基于OpenMC的瞬发中子衰减常数计算模块开发与验证

瞬发中子基波衰减常数α可定量描述反应堆内中子随时间的变化，是计算绝对反应性所需的中子动力学参数之一，对次临界（特别是较深次临界）绝对反应性的精确测量具有重要意义。本文在开源程序OpenMC基础上，基于k α迭代方法，以中子径迹长度上的平均时间吸收权重修正作为k α迭代参数因子，在输运过程中对瞬发、缓发中子分别考虑，开发了具有瞬发α本征值问题计算功能的OpenMC PA模块。以Godiva衍生基准题和MUSE 4次临界实验装置为计算对象，对程序计算瞬发α本征值问题能力进行验证。结果表明，该计算模块有优于MCNP4C的计算速度与计算范围，计算值与参考值的相对误差小于05%。OpenMC PA能满足次临界系统瞬发α本征值和中子动力学参数计算需求。

Development and Verification of Calculation Module for Prompt Neutron Attenuation Constant Based on OpenMC

Neutron kinetic parameters such as effective delayed neutron fraction βeff and mean generation time of prompt neutron are the bridges that between reactivity (in unit of dollar) measured by experiment and reactivity by calculation. Accurate measurement and calculation of subcritical reactivity is an important problem in the development of accelerator driven subcritical reactor and control rod calibration in subcritical condition. To compare subcritical reactivities between experiment and calculation, experimental measurement methods that based on fundamental prompt neutron attenuation constant α need neutron kinetic parameters from calculation using fundamental prompt neutron flux density of α mode. In this paper, based on open source code OpenMC and the k α iteration method, taking the average time absorption weight of the neutron track length as a parameter of the k α iteration factor, and neglecting delayed neutron in the transportation process, the OpenMC PA module with the function of calculating prompt α eigenvalue problem was developed. The ability of the code to calculate prompt α eigenvalue problem was verified by using the Godiva derivative benchmark and the MUSE 4 subcritical experiment device. The results indicate that for the Godiva derivative benchmark, results of OpenMC PA are in good agreement with those of TART code. In addition, under the same computing hardware, the calculation speed of OpenMC PA is faster than that of MCNP4C, and the subcriticality that can be calculated is deeper. For the MUSE 4 subcritical experiment device with complex geometry and materials, the relative error of prompt α eigenvalue between the calculated value of OpenMC PA and the experiment is less than 05%, and the absolute error between the keff by regression calculation using calculated prompt α eigenvalue and the keff from experiment is less than 002%. The developed OpenMC PA can meet the requirements of prompt α eigenvalue and kinetic parameters calculation for subcritical systems.