enriched, was accidentally poured on the ground and into a river at the Tricastin nuclear site.
The incident occurred on Monday at 2300 local (2100 GMT) and was only reported to the ASN eight hours later, drawing sharp criticism from green groups. The affected residential areas were only informed at 1300 (1100 GMT) on Tuesday.
The ASN said that the latest uranium measurements taken by Areva subsidiary Socatri in rivers close to the site showed that the levels were within the guidelines of the World Health Organization for water destined for human consumption.
The ASN inspected the site on Thursday to determine the precise causes of the incident.
The nuclear watchdog added it had requested that the institute for radioprotection and nuclear safety (IRSN) to take new independent tests.
The prefecture of Vaucluse is maintaining a ban on fishing, bathing and irrigation as well as restrictions on water consumption in the affected area.
Judicial measures are not being ruled out, with the Commission for Research and Independent Information (Criirad) saying it intends to register a complaint with the Environment Minister which has indicated the possibility of recourse to the courts.
Newspaper La Provence published on Thursday extracts of a May 2007 report which said that the Socatri site had already seen repeated leaks due to old pipes that carry waste liquid.
(Reporting by Joseph Tandy)