LOCA analysis of reactor internals for Yonggwang nuclear units 3 and 4

In the design of nuclear power plants, many hypothetical accidents are postulated and the plants shall be designed to withstand these accidents. To show the structural integrity for loss-of-coolant-accident (LOCA), one of the severest accidents, a series of analyses are performed such as reactor coolant system (RCS) analysis, blowdown analysis and reactor internals analysis. A 14 inch safety injection nozzle break for YGN 3 and 4 was postulated and analysis results on the internals and fuel were compared with those of MCL breaks. The comparative evaluation of reactor internals responses verified that the postulation of tributary pipe breaks in lieu of MCL pipe breaks has consistently, and in some cases substantially, reduced reactor internals responses. This result guarantees the sufficient safety margin of YGN 3 and 4 reactor internals design and may be used to simplify the internal structures in the future plant design