"Reactor Shutdown During Typhoon Due to External Power Supply Interruption Caused by Islanding"

[Image source=Yonhap News]

[Asia Economy Reporter Kim Bo-kyung] It has been revealed that the recent shutdown of some nuclear power plants due to typhoons was caused by a 'flashover phenomenon' triggered by strong winds. Flashover occurred in the nuclear power plant equipment, interrupting the power supply from external sources. Flashover refers to the phenomenon where sparks fly momentarily when electricity flows.

The Nuclear Safety and Security Commission and the Ministry of Trade, Industry and Energy announced the investigation results on the 25th regarding a total of eight nuclear reactors, including six that were shut down earlier this month due to typhoons.

On the 3rd, Typhoon Maysak made landfall in Busan, bringing strong winds with a maximum speed of 32.2 m/sec to the Kori Nuclear Power Plant. As a result, the off-site power supply was cut off at six reactors (Kori Units 1, 2, 3, 4, and Shin-Kori Units 1 and 2), and emergency diesel generators were activated. Among these, four reactors that were in normal operation were shut down. Kori Unit 1 was permanently shut down, and Kori Unit 2 was under maintenance at the time.

On the 7th, Typhoon Haishen brought strong winds with a maximum speed of 33.1 m/sec to the Wolseong Nuclear Power Plant site. While the turbines and generators of Wolseong Units 2 and 3 stopped, the off-site power supply was maintained, allowing the reactors to operate at 60% output.

At nuclear power plant sites, heat energy is generated in the reactor to rotate turbines and produce electricity, which is transmitted to external substations through transmission facilities. At the same time, facilities are in place to supply power needed for safety equipment such as the reactor cooling system from external transmission facilities.

In the case of Kori Units 1, 2, 3, 4 and Wolseong Units 2 and 3, flashover occurred due to salt deposits carried by strong winds adhering to the 'instrument transformers' that measure the amount of power generated by the nuclear power plants.

The incident began when circuit breakers in the switchyard opened, cutting off the off-site power supply at Kori Units 1, 2, 3, and 4, which automatically triggered the emergency diesel generators.

In particular, for Kori Units 3 and 4, even on the 4th and 5th, after the typhoon had passed, flashover caused by salt deposits absorbed during the typhoon cut off the power to the standby auxiliary transformers, activating the emergency diesel generators.

In the case of Shin-Kori Units 1 and 2, flashover occurred when jumper lines transmitting electricity generated at the plant to the 765kV transmission towers came close to the tower structures due to strong winds. This caused the off-site power supply to be cut off, shutting down the reactors and activating the emergency diesel generators.

Meanwhile, some damage and malfunctions such as flashover caused by salt damage and facility detachment due to strong winds were confirmed in the Korea Electric Power Corporation’s transmission and transformation facilities near the power plants. However, analysis of malfunction records showed that these were unrelated to the nuclear plant shutdowns.

In other words, the shutdowns were concluded to have been caused by flashover due to salt damage occurring in exposed equipment such as transformers.

Accordingly, the government plans to minimize exposed parts by converting sections such as transformers, standby transformers, and instrument transformers around Kori Units 2 to 4, Wolseong Units 2 to 4, and Hanbit Units 1 and 2 into enclosed facilities to prevent recurrence.

Considering the impact range of natural disasters such as typhoons, the government intends to establish safe operation measures for nuclear plants, including preemptive power reduction or preventive shutdowns.

Once Korea Hydro & Nuclear Power completes measures for normal operation such as replacing damaged parts and removing salt deposits, the Nuclear Safety and Security Commission will verify this and permit each nuclear plant to restart.

Both agencies plan to establish and continuously monitor the implementation plan for recurrence prevention measures, including preparing related procedures reflecting transmission facility management programs.

This content was produced with the assistance of AI translation services.