SEOUL - The resumption of South Korea's oldest nuclear reactor has been postponed indefinitely as the country has decided to carry out a close examination of the troubled nuclear reactor, a state-run nuclear agency said Monday.

Related reading:  S Korea's oldest reactor shut down after power fails

The Korea Institute of Nuclear Safety (KINS) said reactor No 1 at the Kori nuclear power plant, which started its operation in 1978, was shut down on April 12 due to a glitch in the circuit breaker of an electrical system.

KINS said an exact time for the resumption can't be determined at this point because safety checks on other parts of the nuclear reactor are being conducted. KINS director Yoon Chul-ho said special safety checks have been decided due to high public concerns over nuclear safety, according to Seoul's YTN news.

The Kori reactor, located in Busan, has been in operation past its initially intended 30-year life but has undergone extensive renovation to extend its use by another decade through 2017.

South Korea, which depends on nuclear energy for 33 percent of its electricity output, has started safety checks on all its 21 reactors as Japan is struggling to contain radioactive leakage at the Fukushima nuclear plant damaged by the massive earthquake and tsunami on March 11.