Analysis of observations on surface film formation has indicated a single process to be primarily responsible. This process involves transport of particles present in the coolant to the surface, and attachment there through the establishment of chemical bonds. Brownian motion is the principal mechanism bringing partiales into contact with the surface, but many factors can be important in determining whether a given encounter will lead to permanent attachment of a particle. One of these factors, frequently present in reactor cores, is a surface electrostatic force caused by the flow of electrical currents. These currents are primarily the result of beta electron and photoelectron emission. Details of the various electrical parameters are analyzed for situations encountered in heterogeneous and homogeneous reactors. It is shown that the surface electrostatic force is critically dependent on the current density crossing the coolant-film interface, and on the electric resistivity of the surface of the film in contact with the coolant. Recommendations are made for means to prevent the formation of objectionable surface films. Attention is directed to the fact that the homogeneous slurry type of reactor combines conditions which can lead to the deposition of fuel bearing films on in-core surfaces.