Prestressed Concrete Containment Vessel Research Articles

Stochastic model updating for analysis of a nuclear containment vessel under internal pressure

The prestressed concrete containment vessel (PCCV) is a critical safety measure for nuclear power plants. In the analysis of PCCV, the parameters of PCCV are usually determined through experience and a small number of experiments, which are highly accidental, and this paper provides a new idea for clarifying the scope of PCCV material parameters and clarifying some parameters that are important to PCCV based on the Bayesian updating method. Finite element models consisting of multilayer shell elements were established based on the 1:4 PCCV experiment conducted at Sandia National Laboratories (SNL) in this paper. The model was used to identify the most influential 5 parameters during the late loading stage, and a Bayesian model updating method was applied to adjust these parameters. The finite element model, incorporating the modified posterior parameters, effectively predicted the displacements of measurement points and failure mechanisms of the model.

Failure analysis of prestressed concrete containment vessels under internal pressure considering thermomechanical coupling

After a loss of coolant accident (LOCA) in the prestressed concrete containment vessels (PCCVs) of nuclear power plants, the coupling of temperature and pressure can significantly affect the mechanical properties of the PCCVs. However, there is no consensus on how this coupling affects the failure mechanism of PCCVs. In this paper, a simplified finite element modeling method is proposed to study the effect of temperature and pressure coupling on PCCVs. The experiment results of a 1:4 scale PCCV model tested at Sandia National Laboratory (SNL) are compared with the results obtained from the proposed modeling approach. Seven working conditions are set up by varying the internal and external temperatures to investigate the failure mechanism of the PCCV model under the coupling effect of temperature and pressure. The results of this paper demonstrate that the finite element model established by the simplified finite element method proposed in this paper is highly consistent with the experimental results. Furthermore, the stress-displacement curve of the PCCV during loading can be divided into four stages, each of which corresponds to the damage to the concrete, steel liner, steel rebar, and prestressing tendon. Finally, the failure mechanism of the PCCV is significantly affected by temperature.

The performance enhancement of containment with fiber reinforcement following a LOCA considering different ambient conditions

The prestressed concrete containment vessels (PCCVs) will be exposed to the temperature action followed by the internal pressure increasing after a loss of coolant accident (LOCA) with safety system failure. The damage evolution of the PCCV under the effect of thermal-pressure coupling deserves in-depth study. Moreover, different containment external temperatures are seldom considered in previous studies whereas they may further pose a great challenge for the design and safety of containments. Just as important, an attempt is first made in this paper to involve steel fiber in the construction of the containment to observe the performance of the containment with steel fiber strengthening under the effect of thermal-pressure coupling. Therefore, the influence of the possible outside temperature (i.e. −30 °C, −15 °C, 0 °C, 15 °C, and 30 °C) determined from the 5 existing or planned nuclear power plant sites in China on the distribution of temperature field of containment is researched firstly. Then, the damage indices corresponding to the containment are defined to represent the actual damage performance and failure mechanism of the structure. Finally, the comparative damage performance and failure mechanism between conventional and steel fiber reinforced concrete (SFRC) containments taking into account the effect of coupling temperature and internal pressure is detailedly discussed. The results show that the SFRC is more expeditious in restraining radial and vertical displacement of containment under lower external temperatures for subsequent internal pressure. Under the ultimate internal pressure, the SFRC containment has a reduction rate of 5.37% for radial displacement and 35.52% for vertical displacement at an external temperature of −30 °C, while 2.23% and 15.33% at an external temperature of 30 °C, respectively. Furthermore, SFRC containment has better performance under the effect of coupling of temperature and internal pressure compared to conventional containment. For example, at an internal pressure of 1.2 MPa, the damage reduction rate for concrete is 94.18% at an external temperature of −30 °C and 81.37% at 30 °C; for the steel liner, the damage reduction rate is 50.22% at an external temperature of −30 °C and 87.83% at 30 °C. For the containment prestressing tendons, the damage reduction rate is around 60% under ultimate internal pressure. The study can provide important guidance for siting and design of nuclear containments and alternative retrofitting measures for nuclear containments.

Optimization of non-prestressing reinforcement around the equipment hatch of a prestressed concrete containment vessel

An optimization of non-prestressing reinforcement arrangement was performed with the help of nonlinear finite element analysis in this study to alleviate the congestion of reinforcement around the equipment hatch (E/H) of a prestressed concrete containment vessel (PCCV). A 3D nonlinear finite element model of the PCCV was first established. Then simulations were carried out on the PCCV with different contents of non-prestressing reinforcement in the E/H area. The mechanical responses of the numerical models under two most concerned load effect combinations, i.e. ultimate safety ground motion plus design basis pressure and 1.5 times of design basis pressure only were compared. Furthermore, the temperature effect was investigated. It is found that the optimum value is 70% of the original reinforcement area, which can satisfy the safety requirement and simultaneously decreases the reinforcement usage. The current preliminary study shows that the adoption of nonlinear finite element analysis in the design can reduce the reinforcement in the E/H area.

Reevaluation of failure criteria location and novel improvement of 1/4 PCCV high fidelity simulation model under material uncertainty quantifications

Reactor containment buildings serve as the last barrier to prevent radioactive leakage due to accidents and their safety is crucial in overpressurization conditions. Thus, the Regulatory Guide (RG) 1.216 has mentioned the global strain as one of failure criteria in the free-field for cylindrical prestressed concrete containment vessels (PCCV) subject to internal pressure. However, there is a limit that RG 1.216 shows the free-field without the specific locations of failure criteria and also the global strain corresponding to only azimuth 135° has been mentioned in NUREG/CR-6685, regardless of the elevations of the structure. Therefore, in order to reevaluate the failure criteria of the 1:4 scaled PCCV, the high fidelity simulation model based on the experimental test was significantly validated in this study, and it was interesting to find that the experimental and numerical result was very close to each other. In addition, for the consideration of the material uncertainties, the Latin hypercube method was used as a statistical approach. Consequently, it was revealed that the radial displacements of various azimuth area such as 120°, 135°, 150°, 180° and 210° at elevations 4680 mm and 6,200 mm can represent as the global deformation at the free-field, obtained from the statistical approach.

Feasibility study of a prestressed-concrete containment vessel for a novel GFR nuclear reactor

The latest modern nuclear energy systems currently researched and developed are the Generation IV (Gen IV) nuclear reactors, and one of the more promising Gen IV designs is the Gas-cooled fast reactor (GFR). Among the number of challenging problems of the design of GFR, the development of passive safety systems ensuring passive decay heat removal (DHR) during loss-of-coolant-accidents (LOCA) is of the highest importance. The currently proposed DHR strategy relies on intentionally increasing pressure inside a gas-tight guard vessel containing the reactor to approximately 4 bar. This, however, presents a significant engineering challenge as the vessel must be capable of withstanding high pressure of up to 10 bar, due to pressure spikes and safety coefficients, while also withstanding increased temperatures during the LOCA. As no GFR guard vessel has ever been designed, this paper presents a feasibility study establishing whether such vessel can be designed. The feasibility study is aimed at the assessment of a preconceptual design of a prestressed concrete vessel previously created by the authors. In the study, stresses in the structure induced by normal-operation loads and LOCA loads are calculated for three types of extreme constraint conditions covering all possible real constraints of the structure. The calculations are based on heat transfer equations, Euler–Bernoulli theory, and Lamé equation implemented in a in-house Python code. In the results, stresses in the vessel are presented and compared to design criteria. The main conclusion of the paper is that the vessel can be designed; however, certain adverse phenomena which complicate the design process, such as non-linear creep of concrete and occurrence of tensile stress up to 1MPa, will have to be addressed and considered during future detailed design. Following on from this affirmative conclusion, the authors will create the detailed design using advanced three-dimensional modelling in their future work.

Pretest analysis of a prestressed concrete containment 1:3.2 scale model under thermal-pressure coupling conditions

In nuclear power plant (NPP) accidents, the containment is subject to high temperatures and high internal pressures, which may further trigger serious chain accidents such as core meltdown and hydrogen explosion, resulting in a significantly higher accident level. Therefore, studying the mechanical performance of a containment under high temperature and high internal pressure is relevant to the safety of NPPs. Based on similarity principles, the 1:3.2 scale model of a prestressed concrete containment vessel (PCCV) of a NPP was designed. The loading method, which considers the thermal-pressure coupling conditions, was used. The mechanical response of the PCCV was investigated with a simultaneous increase in internal pressure and temperature, and the failure mechanism of the PCCV under thermal-pressure coupling conditions was revealed.

Failure Mechanism of Fiber-Reinforced Prestressed Concrete Containments under Internal Pressure Considering Different Fiber Types

Current investigations of performance improvement in prestressed concrete containment vessels (PCCVs) with fiber reinforcement are scarce, and the type of fiber to select for PCCVs is not explicitly stated. The failure mechanism of PCCVs with fiber reinforcement under internal pressure is investigated in this paper. The effects of different fiber types, including rigid fiber, flexible fiber, and hybrid fiber, are considered for the creation of fiber-reinforced PCCVs. The mechanical behavior between conventional and fiber-reinforced PCCVs is scientifically compared and identified. The results demonstrate that to achieve the aim of inhibiting early cracking of the concrete, any type of fiber can be taken into account. The performance of the ultimate pressure capacity and yielding of the liner can be promoted, respectively, by introducing steel, steel-PP, and steel-PVA fiber-reinforced concrete. Additionally, the failure regions can be controlled to a certain extent under ultimate internal pressure via the appropriate use of FRC.

Quantitative damage evaluation of prestressed concrete containments with steel fiber strengthening under internal pressure

Current investigations cannot quantitatively predict the overall damage performance of prestressed concrete containment vessels (PCCVs) under internal pressure and the effect of steel fiber strengthening on the damage performance improvement has not been investigated. A new parameter definition is proposed to characterize the entire damage performance of conventional and steel fiber-reinforced concrete (SFRC) PCCVs under internal pressure in this study. The prestress loss is precisely calculated considering 40 years of the service period of PCCV. To review the possibility of operating lifetime extension of PCCV, the subsequent 60 years are also considered. Firstly, elaborate three-dimensional numerical models of conventional and SFRC containments were established. Then, three parameters to represent the extent corresponding to concrete, steel liner, and prestressed tendons of containment under damage were proposed. Finally, damage performance of conventional and SFRC containments considering the impact of prestress loss was discussed in depth. The results show that by introducing the SFRC and considering the five-year prestress loss, the pressure capacities for containment concrete, steel liner, and prestressed tendons are increased by 22.16%, 18.99%, and 12.35%, respectively. What's more, the proposed parameters can reflect the changing trend of the damage extent of containments under internal pressure and inclusion of steel fibers can improve damage performance significantly. To examine the realistic damage performance under internal pressure, the five-year prestress loss requires to be specifically considered.

Fragility analysis of a prestressed concrete containment vessel subjected to internal pressure via the probability density evolution method

The prestressed concrete containment vessel (PCCV) is the final barrier to prevent radioactive material leakage from a nuclear power plant to the outside. Therefore, the fragility evaluation is very important for the design and analysis of the PCCV. In this paper, the fragility analysis of the PCCV (tested at Sandia National Laboratories (SNL)) subjected to internal pressure is conducted using the probability density evolution method (PDEM). First, a high-fidelity finite element analysis procedure is introduced to perform the deterministic analysis of the PCCV. In the following stochastic analysis and fragility evaluation, the material properties are selected as the uncertain resources. By applying the PDEM, the probability surface and probability density function (PDF) of the stochastic responses are obtained. Furthermore, the limit state of the PCCV is evaluated by the global average strain, which is defined as the ratio of radial displacement to the radius of the PCCV, and the PCCV reaches its functional and structural failure states when the global average strain reaches 0.4% and 1.5%, respectively. To consider more than one failure mode in the fragility evaluation, an equivalent extreme-value event combined with the PDEM is adopted to obtain the failure probability and the fragility curve of the PCCV to evaluate its fragility behavior. The results show that the fragility of the PCCV is still zero until the internal pressure increases to 2.890 times and 3.155 times the design pressure and then increases rapidly and reaches 1 at 3.560 times and 3.955 times the design pressure of the functional and structural failure criteria, respectively.

The optimum steel fiber reinforcement for prestressed concrete containment under internal pressure

This paper investigates the optimum fiber reinforcement for prestressed concrete containment vessels (PCCVs) under internal pressure. To achieve this aim, steel fiber, which is the most widely used fiber type in current engineering applications, is adopted to constitute steel fiber-reinforced concrete (SFRC) to substitute the conventional concrete in the PCCV. The effects of characteristic parameters, λsf, of the steel fiber affecting significantly the mechanical behavior of the concrete are first taken into account. Partial or complete concrete regions of the PCCV are also considered to be replaced by SFRC to balance the economy and safety. By adopting the ABAQUS software, the ultimate bearing capacity and performance for the fiber-reinforced PCCV are scientifically studied and quantified, and the recommendations for the optimum way of fiber reinforcement are presented.

High-fidelity numerical analysis of the damage and failure mechanisms of a prestressed concrete containment vessel under internal pressure

The safety of nuclear power plants, which is of great public concern, depends largely on the safety of prestressed concrete containment vessels (PCCVs). To ensure the safety of PCCVs, researchers have conducted many experimental investigations and numerical simulations in recent decades. In this paper, we present an enhanced finite element framework for damage and failure analysis of PCCVs. The framework incorporates element formulations, material models and structural solution algorithms. The multilayered shell element is used to simulate the in-plane/out-of-plane behaviors of the vessels, the softened damage-plasticity model is used for modeling the concrete under the complex stress state, and the quasi-Newton method with a two-level secant stiffness updating strategy is adopted to improve the computational convergence performance and robustness. To demonstrate the performance of the framework, the 1:4-scale PCCV model tested by the Sandia National Lab is applied. The ultimate capacity, whole deformations and damage patterns are all captured well. In addition, the local deformation at different parts is also consistent with the experimental results. Good agreement between the numerical results and the experimental data indicates that this analysis framework is a high-fidelity, relatively simple and efficient procedure for simulating the behavior of PCCVs.

Fire resistance of bi-directionally prestressed concrete under extreme fire loading

Infrastructures such as prestressed concrete containment vessels (PCCVs) and liquid gas storage tanks are constructed as bi-directional prestressed concrete (PSC) structures to ensure outstanding leak-tight storage and shielding performance. However, PSC structures exhibit severe vulnerability to high-temperature fire due to the high-strength concrete used and the application of prestressing (PS) stresses to increase the strength of the structures. The PCCV of a 1400 MW advanced power reactor was selected as the target for study. A scaled-down model of the PCCV outer wall was fabricated and tested to determine its resistance to a standard fire-loading scenario. Furthermore, different PS forces were applied to the specimens to evaluate the effect of concrete confinement on the fire resistance. Test data of temperature distribution, PS force loss and residual strength capacity were obtained. The experimental data were used for calibration of a commercial finite-element simulation program (Midas FEA) for structural fire analysis of real-scale concrete structure and infrastructure. The simulation and test results showed significant similarity and the result trends were accurate.

Evaluation of the internal blast resistance of a bi-directionally prestressed concrete tubular structure according to ANFO explosive charge weight

When an extreme internal loading is applied to prestressed concrete (PSC) structures, serious property damage and human casualties may occur. However, the existing designs for PSC structures such as prestressed concrete containment vessels (PCCVs) do not include features to protect the structure from forces such as explosive blasts. Therefore, we evaluated the internal blast-resistance of PSC structures using blast tests on bi-directionally prestressed tubular concrete members. The goal of the study was to examine structural behavior data after an internal detonation. Explosive charges (ammonium nitrate – fuel oil; ANFO) were detonated at the center of the mid-span of the concrete tube with a standoff distance of 1000 mm. The data acquired included blast pressure, deflection, strain, crack pattern, and prestressing loss. The data were used to calculate the internal blast charge weight required to cause a PCCV to fail and to calibrate a simulation program to be used commercially for internal blast simulations at real scale structure.

Damage assessment of prestressed concrete containment vessels behaviour under blast induced fire loading

Recently, explosions, collisions, and fires have occurred frequently around the world due to terror attacks, and impact accidents. Particularly, since the 9.11 terror attack, public anxiety heightened due to lack of safety in our society. The incidents can be viewed as examples of possible extreme loading scenarios that can occur in structures and infrastructures. Among all of structures and infrastructures, prestressed concrete containment vessels (PCCVs) are the most vulnerable structures from terrors and accidents. Therefore, in this study, finite element software LS-DYNA and MIDAS FEA, are used to evaluate of PCCVs applied with blast induced fire loading resistance. Since the blast test on a full-scale PCCV is not realistically possible, it is necessary to develop a precise simulation tool to accurately evaluate the damage level of a full-scale PCCV. This study aims to improve the accuracy of the simulation tool by calibrating numerical software using experimental test data. Then, the parametric study is conducted according to the explosive charge weight, standoff distance, and concrete compressive strength of a PCCV using calibrated blast and fire simulation tools. Based on the study results, the level of damage assessment to PCCVs applied with blast-fire loading can be precisely evaluated.

Study on failure mechanism of prestressed concrete containments following a loss of coolant accident

A loss of coolant accident (LOCA) is considered as a severe accident in the safety of nuclear power plant. LOCA has significant negative influences on the containment structures. Because the characteristics of temperature variation are instantaneous, the thermal field in the inner wall of the containment has a remarkably non-uniform distribution, which leads to complex mechanical behavior. In this study, the distribution of the thermal field of a prestressed concrete containment vessel (PCCV) at different times under a LOCA is analyzed. On this basis, the mechanical behavior of the PCCV under the coupling effect of thermal load and internal pressure are systematically investigated, and the failure mechanism and failure mode of the structure are revealed. The results show that the structure fails with a large deformation near the largest hole and evident expansion at the dome considering the thermal load. However, the deformation develops deficiently under the high temperature of the LOCA. Finally, design suggestions are proposed for a containment under thermal–pressure coupling action.

Failure mechanism of a prestressed concrete containment vessel in nuclear power plant subjected to accident internal pressure

The leakage of the internal gas could cause structural expansion and cracking of the containment structures in nuclear power plant (NPP). Predicting the ultimate internal pressure resistant capacity and investigating the failure mechanism for the containment structures above the design-basis accident pressure is of great importance. The structural model of a prestressed concrete containment vessel (PCCV) was established accurately by FE software ABAQUS. The tensioning process of prestressed tendons is simulated by the cooling method to establish initial stress of prestressed tendons. The mechanical behavior of the PCCV subjected to the internal pressure above the design-basis accident pressure is investigated in detail. The cracking internal pressure and ultimate internal pressure resistant capacity of the structure are obtained and the failure mechanism of the PCCV is revealed. The influence of prestressing of tendons, the steel liner and the reinforcements on the failure mechanism of the PCCV is revealed systematically.

Ultimate pressure bearing capacity analysis for the prestressed concrete containment

PWR nuclear power technology has been developed in China according to the experience feedback of the Fukushima accident and the global latest safety requirements, in which the double-containment design with hemisphere dome having larger free space is adopted. Ultimate pressure bearing capacity of the Prestressed Concrete Containment Vessel (PCCV) is analyzed in this study to provide technical support for development of Severe Accident Management Guidelines (SAMG) in nuclear power plants. Firstly, the finite element model of the PCCV is built, including the concrete, the rebars, the prestressed tendons, the steel liner, and penetrations. Combining of free-sweep mesh is adopted according to the characteristics of the containment structure. Proper mesh size is determined through mesh sensitivity analysis. Prestressing loss is calculated for four types of prestressed tendons, and decreasing temperature method is adopted in prestressing simulation. Temperature field of the containment is calculated, and stratified temperature method is adopted in temperature simulation. Ultimate pressure bearing analysis results show that, with the increase of internal pressure, the containment gradually expands outward, and the maximum stress and maximum radial deformation of the containment appear near the equipment hatch. When the internal pressure load reaches 1.26 MPa (g), the equivalent plastic strain of the steel liner in the right area of the equipment hatch is 0.15%. At this time, the concrete cracks on a large area, and the prestressed tendons do not yield.

Numerical modeling and simulation of a prestressed concrete containment vessel

This work addresses the numerical modeling and simulation of prestressed concrete containment vessels (PCCVs) using the damaged-plasticity model for concrete and accounting for its interactions with the steel materials (i.e., the steel rebars, liner plate and prestressed tendons). Specifically, the 1:4-scale PCCV model tested by the Sandia National Lab (SNL) is considered. For concrete a novel fracture energy based method is employed to produce the data for the softening curve and damage evolution law such that mesh size independent numerical results can be guaranteed. To facilitate the finite element modeling, the interactions between steel and concrete are indirectly modeled by modifying appropriately the stress-strain relations of the steel materials as in Hsu and Mo (2010). The SNL PCCV model is then numerically modeling and symmetrically investigated. The effects of various strategies in modifying the steel stress-strain relations are discussed. It is found that, in addition to the prestressed tendons, the interactions between the liner plate/steel bars and concrete play non-negligible roles in correctly predicting the limit capacity and ultimate failure mode of the PCCV model. The numerical results obtained from the presented method, i.e., the limit capacity, failure mode, deformations and strains around crucial locations, etc., agree well with the experimental data, illustrating its capability in modeling the mechanical behavior of the PCCV like structures.

Structural Health Monitoring (SHM) of Civil Structures

As newer and more reliable ways of construction were developed, civilization began to spread out further and retain functional infrastructure for longer periods of time.[...]