The reactor core is the central part of a nuclear reactor where nuclear fission occurs. It consists of four basic systems and components: the fuel (including fuel rods and the fuel assembly structure), the coolant, the moderator and the control rods, as well as additional structures such as reactor pressure vessel internals, core support plates, and the lower and upper internal structure in light water reactors. This Safety Guide provides recommendations on meeting the safety requirements established in IAEA Safety Standards Series No. SSR-2/1 (Rev. 1), Safety of Nuclear Power Plants: Design, applied to the design of the reactor core for nuclear power plants. The publication addresses the safety aspects of the core design and includes neutronic, thermohydraulic, thermomechanical and structural mechanical aspects. Other aspects considered are those relating to reactor core control, shutdown and monitoring, and core management.

REPP, a digital computer method for designing pressure water and boiling water reactor cores within specified heat transfer and fuel centerline temperature limits is presented. The method incorporates the Westinghouse W-2 and W-3 empirical correlations and a theoretical hot channel model to predict burnout conditions in a rod bundle. Two geometries are considered; rods in a triangular array and rods in a square lattice. The heat transfer problem solved is a one-dimensional analysis. Pressure drop is considered for four types of fuel-pin spacers. Variable heat generation rate through the fuel-pin and sintering in low density fuels are also included.

Information on heat transfer and hydraulics pertinent to the design and operation of boiling water reactor power plants is presented. The following areas of discussion are covered: heat transfer, two-phase density studies, two-phase pressure drop, critical heat flux and burnout, boiling stability, calculation procedures for boiling systems, and thermal-hydraulic design procedures for boiling water reactors.