Effects of pH on the speciation of radioactive nuclides in groundwater of Beishan area, Gansu province, China

Speciation of radioactive nuclides is one the most important aspects in the study of migration and precipitation of the nuclides related to deep geological disposal of high level radwastes. Theoretical speciation analysis with assistance of thermodynamic equilibrium codes is an effective method. The authors have employed the EQ3NR, a geochemical code for aqueous equilibrium and speciation calculation, to model the speciation of the key nuclides in the groundwater of Beishan Area, a potential area for hosting the HLW repository of China. It has been identified that pH value has great impact on the speciation of key nuclides such as Neptunium, Plutonium, Americium, Uranium and Thorium, which would be released from HLW to the groundwater of Beishan Area, while the speciation is related to the chemical composition of the water. In addition, it has been found that the distribution patterns of speciation of nuclides are varied from one on another. However, the speciations are relatively simple under alkaline condition, and hydroxyl compounds are dominated