NSSC "Additional Leak Blocked and Under Investigation...
Effective Radiation Dose Below Annual Dose Limit"
At the Wolsong Unit 4 nuclear power plant, which had been shut down for regular inspection, 2.3 tons of storage water from the spent nuclear fuel storage pool was released into the sea. However, the effective radiation dose of the released storage water was found to be far below the annual dose limit for the general public.
On the 22nd at 7:53 a.m., the Nuclear Safety and Security Commission (NSSC) received a report from Korea Hydro & Nuclear Power (KHNP), the operator of the nuclear power plant, about the release of storage water at Wolsong Unit 4 during its planned preventive maintenance. The NSSC immediately dispatched experts from the Korea Institute of Nuclear Safety (KINS) to investigate the exact leakage amount and cause.
According to the report, KHNP discovered a decrease in the water level of the spent nuclear fuel storage pool at around 4:34 a.m. that day and took measures to stop the leakage. Based on the estimated leakage amount, KHNP evaluated the environmental impact and reported to the NSSC that the effective dose was 0.000000555 mSv (millisieverts) annually. The annual dose limit for the general public is 1 mSv.
Upon receiving the report, the NSSC began an investigation and instructed KHNP to collect seawater samples near the nuclear power plant to conduct a detailed environmental impact assessment. The NSSC plans to disclose the specific environmental impact assessment results and the appropriateness of safety measures after further investigation.
An NSSC official explained, "It is presumed that a problem such as leakage occurred between the cooling water that cools the spent nuclear fuel and the heat exchange device that cools this cooling water. We have temporarily blocked the leakage with valves to prevent additional leakage of storage water and are investigating the exact cause."
Wolsong Unit 4 has been shut down since April 20 for planned preventive maintenance. Last month on the 13th, during a test of the emergency diesel generator, it was reported through the Nuclear Safety Ombudsman that the voltage of the safety bus (the line supplying power to safety equipment) temporarily dropped, but safety equipment such as the equipment cooling water pump, which should have operated automatically, did not function. The NSSC is currently investigating this matter.
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