In November 2012 it was discovered that over 5,000 small components used in five reactors at Yeonggwang Nuclear Power Plant had not been properly certified; eight suppliers had faked 60 warranties for the parts. Two reactors were shut down for component replacement, which is likely to cause power shortages in South Korea during the winter.[13] Reuters reported this as South Korea's worst nuclear crisis, highlighting a lack of transparency on nuclear safety and the dual roles of South Korea's nuclear regulators on supervision and promotion.[14] This incident followed the prosecution of five senior engineers for the coverup of a serious loss of power and cooling incident at Kori Nuclear Power Plant, which was subsequently graded at INES level 2.[13][15]

In 2013, there was a scandal involving the use of counterfeit parts in nuclear plants and faked quality assurance certificates. In June 2013 Kori 2 and Shin Wolsong 1 were shutdown, and Kori 1 and Shin Wolsong 2 ordered to remain offline, until safety-related control cabling with forged safety certificates is replaced.[16] Control cabling in the first APR-1400s under construction had to be replaced delaying construction by up to a year.[17] In October 2013 about 100 people were indicted for falsifying safety documents, including a former chief executive of Korea Hydro & Nuclear Power and a vice-president of Korea Electric Power Corporation.[18]

http://en.wikipedia.org/wiki/Nuclear_power_in_South_Korea