Five workers were contaminated during refuelling of the reactor at Daya Bay nuclear power station. The incident happened when the workers accidentally turned on a pump, spilling radioactive water. Yesterday, an environmentalist and a legislator said they were alarmed at news of the accident, which happened in April. One per cent of the water, used in the cooling system, escaped into the concrete shell surrounding the reactor, but did not go outside the power station. The workers were checked for radiation and found to contain levels similar to the average person. Spokesman for the Hong Kong Nuclear Investment Company, John Tang Ho-pak, said the level of radioactivity in the water was so low the maximum dose absorbed by the workers was barely measurable. He denied the incident was an accident and said it was 'an anomaly' caused by human error. Frontier legislator Emily Lau Wai-hing said a full inquiry should be conducted and the results made public. 'Any kind of accident would cause concern. We don't want to be unnecessarily alarmist but if they can have more transparency I think people would be more encouraged.' Greenpeace China director Anne Dingwall said: 'There is no room for operator error in a nuclear plant.'