Workers at the nuclear disaster zone in Fukushima were doused in radioactive water after they pulled out the wrong piece of pipe.
Six officials taking part in the clean-up operation at the site in Japan were sprayed with contaminated liquid from a desalination system, in an incident which Japan's nuclear watchdog has attributed to carelessness.
A spokesperson for the Tokyo Electric Power Co, which is overseeing the clean-up, claims the radioactive water posed little health risk to the six workers, because they were wearing protective gear at the time.
"It is serious in that it was another problem caused by carelessness, but I do not believe it is a seriously troubling dosage," said an official.
"The water did not come into contact with their faces, so there is a little possibility that the workers ingested."
However the incident has sparked further criticism of the way Tepco is handling the clean-up operation, which began after Fukushima went into meldown in March 2011.
Efforts to clean up Fukushima following the worst nuclear disaster in a quarter of a century have been dogged by mishaps.
Only last week, a plant worker switched off the pumps being used to keep the damaged nuclear reactors cool. Days before that, a storage tank for radioactive liquid was overfilled, causing a leak.
In August, 300 tonnes of radioactive water leaked into the ground from another storage tank, a month after officials admitted contaminated water was flowing into the sea.
In March, a rodent was blamed for chewing through a cable which caused a power cut and shut down the cooling systems.