Nuclear Power Plant Buildings Research Articles

Incremental dynamic analysis of SRC frame-bent structures in CAP1400 NPP

Under the earthquake, the collapse or damage of buildings would result in significant casualties and economic losses. Especially when essential lifeline projects such as nuclear power plants and thermal power plants were affected by earthquakes, they also resulted in severe consequences, such as the paralysis of urban functions, delays in post-earthquake disaster relief, and social chaos. In this paper, the conventional island steam turbine main building of the CAP1400 nuclear power plant (NPP) in Shidaowan, Shandong Province was taken as the research object, and the seismic performance of the main building structure of the SRC frame-bent was studied by using the incremental dynamic analysis (IDA) method. Firstly, the dynamic characteristics of the substructure of the steel reinforced concrete (SRC) frame-bent main building structure were obtained by experiments. Then, the prototype structure model of the main building was established and verified with the experimental results. Finally, 15 natural ground motions were selected and the corresponding torsional components were calculated. With peak ground acceleration (PGA) and Sa (T1, ξ) as IM indicators, top displacement of structure (Dt) and maximum inter-story drift ratio (θmax) as engineering demand parameters (EDP) parameters, the IDA of the structure were carried out, and the IDA curve cluster and percentile curve of the structure under multidimensional ground motion were obtained. The results show that the discreteness of the IDA curve cluster with Dt-Sa index was relatively small compared with the other three groups; the discreteness of the IDA curve cluster with Dt-PGA as the index was large. In addition, the results of the IDA conducted on the SRC frame-bent main building structure with PGA as an intensity measure (IM) parameter were deemed more conservative.

Multidimensional Seismic Response Analysis of Large-Scale Steel-Reinforced Concrete Frame-Bent Structures in CAP1400 Nuclear Power Plant

Irregularity in the plane layout of a building structure and the vertical discontinuity of lateral resistance components could lead to torsion and result in the brittle failure of a structure. According to the characteristics of the conventional island main building of nuclear power plants, this paper focuses on the conventional island main building of the CAP1400 nuclear power plant (NPP) in Shidaowan as the research object. A prototype structure model of the main building was developed using ABAQUS software. The seismic response of the structure under multidimensional ground motion was studied by inputting the X-direction and Y-direction translational and torsional components of ground motion in ABAQUS. The results demonstrate that the overall transverse displacement of the structure under bidirectional ground motion was significantly higher than that under unidirectional earthquakes, which was about 20%. Under a multidimensional frequent earthquake, the transverse displacement of the structure increased by about 13% on average compared with that under a bidirectional earthquake; the longitudinal increase was the largest, at about 28%. Finally, the lateral displacement of each layer of the steel-reinforced concrete (SRC) frame-bent main building structure with few walls proposed in this article decreased by an average of about 17% compared to the traditional SRC frame-bent main building structure. The longitudinal displacement was reduced by about 14% compared to the traditional SRC frame-bent main building structure.

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.

An IT2FS-ANP- and IT2FS-CM-Based Approach for Conducting Safety Risk Assessments of Nuclear Power Plant Building Projects

This study proposes an approach for simultaneously treating fuzziness and randomness when conducting safety risk assessments of nuclear power plant building projects (NPPBPs). First, the interval type-2 fuzzy set (IT2FS) and analytic network process (ANP) were employed to establish an IT2FS-ANP method for modifying the solution for the weight vector and determining the mutual relationships between the assessment indexes and their weights. Second, the IT2FS and cloud model (CM) were used to establish the IT2FS-CM method to modify the solution for the expectation value. Third, the IT2FS-ANP and IT2FS-CM methods were combined to establish a model for ranking the safety risks and determining the overall safety risk level. Finally, the approach was applied to an NPPBP in northeast China to validate its applicability.

Effect of slab stiffness on floor response spectrum and fragility of equipment in nuclear power plant building

The floor response spectrum (FRS) is used to evaluate the seismic demand of equipment installed in nuclear power plants. In the conventional design practice of NPP structure, the FRS is simplified using the lumped-mass stick model (LMSM), assuming the floor slab as a rigid diaphragm. In the present study, to study the variation of seismic response in a floor, the FRSs at different locations were generated by 3-D finite element model, and the response was compared to that of the rigid diaphragm model. The result showed that the FRS significantly varied due to the large opening in a floor, which was not captured by the rigid diaphragm model. Based on the result, seismic fragility analysis was performed for the anchorage of a heat exchanger, to investigate the effect of location-dependent FRS disparity on the high confidence low probability of failure (HCLPF).

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.

Improvement in Runtime Speed for Frequency Domain Soil–Structure Interaction Analysis Using a Coarray Parallel Processing Technique

In this paper, we propose a new algorithm for introducing Coarray Fortran (CAF) into a program that dynamically analyzes the frequency domain in soil–structure interactions. This was implemented in KIESSI-3D, which is frequency domain soil-structure interaction analysis computer code based on finite and infinite element techniques, and the performance of analysis speed based on the number of images (or coarrays) and cores per image was evaluated. For the performance evaluation, we used examples of full-scale nuclear power plant buildings with a shallow foundation model as well as a deep foundation model. In terms of analysis speed, the new KIESSI-3D improved the analysis speed by an average of 2.78 times for the shallow foundation problem and 2.69 times for the deep foundation problem, compared with the existing KIESSI-3D, because of the new algorithm and CAF. Further, as the number of cores and the internal memory size in the computer systems increased, the efficiency of also parallel processing increased.

Research on terrain grids generation in computational fluid dynamics software

Traditional research of environmental impact of natural draft cooling tower in nuclear power plant is based on diffusion model or tunnel experiment, and with the development of modern mainframe computers and turbulence models, it is possible to use CFD method to simulate plume drift. The CFD software, due to its powerful computing ability, can simulate and display the plume drift more accurately. This paper presents an effective way of generating terrain grids which can be used in StarCD, a CFD software. The SRTM terrain data is obtained from internet and IDW interpolation method is used in the co-ordinates translation process. A powerful program named GridInter is developed using Fortran90 to convert terrain data to StarCD vertex file, terrain grids generation process in StarCD including nuclear power plant building grids combination is also introduced, this model can be directly used in the numerical simulation of plume dispersion.

Research of the Stress-Strain State for Steel Support Structures of Nuclear Power Plant Components under Seismic Loads

Seismic resistance of equipment and piping of nuclear power plant units is determined, particularly, by seismic resistance of their steel support structures. A significant number of these structures are located in the reactor building of nuclear power plants and belong to seismic resistance categories I and II. Therefore, such support structures of nuclear power plant equipment and piping, in general, shall perform their functions under seismic hazards that correspond to the safe shutdown earthquake and design-basis earthquakes, respectively.
 Steel support structures of serial equipment (piping valves, electric and pneumatic drives of piping and pump valves, expansion tanks, etc.) are often designed “on site” in the limited conditions of their actual location. Therefore, it is necessary to design steel support structures of a number of equipment taking into account the fact that it can be connected, in particular, to existing piping with their actual routing. In connection with the above, the research of operation for such support structures under seismic loads is relevant.
 The article presents the research results for the spectrum of natural oscillation frequencies of the equipment support structure, and the stress-strain state of the considered structure under seismic loads is determined. At the same time, the parameters during normal operation and maximum design basis accident at the nuclear power plant power unit are considered. The calculated combination of loads, which simultaneously includes two episodic impacts (maximum design basis accident and an earthquake) is considered.

Site characterization study with microtremor data: A case study at the West Borneo NPP potential site

ABSTRACTA site characterization using a microtremor measurement study was conducted at the West Borneo nuclear power plant (NPP) potential site as a preliminary feasibility study. This study measured the natural resonant frequency of soil and estimated the subsurface VS as prior information for the design planning of an NPP building foundation. The single station microtremor data were processed using the horizontal‐to‐vertical spectral ratio (HVSR) method to obtain the f0 and A0 values, and the array data were processed using the spatial autocorrelation (SPAC) method. The study area was classified based on the f0 and A0 values. Due to the unavailability of borehole data and limited array data, the HVSR curve was used to estimate the VS profile. The HVSR curve VS estimation was calculated using Rayleigh wave ellipticity inversion. The inversion results were constrained by VS profiles from SPAC and regional geology data to ensure that the inverted model was rational. It was demonstrated that the constrained inversion process could generate a rational subsurface model for Pantai Gosong's coastline. Based on the result, the feasible bedrock for the NPP building foundation was found at a depth of 40 m in the coastline area.

Impact-resistant design of RC slabs in nuclear power plant buildings

The concrete structures related to nuclear safety are threatened by accidental impact loadings, mainly including the low-velocity drop-weight impact (e.g., spent fuel cask and assembly, etc. with the velocity less than 20 m/s) and high-speed projectile impact (e.g., steel pipe, valve, turbine bucket, etc. with the velocity higher than 20 m/s), while the existing studies are still limited in the impact resistant design of nuclear power plant (NPP), especially the primary RC slab. This paper aims to propose the numerical simulation and theoretical approaches to assist the impact-resistant design of RC slab in NPP. Firstly, the continuous surface cap (CSC) model parameters for concrete with the compressive strength of 20–70 MPa are fully calibrated and verified, and the refined numerical simulation approach is proposed. Secondly, the two-degree freedom (TDOF) model with considering the mutual effect of flexural and shear resistance of RC slab are developed. Furthermore, based on the low-velocity drop hammer tests and high-speed soft/hard projectile impact tests on RC slabs, the adopted numerical simulation and TDOF model approaches are fully validated by the flexural and punching shear damage, deflection, and impact force time-histories of RC slabs. Finally, as for the two low-velocity impact scenarios, the design procedure of RC slab based on TDOF model is validated and recommended. Meanwhile, as for the four actual high-speed impact scenarios, the impact-resistant design specification in Chinese code NB/T 20012-2019 is evaluated, the over conservation of which is found, and the proposed numerical approach is recommended. The present work could beneficially guide the impact-resistant design and safety assessment of NPPs against the accidental impact loadings.

Assessment of spectrum-matched time histories for floor response spectra generation

The floor response spectra (FRS) are usually determined by time history analyses using spectrum-matched time histories. However, previous studies reported that spectrum-matched time histories may cause a biased estimate of FRS, which raises a challenge of FRS generation for nuclear power plant structures. The study focuses on resolving the challenge. We begin the study by discussing characteristics of amplitude-scaled and spectrum-matched ground motions for seismic design and analysis of nuclear facilities. Then, we explore the influence of spectral matching on the change of ground motion parameters. Using suites of amplitude-scaled and spectrum-matched ground motions, we determine FRS for examples of typical structures, and investigate how the change of ground motion parameters due to spectral matching affects the biased estimate of FRS. The investigation shows that, the change of damping scaling factor is remarkably correlated with the biased estimate of FRS. Thus, we propose the improved spectrum-matched time histories for floor response spectra generation. Taken a service building of nuclear power plants as an example, the study shows that, the improved spectrum-matched are adequate to achieve approximate unbiased estimate of FRS under different damping values.

Dynamic seismic analysis of nuclear power plant buildings and bearing stratum

Various approaches are used for simulating seismic loading and collaboration of a structure and a bearing stratum when carrying out dynamic seismic analysis in specialized software. In the present work, the kinematic parameters of various structures and bearing stratum were calculated using SCAD and STAR_T software. Seismic performance of a reference tower type supporting frame was calculated for 7 grade earthquake. As a result, the floor accelerograms were calculated, and the floor response spectra were built. The calculation results obtained by various methods and structure models were analyzed and compared.

Evaluation of design equations for out-of-plane shear strength of deep concrete sections in nuclear power plant buildings

Reinforced concrete walls in nuclear power plant buildings, which are generally more than one-meter thick, are typically designed to resist out-of-plane shearing force using concrete resistance only, namely, through-thickness shear reinforcement is not provided. Standard ASCE 43, which addresses design of safety-related nuclear facilities in the United States, references ACI 349 for design of reinforced concrete nuclear structures and components, with exceptions as deemed necessary. The code ACI 349–13, assumes, identically to ACI 318–08 and ACI 318–14, that the nominal shear stress capacity of longitudinally reinforced concrete sections is independent of cross-section depth: an assumption not supported by data. In the last revision cycle of ASCE 43, the ACI 349–13 design equation for concrete shear stress capacity was evaluated for conformance with the performance target of the standard, namely, a 98% or higher probability of exceedance, and found to be inadequate. A correction to the ACI 349–13 equation was developed and implemented in ASCE 43–19 to account for the effects of effective depth and longitudinal reinforcement ratio on concrete shear stress capacity. In parallel with the revision of shear provisions in ASCE 43, a size-effect modification factor, λs, was introduced in ACI 318–19 to account for the reduction in concrete shear stress capacity with increasing effective depth. In this paper, the technical basis for the correction factor included in ASCE 43–19 is developed and the ACI 318–19 equation is assessed to judge whether it achieves the ASCE 43 performance target. The assessment utilized the test data of longitudinally reinforced beams assembled by Reineck and his co-workers for slender sections (ratio of shear span-to-effective depth greater than or equal to 2.4) and non-slender sections (ratio of shear span-to-effective depth less than 2.4). For slender sections, the probability of exceedance of the ASCE 43–19 (ACI 318–19) design strength is greater than 98% (99%). For non-slender sections, the exceedance probabilities are greater than 99%. Because the ACI 318–19 equation meets the ASCE 43 performance target for both slender and non-slender sections, the correction invoked in ASCE 43–19 could be retired once ACI 349 adopts the shear provisions of ACI 318–19 for longitudinally reinforced concrete.

Residual seismic performance of damaged reinforced concrete walls

Structural engineers face a dilemma in assessing the residual seismic capacity of damaged buildings after an earthquake, especially for buildings with lightly to moderately damaged elements that might not need repair but require to be assessed for their performance in aftershocks and future major earthquakes. The main purpose of this paper is to investigate the influence of pre-damage levels on residual seismic capacity of reinforced concrete (RC) wall tests, by conducting quasi-static, cyclic loading tests of reinforced concrete shear walls. A comparison of the reduction in stiffness, deformation capacity, and strength to existing guidelines regarding residual seismic evaluation is investigated. This study presents experimental results of eleven ¼ scaled RC wall tests that were divided into three series based on the wall reinforcement ratio and the shape of the wall boundary elements. Within each series, the effect of four levels of initial damage on the wall performance was investigated. The specimens were designed to fail in shear to represent the shear walls in Onagawa nuclear power plant buildings in Japan. The results showed that no significant deterioration in ultimate strength and maximum deformation capacity due to slight to severe previous damage. RC walls with flange boundary elements had relatively greater stiffness degradation due to prior damage than walls with boundary columns.

Methodology for constructing digital twins in railway transport

Fourth industrial revolution covers all areas of human economic activity, including areas related to the design and operation of various products (nuclear power plant building, freight car, MEMS devices, etc.) throughout their entire life cycle. One of the main tools for digital transformation of industry to meet new competitive requirements is the Digital Twin, which is always built for a specific physical object. The introduction of digital twins technology into the life cycle of a freight car will increase economic efficiency throughout its life cycle.Effective use of the digital twin technology is possible only when an adequate virtual model of the space surrounding this physical object is created. In this regard, predicting the behavior of a structure during motion on the basis of a high-precision model of a digital twin of a physical object requires the creation of a virtual space in which a virtual operation area will be implemented, which provides the possibility of mathematical modeling of motion. To do this, it is necessary to create virtual stands and operation areas, where it will be possible to carry out numerical tests. Creation of a high-quality virtual space will drastically reduce the number of field tests carried out, and study the effect of a larger number of parameters on the performance characteristics of a physical object.Creation and use of digital twins is consistent with the goals, objectives and action plan of the Strategy for the development of transport engineering in the Russian Federation for the period up to 2030. The introduction of digital twins in railway transport, in particular in freight rolling stock, will make it possible to correctly assign the service life, overhaul times, and increase operational efficiency, collect information about the real load, etc. To maintain competitive advantages over other modes of transport, the transport industry needs to develop towards the introduction of elements of the fourth industrial revolution, including digital twins.

Some Aspects of International Cooperation in Environmental Issues in Nigeria

The paper discusses the issues of international cooperation on environmental issues in Nigeria: the role of international agreements in the field of environmental ecology; basic principles of international cooperation in the field of environmental protection; environmental education in Nigeria; principles of environmental project management; and a number of measures to reduce atmospheric pollution. The issues of coordination both between the state and between international organizations dealing with similar problems, as well as issues of mutually beneficial cooperation in the field of environmental ecology are considered in the research paper. The issues under consideration acquire particular relevance in connection with the discussion of the possibility of nuclear power plant building in Nigeria.

Seismic Response Characterization of Shear Wall in Auxiliary Building of Nuclear Power Plant

Seismic Response Characterization of Shear Wall in Auxiliary Building of Nuclear Power Plant

Damage and vibrations of nuclear power plant buildings subjected to aircraft crash part II: Numerical simulations

Investigations of large commercial aircraft impact effect on nuclear power plant (NPP) buildings have been drawing extensive attentions, particularly after the 9/11 event, and this paper aims to numerically assess the damage and vibrations of NPP buildings subjected to aircrafts crash. In Part I of present paper, two shots of reduce-scaled model test of aircraft impact on NPP were conducted based on the large rocket sled loading test platform. In the present part, the numerical simulations of both scaled and prototype aircraft impact on NPP buildings are further performed by adopting the commercial program LS-DYNA. Firstly, the refined finite element (FE) models of both scaled aircraft and NPP models in Part I are established, and the model impact test is numerically simulated. The validities of the adopted numerical algorithm, constitutive model and the corresponding parameters are verified based on the experimental NPP model damages and accelerations. Then, the refined simulations of prototype A380 aircraft impact on a hypothetical NPP building are further carried out. It indicates that the NPP building can totally withstand the impact of A380 at a velocity of 150 m/s, while the accompanied intensive vibrations may still lead to different levels of damage on the nuclear related equipment. Referring to the guideline NEI07-13, a maximum acceleration contour is plotted and the shock damage propagation distances under aircraft impact are assessed, which indicates that the nuclear equipment located within 11.5 m from the impact point may endure malfunction. Finally, by respectively considering the rigid and deformable impacts mainly induced by aircraft engine and fuselage, an improved Riera function is proposed to predict the impact force of aircraft A380.

Damage and vibrations of nuclear power plant buildings subjected to aircraft crash part I: Model test

Investigations of large commercial aircraft impact effect on nuclear power plant (NPP) buildings have been drawing extensive attentions, particularly after the 9/11 event, and this paper aims to experimentally assess the damage and vibrations of NPP buildings subjected to aircraft crash. In present Part I, two shots of reduce-scaled model test of aircraft impacting on NPP building were carried out. Firstly, the 1:15 aircraft model (weighs 135 kg) and RC NPP model (weighs about 70 t) are designed and prepared. Then, based on the large rocket sled loading test platform, the aircraft models were accelerated to impact perpendicularly on the two sides of NPP model, i.e., containment and auxiliary buildings, with a velocity of about 170 m/s. The strain-time histories of rebars within the impact area and acceleration-time histories of each floor of NPP model are derived from the pre-arranged twenty-one strain gauges and twenty tri-axial accelerometers, and the whole impact processes were recorded by three high-speed cameras. The local penetration and perforation failure modes occurred respectively in the collision scenarios of containment and auxiliary buildings, and some suggestions for the NPP design are given. The maximum acceleration in the 1:15 scaled tests is 1785.73 g, and thus the corresponding maximum resultant acceleration in a prototype impact might be about 119 g, which poses a potential threat to the nuclear equipment. Furthermore, it was found that the nonlinear decrease of vibrations along the height was well reflected by the variations of both the maximum resultant vibrations and Cumulative Absolute Velocity (CAV). The present experimental work on the damage and dynamic responses of NPP structure under aircraft impact is firstly presented, which could provide a benchmark basis for further safety assessments of prototype NPP structure as well as inner systems and components against aircraft crash.