The Korea Institute of Nuclear Safety says its unclear when operations will resume at South Korea's oldest nuclear reactor.

The operator of the Gori-1 reactor was planning to bring it back online last Friday. The institute is now conducting additional inspections on the reactor's reserve switch and cooling device.

Activity at the reactor located in northeastern Busan came to a halt last Tuesday due to a malfunctioning circuit breaker.

The Gori-1 reactor has been in commercial operation since 1978.