Japanese research lab reports radiation leak, but no injuries or emissions outside facility

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A nuclear research lab in northern Japan has reported a radiation leak that may have affected 55 people, though none were hospitalized and no impact was expected outside the facility.

The Japan Atomic Energy Agency said Saturday that the accident occurred Thursday at a nuclear physics lab in Tokaimura, the site of at least two previous radiation accidents.

Four researchers were tested afterward, with the highest radiation dose found to be 2 millisieverts. Nuclear workers generally are limited to 100 millisieverts of exposure over five years.

The leak occurred when experimental equipment overheated, causing the evaporation and release of radioactive gold. Since the leak originally was thought to have been contained inside the lab, the incident was not initially reported, and workers used a ventilation fan, causing radiation to spread.