[en] The proceedings contain 29 papers of which 10 fall under the INIS Subject Scope. The papers deal with the corrosion effects and behavior of materials for the components and pipes of WWER type and sodium cooled fast reactors, and with the general questions of corrosion resistance of materials used in nuclear power plants. (Z.M.)

[en] The travel of steam from slightly overheated to moist steam of a moisture content lower than 20% is a characteristic feature of the low-pressure part of turbines. Problems are briefly discussed associated with material degradation in such an environment as a result of corrosion and corrosion-erosion processes. They may be eliminated by the development of materials showing high-grade mechanical properties and low susceptibility to corrosion damage, and by the achievement of high steam purity. (Z.M.)

[en] The results are summed up of experiments devoted to testing the technique and the selection of microorganisms and of the medium for studying the effect of microorganisms on the corrosion of austenitic materials. The experimental results show that the technique described is satisfactory. In the bacterial media of strains Thiobacillus, Ferrobacillus and Gallionella in the presence of Cl^- ions, point corrosion damage of austenitic materials can be expected. Generally, corrosion damage can be expected in media with reduced pH and the simultaneous presence of chloride ions, and in solutions with increased oxidation-reduction potential. (Z.M.)

[en] The effect was studied of surface treatment of austenitic steels of the CrNiMo type on their corrosion resistance. The chemical processing of the surface modelling pickling, decontamination processes and electrochemical polishing proceeded in laboratory conditions. Corrosion testing proceeded using common techniques. An adverse effect was found of C, S, Mn, Ti, and N on the resistance of stabilized steels to point corrosion following chemical treatment of the steels. It was also found that the chemical treatment of the surfaces of stabilized steels should be performed with respect to the possible different course of surface formation because the resulting corrosion resistance not only depended on the chemical state produced but also on the physical state of the surface, such as the presence of microcracks, and on the cumulation of phases accelerating the cathode reaction rate. (Z.M.)

[en] The application of austenitic material especially susceptible to local corrosion and corrosion cracking, in both circuits of WWER nuclear power plants necessitated the investigation of the effects of possible electrolyte changes on the individual parameters of local corrosion. The methods are described of assessing the properties of oxide layers and deposits, such as the determination of the weight of an area unit of the oxide layer, the determination of porosity of layers and deposits, their mechanical strength, thickness and properties characterizing heat transfer in the layers. Attention is also paid to the physical and chemical properties of oxide layers and deposits, to their crystal structure, and to the determination of their chemical properties. It is shown that only a set of methods offering a complex picture of the whole problem area should be used in determining all properties. Results thus obtained can be used in the study of corrosion processes in the water-steam environment in nuclear power plants. (Z.M.)

[en] The material properties were studied in detail of samples removed from experimental reactor BOR-60 after 35,000 hours of operation in the sodium-water steam mixture in order to establish the effects of radiation, high temperatures and corrosion on materials used in fast reactor steam generators. Microstructure changes, fatigue properties and creep strength were investigated of materials of the 03Cr18Ni11, 05Cr21Ni32Ti0.5Al and 08Cr2.25Mo1NiNb types. The test results are shown in graphs and discussed in detail. They show that most problems arise with pitting corrosion in material 08Cr2.25Mo1NiNb which, at more exposure, will result in reducing the material fatigue resistance. (Z.M.)

[en] The reactivation technique was used for assessing susceptibility of steel 03Cr18Ni12Mo3 to intergranular corrosion. The technique uses the principle of passive state reactivation in dependence on the chromium content in the solid solution. It shows resistance or susceptibility to intergranular corrosion from differences between the chromium-depleted range and that where the chromium content was not reduced. Data were cumulated on increasing susceptibility of the steel to intergranular corrosion with increased annealing time at a temperature of 650 degC in an interval of 3 to 500 hours. It was also found that the use of the reactivation technique can sensitively indicate the initial stage of development of susceptibility to intergranular corrosion which is not yet manifest during testing in a standard solution. (Z.M.)

[en] The permissible crack depth on the inner surface of tubes for WWER-440 steam generatos is 0.07 mm. The tubes are manufactured from austenitic stainless steel of the 08Kh18N10T type with a diameter of 16 mm and thickness of 1.4 mm. The operating conditions given primarily by the overpressure of 12 MPa on the primary side as against 3 to 5 MPa on the secondary side, and a temperature gradient of 250 to 300 degC on the primary side as against 230 to 260 degC on the secondary side vary during operation and may thus be the cause of fatigue crack initiation and propagation, this especially on technological defects on inner tube surfaces. Experimental research of initiation and propagation of fatigue cracks and studies of corrosion fatigue confirmed that with respect to steam generator ilfe, technological defects on the inner tube surface down to a depth of 0.10 mm are permissible. (Z.M.)

[en] Secondary circuit measurements in the V-1 nuclear power plant in Jaslovske Bohunice showed a high iron concentration in feedwater. The inspection of the machinery confirmed that this was the result of erosion corrosion. The steam pipes after the high pressure turbine stage prior to the steam separator, and the pipes of heat steam at the inlet of the first superheater stage were attacked into the largest extent. The steam pipes were repaired by lining with austenitic steel sheets at the most exposed points, and this treatment was incorporated in the production of new equipment for other power plants. Only part of the corrosion product sources in feedwater, however, was removed. Therefore, brass as the material for the condenser pipes was recommended to be replaced with titanium alloys, which would allow increasing the pH value of the secondary circuit water, thus significantly reducing the erosion corrosion in the circuit. Also, the need would be eliminated to use austenitic materials for the secondary circuit pipes and components. In addition, the period of the cleaning of the steam generator secondary side would be extended. (Z.M.)

[en] The effect was studied of annealing on the nature of corrosion damage of austenitic stainless steel type 08Cr18Ni10Ti in an oxidation medium with the aim of clarifying the views on precipitation processes taking place within the tempeature range 550 to 850 degC. It was found that a time interval exists for each temperature in the said range when corrosion rate in boiling 65% HNO₃ increases, which is associated with intergranular corrosion damage. It was shown that intergranular corrosion of nonsusceptibilized specimens was initiated by the dissolution of TiC discontinuously extracted on grain boundaries. The application of three-stage annealing in a temperature range of 680 to 800 degC significantly reduced the corrosion rate when compared to the effect of single-stage annealing under comparable conditions. The combination of temperatures used obviously affected both the precipitation kinetics and the chemism of the precipitating phases. (Z.M.)