This book contains detail information on the various reactor physics calculations for core conversion studies of Research Reactor. It provides detail information about the procedure for generating fine group and broad-group cross section libraries for the HEU and the proposed LEU fueled Nigeria Research Reactor (NIRR-1). It also provides information about various reactor models used in the generation of broad group cross section library for reactor physics calculation. In addition, detail information about the development of a 2-D RZ computational model for the HEU and the proposed LEU core configuration can be found in this book. The reactor design parameters generated for the two cores of NIRR-1 were as expected and the result from the preliminary calculation was used to verify the accuracy of the broad group cross section generation process. The data and models developed in this book can be very helpful in future analyses of the HEU/LEU fueled research reactors (i.e. NIRR-1). It can serve as a very useful material during the start up activities and operations of the proposed LEU fueled NIRR-1.