动态参数形状函数和权重函数对加速器驱动次临界反应堆中子动力学的影响

The effects of the shape function and weighting function on the kinetics of the ADS sub-critical reactor

在准静态框架下,动态参数由权重函数、动力学量算符、形状函数的卷积得到。传统方法的形状函数和权重函数并不能满足外源驱动次临界系统的中子动力学分析。本文分别采用λ基波中子通量密度、α基波中子通量密度、加速器驱动次临界系统(Accelerator Driven Sub-critical System,ADS)反应堆稳态中子通量密度作为初始形状函数,采用共轭λ基波中子通量密度、共轭瞬发α基波中子通量密度、ADS反应堆稳态共轭中子通量密度作为权重函数,通过改进的准静态方法对外源驱动次临界系统的启堆过程和断束工况中子动力学进行模拟。通过与时空动力学方程直接求解结果对比发现:权重函数是影响中子动力学结果的主要因素;对于启堆过程,适合采用ADS反应堆稳态中子通量密度作为初始形状函数、共轭λ基波中子通量密度作为权重函数;对于断束工况,适合采用ADS反应堆稳态共轭中子通量密度作为权重函数。权重函数相对于外源瞬变的滞后现象表明,在外源瞬变后的短时间内,外源中子对中子价值和权重函数的影响具有非均匀性,在建立优化的权重函数模型时,需要将共轭外源项的非均匀分布纳入考虑。

[Background] According to the quasi-static method, the kinetic parameters can be calculated by the convolution of the weighting function, kinetic operators and the shape function. The traditional shape function and weighting function are not suitable for kinetic analysis of source driven sub-critical system. [Purpose] In order to improve the calculation accuracy and understand physical characteristics of the source driven sub-critical system better, different shape functions and weighting functions were applied to improved quasi-static method, and they were evaluated respectively. [Methods] Individually, the 2 regular flux, α regular flux and the steady flux of source driven sub-critical system are adopted as the initial shape functions. The λ-eigenequation and α-eigenequation of the critical weighting function of kinetic parameter model, and the global weighting function of kinetic parameter model are used for the weighting function. Then the kinetic parameters and the neutron kinetic results of the starting progress and beam loss conditions can be calculated in the sub-critical system. [Results] The results of the IQS method are compared with the results obtained directly from the spatio-temporal dynamics equation. We can find that the weighting function is the dominant factor that affect the kinetic parameters and the kinetic results. And during the starting progress, the steady flux of source driven sub-critical system and the 2-eigenequation of the critical weighting function model have obvious superiority in describing the kinetic characters of the source driven sub-critical system; for the beam loss conditions, adopting the global weighting function model to calculate the weighting function is suitable for the sub-critical system. [Conclusion] The phenomenon that the change of weighting function falls behind the transition of the external neutron source indicates that the extraneous neutron source＇s effect on neutron importance is inhomogeneous and the inhomogeneous character should be taken into consideration when optimizing the weighting function models.