Processes of filter meshes clogging of emergency core cooling system sump intended for cleaning water incoming in recirculation system from sump are studied. Test rig for study of hydraulic characteristics of filter elements, which is a closed circulation loop are described. Basic principles of modeling of coolant recirculation through a filter element, occurring in event of an emergency depressurization of primary circuit, and experimental research methods are presented. Dependences of pressure drop on meshes on flow rate and amount of debris for several types of meshes on ordinary and borated water are obtained and analyzed. It is shown that the use of borated water leads to an increase in both time to reach steady state and pressure loss on meshes. Constructive measures to reduce pressure losses are proposed.