The Nuclear Safety and Security Commission has concluded that the power outage at the Gori-1 reactor on Feb. 9 had been caused by a combination of a worker’s mistake, a defect in the emergency diesel power generator and a weak safety culture.

According to the commission, external power supply to the Gori-1 reactor was suspended while a worker tested the protection system for the back-up diesel power generator. He was found to have not followed the instructions of his supervisor.

The emergency power generator, which was supposed to automatically come online to supply power, did not work due to a defect in the air supply valve.

Furthermore, the head of the Gori-1 reactor was found to have attempted to cover up the 12-minute blackout. After discussion with senior staff, he chose not to report the accident to management of Korea Hydro and Nuclear Power Co., a state-run company that oversees the nation’s 21 nuclear reactors in operation, and the NSSC. By law, nuclear accidents must be reported to the commission within 15 minutes.

To conceal the power loss, the Gori-1 unit staff omitted it from the daily operation log. As a result, KHNP top management remained in the dark for a month. They learned about it only after a Busan City Council member, who overheard a conversation between plant engineers at a restaurant, formally inquired what had happened.

The commission’s findings demonstrate that safety culture has not taken root at domestic nuclear power plants. Following the Fukushima disaster, nuclear safety has become the overriding motto for providing nuclear power. Yet this watchword apparently has not been firmly planted in the hearts of workers at domestic plants.

To prevent similar cases in the future, the commission needs to ensure, among other things, that safety culture is deeply embedded in practices at nuclear power plants.

The accident also showed that important facilities at nuclear power plants have not been properly maintained. KHNP said the back-up power generator was checked a month ago but its failure to operate in an emergency suggests the test was perfunctory.

In addition, the attempted cover-up illustrates that KHNP officials have learned no lesson at all from the Fukushima debacle, which has taught us that transparency is the key to enhancing public trust in nuclear power generation.

The commission needs to take steps to strengthen the safety and transparency mindset of workers at nuclear power plants. Government officials and nuclear energy industry people have kept saying that Korean nuclear power plants are safe. But safety is not guaranteed unless they are managed with maximum care.