South Korea shut down one of its nuclear reactors on the east coast Tuesday after a warning signal went off indicating a possible problem, the country's atomic energy operator said.

The Korea Hydro & Nuclear Power Corp. said the 950,000 kilowatt Hanul No. 1 was shut down at 11:39 a.m. after a "reactor warning light" went off at the plant located in Uljin, some 330 kilometers southeast of Seoul.

It said preliminary checks showed no radioactive contamination near the reactor and that there is no immediate problem with the integrity of the reactor or the Hanul Nuclear Power Plant as a whole that has a total of six reactors.

"The alarm light can go off if there is something really wrong with the reactor, or in the case of faulty sensors," the KHNP said.

It said built-in systems at the plant automatically shut down the affected reactor as a precautionary measure.

It said an emergency response team has been sent to check the reactor in detail and find out what caused the problem.

The Hanul 1 unit went on line in September 1988 and is one of the country's oldest reactors. Asia's fourth-largest economy currently has 23 operational commercial reactors, not counting one unit that is being dismantled. (Yonhap)