Basic principles of nuclear reactors are explained. Nuclear and neutron physics fundamentals are outlined, including the atomic structure theory, radioactivity, and nuclear reactions. The reactor physics text concentrates on the neutron balance of the fission chain reaction, neutron diffusion, neutron moderation, nuclear reactor theory, the reactor in the steady state and in operating conditions, and nuclear reactor shielding. Nuclear reactor dynamics is described. The treatment of the research reactor thermohydraulics is focused on the generation of heat in the reactor, heat convection in the fuel elements, heat transfer, temperature distribution in the fuel channel, and reactor core hydrodynamics. Emergency reactor analyses are also dealt with. The text is adapted to the study of research and experimental reactors. (J.B.). 3 tabs., 36 figs., 10 refs.