[en] Field and laboratory experiments were carried out in fresh water (used in the cooling system of a fast reactor) using mild steel to study the type and extent of corrosion at different pH and Langelier indices. The corrosion products were analysed using Infrared Absorption Spectroscopy (IRAS), Energy dispersive x-ray analysis (EDAX), x-ray diffraction analysis (XRD), scanning-electron microscopy (SEM), and a particle-size analyser. Laboratory static experiments showed a maximum corrosion rate of 43.2mpy after seven days, which then decreased gradually and reached a steady value of 9mpy after 130 days. Field experiments in open reservoir water, from where the reactor draws water, showed that corrosion rates in the field were much higher than the laboratory static experimental values. Particle size analysis of the corrosion products showed size distributions ranging from 30-60μ in the laboratory samples, and 60-100μ in the field samples. (EDAX) analysis showed the composition of the corrosion products to be in the following order of abundance: iron > calcium > silica (non reactive). (author)