This paper investigates the dynamic characteristics of a multilevel structure for the transportation and storage of spent nuclear fuel (SNF) from commercial power plants. The nuclear fuel is stored in slender rods that are grouped together into fuel assemblies (FA). In a sealed cylindrical container called “canister”, the FA are inserted into a honeycomb basket. The objective of this paper is to develop a computational model that accurately represents the structural dynamics of the canister as seen from its external surface, such that this computational model can be used in the context of structural integrity assessment of the internal components (FA and fuel rods) based on external vibration measurements. The numerous components lead to a large finite element model, and correspondingly, vibration modes and eigenfrequencies. Nevertheless, the localized connections between components enable an efficient domain decomposition with few interface coordinates. Craig–Bampton (CB) substructuring is thus used to perform the modal analysis. However, the high modal density yields a large-scale CB eigenvalue problem that necessitates a sparse solver. A block factorization by Schur complement that exploits the sparsity of the CB matrices allows an efficient calculation of the numerous eigenpairs. Many local vibration modes contribute little to the dynamics of the SNF canister. The main contribution of this paper is the development of an efficient methodology for determining the importance of each of the substructural modes of the CB model. The removal of the least dominant substructural modes allows for reducing the CB model. Using a 75% filtering, a significant speed-up is obtained, without noticeable loss of accuracy.

中文翻译：

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满载乏核燃料罐的主要结构振动模式

本文研究了用于运输和储存商业发电厂乏核燃料 (SNF) 的多层结构的动态特性。核燃料储存在细长棒中，这些棒组合在一起形成燃料组件 (FA)。在称为“罐”的密封圆柱形容器中，FA 被插入蜂窝篮中。本文的目的是开发一个计算模型，该模型能够准确地表示从其外表面看到的罐的结构动力学，以便该计算模型可用于内部组件（FA 和燃料）的结构完整性评估。杆）基于外部振动测量。众多组件导致大型有限元模型，以及相应的振动模式和特征频率。尽管如此，组件之间的局部连接能够以很少的界面坐标实现高效的域分解。Craig-Bampton (CB) 子结构因此用于执行模态分析。然而，高模态密度会产生一个大规模的 CB 特征值问题，需要一个稀疏求解器。利用 CB 矩阵的稀疏性的 Schur 补集的块分解允许有效计算众多特征对。许多局部振动模式对 SNF 罐的动态影响很小。本文的主要贡献是开发了一种有效的方法来确定 CB 模型的每个子结构模式的重要性。去除最不占优势的子结构模式可以减少 CB 模型。使用 75% 的过滤，获得了显着的加速，