IN AN 11-week period workers at Daya Bay nuclear power station may be exposed to the largest dose of radiation considered acceptable for members of the public over the course of a year, the power company revealed yesterday. But the estimated average dose of five millisieverts (mSv) during the station's first annual refuelling process starting on Saturday is less than that received from a chest X-ray, according to Hong Kong Nuclear Investment Company (HKNIC) managing director Lee Yui-bor. The International Commission on Radiological Protection sets a maximum five mSv for the general public and 10 times that amount for those working at nuclear plants. Mr Lee said the average person in Hong Kong was exposed to 3.3 mSv a year. During the station's refuelling, the reactors will be opened and the highly radioactive fuel rods removed. A third of the rods will be replaced. The other two-thirds will be put back. Inspection of highly contaminated components is expected to increase radiation levels. During the process, air and water contamination around Daya Bay could jump by as much as 1,000 per cent but the company said this was still considered safe. The station's normal radiation output is already 10 times that of similar plants in France. But HKNIC safety adviser Jacques Pretti said it was unfair to compare the new Daya Bay with ones that had more than a decade to perfect their safety equipment and procedures. 'If you compare levels in Daya Bay with levels in France 15 years ago, Daya Bay is better,' he said. The refuelling is not expected to affect power supplies in Hong Kong.