PSI - Issue 64

Federico Pinto et al. / Procedia Structural Integrity 64 (2024) 766–773 Author name / Structural Integrity Procedia 00 (2019) 000–000

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1. Introduction The Embalse NPP (CNE- for Central Nuclear de Embalse), provided with a 683 MWe CANDU reactor in commercial operation since 1984, has recently completed a life extension program consisting on overhaul of the main electromechanical and functional components and instrumentation of the plant. As part of that program, a number of structural assessments have also been carried out over the last 12 years on the civil structures, such as its capacity to sustain upgraded seismic demands based on actual seismic records and enhanced numerical models, as compared with the original design procedures of the 1970’s. Some of such studies were reported by Pinto et al. (2007) and by Ceballos et al. (2007). Work presented here is a summary of the main results of the pressure leak-rate test performed after completion of the life extension program. The containment structure (CS) of the CNE consists of a post-tensioned cylindrical shell capped by the spherical casket connected to the cylinder by a massive rectangular ring beam. The cylindrical part with a thickness of 1.10 m is stiffened by four vertical buttresses of 1.90 m thick that connect the base slab foundation with the upper ring beam (Fig. 1). The post-tensioned concrete cylindrical shell was built with sliding formwork leaving some significant temporary openings to allow installation of major electromechanical components. The spherical roof, built in successive complete rings without meridian stiffeners, has a uniform wall thickness of 0.65 m. The base slab is a 1.70 m thick post-tensioned concrete slab that also supports the reinforced concrete internal structure (IS).

Fig. 1. General layout (left) and diametric cut of the FEM (right) of the Containment Structure.

2. Numerical model A linear elastic finite element model (FEM) of the CS was developed by means of ABAQUS (2010) to assist in the evaluation of the structural response to the pressure leak-rate test carried out during December 2018. Fig. 1 shows a diametric cut of the FEM mesh used to represent the main structural components of the CS that consists of about 240.000 eight-node solid elements (C3D8R) and 300.000 nodes. The flexibility of the foundation soil has been modeled by horizontal and vertical, uniformly distributed springs that represent the static behavior of the CS. The cylindrical shell part was modeled with 5 elements across its thickness, 9 for the ring beam and the buttresses, and 4 for the dome and the base slab. The internal structure, also supported on the base slab, was not included in the model except for an estimated increase of the modulus of elasticity of the slab. The initial estimate of elastic parameters of concrete for the numerical model given in Table 1 was based on wave propagation measurements across the wall thickness. Strength parameters are not required since the analysis is performed in the linear elastic field.