PARIS (Reuters) - France's nuclear safety authority (ASN) said on Friday that Areva-subsidiary Socatri had poorly managed a leak of liquid containing uranium that occurred in southeastern France this week.
The nuclear watchdog inspected the site on Thursday.
"The management of the crisis by the company involved has shown omissions in terms of communication to the authorities," the ASN said in a statement.
A formal report on the event will be delivered to France's attorney general, the ASN said, adding that the incident was officially classified at level one on the International Nuclear Event Scale.
The scale has seven levels, the lowest of which is zero.
Areva said 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.
This led local authorities to ban fishing and swimming in the affected areas, as well as the use of contaminated water for consumption or irrigation.
The ASN inspection also revealed that security measures put in place by Socatri to prevent further leaks were not satisfactory, and that operational conditions at the site at the time of the event displayed irregularities.
The ASN also indicated that Socatri had ignored a leak found in tank a week ago.
ASN's local official Philippe Ledenvic said the error was "rare" and "unacceptable".
The ASN added it had asked Socatri to halt the arrival of liquid effluent for treatment at the site and for security measures to be put in place.
The nuclear watchdog requested a reinforced surveillance plan with regular tests on rivers and groundwater.
But French anti-nuclear group Sortir du Nucleaire also attacked the nuclear watchdog for warning the local authorities too late and said it would file a complaint against the ASN.
"The ASN is trying to hide its own responsibilities because it withheld information," said Stephane Lhomme, head of the anti-nuclear group.
The incident occurred on Monday evening and was only reported to the ASN at 0730 (0530 GMT) on Tuesday, which in turn communicated safety procedures to the relevant prefectures -- local councils -- just before noon, the ASN said.
"When I received the first phone call at 0730, I was not informed of the leak in the water," Charles-Antoine Louet, head of the regional ASN told Reuters, adding that it was only two hours later that he was given the full details of the event.
The ASN then drew up safety measures that it communicated to the Vaucluse and Drome prefectures. "We are convinced that the sanitary impact on the environment is negligible," Louet added.
(Additional reporting by Catherine Lagrange in Lyon)