The Nuclear Safety and Security Commission announced on October 10 that it had authorized the criticality of Shin-Gori Unit 1, which had undergone a scheduled inspection since August 27.
Criticality refers to a state in which a nuclear reactor sustains a continuous chain reaction of nuclear fission, with the number of neutrons produced equaling those lost, resulting in a balance of neutrons. Granting criticality essentially means the nuclear power plant is being restarted.
The commission explained that, out of a total of 97 items in this scheduled inspection, it had completed checks on 86 items that must be performed prior to criticality. As a result, it confirmed that the reactor can safely achieve criticality going forward.
During this inspection, the commission reviewed the cause of the generator excitation system failure, which led to a power shutdown on August 21, as well as measures to prevent recurrence. The excitation system is a core control device in a nuclear power plant that keeps the generator's output voltage stable.
The cause of the damage was found to be an arc generated due to poor contact between the brush and collector ring inside the exciter (equipment that supplies direct current to the internal coil to create electromagnetic force in the exciter). The damaged parts were replaced with new ones, and a detailed inspection confirmed that they met the relevant standards. The commission stated that it plans to strengthen brush quality management and current measurement during operation to prevent recurrence.
Additionally, during this inspection period, 11 foreign objects, including small wires, were removed from the steam generator, and an inspection of the heat transfer tubes found no anomalies.
The commission stated, "Based on the results of the scheduled inspection so far, we have authorized the criticality of Shin-Gori Unit 1. We will conduct 11 additional follow-up tests, including power ascension testing, to confirm safety before final approval."
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