원안위 "Fire at Shin-Kori Unit 4... Inadequate fastening of distribution ring fixed bolts is the cause"

Plan to Approve 'Restart' Upon Completion of Maintenance Work by the End of This Month

A fire broke out on May 29 at Shin-Kori Nuclear Power Plant Unit 4 in Ulju-gun, Ulsan City. [Image source=Yonhap News]

[Asia Economy Reporter Kim Daehyun] The fire at Shin-Kori Nuclear Power Plant Unit 4 on May 29 was found to have been caused by the distributor ring fixing bolts inside the generator not being properly tightened.

On the 15th, the Nuclear Safety and Security Commission (NSSC) announced the results of the investigation into the turbine generator auxiliary equipment fire incident at Shin-Kori Unit 4, conducted by the Korea Institute of Nuclear Safety (KINS).

On that day, the NSSC stated, "The tightening force of the distributor ring fixing belt was found to be partially unsatisfactory compared to the manufacturer's work manual standard," and "the insufficient fastening of the distributor ring fixing bolts increased contact resistance, which caused the internal temperature of the collector ring to rise." The distributor ring refers to the equipment attached to the collector ring body, which is a device that sends current to the generator rotor.

The NSSC evaluated that "melting occurred at the contact area between the distributor ring and the collector ring, insulation deteriorated, and sparks were generated," and explained that related external experts also observed areas on the distributor ring without tightening marks, suggesting that the fixing bolts were not properly tightened during initial installation.

Furthermore, the NSSC identified that the fire progressed inside the collector housing (an auxiliary power production facility supplying DC power to the generator rotor) through the distributor ring, brush holder, lower rigging, collector ring body, and along the generator shaft direction.

The NSSC added, "To prevent recurrence of the fire, Korea Hydro & Nuclear Power (KHNP) will install smoke detectors and alarms inside the collector housing and check the tightening force of the collector distributor ring fixing bolts during planned preventive maintenance," and "It was also confirmed that procedures and methods for supplying turbine sealing steam to maintain turbine sealing steam pressure during turbine shutdown have been improved."

Meanwhile, the NSSC plans to verify the safety of the power plant and approve the restart once KHNP completes maintenance work such as turbine bearing equipment assembly at Shin-Kori Unit 4 by the end of this month.

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