Verification of improved load sequence logic of emergency diesel generator

In 2016, the licensee found that load sequence logics for the emergency diesel generator (EDG) of some Nuclear Power Plants (NPPs) in Korea were errors that can operate two component cooling water pumps (CCWP) in a train. The rated power of the EDG is designed with consideration for one CCWP. An increase of the load due to operation of two CCWPs can exceed the rated power of the EDG and cause a serious transient state. To improve this problem, the licensee modified to the logic of load sequence which operates one CCWP per a train. We evaluated the integrity for the modification of the load sequence logic through the review of the software verification and validation (V&V) activities and the result of the test.