This educational module utilizes techniques used to calculate the core reactivity, power distribution, and isotopic inventory for the first and subsequent cores of a nuclear power plant to maintain adequate safety margins and operating lifetime for each core. Some reloading schemes studied minimize energy costs. The module is written more for classroom presentation and self-study by students than for the practicing nuclear engineer; however, the first two sections cover in-core fuel management in a way that should be helpful to a utility manager having the purview of core analysis. The major emphasis is on light water reactors, but in-core fuel management for the high temperature gas-cooled reactor and the liquid-metal fast breeder reactor is included. The module involves detailed information on the systematic application of nucleonic codes, e.g., cross-section generating codes and nodal and diffusion theory multigroup codes, to calculate the depletion and reloading of nuclear power reactors. It is not intended to be a reactor physics text, but detailed derivations of formulas, e.g., the B1 approximation in LEOPARD, FLARE recursion formula, used in the relevant nucleonic codes, are given in greater detail than normally found in a text to eliminate the “black box” use of computer codes.