Simfuel Leaching Experiments in Presence of Gamma External Source ( 60 CO)
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EXTERNAL SOURCE (NCO)
J.A. Serrano, J. Quifilones*, P.P. Diaz Arocas, J.L. Rodriguez Almazin, J. Cobos*, J.A. Esteban", A. Martinez-Esparza*" * Departamento de Fisi6n Nuclear. CIEMAT. Avda. Complutense, 22.28040 Madrid. SPAIN
00 ENRESA, C/ Emilio Vargas, 7.28043 Madrid. SPAIN
ABSTRACT One of the factors considered within the studies of performance assessment on spent fuel under final repository conditions is the effect of the radiation on its leaching behavior. Radiation from spent fuel can modify some properties of both solid phase and leachant and therefore it would alter the chemical behavior of the near field. Particularizing in the effect of the radiation on the leachant, it will cause generation of radiolytic species that could change the redox potential of the environment and therefore may bring on variations in the leaching process. In this work, the chemical analogue utilized was SIMFUEL (natural U0 2 doped with non-radioactive elements simulating fission products) and the leachants selected were saline and granite bentonite waters both under initial anoxic conditions. To emulate y radiation field of a spent fuel, leaching experiments with external 6°Co sources in a irradiation facility (Nayade) were performed. Initial dose rate used was 0.014 Gy/s. Preliminary results indicate that radiation produces an increase of the uranium dissolution rate, being the concentrations measured close to those obtained in oxic atmosphere without radiation field. In addition the solubility solid phases from experimental conditions were calculated, for both granite bentonite water and 5 m NaCI media. On the other hand, a tentative approach to model the role of y radiolysis in these SIMFUEL tests has been carried out as well. INTRODUCTION The long-term interactions between spent fuel and groundwater has to be understood in order to dispose the fuel in a safe final underground repository. With this goal in mind, and given the limitations related to the handling of irradiated fuel, spent fuel dissolution experiments combined with more detailed studies using non-irradiated chemical analogues are very useful for performance assessment (PA) studies. One of the factors considered within the PA studies on spent fuel behavior under final underground repository conditions is the effect of the radiation on the leaching processes. The radiation emitted by spent nuclear fuel alter the properties of the solid and the leachant, in such way that it modifies the chemistry of the near field [1, 2, 3, 4 and their references]. Radiolysis of the groundwater in contact with the used fuel produces oxidants for the oxidative dissolution of the nuclear fuel. The highest initial absorbed dose rate is generated by the 03and y radiation and after a long period the a radiation will be higher than those. Experimental measurements of the effects of radiolysis on the matrix dissolution rate are complicated by the fact that the effects of a, P3and y radiolysis can not be separated. Particularizing in the effect y radiation, SIMFUEL leaching experiments w
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