Matters concerned with making efficient use of the information-analytical system on the flow-accelerated corrosion problem in setting up in-service examination of the metal of pipeline elements operating in the secondary coolant circuit of the VVER-440-based power units at the Novovoronezh NPP are considered. The principles used to select samples of pipeline elements in planning ultrasonic thickness measurements for timely revealing metal thinning due to flow-accelerated corrosion along with reducing the total amount of measurements in the condensate-feedwater path are discussed.

The results of computational hydrodynamic simulation of the flow of a working medium in the flow path of the feedwater control assembly used in power units of nuclear power plants (NPPs) equipped with the reactors of the RBMK-1000 type are presented It was established that the rate of control valve opening has an influence on the position of the areas of the intense local erosion-corrosion thinning of metal of the diffuser section downstream of the valve.

Results obtained from investigations of erosion-corrosion processes that occur during operation of the feedwater supply control systems used in power units of nuclear power stations equipped with RBMK-1000 reactors and the sensitivity of these processes to variations in the chemical composition of metal and in the flow path geometry are presented. It is found that local erosion-corrosion thinning of the walls in the diffuser segments of feedwater supply control systems occur mainly due to intense mass transfer in the near-wall region taken in combination with a low content of chromium. Hydrodynamic simulation was carried out, and it was shown based on its results that local erosion-corrosion thinning of the walls of pipeline segments downstream of the valves controlling the supply of feedwater to power units of nuclear power stations equipped with RBMK-1000 reactors can be prevented by subjecting them to appropriate modernization. It is found that the above mentioned diffuser parts can be made more resistant to erosion-corrosion wear by keeping the content of chromium in the main metal and weld joints at a level of no less than 0.25% and concurrently reducing the hydrodynamic effect in the zones of weld connections.

Results from a study aimed at analyzing the damageability and determining the mechanism due to which thinning occurs in the metal of welded connections in the feed water supply control assemblies used in power units of nuclear power stations equipped with RBMK-1000 reactors are presented together with the outcomes from calculation studies aimed at analyzing the effect of hydrodynamic characteristics on the kinetics characterizing the thinning of a welded joint and adjacent elements of a pipeline. Data from a calculation of the erosion-corrosion rate of welded connections in the divergent parts of assemblies controlling the supply of feed water in power units of nuclear power stations equipped with RBMK-1000 reactors are given.

The peculiarities of the cavitation effect are considered and some engineering criterion-parametric methods are proposed for estimating the possibility of manifestation and the level of intensity of the cavitation action on components of narrowing devices of circuit II of nuclear power plant (NPP) power units. Results of computational and experimental studies are presented which have shown that up to 30% of throttling devices of the condensate-feed channel of NPP power units are subject to the cavitation erosion. The possibilities of practical application of the developed methods were established for revealing the causes of wall thinning of narrowing devices in the NPP working channel and for preventing it.