Nonlinear seismic analysis of the US Department of Energy graphite N-Reactor core

The US Department of Energy N-Reactor core consists of a graphite stack 33 feet wide by 33 feet high by 39 feet long enclosed by steel-lined concrete walls approximately 3-1/2 feet thick. Figure 1 schematically shows the general arrangement of these structures. The graphite core serves as a moderator and also serves to locate and support pressure tubes and safety systems (horizontal control rods and ball channels) which penetrate the core as shown in Figure 2 . The stack is composed of 89 layers of graphite blocks which are assembled in a lattice to permit venting of steam in the event of a pressure tube rupture. The graphite blocks are typically 6 × 6 inches by 32 inches long or 6 × 4 inches by 48 inches long. They are keyed such that they interlock with adjacent blocks above and below.