Up to 800 people are being examined for contamination after a leak of radioactive material at a nuclear plant in northeast Spain last November, the nuclear watchdog said on Monday.

The Nuclear Safety Council (CSN) said it had so far examined 579 out of between 700 and 800 people who had been through the Asco I nuclear plant in Tarragona since the leak and none had been found to have been contaminated.

The CSN said it was considering sanctions against the plant's operators for not providing it with enough information about the leak, which it considered to be more serious than originally classified.

The CSN was not advised until April 4 of the leak, which occurred during refuelling at the 1,000 megawatt Endesa-owned Plant.

The leak was first made public by environmental group Greenpeace on April 5 and confirmed shortly afterwards by the CSN, which sent inspectors to the site.

In a statement the CSN said it had raised its rating of the leak to 2 on the International Nuclear Event Scale (INES) for "inadequate control of nuclear material and for supplying incomplete and deficient information to the regulator".

The CSN said it would demand those responsible be found.

"From the sequence of events it may be deduced that the operator knew on April 9 that the information on total activity spilled was not correct and not forwarded to the CSN," it said.

The watchdog added that the plant's management now estimated that a maximum of 84.95 million becquerels (Bq) of radioactivity had been leaked, which compares to a figure of 235,000 Bq published on April 8.

"The radiological impact derived from the new data is still of very little significance to the population around the plant," the CSN said.

RENEWABLE ENERGY

Manuel Rodriguez, head of radiological protection, told Spanish state radio that those who had passed through the plant were being checked for contamination as a safety precaution.

"In the same way we are taking measures outside the site," he said.

In an earlier statement, the CSN said its inspectors had found radioactive materials including cobalt-60.

Cobalt-60 is produced when materials like steel absorb radioactivity from reactors, according to the U.S. Environmental Protection Agency. It has medical uses, like radiotherapy, but can be dangerous as it emits gamma rays, exposure to which over time can cause cancer.

CSN president Carmen Martinez has asked to give evidence to parliament.

The Asco I plant was shown as working normally on the CSN Web site.

Greenpeace called for the plant's operation to be suspended.

Asco I has a pressurised water reactor (PWR) and is owned by Spain's second largest utility Endesa. It came on stream in August 1983 and its operating permit is due to expire in 2011.

Spain's recently re-elected Socialist government has pledged to phase out the country's eight nuclear plants and step up electricity generation from renewable energy sources.