The specification of supervision and control tasks in complex processes requires definition of plant states on various levels of abstraction related to plant operation in start-up, normal operation and shut-down. Modes of plant operation are often specified in relation to a plant decomposition into subsystems or components or defined in relation to phases of the plant process. Multilevel Flow Modeling (MFM) is a methodology for representing goals and functions of complex process plants on multiple levels of means-end abstraction and is based on conceptual distinctions between purposes or goals of the process plant, its function and its structural elements. The paper explains how the means-end concepts of MFM can be used to provide formalized definitions of plant operation modes. The paper will introduce the mode types defined by MFM and show how selected operation modes can be represented for the Japanese fast breeder reactor plant MONJU.