The microbial impact on U, Pu, Np, and Am immobilization on aquifer sandy rocks, collected at the deep LRW injection site

In this work the analysis of biogeochemical factors influencing on immobilization of Np, U, Pu and Am on rocks taken from a depth of 450 m in a deep repository of liquid radioactive waste of the Siberian Chemical Combine is carried out. It was found that the development of microbial processes on aquiferous sandy rocks leads to a significant increase in the sorption efficiency of Np and U due to the formation of microbial biofilms and new biogenic mineral phases (Fe sulfides, Fe carbonates, amorphous iron oxides). The high values of Pu immobilization did not deteriorate and the effect on quantitative Am immobilization was negligible, but it led to an increase in the low-desorbed fraction. It is important to note the role of amorphous SiO2, formed after the biogenic dissolution of the clay fraction, in the distribution of U, Np and Am bond forms on rock samples. Development of microbial processes can lead to a redox potential decreasing, which leads to the formation of biogeochemical barrier zones for actinides in reduced oxyhydmxide forms. Thus, complex multifactorial models of radionuclide migration should be based not only on the Kd model and various hydrodynamic parameters of facilities, but also on data obtained from detailed laboratory investigation of the influence of microbial processes on Kd taking into account geochemical conditions determining the intensity of biological processes in the waterrock system.

Automated summary

This work analyzes the biogeochemical factors influencing the immobilization of Np, U, Pu, and Am, and finds that the development of microbial processes can significantly increase the sorption efficiency of Np and U. The immobilization of Pu remains high, while the effect on Am immobilization is negligible. The formation of amorphous SiO2 plays an important role in the distribution of U, Np, and Am bond forms on rock samples.