In the paper, principles of constructing systems of information support of human-operators (IOSS) of power units of nuclear power plants (NPP) and their place within the system of upper unit-level of automated process control systems (APCS) of NPP. The purpose of implementation of the NPP IOSS is preventing or decreasing the frequency and heaviness of operator errors appearing under transients and non-regular situations, when human-operators perform under the conditions of lack of the time, fast change of the actual status, and huge volumes of information, conditioning the excessively high work load. One of tasks solved within the information support system is the task of calculating technical and economical indexes, based on intelligent data analysis.