Evaluation of the Radioactivity Release Event in December 2003 at Yonggwang Nuclear Power Plant Unit

As of March 4, 2004, Oeko-Institut was commissioned by the Korean Company KHNP to review an incident in NPP Yonggwang Unit 5.

Starting December 22, 2003, this incident lead to a contamination of a usually non-nuclear (clean) system of the plant, the Demineralized Water System, by contaminated reactor coolant in the Shutdown Cooling System. These two systems are usually separated by valves and check-valves. A high leakage rate of a valve was later identified by tests. The Leakage was caused by incomplete closure due to the deposition of foreign material inside the valve.