Dominance Ratio Assessment and Monte Carlo Criticality Simulations: Dealing with High Dominance Ratio Systems
Dominance Ratio Assessment and Monte Carlo Criticality Simulations: Dealing with High Dominance Ratio Systems
复制标题
优势比评估和蒙特卡罗临界性模拟：处理高优势比系统
DOI：
10.13182/nt10-a10899
复制
发表时间：
2010
影响因子：
1.5
通讯作者：
T. Courau
中科院分区：
文献类型：
--
作者：
Eric Dumonteil;T. Courau
大型中子系统的典型尺寸通常比中子的平均自由程大两个数量级。这样的高优势比系统代表了一个特别具有挑战性的问题时，进行蒙特卡罗临界模拟。事实上，这些模拟被周期与周期的相关性所污染，这大大减缓了通量收敛。在本文中，我们将首先讨论主导比和周与周之间的相关性之间的联系，这是造成通量收敛差的原因。然后，我们将提出一个新的和原始的技术来评估一个给定的蒙特卡罗模拟的优势比。它包括拟合中子场的弛豫过程后，从一个裂变源的狄拉克δ函数形状的初始激发。在证明了这些通量收敛问题是由优势比驱动的之后，我们将提出使用“独立副本”方法来处理统计中的预测不足偏差。本文提出的不同的理论点将被验证与Monte Carlo代码TRIPOLI4模拟的针电池测试用例。提供了基于三维压水反应堆堆芯计算的附加结果，以确认所述拟合技术的可靠性。
Abstract Typical dimensions of large neutronic systems are often two orders of magnitude greater than the mean free path of the neutrons. Such high dominance ratio systems represent a particularly challenging issue when performing Monte Carlo criticality simulations. As a matter of fact, these simulations are contaminated by a cycle-to-cycle correlation that strongly slows down the flux convergence. In this paper, we will first discuss the link between the dominance ratio and the cycle-to-cycle correlations that are responsible for the poor flux convergence. Then, we will present a new and original technique to assess the dominance ratio of a given Monte Carlo simulation. It consists of fitting the relaxation process of the neutron field after an initial excitation from a fission source with a Dirac delta function shape. Having showed that these flux convergence issues are dominance ratio driven, we will then propose the use of an “independent replicas” approach to deal with the underprediction bias in statistics. The different theoretical points presented in this paper will be verified on a pin cell test case simulated with the Monte Carlo code TRIPOLI4. Additional results based on a three-dimensional pressurized water reactor core calculation are provided to confirm the reliability of the fitting technique described.