The level of radiation to which workers at south China's Daya Bay nuclear plant were exposed was well within safe limits, nuclear power company said Friday.

The level of radiation to which workers at the Daya Bay Nuclear Power Station were collectively exposed more than doubled from 175 millisieverts (mSv) in October to 355 mSv in November, said a statement from China Guangdong Nuclear Power Group (CGNPG), which operates the plant.

The statement said the plant had suffered no radiation leaks in the period when the measurements increased, it said.

The company gave two reasons for the dramatic rise in collective exposure.

An increase in the number of workers during routine maintenance of facilities at the station had increased the number of people in the collective measurement of exposure, said the statement.

The second reason was that radiation levels had risen when the core nuclear facilities were opened to enable maintenance, but the levels remained well within safe limits, said a company spokesman.

CGNPG started facility maintenance and nuclear fuel replacement at the Daya Bay No. 1 generating unit on Oct. 22.

A total of 1,743 staff and contract workers took part in the maintenance work, which ended on Nov. 28, said the statement. It gave no figures for the number of workers at the plant during normal periods.

Individual radiation levels measured during the period were recorded at under 1 mSv, well within the national safe limit of 50 mSv per year and the annual 20-mSv limit set by the company, said the statement.

The millisievert is the unit used to measure the average accumulated background radiation absorbed by a person.

Radiation levels at the nuclear power plant were lower than the international average, the company said.

Up to Dec. 9, the No. 1 generating unit had operated without any equipment failures for 3,000 days since Jan. 12, 2002, said the statement

On that date the company reported an "unplanned breakdown," saying there was no radiation leakage as a result.

The Daya Bay Nuclear Power Station, jointly owned by CGNPG and Hong Kong-based electricity company CLP Holdings, has an annual electric output of around 15 terawatt hours and supplies 70 percent of its output to Hong Kong.