Heavy water leak at Wolseong Nuclear Power Plant Unit 2 in South Korea found to be far larger than initially reported

The actual scale of the heavy water leak that occurred at Wolseong Nuclear Power Plant Unit 2 in Gyeongju, North Gyeongsang Province, South Korea, in September last year, is reported to be far larger than the initially disclosed figure. The Gyeongju Environmental Movement Alliance disclosed on the 30th that a detailed internal report obtained from Korea Hydro & Nuclear Power (KHNP) shows the total amount of heavy water leaked was 1,311.15 kg, approximately five times the initially reported 256 kg, of which 5.14 kg was recorded as having leaked outdoors.

After the incident, Korea Electric Power Corporation (KEPCO) had reported a heavy water leak of 256 kg and stated that no external leakage occurred. The detailed report now made public reveals that the heavy water leak was ongoing and that a small amount had leaked externally.

The report also shows that the heavy water leak detector should have been installed 11 cm from the bottom of the sump tank, but was actually installed at a height of 83 cm. Based on this, the Gyeongju Environmental Movement Alliance pointed out that relevant personnel did not follow the emergency response plan for leak confirmation procedures, and that leakage issues with some valves had not been addressed for a long time. Even when individual valves were still leaking, maintenance was not carried out in a timely manner.

Heavy water is composed of oxygen and the hydrogen isotope deuterium, and can be used as a coolant or moderator in nuclear reactors. The heavy water used during nuclear power plant operation may contain radioactive substances, thus requiring strict management.

Data shows that the incident at Wolseong Nuclear Power Plant Unit 2 occurred on September 19 last year, with the leak originating from the moderator purification system. This system is used to remove impurities generated in the reactor moderator heavy water and maintain its quality.

The Gyeongju Environmental Movement Alliance stated that the scale of the incident was downplayed, and the total amount of leakage and the external leakage situation were not fully disclosed. It called for the prompt shutdown of Wolseong Nuclear Power Plant Unit 2. A relevant official from Korea Electric Power Corporation responded that the contents of the report are factual, but there was no intentional concealment; the amount of leakage confirmed at the time of the incident differed from the amount confirmed through subsequent investigation.