Analysis of Post-Tensioned Containment Building for Large Nuclear Components Replacement

1. Analysis of Post-Tensioned Containment Building for Large Nuclear Components Replacement Luis M. Moreschi, Ph.D., P.E. and Farhad Farzam, P.E. Bechtel Power Corporation GT STRUDL Users Group 2005 Annual Meeting, Las Vegas - Nevada As nuclear stations get older, key components wear out and must be replaced. The removal and replacement of large nuclear components, such as steam generators, reactor pressure vessel heads and pressurizers, usually require a temporary construction opening on the cylindrical walls of the containment building. For prestressed concrete shell structures, the post-tensioning tendons in the area of the construction opening need to be detensioned and removed before starting the chipping of the concrete. Additional tendons adjacent to the opening also need to be detensioned to minimize compressive stresses in and around the opening area. Therefore, analytical studies need to be performed to determine the total number of tendons that need to be detensioned such that the stresses in concrete and reinforcing steel are maintained within allowable limits during the various construction stages, as well as for plant operating conditions. Today�s presentation describes the use of GT STRUDL software to perform these analytical studies.As nuclear stations get older, key components wear out and must be replaced. The removal and replacement of large nuclear components, such as steam generators, reactor pressure vessel heads and pressurizers, usually require a temporary construction opening on the cylindrical walls of the containment building. For prestressed concrete shell structures, the post-tensioning tendons in the area of the construction opening need to be detensioned and removed before starting the chipping of the concrete. Additional tendons adjacent to the opening also need to be detensioned to minimize compressive stresses in and around the opening area. Therefore, analytical studies need to be performed to determine the total number of tendons that need to be detensioned such that the stresses in concrete and reinforcing steel are maintained within allowable limits during the various construction stages, as well as for plant operating conditions. Today�s presentation describes the use of GT STRUDL software to perform these analytical studies.

2. Presentation Outline Background Information Finite Element Analysis � GT STRUDL Automatic Generation Commands Modeling of Prestressing Loads Coordinate Systems: Global & Local Planar Axis Sequential Construction Simulation Summary and Conclusions As part of this presentation, I�ll first provide general information on some of the steps involved in the replacement of Large Nuclear Components that are relevant to the analytical studies. To perform the analysis studies, a finite element model of the post-tensioned containment structure was first created using GT STRUDL. I�ll provide details on the commands used to generate the geometry of the model, as well as on the approach implemented to model the prestressing loads. I�ll then describe how the selection of the global axis of the model may affect the finite element results obtained though the averaging process. I�ll conclude my presentation with a description of the GT STRUDL data base management features used to simulate the various construction stages. As part of this presentation, I�ll first provide general information on some of the steps involved in the replacement of Large Nuclear Components that are relevant to the analytical studies. To perform the analysis studies, a finite element model of the post-tensioned containment structure was first created using GT STRUDL. I�ll provide details on the commands used to generate the geometry of the model, as well as on the approach implemented to model the prestressing loads. I�ll then describe how the selection of the global axis of the model may affect the finite element results obtained though the averaging process. I�ll conclude my presentation with a description of the GT STRUDL data base management features used to simulate the various construction stages.

3. Finite Element Analysis Purpose: Determine Total Number of Tendons to be Detensioned GT STRUDL Computer Program - Validated & Verified Plate/Shell Elements for Containment Cylindrical Wall and Dome Spatial Truss Members for Helical Tendons Model for Prestress Load Coordinate System Selection Sequential Construction Simulation To determine the total number of tendons that need to detensioned, a 3-D finite element model was created using the GT STRUDL computer program. GT STRUDL is a validated and verified program for use on Nuclear Power Projects. Plate elements were used to model the cylindrical walls and dome. The finite element mesh was generated to match the spacing between the helical tendons. Spatial truss members were used to model the helical tendons in the cylindrical walls. The model for prestress load was created by combining both plate elements and spatial truss members. Another important consideration in the creation of the model was the proper selection of the global coordinate system. Different models were created to simulate the various construction stages of the containment openingTo determine the total number of tendons that need to detensioned, a 3-D finite element model was created using the GT STRUDL computer program. GT STRUDL is a validated and verified program for use on Nuclear Power Projects. Plate elements were used to model the cylindrical walls and dome. The finite element mesh was generated to match the spacing between the helical tendons. Spatial truss members were used to model the helical tendons in the cylindrical walls. The model for prestress load was created by combining both plate elements and spatial truss members. Another important consideration in the creation of the model was the proper selection of the global coordinate system. Different models were created to simulate the various construction stages of the containment opening

4. Containment Configurations