The "SPb SEC" Association has developed a standard of the organization (STO) "Refractories. Method for Determining Hydration Resistance." The standard covers powders and articles based on magnesium oxide. The hydration resistance of powders is evaluated in terms of the change in the mass or in the grain composition of a sample after treating it with steam under pressure; the hydration resistance of articles is estimated from the change in their appearance.Refractories based on periclase (magnesium oxide) and bearing calcium oxide can undergo hydration in a warm humid atmosphere. In this case the powder grains break, the material is pulverized, and the articles crack. Various methods exist for determining the hydration resistance of refractories. The most frequently used methods are (1) treatment of the tested material with steam at normal or elevated pressure and a temperature corresponding to the steam pressure and (2) holding in a climatic chamber at a temperature below 100°C at a high moisture content. The second method is closer to natural conditions under which such articles are stored, especially in a humid tropical climate, but the test takes a long time. In Great Britain and in the USA the methods for determining the hydration resistance of refractories have been standardized. The main items of the standards are presented in Table 1.In Russia, where periclase and periclase-containing refractories are produced in considerable volumes, such standards are absent. In this connection it seems appropriate to evaluate the hydration resistance of domestic and imported refractories used in the RF. It has been decided that a method for determining hydration resistance should be developed and standardized.The "St. Petersburg Scientific-and-Engineering Center" Association of Producers and Consumers of Refractories ("SPb SEC" Association) has developed a standard of the organization (STO) "Refractories. Method for Determining Hydration Resistance." The STO has been created with allowance for the experience of foreign standardization and for the results of an experimental study. The method consists in treating the studied samples and refractory specimens with steam under specified conditions and subsequent evaluation or visual estimation of the changes that have occurred.The choice of the method for preparing samples of granular materials (powders) was preceded by an analysis of standards for periclase powders (GOST 24862, GOST 10369, etc.) [1,2]. It was established that the majority of such powders consist of fractions finer than 4 mm. Accordingly, a representative sample for the test is prepared by milling the powder for passage through sieve No. 4 and screening the undersize through screen No. 0.1. It should be noted that producers in Great Britain and in the USA use periclase powders with coarser grain composition and thus test samples with larger grains (see Table 1).The material can be partially hydrated during storage, milling, and screening. In order to ensure the same initial state the samples are baked at ...

diam., 5.5 nun; height, 5 mm; density, 9 g/cm 3) of a solid solution of 8570 UO 2 and 15% PuO 2 and produced by mixing the oxides by mechanical means, molding the tablets from the mix, and firing them in vacuo at 1750~The tablets of (U, Pu)O2 and the zircon cylinders were tested in a molybdenum ampoule in an inert atmosphere at 1500~ for 20 h with the specimens in contact under a load of 2 kgf/cm 2. Radiographic and chemical analyses revealed slight migration of U (up to 0.03%) and Pu (up to 0.02%) into the zircon composition and of the components of the refractory composition (Zr, Si, A1, and Cr) into the nuclear fuel (up to 0.01% of the original amount), and the absence of caking between the zircon specimens and the (U, Pu)O 2 tablets. These findings make it possible to recommend the ACP-bonded zircon composition for the production of crucibles for the melting unit of installations for the thermal stripping of spent fuel elements. CONCLUSIONSAn investigation was carried out of the physic,-and thermomechanical properties of ACP-bonded zircon ramming compounds, of the conditions for their drying and firing processes, and of their solid-solution interaction with a mixed (U, Pu)O 2 nuclear fuel.The optimal composition of the ramming compound is as follows: 95?0 zircon of particle-size fraction 0.06-3.0 ram, 5% refractory clay finer than 0.5 ram, and 7% ACP binder of density 1.5 g/cm 3 (on 100%). The composition is characterized by high strength and low porosity and water absorption.

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A furnace construction has been developed in order to determine refractoriness according to According to the level of reproducibility of results, the accuracy of determining the refractoriness of test materials, and values of the life characteristics, the construction surpasses domestic analogs.One of the most important properties governing the desired choice of refractories for heating units is refractoriness. Refractories that are heterogeneous multiphase systems melt in a certain temperature range, and therefore they are characterized not by the melting temperature, but by refractoriness determined according to the temperature of the collapse of a pyrometric cone. Reliable determination of refractoriness is very important for the classification and use of refractories.In Russia determination of refractoriness is regulated by GOST 4069-69 and abroad by national standards that are versions of MS ISO 528-83. In order to determine refractoriness special equipment is necessary for which there are a number of serious specifications: uniformity of temperature field in the working space, a controlled heating rate, the possibility of controlling temperature in an automatic regime with sufficiently high accuracy, high indices for life characteristics of heating elements and materials of the working chamber, presence of free oxygen in the furnace atmosphere during the whole process, conformity to contemporary health standards, and accuracy of determining the instant of contact of the tip of cones with the support.Technical solutions developed in the USSR and abroad for implementing this method have marked differences, advantages and disadvantages (Tables 1 and 2). Determination of refractoriness in kryptol furnaces is connected with the complexity of regulating the temperature regime and creating a uniform temperature field. This is connected with the nonuniform change in petroleum coke resistance that during heating sinters and is partly oxidized with formation of carbon monoxide. Graphite and gas-flame furnaces have the same disadvantages as kryptol furnaces, and performing tests in different atmospheres leads to divergence of test results.Thermal decomposition of lanthanum chromite at high temperature, as a result of which there is release into the atmosphere of hexavalent chromium, leads to degradation of the whole working chamber, ecological safety is undermined, and to all appearances the behavior of a cone during testing is affected. In addition, domestic heating elements

The All-Union Institute of Refractories has developed the technology for producing periclase--lime clinkers based on natural raw materials: dolomite and magnesite [I].Some of the properties of these refractories prepared from clinkers with a CaO concentration of 2-60% have been studied.* The clinkers were prepared by firing briquettes made from raw powdered dolomite and magnesite at 1600~The chemical composition of these materials is given in Table I. The apparent density of the magnesite clinkers with I0, 20, or 40% CaO and the dolomite clinker was, respectively, 3.29, 3.33, 3.32, 3.24, and 3.24 g/cm 3.The specimens of refractory were made from a batch of the following grain composition [2]:40% fractions from 2-0.5 mm; 25% from 0.5-0.06 mm; and 35% <0.06 mm.As the bonding material, we used a "solid" carboniferous resin and paraffin as the temporary bonding in the preparation of the fired specimens.Before the study of their properties, the unfired specimens were heat-treated at higher temperatures in a nonoxidizing medium at 400~As the resistance of the resin-impregnated fired refractories during service are significantly higher than that of the unimpregnated, some of the specimens fired at 1700~ were impregnated with carboniferous pitch preceded by vacuum treatment [3].