The Nuclear Safety And Security Commission announced that it allowed the criticality of the Hanul Unit 1, which underwent regular inspections starting May 23, on the 4th. Criticality refers to the state in which the number of neutrons produced and the number of neutrons eliminated are equal, resulting in a balance of neutrons in a nuclear reactor where a chain reaction of nuclear fission occurs continuously.
In this regular inspection, the Nuclear Safety And Security Commission confirmed that out of a total of 90 items, inspections were conducted on 79 items that need to be completed before criticality, ensuring that refueling would be done safely in the future.
In particular, during the regular inspection period, an investigation into an incident on May 26 revealed that an emergency diesel generator did not start due to the low-voltage state of the safety line, and the causes were identified as poor contact of the main control room's operating switch and inadequate lubrication of the circuit breaker’s driving part.
Accordingly, maintenance has been completed on the problematic switch (1) and circuit breakers (2), along with all switches (631) and circuit breakers (23) in the main control room, and especially for switches and circuit breakers related to reactor shutdown and safety equipment, operational status tests were conducted to confirm compliance with relevant standards.
During this regular inspection period, inspections were performed on the replacement of the reactor coolant pump sealing device and the leakage test of the sealing injection water, the integrity of the pressurizer heat exchanger, and the calibration of liquid radiation monitors, all of which were confirmed to meet the relevant technical standards.
Based on the results of the regular inspections conducted so far, the Nuclear Safety And Security Commission has permitted the criticality of the Hanul Unit 1 and plans to ultimately confirm safety through 11 follow-up inspections, including output rise tests.