Excitation Tests on Elbow Pipe Specimens to Investigate Failure Behavior Under Excessive Seismic Loads

2015 ◽  
Author(s):  
Izumi Nakamura ◽  
Naoto Kasahara
Keyword(s):  
Nuclear Power ◽  
Power Plants ◽  
Failure Modes ◽  
Safety Management ◽  
Dominant Frequency ◽  
Failure Behavior ◽  
Seismic Loads ◽  
Energy Agency ◽  
Piping Systems ◽  
Input Acceleration

After the accident at Fukushima Dai-ichi Nuclear Power Plant in the 2011 Great East Japan Earthquake, the International Atomic Energy Agency (IAEA) requires to consider the design extension conditions (DEC) for the safety management of nuclear power plants (NPPs). In considering DEC, it is necessary to clarify the possible failure modes of the structures and their mechanism under the extreme loadings. Because piping systems are one of the representative components of NPP, and there is a possibility to failure at seismic events, the authors conducted an experimental investigation on failure modes and their mechanisms of piping systems under excessive seismic loads. The experiments are categorized into the fundamental plate tests and pipe component tests. In this paper, the results of the pipe component tests would be described. In the pipe component tests, the authors used piping specimens constituted with one steel elbow and a weight. Though the input acceleration level was much over the allowable level to prevent collapse failure by the seismic design, the failure mode obtained by the excitation tests were mainly the fatigue failure. The reduction of the dominant frequency and the increase of the hysteresis damping were clearly observed in the high-level input acceleration due to the plastic deformation, and they affected the specimens’ vibration response greatly.

Excitation Tests on Elbow Pipe Specimens to Investigate Failure Behavior Under Excessive Seismic Loads

2017 ◽  
Vol 139 (6) ◽  
Author(s):  
Izumi Nakamura ◽  
Naoto Kasahara
Keyword(s):  
Nuclear Power ◽  
Failure Modes ◽  
Dominant Frequency ◽  
Failure Behavior ◽  
Seismic Loads ◽  
Experimental Stress ◽  
Safe Management ◽  
Piping Systems ◽  
Input Acceleration ◽  
High Level

The accident at the Fukushima Dai-ichi Nuclear Power Plant (NPP) resulting from the 2011 Great East Japan Earthquake raised awareness as to the importance of considering Beyond Design Basis Events (BDBE) when planning for safe management of NPPs. In considering BDBE, it is necessary to clarify the possible failure modes of structures under extreme loading. Because piping systems are one of the representative components of NPPs, an experimental investigation was conducted on the failure of a pipe assembly under simulated excessive seismic loads. The failure mode obtained by excitation tests was mainly fatigue failure. The reduction of the dominant frequency and the increase of hysteresis damping were clearly observed in high-level input acceleration due to plastic deformation, and they greatly affected the specimens’ vibration response. Based on the experimental results, a procedure is proposed for calculating experimental stress intensities based on excitation test so that they can be compared with design limitations.

Seismic Fragility of Piping Nozzles in Nuclear Power Plants: A Case for Updating the Current State-of-Practice

2021 ◽  
Author(s):  
Abhinav Gupta ◽  
Ankit Dubey ◽  
Sunggook Cho
Keyword(s):  
Nuclear Power ◽  
Power Plants ◽  
Seismic Analysis ◽  
Nuclear Industry ◽  
Life Extension ◽  
Seismic Loads ◽  
Thermal Loads ◽  
Loss Of Coolant Accident ◽  
Piping Systems ◽  
Recent Developments

Abstract Nuclear industry spends enormous time and resources on designing and managing piping nozzles in a plant. Nozzle locations are considered as a potential location for possible failure that can lead to loss of coolant accident. Industry spends enormous time in condition monitoring and margin management at nozzle locations. Margins against seismic loads play a significant role in the overall margin management. Available margins against thermal loads are highly dependent upon seismic margins. In recent years, significant international collaboration has been undertaken to study the seismic margin in piping systems and nozzles through experimental and analytical studies. It has been observed that piping nozzles are highly overdesigned and the margins against seismic loads are quite high. While this brings a perspective of sufficient safety, such excessively high margins compete with available margins against thermal loads particularly during the life extension and subsequent license renewal studies being conducted by many plants around the world. This paper focuses on identifying and illustrating two key reasons that lead to excessively conservative estimates of nozzle fragilities. First, it compares fragilities based on conventional seismic analysis that ignores piping-equipment-structure interaction on nozzle fragility with the corresponding assessment by considering such interactions. Then, it presents a case that the uncertainties considered in various parameters for calculating nozzle fragility are excessively high. The paper identifies a need to study the various uncertainties in order to achieve a more realistic quantification based on recent developments in our understanding of the seismic behavior of piping systems.

Investigation on Failure Behavior of Two-Elbow Piping System Models Made of the Simulation Material Under Excessive Seismic Loads

2020 ◽  
Author(s):  
Izumi Nakamura ◽  
Naoto Kasahara
Keyword(s):  
Failure Modes ◽  
Shaking Table ◽  
System Model ◽  
Failure Behavior ◽  
Piping System ◽  
Seismic Loads ◽  
Sinusoidal Wave ◽  
Additional Mass ◽  
System Models ◽  
Piping Systems

Abstract To investigate the failure behavior of piping systems under excessive seismic loads, shaking table tests on piping system models made of a simulation material have been executed. The simulation material adopted in the experiment was lead-antimony (Pb-Sb) alloy. The piping system model was composed of two elbows made of Pb-Sb alloy, one additional mass, and two fixed anchors. Input motions were sinusoidal wave. The failure modes of the piping system were examined by varying the additional mass and frequency of the input sinusoidal wave. Through the excitation tests, the failure mode which was named as “ratchet and subsequent collapse” was obtained successfully. The result which was classified as “no failure after 500 cycles” was also obtained. It was found that the occurrence of the failure depended on the ratio of the input frequency to the specimen’s natural frequency, and the ratio of additional mass weight to the limit mass weight. Though the effect of higher modes on the failure behavior was necessary to be more investigated, it seemed that the tendency of dominant failure behavior was similar to that of the single-elbow specimen investigated in the previous study. Moreover, it was confirmed that the experimental approach to use a simulation material was applicable for piping system model with multiple elbows.

Discussion On Failure Behavior of Piping Systems Under Extremely Large Seismic Loads in BDBE

2021 ◽  
Author(s):  
Izumi Nakamura ◽  
Naoto Kasahara
Keyword(s):  
Static Loading ◽  
Failure Modes ◽  
Shaking Table ◽  
Failure Behavior ◽  
Seismic Loads ◽  
Shaking Table Tests ◽  
Additional Mass ◽  
Pure Lead ◽  
Piping Systems ◽  
Loading Tests

Abstract To investigate the failure behavior of piping systems under severe seismic loads considering beyond design basis event (BDBE), an experimental approach to use pipes made of simulation materials was applied. "Simulation material" means the substitute material for steel to realize the structural experiment by the existing testing facilities. The simulation materials adopted in this study were pure lead (Pb) or lead-antimony (Pb-Sb) alloy. Using pipe elbows made of simulation materials, static loading tests on elbows and shaking table tests on simple piping system models composed of one or two elbows and an additional mass were conducted. From the static loading tests, the load-deflection relationship of an elbow under monotonic loading was obtained as well as the fatigue failure modes under cyclic loading depending on the several cyclic displacement levels. From the shaking table tests, several failure modes were obtained, namely, "Collapse by self-weight", "Collapse by a few cycles of input", "Ratchet and subsequent collapse", "Overall deformation", and "No failure". It was considered that the occurrence of these failure modes was affected by the ratio of the input frequency to the specimen's natural frequency, the ratio of additional mass weight to the limit mass weight, the configuration of the specimen, and the input acceleration level. The experimental results indicated that it was crucial to understand the structure's ultimate behavior when treating BDBE, and that the research approach using simulation material is effective to investigate the ultimate behavior of piping systems.

Failure Behavior of Piping Systems With Wall Thinning Under Seismic Loading

2004 ◽  
Vol 126 (1) ◽  
pp. 85-90 ◽  
Author(s):  
Izumi Nakamura ◽  
Akihito Otani ◽  
Masaki Shiratori
Keyword(s):  
Failure Modes ◽  
Low Cycle Fatigue ◽  
Three Dimensional ◽  
Seismic Loading ◽  
Shaking Table ◽  
Failure Behavior ◽  
Shaking Table Tests ◽  
Wall Thinning ◽  
Piping Systems ◽  
Input Acceleration

Shaking table tests of three-dimensional piping models with degradation were conducted in order to investigate the influence of degradation on dynamic behavior and failure modes of piping systems. The degradation condition induced in the piping models was about 50 percent full circumferential wall thinning at elbows. Four types of models were made for the shaking table tests by varying the location of wall thinning in the piping models. These models were excited under the same input acceleration until the models failed and a leak of pressurized internal water occurred. Through these tests, the change of the vibration characteristics and processes to failure of degraded piping models were obtained. The deformation of the piping models tended to concentrate on the degraded elbows, and the damage was concentrated on the weakest elbow in the piping models. The failure mode of the piping models was a low-cycle fatigue failure at the weakest elbow.

Failure Behavior of Piping Systems With Wall Thinning Under Seismic Loading

2002 ◽  
Author(s):  
Izumi Nakamura ◽  
Akihito Otani ◽  
Masaki Shiratori
Keyword(s):  
Failure Modes ◽  
Low Cycle Fatigue ◽  
Seismic Loading ◽  
Shaking Table ◽  
Failure Behavior ◽  
Vibration Characteristic ◽  
Shaking Table Tests ◽  
Wall Thinning ◽  
Piping Systems ◽  
Input Acceleration

In order to investigate the influence of degradation on dynamic behavior and failure modes of piping systems, shaking table tests of 3-D piping models with degradation were conducted. The degradation condition induced in the piping models was about 50% full circumferential wall thinning at an elbow or elbows. By varying the induced parts in the piping model, 4 kinds of models were made for the shaking table tests. These models were excited under the same input acceleration until the models failed and caused leak of pressurized internal water. Through these tests, the change of the vibration characteristic and the process to failure of degraded piping models were obtained. The deformation of the piping models tended to concentrate on the degraded elbows, and therefore the damage concentrated to a weakest elbow in the piping models. The failure mode of the piping models was a low-cycle fatigue failure at the weakest elbow.

Human reliability in non-destructive inspections of nuclear power plant components: modeling and analysis

2019 ◽  
Vol 7 (2B) ◽  
Author(s):  
Vanderley Vasconcelos ◽  
Wellington Antonio Soares ◽  
Raissa Oliveira Marques ◽  
Silvério Ferreira Silva Jr ◽  
Amanda Laureano Raso
Keyword(s):  
Power Plant ◽  
Nuclear Power Plant ◽  
Human Factors ◽  
Nuclear Power ◽  
Power Plants ◽  
Failure Modes ◽  
Cooling System ◽  
Human Reliability ◽  
Non Destructive ◽  
Plant Components

Non-destructive inspection (NDI) is one of the key elements in ensuring quality of engineering systems and their safe use. This inspection is a very complex task, during which the inspectors have to rely on their sensory, perceptual, cognitive, and motor skills. It requires high vigilance once it is often carried out on large components, over a long period of time, and in hostile environments and restriction of workplace. A successful NDI requires careful planning, choice of appropriate NDI methods and inspection procedures, as well as qualified and trained inspection personnel. A failure of NDI to detect critical defects in safety-related components of nuclear power plants, for instance, may lead to catastrophic consequences for workers, public and environment. Therefore, ensuring that NDI is reliable and capable of detecting all critical defects is of utmost importance. Despite increased use of automation in NDI, human inspectors, and thus human factors, still play an important role in NDI reliability. Human reliability is the probability of humans conducting specific tasks with satisfactory performance. Many techniques are suitable for modeling and analyzing human reliability in NDI of nuclear power plant components, such as FMEA (Failure Modes and Effects Analysis) and THERP (Technique for Human Error Rate Prediction). An example by using qualitative and quantitative assessesments with these two techniques to improve typical NDI of pipe segments of a core cooling system of a nuclear power plant, through acting on human factors issues, is presented.

Operating Reliability Assessment of FPGA-Based NPP I&C Systems: Approach, Technique and Implementation

2017 ◽  
Author(s):  
Eugene Babeshko ◽  
Ievgenii Bakhmach ◽  
Vyacheslav Kharchenko ◽  
Eugene Ruchkov ◽  
Oleksandr Siora
Keyword(s):  
Integrated Circuits ◽  
Nuclear Power ◽  
Power Plants ◽  
Failure Modes ◽  
New Technologies ◽  
Systems Approach ◽  
Reliability Assessment ◽  
Design Stage ◽  
Fpga Design ◽  
Operating Reliability

Operating reliability assessment of instrumentation and control systems (I&Cs) is always one of the most important activities, especially for critical domains like nuclear power plants (NPPs). Intensive use of relatively new technologies like field programmable gate arrays (FPGAs) in I&C which appear in upgrades and in newly built NPPs makes task to develop and validate advanced operating reliability assessment methods that consider specific technology features very topical. Increased integration densities make the reliability of integrated circuits the most crucial point in modern NPP I&Cs. Moreover, FPGAs differ in some significant ways from other integrated circuits: they are shipped as blanks and are very dependent on design configured into them. Furthermore, FPGA design could be changed during planned NPP outage for different reasons. Considering all possible failure modes of FPGA-based NPP I&C at design stage is a quite challenging task. Therefore, operating reliability assessment is one of the most preferable ways to perform comprehensive analysis of FPGA-based NPP I&Cs. This paper summarizes our experience on operating reliability analysis of FPGA based NPP I&Cs.

Nuclear Power Plant Fires and Explosions: Part IV — Water Hammer Explosion Mechanisms

2017 ◽  
Author(s):  
Robert A. Leishear
Keyword(s):  
Nuclear Power ◽  
Power Plants ◽  
Nuclear Power Plants ◽  
Nuclear Reactor ◽  
Water Hammer ◽  
Compression Process ◽  
Flammable Gas ◽  
Piping Systems ◽  
Fukushima Daiichi ◽  
Accident Conditions

Water hammers, or fluid transients, compress flammable gasses to their autognition temperatures in piping systems to cause fires or explosions. While this statement may be true for many industrial systems, the focus of this research are reactor coolant water systems (RCW) in nuclear power plants, which generate flammable gasses during normal operations and during accident conditions, such as loss of coolant accidents (LOCA’s) or reactor meltdowns. When combustion occurs, the gas will either burn (deflagrate) or explode, depending on the system geometry and the quantity of the flammable gas and oxygen. If there is sufficient oxygen inside the pipe during the compression process, an explosion can ignite immediately. If there is insufficient oxygen to initiate combustion inside the pipe, the flammable gas can only ignite if released to air, an oxygen rich environment. This presentation considers the fundamentals of gas compression and causes of ignition in nuclear reactor systems. In addition to these ignition mechanisms, specific applications are briefly considered. Those applications include a hydrogen fire following the Three Mile Island meltdown, hydrogen explosions following Fukushima Daiichi explosions, and on-going fires and explosions in U.S nuclear power plants. Novel conclusions are presented here as follows. 1. A hydrogen fire was ignited by water hammer at Three Mile Island. 2. Hydrogen explosions were ignited by water hammer at Fukushima Daiichi. 3. Piping damages in U.S. commercial nuclear reactor systems have occurred since reactors were first built. These damages were not caused by water hammer alone, but were caused by water hammer compression of flammable hydrogen and resultant deflagration or detonation inside of the piping.

Development of Ultimate Strength Evaluation Method for Piping Subjected to Seismic Loads

2013 ◽  
Author(s):  
Hideo Machida ◽  
Hiromasa Chitose ◽  
Tatsuhiro Yamazaki
Keyword(s):  
Power Plants ◽  
Evaluation Method ◽  
Failure Modes ◽  
Limit State ◽  
Seismic Loading ◽  
Earthquake Resistance ◽  
State Function ◽  
Limit State Function ◽  
Input Acceleration ◽  
Resistance Tests

This paper reports the results of the study on the failure modes and limit loads of piping in nuclear power plants subjected to cyclic seismic loading. By investigating the past fracture tests and earthquake resistance tests, it became clear that dominant failure mode of piping was fatigue, and the effect of ratchet strain was negligible. Until now, the stress generated with the acceleration of an earthquake was classified into the primary stress. However, the relationship between the input acceleration and the seismic response displacement of the pipe observed from earthquake resistance tests is non-linear, and increasing rate of displacement is lower than that of input acceleration in elastic-plastic stress condition. Therefore, the seismic loading can be treated as displacement controlled loading. To evaluate the reliability-based critical acceleration, a limit state function was defined taking the variations in the fatigue strength or some parameters into consideration. By using the limit state function, the reliability was evaluated for the typical piping of boiling water reactor (BWR) plants subjected to cyclic seismic loading, and a partial safety factors were calculated. Based on these results, a fatigue curve corresponding to the target reliability was proposed.

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