Accident Process Research Articles

Technical research on rapid source term calculation and prediction technology of nuclear accidents based on Bayesian network

ABSTRACT How to evaluate and predict potential source terms quickly and effectively is very important for emergency response. In this paper, the traditional forward analysis calculation based on deterministic method was combined with probability theory calculation, and a large number of typical accident sequences were calculated with severe accident analysis software to obtain data of source terms. According to expert knowledge base, probabilistic safety analysis, and other information, a model of nuclear power plant was established based on Bayesian network algorithm, so as to carry out researches on rapid source term calculation and prediction methods. Based on the Bayesian network model of a specific power plant and the pre-calculated source term results of typical accident scenarios, the best available knowledge and observation results of events were used to estimate the relevant typical source terms and their possibilities, which provide a strong basis for effectively grasping and predicting the accident process, quickly predicting source terms and release characteristics of radioactive materials, and quickly and accurately evaluating the radioactive consequences.

Bubble fragmentation characteristics during the injection of subcooled water jet into hot liquid pool

Bubble fragmentation and size distribution in hot and cold fluid jet interaction are fundamental for industries such as energy and metallurgy, especially for safety analysis after steam generator tube rupture (SGTR) accidents in lead-cooled fast reactors. The opaqueness to light of the molten lead pool makes it difficult to capture the gas-liquid interface behavior and thus lacks relevant data. In this paper, silicone oil was used instead of lead to simulate the injection process of the SGTR accident. Then the jet visualization experiments were carried out to investigate the bubble fragmentation characteristics. The visualization results show that the jet between the hot and cold fluids process is accompanied by strong thermal interactions, eventually leading to many bubbles dispersed in the high-temperature liquid pool. Secondly, four mechanisms of action affecting bubble size were elaborated in this paper, among which local vapor explosion is the primary mechanism of bubble fragmentation. Finally, the data revealed that bubble size presented a lognormal distribution, and the fragmented bubble size distribution was modeled. This study is promising to provide guidance for the bubble behavior characteristics after SGTR accidents in lead-cooled fast reactors.

Quantitative risk assessment of industrial hot work using Adaptive Bow Tie and Petri Nets

Hot work poses great hazards to industrial operation site. Although regulatory and guidance exist, accidents caused by hot work continue to occur. Risk assessment has proved to be an effective method for risk control. However, current studies paid less attention to the evolution process of industrial hot work accidents and the quantitative risk assessment seems to be insufficient. In this context, we aimed to perform comprehensive risk evolution analysis and quantitative risk assessment of hot work using adaptive bow tie (ABT) and Petri nets (PNs). The ABT model is improved to analyze deep causes, consequences, and their relationships. PNs are employed to conduct quantitative risk assessment. To address uncertainties, the triangular membership function and improved regional center method are proposed to calculate the confidences of all places and transitions in the PNs. The probabilities are finally obtained by data fitting method. The study found that the most likely consequence of hot work accident is near miss. The results also indicate that hot work accident prevention measures should emphasize on the isolation of workplace, combustible gases test, removal of combustible substances, job organization, and job training. Besides, emergency devices maintenance and emergency drilling are critical to prevent accidents from expanding.

아차사고를 통한 위험성(R)과 시간(t)의 특성곡선 유도와 분석에 대한 연구

The purpose of this study is to find the key factors to reduce the damage caused by accidents by expressing the correlation between risk (R) and time (t) for near-miss accidents as a curve through literature review and inducing it as a mathematical function. In other words, it is to investigate various near-miss accidents that occur in industrial sites based on key factors and use them as learning materials to reduce the damage of accidents with the strengthened individual capabilities of workers. In addition, a simulation experiment was conducted to increase the realism of the change in risk (R) according to time (t).
 The proceeding method is first expressed as a curve of risk (R) and time (t) according to literature review, and second, the stages of prediction → monitoring → response discussed in literature review are distinguished from the corresponding curve. Third, the time required for each step is reviewed through simulation, and fourth, a function with a curve similar to the corresponding curve is derived. Fifth, analyze the R-t characteristic curve through the function and review the key elements. Here, the meaning of the simulation experiment is to distinguish the stages of thinking from the theoretically obtained curve to the stages of prediction→monitoring→response, and to emphasize the importance of the time required for each stage.
 The result obtained through the risk function (R(t)) is, First, it is a method of preventive activities that reduce the size of the risk itself. Currently, in Korea, efforts are being strengthened to prevent accidents through risk assessment. Second, it is a method of responding to an accident by reducing the time required (Δt1) to reach the maximum risk. This is a key element to be found in this study based on the resilience theory, and the effectiveness of education can be enhanced by specifying the time required (Δt1) for the accident process.
 The conclusion of this study is that it is as important to strengthen the individual's ability to increase the size of b, that is, to improve judgment immediately after an accident, as much as to prevent accidents by reducing the size of a through function , ( 0 < t ≤ c ). Therefore, the way to strengthen individual capacity to reduce the damage caused by an accident is to add information on the time required (Δt1) in the near-miss investigation and use it as an educational material. This provides realistic help for recognition and judgment of individual thinking.

Dynamic risk investigation of urban natural gas pipeline accidents using Stochastic Petri net approach

The safety of urban gas pipelines is challenged by a series of adverse factors, and the unexpected accidents may pose a catastrophic threat to humans, the environment and assets. The existing studies mainly focused on causation investigation of natural gas pipeline accident, the dynamic evolution process of urban natural gas pipeline accident is still challenging task for accident prevention. To find out the unfavorable factors that cause accidents, this study presents a dynamic risk modeling of urban natural gas pipeline accidents using Stochastic Petri net (SPN). An SPN model of an accident evolution process is constructed based on the discrete events in an accident flowchart, and the critical places and transitions are evaluated through this model. Considering the slow development of the early events leading to accidents, the delay time of the transitions at this stage cannot be determined, Bayesian theory is used to dynamically update SPN model. Critical accident nodes and their occurrence probabilities are estimated, which are used to support the efficient risk management strategies. The gas explosion accident in Shiyan, Hubei, as a representative case is investigated, and the results show that pipeline corrosion, ignition sources, inefficient information feedback and unreasonable solutions are critical accident causations. The probabilities of critical accident nodes increase over time, which means that these factors need to be managed efficiently to prevent the accidents. The application shows that the model can be used as a tool for gas companies and governments to investigate urban gas pipeline accidents.

Construction and application of knowledge graph for grid dispatch fault handling based on pre-trained model

With the construction of new power systems, the power grid has become extremely large, with an increasing proportion of new energy and AC/DC hybrid connections. The dynamic characteristics and fault patterns of the power grid are complex; additionally, power grid control is difficult, operation risks are high, and the task of fault handling is arduous. Traditional power-grid fault handling relies primarily on human experience. The difference in and lack of knowledge reserve of control personnel restrict the accuracy and timeliness of fault handling. Therefore, this mode of operation is no longer suitable for the requirements of new systems. Based on the multi-source heterogeneous data of power grid dispatch, this paper proposes a joint entity–relationship extraction method for power-grid dispatch fault processing based on a pre-trained model, constructs a knowledge graph of power-grid dispatch fault processing and designs, and develops a fault-processing auxiliary decision-making system based on the knowledge graph. It was applied to study a provincial dispatch control center, and it effectively improved the accident processing ability and intelligent level of accident management and control of the power grid.

Risk Propagation Mechanism and Prediction Model for the Highway Merging Area

The merging area is one of the most accident-prone areas on highways. After an accident occurs, the risk will propagate along the main road over a certain range and time. Therefore, the study of the propagation mechanism of accident risk will help to quantify the driving risk in this region. An effective risk prediction model is important for improving traffic control measures in this specific area. In this study, simulation experiments were conducted in SUMO (Simulation of Urban Mobility) to obtain the accident and risk propagation data in merging areas. Firstly, the Gaussian plume model was optimized for the merging area situation to determine and divide the impact range of the accidents. Then, different accident scenarios in the merging area and downstream were simulated with different input flow rates to study the time and speed of risk propagation in the three-level affected areas. Finally, LSTM (long short-term memory) and RNN (recurrent neural network) models were built to predict the accident risk in the merging area. The results showed that the LSTM model had higher accuracy. This study provides an innovative insight into the propagation process of merging area accidents. It is of benefit to the development of post-accident control measures.

Experimental evaluation of vehicle braking efficiency considering the influence of tires

Problem. Checking the brake system of a vehicle is crucial in terms of assessing its operational safety, and performance indicators and permissible modes are determined by the state standards of Ukraine. However, there are challenges related to the accuracy and objectivity of evaluating the braking efficiency of a car. The coefficient of adhesion between the wheel and the road surface is the primary factor that significantly affects the braking dynamics of a vehicle. This coefficient constantly changes due to various factors such as road surface conditions, tire design and properties, tire effectiveness, and car speed. Assessing the impact of these factors on a car's braking performance is difficult. Goal. The aim of this study is to experimentally determine the influence of tire properties on vehicle braking efficiency by conducting a multifactorial experiment on cars of different brands with different types of tires. Methodology. The study employs the method of conducting braking tests under road conditions using the necessary equipment. Statistical data on braking efficiency parameters were collected from cars equipped with different tire brands. Experimental tests were conducted on Mazda 323F and Hyundai Elantra cars, using tires from various manufacturers such as Sava, Tigar, Nokian, and MICHELIN. The tests were performed on asphalt-concrete surfaces under dry and wet conditions, and the braking efficiency indicators were measured. Originality. The experiment revealed that the quality of the rubber used in car tires has a significant impact on their braking efficiency within a wide range. The deceleration of a category М1 vehicle can exceed the minimum requirements for braking efficiency, established by national and international standards, by 29-67%, depending on the tire brand. This research presents prospects for further development of experimental and statistical studies in this field, aiming to provide a better understanding of car braking efficiency parameters based on tire quality. Practical Value. The data obtained from this study are of practical importance for evaluating the effectiveness of car braking during expert investigations of traffic accidents. This enables experts to draw more objective conclusions about the accident process and determine the driver's ability to avoid such incidents.

FRAM-based causal analysis and barrier measures to mitigate dust explosions: A case study.

Both the number of dust explosion accidents and the resulting number of casualties have increased dramatically in recent years. To reduce this risk of dust explosions, we use the functional resonance analysis method (FRAM) to analyze the cause of the dust explosion accident at the Kunshan factory and propose barrier measures to prevent such accidents. The functional units that changed in the production system during the accident and how these functional units coupled to eventually cause the dust explosion were examined and explained. In addition, barrier measures were developed for functional units that changed during production and emergency systems defined to block the propagation of changes between functions and prevent resonance. Through case study, the identification of key functional parameters in both triggering the initial explosion and in then allowing its spread are key to define barriers to prevent a recurrence of such an event. FRAM uses system function coupling instead of traditional linear causality to explain the accident process, and develops barrier measures for changing function units, providing a novel thinking strategy and method for the analysis of accidents and their prevention.

Verification and validation (V&V) for fast reactor system analysis code FASYS

The fast reactor system analysis code FASYS is developed by CIAE for transient accident analysis in CEFR. By referring to the application scope of FASYS, the basic requirements of FASYS and PIRT in CEFR are established. A comprehensive verification and validation for the accuracy of FASYS is performed, which consist of bottom-up assessment, top-down assessment and uncertainty assessment. The bottom-up assessment applies the static analysis and dynamic analysis to verify the basic function of FASYS. The separate effect tests and integral effect tests are employed in the top-down assessment to validate the availability to simulate model and system. The calculated results confirms that the basic function and model in FASYS are reasonable and credible. The uncertainty assessment results show that FASYS can still calculate IET under the reasonable uncertainty of input parameters, indicating that the FASYS can simulate and analyze the transient accident processes of sodium-cooled fast reactor.

Large leakage sodium-water reaction accident analysis in a sodium-cooled fast reactor with paralleling steam generators

In modern sodium-cooled fast reactor (SFR) designs, paralleling steam generators (SGs) are used to improve the economy. However, large leakage sodium-water reaction (SWR) models were developed only for designs using one SG. It is necessary to derive a pressure wave propagation model with parallel channels. Thus, a detailed pressure wave propagation model based on conversion equations was derived and verified with experimental data in this study. Using the developed model, a large leakage SWR accident in the SFR with four parallel SGs was simulated. The accident process was analyzed, and the design was verified to accommodate a large leakage SWR. Sensitivity analysis of critical parameters on large leakages was simulated and investigated. The SG pipe area, rupture disk bursting pressure, failure of the rupture disk, and release pipe area were found to have significant influences on the maximum pressure. Thus, the findings of this study are valuable for SG designs and protection from large leakage SWR accidents.

Improvement of the Segment‐Valve Model for Solving the Valve Isolation Problem and Evaluating the Reliability of Water Distribution Networks

AbstractThe segment‐valve graph model is widely used in the reliable evaluation of water distribution networks (WDNs). However, as an undirected graph, a segment‐valve graph does not express the upstream‐downstream relationships between segments, which hinders finding valves that need to be closed when a pipe bursts and the water outage region. Therefore, in this paper, directed edges applied to a segment‐valve graph are introduced to demonstrate the downstream segments of critical segments, and an improved segment‐valve graph with flow directions is proposed. The improved model is used to solve the valve isolation problem and evaluate the reliability of WDNs. The results show that the improved model can determine that the valve needs to be closed more quickly when a pipe burst occurs. In addition, we improve the traditional classical indicators based on the segment‐valve graph model. The new indicators based on the improved model can reflect the actual impact and the disposal difficulty of pipe network accidents more accurately and clearly. The proposed method can play a critical role in accident processing and reliability analysis of WDNs.

A simulation-based optimization for deploying multiple kinds road rescue vehicles in urban road networks

In the rescue process of urban road traffic accidents, the decision-making support system is of great importance since it will affect the rescue response time, and the response time is used as an evaluation index of the system performance. A shorter response time can ensure that casualties are rescued timely and can help restore the road as soon as possible. This paper provides a decision tool for traffic accident rescue vehicles’ integrated deployment problem in urban areas. In order to better simulate the stochastic rescue requests, the time and space distribution of traffic, and the dynamic rescue process, a simulation optimization model is established. This model determines the optimal deployment plan for three kinds of road rescue vehicles, i.e., ambulances, wreckers, and sweepers, in several time intervals in one day. To find a better solution, we incorporate a particle swarm optimization (PSO) method into the simulation and optimization procedures. The proposed method is validated by a case study in Shanghai. Additionally, sensitivity analysis is included to study the effects of various parameters and to confirm effectiveness and efficiency of the proposed method. The numerical experiments indicate that simply increasing the number of road rescue resources does not always improve the efficiency of road rescue.

Systemic relations among the variables involved in occupational accidents of the nursing team in a psychiatric hospital

BackgroundThe occupational activities carried out in hospital environments pose occupational risks to professionals. In psychiatric hospitals, due to the characteristics of the patients treated, professionals are also subjected to other risks, such as physical aggression. ObjectiveThis research aimed to identify the systemic context, highlighting the cause-and-effect relationships that culminate in occupational accidents that occurred with the nursing staff in a psychiatric hospital in Brazil. MethodsThe current study is an applied research and was divided into three stages. First, the collection of data related to the case study was made and accidents were analyzed and occupational hazards were identified. In the second stage, from the collected information, occupational safety indicators were defined. Lastly, in the third stage, the qualitative aspect of System Dynamics was applied to perform the systemic analysis and to identify how the different variables were related. ResultsThe results showed that physical aggression was the main cause of accidents. Regarding safety indicators, while both the level of use of Personal Protective Equipment (PPE) by professionals and the high level of PPE protection were positive aspects, the level of training of professionals to use PPE was a negative aspect. The Causal Link Diagram (CLD) showed that the perception of risk influenced the level of use of PPE and those organizational measures influenced the accident rate. ConclusionIn conclusion, the systemic analysis of the system dynamics can optimize the diagnostic process of occupational accidents in psychiatric hospitals, and especially help to identify the cause and effect among the variables involved.

Research on energy loss characteristics during transient process of reactor coolant pump shaft stuck accident

After the stuck shaft accident (SSA), the unstable flow in the reactor coolant pump (RCP) will cause huge energy loss. In order to accurately elucidate the mechanism of energy loss in the pump, this paper realizes the total resistance matching and operating condition regulation of the system piping based on the isoflow cross-section method. A full three-dimensional simplified model of HPR1000 reactor coolant system (RCS) of three loops is established. And the transient flow inside the system is reproduced by numerical simulation method. The weak compressibility theory and entropy production theory are introduced to quantitatively analyze the energy loss characteristics of RCP Ⅰ in the accident loop under six typical operating conditions. The results show that: after the SSA, the flow rate and head of RCP I change abruptly in a short time, and then the change slows down gradually. The reverse flow in the accident loop starts to occur around 1 s, and the system reaches dynamic equilibrium again at 3 s. Comparing different operating conditions, the energy loss in the impeller and guide vane flow path is the most drastic. Due to the migration and development of the vortex, the energy losses of two components reach the maximum at TN0 and 0.5TQi, respectively, there is a peak misalignment phenomenon. When the liquid flow is positive, the energy losses are mainly concentrated in the working surface side in the impeller and guide vane passages, and the interference region of the two components. When the liquid flow is reversed, the energy losses are mainly concentrated the middle of the impeller passage and the interference region of the two components. During transient process of the SSA, the impact, vortex, flow separation, wall friction and other unstable flow is the internal cause of energy losses in the pump.

Simulation of scenario characteristics of LPG tank explosion accident and its contribution to emergency planning: A case study

Leakage and explosion of hazardous chemicals during road transportation can cause serious building damage and casualties, and adoption of highly-efficient emergency rescue measures plays a critical role in reducing accidental hazards. Considering a liquefied petroleum gas (LPG) transport tanker explosion accident that occurred in Wenling, Zhejiang Province, China on June 13, 2020 as example, this study proposes a risk assessment framework. This framework recreates the leakage and explosion of the accident process using FLACS v10.9, suggests plans for evacuation, describes the rescue areas of different levels, and explores the influence of environmental factors on the evacuation and rescue areas. The results show that simulated and predicted distributions of fuel vapour cloud concentration and explosion overpressure can provide a reference basis for rapid rescue activities; the characterization of the dynamic effects of wind speed, wind direction, and temperature with respect to the evacuation and rescue areas can be used as theoretical support for on-site adjustment of rescue forces. The role of obstacles can prevent the expansion of the evacuation areas under low wind-speed conditions, and the presence of highly congested obstacles determines the level of the rescue area. The results obtained are important for the risk analysis and the development of emergency rescue measures in case of explosion accidents associated with transportation of hazardous chemicals on high-hazard and high-sensitive road sections.

An integrated EDIB model for probabilistic risk analysis of natural gas pipeline leakage accidents

Natural gas pipeline construction is developing rapidly worldwide to meet the needs of international and domestic energy transportation. Meanwhile, leakage accidents occur to natural gas pipelines frequently due to mechanical failure, personal operation errors, etc., and induce huge economic property loss, environmental damages, and even casualties. However, few models have been developed to describe the evolution process of natural gas pipeline leakage accidents (NGPLA) and assess their corresponding consequences and influencing factors quantitatively. Therefore, this study aims to propose a comprehensive risk analysis model, named EDIB (ET-DEMATEL-ISM-BN) model, which can be employed to analyze the accident evolution process of NGPLA and conduct probabilistic risk assessments of NGPLA with the consideration of multiple influencing factors. In the proposed integrated model, event tree analysis (ET) is employed to analyze the evolution process of NGPLA before the influencing factors of accident evolution can be identified with the help of accident reports. Then, the combination of DEMATEL (Decision-making Trial and Evaluation Laboratory) and ISM (Interpretative Structural Modeling) is used to determine the relationship among accident evolution events of NGPLA and obtain a hierarchical network, which can be employed to support the construction of a Bayesian network (BN) model. The prior conditional probabilities of the BN model were determined based on the data analysis of 773 accident reports or expert judgment with the help of the Dempster-Shafer evidence theory. Finally, the developed BN model was used to conduct accident evolution scenario analysis and influencing factor sensitivity analysis with respect to secondary accidents (fire, vapor cloud explosion, and asphyxia or poisoning). The results show that ignition is the most critical influencing factor leading to secondary accidents. The occurrence time and occurrence location of NGPLA mainly affect the efficiency of emergency response and further influence the accident consequence. Meanwhile, the weight ranking of economic loss, environmental influence, and casualties on social influence is determined with respect to NGPLAs.

Evolutionary game and simulation analysis on management synergy in China’s coal emergency coordination

Once coal mine accidents occur, a series of chain reactions will bring radiation effects that are difficult to solve in the short term to the normal operation of the economy and society. Therefore, the post-disaster management of coal mine accident is particularly important. Coal mine emergency response involves many stakeholders, and it needs various regions, departments to achieve multi-agent, multi-level effective collaboration to ensure that the coal mine accidents are controlled as soon as possible. Local governments and coal mine enterprises are the main forces in the post-accident emergency management of coal mines, but the differences in their interest motives, preferences and cognitive structures make it difficult for the relevant emergency managers to make correct decisions in the complex accident management environment, therefore, the game relationship between conflict and cooperation among related subjects is explored based on the perspective of game theory. This study establishes a game model of coal mine accident response behavior between coal mining enterprises and local governments, and quantitatively adopts the method of numerical simulation analysis to conduct in-depth analysis of the influencing factors of their decision-making behavior. The results reveal that: 1) the establishment of an information sharing mechanism is an important condition for local governments to efficiently and quickly start the incident response process for coal mine accidents; 2) Under the proper supervision of local government, the impact of the reduction of emergency response cost on the active response of coal mining enterprises is more significant and direct, that is, The cost of emergency response is the decisive factor affecting the incident response work of coal mining company; 3) the establishment of emergency cost compensation mechanism and incentive mechanism should also be the focus of local governments in formulating emergency coordination policies in the future. This study provides scientifc and reasonable management suggestions in line with the actual situation of China and provides a useful reference for local government to formulate the optimal strategy for emergency coordination in coal mine emergencies, to improve the motivation of each coordinating subjects and to improve the current situation of emergency coordination in China’s coal mines.

CFD-based assessment and visualization of the failure consequences of LPG tankers

This paper presents a simulation analysis of the explosions following an LPG leak and visualizes the consequences of the accident to reduce the consequences of the LPG leak explosion. Firstly, this paper proposes a CFD numerical simulation-based method for visualizing the consequences of LPG tanker failure. The method combines satellite maps and CFD numerical simulation data to visualize the consequences of LPG leaks and explosions, taking into account the influence of obstacles on the danger range of leaks and explosions; Secondly, this paper applies the method to a liquefied petroleum gas accident that occurred in the Wenling section of the Shenhai Expressway and performs CFD numerical simulation on the accident process and visualizes the consequences of the accident. Therefore, this method can provide a theoretical reference for the prior prevention of LPG accidents and the analysis of the consequences of accidents, as well as certain practical guidance instructive.

Choroid Theory Guides the Theory of Cardiovascular Event Chain

The theory, cardiovascular disease is one of the most common clinical chronic diseases. Modern medicine has confirmed that cardiovascular diseases are caused by the long-term accumulation and deposition of various pathological products caused by a variety of causes, and most of them are non-specific. Cardiovascular events such as acute myocardial infarction and stroke mainly occur in the occurrence process of cardiovascular diseases and cerebrovascular accidents, so the pathogenesis of cardiovascular and cerebrovascular diseases is very complex and difficult to predict. Therefore, this paper carries out the corresponding discussion on it.