South Korea has shut down two nuclear reactors after it was revealed that some parts used were not properly vetted.
Knowledge Economy Minister Hong Suk-woo says they are "non-core" parts and are not a safety threat but the shutdown means there could be "unprecedented" power shortages in the next few months.
The more than 5000 parts - including fuses, cooling fans and power switches - did not have the required nuclear industry certificates, the BBC reports.
The minister says they can be used in other industries but need international certification for nuclear power plant usage.
Almost all the parts were used at the Yeonggwang Nuclear Power Plant, in the south-west, where the two reactors were shut down.