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

• Published in: Radiation physics and chemistry (Oxford, England : 1993) England : 1993), 2019-06, Vol.159, p.81-88
• Main Authors: Du, Bo, Yu, Suping, Zhao, Qingkai, Cheng, Xuzhou, Wei, Jiying, Zhao, Xuan
• Format: Article
• Language: English
• Subjects: Anions; Chromium; Cobalt; Colloidal Cobalt hydroxide; Colloidal radionuclide; Colloids; Corrosion products; Hydrogen peroxide; Ion exchange; Manganese dioxide; Manganese ions; Metal particles; Nuclear power plants; Nuclides; Organic chemistry; Oxidation; Primary coolant of nuclear power plant; Radioactivity; Shutdowns; Silver; Silver nano-metal particles; Speciation; Speciation analysis
• ISSN: 0969-806X; 1879-0895
• DOI: 10.1016/j.radphyschem.2019.02.023

Corrosion products, such as 110 mAg, 58Co, 60Co, 51Cr, 54Mn and 125Sb 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 51Cr, 54Mn, 58Co and 60Co are mainly present as ions of Mn2+ and Cr2+, as well as Co2+ with the possibility of forming Co(OH)n2-n colloid in a high activity. Meanwhile, 110 mAg can be reduced to Ag0 with a form of nano-silver cluster or nano-silver metal particles in a size of 10–100 nm, and 125Sb mainly exists in the form of soluble anion SbO2- or hydrolyzed granular Sb2O3. During shutdown oxidation process, 110 mAg and 125Sb can be oxidized by the added hydrogen peroxide into Ag+ ions and anion SbO3- leading to an increased solubility in coolant. Meanwhile 51Cr and 54Mn can be oxidized into Cr(III) and Mn (IV), which can form the co-existing state of many hydroxyl complexes, such as Cr(OH)n3-n, Mn(OH)n4-n or MnO2. It indicated that metallic silver particles Ag0 and some metal hydrated hydroxide, such as Co(OH)n2-n, Cr(OH)n3-n and Mn(OH)n4-n may be responsible for the formation of colloids in the primary coolant. •Ag exists mainly as Ag0 particles in size of 10–100 nm in primary coolant.•110 mAg emission increase since Ag0 is oxidized into Ag+ by H2O2 in shutdown process.•Colloids of Co(OH)n2-n, Cr(OH)n3-n and Mn(OH)n4-n may be formed in core coolant.•Sb mainly exists in SbO2- or hydrolyzed granular Sb2O3 at power operation stage.•Anion SbO3- is formed in shutdown process due to the oxidation by H2O2 in coolant.