The Nuclear Safety and Security Commission (Chairman Choi Won-ho, hereinafter referred to as the Commission) announced that it has allowed the criticality of Shin Kori Unit 1 as of October 10, following its regular inspection that began on August 27.
Criticality refers to the state in which a nuclear fission chain reaction is sustained steadily within a reactor, maintaining a balance between the number of neutrons produced and those lost.
During this regular inspection, the Commission completed the examination of 86 out of a total of 97 items that needed to be checked before reaching criticality, and reported that it confirmed the reactor could safely achieve criticality.
This inspection primarily focused on identifying the causes of the power generation shutdown accident on August 21 and the measures to prevent reoccurrence. The investigation revealed that the damage was caused by arc formation due to poor contact between the brush and collector ring inside the generator’s exciter equipment.
As a result, the operators plan to prevent recurrences by improving brush quality management and enhancing current value monitoring during operation. Damaged parts have been replaced with new ones, and precise inspections confirmed they meet all related safety standards.
During the inspection period, 11 foreign objects such as wires were removed from inside the steam generator, and no anomalies were detected during inspections of the heat transfer tubes.
Based on the inspection results so far, the Commission has authorized the criticality of Shin Kori Unit 1 and will subsequently perform 11 additional follow-up tests, including a power ascension test, to finally verify safety.
