Ultimate Pressure Capacity Research Articles

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.

A numerical approach for assessing internal pressure capacity at liner failure in the expanded free-field of the prestressed concrete containment vessel

Since containment building is the major shielding structure to ensure safety of nuclear power plant, the structural behavior and ultimate pressure capacity of containments must be studied in depth. This paper addresses ambiguous issue of determining free-field position for liner failure by suggesting an expanded free-field region and comparing internal pressure capacities obtained by test data, conservative assumption and suggested free-field region. For this purpose, a practical approach to determine the free-field position for the evaluation of liner tearing is carried out. The maximum principal strain histories versus internal pressure capacities among different free-field positions at various azimuths and elevations are compared with those at the equipment hatch as a conservative assumption. The comparison shows that there are considerable differences in the internal pressure capacity at liner failure within the expanded free-field region compared to the vicinity of the equipment hatch. Additionally, this study proposes an approximate correlation with conservative factors by considering the expanded free-field ranges and material characteristics to determine realistic failure criteria for liner. The applicability of the proposed correlation is demonstrated by comparing the internal pressure capacities of full-scale containment buildings following liner failure criteria according to RG 1.216 and an approximate correlation.

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.

Fragility analysis and probabilistic safety performance evaluation of nuclear containment structure under local prestressed tendons fracture conditions

Prestressed tendon in nuclear containment structure may occur unexpected fracture during the service life of the nuclear power plant. Fracturing of the prestressed tendon will pose great threat to the integrity of the nuclear containment structure. Based on detailed three-dimensional finite element model of the nuclear containment structure and reasonable constitutive model, this study presents fragility analysis and probabilistic safety performance evaluation of the nuclear containment structure under prestressed tendon fracture conditions. Change for the compressive stress state of the concrete and ultimate pressure capacity of the nuclear containment structure is discussed. Fragility curve and probabilistic safety margin of the nuclear containment structure under prestressed tendon fracture conditions is analyzed. Results indicate that for different types of fractured prestressed tendons, the influence of hoop prestressed tendons is greater than that of vertical prestressed tendon. Meanwhile, as for fracture locations, equipment hatch is the most vulnerable location. Ultimate pressure capacity of the containment structure decreases by no more than 2% under prestressed tendon fracture conditions considered in this study, which means that the impact for fracturing of the prestressed tendons on ultimate pressure capacity of the nuclear containment structure is small. Considering various uncertainties, 95% percentile pressure capacity corresponding to the most unfavorable fracture condition is 3.27 times the design pressure and it can meet the requirement that safety margin larger than 2.5.

Pressure capacity of sandwich pipe with cement-based core configuration under deep-water external pressure

Sandwich pipe, consisting of two steel tubes and a polymeric or cement-based material core layer, has been considered as an attractive solution for oil and gas transporting in deep water. In this paper, the characteristic responses and pressure capacity of sandwich pipes having fiber-reinforced cementitious composites core configuration under external hydrostatic pressure were investigated. The interface adhesion behavior between the fiber-reinforced cementitious composite core and the surrounding steel pipes was modeled based on the inter-layer shear strength test experiments conducted on the sandwich pipe specimens. The parametric studies were carried out to evaluate the influence of geometry parameters and steel grade on the buckling response and ultimate pressure capacity. Furthermore, 768 FE models of sandwich pipes covering a wide range of practical design configurations were rapidly constructed and analyzed using FE software package ABAQUS with the help of programming language Python. Finally, a simplified equation for predicting the pressure capacity of sandwich pipes within the scope of this study was proposed using dimensional analysis combined with singular value decomposition methodology.

Ultimate External Pressure Capacity of Deepsea Dented Pipeline with Combined Axial Compressive Force

As a common defect of deepsea pipeline, dents will weaken the residual strength of the pipeline. In this paper, nonlinear finite element method is adopted to investigate the collapse failure of deepsea dented pipeline under the combined external pressure and axial compressive force. The influence of the axial compressive force on the collapse pressure of dented pipelines with different diameter-thickness ratio and dent depth are investigated based on numerical simulation. It is concluded that relative large axial compressive force will reduce the collapse pressure capacity significantly for deep dent case.

Mechanical Behavior of Dented Steel Pipes Subjected to Bending and Pressure Loading

The presence of dents on steel pipeline wall may constitute a threat for pipeline structural safety. Experimental testing results supported by numerical simulations are reported, in an attempt to assess the structural integrity of smoothly dented (nongauged) steel pipes. Ten experiments on 6 in diameter X52 steel pipes are reported, where dented steel pipes are subjected to bending and pressure loading, in order to estimate their residual strength and remaining fatigue life. Six specimens were subjected to cyclic bending loading, whereas four dented pipe specimens, following cyclic pressure loading, have been pressurized to burst to determine their ultimate pressure capacity. Numerical simulation of the testing procedure and, in particular, the loading pattern of each specimen (denting and cyclic loading) has also been performed so that local stress and strain distributions at the dented region are calculated accurately. Based on the finite element results, a simple and efficient fatigue assessment methodology is adopted, to estimate the remaining fatigue life and the predictions were found to compare with the experimental results. Finally, following a parametric numerical study, strain concentration factors (SNCFs) for dented pipes subjected to bending are calculated, to be used in fatigue life assessment.

Ultimate pressure capacity of nuclear reactor containment buildings under unaged and aged conditions

Using ABAQUS, a non-linear finite element analysis (FEA) was performed to evaluate and compare the effects of degradation mechanisms by aging on the ultimate pressure capacity (UPC) of APR1400 reactor containment building (RCB). As the primary degradation mechanisms, prestress loss, concrete aging, rebar corrosion, and liner corrosion were simulated in the modelling and calculations. The results for unaged reactor containment buildings showed that the failure sequence by the internal pressure build-up consisted of 4 stages and reinforcement yielding strain of reinforced concrete would be the most important factor governing the UPC of RCBs. Among the four degradation mechanisms, corrosion occurring on the outer and inner rebar layers was identified as the main degradation mechanism affecting most significantly the ultimate pressure capacity of the APR1400 reactor containment building.

Nonlinear analysis of pre-stressed concrete containment vessel (PCCV) using the damage plasticity model

This paper describes the nonlinear analyses of a 1:4 scale model of a pre-stressed concrete containment vessel (PCCV). The analyses are performed under pressure and high temperature effects with considering anchorage details of liner plate. The temperature-time history of the model test is considered as an input boundary condition in the coupled temp-displacement analysis. The constitutive model developed by Chang and Mander (1994) is adopted in the model as the basis for the concrete stress–strain relation. To trace the crack pattern of the PCCV concrete faces, the concrete damage plasticity model is applied. This study includes the results of the thermal and mechanical behaviors of the PCCV subject to temperature loading and internal pressure at the same time. The test results are compared with the analysis results. The analysis results show that the temperature has little impact on the ultimate pressure capacity of the PCCV. To simulate the exact failure mode of the PCCV, the anchorage details of the liner plates around openings should be maintained in the analytical models. Also the failure mode of the PCCV structure hasn’t influenced by hoop tendons pre-stressing force variations.

Containment performance evaluation of prestressed concrete containment vessels with fiber reinforcement

Abstract Background Fibers in concrete resist the growth of cracks and enhance the postcracking behavior of structures. The addition of fibers into a conventional reinforced concrete can improve the structural and functional performance of safety-related concrete structures in nuclear power plants. Methods The influence of fibers on the ultimate internal pressure capacity of a prestressed concrete containment vessel (PCCV) was investigated through a comparison of the ultimate pressure capacities between conventional and fiber-reinforced PCCVs. Steel and polyamide fibers were used. The tension behaviors of conventional concrete and fiber-reinforced concrete specimens were investigated through uniaxial tension tests and their tension-stiffening models were obtained. Results For a PCCV reinforced with 1% volume hooked-end steel fiber, the ultimate pressure capacity increased by approximately 12% in comparison with that for a conventional PCCV. For a PCCV reinforced with 1.5% volume polyamide fiber, an increase of approximately 3% was estimated for the ultimate pressure capacity. Conclusion The ultimate pressure capacity can be greatly improved by introducing steel and polyamide fibers in a conventional reinforced concrete. Steel fibers are more effective at enhancing the containment performance of a PCCV than polyamide fibers. The fiber reinforcement was shown to be more effective at a high pressure loading and a low prestress level.

Ultimate analysis of PWR prestressed concrete containment under long-term prestressing loss

Numerical analyses are carried out by using the Abaqus finite element program to predict the ultimate pressure capacity and the failure mode of the PWR prestressed concrete containment at Maanshan Nuclear Power Plant, Taiwan, R.O.C. under long term prestressing loss. Material nonlinearity such as concrete cracking, tension stiffening, shear retention, concrete plasticity, yielding of prestressing tendon, yielding of steel reinforcing bar, yielding of liner plate and relaxation of prestressing tendon are all simulated with proper constitutive models. The results of the numerical analysis show that after the 40years of service, the prestresses in the prestressing tendons would lose about 19% of their initial values. However, under long term prestressing loss, the ultimate pressure capacity of the containment is still higher than the design pressure 482kPa by 58%.

Capacity assessment of concrete containment vessels subjected to aircraft impact

The paper describes the procedure and the results from the assessment of the vulnerability of a generic pre-stressed containment structure subjected to a large commercial aircraft impact. Impacts of Boeing 737, Boeing 767 and Boeing 747 have been considered. The containment vulnerability is expressed by fragility curves based on the results of a number of nonlinear dynamic analyses. Three reference parameters have been considered as impact intensity measure in the fragility curve definition: peak impact force (PIF), peak impact pressure (PIP) and Momentum over Area (MoA). Conclusions on the most suitable reference parameter as well on the vulnerability of such containment vessels are drawn. The influence of the aircraft impact induced damages on the containment ultimate pressure capacity is also assessed and some preliminary conclusions on this are drawn. The paper also addresses a conceptual design of a protective structure able to decrease the containment vulnerability and provide a preliminary assessment of the applicability of such concept.

Assessment of the Internal Pressure Fragility of the PWR Containment Building Using a Nonlinear Finite Element Analysis

Abstract In this study, the probabilistic internal pressure fragility analysis was performed by using the non-linear finite element analysis method. The target structure is one of the containment buildings of typical domestic pressurized water reactors(PWRs). The 3-dimensional finite element model of the containment building was developed with considering the large equipment hatches. To consider uncertainties in the material properties and structural capacities, we performed the sensitivity analysis of the ultimate pressure capacity with respect to the variation of four important uncertain parameters. The results of the sensitivity analysis were used to the selection of the probabilistic variables and the determination of their probabilistic parameters. To reflect the present condition of the tendon pre-stressing force, the data of the pre-stressing force acquired from the in-service inspections of tendon forces were used for the determination of the median value. Two failure modes(leak, rupture) were considered and their limit states were defined to assess the internal pressure fragility of target containment building. The internal pressure fragilities for each failure mode were evaluated in terms of median internal pressure capacity, high confidence low probability of failure(HCLPF) capacity, and fragility curves with respect to the confidence levels. The HCLPF capacity was 115.9 psig for leak failure mode, and 125.0 psig for rupture failure mode.

Shell finite element of reinforced concrete for internal pressure analysis of nuclear containment building

This paper describes a 9-node degenerated shell finite element (FE), an analysis program developed for ultimate pressure capacity evaluation and nonlinear analysis of a nuclear containment building. The shell FE developed adopts the Reissner–Mindlin (RM) assumptions to consider the degenerated shell solidification technique and the degree of transverse shear strain occurring in the structure. The material model of the concrete determines the level of the concrete stress and strain by using the equivalent stress–equivalent strain relationship. When a crack occurs in the concrete, the material behavior is expressed through the tension stiffening model that takes adhesive stress into account and through the shear transfer mechanism and compressive strength reduction model of the crack plane. In addition, the failure envelope proposed by Niwa is adopted as the crack occurrence criteria for the compression–tension region, and the failure envelope proposed by Yamada is used for the tension–tension region. The performance of the program developed is verified through various numerical examples. The analysis based on the application of the shell FE developed from the results of verified examples produced results similar to the experiment or other analysis results.

An Approach for Performance-Based Capacity Assessment of Prestressed Concrete Containment Vessels for Internal Accidents Application to VVER 1000 Containment Vessel

A direct procedure is proposed for capacity assessment of prestressed concrete containment structures subjected to internal accident loads. The assessment procedure is based on graphical comparison between the structural capacity and the load intensity by plotting both parameters in the same “temperature gradient – overpressure” coordinate system. Furthermore, the capacity in terms of structural integrity and leak tightness is evaluated, corresponding to different limit states or performance levels. A new damage index is proposed in order to correlate the intensity of damages on the containment structure with the load intensity. The criteria for leak tightness and structural integrity are adopted for VVER-1000 containment structure. The ultimate pressure capacity, the failure mode and the capacity corresponding to different performance levels of the containment structure are assessed. The influence of the temperature load on the structure response is also studied. Conclusions are drawn on the VVER-1000 containment vessel overpressure capacity and its response to different design basis and severe accidents. The main failure mode and the critical zones of the structure are also determined.

Experimental verification of capture coefficients for a cylindrical cryopanel of closed cycle refrigerator cryopump

A closed cycle refrigerator based cryopump of 1000 lit/s pumping speed for nitrogen was developed, using indigenously developed two stage GM-cryocooler at cryogenic section of Raja Ramanna Centre for Advanced Technology (RRCAT). Performance tests of cryopump were carried out to establish cool-down time, ultimate pressure, pumping speed, crossover rating, maximum throughput and gas capacity for nitrogen. This cryopump has successfully completed more than 4,000 hrs of operation. Capture coefficient or pumping efficiency for cylindrical cryopanel of this cryopump was calculated by method reported by J W Lee and Y K Lee. This method uses geometric view factors between surface elements of cryopump. The effect of cryopanel diameter on the pumping characteristics of the nitrogen (Type-II gas) was studied for this cryopump and experimentally verified by carrying out pumping speed tests of nitrogen with different cryopanel diameter in our laboratory. The calculated values of capture coefficients for this cryopump gave reasonably good agreement with the experimental values.

ANALYSIS OF PRESTRESSED CONCRETE CONTAINMENT VESSEL (PCCV) UNDER SEVERE ACCIDENT LOADING

This paper describes the nonlinear analyses of a 1:4 scale model of a prestressed concrete containment vessel (PCCV) using an axisymmetric model and a three-dimensional model. These two models are refined by comparison of the analysis results and with testing results. This paper is especially focused on the analysis of behavior under pressure and the temperature effects revealed using an axisymmetric model. The temperature-dependent degradation properties of concrete and steel are considered. Both geometric and material nonlinearities, including thermal effects, are also addressed in the analyses. The Menetrey and Willam (1995) concrete constitutive model with non-associated flow potential is adopted for this study. This study includes the results of the predicted thermal and mechanical behaviors of the PCCV subject to high temperature loading and internal pressure at the same time. To find the effect of high temperature accident conditions on the ultimate capacity of the liner plate, reinforcement, prestressing tendon and concrete, two kinds of analyses are performed: one for pressure only and the other for pressure with temperature. The results from the test on pressurization, analysis for pressure only, and analyses considering pressure with temperatures are compared with one another. The analysis results show that the temperature directly affects the behavior of the liner plate, but has little impact on the ultimate pressure capacity of the PCCV.

Ultimate analysis of PWR prestressed concrete containment subjected to internal pressure

Numerical analyses are carried out by using the ABAQUS finite element program to predict the ultimate pressure capacity and the failure mode of the PWR prestressed concrete containment at Maanshan nuclear power plant. Material nonlinearity such as concrete cracking, tension stiffening, shear retention, concrete plasticity, yielding of prestressing tendon, yielding of steel reinforcing bar and degradation of material properties due to high temperature are all simulated with proper constitutive models. Geometric nonlinearity due to finite deformation has also been considered. The results of the analysis show that when the prestressed concrete containment fails, extensive cracks take place at the apex of the dome, the junction of the dome and cylinder, and the bottom of the cylinder connecting to the base slab. In addition, the ultimate pressure capacity of the containment is higher than the design pressure by 86%.

Strengthening of BWR Mark III reinforced concrete containment with fibre composite laminate material

Zusammenfassung Numerical analyses are carried out by using the abaqus finite element program to predict the ultimate pressure capacity and the failure mode of the BWR Mark III reinforced concrete containment strengthened by composite materials or steel plates at various positions. Material non-linear behaviour for concrete, steel, and fibre composite laminate material are all simulated with proper constitutive models. It has been shown that the use of [±θ/90/0]5S composite materials with 50≤θ≤90° to strengthen the containment at the upper cylinder and the dome achieves the most satisfactory strengthening results. (The fibre angle of the lamina is measured counter-clockwise through the outward normal direction from the meridian of the containment shell structure.)

Inelastic stability of tightly fitted cylindrical liners subjected to external uniform pressure

The critical external pressure at which a thin cylindrical liner may buckle elastically has gained many researchers' attention. In contrast, the inelastic buckling pressure of thick cylindrical liners has never been examined thoroughly. A previous attempt was reported by Jacobsen who had limited the critical external pressure to the value that coincided with the onset of yielding of the most heavily stressed part of the cylindrical liner. The liner thickness-to-diameter and yield stress-to-Young's modulus ratios, both control the ultimate capacity of any liner. This paper presents a parametric study using the Finite Element Method (FEM), evaluates Jacobsen solution and provides charts that help in estimating the ultimate pressure capacity of such cylindrical liners.