- (99) Tc In Bentonite Material Adsorption And Diffusion Of Behavioral Research

With the development of nuclear energy, China accumulates one thousand tons of spent fuel to 2010. After 2020, nearly thousand tons of deficiency fuel will be dismounted every year. The pressure China faces will be rapidly increased with the increase of the mount of the high-level radioactive waste, therefore, studies and performs must be carried on. Generally, deep geological disposal is supposed to be the most feasible method for the procession of the high-level radioactive waste. By the deep geological disposal, with the time moves on, as the result of the ground water corrosion, the geological condition change and so on, the waste repository as well as the waste packing body can be destroyed inevitably. Radionuclide may migrate with the ground water into the biosphere. Therefore, the research on the radionuclide migration behavior is an extremely essential question for the high-level radioactive waste disposal. ⁹⁹Tc, as a long-lived fission product, is one of the main components of high-level radioactive waste. Because of its toxicity and long-lived, it is always the key point in the research ,and what is more , it occupies an important position in the geological disposal of the high level radioactive waste in the evaluation of safety and environmental.This work mainly is under the atmosphere and the low oxygen condition, use the Beishan Mountains ground water, study adsorption behavior of ⁹⁹Tc on Gao Miaozi bentonite by batch method, discuss pH(3-10), the SO₄^2- density, the chemical additive type (including FeO, Fe₂O₃, Fe₃O₄) and so on the factors to Tc in the bentonite adsorption influence. The experimental result indicated that, under the atmospheric condition, ⁹⁹Tc is very weak in the bentonite adsorption, its Kd=1.01mL/g, but under the low oxygen condition, the bentonite has certain adsorptive capacity to ⁹⁹Tc, its Kd=183.38mL/g; The solution pH value, the SO₄^2- density, Fe₂O₃ and Fe₃O₄ have not affected to ⁹⁹Tc adsorption on the bentonite; Add the FeO into the bentonite would enhance ⁹⁹Tc adsorption on the bentonite, the FeO quantity is greatly 0.030mg,0.15mg,0.30mg, under its atmospheric Kd value respectively is 7.42 mL/g,83.9 mL/g,127 mL/g; But under low oxygen Kd value then respectively is 216.31 mL/g, 250.18 mL/g, 319.47 mL/g.The diffusion of ⁹⁹Tc was studied under aerobic and anoxic conditions. Under the aerobic and anoxic conditions, the diffusion coefficients of ⁹⁹Tc in bentonite are 1.64×10^-9 m²/s and 6.07×10^-10 m²/s; under the aerobic and anoxic conditions, the coefficients of ⁹⁹Tc in bentonite added sands are 3.64×10^-9 m²/s and 7.00×10^-10 m²/s; under the aerobic conditions the coefficients of ⁹⁹Tc in bentonite added FeO is 5.91×10^-11 m²/s.And the results seems :under aerobic conditions, the migration of ⁹⁹Tc in bentonite is faster than that under anoxic conditions; And it's faster in the bentonite added sands than pure bentonite; what's more ,the diffusion coefficient will decrease while adding Fe into the bentonite.In summary, under the deep geological disposal condition, the bentonite can goodadsorb ⁹⁹Tc, it has be able effective to hinder ⁹⁹Tc in the geological migration,specially add into the FeO, ⁹⁹Tc adsorption on the bentonite has big enhancement, that could provide parameters for choosing backfill material of the high- level radioactive waste deep geology disposal repository.