Loss Of Accident Research Articles

VVUQ of a thermal-hydraulic multi-scale tool on unprotected loss of flow accident in SFR reactor

Within the framework of the French 4th-generation Sodium-cooled Fast Reactor safety assessment, methodology on VVUQ (Verification, Validation, Uncertainty Quantification) is conducted to demonstrate that the CEA's thermal-hydraulic Scientific Computation Tools (SCTs) are effective and operational for design and safety studies purposes on this type of reactor. This VVUQ-based qualification is a regulatory requirement from the French Nuclear Safety Authority (NSA). In this paper, the current practice of VVUQ approach application for a SFR accidental transient is described with regard to the NSA requirements. It constitutes the first practical, progressively improvable approach. As the SCT is qualified for a given version on a given scenario, the transient related to a total unprotected station blackout has been selected. As it is a very complex multi-scale transient, the SCT MATHYS (which is a coupling of the CATHARE2 tool at system scale, TrioMC tool at component scale and TrioCFD tool at local scale) is used. This paper presents the preliminary VVUQ application to the qualification of this tool on this selected transient. In addition, this work underlines some feedback on design and R&D aspects that should be addressed in the future to improve the SCT.

Reactor dynamic simulation to analyze possible scenarios after a spurious opening of the safety flapper valve of TRR during the normal operation regarding the inherently safety features and Design Extension Conditions (DEC) by using the RELAP5 code

LOFA is one of the most important PIE in nuclear reactors. For the pool-type research reactor, the safety flapper valve is usually located below the reactor core and have a very important rule on the reactor safety especially during the loss of the pump accident. In this paper, TRR has been simulated and analyzed against the spurious opening of the safety flapper valve during normal full power operation. First of all, the steady state parameters are successfully benchmarked against the operational data of TRR. Then, the reactor dynamic calculations are successfully benchmarked against a sophisticated experimental dynamic test to evaluate the reactor power changes due to reactivity feedback. Then three different types of possible scenario including both types of DBA and DEC are simulated and analyzed. Furthermore, inherently safety features are evaluated against temperature rises. Results indicate that if the anticipated emergency shutdown signal is triggered successfully, the reactor core remains safe against any physical damage. If the reactor reactivity control system is completely disabled, the inherently safety features of the reactor decrease the reactor power effectively via negative reactivity feedback and the reactor fuel assemblies remain safe again. But if the fault diagnosis system of the spurious opening of the safety flapper valve fails to detect the occurrence or it does not send the emergency shutdown signal, and at the same time, the automatic power regulation system keeps the normal operating conditions, the hot spot may reach to the fuel melting point just a few seconds after the accident occurrence.

Probabilistic Safety Analysis for Loss of Offsite Power Accident in Dual-units Nuclear Power Plant

In order to explore the risk assessment method of the multi-unit nuclear power plant site, this paper selects the dual-unit plant nuclear site to analyze lose off-site power accident. By combining and improving the single-unit ET/FT model, to establish the dual-unit ET/FT model. From the analysis of the accident sequence, it can be concluded that the common cause failure of equipment is the main challenge faced by the dual-units. Especially the RPC sub-channel in the reactor protection system and the failure of emergency diesel engine circuit breaker. As can be seen from the high proportion of core CD occurring simultaneously in both uints, it has a great significance to study the risk of mult-units sites.

Privacy Preserving Dynamic Provable Data Possession with Batch Update for Secure Cloud Storage

Cloud Server (CS) is an untrusted entity in cloud paradigm that may hide accidental data loss to maintain its reputation. Provable Data Possession (PDP) is a model that allows Third Party Auditor (TPA) to verify the integrity of outsourced data on behalf of cloud user without downloading the data files. But this public auditing model faces many security and performance issues such as: unnecessary computational burden on user as well as on TPA, to preserve identities of users from TPA during auditing, support for dynamic updates etc. Many PDP schemes creates computational burden either on TPA or Cloud User. To balance this overhead between TPA and User, this paper proposes Privacy-Preserving Dynamic Provable Data Possession (P2DPDP) scheme, which is based on ODPDP scheme. In ODPDP scheme, user relieves the burden by signing a contract with TPA regarding verification of his outsourced data. But this scheme generates computation overhead on TPA. To reduce this computation overhead of TPA, our P2DPDP scheme uses Indistinguishability Obfuscation (IO) with one-way function such as message authentication code to make a lightweight auditing process. P2DPDP scheme uses Rank-based Merkle Tree (RBMT) to support dynamic updates in batch mode which greatly reduces computation overhead of TPA. ODPDP lacks privacy which is maintained in P2DPDP using ring signature technique. Our experimental results demonstrate the reduced verification time and computation cost compared to existing schemes.

Research on Characteristics of Perpetrators and casualties in Road Traffic Accidents in China——Based on the panel data analysis of national traffic accidents from 2006 to 2019

Under the background of the rapid development of Internet technology, the emergence of Internet platform accelerates the industrial agglomeration. As a chain connecting the material circulation between industries, the rise of logistics industry is inevitable. As a key link of logistics industry, transportation, along with the rise of logistics industry, has led to an increase in traffic accidents year by year. Therefore, based on the national road traffic accident data from 2006 to 2019, this paper uses SPSS 26.0 to analyse the accident incidence, casualties and direct property loss indicators of different regions and occupation, and study the characteristics of perpetrators and casualties. The results show that the traffic accidents in the whole country show a downward trend, but they are unbalanced. Workers and farmers accounted for the largest proportion, but the death and injury rate showed a downward trend. Other showed an upward trend in the past five years, especially in the delivery industry. Future road traffic safety management should take corresponding measures to reduce the accident rate from the perspective of the development of related industries.

Study on Protective Effect of Different Kinds of Labor Protection Products in Power Supply Enterprises

Scientific and reasonable use of labor protection equipment can not only eliminate the economic loss of accidents, but also improve the efficiency of workers, and even improve the economic benefits of power supply enterprises. The evaluation of the protective effect of labor protective articles can provide reference for the equipment of labor protective articles. In this paper, starting from personal protection, a whole set of protective effect evaluation system is established from the aspects of protective ability, abrasion resistance and tear resistance, comfort and others according to the requirements of power supply protection, and then conduct empirical analysis to discuss the different protective effects of different types of protective articles. The results showed that protective clothing C and E with the best protective effect not only had higher anti-seepage and anti-penetration ability, but also had anti-static and anti-radiation ability, the protective effect of which is 36.9% than that of the worst one. Antis-eepage and anti-penetration ability can be used as the primary selection standard of protective clothing. When selecting protective products, if the economic conditions permit, choose a higher-priced protective product, and the protection effect is better. If there are special protection needs, such as protection shoes against cold or high temperature, you can choose protective products with special protective properties according to your needs. The results obtained can be used as a reference for different post protection products.

Гражданско-правовой принцип сотрудничества в доктрине континентального права: распространение за пределы договорных правоотношений

Introduction: the article analyzes the possibility of the civil law principle of cooperation being implemented in various types of relations under civil law. Traditionally, the cooperation principle is considered in both Russian and foreign literature as the principle of fulfillment of a contractual obligation or as a group of additional obligations imposed on the parties to the contract and arising from the good faith principle. A more detailed consideration of the idea if cooperation allows us to draw a conclusion about the feasibility of this principle in other types of relations under civil law. Purpose: to justify the possibility of the cooperation principle being implemented in civil law relations other than contractual relations, namely in property legal relations, pre-contractual legal relations, and obligations from causing harm (protective legal relations). Methods: general scientific dialectical method; special scientific methods such as the method of comparative law, the technical method, the legal-dogmatic method, the historical-legal method. Results: analysis of legal regulation of such relative legal relations as contractual, pre-contractual, and protective, as well as property legal relations as a form of absolute legal relations, has shown that the cooperation principle is successfully implemented in these types of legal relations. Therefore, it is possible to consider this principle to pertain to the branch of civil law as a whole. Conclusions: the cooperation principle performs two functions: first, based on this principle, it is possible to achieve the purpose of civil law relations in a more effective way; second, this principle serves as a mechanism to overcome unforeseen circumstances that prevent the purpose of legal relations from being achieved. These functions are carried out in all the types of legal relations considered: in contractual relations – when there arise obstacles to the performance of a contract not specified in the contractual provisions; in pre-contractual relations – when there arise obstacles to achieving the purpose of negotiations (i.e. conclusion of a civil law contract); in protective relations – when there is a risk of an increase in harm or a risk of inability to fully reimburse damage in a timely manner; in property relations – when there occurs an accidental loss of a thing by the rightsholder.

Analysis of Special Consequences and Losses of Equipment Accident in Thermal Power Plant

Many types of equipment in the thermal power plant has special risks. Once a safety accident occurs, it often causes special consequences and losses. The indirect losses are difficult to calculate in general due to the special property. In this paper, a calculation model was proposed, considering collateral production impact on upstream and downstream industries, the inconvenience impact on people’s electricity and gas supply, and social security panic by rapidly spreading to media and public opinion. An example of a main steam pipe burst accident in a thermal power plant was analysed. The ratio of indirect economic losses and direct economic losses was obtained. Results showed that the ratio value (35.4) was much higher than the value (4) of general industrial accident loss. The ratio value maybe even much higher if the internal medium of special equipment has strong toxic and harmful effects. It is quite important to make concerted efforts to manufacture, usage, management, inspection, safety monitoring, and scientific supervision, in order to detect and eliminate hidden dangers early and ensure the safe operation of special equipment.

Drivers’ workload measures to verify functionality of ferry boats boarding area

Functionality of a square used for ferry boats boarding has repercussions on safety and comfort of users, as well as on the efficiency of maritime transport. Inadequate use of the infrastructure causes driving errors followed by corrective manoeuvres, loss of time and potential accidents with consequences for community and the maritime transport compa-ny. The wide diversification of traffic components and payment methods are generally managed through a traditional horizontal and vertical signage system that does not refer to any current legislation. Therefore, the purpose of this research is to investigate driver's behaviour and the interaction that takes place between the latter and the environ-mental context. In particular, the authors focused on the study of the driver’s workload in a simulated environment, considering a users' sample and different driving scenarios inside the boarding area, concerning traffic conditions (isolated vehicle or presence of disturbing vehicles) and signs position. All this, in order to evaluate whether any change in a virtual context could bring real benefits to drivers, before being transferred to the real context. The results obtained, in terms of subjective workload and performance measures, have made it possible to judge the different solutions proposed in a simulated environment through synthetic indices referring to the entire boarding place or at certain parts of it. In this way, the manager can decide to change the circulation of the entire square or only some aspects of detail, such as some signals, in the event that they manifest an evident difficulty in the transfer of infor-mation. The use of the simulated environment allows greater speed in identifying the best solution, lower costs (avoid-ing the creation of a critical configuration for circulation) and greater user safety, since risky manoeuvres are identi-fied and corrected by the simulator. The proposed procedure can be used by managers for a correct arrangement of the signs, for the purpose of correctly directing the flows and maximizing the flow rate disposed of.

CFD simulation on the transient process of coolant mixing phenomenon in reactor pressure vessel

The emergency coolant cooling system (ECCS) is designed to inject coolant into reactor pressure vessel (RPV) during loss of coolant accidents, ensuring the sufficient coolant inventory in the nuclear reactor core. During this process, the cold water mixes with high temperature coolant in the primary loop, making the wall of RPV and cold legs suffer severe pressurized thermal shock (PTS) and threatens the integrity of primary loop. In this study, coolant mixing phenomena in the experiment UPTF, which is a 1/1 full-scale model of the PWR with four coolant loops in Germany, was studied numerically using the CFD software Fluent. The best practice guideline for coolant mixing study using CFD method in the reactor primary loop and RPV, including the suitable turbulent model, geometry simplification and mesh conditions, was concluded. The detailed three dimensional thermal hydraulic parameter distributions were achieved and the effect of coolant injection rates on the mixing process is also obtained. Results show that the mixing effect is enhanced due to the existence of reverse flow at the core entrance sections. The high injection rate provides more timely coolant supplement and reduces the possible core exposure time. However, as the injection rate increases, more intensive disturbance on the temperature and velocity fields appear, which is more likely to cause the thermal fatigue.

Посттравматический стресс и предшествующий травматический опыт в раннем взрослом возрасте

The paper presents the results of an empirical study of psychotraumatic experience in respondents of early adult age (20–35 years). Based on the generalization of the responses of the study participants (n = 509), a classification of potentially traumatic difficult life situations was developed and described. The most frequent traumatic events at this age were situations related to the loss of loved ones, life-threatening diseases, road accidents, and physical violence experienced. The relationship between the duration of the event and the intensity of signs of posttraumatic stress caused by the experience of this event was studied. Previous traumatic experience is also considered as a factor of intense actual experience of a traumatic event. It is shown that the more traumatic situations a person has experienced in the past, the more pronounced signs of posttraumatic stress and psychopathological symptoms they experience at present.

Numerical simulations of radioactive dust particle releases during a Loss Of Vacuum Accident in a nuclear fusion reactor

A loss of vacuum accident is one of the possible phenomena that may be triggered by off-normal events in nuclear fusion reactors, such as disruptions. After a break of the isolation system and the formation of a penetration line, the air flows inside the Tokamak due to the large pressure gradient, resuspending toxic and radioactive dust. At the end of the event, an over pressurisation of the vacuum vessel may occur due to inertia effects and the heating of the air through the first wall, that may have still high temperatures. Thus, air will flow from the inside to the outside, dragging the dust particles and involving a radiological and toxic release. This work aims to provide, by numerical simulations, an analysis of particle release as a function of main parameters that characterise the release: diameter of the penetration line, wall temperature and particle sizes. The numerical simulation is based in a one-way coupling. Starting from the simulation of the velocity, pressure and density fields of the continuous phase(air) by a monophasic compressible CFD model, the motion of the particles inside the vessel is simulated.

A sensitivity study of physical models using in RELAP5 code based on FEBA experimental data

In the thermal-hydraulic safety analysis, simulation results using thermal-hydraulic codes depend mainly on modeling the physical phenomena built-in the codes. These models are the equations, and empirical formulas developed based on matching them to experimental data or based on the assumptions, simplifications for solving theoretical equations. Therefore, it is recommended that these physical models need to take into account the uncertainty they cause. The sensitivity study is performed to investigate the influence of physical models on the calculation results during the reflood phase after the loss of coolant accident. It is allowable to choose the physical models that have the most significant influence on the calculation results. This study conducted a sensitivity analysis of physical models in RELAP5 code based on experimental data measured on the FEBA test facility. Sixteen physical models have been selected for sensitivity analysis to find the most important models that influence the calculation results. Based on two criteria, the maximum cladding temperature and the quench time, the sensitivity analysis results show that four physical models significantly impact the calculation result. Four chosen physical models are considered further in the next step of their uncertainty evaluation.

Study on the thermal hydraulic characteristics of a simulated pressurizer during the blowdown process

The small break loss of coolant accident (SBLOCA) is a typical accident studied by many researchers. However, blowdown characteristics of the SBLOCA have not received sufficient attention. In this study, an experimental system for simulating the inherent characteristics of a pressurizer during the blowdown process is built under a low-pressure condition, and a mathematical model for predicting the thermal–hydraulic characteristics during this blowdown process is established. The simulation results are compared with experimental results to verify the accuracy of the mathematical model; the simulation and experimental results were in good agreement. The effects of different nozzle diameters and different initial pressures on the thermal–hydraulic characteristics are analyzed according to these simulation and experimental results. The results show that the steam temperature and pressure in the heating container have a high decline rate during the early stage of the blowdown process, and the decline rate subsequently decreases and remains steady, while the water temperature during the blowdown process decreases steadily. During the blowdown process, the nozzle diameter and initial pressure have little effect on the steam temperature, water temperature, and pressure, but the decline rates of both the liquid level and mass flow exhibit an increasing trend as the nozzle diameter and initial pressure increase. Compared to the water temperature, steam temperature, and container pressure, the liquid level and mass flow are more appropriate parameters for predicting the characteristic parameters of the blowdown process.

Off-site consequence analyses of ISLOCA & MSGTR severe accidents in CANDU-6 plants using the WinMACCS code

For interfacing system loss of coolant accident (ISLOCA) and multiple steam generator tube rupture (MSGTR) sequences, which are reactor building (RB) bypass accidents in CANDU-6 type reactors, off-site consequence analyses were performed based on an optimization method for the WinMACCS input model that reflects CANDU-6 nuclear power plant design-specific and nearby site-specific features, with related sensitivity analyses performed for important variables. As a result of assessment, it was confirmed that there is exceedingly low early fatality risk in the unmitigated case from MSGTR and ISLOCA accidents. For cancer fatality risk, it was confirmed that the averaged risk from the RB bypass accidents in CANDU-6 plants sufficiently satisfies NSSC safety goal (1.0E−6/year). Sensitivity analyses found surface roughness to be the most influential parameter in the MSGTR accident, with other parameters confirmed to be insignificant considering uncertainty in the off-site consequence analysis. Through the sensitivity analyses, long-term improvement items related to surface roughness, dry deposition velocities, initial radioactive clouds, the domestic public protection measures model, and dose conversion factors were derived for future off-site consequence analyses. The proposed long-term improvements for the best-estimate analysis of off-site consequence are applicable to all similar CANDU plants and can provide valuable insights into Level 3 PSA.

2D and 3D numerical investigations of sodium boiling in sodium cooled fast reactor with MOX fuel and low sodium void reactivity effect during unprotected loss of flow accidents

• Behavior of SFR under ULOF simulated for Low Sodium Void Worth design. • No core melting simulated and stable boiling behavior predicted by both codes. • Different frequencies and amplitudes of boiling regimes with SIMMER and COREMELT. • 3D modeling performed with COREMELT confirms oscillating behavior and absence of core melting. • If confirmed by enough experimental evidence, could make safety demonstration of SFR more robust.

Safety Investment Decision Problem without Probability Distribution: A Robust Optimization Approach

Accidents occur frequently, causing huge losses to enterprises and individuals. Safety investment is an important means to prevent accidents, but how much to invest is a dilemma. Previous studies have assumed that the demand of safety investment follows some probability distribution. In practice, the distribution information of safety investment is usually limited or difficult to obtain, i.e., it is unknown. To deal with this kind of problem without a probability distribution, we construct the measures of marginal accident loss (MAL) and marginal opportunity loss (MOL) from the perspective of demand uncertainty. Robust optimization technology is utilized to establish three robust optimization models, which are the absolute robust models (ARM), deviation robust models (DRM), and relative robust models (RRM). The results of numerical analysis show that MAL is positively correlated with safety investment and MOL is negatively correlated with the uncertainty of safety investment. The above robust optimization models in this study can be applied to different enterprise’s risk scenarios. ARM, DRM, and RRM are suitable for high- and nonhigh-risk industries and other industries, respectively.

The investment model of safety management in port enterprises and its analysis under uncertainties

Regulating the expenditures and capital investment in safety management is one of the effective ways to improve the level of safety in port enterprises. Such spending’s aims to reduce accident losses and improve productivity but capital investment is subject to uncertainties. This paper develops a safety management model taking into account investment uncertainties in operation and management conditions. A numerical simulations analysis based on this model shows that (1) the stability of operational safety delays the investment in safety management, and the amount of investment in safety management is reduced if the stability lasts for a long time, and (2) the stability of safety management conditions also delays the investment, but policy mandatory requirements and government subsidies offset these delays.

Договор лизинга по гражданскому праву Республики Узбекистан: особенности правового регулирования

в статье дано правовое определение договора лизинга на основе норм гражданского законодательства Республики Узбекистан, рассмотрены особенности договора финансовой аренды и форма его заключения; проанализированы существенные условия договора лизинга, а так же права и обязанности сторон – лизингодателя, лизингополучателя и продавца. Рассмотрен вопрос о возможных рисках, связанных с объектом лизинга, - риск случайной гибели или тайной порчи арендованного по лизингу имущества; риски, связанные с несостоятельностью продавца или несоответствием предмета лизинга целям его использования. Определены отношения об уступке лизингодателем и лизингополучателем своих прав третьим лицам. Рассмотрена ответственность сторон по договору лизинга. Сформулированы предложения по совершенствованию гражданского законодательства в области регулирования лизинговых отношений.

Characterization on the melting failure of CuCrZr cooling tube of W/Cu monoblocks during plasma operations in EAST

Abstract The behavior of ITER-like W/Cu plasma facing components under complex conditions in current tokamaks is one of the main concerns for ITER. EAST has installed a full upper W divertor with the ITER-like W/Cu monoblocks as targets since 2014. A melting failure of CuCrZr cooling tube of W/Cu monoblocks has occurred during the plasma campaigns in 2019. Due to the loss of cooling water, the leading edge-induced thermal loading can lead to the melting of both W armor and CuCrZr cooling tube, which has been confirmed by thermal simulation and analysis. With movement and migration of the melted Cu through gaps, the structure and function of the CuCrZr cooling tube for W/Cu monoblocks was severely destroyed. As a result, those failed W/Cu monoblocks had to be replaced. Such case in EAST just simulates the extreme condition of accidental loss of coolant in future devices. The melting failure of CuCrZr cooling tube was caused by operation without coolant water at largely misaligned monoblocks, which is a key lesson referenced to other tokamaks which adopt or plan to apply such type of W/Cu monoblocks.