Abstract

Criticality control of random media such as fuel debris is one of the most important safety issues in postaccident management. A 1/f^β spectrum randomizing model is expected to simulate such random media because it is well known that 1/f^β noise can describe a diverse range of random and disordered natural phenomena. In this paper, we focus on the relationship between the multiplication factor and moderation condition in the 1/f^β random media. A number of random media were realized with the 1/f^β spectrum randomizing model that is based on the randomized Weierstrass function (RWF). The volume ratio of concrete to fuel was adopted as an index for the moderation condition. The multiplication factors were calculated with a two-energy-group Monte Carlo calculation. The calculation results were analyzed by using standard deviation, skewness, and kurtosis. Those statistical parameters had an extreme value around the optimum moderation condition. This result suggested that it is possible to predict the rough trend of variation range, distortion, and outlier of multiplication factors in the 1/f^β random media.

摘要

燃料碎片等随机介质的临界控制是事故后管理中最重要的安全问题之一。1/f ^β频谱随机化模型有望模拟此类随机介质，因为众所周知，1/f ^β噪声可以描述各种随机和无序的自然现象。在本文中，我们重点研究了 1/f ^β随机介质中倍增因子与调节条件之间的关系。使用 1/f ^β实现了许多随机介质基于随机化 Weierstrass 函数 (RWF) 的频谱随机化模型。采用混凝土与燃料的体积比作为缓和条件的指标。乘法因子是用二能群蒙特卡罗计算来计算的。计算结果采用标准差、偏度和峰态进行分析。这些统计参数在最佳调节条件附近具有极值。该结果表明，可以预测 1/f ^β随机介质中倍增因子的变化范围、失真和异常值的粗略趋势。