The plant which manufactures oil rigs in the southern port of Vung Tau had raised the alarm on Friday after a device that uses a radioactive substance to test for cracks in welding joints was misplaced for more than an hour.

More than 380 workers were sent for testing at a local hospital, some complaining of headaches and vomiting, said Phan Thanh Tung, director of the M and C Petroleum Technical Services Company.

Tung said five workers who had complained of dizziness remained in hospital for treatment Monday, while the others had returned to work.

"Some of them were nervous at first", said Nguyen Nhi Dien, director of the Dalat Nuclear Research Institute, were 28 workers additionally underwent chromosome tests, the results of which are to be released next week.

Dang Thanh Luong, deputy director of Vietnam's Agency for Radiation and Nuclear Safety and Control, on Monday told AFP: "After relevant tests, we confirm that there was no radiation leak."

Communist Vietnam operates a small reactor at Dalat for training and research and plans to build its first nuclear power plant by 2020.

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