Nuclear Safety and Security Commission

222nd Meeting of Commission


The Nuclear Safety and Security Commission (Chairperson Choi Won-ho, hereinafter referred to as the ‘NSSC’) held the 222nd meeting of the Commission on September 25th (Thurs). One agenda item is resolved and deliberated, while the other two items are decided to be reintroduced at a later time.

[Deliberation/Resolution Item 1]

The NSSC decided to abolish the regular Notice regarding the location of reactor facilities, and enact three new Notices: ‘Investigation/Analysis/Assessment Standards on Geology/Earthquake at Reactor Facility Sites,’ ‘Standards on Location Restriction of Reactor Facility Sites,’ and ‘Impact Investigation/Assessment Standards on Artificial Accidents at Nuclear Power Plant Sites’. Additionally, in order to prepare the basis for the Notice, the ‘Regulations on Technical Standards for Reactor Facilities' will be partially revised.

The regular Notice on location only corresponds to past US regulations, which limit the reflection of the latest scientific technologies and make it challenging for people to understand the regulatory standards. Therefore, with these newly enacted three Notices, the advanced scientific technologies and up-to-date regulatory experiences will be reflected, providing more detailed standards that can evaluate the site safety of various facilities such as large-scale NPPs, research reactors, fuel cycle facilities, and small modular reactors (SMRs).

However, the regular reactor facilities, which already have construction permits or have applied for them, will remain subject to the previous Location Notices by transitional measures, as outlined in an Addendum, considering the continuity of the regulation. These three new Notices will be applied to reactor facilities that request CPs in the future.

This revision and enactment (draft) underwent the final deliberation after its definition and evaluation period of accidents was clarified at the ‘Standards on Location Restriction of Reactor Facility Sites’, which was discussed at the 221st meeting of the Commission (September 11th). Afterward, it will be implemented following the completion of related procedures, such as collecting opinions and regulatory reviews.

[Deliberation/Resolution Unit 2]

The NSSC initiated deliberations on the approval of the accident management program for Kori Unit 2 (draft), as requested by Korea Hydro and Nuclear Power (KHNP), and received the review results from the Korea Institute of Nuclear Safety (KINS). It was concluded that this agenda item requires further discussion; therefore, it will be reintroduced later.

An accident management program is a comprehensive document that describes procedures, organizations, education, and training to maintain and recover essential safety functions during various emergencies, including severe accidents that may occur at NPPs. In June 2019, the KHNP submitted the AMP for Kori Unit 2, and KINS conducted its safety review. Lastly, the Nuclear Safety Council preliminarily reviewed it six times and presented it at the Commission meeting.

[Deliberation/Resolution Item 3]

The NSSC launched the deliberation on the continued operation of Kori Unit 2 (a pressurized water reactor, 1876MWth) (draft) and received the review results from the Korea Institute of Nuclear Safety. It was concluded that this agenda item requires further discussion, so it was decided to be reintroduced at a later time.

Kori Unit 2 received its construction permit in 1978 and began operating in 1983. It ceased its operation on April 8th, 2023, as its design life had expired after exceeding its 40-year limit.

In response, the KHNP requested the continued operation of Kori Unit 2 on April 4, 2022, according to Article 23-1 of the ‘Nuclear Safety Act’ and Article 36-4 of the Enforcement Decree of the NSA to extend the operation for an additional 10 years from the expiration of its design life. The agenda item was presented after KINS’ safety review and following seven preliminary reviews by the Nuclear Safety Council.

NSSC Launched Investigation on Heavy Water Leak Incident from Moderator Purification System of Wolsong Unit 2


The Nuclear Safety and Security Commission (Chairperson Choi Won-ho, hereinafter referred to as the ‘NSSC’) announced that it received a report from Korea Hydro and Nuclear Power (hereinafter called ‘KHNP’) on September 19th at 4:30 AM that heavy water had leaked from the moderator purification system of Wolsong Unit 2.

※ The KHNP reported the incident at 5:16 AM to the NSSC Wolsong Regional Office. The Regional Office arrived at the site at 5:50 AM and started its inspection.

Right after confirming the heavy water leakage, the KHNP stopped the relevant pumps to block the leak. The leaked heavy water was collected in the filter room (compartment) and the inner sump at the nuclear auxiliary building, with no external leak. As of 12 PM, the total leakage is estimated to be around 265kg, and the KHNP said that it will calculate the exact amount and report the number later.

Wolsong Unit 2 was tripped during its planned preventive maintenance, and it was confirmed that there was nothing significant to report regarding external radiation.

Currently, the NSSC is checking the site safety through the Wolsong Regional Office and plans to dispatch a research team, comprising the Korea Institute of Nuclear Safety (KINS), to the site.

NSSC Chairperson Joined IAEA General Conference to Discuss on Regulatory Issues with Major Countries


- The Chairperson of the NSSC will participate in the 69th General Conference of the International Atomic Energy Agency (IAEA).

Scheduled to join the 56th International Nuclear Regulators Association (INRA) meeting and have a multilateral meeting with nine countries

- A chain of bilateral meetings with five countries including France and Sweden.

Chairperson Choi Won-ho of the Nuclear Safety and Security Commission (hereinafter referred to as the NSSC) will attend the 69th International Atomic Energy Agency (IAEA) General Conference in Vienna, Austria, from September 15 to 19 (CET). The conference will cover various regulatory issues with the international community and is expected to have 180 member-state representatives participating as an annual event.

During the GC, Chairperson Choi will participate in the 56th International Nuclear Regulators Association (INRA)* meeting and hold a series of bilateral meetings with the heads of major nuclear regulatory agencies.

* A consultative body launched in 1997, composed of leaders from nine major nuclear power countries—Korea, US, Canada, UK, Japan, Germany, France, Sweden, and Spain—to discuss nuclear and radiation regulatory policies.

Chairperson Choi will join the 56th INRA meeting to share each country’s regulatory experience and exchange views on regulatory efficiency for managing increasing regulatory demands with leaders from nine nuclear energy regulatory agencies, including those from the US and Japan.

Furthermore, NSSC aims to strengthen the global regulatory cooperation network with France and Sweden by discussing nuclear safety agenda items, regulatory experiences related to spent fuel disposal facilities, and future technical cooperation measures. France has the second-largest reactor operation capacity (57 Units) in the world, and Sweden has a high-level radioactive waste disposal facility.

※ (Regulatory body) French Nuclear Safety and Radiation Protection Authority (ASNR), and Swedish Radiation Safety Authority (SSM)

In particular, the NSSC will share regulatory experiences needed for new NPPs, including the APR1000 standard design approval review status and capacity enhancement measures, with the Czech Republic, which has signed a contract for new NPPs with Korean companies.

※ (Regulatory body) Czech State Office for Nuclear Safety (SUJB)

The NSSC plans to discuss with the United Arab Emirates (UAE) its regulatory experiences with the APR1400 and the status of nuclear fuel regulation. The UAE has adopted four Korean-type reactors (APR1400) and is operating them commercially.

※ (Regulatory Body) UAE Federal Authority for Nuclear Regulation (FANR)

As Vietnam considers new NPP construction, NSSC will introduce South Korea's nuclear safety regulatory system and listen to Vietnam’s. The example of regulatory cooperation with the UAE will also be shared to foster a partnership between the two regulatory agencies.

※ (Regulatory body) Vietnam Agency for Radiation and Nuclear Safety (VARANS)

Chairperson Choi said, “Cooperation with the international community is essential when using nuclear energy, which prioritizes safety the most. Through bilateral and multilateral cooperation, NSSC will share our regulatory experiences and expertise, using this opportunity to exchange insights on safety regulatory matters.” 

221st Meeting of Commission


The Nuclear Safety and Security Commission (Chairperson Choi Won-ho, hereinafter referred to as the NSSC) held the 221st meeting of the Commission on September 11th (Thurs) to deliberate and resolve three agenda items.

The NSSC approved modifications to the pressure and temperature limits for the reactor coolant system of Hanbit Units 1 and 2, requested by Korea Hydro and Nuclear Power, as well as changes to the structures of the Kijang Research Reactor, requested by Korea Atomic Energy Research Institute.

Hanbit Units 1 and 2 are considering reflecting the pressure and temperature limits for the reactor coolant system, based on the result of the reactor pressure vessel (RPV) integrity assessment. The Commission confirmed that the safety impact of changing RPV materials as radiation exposure duration increases meets the technical standards.

Kijang research reactor adjusted the interior of the transfer device room, which is used to transfer neutron-exposed samples, to reduce the exposure dose. Additionally, the height of the tank room was adjusted to match the increased height of the reactor pool tank. As a result, it was confirmed that both the radiation impact and structural safety comply with the relevant technical standards.

The NSSC decided to abolish the regular Notice regarding the location of reactor facilities, and enact three new Notices: ‘Investigation/Analysis/Assessment Standards on Geology/Earthquake at Reactor Facility Sites,’ ‘Standards on Location Restriction of Reactor Facility Sites,’ and ‘Impact Investigation/Assessment Standards on Artificial Accidents at Nuclear Power Plant Sites’. Additionally, in order to prepare the basis for the Notice, the partial modification of ‘Regulations on Technical Standards for Reactor Facilities' was also discussed, but it was decided to be reintroduced at a later time after some supplement.

The NSSC decided to improve the deliberation method of the alteration permit for extra nuclear facilities, including research and education reactors, nuclear fuel cycle facilities, and radioactive waste management facilities, in the future.

So far, an alteration permit for facilities has been discussed in person. However, it will match with the deliberation method* of the alteration permits for power reactors and relevant facilities—an in-person deliberation for items for accident analysis and safety assessment with high safety significance, and an in-paper deliberation for the others. Additionally, if even one Commissioner disagrees with the written deliberation, it will be converted to an in-person deliberation and reconsidered, ensuring its safety is thoroughly reviewed.

* Improvement Method for Deliberation on Alteration Permits for Power Reactors and Related Facilities (draft) (199th Meeting of the Commission, August 29th, 2024)

Root Out Overseas Direct Purchase of Radiation Materials Flows into Country


- Chairperson Choi Won-ho visited the site to review how the radiation monitoring is conducted on express cargo on-site at the Incheon Airport

The Nuclear Safety and Security Commission (Chairperson Choi Won-ho, hereinafter referred to as the ‘NSSC’) will enhance the radiation monitoring at the airport as the number of overseas direct purchase items has increased recently.

Chairperson Choi inspected the radiation monitoring activities for overseas direct purchase cargo at the express logistics center under Incheon Airport Regional Customs on September 9th.

The NSSC currently has 152 radiation monitors installed and in operation at airports and harbors nationwide. They prevent radiation materials that may be mixed in imported cargo or metals from entering the country.

Direct purchases from foreign markets have gone up recently. It drove e-commerce imports through aircraft express cargo to skyrocket, making airport radiation monitors even more essential.

Therefore, the NSSC will secure five additional radiation monitors, bringing the total to 27, up from the current 22 monitors, at Incheon Airport. The monitoring rate for overseas direct purchases is planned to be enhanced from 72% to 85% or above.

For 2026, the NSSC allocated 3.4 billion and 49 million won to install and operate monitors that prevent the domestic inflow of radiation-suspected materials. It will continue to prioritize strengthening the airport monitoring network, in line with the increased imports, and fundamentally block radioactive materials from entering the country through direct overseas purchases.

Chairperson Choi Won-ho encouraged employees at the express logistics center by saying, “Unlike harbor cargo, airport overseas direct purchase express cargo is directly connected to our people’s safety in their daily lives. Please continue to protect the public safety through flawless radiation monitoring.”

Allow Criticality of Hanbit Unit 5 During Periodic Inspection

Checked the safety of penetration tubes in the reactor head

Replaced the control card, which caused the emergency diesel generator to start automatically

Will confirm the final safety through follow-up tests, such as a power ascension test, after reaching its criticality

On September 9th, the Nuclear Safety and Security Commission (Chairperson Choi Won-ho, hereinafter referred to as the ‘NSSC’) allowed the criticality* of Hanbit Unit 5, following a periodic inspection that began on April 7th, 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.

The NSSC confirmed the entire NPP safety through this periodic inspection to see if the leakage from the penetration tube of the reactor head is properly maintained, and the event in which the emergency diesel generator was automatically operated is well-managed.

In particular, a cause analysis for penetration tube defects* and a detailed inspection were performed during this periodic inspection in response to the leak from the newly replaced reactor head that occurred on July 5th.

* A cylinder-shaped metal tube where the control element driving mechanism (CEDM) is located at the upper part of the reactor head. The seal near the middle of the welding joints (Omega Seal) witnessed a 0.7mm hole.

It was confirmed* that the defect occurred due to porosity (bubbles) that remained inside the steel during the manufacturing of the penetration tubes. Detailed ultrasound inspections of similar areas and hydraulic pressure tests were conducted on all penetration tubes (83 tubes), and no other defects were found.

* Tiny porosity was left in the thin part of the tubes in the process of manufacturing. The area was continuously pressured due to hydraulic pressure tests and other factors, which resulted in defects.

The defective area was repaired and welded, and its safety was checked through hydraulic pressure tests and non-destructive tests.

In the future, the NSSC will prevent the accident recurrence by improving* the manufacturing process for penetration tubes. It also plans to install surveillance cameras and radiation monitors for the existing reactor heads to strengthen leak monitoring.

* Prevent porosity by melting metals in a vacuum state

Meanwhile, on April 9th, one of the two emergency diesel generators was automatically operated*, while the reactor was shut down for its periodic inspection. It happened because a control card, which regulates breakers for the safety bus, failed. In response, it was checked that the responsive measures were properly implemented by replacing the control card correctly and installing the control relay** on site adequately.

* The NSSC Press Release was announced on April 9th, 2025, according to the Regulation on Report/Disclosure in Case of Accident/Failure (Notice)

** A device that separates control signals between the safety system and the non-safety system

In addition, the NSSC tested 86 out of 97 required items, which should be done before reaching criticality, such as safety inspection after replacing anchor bolts in the essential service water system, and confirmed that the reactor could safely attain the state.

Based on the results of these periodic inspections, the NSSC approved Hanbit Unit 5 to reach criticality. Safety will be finally confirmed through 11 follow-up tests, including a power ascension test.