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NSSC approves restart of Hanbit Unit 2

The Nuclear Safety & Security Commission (NSSC) approved the restart of Hanbit Reactor Unit 2 after identifying the cause of shutdown and confirming the adequacy of recurrence prevention measures. Previously, the reactor was shut down around 10:50 on February 28.

The shutdown of the reactor was found to have been caused by abnormal circuit connections in testing the Automatic Seismic Trip System (ASTS), which was installed as a follow-up to the Fukushima nuclear disaster.

Electric current should bypass the power system of the control rod, but this was not reflected in the design changes (Aug. 1, 2011) made for ASTS installation. The reactor was shut down when the control rod dropped with activation.

Meanwhile, the continued operations of turbines led to reduced pressure and induced safety injection. This did not affect the safety of the facilities.

※ Automatic Seismic Trip System (ASTS): This system automatically shuts down the reactor when an earthquake exceeding 0.2 g occurs at the reactor site.
※ Safety Injection: In case of accidents, boric acid is injected into the reactor to trigger reactor shutdown and cooling.

To prevent recurrences of such incidents, NSSC has ordered proper circuiting between ASTS and the control rod, and enforced follow-up to design and engineering changes of key equipment.
[Source:Nuclear Safety and Security Commission (NSSC)]

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