The Nuclear Safety and Security Commission allowed criticality, a key step for restarting the reactor of Hanbit Nuclear Power Plant Unit 6.
The Nuclear Safety and Security Commission said it allowed criticality on the 27th after concluding from a regular inspection that began on Feb. 7 that there were no safety issues in the items that must be checked before reactor criticality.
Criticality refers to a state in which the nuclear fission chain reaction in a reactor continues stably. Simply put, it is the stage of checking whether the fission reaction can be maintained at a steady level before the reactor begins to raise power in earnest. If the number of neutrons produced and the number that disappear are in balance, the reactor can be considered to have entered a stable state of readiness for operation.
There are 97 items in this regular inspection. The Nuclear Safety and Security Commission said it completed inspections of 86 items that must be performed before criticality and confirmed that the reactor criticality of Hanbit Unit 6 can proceed safely.
Some equipment was also serviced during the inspection. A defect was found at one welded joint of a small-diameter pipe in the reactor coolant system, and the maintenance method for the pipe was carried out after review and approval by the Nuclear Safety and Security Commission. The commission approved the maintenance method on Apr. 23 and then confirmed that the maintenance was completed as planned.
The Nuclear Safety and Security Commission also checked the replacement status of the passive autocatalytic recombiner (PAR) for preparedness against design-basis accidents. A PAR is a device that reduces hydrogen in the reactor containment if hydrogen is generated during an accident.
The Nuclear Safety and Security Commission also verified whether fire barriers installed on conduits inside the reactor containment and elsewhere were installed in accordance with relevant technical standards. Fire barriers are protective equipment intended to prevent damage to cables or key equipment in the event of a fire.
The Nuclear Safety and Security Commission said, "Based on the results of the regular inspection to date, we have allowed criticality for Hanbit Unit 6," adding, "We plan to confirm the plant's safety definitively through the remaining 11 follow-up inspections, including a power ascension test."