Abstract: An upper guide structure for simplification of a refueling procedure in a nuclear power plant includes an upper guide cylinder inserted in an upper end portion of a core support barrel installed inside a nuclear reactor vessel to guide a control rod assembly, a support plate installed at a lower end of the upper guide cylinder and having a plurality of first control rod insertion holes formed therein, hollow control rod assembly upper guide tubes respectively installed in the first control rod insertion holes, and a nuclear fuel alignment plate installed at lower ends of the control rod assembly upper guide tubes and including a plurality of second control rod insertion holes formed at positions corresponding to the control rod assembly upper guide tubes, each of the second control rod insertion holes having an inner diameter which increases to an lower end thereof so that the nuclear fuel assembly guide rod is inserted even when a position alignment error of the nuclear fuel assembly is great, and first cool