This standard provides guidance for performing and validating the sequence of steady state calculations leading to prediction, in all types of nuclear reactors, of: (1) Reaction rate spatial distributions (2) Reactivity (3) Change of isotopic compositions with time. The standard provides: (1) Guidance for the selection of computational methods. (2) Criteria for verification of calculational methods used by reactor core analysts (3) Criteria for evaluation of accuracy and range of applicability of data and methods (4) Requirements for documentation of the preceding. The scope of the standard is shown schematically in Figure 1.