By Meeyoung Cho
SEOUL, Dec 12 (Reuters) - South Korea will start a winter campaign on Monday to curb peak power demand as a quarter of its nuclear units are offline, including one shut as planned on Thursday for maintenance.
Such campaigns in Asia's fourth-largest economy have become routine during peak demand periods since late last year due to the nuclear safety scandal that has shut some nuclear units and delayed others from starting up operations.
The energy ministry said on Thursday power-saving measures include keeping indoor temperatures at 18 degrees Celsius, and limiting lighting and the use of individual electrical heaters at public firms, "as anxiety over winter power supply could be hiked depending on when three nuclear reactors are restarted."
If the restarts of the three reactors shut in late May to replace control cables supplied with fake certificates are delayed beyond the end of this year, this could cause unstable power supply during the coldest winter months, the ministry said in a statement.
The government plans to impose penalties of up to 3 million won ($2,900) from Jan. 1 on any shops which turn on heaters while leaving doors wide open.
Of South Korea's 23 reactors, which account for a third of the country's power supply, six are offline as of Thursday including the three for cable replacement.
A fourth shut earlier on Thursday for a scheduled maintenance through Jan. 19 according to reactor operator Korea Hydro & Nuclear Power, owned by state-run utility Korea Electric Power Corp (KEPCO).
Another reactor is awaiting an extension of its licence after its 30-year lifespan expired in November last year; a sixth is shut by scheduled maintenance extended to mid-January to repair cracks found on the reactor head.
A spokesman for Korea East-West Power, also owned by KEPCO, said its two coal-fired power units with a combined capacity of 1,000 megawatts were also shut for a technical glitch on Thursday, but would be restarted later in the evening.
South Korea is in the midst of reviewing a draft energy policy that calls for it to cut its reliance on nuclear power to 29 percent by 2035, down from an earlier plan to increase the dependence to 41 percent by 2030.
Seoul has been under pressure to curb nuclear power use after the scandal that erupted when some reactors were found to have received replacement parts with fake safety documentation.
Anti-nuclear groups have said the draft energy policy is an "expansion" plan because it will still require South Korea to build more nuclear-fired plants over the next two decades as its power demand grows.
($1 = 1,052 Korean won) (Editing by Tom Hogue)