Effects Of Microorganism On Radionuclide Disposal Of Materials Copper And Bentonite

For the scientific issues of microbiological corrosion on radionuclide disposal materials, the copper and bentonite were used as research object, which acted as the pre-selected materials for high-level radioactive waste repository. This paper explored the corrosion influence on this two materials by dominant actinomycetes, fungi and bacteria flora, which were isolated from the soil of Beishan in Gansu. The 360 d liquid-immersion and solid-landfill corrosion environment were built by fed-batch method and wheat medium respectively. In this study, surface analytical（SEM and EDS） and electrochemical techniques（Tafel polarization curves and EIS） were used for analyzing the corrosion behaviour of copper by these three microfloras. Blue absorption power, Cation exchange capacity（CEC）, Thermogravimetry（TG）, Differential thermal analysis（DTA）, and X-ray diffraction（XRD） were used for analyzing the corrosion influence of bentonite by these three microfloras. This research provided a scientific reference to the engineered design and barrier material select for high-level radioactive waste geological disposal. The results were as follows:（1） In the liquid-immersion environment, the sustain activity of these three microfloras in a certain period could be maintained by adding 5.5-fold high concentration medium. The biofilms were formed by microorganism attached on the copper surface, which promotes the corrosion process. Many pits and craters were presented on the copper surfaces after incubation with these three microfloras, and clear differences of the morphologies of corrosion products were observed in the fungi and bacteria groups compared with the control. The different components of biofilm layer and its content were associated with the micro-cell corrosion environment on the copper surface, whi ch was related to the difference corrosion behavior of copper by actinomyces, fungi and bacteria. The corrosion process of copper was accelerated and the corrosion rate was descending at the orders of bacteria, fungi, actinomyces.（2） In the solid-landfill environment, the imperfect and incompleted biofilms were covered on the copper surface. Two obvious partition were formed in which many small corrosion pits were covered on the shedding area, and the cracks were distributed on the non-shedding area. The composition and accumulated state o f corrosion products were associated with the corrosion behavior of copper. The corrosion process of copper was accelerated by these three microfloras, and the corrosion rate was descending at the orders o f fungi, bacteria, actinomyces.（3） In the liquid-immersion environment, the values of blue absorption power of bentonite were decreased in actinomyces, fun gi and bacteria groups compared with the control respectively. The decreased value was descending at the orders of fungi, actinomyces and bacteria after 360 d immersion. The values of cation exchange capacity（CEC） were also decreased in these three microfloras groups compared with the control respectively. These three microfloras acted as a promotion role to the emission of Mg2+ that was descending at the orders of actinomyces, fungi and bacteria, and as an inhibition role to the emission of Ca²⁺ that showed minimum value in the actinomyces group compared to fungi and bacteria. The weight loss rate of A and C stage of bentonite were decreased while the B stage was significantly increased, which indicated the thermostability of bentonite decreased. Due to the microorganism resided in bentonite, the content of adsorbed water and inter-layer water were decreased, and the adsorption capacity of bentonite was also declined, which affect ed indirectly to the structural water and advanced structure of bentonite. These three microflora were mainly influence the small angle area of XRD diffraction peak of bentonite in which the peak of montmorillonite, quartz and calcite were attenuated and broaden in a certain extent. There were two kinds of comp ound in the site of montmorillonite peak in the small angle area, one was containing carbon（C）, and the other was similar to the elementary composition of montmorillonite.（4） In the solid-landfill environments, the values of blue absorption power of bentonite were decreased in actinomyces, fun gi and bacteria groups compared with the control respectively. The decreased value of blue absorption power has minimum value in the bacteria groups compared to actinomyces and fungi groups after 360 d immersion.The value of cation exchange capacity（CEC） were also decreased in actinomyces, fungi and bacteria groups compared with the control respectively. They acted as a promotion role to the emission of Mg2+ and as a inhibition role to the emission of Ca²⁺. Due to the influence of these three microflora on bentonite, the weight loss rate of the first and third stage of bentonite were decreased, the second stage was significantly increased and the total weightlessness rate were decreased, which indicate d the thermostability of bentonite declined. There were two kinds of compounds in the site of montmorillonite peak in the small angle area, one was containing carbon（C）, hydrogen（H） and nitrogen（N）, and the other was similar to the elementary composition of montmorillonite, which indicated some corrosive substances from microfloras metabolite affected the layer structure of bentonite, causing the blue absorption power, the cation exchange capacity, and the thermostability of bentonite declined.