This paper is the first of three that overview the main mechanisms that drive the microstructure evolution in Fealloys under irradiation. It focuses on pure α-Fe and compiles the parameters that describe quantitatively themobility and stability of point-defects and especially their clusters, including possible reactions and criteria todecide when they should react. These parameters are the result of several years of calculations and application inmicrostructure evolution models. They are mainly collected from the literature and the parameter choice tries toreconcile different sets of values that, while being in general qualitatively similar, are often quantitatively notcoincident. A few calculation results are presented here for the first time to support specific approximationsconcerning defect properties or features. Since calculations cannot cover all possible defect configurations, thedefinition of these parameters often requires educated guesses to fill knowledge gaps. These guesses are herelisted and discussed whenever relevant. This is therefore a “hands-on” paper that: (i) collects in a single reportmost microstructure evolution parameters that are found in the literature for irradiated α-Fe, including a discussionof the most important mechanisms at play based on current knowledge; (ii) selects a ready-to-use set thatcan be employed in microstructure evolution models, such as those based on object kinetic Monte Carlo (OKMC)methods. This work also identifies parameters that are needed, but not known, hopefully prompting correspondingcalculations in the future.