Shield Building Research Articles

Performance of SRC unequal-depth beam-column irregular joint in NPP under progressive collapse

The prototype structure of this study is taken from the main shield building of nuclear power plant (NPP) conventional island facilities. Emphasis is on steel reinforced concrete (SRC) unequal-depth beam-column irregular joints, studying their resistance to progressive collapse via analysis of two 1/5 scale irregular joints. Vertical monotonic loading tests were conducted on the joints, followed by numerical simulations to analyze their mechanical properties, failure modes, and progressive collapse resistance. Experimental analyses focused on irregular joint failure modes, central column load changes with displacement, beam deformations, strain variations in critical sections, and resistance mechanism development. Finite element (FE) software modeled these behaviors and was validated against experimental data. Then, according to the various beam section depths of the connected beams, this research applied the validated numerical models to examine the load-bearing capacity of the irregular joints. The results indicate that the damage of the unequal-depth beam-column irregular joint exhibits significant asymmetric characteristics. In terms of load performance, the performance of the irregular joint depends on the component performance of the shallow beam section. Within a certain range, the greater the height difference between the various beams, the greater the joint bearing capacity, but the stability of the bearing performance deteriorates. The fracture yield of H-shaped steel significantly reduces the bearing capacity, and it is recommended to reinforce shallow beams. Providing data reference for the design of the irregular joints has important practical significance.

Seismic fragility analysis of shield building considering strength ratio of mainshock and aftershocks

The shield building of the AP1000 nuclear power plant serves as a crucial protective barrier against radioactive substances. However, past research indicates that structures are susceptible to experiencing aftershocks, which may lead to unforeseeable damage and potential radioactive material leakage. To address this issue, a finite element model of the shield building was established with the damage indexes of the tensile and compressive damage selected for further model analysis. According to the fundamental theory of reliability, the traditional incremental dynamic analysis method was used to analyze the seismic fragility of the shield building by inputting mainshock and aftershock sequences with three strength ratios. The results indicate that the seismic fragility of shield building may be underestimated without considering the influence of aftershocks and the damage state presents an upward tendency as the strength ratio increases. However, the cumulative damage caused by aftershocks is unlikely to exceed the initial damage induced by the corresponding mainshock. Overall, the aggravation of the compressive damage is less pronounced than the increase of the tensile damage as the strength ratio increases.

Resistance of Gable Structure of Nuclear Island to Progressive Collapse in Conventional Island Shield Building of Nuclear Power Plants

The gable wall of the conventional island of a nuclear power plant carries various pipeline loads connecting the nuclear island and the conventional island. If the gable wall collapses and is damaged due to the progressive collapse of the main plant structure of the conventional island, it will directly threaten the safety of the nuclear island. Therefore, it is of great significance to systematically study the resistance of the gable structure of the nuclear island to progressive collapse for the safe operation of nuclear power plants. Based on the SAP2000 finite element analysis platform, this paper established a model of the reinforced concrete frame structure of the first span of the shield building on the conventional island of a nuclear power plant, including the gable. According to the alternate path method, the node displacement and bearing capacity responses were used to determine the critical components in the gable, and single column failures of the top four in importance were selected as different analysis conditions. Nonlinear static and dynamic methods were used to analyze the displacement, internal force change, hinge sequence of the gable structure on the side of the nuclear island, and the ability of the gable to resist progressive collapse. The analysis results showed that the gable structure of the nuclear island had good resistance to progressive collapse under four single column failure conditions, whether by nonlinear static or dynamic analysis, and the overall vertical displacement obtained by the nonlinear static analysis was larger than that obtained by the dynamic analysis.

Experimental and numerical studies on shield building on non-rock site

Fluid-structure interaction (FSI) and soil-structure interaction (SSI) affect the seismic response of third-generation pressurized water reactor (PWR) nuclear power plants on non-rock site. In this paper, two 1/50 scaled simplified models were designed and a series of shaking table tests were carried to study the seismic responses of models considering FSI and SSI effect. Dynamic characteristics, acceleration, strain, hydrodynamic pressure and experimental phenomenon of the two models were analyzed. Moreover, the numerical analysis was performed and numerical results were compared with test data. The results show that the presence of model soil reduces the system’s frequency, and the presence and sloshing of water reduce the seismic response of model structure. The reasonableness and feasibility of the method used for the numerical simulation is verified. This study could provide a reference for analyzing the seismic response of prototype structure of nuclear power plant.

Experimental and Numerical Studies of AP1000 Shield Building considering Fluid-Structure Interaction

The gravity cooling water tank is a remarkable structural feature of third-generation pressurized water reactor nuclear power plant. To investigate the influence of fluid-structure interaction (FSI) on the seismic response of the structure, this study designed two 1 : 50 simplified models of the AP1000 shield building. A series of shaking table tests were conducted to study the seismic responses with and without FSI effect. The natural frequency, acceleration, strain, and hydrodynamic pressure of the two models were analyzed, and the seismic reduction effect of the water tank was evaluated. Moreover, the test data were compared with the results of numerical analysis using the ABAQUS software. The results show that the presence of water and the sloshing of water reduce the natural frequency and seismic response of the model structure. Thus, the gravity cooling water tank has a certain seismic reduction effect. The simplified model of water sloshing can be used to analyze the seismic response of the shield building.

The Lord Howe Volcanic Complex, Australia: its geochemistry and origins

ABSTRACT The Lord Howe Volcanic Complex (LHVC) is part of a seamount chain associated with the detached continental crust of Zealandia. We present petrographic and geochemical data for the LHVC, including the first reported data for Balls Pyramid and the first trace element data for Lord Howe Island, clarifying the tectonic affiliation and general mantle source characteristics. Classification and discrimination diagrams based on concentrations and ratios of immobile elements, such as rare earth and high field strength elements, Th, Ti, Y, and Mg, show the LHVC comprises transitional to alkali basalts and at least two, and probably three, shield building complexes, consistent with an intraplate tectonic setting. Primitive-mantle normalised trace element patterns, variation in Dy/Yb for a restricted range of Dy/Dy*, Zr/Yb > 90, and variations in Zr/Hf and P2O5/TiO2 through the eruptive sequences indicate the mantle source may be a laterally heterogeneous enriched garnet peridotite that has undergone varying degrees of partial melting and carbonatitic metasomatism, both within the LHVC and along the Lord Howe Seamount Chain. The LHVC is thus an ideal natural laboratory for probing the probability of small intraplate volcanic fields originating via mantle plumes or from previously subducted slabs stagnating at the mantle transition zone.

Evidence for transitional and mildly alkalic eruptions during Hawai'i's dominantly tholeiitic shield-building stage: Insights from the Kulanaokuaiki Tephra (≥1.0 ka) at Kīlauea Volcano, HI

Vitric clasts from a marker horizon in the Kulanaokuaiki Tephra, deposited on the summit and flanks of Kīlauea Volcano, HI, during a prolonged period of explosive eruptions and low magma supply >1.0 ka, show unusual enrichments in alkalis relative to silica and in incompatible elements, in contrast with the volcano's dominantly tholeiitic shield-building lavas. The clasts are transitional basalts, with compositions near the tholeiitic-alkalic boundary (Macdonald and Katsura, 1964). Nearly uniform in composition across ∼200 km2, the clasts are the most proximal to the summit among rare occurrences of transitional and mildly alkalic shield-stage eruptions at Kīlauea. In contrast with the volcano's effusive shield-building style, stratigraphic evidence suggests the clasts were deposited in one of Kīlauea's most vigorous explosive eruptions in the past 2.5 ka—an episode punctuated by high fountaining along with an ∼12 km-tall ash plume. The tephra's composition is consistent with those of five unusual shield-stage Kīlauea lavas. All contain <50.0 wt% SiO2 and 3.0–4.0 wt% Na2O + K2O. All but one contain ≥0.70 wt% K2O, ≥3.0 wt% TiO2, and > 0.30 wt% P2O5. The transitional Kulanaokuaiki clasts also display elevated abundances and ratios of incompatible trace elements (e.g., ∼19 ppm La, La/Yb ∼ 8.6). Compositionally, these early shield-stage clasts and lavas resemble those erupted at the end of shield building at older Hawaiian volcanoes, attributed to lower degrees of partial mantle melting. Chemical constraints and extrinsic circumstances suggest that similar episodes of transitional and mildly alkalic volcanism will likely recur throughout shield building.

Seismic fragility assessment on the post-mainshock damaged shield building considering aftershock duration and damage ratio

Seismic fragility assessment on the post-mainshock damaged shield building considering aftershock duration and damage ratio

Petrogenesis of Lava from Christmas Island, Northeast Indian Ocean: Implications for the Nature of Recycled Components in Non-Plume Intraplate Settings

Lava samples from the Christmas Island Seamount Province (CHRISP) record an extreme range in enriched mantle (EM) type Sr-Nd-Pb-Hf isotope signatures. Here we report osmium isotope data obtained on four samples from the youngest, Pliocene petit-spot phase (Upper Volcanic Series, UVS; ~4.4 Ma), and four samples from the earlier, Eocene (Lower Volcanic Series, LVS; ~40 Ma) shield building phase of Christmas Island. Osmium concentrations are low (5–82 ppt) with initial Os isotopic values (187Os/188Osi) ranging from (0.1230–0.1679). Along with additional new geochemical data (major and trace elements, Sr-Nd-Pb isotopes, olivine δ18O values), we demonstrate the following: (1) The UVS is consistent with melting of shallow Indian mid-ocean ridge basalt (MORB) mantle enriched with both lower continental crust (LCC) and subcontinental lithospheric mantle (SCLM) components; and (2) The LVS is consistent with recycling of SCLM components related to Gondwana break-up. The SCLM component has FOZO or HIMU like characteristics. One of the LVS samples has less radiogenic Os (γOs –3.4) and provides evidence for the presence of ancient SCLM in the source. The geochemistry of the Christmas Island lava series supports the idea that continental breakup causes shallow recycling of lithospheric and lower crustal components into the ambient MORB mantle.

Seismic fragility analysis of nuclear shield building based on zoned structure

This paper focuses on the seismic fragility analysis of nuclear shield building. Combined with the characteristics of structural catastrophic damage, it is divided into 9 zones (RS-1, RS-2, RC-1 ∼ RC-7) along the height direction. An incremental dynamic analysis of 200 working conditions (PGA 0.3 g-2.1 g with an interval of 0.2 g) is carried out on the dynamic catastrophic behavior of the nuclear shield building. The seismic fragility analysis of nuclear shield building based on zoned and overall structure idea is compared and studied. The results show that the damage and failure of both the overall structure and the zoned structure are deepened as the PGA increases. In the light damage state and extended damage state (especially the latter), the overall structure has a lower failure probability of the tension and compression damage than the zoned structure (such as RC-1 ∼ RC-4 and RC-7). Based on the zoned structure, the seismic fragility analysis demonstrates that the nuclear shield building with shear failure characteristics has different damage state for each zone, which can effectively show the failure mode and provide a more accurate assessment basis for the damage state and the failure mode of such structures.

Seismic fragility analysis of nuclear power plants based on the substructure method

This paper focuses on seismic fragility analysis of the AP1000 Nuclear Power Plant (NPP) with a substructure (SUB) model. To improve the efficiency of the analysis and calculation, this study treats the steel vessel containment (SVC) and equivalent equipment as a substructure and connects them with the residual structure to form an SUB model. The SUB model is verified to determine its rationality. Based on the verified model, 160 working conditions are calculated, and an incremental dynamic analysis (IDA) is performed. The AP1000 NPP is divided into 11 zones and 6 layers to investigate the seismic fragility analysis in detail. The results illustrate that (i) the calculation time of the SUB model is reduced by 1/4 compared to that of the full finite element model of the AP1000 NPP (FULL model) under the premise of ensuring calculation accuracy; (ii) the divided zones provide an accurate judgment basis for the failure mode and damage state directly; (iii) for the reinforced concrete shield building (RCSB), the damage gradually expands upon a sudden change in structural stiffness at the upper junction of the reinforced concrete auxiliary building (RCAB); (iv) seismic fragility analysis of the RCAB presents the form of gradual reduction of damage from the upper layer to the lower layer.

Comparative analyses of a shield building subjected to a large commercial aircraft impact between decoupling method and coupling method

Comparative analyses of a shield building subjected to a large commercial aircraft impact between decoupling method and coupling method are performed in this paper. The decoupling method is applying impact force time-history curves on impact area of the shield building to study impact damage effects on structure. The coupling method is using a model including aircraft and shield building to perform simulation of the entire impact process. Impact force time-history curves of the fuselage, wing and engine and their total impact force time-history curve are obtained by the entire aircraft normally impacting the rigid wall. Taking aircraft structure and impact progress into account some loading areas are determined to perform some comparative analyses between decoupling method and coupling method, the calculation results including displacement, plastic strain of concrete and stress of steel plate in impact area are given. If the loading area is determined unreasonably, it will be difficult to assess impact damage of impact area even though the accurate impact force of each part of aircraft obtained already. The coupling method presented at last in this paper can more reasonably evaluate the dynamic response of the shield building than the decoupling methods used in the current nuclear engineering design.

Nyiragongo and Nyamuragira: a review of volcanic activity in the Kivu rift, western branch of the East African Rift System

Nyiragongo and Nyamuragira are two active volcanoes of the Western branch of the East African Rift in the Virunga area. They were built at the Kivu rift axis ca. 12,000 years ago and set above two tectonic steps separated by the Kameronze Fault. Both volcanoes have displayed a succession of intra-crater and flank eruptions that have been observed and documented since the end of the nineteenth century. Here, we have collated and reviewed these publications and reports. Nyiragongo is famous for its semi-permanently active lava lake, which at the time of writing (2020) was the largest in the world. During the construction of the main stratovolcano, which ended a few centuries ago with a caldera collapse, the lava composition changed from melilitite to leucite and then to melilite-bearing nephelinite. The historically active lava lake is believed to be directly fed from an upper intra-volcano reservoir, a shallow reservoir situated a few kilometres below the volcano in the granite basement, and a deeper intra-crustal magma chamber. Historic activity has been documented since 1894 and can be divided into eight stages, on the basis of sudden changes between lava filling and draining, with cycles of rising lava lake activity and overflows, followed by sinking and complete or partial drainage. Twice in recent history (in 1977 and 2002), major flank eruptions were accompanied by complete drainage of the lava lake and the upper plumbing system. The lava that filled the crater since 1948, and then again after the 1977 and 2002 drainage events have been calculated at a cumulative volume of around 324 × 106 m3. In comparison, the 1977 and 2002 flank eruptions involved 47 × 106 m3 of lava. The average annual output rate associated with crater filling is thus estimated at between 4 and 13 × 106 m3. Lava lake behaviour changes from equilibrium, with alternation between gas pistoning and spattering regimes through disequilibrium with intermittent activity, to complete disappearance of the lava lake. These changes can be related to the conditions of the descent of dense degassed magma from the upper conduit into the shallow reservoir. However, since 1959, the chemical composition of the leucite and melilite-bearing nephelinite lavas has not significantly changed, which implies a magma supply from the same magma batch. Nyamuragira was characterised by a shield building phase of activity until a caldera collapse, ca. 300 to 500 years ago. The post-caldera phase has involved effusive activity in the caldera and at numerous flank fissures. The plumbing system consists of an upper reservoir roughly at the basement-volcano interface and averaging a volume of 400 × 106 m3, a shallow upper-crust stratified reservoir, and a middle-crust mafic magma chamber. Volcanic activity has involved a succession of filling and emptying events at the upper reservoir. Lava volumes of historic eruptions reveal annual output rates averaging 14 × 106 m3 between 1901 and 1976, and 40 × 106 m3 between 1976 and 2012. A drastic increase in activity occurred in December 1976. This event coincided with the January 1977 flank eruption of Nyiragongo and resulted from a main tectonic event in the rift basement that improved the efficiency of magma ascent at both volcanoes. The historic lava composition can be related to six cycles of magma accumulation in, and withdrawal of, the upper reservoir from the shallow stratified reservoir. Similar magma storage and transport systems are known in many effusive systems: the Nyiragongo lava lake shares behavioural characteristics similar to those observed at Kilauea, Erebus, and Erta’Ale. At Nyiragongo and Nyamuragira, magma supply and persistent activity with sudden changes of the magma output rates in relation to tectonic events are also comparable with those of Kilauea, Piton de la Fournaise of Reunion island, and Mount Etna.

Research on the impact effect of AP1000 shield building subjected to large commercial aircraft

This study addresses the numerical simulation of the shield building of an AP1000 nuclear power plant (NPP) subjected to a large commercial aircraft impact. First, a simplified finite element model (F.E. model) of the large commercial Boeing 737 MAX 8 aircraft is established. The F.E. model of the AP1000 shield building is constructed, which is a reasonably simplified reinforced concrete structure. The effectiveness of both F.E. models is verified by the classical Riera method and the impact test of a 1/7.5 scaled GE-J79 engine model. Then, based on the verified F.E. models, the entire impact process of the aircraft on the shield building is simulated by the missile-target interaction method (coupled method) and by the ANSYS/LS-DYNA software, which is at different initial impact velocities and impact heights. Finally, the laws and characteristics of the aircraft impact force, residual velocity, kinetic energy, concrete damage, axial reinforcement stress, and perforated size are analyzed in detail. The results show that all of them increase with the addition to the initial impact velocity. The first four are not very sensitive to the impact height. The engine impact mainly contributes to the peak impact force, and the peak impact force is six times higher than that in the first stage. With increasing initial impact velocity, the maximum aircraft impact force rises linearly. The range of the tension and pressure of the reinforcement axial stress changes with the impact height. The perforated size increases with increasing impact height. The radial perforation area is almost insensitive to the initial impact velocity and impact height. The research of this study can provide help for engineers in designing AP1000 shield buildings.

Nonlinear Seismic Response Characteristics of CAP1400 Nuclear Island Structure on Soft Rock Sites

CAP1400 nuclear island structure is an advanced and novel nuclear power plant structure. In order to explore the seismic response characteristics of CAP1400 nuclear island structure on soft rock sites, a three-dimensional refined nonlinear seismic response analysis model was established for a soft rock foundation-nuclear island structure system using ABAQUS software. The influences of the input ground motion intensity and the frequency spectrum characteristics on the acceleration, relative displacement, and floor response spectrum, as well as the critical shear wave velocity of nonbedrock sites for CAP1400 nuclear island structure, were proposed. The results suggested that the increasing amplitude of the peak acceleration and relative displacement of nuclear island structure decreased as the soft rock site entered a nonlinear state, and the high-frequency components of the input ground motion became more abundant. Specifically, the earthquake response was the largest at the cooling water tank on the top of the shield building, which was the focus of the seismic research on nuclear island structure. Due to the influence of the ground motion frequency spectrum characteristics and the nonbedrock site effect, the peak acceleration, peak relative displacement, and acceleration response spectrum of the nuclear island structure showed different changing trends for the near-field and far-field ground motions. Based on the influence of the site shear wave velocity on the seismic response of nuclear island structure, it was recommended that the critical shear wave velocity of nonbedrock sites for CAP1400 nuclear island structure should be 1250 m/s, and the nuclear island structure-foundation dynamic interaction could be ignored at this time. The research conclusions could provide some technical support and theoretical basis for the construction and seismic performance research of CAP1400 and other nuclear power plants.

Seismic fragility analysis of nuclear power plant structure under far-field ground motions

This manuscript presents a fragility assessment to evaluate the effects of far-field earthquakes on the damage of the AP1000 nuclear island building (NIB), by using Incremental Dynamic Analysis (IDA) and Multiple Stripes Analysis (MSA) methods. Five categories of performance levels (PL), four limit states (LS) and the relative intensity measure (IM) having a high relation with the ground motion are defined to calculate the fragility of the AP1000 NIB under 15 earthquake sequences. A comparison of the results shows that the probabilities of minor damage, severe damage, and collapse damage for concrete are much higher than the reinforcement bar, which indicates that the fragility of concrete dominates the damage probability of the NIB. The fragility curves of the auxiliary building (AB) and shield building (SB) obtained by IDA and MSA are consistent with each other, but the distinction is mainly on the peak values or increasing ratio. Additionally, the probabilities of minor damage, moderate damage, severe damage and collapse damage of AB are less than the cases of SB. Lastly, the results also indicate that fragility curves are efficiently assessed and essential for risk assessments of the NIB.

Analysis of the impact of rock hardness on the seismic response characteristics of CAP1400 nuclear island structure

With the rapid development of the nuclear power industry, appropriate sites for nuclear power plants have become a scarce resource. The construction of a nuclear power plant is subject to stringent requirements of site selection, and it is necessary to ensure that the plant will have sufficient seismic resistance. In this study, targeting the CAP1400 nuclear island structure as the research object, a three-dimensional finite element model of the dynamic interaction between the nuclear island structure and the foundation is established by considering the nonlinear characteristics of rocks using ABAQUS software. Our objective is to analyse the impact of rock hardness on the acceleration, displacement and floor response spectrum of the nuclear island structure caused by earthquake based on a total of 4 types of rock foundations with different degrees of hardness. The results show that, with the increase of rock hardness, the acceleration of the nuclear island structure increases, the displacement decreases, while the peak of floor response spectrum increases and moves towards the short period (high frequency band) direction. The seismic response of the nuclear island structure increases with the increase of elevation, and the greatest level of response is observed at the cooling water tank of the shield building, which therefore should be targeted as the key for seismic design. For rock foundations with high hardness, the seismic design for the nuclear island structure can follow the standard for rigid foundations so as to ignore the effect of the soil-structure dynamic interaction.

A Study on the Transport Reinforcement of the Whole Ring Cylinder of the Shield Building Cylindrical Wall (SC) based on Finite Element Analysis

The Shield Building Cylindrical Wall (referred to as SC below) is a large still ring cylinder. As an important part of the shielding construction of CAP1400, it was subjected to deformation during trassnsportation due to its relatively thin wall, a large weight, and special shape. Therefore, it is necessary to analyze the influence on the rigidity, intensity, and stability of the cylinder of the vehicle’s start and brake, the wind load, and its self-weight so as to reinforce the weak position to avoid permanent deformation or cracking damage during transportation. In this paper, the finite element analysis software is used to simulate and analyze the transport load of the SC whole ring cylinder. Rational reinforcement research has been performed in accordance with its deformation trend.

Seismic fragility analysis of AP1000 SB considering fluid-structure interaction effects

AP1000 nuclear power plant has an advanced passive cooling system with a vast water tank located above the shield building, which may affect the seismic performance of the structure. This paper conducts a fragility assessment of shield building and considers the fluid-structure interaction (FSI) effect on the damage of the shield building. Arbitrary Lagrangian Eulerian algorithm is applied to calculate the FSI and eight cases of water levels are considered. Three different fragility analysis methods, namely linear regression, quadratic regression and truncated maximum likelihood estimation, are adopted for assessing the seismic vulnerability of shield building. It is indicated from the results that the regression and the truncated maximum likelihood estimation are close to each other. The maximum likelihood estimation not only can effectively save the computational cost, but also can assure the reasonable calculated results. It is observed that different water levels have the individual probabilities of failure, and case 6 has the smallest probability of failure with a more considerable seismic reduction, whereas the case 1 and case 2 have the higher failure probabilities. The fragility analysis framework can thus be applied for evaluating the vulnerability of shield building under earthquakes considering the FSI effect.

Seismic performance of base-isolated AP1000 shield building with consideration of fluid-structure interaction

Seismically-induced FSI effect on dynamic responses of AP1000 shield building with base isolation is focused in this study using numerical simualtion. The numerical model is firstly validated by comparison with existing experimental results, which is capable of simulating dynamic behaviors of the water partially-filled shield building with seismic isolation using high damping rubber (HDR) bearings. The influences of FSI on seismic performance of the base-isolated and base-fixed AP1000 shield building with various water levels and on the corresponding isolation effectiveness are comparatively explored in details. Results show that base isolation can reduce the fundamental frequency of the shield building and make it close to water sloshing frequency. It is necessary to ensure an reasonable isolation design to keep the fundamental frequency away from the sloshing frequency and then to avoid the water resonance. Seismic isolation can offer a substantial benefit for the earthquake-resistant design of the shield building even filled with different levels of water, because the structural primary resonance is effectively transformed to the sub-resonance by application of base isolation. Dynamic responses of base-isolated models are influenced significantly by FSI and an optimal water level ratio of 0.8 is suggested to achieve excellent seismic performance for such structures.