Exposure to the workers, who were wearing face masks with filters, protective hazmat suits and raingear, is believed minor but still under investigation. The six were part of an 11-member team, and the remaining five were not affected. The workers managed to reattach the pipe.

The accident is the latest in a spate of leaks and other problems caused by human error that have added to public criticism of Tepco’s handling of the crisis at the Fukushima Dai-ichi, which is still in precarious condition since its triple meltdowns following the March 2011 earthquake and tsunami.

To keep the melted reactors cool, they must be continuously doused with water that then becomes contaminated with radiation and must be pumped out and stored in tanks at the site.

Last week, workers overfilled a storage tank without fully checking water levels, causing a leak, possibly to the sea.

In August a 300-ton leak seeped from another storage tank. That came after the company and the government acknowledged that contaminated groundwater was seeping into ocean at a rate of 300 tons a day for some time.

Japan’s Nuclear Regulation Authority Chairman Shunichi Tanaka said repeated mishaps could be a sign of the harsh work environment.

“Careless mistakes are often linked to (declining) morale,” he said. “People usually don’t make silly, careless mistakes when working in positive environment and motivated. The lack of it, I think, may be related to the recent problems.”

-AP