NSSC: "Hanbit Unit 5 Automatically Shut Down Due to Worker Error... Approved for Restart After Inspection"

Shutdown Due to Not Fully Opening the Pressure Transmitter Shear Valve Inside the Nuclear Power Plant

[Sejong=Asia Economy Reporter Joo Sang-don] The investigation revealed that the automatic shutdown of Hanbit Nuclear Power Plant Unit 5 was caused by operator error. The safety equipment was activated and the plant automatically shut down last year because the shear valve of the pressure transmitter inside the nuclear power plant, which should have been open, was almost closed.

The Nuclear Safety and Security Commission announced on the 22nd that it had completed the incident investigation and special inspection of Hanbit Unit 5, which automatically shut down on October 26 last year, and approved its restart.

During the power output fluctuation test at Hanbit Unit 5, the 'steam bypass control system,' which maintains the balance between reactor and turbine output, did not operate, causing the steam generator water level to rise and triggering the reactor shutdown signal. The investigation confirmed that the reason the steam bypass control system did not operate was that the shear valve of the pressure transmitter, which generates the system operation signal, was not open as it should have been but was almost closed.

The NSSC confirmed that the safety equipment operated normally as designed, and the reactor safely shut down automatically. It also confirmed that there was no abnormal increase in radiation inside or outside the power plant due to this reactor shutdown.

Additionally, the NSSC verified the adequacy of the operator's plan to strengthen the work management system to prevent recurrence, as well as the plan to improve procedures for expanding and standardizing the valve status inspection checklist.

Accordingly, the NSSC approved the restart of Hanbit Unit 5, which is undergoing regular inspection, and plans to finalize safety confirmation through follow-up tests (eight in total), including the power increase test, and a new steam generator safety verification test (one test).