压水堆一回路注锌的热力学与动力学特性

Thermodynamics and Kinetics of Zinc Additionin Pressurized Water Reactor Primary Circuit

堆芯腐蚀产物沉积会引起垢致功率偏移和垢致局部腐蚀,威胁反应堆的安全性和经济性。根据反应堆运行经验,注锌能有效缓解堆芯腐蚀产物沉积,但锌在一回路中热力学平衡、动力学置换和质量平衡理论尚不清晰。基于此,本文从理论机理和数值计算分析的角度分析一回路中锌的平衡与热力学动力学行为。理论分析表明,锌在冷却剂水化学条件下主要以氢氧化锌形式存在,锌对反尖晶石中二价离子的置换能力可以结合锌浓度与水解化学平衡进行求解。数值分析表明,模型预测值与核电站观测值有良好的吻合度,逐步降低注锌量是维持锌浓度在特定最优化范围内的有效手段,注锌有效缓解腐蚀释放的程度可达约50%,注锌后的污垢厚度约为注锌前的42%。本文研究结果能为核反应堆采取最优化注锌技术提供理论支撑。

The deposition of corrosion products in the core causes CRUD(corrosion related unidentified deposit)induced power shift and CRUD induced localized corrosion,threatening the safety and economy of the reactor.Zinc addition is regarded as a widely used method to effectively alleviate corrosion product deposition in reactor core.Despite the wide spread use of zinc,the understanding of mass balance,thermodynamic equilibrium and kinetic substitution of zinc in the primary circuit is still not clear.This paper focuses on the balance and thermodynamic kinetic behaviors of zinc in the primary circuit from the perspectives of theoretical mechanism and numerical calculation analysis.A mass balance model of zinc in the primary circuit was established to evaluate the addition,removal,deposition,precipitation and substitution of zinc in the primary circuit.The thermodynamic equilibrium and substitution kinetics of zinc in coolant were also evaluated.Theoretical analysis shows that zinc in the coolant is involved in hydrolysis and chemical reactions with iron,nickel,silicon and other elements.Zinc mainly exists in the form of zinc hydroxide under the prototypical conditions of coolant water chemistry.When zinc replaces the iron and nickel elements in the oxide corrosion layer,it tends to replace the divalent ions at the tetrahedral positions in the normal spinel,and the ability of zinc to replace the divalent ions in the inverse spinel needs to be evaluated in combination with the hydrolysis and chemical equilibrium of zinc.Numerical analysis shows that the mass balance prediction results of the model are in good agreement with the observation value from Diablo Canyon 1 reactor plant.Gradually reducing zinc addition amount is an effective means to maintain the zinc concentration in the specific optimal range.Zinc addition can effectively alleviate corrosion release up to about 50%and the thickness of CRUD deposition after zinc addition is 42%of that before zinc addition.This study can provide theoretical support to develop the optimal zinc addition technique.