Concrete Containment Structures Research Articles

Seismic fragility analysis of nuclear containment structure with Bayesian cloud analysis framework

Nuclear containment structure plays a critical role in safe operation of nuclear power plant. Seismic safety of nuclear power plant structures has become a hot issue in nuclear engineering community following Fukushima nuclear accident. Seismic fragility analysis, as a key element in probabilistic safety assessment of nuclear power plants, is widely used in nuclear power plant structures. This study presents an innovative method for seismic fragility analysis of engineering structures. The proposed methodology combines conventional Cloud analysis method and Bayesian framework. The accuracy and efficiency of the proposed methodology were demonstrated by a single-degree-of-freedom system, heavy computational efforts but high accuracy seismic fragility analysis method was adopted for comparison. Seismic fragility analysis of a typical prestressed concrete nuclear containment structure was analyzed using the proposed method. Results indicated that method proposed in this study can improve the accuracy of seismic fragility analysis. Furthermore, with the enhance of performance level, the increasing ratios for median seismic capacity of the nuclear containment structure was decreasing.

Advanced Analysis of Structural Performance in Novel Steel-Plate Concrete Containment Structures

This paper investigates the structural performance of novel steel-plate concrete containment structures, focusing on third-generation nuclear power plants. To address the challenges of increased complexities and costs associated with double-layer containment designs, this study explores the potential of steel-plate concrete structures to enhance safety, economic efficiency, and construction simplicity. The steel-plate concrete structure, characterized by its core concrete and dual steel plates, shows superior compressive strength, bending resistance, and elastoplasticity. Extensive numerical analyses, including finite element modeling and thermal-stress coupling, were conducted under various load conditions. Under structural integrity test conditions, the maximum radial displacement observed was 24.59 mm. Under design basis conditions, the maximum radial displacement was 47.61 mm; under severe accident conditions, it was 53.83 mm. The ultimate bearing capacity was 0.91 MPa, 2.17 times the design pressure. This study concludes that the steel-plate concrete containment structure maintains a high safety margin under all tested conditions, with stress and strain well within acceptable limits. It can effectively serve as a robust barrier against radioactive leakage and malicious impacts, providing a viable alternative to conventional containment designs.

Investigation on structural failure criteria and material property uncertainties of prestressed concrete containment structure

This study is to examine load-carrying capacity of a prestressed concrete containment vessel under the structural failure mode test via non-linear finite element (FE) analyses. Firstly, suitability of three candidate structural failure criteria was evaluated at ambient temperature condition, of which results showed that the maximum principal strain-based one predicts ultimate pressure capacity (UPC) most closely with the test data. Effect of increasing temperature corresponding to a postulated severe accident-induced condition was investigated and the UPC exhibited reduction ratios of 1.19–1.49% at the peak temperature of 200 °C approximately depending on each failure criterion. Finally, parametric FE analyses at 95% confidence level were performed to quantify effect of material property uncertainties. Overall, the impact of altered material properties of concrete and rebar was higher than that of tendon prestress, and the increase of UPC in upper bound cases exceeded the decrease of UPC in lower bound cases.

Evaluation of the Structural Response of the Containment Structure of a NPP to Internal Pressure and Thermal Gradients

As a final task for the life-extension program of the Embalse NPP located in Córdoba, Argentina, the pre-stressed concrete Containment Structure (CS) has recently been subjected to a pressure leak-rate test after more than 30 years of service. The test was carried out at the start of the summer season, following the completion of a general overhaul of main functional components; the CS had previously been inspected, and successfully passed a first evaluation before the implementation of its life extension process. This paper is concerned with the analysis of the structural response of the CS to internal pressure and comparison of model predictions with full-scale test results. The stated purpose is focused on assessing the structural response of the CS through the measured displacements and strains caused by the prescribed pressurization sequence. Special attention is given to thermal changes caused by exposure to sun radiation and daily temperature changes over the course of almost one-month duration of the test sequence.

Time-dependent fragility analysis of a nuclear containment structure under internal pressure and chloride-induced corrosion

The prestressed concrete containment structure, serving as the ultimate barrier against nuclear fuel leakage, holds paramount importance in ensuring the uninterrupted operation of nuclear power plants. Particularly in the aftermath of the Fukushima nuclear disaster, the influence of material aging and degradation of containment structures has been emphasized. Consequently, a probabilistic performance assessment of containment structures under chloride-induced corrosion condition is of significant relevance. This study presents a method for time-dependent fragility analysis of nuclear containment structures subjected to internal pressure, considering the effect of chloride-induced corrosion of steel reinforcement. A highly efficient and accurate finite element model with multi-layered shell element is formulated for damage and failure analysis. Furthermore, a corrosion degradation model of reinforced concrete, aligned with the attributes of multi-layered shell elements, is derived to reduce the reduce parameter samples generated by Latin Hypercube sampling technique. Material uncertainties and time-dependent effects are jointly integrated into the finite element analysis process, culminating in the establishment of fragility curves for the containment structure under various service lifetimes. The results indicate that within first 40 years of service, the load-bearing capacity of the containment structure has slightly decreased, while the probabilities of functional and structural failures in the containment structure will significantly increase after 60 years of service.

Statistical approach of performance-based uncertainty quantification of prestressed concrete containment structures for internal pressure capacity

With several experiences on economic losses and environmental impacts caused by serious accidents, the ultimate internal pressure and failure modes of Prestressed Concrete Containment Structures (PCCSs) during severe accidents have gained greater attention. Regulatory Guide allows the use of a 3D Finite Element (FE) model to determine the containment internal pressure capacity, because the experiments of PCCSs are a very cost and time-consuming process. In this study, an FE model of PCCS tested at Sandia National Laboratories is developed to identify an effect of parameters in the Concrete Damage Plasticity (CDP) model on the response of the PCCS and is validated from the experimental data. In addition, a closed-form equation is developed to predict the responses of the PCCS through a regression analysis in conjunction with the validated FE model and performance-based uncertainty quantification of the PCCS is estimated by numerical analysis and the closed-form equation. The developed closed-form equation achieves high accuracy of 98% and the probabilistic characteristic of the PCCS obtained from the equation well represents the one obtained from the validated FE model. The closed-form equation rarely requires computational cost to investigate the probabilistic responses of the PCCS.

Review on Comparative Analysis of Water Tank Rest on Ground

Abstract: Water is the basic need of all living organisms for survival. Portable water is essential for good human health. It is important to provide portable water to every individual and every community; therefore it is very important to save water. Usually, water is stored in tanks and then the stored water is delivered through pipelines to each location. Usually, a water tank resting on the ground is a tank for storing water. This case study gives an idea of a safer and more economical design with greater reliability and simplicity. This article helps to understand the philosophy of safe tank optimization. For the safe and economical design of the tank, this study provides various design requirements that affect the strength and support of the structure. This case study is conducted on a reinforced concrete liquid containment structure resting on the ground.

Effects of steel liner corrosion on the leak-tightness of prestressed concrete containment structure under severe accident loads

This study evaluates the effect of steel liner corrosion on the leak-tightness of the prestressed concrete containment structure under severe accidents. Based on the nonlinear finite element method and sub-model technique in the ABAQUS platform, a global model of the containment structure and a detailed sub-model of the corroded steel liner are established. Different calculation methods for the multiaxial stress factor in the failure criterion of the steel liner are compared, and the failure criterion is modified by combining the uniaxial tensile test results of corroded steel liners. According to the modified failure criteria, the corrosion shape and corrosion degree of the steel liner, as well as the thermal effect on the containment structure, are studied in depth. Results indicate that the mechanical properties of the steel liner degrade significantly after corrosion, and the simulation method proposed in this study can reflect the corrosion state of the steel liner well. The multiaxial stress factor based on the Davis triaxiality coefficient is conservative in evaluating functional failure of the containment structure, and the calculation method of the corrosion factor proposed in this study can directly reflect the effect of the corrosion degree on the ductility of the steel liner. Considering that a less conservative calculation result will be obtained based on regular corrosion shapes, the corrosion shapes established from actual corrosion cases of steel liners in this study are available for reference. Pressure capacity of the containment structure corresponding to functional failure decreases with the increase in corrosion degree of the steel liner. When corrosion rates range from 10% to 50%, pressure capacity under the only pressure case and the coupled temperature and pressure case is decreased by 9.21% to 28.58% and 11.35% to 31.06%, respectively. The behavior of the steel liner is significantly affected by the temperature under corrosion conditions.

Identification and assessment of seismic damage for RC containment structures considering prestressing effect

Containment structures shall remain viable even after strong ground motions to save lives and valuables. Therefore, the current study exploits the prestressing effect to mitigate seismic damage and prevent function and structural failure during seismic events. The seismic response of the studied reinforced concrete containment (RCC) structure is well captured and investigated. The results reveal that the prestressing could significantly mitigate the seismic damage and the RCC structure’s bottom is the most vulnerable region. Hence, the prestressing value might be designed to mitigate the seismic damage of the RCC structure not only to keep its integrity under overpressure. Moreover, damage assessment using different damage indices has been presented, and a modification for the Park-Ang damage index has been formulated. Furthermore, a new formula has been proposed to predict the RCC structure’s damage ratio accurately, and a new classification for the damage states has been developed to identify the performance level.

Bayesian updating for nuclear containment buildings using both mechanical and hydraulic monitoring data

Leak tightness of concrete containment structures such as Nuclear Containment Buildings (NCB) plays a key role in their serviceability and the safety of their surrounding environment. Under the action of operating loads and aging process, leak tightness may evolve over time, which makes numerical forecasting strategies a crucial tool for improving anticipation of overpassing threshold limits, as well as decision aid in the framework of containment structures maintenance. In this paper, a Bayesian updating framework for NCB under serviceability loads is presented. Based on the Bayesian inference process, it allows to incorporate both mechanical and hydraulic NCB monitoring data to numerical predictions in a probabilistic framework, for updating a prior into a posterior state of knowledge related to model parameters. For computational purposes, the approach uses a Transitional Markov Chain Monte Carlo (TMCMC) algorithm for estimating the posterior distribution of model parameters. In order to provide a suitable approach for engineering practice in terms of computational cost, sparse Polynomial Chaos Expansions (PCE) are used for accelerating the TMCMC algorithm. The information gain resulting from Bayesian updating is quantified using a measure taken from information theory, namely the Kullback–Leibler Divergence (KLD). The proposed approach is illustrated through an application to a 1:3 scale NCB. By extracting information from various auscultation data of the structure, the knowledge on uncertain parameters of a complex finite element model is updated throughout the structure operational phase, and new predictions of the structure’s strains and leakage responses are subsequently performed.

Optimization of sensor location and method analyzing for in-situ monitoring of concrete containment structures: a case involving embedded moisture sensors

Optimization of sensor location and method analyzing for in-situ monitoring of concrete containment structures: a case involving embedded moisture sensors

Effects of Steel Liner Corrosion on the Leak-Tightness of Prestressed Concrete Containment Structure Under Severe Accident Loads

Effects of Steel Liner Corrosion on the Leak-Tightness of Prestressed Concrete Containment Structure Under Severe Accident Loads

Statistical Approach of Advanced Uncertainty Quantification of Prestressed Concrete Containment Structures in Nuclear Power Plants

Statistical Approach of Advanced Uncertainty Quantification of Prestressed Concrete Containment Structures in Nuclear Power Plants

Ultrasonic monitoring of stress and cracks of the 1/3 scale mock-up of nuclear reactor concrete containment structure

To evaluate the stress level and damage of a reinforced concrete containment wall (similar to those used in nuclear power plants) and its reaction to pressure variations, we conducted successive ultrasonic experiments on the exterior surface of the containment wall in the gusset area for three consecutive years (2017, 2018 and 2019). During each experiment, the pressure inside the containment wall increased gradually from 0 MPa to 0.43 MPa and then decreased back to 0 MPa. From the analysis of the ultrasonic coda waves obtained in the multiple scattering regime (80–220 kHz), we performed Coda Wave Interferometry to calculate the apparent velocity changes in the structure (denoted by dV/V a ) and Coda Wave Decorrelation (DC) measurements to produce 3D cartographies of stress and crack distribution. From three source–receiver pairs, located at the top, middle and bottom of the experimental region, we observe that coda waves dilate, shrink and remain almost unchanged, respectively. This corresponds to the decreasing, increasing and invariant pressure inside the concrete. The comparison of 3 years’ results demonstrates that the variation of dV/V a and DC under the same pressure test increases through the years, which indicates the progressive deterioration and ageing of the concrete. From a large collection of source–receiver pairs at different times, the spatial–temporal variations of dV/V a and DC are then used to produce a map of the structural velocity and scattering changes, respectively. We observe a decreasing velocity on the top part and an increasing in the middle one, which is in line with the dV/V a analysis. The reconstructed scattering changes (or structural changes) highlight the active region during the inflation–deflation procedure, corresponding to the opening and closing (and sometimes the development) of cracks. The larger magnitude in 2019 than in 2017 indicates the increasing damage in the concrete.

Microstructure homogenization of concrete used in nuclear power plants

Nearly all nuclear power plants in the United States are operating past their intended lifetimes or are requesting lifetime extensions. Therefore, understanding changes to the concrete containment structure over time is crucial to evaluate the structure’s continued viability. Concrete materials are heterogeneous particulate composites that exhibit viscoelastic material properties, which can lead to slow deformation over time, causing stress redistribution and the potential for creep cracking. A code to generate random, three dimensional (3D) concrete microstructures has been developed and paired with finite element analysis to predict the long-term viscoelastic properties of concrete. Data from these simulations are used to develop constitutive equations for the viscoelastic behavior of the homogenized concrete. The codes in this work are used to virtualize laboratory experiments, to obtain long-term creep data in a faster, cheaper manner. To validate this work, the simulated creep behavior of concrete is compared to 800 d of experimental data that has been extended to 27 y of data using the Time-Temperature superposition (TTS) principal. Excellent agreement between the simulation results and experimental data is seen.

Damage performance based seismic capacity and fragility analysis of existing concrete containment structure subjected to near fault ground motions

Containment structures fill the critical role of providing the final barrier against release of radioactive materials. Near fault earthquake pose great threaten to the function of existing containment structure. There is a growing necessity of performing a detailed seismic capacity and fragility analysis of existing containment structure. This paper presents seismic capacity and fragility analysis of existing containment structure subjected to near fault ground motions from damage performance based perspective. To capture uncertainties associated with the ground motions, incremental dynamic analysis technique is conducted, and three damage levels are proposed based on tensile damage factor provided in concrete damaged plasticity (CDP) model. Fragility curves of containment structure under minor damage, moderate damage and severe damage is obtained with MATLAB optimization program. Results of this study reveal that tensile damage of containment structure within 8 m of the bottom of the containment is most vulnerable locations in containment structure. The bottom location of the containment structure is dominant by bending cracks, and the lower location of the containment structure (except the bottom location) is governed by diagonal shear cracks. With the increase of ground motion intensity, shear behavior of the containment structure becomes more obvious.The HCLPF seismic capacity of this containment structure under minor damage, moderate damage and severe damage is 0.452 g, 0.631 g and 0.790 g, respectively.

Acoustic emission monitoring of containment structures during post-tensioning

This paper introduces a method based on acoustic emission (AE) to monitor the onset of delamination in post-tensioned concrete containment structures. The method is based on clustering AE occurring during post-tensioning and/or re-tensioning such structures. In particular, the investigation is focused on AE of a large-scale, curved concrete wall subject to monotonically increasing prestressing forces. This specimen is a representative of typical cylindrical concrete structures, such as water storage tanks, silos, bins, and nuclear containment structures. To analyze AE data, this paper uses both time-driven and hit-driven features extracted from AE. To this end, a novel approach is proposed to analyze and visualize hit-driven features. To detect and localize such defects, the proposed approach identifies an optimal number of clusters in AE data and interprets each cluster based on the physical mechanism that generates it. Such interpretations are compared with the state of stresses and modified Mohr–Coulomb failure criteria. The results show that the AE events are due to three categories of source mechanisms, micro shear cracking, micro tensile cracking, and macro delamination cracking. To validate the results, comparisons are made with through-thickness expansion measurements of the wall. The results demonstrate that the proposed approach can detect delamination defects and enable decision makers to take remedial and preventive actions.

Evaluation of the thermal strain of an NPP containment structure during leakage rate tests

A strategy for isolating the thermal strain due to solar radiation from the total measured strain during the Integrated Leak Rate Test of a nuclear containment structure is presented in this paper. In the proposed method, a series of numerical models are developed to estimate the temperature change on the prestressed concrete containment structure and to predict the strain due to temperature and applied pressure. The effects of the solar radiation, heat exchange with internal and external air and heat conduction are considered in the proposed method. The developed method is validated by reproducing the total strain profiles measured from the leak rate tests conducted at the Point Lepreau CANDU®11CANDU (CANada Deuterium Uranium Reactor) is a registered trademark of the Atomic Energy of Canada Limited (AECL), used under exclusive license by Candu Energy Inc. 6 containment structure.

Structural integrity assessment of nuclear containment through fracture characterization

AbstractThe paper deals with the study of structural response of partially cracked nuclear containment model structure in over pressurized condition with the simulated experiments conducted under severe accidents analysis program for Indian nuclear containment structures. In this research, the fracture characterization of concrete containment structure is also investigated through the over pressure experiments on the BARC Containment (BARCOM) test model structure, which represents 1:4 scale of the prototype 540 MWe Tarapur pre‐stressed nuclear containment structure. In addition to the surface‐type electrical resistance, strain gauges conventionally and commonly deployed for containment proof‐test and ultimate load capacity evaluation of containment models, embedded vibratory wire strain gauges (VWSGs), the digital image correlation (DIC) technique, and soap bubble tests are employed in this study. For fracture characterization, an optical crack profile (OCP) technique is developed through DIC full‐field experiment conducted at the identified critical locations with conventional strain gauges to evaluate the fracture energy and the characteristics of the fracture process zone of concrete containment model structure subjected to the over‐pressure condition for its performance assessment in the case of the beyond design basis accidents. The combination of conventional sensors and full‐field DIC deployed for the first time on the largest scale containment model along with the associated analysis is shown to be effective in fracture characterization and improved structural integrity assessment of the containment model.

Nonlinear Rayleigh surface waves to characterize microscale damage due to alkali-silica reaction (ASR) in full-scale, nuclear concrete specimens

Nonlinear Rayleigh surface waves are used to monitor the damage state due to alkali-silica reaction (ASR) in full-scale reinforced concrete block specimens created as part of a full-scale testing program for concrete nuclear containment structures. The measurement technique uses a wedge/transducer source to generate and a non-contact, air-coupled receiver to detect nonlinear Rayleigh surface waves to obtain the acoustic nonlinearity parameters for three different reinforced block concrete specimens – a confined and an unconfined ASR specimen, plus a control specimen – at three different time intervals. These results further validate the utility of nonlinear Rayleigh waves to quantify the progress of microscale damage due to ASR in full-scale, concrete structures.