This book presents a descriptive account on nuclear reactors. It comprises of an extensive review of studies in nuclear reactors technology contributed by authors around the world. Some of the major issues included in this book are - thermal hydraulic investigation of TRIGA type research reactor; the use of radiogenic lead recovered from ores as a coolant for fast reactors; decay heat in reactors and spent-fuel pools; current status of two-phase flow studies in reactor components; among others. It also elucidates other topics like the thermal aspects of conventional and alternative fuels in supercritical water-cooled reactor; simulation of nuclear reactors core; fuel life control in light-water reactors; structural materials modeling for the next generation of nuclear reactors; and the application of the results of finite group theory in reactor physics.