Nuclear Safety and Security Commission

The claim that the internal conditions of the Wolsong NPP are worse than the civil investigation team’s findings is not true.

On September 20, MBC made a news report under the title of “[Exclusive] Cracked, Broken, Contaminated Water Leaks from Wolsong NPP,” and claimed that the conditions inside the Wolsong nuclear power plant turned out to be much worse that the result of the investigation done by the NSSC for one year. It also said that water is leaking from the cracks on the external walls of the spent fuel bay (SFB) and many areas of damaged internal epoxy liners were discovered, which led to an allegation that the NSSC tried to understate the actual conditions.

About this news report, the NSSC explains:

For a scientific and objective investigation on the detection of tritium inside the Wolsong site, the NSSC formed and has been running an “civil investigation team to investigate tritium in the Wolsong NPP site (hereinafter referred to as the “investigation team),” comprised of civil experts, and the “Council for Current Issue Communication” (hereinafter referred to as the “communication council”) that delivers opinions from various areas and monitors investigation activities.

* The investigation team is comprised of seven experts recommended by the academic societies of relevant areas including geology, machinery, radiation and civil engineering

** The communication council is comprised of seven members – a non-standing member of the NSSC, representatives of related regions, civil organizations, and nuclear sector.

The investigation team and the communication council publish their plans on investigation, meeting minutes, and other documents on the website for transparent investigation, and announced the interim result of the investigation by releasing press releases in September 2021 and May 2022.

All the issues mentioned in the news report are included in the scope of the investigation and can be found in the second announcement of the interim result of the investigation made in May 2022. All the photos and video footages used for the news report were taken during the investigation thus shared with the investigation team and the communication council.

The investigation team and the communication council together determines by agreement the format of announcements and contents and make meeting results and transcripts publicly available.

The investigation on tritium and the announcement of the interim result have been done in a transparent way. Therefore, the claim about downplaying is not true.

Summary of main findings of the investigation and measures taken with respect to the news report

Regarding the leak from the external floor of the spent fuel bay

In December 2021, the investigation team found a leak in the southern part of the external slab of the SFB where repair work was done in 1997.

The leak started in October after drilling in the region in July 2021, and the point from where the leak started was repaired in December 2021.

Currently, whether there have been additional leaks is being inspected and it is confirmed that there has been no additional leak. (The NSSC site office inspects it on a continual basis.)

※ The photos and video footages were taken while the investigation team’s investigation was underway in the middle of December 2021, and the press release on the second announcement of the interim result in May 2022 contains matters related to the photos and videos.

Regarding the aging of epoxy liner on the floor of the SFB of the Wolsong Unit 2

The investigation team shot video underwater in October 2021 in order to check the integrity of the epoxy liner on the floor of the SFB of the Unit 2, and confirmed swelling and cracking on the surface of the floor.

Currently, the floors of the SFBs of the Units 1 to 4 are inspected according to the extended scope of the investigation (from November 2021 to October 2022), and the schedule and methods for repair will be decided in accordance with findings from the inspection.

※ The photo of the floor was taken in October 2021, and the related content is described on the page 2 of the press release about the second announcement of the investigation result in May 2022.

NSSC Approved Resumption of Shinwolsong Unit 2

On September 20, the Nuclear Safety and Security Commission (Chairperson Yoo Guk-hee, hereinafter referred to as the "NSSC") approved the resumption of the Shinwolsong Unit 2 that had automatically tripped on September 8 as the NSSC confirmed the safety of the Unit.

During the normal operation on September 8, the reactor of the Unit tripped as the control rod fell down when the two output interrupters of the motor generators* to supply power to the Control Rod Drive Mechanism (CRDM) simultaneously opened.

* The motor generators receive input power of 480V and send supply power of 240V to the CRDM and two units operate in parallel during normal operation.

As a result of the investigation of the cause, the output interrupters were opened due to a failure of the variable resistor in the voltage control switch during the process of raising power voltage of one of the motor generators.

After the maintenance was completed, and in the process of re-inserting the motor generators, the voltages of the two motor generators were not synchronized*, resulting in overcurrent**, and it was confirmed that the output interrupters of the two generators were opened at the same time.

* Synchronization means the voltage, phase, and frequency of the input generator and the power system match.

** If the grid is connected in a non-synchronized state, an overcurrent (failure current) occurs depending on the phase difference between the voltages of the two motor generators.

Also, after the reactor automatically tripped, it was confirmed that the stabilization measures of the nuclear power plant operators were carried out in accordance with the relevant procedures, the safety facilities were operating normally, and there was no abnormal increase in radiation inside and outside the power plant.

The NSSC Checked Preparedness Against Typhoon and Started to Work on Emergency Duty

- The NSSC held an emergency meeting to check the preparedness against the 14th typhoon “NANMADOL.”

On September 16, the Nuclear Safety and Security Commission (Chairperson Yoo Guk-hee, hereinafter referred to as the “NSSC”) held an emergency meeting, presided over by Secretary General Lim Seung-cheol, regarding the 14th typhoon “NANMADOL,” ascending north, to check preparedness of nuclear facilities*.

* Nuclear power plants, low and med level radioactive waste disposal facilities, research reactors, etc.

The meeting was held in the emergency room of the NSSC with 5 site offices located in the sites (Kori, Wolsong, Hanbit, Hanul and Daejeon), the Technical Support Organizations (the Korea Institute of Nuclear Safety and the Korea Institute of Non-proliferation and Control), the Korea Hydro and Nuclear Power (KHNP) in the form of video conference. The NSSC checked* the progress of the maintenance of the nuclear facilities damaged by the previous typhoon (HINNAMNOR) and preparedness against possible damages that can be brought by the typhoon “NANMADOL.”

* Matters that were mainly looked at are the progress of maintenance of the Shinkori Unit 1 that had been manually shut down due to the typhoon “HINNAMNOR”, repair of damaged facilities, such as CCTV and fences, preventive measures, and measures done for safety facilities for nuclear power plants, water drains, slopes, and wind-borne debris.

Secretary General Lim said at this meeting, “As we have a case where one of our nuclear power plants were shut down due to the previous typhoon, we need to check safety more thoroughly and prepare against the approaching typhoon.” He also encouraged the staff to work on emergency duty until the typhoon holds no effect on the facilities and report promptly when an abnormal event occurs.

The 163rd Meeting of the Commission Was Held

- The commissioners deliberated and passed the bills, including the modification of the deadline for the submission of periodic safety review reports of nuclear facilities. -

The Nuclear Safety and Security Commission (Chairperson Yoo Guk-hee, hereinafter referred to as the NSSC) held the 163rd meeting of the Commission on Thursday, September 15, 2022 where the commissioners deliberated and passed two bills and were briefed on two agenda items.

Regarding the first agenda item, the commissioners passed the bill to modify the Enforcement Decree of the Nuclear Safety Act. The modified Decree will let the timing for the submission of periodic safety review reports be moved forward before the review date so that the safety of nuclear power plants for 10 years forward can be verified preemptively, and will change the deadline for the submission of safety evaluation report for continued operation of a nuclear power plant to 5 to 10 years before the end of the license expiration date so that the regulatory authority have enough time for review.

Regarding the second agenda item, the commissioners passed the 「bill to modify the operating license of nuclear facilities」, applied by the Korea Hydro and Nuclear Power, for the replacement of regional radiation monitors of the containment buildings of the Hanbit Units 5 and 6.

Meanwhile, the commissioners were briefed on the result of the experiment conducted by the Korea Atomic Energy Research Institute on the same Passive Autocatalytic Recombiner products as the ones installed at the Shinhanul Unit 1 by utilizing SPARC equipment according to the conditions of the operating license of the Shinhanul Unit 1 and the result of the review conducted by the Korea Institute of Nuclear Safety.

Shinkori Unit 1 to Go Under Maintenance after Manual Shut Down

Regarding the Shinkori Unit 1 of which turbine and generators tripped on September 6 due to the typhoon (HINNAMNOR), the Nuclear Safety and Security Commission (Chairperson Yoo Guk-hee, hereinafter referred to as the “NSSC”) announced that it had received a report from the Korea Hydro and Nuclear Power (KHNP) that it was planning to manually shut down the reactor.

※ The Shinkori Unit 1 had been in operation with reactor power reduced to 79% to prepare for a typhoon, and the power decreased to 30% due to trip during operation. The NSSC confirmed that there has been no effect on safety of the reactor and radiation after the trip.

As a result of on-site inspection, the KHNP confirmed that the transmission-related facilities of the Shinkori Unit 1 were damaged, and reported to the NSSC that it would manually shut down the reactor for maintenance of the facilities.

The NSSC plans to organize and dispatch an investigation team made up of experts from the Korea Institute of Nuclear Safety, and to check the overall safety of the facilities, including the cause of damage and the appropriateness of maintenance work.

Meanwhile, as the KHNP manually shut down the Shinkori Unit 1, the periodic inspection, originally scheduled for September 14, will begin early on September 8.

NSSC Started Investigation on Automatic Trip of Shinwolsong Unit 2

The Nuclear Safety and Security Commission (Chairperson Yoo Guk-hee, hereinafter referred to as the “NSSC”) received a report from the Korea Hydro and Nuclear Power (KHNP) that the Shinwolsong Unit 2 automatically tripped at 10:40 a.m. on September 8, and is investigating the initial situation through the site office located at the site. It said that it dispatched an investigation team made up of experts from the Korea Institute of Nuclear Safety (KINS).

The Shinwolsong Unit 2 had been operating normally since the NSSC allowed its criticality* on July 29, and the reactor automatically tripped** as the control rod fell due to an error in the power supply of the Control Rod Drive Mechanism (CRDM).

* Criticality means to make nuclear fissions in the reactor occur continuously, resulting in the state where the generated neutrons are equal to the extinct neutrons and therefore, the number of neutrons is in equilibrium

** Nuclear reactors are designed to safely stop by dropping their control rod by gravity when there is no supply of power to the control rod that controls reactor power.

Currently, the power plant is in a state of safety shutdown, and it is confirmed that the radiation levels in the site are maintained at the usual level.

The NSSC plans to thoroughly investigate the cause of the control rod drop and review the KHNP's measures to prevent recurrence.