Fast reactors for purposes of efficient utilization of plutonium from power plants and weapons are currently under study and development in Russia and other countries (France and Japan). It is important in this connection to develop and substantiate new plutonium-containing fuel compositions with 238U replaced by an inert diluent.The Main Science Center of the Russian Federation -Power-Engineering Institute has been conducting since 1994 work on choosing a technology and studying the properties of a fuel material in a magnesium oxide matrix. Magnesium oxide was not chosen randomly as an inert diluent [1-3]: it does not form intermediate phases with plutonium dioxde; it does not interact with sodium; it is highly radiation resistant; it is easily reprocessed by dissolution; and, it possesses a satisfactory thermal conductivity (12 W/(m-deg) at 900"C in nonporous samples).The objective of the present work was to develop a technology for producing PuO 2-MgO fuel pellets. It was determined by means of a physical calculation that the actual volume fraction of plutonium dioxide in an inert matrix equals approximately 15%. Two technological schemes for preparing fuel pellets with the composition 15% uranium dioxide -85 % magnesium oxide were compared in advance using uranium dioxide as a simulator: by means of mechanical mixing of powders and coprecipitation of magnesium hydroxide and ammonium polyuranate from a nitrate solution [4]. Preference was given to the technology for preparing pellets by coprecipitation from solutions, since this gives the most uniform distribution of plutonium dioxide, a high density, and a higher thermal conductivity. Furthermore, the technology contains the standard operations and equipment used in nuclear fuel production plants. The samples were investigated by metallographic, x-ray, and other forms of analysis, their thermal conductivity was determined, and the possibility of chemical reprocessing of the samples was assessed.Preparation of PuOz-MgO Pellets (Fig. 1). The work was performed in hermetically sealed glove boxes at the hot laboratory at the Physics and Power-Engineering Institute. The pellets were prepared by a technological regime chosen on the basis of experiments with uranium dioxide simulator.A solution of plutonium and magnesium nitrates was prepared with 18.1 g of plutonium and 36.3 g of magnesium oxide. The solution was dissolved in nitric acid, yielding 460 ml of the solution with the concentrations (g/liter): Mg 51.5, Pu 42, and HNO 3 -30. The hydroxides PU(OH)4-Mg(OH)2 were precipitated using a 25% solution of ammonia by the method of simultaneous decantation in the precipitation apparatus. To achieve a pH of 10.5, 1030 ml of ammonia were consumed in order to precipitate plutonium and magnesium hydroxides from a 460 ml of the nitric-acid solution. The precipitation process lasted for 3 h, and the temperature of the pulp during the precipitation process was maintained equal to 40-42~ When the decantation process was finished, the pulp was mixed for 1 h at 40-42~ and the...
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