[en] In order to realize the fast execution of a nuclear code using a vector-processing computer, it is necessary to select an appropriate numerical method and to use efficient programming techniques for this computer. In this report, first the details of nuclear codes frequently used in JAERI are analyzed, then the numerical methods employed there are discussed from the viewpoint of vectorization. The vectorization method of a nuclear code is systematically described, and examples of vectorizations are shown for individual numerical methods. (author)