"Nuclear Research Institute Radioactive Material Leak Due to Floor Drainage Tank Installation Not Subject to Permits... Unaware for 30 Years"

According to the Ministry of Science and ICT's approval, it should be a closed circulation system
Leakage due to a 600ℓ floor drainage tank not included in the approved design
"Operated annually from April to November since August 1990... was unaware"

Korea Atomic Energy Research Institute. (Photo by Asia Economy DB)

[Asia Economy Reporter Moon Chaeseok] The government announced that the reason radioactive materials were released from the natural evaporation facility at the Korea Atomic Energy Research Institute (KAERI) in Deokjin-dong, Yuseong-gu, Daejeon last year was because a drainage tank was installed on the floor, contrary to the design approved by the Ministry of Science and ICT. The facility has been in operation for 30 years since 1990.

On the 20th, the Nuclear Safety and Security Commission (NSSC) announced the results of its two-month investigation into the KAERI artificial radionuclide release incident that occurred after the 21st of last month.

The normal operation path is '①→②→③→④→⑤→⑥→⑦ cycle'. When the intermediate storage tank water level decreases, it is replenished from the underground storage tank. Every year at the end of operation, the remaining liquid radioactive waste is recovered to the underground storage tank. (Image provided by the Nuclear Safety and Security Commission)

According to the NSSC, KAERI's natural evaporation facility was designed to transfer extremely low-level liquid radioactive waste with a concentration below 185 Bq/ℓ from an 860,000-liter underground storage tank, lift it, and then flow it from the supply tank on the third floor to the evaporation bed on the second floor. The waste is naturally evaporated through sunlight, and the remaining radioactive waste is sent back to the underground storage tank in a closed-loop system approved by the Ministry of Science and ICT.

Floor plan of the underground natural evaporation facility at the time of installation approval in 1988. (Image provided by the Nuclear Safety and Security Commission)

In reality, a 600-liter floor drainage tank, which was not included in the design approved by the Ministry of Science and ICT, was installed on site and connected to an underground external pipe. Since August 1990, 30 years ago, some floor drains on the first floor of the facility have been connected to the floor drainage tank and operated annually from April to November. For 30 years, operators were unaware of the existence of the floor drainage tank in addition to the underground storage tank. They believed all floor drains on the first floor were connected to the underground storage tank and operated in a closed-loop system.

Construction drawing of the underground floor of the natural evaporation facility during construction (Image provided by the Nuclear Safety and Security Commission)

The investigation confirmed that approximately 510 liters of liquid radioactive waste leaked. This was due to immature operation after excessively opening a valve following filter replacement on September 26 last year, causing the liquid radioactive waste to overflow from the collection channel.

It was also detected that about 470 to 480 liters of some radioactive waste annually flowed into the floor drainage tank and leaked outside. The waste flowed into the floor drainage tank through the drain at the bottom of the filter and leaked outside.

The leak occurred during the process of stopping operation around November each year to prevent freezing in winter and recovering all liquid radioactive waste back to the underground storage tank.

Analysis results of radioactivity concentration in river soil in front of the main gate of Korea Atomic Energy Research Institute (KAERI) from 1995 to 2019. (Image provided by the Nuclear Safety and Security Commission)

Fortunately, all river water samples were confirmed to be below the minimum detectable concentration. Except for a notable value of 25.5 Bq/kg in the soil of the stream in front of KAERI’s main gate during the fourth quarter of last year, no other abnormalities were observed.

It was explained that heavy rainfall of 200mm between October and November last year caused some radioactive materials to flow outside the site. The external impact is considered minimal.

Radiation level measurement results inside the site of Korea Atomic Energy Research Institute (KAERI). (Image provided by the Nuclear Safety and Security Commission)

The NSSC explained that artificial radionuclides such as cesium-137, which were released, were hardly detected in river water and soil due to their strong adsorption characteristics to soil and other materials.

According to the Korea Institute of Nuclear Safety (KINS), which conducted the investigation, the released cesium-137 and others flowed about 1.5 km from the natural evaporation facility through stormwater pipes, 10 manholes, and finally to Deokjin Stream in front of the main gate within the KAERI site.

Measurement results of radioactivity concentration in external river soil by Korea Atomic Energy Research Institute (KAERI). (Image provided by the Nuclear Safety and Security Commission)

Most of the released materials are presumed to be adsorbed on the surfaces of stormwater pipes and manhole sediments within the research institute. Assuming all radioactive materials were released into the external environment, the annual radiation dose was evaluated to be about 1/3,000,000 to 1/3,700 of the general public dose limit (1 mSv).

Eom Jae-sik, Chairman of the Nuclear Safety Commission (Photo by Yonhap News)

The NSSC analyzed that the fundamental causes of this release were KAERI’s lack of enterprise-wide management system and design-based configuration management, manual operation system, and lack of safety awareness. Accordingly, KAERI was requested to conduct a comprehensive investigation to verify whether there are discrepancies between the licensing conditions and construction drawings of about 100 nuclear and radiation-utilizing facilities and the current facility status.

They also instructed KAERI to expand environmental radiation monitoring points within the institute, modernize the operation systems of radioactive waste-related facilities, strengthen the overall functions of the safety management organization, and conduct safety culture inspections led by external agencies. Through this, KAERI was directed to establish a detailed implementation plan for comprehensive safety enhancement measures and report it to the next NSSC meeting.

An NSSC official stated, "We will double the frequency of regular inspections for nuclear fuel cycle facilities such as the natural evaporation facility," and added, "We plan to improve the system by establishing a dedicated team for on-site inspections at KAERI and strengthening NSSC’s safety regulatory responsibilities for nuclear fuel cycle facilities."

This content was produced with the assistance of AI translation services.