Accelerated Dissolution Process of the Spent Fuel (UO2) under Repository Conditions
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1104-NN03-07
Accelerated Dissolution Process of the Spent Fuel (UO2) under Repository Conditions Eduardo Iglesias, Javier Quiñones, and Nieves Rodriguez Energy, CIEMAT, Avda. Complutense 22, Madrid, 28040, Spain
ABSTRACT Nowadays, nuclear energy is one of the options for developed countries in order to maintain the demand of electric energy. One of the key problems associated with kind of energy generation is the residual waste formed after a fuel cycle (spent nuclear fuel). The thermal treatment received in the reactor and there composition renders these materials very difficult to characterize and thus exhaustive studies are required to obtain knowledge that will help to build a complete, reliable and very safety underground facility. In this way, the option known as the Deep Geological Repository (DGR) is under development by each country taking part in the nuclear energy industry. The unique pathway for the migration to the biosphere of the radionuclide, actinide and lanthanides content in the spent fuel pellet (UO2) after the closing of the deep geological repository is by a water transport phenomena. It is a fundamental question to know how much time they will spend on their trip and the first step is the rate of liberation of these radionuclides from the spent fuel pellet. In this way the matrix dissolution rate of the spent fuel pellet, which is not dependent on the specific surface area after normalization by the initial value is a key parameter to begin the performance assessment for any deep geological repository. The specific surface value is, following the Matrix Alteration Model (MAM) sensitivity analysis, one of the most important parameters controlling the radionuclides liberation. In this way, several measurements were carried out to obtain values in different conditions for different sieves of UO2 powder treated as fresh fuel. First of all, the specific surface area was measured with a multi-point isothermal procedure with N2 and Kr for both. The values obtained are presented in order to obtain a general law for the rate of evolution with the particle size. These data are part of a bigger project about the complete description of the spent fuel analogues, which are very useful for obtaining new dissolution rates for spent nuclear fuel under repository simulated conditions. INTRODUCTION The Matrix Alteration Model (MAM) has been developed at CIEMAT. It simulates the behaviour of the spent fuel under repository conditions1,2 (Figure 1). This allows evaluating, from experimental results, the processes that will control the matrix dissolution (Figure 1) and the consistent radionuclides release to the biosphere. Taking into account that this fact will be the only one existing for the migration of the active radionuclides (actinides and lanthanides, the most of them), all the variables concerning to the matrix dissolution are very important regarding to the security of the performance assessment. As it can be seen in Figure 2, this model is very sensitive to the specific surface area initial conditions
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