Nuclear Island (NI) basemat is a very thick reinforced concrete mat sitting on sub-grade soil to function as one-piece-foundation to support all super-structures anchored above the basemat. The Generation III (GEN III) NI is designed with more structures housing on the basemat, as such it is even greater in dimensions compared to GEN II. In the design process of a GEN III Passive-Safety-Plant (PSP), NI base mat is the most critical part for foundation design, since it is not only serves as the pressure boundary in foundation system but also support the whole nuclear island, carrying vertical load from upper structures, seismic loads both in vertical and horizontal directions, lateral soil pressures and buoyant force due to water table etc. For a typical AP plant the main structural systems which are housing within NI comprises of steel containment vessel (SCV), shield building (SC wall), internal structures, and auxiliary buildings etc. The scope for this paper is to investigate the approach and method which are suitable for modeling GEN III passive-safety-plant basemat. The investigation scopes are focused on (1) concrete basemat FE modeling and related subgrade medium (soil) modeling; (2) Design loads evaluation method and application for a typical basemat FE static analysis. Structurally speaking SCV is designed to directly anchored in concrete basemat, the interface between upper structure and foundation, its geometry and connection are unique and complicated, this lead to the modeling of basemat not only have to consider an appropriate FE meshing and element type selection but also need to consider the load application and transferring from the SCV to the basemat basin.

Since passive-safety-plant NI basemat is a deep foundation, basemat is deeply buried below the grade, the complete foundation model not only shall consider the basemat and immediate soil under the basemat, but also need to consider the backfill soil, the surrounding soil in vicinity, fill concrete under the basemat and deeper soil condition under the basemat. Since seismic loads pose great effects on basemat and its foundation design, how to evaluation seismic loadings and simplified their application for basemat static analysis is critical for such type of foundation.

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