Influence of Container Base Material (Fe) on SIMFUEL Leaching Behavior
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Influence of Container Base Material (Fe) on SIMFUEL Leaching Behavior J. Quiñones1, J.A. Serrano1, P.P. Díaz Arocas1, J.L. Rodríguez Almazán1, J. Cobos1, J.A. Esteban2 and A. Martínez-Esparza2 1 CIEMAT. Departamento de Fisión Nuclear. Avda. Complutense, 22. 28040 Madrid, Spain 2 ENRESA. C/ Emilio Vargas, 7. 28043 Madrid, Spain ABSTRACT The chemical stability of spent fuel will be greatly influenced by the redox potential of the near field. Presence of reductants such as iron is likely to be an important factor to maintain the original integrity of spent fuel. In this work experimental data about the influence of metallic iron (container base material) on SIMFUEL leaching behavior under simulated granite and saline repository conditions is presented. In the presence of iron uranium concentration undergoes a sharp decrease. This is much more noticeable in the experiments performed under initial oxic conditions. The effect of iron on simulated fission products of SIMFUEL is very important for the elements with high redox sensitivity such us molybdenum. On the contrary, strontium remains stable during the entire tests and it seems not be affected by changes in redox potential. INTRODUCTION The aim of spent fuel leaching experiments is to understand high level waste behavior toward dissolution in a multibarrier system of an underground repository. Radionuclides released from spent fuel could result from oxidative dissolution of the UO2 waste form to form an oxygen richer uranium oxide or other complex U(VI) solid. Therefore, the chemical stability of spent fuel will be dramatically influenced by the redox potential of the near field and, in particular, the spent fuel surface [1 and their references]. The redox potentials in deep groundwater systems have been found to be consistent with redox reactions involving Fe(II) in solutions and hydrous Fe(III)-oxide phases [2]. Consequently, reducing conditions are expected to prevail in a deep repository for high level nuclear wastes. However, in the surrounding of the spent fuel, due to the ionizing radiation emitted by itself, the presence of oxidants by the radiolytic decomposition of water is expected. The presence of reductants such as H2 from radiolysis and corrosion processes and Fe+2 from groundwater and from container and other structural parts of the underground repository will play an important role to inhibit oxidation of UO2 spent fuel matrix. In this work experimental data about the influence of container base material Fe on SIMFUEL leaching behavior under simulated granite and saline repository conditions will be presented.
EXPERIMENTAL CONDITIONS Batch leaching tests have been carried out using powder of SIMFUEL (chemical analogue of spent fuel [3]) with a particle size distribution of 100 - 315 µm and a specific surface area of about 4·10-2 m2·g-1. Leachant solutions for the tests were 5 m NaCl and granite bentonite water (GBW, Table I) [4]. The surface to solution volume ratio used in all tests was 1000 m-1. Table I. Synthetic groundwater composition used at
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