Evaluation of dropped rod accident after elimination of NFRT and correction of hot channel factor reduction rate

In recent years, NFRT(Negative Flux Rate Trip) is eliminated in order to prevent the reactor trip during dropped rod accident in domestic Westinghouse type plants. The theoretical background of dropped rod accident is introduced and the correlations related FΔH are verified for KORI unit 1 which is 2-loop plant. The results show that the default line of Hot Channel Factor Reduction Rate(HCFRR) for low level leakage loading pattern isn't conservative. So, new correlation is generated and applied to the analysis of the dropped rod accident. The minimum pre-drop FΔH is decreased about 2.6% because of NFRT elimination and new HCFRR correlation. According to the sensitivity study on compensation for the reduction, the Rod Insertion Limit(RIL) is shifted 14 steps upward. So, the minimum pre-drop FΔH is increased about 2.5%. The effect of RIL change on plant operation is additionally evaluated