Three-dimensional analysis of AP600 standard plant shield building roof

摘要

The AP600 passive containment vessel is surrounded by a concrete cylindrical shell covered with a truncated conical roof. This roof supports the passive containment cooling system (PCS) annular tank, shield plate and other nonstructural attachments. When the shield building is subjected to different loading combinations as defined in the Standard Review Plan (SRP), some of the sections in the shield building could experience forces in excess of their design values. This report summarized the three-dimensional finite element analysis that was conducted to review the adequacy of the proposed Westinghouse shield building design. The ANSYS finite element software was utilized to analyze the Shield Building Roof (SBR) under dead, snow, wind, thermal and seismic loadings. A three-dimensional model that included a portion of the shield building cylindrical shell, the conical roof and its attachments, the eccentricities at the cone-cylinder connection and at the compression ring and the PCS tank was developed. Mesh sensitivity studies were conducted to select appropriate element size in the cylinder, cone, near air intakes and in the vicinity of the eccentricities. Also, a study was carried out to correctly idealize the water-structure interaction in the PCS tank. Response spectrum analysis was used to calculate the internal forces at different sections in the SBR under Safe Shutdown Earthquake (SSE). Forty-nine structural modes and twenty sloshing modes were used. Two horizontal components of the SSE together with a vertical component were used. Modal stress resultants were combined taking into account the effects of closely spaced modes. The three earthquake directions were combined by the Square Root of the Sum Squares method. Two load combinations were studied. The load combination that included dead, snow, fluid, thermal and seismic loads was selected to be the most critical. Interaction diagrams for critical sections were developed and used to check the design adequacy. The results demonstrated that provided area of steal on each face of several sections of the AP600 SBR was inadequate. This was also noticed when comparing the total provided area of steel per section, i.e., the area of steel on both faces. The discrepancy between Westinghouse results and these reported herein could have resulted from the different finite element mesh sizes and the assumption used in Westinghouse design.