A Model for the Study of Molecules Radiochemical Decomposition by Actinides Materials
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1104-NN07-12
A Model for the Study of Molecules Radiochemical Decomposition by Actinides Materials Lilian Berlu1, and Gaëlle Rosa2 1 CEA - Centre de Valduc, Is sur Tille, 21120, France 2 CEA - Centre de VAlduc, Is sur Tille, 21120, France
ABSTRACT The radiochemical decomposition of molecules in storage environment which could lead to the corrosion of container or the formation of dangerous gas mixtures is a critical problem for radioactive materials. The complexity of the chemical system makes numerical models necessary for the reproduction mechanisms and the prediction of phenomena. In this study, a mathematical model for the dose rate distribution in external medium surrounding an α emitter actinide material has been proposed. The model has been implemented in a Monte Carlo scheme. An evaluation of the dose rate in the surrounding medium as a function of the sample size was shown and a discussion of the expected reactivity was made. INTRODUCTION When one considers the nuclear energy as a necessity for the control of greenhouse gas emission and nuclear arsenals reduction as a requirement for world pacification, for example, the problem of nuclear materials storage arises. If radioactive materials are stored in standard atmospheric conditions, their radiations lead to the decomposition of chemical species in their vicinity. For example, the production of hydrogen and oxygen from the decomposition of adsorbed water on PuO2 or UO2 and other oxides was observed and intensively studied [1–5]. The accumulation of hydrogen and oxygen in closed vessel is of great concern due to deflagration risk which could lead from these explosive mixtures [6, 7]. The prevision of consequences of radiolysis phenomena makes the study of radiochemical reactions very important for the nuclear industry and especially for long term storage and geological repositories management. Radiolysis of molecular compounds can lead to their decomposition and to the formation of both reductant and oxidant species. These latter can be molecular hydrogen and oxygen which can react back with other gas in the storage atmosphere, with the surface of nuclear materials or with the container leading to its corrosion [8, 9]. In addition, the proximity of the surface imposes to take into account catalytic effects as well as activation of the interface for reactions between surrounding gas and adsorbed species due to energy transfer [1, 10–15]. Chemical reactions that can occur are of many types including decomposition, reduction, oxidation, hydrogenation, polymerization and a combination of all these processes. The entire system is very complex and numerical models could be of high interest in the comprehension and the prevision of involved phenomena. We are interested in developing a numerical model for prediction of reactions due to radiochemical decomposition. On the way to developing a model, we first limited our study to the estimation of the decomposition rate of molecules in the vicinity of an α emitter actinide surface. A kinetic rate approach for primar
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