The speciation analysis of colloids in the primary coolant in nuclear power plant

Abstract Corrosion products, such as 110 m Ag, 58 Co, 60 Co, 51 Cr, 54 Mn and 125 Sb have great contribution to the radioactivity of primary coolant in nuclear power plant (NPP). It is considered that some of these nuclides are probably in colloidal form, since they cannot be effectively removed by the conventional ion exchange process in NPP. In this paper, the chemical speciation and behavior of these nuclides in the primary coolant was investigated by simulation calculation and validation experiments. In the reductive circumstance of primary coolant during power operation and re-operation preparatory stage in a normal operation process of reactor, nuclides such as 51 Cr, 54 Mn, 58 Co and 60 Co are mainly present as ions of Mn 2+ and Cr 2+ , as well as Co 2+ with the possibility of forming Co(OH) n 2-n colloid in a high activity. Meanwhile, 110 m Ag can be reduced to Ag 0 with a form of nano-silver cluster or nano-silver metal particles in a size of 10–100 nm, and 125 Sb mainly exists in the form of soluble anion SbO 2 - or hydrolyzed granular Sb 2 O 3 . During shutdown oxidation process, 110 m Ag and 125 Sb can be oxidized by the added hydrogen peroxide into Ag + ions and anion SbO 3 - leading to an increased solubility in coolant. Meanwhile 51 Cr and 54 Mn can be oxidized into Cr(III) and Mn (IV), which can form the co-existing state of many hydroxyl complexes, such as Cr(OH)n 3-n , Mn(OH) n 4-n or MnO 2 . It indicated that metallic silver particles Ag 0 and some metal hydrated hydroxide, such as Co(OH)n 2-n , Cr(OH) n 3-n and Mn(OH) n 4-n may be responsible for the formation of colloids in the primary coolant.