SEOUL - South Korea nuclear regulators have found microscopic cracks in tunnels that guide control rods at a nuclear plant under maintenance, government officials said on Friday, raising new concerns over the country's nuclear power sector.

The discovery of the cracks comes after South Korea's state utility shut down two reactors at the same Yeonggwang plant to replace parts that had been provided with forged certificates.

"There are cracks in six tunnels. The reactor has been halted since October 18 for regular maintenance and now the process has been extended by a further 47 days for repair of the cracks," a spokeswoman of the Korea Nuclear Safety and Security Commission said.

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