研究堆用铝合金包壳堆内平均腐蚀速率评估方法研究

Study on the Evaluation Method for the Average Corrosion Rate of Aluminum Alloy Cladding for Research Reactor

研究堆用铝合金包壳的堆内平均腐蚀速率大小直接反映了包壳材料的抗腐蚀性能。高通量工程试验堆(HFETR)每炉段运行经验表明,堆内铝合金包壳经活化腐蚀作用会在一回路冷却剂中产生大量的放射性核素^(24)Na,且较快就达到稳定的活度浓度值。理论上,基于HFETR一回路^(24)Na平衡活度浓度可实现运行期间铝合金包壳堆内平均腐蚀速率的定量评估。本文通过分析HFETR一回路中^(24)Na核素的生成、释放和迁徙机理,将一回路划分为辐照区、冷却剂区和净化区三个节点,建立出铝合金包壳堆内平均腐蚀速率与^(24)Na平衡活度浓度的关系模型;然后使用蒙特卡洛核粒子输运程序对反应堆建模,计算出三节点模型中所需物理参数;最后通过HFETR一回路^(24)Na活度浓度的运行监测值分别对反应堆使用过的三类铝合金包壳进行平均腐蚀速率评估计算,并与堆外腐蚀试验结果开展对比。结果表明,本文提出的方法可以在一定范围内定量估算堆内铝合金包壳的平均腐蚀速率,可为研究堆用铝合金包壳的实际堆内抗腐蚀性能分析提供依据。

The average corrosion rate of aluminum alloy cladding directly reflects the corrosion resistance of the cladding material in research reactor.The operating experience of the high flux engineering test reactor(HFETR)shows that a large amount of radionuclide^(24)Na will be produced in the primary circuit by the activation corrosion of aluminum alloy cladding,and the activity concentration of radionuclide^(24)Na reached an equilibrium value rapidly.The^(24)Na nuclide produced by aluminum alloy cladding in the HFETR is the main source of the activity concentration of the primary circuit.Theoretically,the average corrosion rate of aluminum alloy cladding can be quantitatively evaluated according to the^(24)Na equilibrium activity concentration in the primary circuit of HFETR.Based on the analysis of the formation,release and migration mechanism of^(24)Na nuclide in the primary circuit of HFETR,the primary circuit is divided into three zones:irradiation zone,coolant zone and purification zone.The three-zone transport model between the average corrosion rate and the equilibrium activity concentration of^(24)Na is established.Then the Monte Carlo Nuclear Particle Transport Program(MCNP5)is used to calculate the required physical parameters in the model.Finally,the average corrosion rate of three kinds of aluminum alloy cladding with three different materials or surface pretreatment process is evaluated and calculated by using the operation monitoring value of^(24)Na activity concentration in the primary circuit of HFETR,and the results are compared with the results of out-of-reactor corrosion test.The comparison shows that the method proposed in this paper can accurately and quantitatively evaluate the average corrosion rate of the aluminum alloy cladding in the reactor,and can provide an analysis basis for studying the actual corrosion resistance of the aluminum alloy cladding for the research reactor.