Yuanzineng kexue jishu (Dec 2022)
Influence of pH on Source Term of Activated Corrosion Product in Reactor
Abstract
Activated corrosion product is an important radioactive source term in the primary circuit of pressurized water reactor, which has an important influence on reactor shielding design, personnel protection and accident safety. As a key parameter of pressurized water reactor (PWR) coolant, its pH value plays an important role in the process of material corrosion, dissolution and precipitation of corrosion products. The solubility of corrosion products and the corrosion rate of materials in the coolant can be controlled by adjusting the pH value by coordinating the concentration of boronlithium in the coolant, so as to achieve the purpose of controlling the source term of activated corrosion products. At present, the influence of pH value on the corrosion rate of materials and the solubility of corrosion products is more analyzed in the world. The influence of pH value on the radioactive source terms was described in varying degrees through experiments and feedback data of nuclear power plant operation. However, the cost of obtaining power plant operation data is high, so it is of great application significance to analyze the influence of pH value on radioactive source term from the perspective of simulation calculation. In this paper, the solubility of corrosion products and the corrosion rate of materials under different pH values were calculated, and the radioactive activity in each area of the primary circuit of PWR under different pH values was calculated by substituting it into the selfdeveloped source term analysis CATE code of activated corrosion products. After systematic research and analysis, it is concluded that when the pH value is 56 to 74, the solubility of corrosion products decreases continuously with the increase of pH value, and the decreasing range gradually becomes slow. The corrosion rate of 304 stainless steel decreases with the increase of pH value and reaches a balance after decreasing to a small value. The corrosion rate of Inconel decreases with the increase of pH value, and the decrease amplitude gradually becomes slow. With pH value increasing, the radioactive activity decreases, when the pH value increases to 7.2 or so, the radioactive activity decreases slower, when the pH value is 74, the radioactive activity in the core, steam generator and coolant decreases slightly compared with that when the pH value is 72, but the radioactive activity in coolant pump, transition section and cold pipe section increases slightly. pH value affects the source term of primary corrosion products of PWR through the solubility of corrosion products and corrosion rate of materials. Moderately increasing pH value can increase the corrosion resistance of nickel base alloy and stainless steel materials, and reasonably adjusting pH value can control the release and deposition of corrosion products, so as to achieve the purpose of reducing the level of radioactive activity in primary circuit. Considering the solubility of corrosion products in primary circuit of PWR, corrosion rate of materials and radioactive activity of corrosion products, the pH value should be controlled within 7.2-7.4.
