[Asia Economy Sejong=Reporter Dongwoo Lee] The Nuclear Safety and Security Commission announced on the 10th that it has permitted the criticality (restart) of Hanbit Unit 3, which underwent a regular inspection starting March 22 this year.
Criticality refers to the state in which a sustained nuclear fission chain reaction occurs within the reactor, and the number of neutrons reaches equilibrium. A reactor that has reached criticality can be safely controlled and operated.
The NSSC stated, "As a result of conducting inspections on 85 items that must be completed before criticality during this regular inspection, it was confirmed that the reactor can safely achieve criticality going forward."
During this inspection, the internal steel plates of the containment building of Hanbit Unit 3 were examined. Although no areas were found below the standard thickness, one spot of surface rust was discovered on the upper dome. The NSSC explained that the defect has been repaired.
Additionally, with the replacement of the steam generator, the internal tubes (thin pipes) were replaced with corrosion-resistant materials. The NSSC conducted welding inspections on related piping and non-destructive testing on the tubes to confirm their integrity.
The NSSC also confirmed that the containment building is being kept clean and well-maintained by checking for foreign substances inside the containment building during the steam generator replacement, the fastening status of insulation on pipes and equipment, and the condition of the paint.
Furthermore, reflecting the implementation status of post-Fukushima countermeasures and accident/failure cases over the past three years, the inspection of Hanbit Unit 3 confirmed that it is in a suitable condition.
The NSSC plans to finally verify safety through 10 subsequent tests, including a power ascension test.
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