Seoul Unit 1, Criticality Allowed During Regular Inspection

Seoul Unit 1 (left), Unit 2 (right) panorama

The Nuclear Safety and Security Commission announced that it permitted the criticality of Saewool Unit 1, which began its regular inspection on December 19, 2024, on the 24th. Criticality refers to the state in a reactor where the nuclear fission chain reaction continues steadily, and the number of neutrons produced equals the number of neutrons lost, resulting in a neutron population equilibrium.

The NSSC explained that during this regular inspection, out of a total of 91 items, inspections were conducted on 79 items that needed to be completed before criticality, confirming that the reactor can safely achieve criticality going forward.

During this inspection period, the suitability of maintenance for the emergency diesel generator and the pilot-operated safety relief valve (a device that prevents the pressure of the reactor coolant from exceeding the design pressure) was verified. Additionally, the fire protection status of the fuel storage area and the integrity of the anchor bolts in the component cooling water system were checked, all meeting the relevant technical standards.

Based on the results of the inspections conducted so far, the NSSC permitted the criticality of Saewool Unit 1 and stated that safety will be finally confirmed through follow-up tests (12 items), including power ascension tests.

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