South Korean refiners will maintain sufficient bunker fuel supply in the coming months, even though fuel oil demand is expected to rise marginally due to nuclear power plant shutdowns in the country, industry sources said Friday.

The capacity of fuel-oil fired plants is limited, so there is only so much room for them to boost electricity output, industry sources said.

"The oil-fired power plants are already operating at full capacity," said a bunker trader.

A refining source said power companies have turned to LNG and coal.

"Even though fuel oil demand increases, refiners will import bunker fuel to meet demand," said another bunker trader.

Local refiners SK Energy, GS Caltex and Hyundai Oilbank have already been importing bunker fuel cargoes, he said.

As of late May, 10 of the country's 23 nuclear power reactors were shut due to a scandal over forged safety certificates, malfunctions or maintenance.

Domestic refineries supply most of South Korea's bunker fuel, with imports meeting about 20% of demand. After the nuclear shutdowns, local refiners said they would not cut back their bunker fuel supply.

"We will sell the same volume of bunker fuel," said a source at South Korean refinery.

South Korea sells about 700,000-800,000 mt/month of bunker fuel, with the largest bunkering port being Busan in the southeast.

One nuclear power plant restarted earlier this week, said a source at Korea Hydro & Nuclear Power Co. Ltd, operator of nuclear power plants. The capacity in operation, however, is not enough to meet demand in summer, the source said. It is not clear when the company could restart another nuclear reactor, the source added.

South Korea's 23 nuclear reactors supplied about 30% of the country's total electricity consumption in 2012. Coal met 40% of power demand last year, and LNG met 25%, while oil accounted for just 3%. The remaining 2% came from hydraulic and renewable sources like solar, wind and fuel cell power plants.