CONTAMINATION of the water and air around Daya Bay may leap tenfold during the refuelling process at the nuclear station compared with usual releases, the power company says.
Workers at the station are also likely to face radiation doses of at least 10 times their usual exposure.
But Hong Kong Nuclear Investment Co (HKNIC) safety adviser Jacques Pretti said the changes were not unusual.
The company said the radiation released from the plant was already 10 times that from similar French plants, which an independent consultancy said was high.
But it said the releases were within international guidelines.
The Friends of the Earth said it was concerned about the effects on the environment and was seeking further data from academics and the company.
The news came ahead of the release today, for the first time, of a bulletin giving an insight into the plant's day-to-day operation, following concerns among legislators about secrecy at the plant.
These bulletins would probably be issued monthly, as they were in other plants around the world, said Mr Pretti.
HKNIC managing director Dr Lee Yui-bor will today launch the first leaflet and explain the refuelling shutdown, which starts a week today.
During the 41/2-month operation, the reactors will be opened, all the potentially lethal, highly radioactive fuel rods removed and two-thirds put back, with new ones to replace the other spent third.
Unit one of the twin-reactor station will close for 11 weeks, restarting on February 26. Unit two, which went into service six months after the first, will shut on March 10 for a shorter period.
Apart from the dangerous refuelling - during which the rods are transferred under water, which absorbs radiation - all parts of the reactor and circuits have to be checked for tiny cracks or weak welds that could lead to a disaster if not spotted.
More than 5,000 workers, mostly local contractors, will be involved compared with the usual 2,500.
Yesterday, Mr Pretti said the bulletin would include details of radioactivity released each month as gases from the building that linked the two reactor buildings or in water contaminated as it cools the radioactive reactor core.
Although gases and water were filtered, some radioactivity was bound to remain, he said.
And during the 'outage', particularly if the fuel rods had tiny cracks, extra radiation was bound to leak out, he said.
'If we have to perform inspection of some highly radioactive components, a tenfold increase [in dose to workers] is not unusual. Some components are highly contaminated,' he said.
Between January and October, the company had released 11.1 per cent of the limit of radiation allowed to be released each year, he said.
Michael Schneider of the World Information Service on Energy in Paris said that was 'quite a bit' compared with other plants.