TOKYO—Six workers at Japan’s crippled nuclear power plant have been accidentally doused with highly radioactive water, the plant operator said Wednesday, adding to a growing list of mishaps that are shaking confidence in the utility’s ability to handle the crisis.

The workers removed the wrong pipe from equipment at the plant, sending toxic water spilling onto them and the entire floor of the facility housing a set of three units designed for primary, partial water treatment, said Yoshimi Hitosugi, the spokesman for Fukushima Dai-ichi nuclear plant operator Tokyo Electric Power Co.

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

In order 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, the utility reported a 300-ton leak from another storage tank. That came after the utility 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,” Tanaka said a regular news conference. “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.”

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