[en] Experience of the VK-50 NPP operation is given from the viewpoint of the chosen water-chemical regime on the state of equipnment and pipelines. The 12-year experience of the NPP operation in the correctionless neutral water-chemical regime using various construction materials has permitted to make a conclusion about sufficient reliability and corrosion resistance of carbon steels as the main construction material. To prevent dangerous corrosion on the phase interface in vapour separators made of carbon steels it is necessary to construct a so-called varying level. Utilization of carbon steels excludes carrying-out of elements into the coolant, activation of which leads to production of long-lived radionuclides of deposits accumulating in due course on inner surfaces of reactor the washing-out of the reactor under breakdown should be performed by boron citrate and ammonium citrate solutions inhibited by thiourea before planned maintenance