Experience of creating an in situ biogeochemical barrier in contaminated groundwater at nuclear fuel cycle facilities. Part 2

Background

Technologies based on the principles of “green chemistry” are actively used around the world to treat contaminated areas. Field studies at radiochemical plants in the USA and China have demonstrated bioremediation potential for complex treatment of groundwater. The article presents the experience of applying this approach in the Russian Federation.

Aim

To study the mechanisms of immobilizing redox-sensitive radionuclides in the presence of an in situ biogeochemical barrier for treatment of groundwater with polyelement radioactive contamination at the territories of the Siberian Chemical Plant JSC (SCP) and Chepetsk Mechanical Plant JSC (CMP), as well as to justify optimal compositions for the activation of indigenous microflora.

Materials and methods

The elemental composition of samples was determined using inductively coupled plasma mass spectrometry (ICP-MS); the CGE method of capillary gel electrophoresis was used to determine the ion concentration. Various organic substrates and food production waste were used. Field experiments were conducted on the territories of the CMP (2020), as well as near the SCP B2 pool (2015) and Sublimate Plant (2018).

Results

Whey, molasses, and a mixture of sucrose and phosphates yielded less than 10% of desorbed actinides. Comparatively high desorption rates are characteristic of stillage, glucose, sucrose, and a mixture of microbial metabolites. The maximum effect is observed in distilled water with 3 g/L of nitrate ions: 33, 55, and 45% desorption for U, Pu, and Np, respectively.

Conclusion

Field tests have proven high efficiency of using food production waste for the biological treatment of radioactive areas. The biogeochemical barrier zone reduces colloidal and pseudocolloidal transfer of radionuclides due to the coagulation of iron and clay particles. Oxidized iron phases ensure long-term reliable immobilization of redox-sensitive radionuclides under oxidative conditions. The total cost of materials for treating a formation of more than 600 m³ with a single injection of organic mixtures amounted to about 25,000 RUB. The obtained results allow this approach to be recommended for large-scale use to treat the territories near radioactive waste storage reservoirs during operation and post-mothballing periods.