pH值对反应堆活化腐蚀产物源项影响研究

Influence of pH on Source Term of Activated Corrosion Product in Reactor

活化腐蚀产物是压水堆一回路重要的放射性源项,对于反应堆的屏蔽设计、人员防护和事故安全有重要影响。pH值作为压水堆冷却剂的关键参数,在材料腐蚀和腐蚀产物溶解、沉淀过程中扮演着重要角色。通过协调冷却剂中硼-锂浓度来调节pH值,可控制压水堆冷却剂中腐蚀产物溶解度和材料腐蚀速率等参数,从而达到控制活化腐蚀产物源项的目的。为从模拟的角度系统研究pH值对放射性源项的影响,本文计算了不同pH值条件下的腐蚀产物溶解度以及材料腐蚀速率,并将其代入自主研发的活化腐蚀产物源项分析程序CATE中,计算不同pH值条件下压水堆一回路各区域的放射性活度。结果表明:pH=5.6~7.4范围内,随着pH值的增大,腐蚀产物溶解度和材料腐蚀速率均持续减小;将pH值控制在7.2~7.4,对减少反应堆一回路活化腐蚀产物、降低堆内放射性活度的效果最佳。

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 boron-lithium 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 self-developed source term analysis CATE code of activated corrosion products. After systematic research and analysis, it is concluded that when the pH value is 5.6 to 7.4, 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 7.4, the radioactive activity in the core, steam generator and coolant decreases slightly compared with that when the pH value is 7.2, 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.