South Korea on Monday restarted one of three nuclear reactors shut down for safety reasons, easing fears of power shortages during the harsh winter.

Half of the six reactors at Yeonggwang, one of the country's largest nuclear power complexes, were shut down in November, two of them to replace "non-core" parts that had been provided with forged quality and safety warranties.

The Ministry of Knowledge Economy said operators restarted one reactor at Yeonggwang in the evening following approval by the Nuclear Safety and Security Commission.

"Another reactor is expected to pass our safety checks soon for normal operations," said commission spokeswoman Shim Eun-Jung.

A third reactor was closed after minor cracks were found during maintenance work on control rod tubes.

Although operators insisted there had never been any threat of a radiation leak, the incidents stoked safety concerns heightened by last year's nuclear disaster at Fukushima in Japan.

South Korea has 23 reactors nationwide, which generate around 35 percent of the country's electricity.

The government has vowed to stick to its nuclear power programme despite the Fukushima crisis, and plans to build an additional 16 reactors by 2030.