Nuclear Safety and Security Commission

Hanbit Unit 2 Criticality Approval During Periodic Inspection

- Inspected steam generator tubes and the result showed that it satisfied the technical standards.

- After achieving criticality, finally confirmed the safety through follow-up tests including a power ascension test.

The Nuclear Safety and Security Commission (Chairperson Choi Won-ho, hereafter referred to as the NSSC) approved the criticality of Hanbit Unit 2 on July 14, following regular inspections that began on May 17, 2025.

* A state in a reactor where nuclear fission chain reactions happen continuously, reaching an equilibrium where the number of neutrons generated equals the number of neutrons consumed.

During this periodic inspection, the NSSC tested 84 of the 94 items required to reach criticality, confirming that the reactor could safely attain this state.

During the inspection period, maintenance was performed on 231 out of 16,878 tubes based on the results of leakage testing and eddy current testing*. This included sleeving (224) and pipe plugging (7), all carried out in accordance with technical standards.

* A non-destructive test that identifies surface or near-surface defects in steel materials.

** A maintenance method that reinforces tubes by inserting and welding metal tubes inside them.

Based on the results of these inspections, the NSSC has approved Hanbit Unit 2 to reach criticality. Safety will be finally confirmed through ten follow-up tests, including a power ascension test.

NSSC Chairperson Listens to Radiation-Using Institutions

- Visited the Korea Association for Radiation Application to hold a roundtable discussion with radiation-using institutes.

On July 4, Chairperson Choi Won-ho of the Nuclear Safety and Security Commission (hereinafter referred to as the NSSC) visited the Korea Association for Radiation Application* for a roundtable discussion with institutions that utilize radiation.

* A representative organization founded in 1985 to promote the radiation industry and support economic development.

The purpose of this roundtable was for the NSSC to gather feedback from the industry and emphasize the importance of management’s involvement in safety at radiation-using institutions. During the discussion, management representatives shared their insights on key topics, including medical radiation safety, radiation devices, and import and export.

Chairperson Choi at the roundtable said, “Radiation should be used more safely and rationally. The NSSC will continue to communicate with the public and improve policies.” He added, “In order to establish a radiation safety culture, management’s constant attention and effort are essential,” urging thorough safety management.

NSSC Allowed Criticality of Hanul Unit 1 During Regular Inspection

- After the criticality, power ascension test and other tests will continue to confirm the final safety.

The Nuclear Safety and Security Commission (Chairperson Choi Won-ho, hereinafter referred to as the NSSC) approved the criticality of Hanul Unit 1 on July 4. Hanul Unit 1 has been undergoing regular inspections since May 23, 2025.

* A state in a reactor where nuclear fission chain reactions occur continuously, resulting in a balance between the neutrons generated and decayed.

The NSSC tested 79 of the 90 items during this regular inspection before reaching criticality, confirming that the reactor could safely achieve the state.

During the regular inspection, the emergency diesel generator was not operational, and the safety bus remained at low voltage, which prevented electricity from being supplied (as of May 26, 2025). It was confirmed that the control switch in the main control room was not properly contacted, and the self-actuated circuit breaker lacked lubrication, causing it to fail to operate.

The 631 switches and 23 circuit breakers in the main control room, including a failed switch and two circuit breakers, have completed their maintenance. Specifically, switches and circuit breakers related to reactor trip and safety equipment underwent operational tests and were confirmed to meet standards.

This regular inspection includes replacing the reactor coolant pump seal, performing RCP seal leakage tests, checking the integrity of pressurizer heaters, and adjusting liquid activity monitors. The results show that all complied with the technical requirements.

* Cooling water injected to limit the leakage of the high-pressure coolant along the gap in the RCP shafts.

The NSSC allowed the criticality of Hanul Unit 1 based on the results of regular inspections. Going forward, it will verify the final safety through the following tests (11 tests), including the power ascension test.

NSSC Held National Forum for Radiation Safety Managers for the First Half of 2025

Over 200 safety managers from different sectors participated in the forum to exchange their experiences and expertise.

The Nuclear Safety and Security Commission (Chairperson Choi Won-ho, hereinafter referred to as the NSSC) held the National Forum for Radiation Safety Managers for the first half of 2025 (hereinafter called the Forum) on June 27 at Koreana Hotel in Jung-gu, Seoul. This was the 10th forum since 2021, starting with its kickoff ceremony, and it plays a vital role in enhancing safety management capacity through mutual communication among radiation safety managers across the nation.

Radiation safety managers are responsible for ensuring safety management, including preventing radiation hazards such as operator exposure, at facilities that utilize radiation.

Facilities involved in the production, sale, and use of radioisotopes or radiation generators, such as hospitals, research institutes, and companies, are required to appoint radiation safety managers under the Nuclear Safety Act and report them to the NSSC. As of December 2024, Korea has 1,907 radiation safety managers working in authorized institutions.

The Korea Institute of Nuclear Safety (KINS) shared insights on ‘recent radiation inspections and current safety regulation issues’ at the forum. Managers from medical, public, radiographic testing, business, and reporting institutions showcased their expertise and experiences gained from on-site work as best practices. It offered a valuable opportunity to learn and share solutions for specific situations.

Furthermore, many questions and answers about the analysis and application of radiation safety regulations were discussed, providing an opportunity to improve mutual understanding between regulatory agencies and managers.

In her congratulatory remark, Secretary General Cho Chung-ah emphasized, “A genuine safety will eventually be derived from the people. When each safety manager is equipped with responsibility and a sense of duty, and when the management and employees work together, sites will improve with a stronger safety culture, rooted in the organization.” She also stated, “The NSSC will continue to support radiation safety managers by empowering them so that they can fulfill their role, and by assisting institutionally for a better environment.”

NSSC Approved Korea’s First Decommissioning of a Nuclear Power Plant: Kori Unit 1

- Approximately 12 years for the decommissioning; total cost up to 1.713 trillion won.

- Inspect daily and conduct a detailed inspection twice a year.

- The whole decommissioning process will be openly shared to reassure the public.

The Nuclear Safety and Security Commission (Chairperson Choi Won-ho, hereinafter referred to as the NSSC) approved the decommissioning of Kori Unit 1 at its 216th meeting on June 26, 2025. As a result, South Korea's first commercial nuclear power plant, Kori Unit 1, will begin the official decommissioning process.

Kori Unit 1 began its commercial operation in April 1978 and was permanently shut down in June 2017. Korea Hydro and Nuclear Power (KHNP) submitted a decommissioning approval application to the NSSC in May 2021, in accordance with the relevant regulations.

The NSSC reviewed the application documents, including the final decommissioning plan, based on KINS’s safety review results and the Nuclear Safety Special Committee’s pre-review outcomes. Once it was confirmed that the documentation for Kori Unit 1 decommissioning met the technical requirements outlined in the Nuclear Safety Act, the NSSC approved the decommissioning. The final decommissioning plan includes:

(Decommissioning Organization/Procedure) KHNP will establish and operate dedicated support teams* for the decommissioning project until its completion. The workforce for decommissioning will be increased gradually, and the project will be carried out following the approved guidelines.

* As of June 2025, the organization has approximately 110 employees, with about 70 working at the site office and 40 at the headquarters.

(Decommissioning measures) Facilities with low radiation levels will be decommissioned first to minimize the workers’ exposure and prevent the spread of radioactive materials. During decommissioning, appropriate methods and technologies will be selected based on each facility's contamination level and patterns.

(Decommissioning waste management) The estimated amount of radioactive waste from decommissioning is approximately 170,000 tons. Contamination and hazardous materials from low- to intermediate-level wastes, besides self-disposal waste (about 160,000 tons) with very low radioactivity, are planned to be removed to meet disposal requirements through Decommissioning Support Facilities*.

* Radioactive waste classification, cutting, and decontamination (will be constructed within six years after its decommissioning approval).

(Spent nuclear fuel management) It is currently stored in the wet storage at Kori Unit 1. It will be relocated to the on-site dry storage once it begins its operation afterward.

(Accident Analysis) The maximum radiation exposure doses* to operators and residents are estimated at 33% and 2.1% of the annual radiation dose during abnormal accidents while decommissioning. A radiation protection plan for operators and an environmental monitoring plan for residents will be developed.

* Maximum exposure dose for operators: 16.9 mSv (dose limit: 50 mSv); maximum exposure dose for the general public: 0.021 mSv (dose limit: 1 mSv).

(Decommissioning Expense) The estimate is 1.713 trillion won. The actual cost may be higher, and if that happens, additional cash or corporate bonds will be issued as a response.

KHNP plans to take steps to conduct decommissioning around 12 years after obtaining approval. The NSSC will conduct daily site inspections and receive biannual updates from operators on the decommissioning process for in-depth reviews.

Once decommissioning is finished, the site will go through another inspection to verify if it meets the site reuse standard (0.1mSv), and the regulatory release will be granted based on the result.

“Kori Unit 1 will be the first case of domestic NPP decommissioning. All review items were thoroughly examined. During decommissioning, the process will be carefully monitored and results transparently disclosed to reassure the public,” Chairperson Choi said.

216th Meeting of the Nuclear Safety and Security Commission

Nuclear Safety and Security Commission (Chairperson Choi Wonho, hereinafter referred to as the NSSC) held the 216th meeting of the NSSC Commission on June 26 to deliberate and resolve four agenda items.

[Deliberation / Resolution Item 1]

The NSSC decided to impose an administrative measure (monetary fine) on two radiation facilities for breaching the Nuclear Safety Act, identified during regular and special inspections in the second half of 2024.

Institute A confirmed that a Radiation Generator (RG) was operated without authorization in a facility, lacking the necessary permit, for a certain period. It was fined under Article 57 of the Nuclear Safety Act for altering the scope or conditions of permitted use without approval. However, a fine of 30 million won was ultimately imposed, halved according to Article 175 of the Enforcement Decree of the Nuclear Safety Act, considering the institute’s full admission of the violation and their intention to improve.

Institute B confirmed that a radioactive isotopes facility was used once the construction was completed, and without the required modification permit. The institute was fined for unauthorized modification of the use permit under Article 57 of the Nuclear Safety Act. Additionally, because the institute continued using the facility despite being warned until the permit was obtained, the violation was considered intentional. As a result, a penalty of 90 million won was imposed, with an increase of fifty percent, under Article 175 of the Enforcement Decree of the Nuclear Safety Act.

[Deliberation / Resolution Item 2]

The Nuclear Safety Act was revised on January 21, 2025 (Legislation No. 20270) and will go into effect on January 1, 2026. The partial amendment to the Enforcement Decree of the Nuclear Safety Act and the Enforcement Rules, reflecting this revision, has been approved.

The revision of the Act was meant to clearly specify the requirement to provide evidence for periodic safety review of continued operation under the Nuclear Safety Act, as originally outlined in the Enforcement Decree of the Nuclear Safety Act.

Therefore, this revision of the Enforcement Decree and Rules aims to establish the legal basis in line with the amended Act for periodic safety review on continued operation, as the legislation has been revised.

The NSSC will continue to perform the following amendment procedures, including coordinating with relevant institutes and pre-announcing legislation.

[Deliberation / Resolution Item 3]

The NSSC approved the draft modification permit for the design revision during the construction of the Gijang research reactor*, submitted by Korea Atomic Energy Research Institute (KAERI).

* A research reactor designed to produce medical and industrial isotopes, with a 15MW thermal output (2019.05.10. Construction Permit)

This modification involves ❶relocating the coolant inlet to prevent pump failure caused by air entry during pump damage; ❷adding more pumps as needed; ❸installing additional outlet pipes to prevent uneven coolant flow in the tank; and ❹upgrading cooling equipment and the control system to safely shut down the reactor during accidents, such as by including monitoring variables in the safety control systems to oversee such events.

The NSSC confirmed that the accident analysis results, conducted again after the design change, meet the approval standards.

[Deliberation / Resolution Item 4]

The NSSC approved Korea Hydro and Nuclear Power (hereinafter KHNP) under Article 28 of the Nuclear Safety Act, following KHNP’s May 2021 application, to decommission Kori Unit 1 (draft).

Kori Unit 1 is the first nuclear power plant in South Korea to receive decommissioning approval. The NSSC confirmed that KHNP has the necessary organization, personnel, procedures, financial resources, funding, technical competencies, and an appropriate quality assurance system required for decommissioning.

KHNP’s Final Decommissioning Plan includes a review of the site's radioactive contamination, a decommissioning strategy, decontamination and dismantling activities to remove radioactive contamination and facilities, management of radioactive waste generated during decommissioning, and radiation protection measures for workers and nearby residents. It was confirmed that all comply with the Nuclear Safety Act, the Enforcement Decree, and the Technical Standards.