UO2-Er2O3燃料热物理性能的分子动力学模拟

Simulation of Thermophysical Properties of UO2-Er2O3 Fuel by Molecular Dynamics

为了维持反应堆中核裂变反应的平稳运行,需要在反应堆燃料元件中加入可燃毒物。可燃毒物在反应堆运行初期吸收大量热中子,抑制核燃料的裂变,在反应堆运行后期,随着可燃毒物逐渐被消耗,热中子增多,可以弥补因为可裂变核素减少而逐渐降低的反应性,从而保证核裂变反应在整个反应堆运行寿期的平稳运行。目前,反应堆中使用的可燃毒物主要有Gd 2O 3和ZrB 2,随着燃耗增加,由于Gd 2O 3和ZrB 2消耗过快,毒物消耗与燃料燃耗很难匹配。Er2O3由于具有燃烧缓慢、平稳,反应性惩罚小的特性,被认为适合于未来高燃耗、长寿期的燃料元件。利用Er2O3作为可燃毒物,提高燃料富集度,可以提高燃料元件的卸料燃耗,提高燃料利用率,降低核电运行成本。本工作采用分子动力学方法对Er2O3含量为6mol%的燃料芯块的热物理性能进行了模拟研究,建立了UO2-6mol%Er2O3可燃毒物燃料芯块的理论模型,并基于此计算了UO2-6mol%Er2O3燃料芯块的热物理性能,主要包括:燃料芯块的晶格点阵参数、热膨胀系数、比热容和热导率。研究表明:(1)UO2-6mol%Er2O3燃料的晶格点阵参数随着温度的升高而线性增大,并满足数学关系式:a(T)=0.54265+5.71706×10^-6 T-3.67498×10^-10 T 2+3.4323×10^-13 T 3(nm);(2)UO2-6mol%Er2O3燃料的热膨胀系数随着温度的升高逐渐增大,且增大速率也随温度升高而增大,燃料晶体相对于300K时的平均热膨胀系数与温度的关系式为γ=1.028449×10-5-3.55613×10^-10 T+5.73038×10^-13 T2(K-1);(3)UO2-6 mol%Er2O3燃料的比热容随着温度的升高逐渐增大,且增大速率随温度升高而减小,满足Cp(J·mol^-1·K^-1)=47.545+51.2766×10^-3 T-17.1913×10^-6 T2;(4)UO2-6mol%Er2O3燃料的热导率随着温度的升高逐渐减小,满足关系式k=1/0.145+1.185×10^-4·T。本文采用分子动力学方法计算了UO2-6mol%Er2O3燃料的晶格点阵参数、热膨胀系数、比热容和热导率等性能。通过理论计算,为含Er2O3可燃毒物燃料的进一步研究与工程应用提供支撑。

In order to maintain the smooth operation of the nuclear fission reaction in the reactor,it is necessary to add burnable poison to the fuel elements of the reactor,which could absorb a large amount of thermal neutrons in the initial stage of the reactor operation to suppress the fission of the nuclear fuel.And in the later stages of reactor operation,as the burnable poison are gradually consumed,the number of thermal neutrons increases,which can compensate for the gradual decrease in reactivity due to the reduction of fissile nuclide,thereby maintaining the smooth operation of the nuclear fission reaction throughout the operating life of the reactor.At present,the main burnable poisons used in the reactor are Gd2O3 and ZrB 2,as the fuel burnup increases,the consumption of burnable poison and fuel burnup are difficult to match due to the excessive consumption of Gd2O3 and ZrB2.Er2O3 is considered to be suitable for fuel elements with high fuel burnup and long life in the future due to its slow bur-ning,stability,and low reactivity penalty.Using Er2O3 as burnable poisonous to improve fuel enrichment can improve fuel discharge and fuel consumption,improve fuel utilization and reduce nuclear power operation costs.In this paper,the thermophysical properties of fuel pellets with Er2O3 content of 6 mol%were simulated by molecular dynamics method.The theoretical model of UO2-6mol%Er 2O 3 burnable poisonous fuel pellets was established.Based on this,the thermophysical properties of UO2-6mol%Er 2O 3 fuel pellets were calculated,including lattice lattice parameters,thermal expansion coefficient,specific heat capacity and thermal conductivity of the fuel pellets.Research shows that:(1)The lattice lattice parameters of UO2-6mol%Er2O3 fuel increase linearly with increasing temperature,satisfying the mathematical relationship of a(T)=0.54265+5.71706×10^-6 T-3.67498×10^-10 T 2+3.4323×10^-13 T3(nm).(2)The thermal expansion coefficient of UO2-6%Er2O3 fuel increased with the increase of temperature,and the increase rate increased with the increase of temperature.The relationship between the average thermal expansion coefficient and temperature of the fuel crystal relative to 300K wasγ=1.028449×10-5-3.55613×10^-10 T+5.73038×10^-13 T 2(K-1).(3)The specific heat capacity of UO2-6mol%Er 2O 3 fuel increased with the increase of temperature,and the increase rate decreased with the increase of temperature,which satisfied C p(J·mol^-1·K^-1)=47.545+51.2766×10^-3·T-17.1913×10^-6·T 2.(4)The thermal conductivity of UO2-6%Er 2O 3 fuel decreased with increasing temperature,which satisfied k=1/0.145+1.185×10-4·T.In this paper,the lattice parameters,thermal expansion coefficient,specific heat capacity and thermal conductivity of UO2-6%Er2O3 fuel were calculated by molecular dynamics method.Through theoretical calculations,it provided support for further research and engineering applications of Er2O3 burnable poisonous fuels.