Research On Environmental Advantage Effect Of Microorganism On Radionuclide Disposal Of Materials Steel And Cement Mortar

This paper was supported by the key project of national decommissioning of nuclear facilities and radioactive waste management scientific reseach(12Zg6104). Research on environment advantages of microbial corrosion on high-level radioactive waste disposal of materials, it aimed at researching on corrosion of carbon structureal steel Q235A and cement mortar. The dominant mircrooganism contained bacteria, fungi and actinomycetes which were screened from the soil from typical uranium tailings and preselected area for Chinese high-level radioactive waste repository. The media inoculated served as corrosion media. The corrosion degree of the said carbon structureal steel Q235A at the specific stage can be characterized by its mass loss, morphology change, open circuit potential change, corrosion potential and corrosion current density via scanning electron microscope and electrochemical measurement technology The corrosion degree of the said mortar cement at the specific stage can be characterized by its mass loss, strength loss, the carbonation depth via scanning electron microscope and X-Ray Diffraction. This research provided a scientific basis for the geological disposal of high level radioactive waste safety assessment. The results were as follows:(1) The dominant bacteria called as SB4 and NB3 were respectively screened from the soil of Uranium tailings heavy polluted area and preselected for Chinese high-level radioactive waste repository moderate polluted area. The dominant fungi called as SF4 and NF3 were respectively screened from the soil of Uranium tailings heavy polluted area and preselected for Chinese high-level radioactive waste repository moderate polluted area. The dominant actinomycetes called as SL6 and NL3 were respectively screened from the soil of Uranium tailings low polluted area and preselected for Chinese high-level radioactive waste repository moderate polluted area. The method of culture by addine twice was better than once. The twice feeding time of SB4, NB3, SF4, NF3, SL6 and NL3 were 72 h and 196 h, 60 and 186 h,84 h and 186 h,84 h and 196 h,72 h and 196 h,60 h and 196 h, respectively In the three kinds of microbial media, pH of the one with fungi remained around 6, which was one of the important factors that cause severe corrosion on materials.(2) Through a period of immersion corrosion, SEM results showed that it mainly occurred pitting corrosion in the presence of microorganisms. The corrosion rate on Q235A increased with the time. At the end of 240 d, the groups of SB4 and NB3 increased to 0.164 and 0.165 mm/a respectively, while the sterile culture medium was low, was 0.071 mm/a. The group of SF4 and NF3 increased to 0.184 and 0.201 mm/a, respectively, and the sterile culture medium was 0.085 mm/a. The group of SL6 and NL3 increased to 0.160 and 0.164 mm/a respectively, while the sterile culture medium was 0.076 mm/a. Electrochemical tests showed that when the open circuit potential and corrosion potential all reduced, while, corrosion current increased, in the presence of bacteria. It could be concluded Q235A samples in the mircrobiology media were more susceptible to corrosion by forming local micro battery accelerating the metal anode dissolve. The existence of the microbial promoted the corrosion of the Q235A.(3) Through a period of immersion corrosion, as the growth of the corrosion age, under the action of microorganisms, the compressive strength of the specimens were significantly lower than sterile groups. At the end of 280 d, the corrosion resistance coefficient for the compressive strength of the group of SB4 and NB3 were 0.73 and 0.73 respectively, while, the sterile group was 0.81. The corrosion resistance coefficient for the compressive strength of the group of SF4 and NF3 were 0.71 and 0.72, while, the sterile groups was 0.81. The corrosion resistance coefficient for the compressive strength of the group of SL6 and NL3 were 0.74 and 0.73 respectively, while the sterile group was 0.82. However, mass loss and carbonation depth of group inoculated mircrobiologies were higher than the sterile groups. At the end of 280d, carbonization depth of the groups of SB4 and NB3 were 4.07 mm and 3.98 mm respectively, compared with sterile group, grewed by 178.48% and 168.78%. Carbonization depth of the groups of SF4 and NF3 were 4.21 mm and 4.57 mm respectively, compared with sterile groups, grewed by 308.48% and 328.12%. Carbonization depth of the groups of SL6 and NL3 were 3.96 mm and 3.87 mm respectively, compared with sterile groups, grewed by 189.48% and 178.52%. The microstructure results showed it were more likely to generate ettringite crystal which affected the mechanical properties and durability of mortar that in the presence of microorganisms.(4) At the corrosion age of 2 d, SEM results showed that the microorganisms formed the structure of monolayer membrane in the material surface. As the growth of corrosion age, it formed a complete biofilm of the steel surface at 9d. At 30 d, microbial with unevenly distributed in the specimen surface. According to the results of Infrared spectrum, microbial membrane contained functional groups of O-H, CH3, C=C, C-C and C-O.The results of this study provided reference data for a comprehensive explanation of the advantages of microbial corrosion mechanism of high-level radioactive waste disposal material corrosion, while, it layed the foundation for high-level radioactive waste disposal material microbial corrosion protection.