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• The TRACE 5.0 code was validated against the ATLAS C2.2 experimental data. • The validation includes the pre-test and the post-test calculation. • The ATLAS C2.2 test conducts a 13% IBLOCA in Cold Leg, with the Passive Emergency Core Cooling System. • The key thermal–hydraulic parameters were evaluated by TRACE simulation. TRACE 5.0 code was validated for simulating a 13% IBLOCA in Cold Leg 1A, with an emphasis on evaluating the Passive Emergency Core Cooling System, utilizing the ATLAS facility. Methodologically, after detailed comparisons of transient thermal hydraulic parameters with experimental data, TRACE model and condition were adjusted to reduce the discrepancy between simulation and experiment. ADV depressurization, Safety Injection Tank (SIT) flow rates, and break flow were main contributors impacting safety system activations and core water levels. The sensitivity studies in the simulation led to improved alignment with experimental results, providing enhanced insights into reactor behaviour during IBLOCA. The criticality of precise modelling techniques in accurately simulating nuclear reactor safety systems was undersored and a user dependence of TRACE code during the the validation process was also discussed. [ABSTRACT FROM AUTHOR]

The incorporation of phase change materials (PCMs) in buildings increases their thermal mass and hence improves thermal comfort through internal temperature stabilization. In this paper, the thermal performance of an active PCM system was compared with that of a passive system. Two identical test huts, each equipped with a control system were used to investigate the potential of passive and active systems for energy-saving and peak load shifting. One of the huts was equipped with PCM-impregnated wallboards, while the other hut was provided with active air-PCM heat storage units designed and fabricated at the University of Auckland. Both huts were cooled with an air conditioner or heated using both solar and electric heaters. For space cooling, the hut with active PCM consumed 8% more electricity to maintain comfort, although the energy storage capacity of PCM used was 50% less than that used in the active application. Over ten days in winter, the energy consumed in the hut provided with an active storage system was 22% less when both passive and active systems had the same amount of energy storage capacity. The investigation of peak load shifting showed 32% less in electricity cost when an active storage system was used. Image 1 • The performance of an active PCM system was compared with that of a passive system. • Active system showed a greater energy-saving and a more efficient peak load shifting. • 32% less electricity cost was achieved when an active storage system was used. • Active systems provide better level of control, and less adverse environmental impact. [ABSTRACT FROM AUTHOR]

• A wall system composed by a CO 2 -filled transparent insulation and PCM is evaluated. • A detailed mathematical model for thermal performance evaluation has been developed. • The proposed model has been validated with outputs from complex simulation tools. • The wall system has been modelled considering a Mexico City office as case study. • CO 2 as a gas filling insulation option presents the best technoeconomic potential. Novel thermal insulation materials and wall configurations have the potential to play a major role in reducing energy demand and carbon emissions from the building sector. In this study, a passive heating wall system composed by a CO 2 -filled transparent thermal insulation (TTI) and an organic phase change material (PCM), and a passive cooling system composed by a Tromble Wall with nano-film and a CO 2 -filled TTI are proposed and evaluated. The aim is to present a detailed analytical model for rapidly calculating thermal performance of the proposed wall configurations. As case study, a 108 m2 south façade of a building located in Mexico has been used. Outputs suggest that as a passive heating measure, the system has the potential to supply heat in the order of 118 W, 126 W, 134 W, and 157 W, during the months of December, January, February, and March respectively. Additionally, thermal performance and air velocity simulations suggest that for the heating case, considering an outdoor and indoor temperature conditions of 0 °C and 21 °C respectively, the internal layer surface reaches a temperature of 9.2 °C; while for the cooling case, considering outdoor and indoor temperature conditions of 25 °C and 21 °C respectively, it reaches 22.5 °C with a maximum indoor air velocity of 0.5 m/s. Compared to other gases, CO 2 could hold a greater potential due to its low thermal conductivity and capital costs. Large-scale implementation of such systems could make the building sector an interesting option as an artificial sink for carbon storage. [ABSTRACT FROM AUTHOR]

• The ELSMOR facility has been built to test a passive heat removal system. • ELSMOR test 00099_C has been selected to perform a code benchmark. • AC2, APROS, CATHARE, RELAP and TRACE codes have been adopted. The EU-funded ELSMOR (Towards European Licencing of Small Modular Reactors) project seeks to design methods and tools for stakeholders to assess and verify Light Water SMRs' safety when installed across Europe. Within the project, an experimental facility has been built at SIET (Piacenza, Italy) to test a passive heat removal system. The passive system is based on natural circulation, with a plate-type Compact Steam Generator (CSG) as heat source and an in-pool condenser as heat sink. An experimental campaign has been conducted to investigate the effect of different parameters on the passive system behavior (e.g. secondary side filling ratio, primary system temperature, pool level, presence of non-condensable gases, etc.). Among the various tests, ELSMOR test 00099_C has been selected to perform a code benchmark and ten parameters were selected for the code comparison. The chosen test explores the effect of the secondary side filling ratio from 60.16% to 24.96%. In the benchmark, the codes from the European reference chains have been applied, Apros by VTT, AC2 by GRS and CATHARE by CEA, and they have been compared with the results obtained with RELAP5 by ENEA and TRACE by PSI. In general, all the codes were able to predict the experimental data both from a qualitative and quantitative point of view. The main discrepancies have been observed in some results for the prediction of the secondary side pressure, secondary side CSG inlet temperature and secondary side flow rate. [ABSTRACT FROM AUTHOR]

The past decades have witnessed a growing interest in the knowledge acquisition of smart materials and their applications in different fields, especially in the field of architecture and building technology. Smart materials may not be relatively new, but researchers work to develop smart materials and compose a system that controls and guides the materials to create a living environment with more adaptive qualities and less negative impacts. The research aims to explore the qualities and advantages of smart material systems in the field of architecture, to better understand the impact smart material systems have on the design and construction processes, and to explore the way to create architecture with better adaptive characteristics, to ultimately reach the state of "adaptiveness", providing the optimal environment for the users, reflected on the structural, climatic, and architectural performances. [ABSTRACT FROM AUTHOR]

Abstract In this paper, we extend classical results on (i) signature symmetric realizations, and (ii) signature symmetric and passive realizations, to systems which need not be controllable. These results are motivated in part by the existence of important electrical networks, such as the famous Bott–Duffin networks, which possess signature symmetric and passive realizations that are uncontrollable. In this regard, we provide necessary and sufficient algebraic conditions for a behavior to be realized as the driving-point behavior of an electrical network comprising resistors, inductors, capacitors and transformers. [ABSTRACT FROM AUTHOR]

Abstract A battery thermal management system (BTMS) has become an essential part in battery-driven electric vehicles (EVs) in order to remove the generated heat from the battery which leads to enhanced performance. BTMSs have been implemented in EVs by adopting different technologies that include natural air cooling systems, forced air cooling systems, liquid cooling systems, and using heat pipes and fins. However, phase change material (PCM) embedded systems have gained a lot of attention due to their availability, low cost, and high sensible and latent heat in the field of BTMS. In the last two decades, thermoelectric coolers (TECs) have also been applied to BTMSs to make an active or semi-passive system with another cooling system. In this paper, a state of the science comprehensive literature review is presented on PCM (a passive system) and TEC (an active system) based BTMSs. A synthesis of the literature is presented in a tabular format to give a clear indication on the relative performances of the BTMSs. Moreover, limitations of the batteries, PCMs, and TECs are also discussed to identify the future research possibilities in the area of BTMS for EVs. Highlights • A comprehensive survey of PCM and TEC based BTMS has been presented. • This paper will help to develop a new configuration of BTMS in future. • This paper will help to identify the application fields of different PCM based BTMS. • This review provides a list of limitations which will help to do further research. • This paper will allow developing hybrid BTMS. [ABSTRACT FROM AUTHOR]

In a recent paper, it was shown that (i) any reciprocal system with a proper transfer function possesses a signature-symmetric realization in which each state has either even or odd parity; and (ii) any reciprocal and passive behavior can be realized as the driving-point behavior of an electric network comprising resistors, inductors, capacitors and transformers. These results extended classical results to include uncontrollable systems. In this paper, we establish new lower bounds on the number of states with even parity (capacitors) and odd parity (inductors) for reciprocal systems that need not be controllable. [ABSTRACT FROM AUTHOR]

Battery thermal management is necessary for electric vehicles (EVs), especially for Li-ion batteries, due to the heat dissipation effects on those batteries. Usually, air or coolant circuits are employed as thermal management systems in Li-ion batteries. However, those systems are expensive in terms of investment and operating costs. Phase change materials (PCMs) may represent an alternative which could be cheaper and easier to operate. In fact, PCMs can be used as passive or semi-passive systems, enabling the global system to sustain near-autonomous operations. This article presents the previous developments introducing PCMs for EVs battery cooling. Different systems are reviewed and solutions are proposed to enhance PCMs efficiency in those systems. [ABSTRACT FROM AUTHOR]

This research is focused on the energy estimation of 3-SWH systems installed near each other. Two of them are active systems and the third is a passive one. In these systems are utilized heat pipe evacuated tube collectors with dry connection and flat-plate collectors. With the aim to perform the energy estimation of the systems, the mathematical model is built. Experimental data obtained from their database are used. The recorded data for the three considered solar water heating systems refer to a 1-year time period. Monthly values for the solar irradiation on tilted area of the collectors, temperatures, specific solar yields, and system efficiencies are shown in respective graphs. Referring to the considered climate conditions, where the annual solar irradiation on tilted area of the SWHS collectors is 1499 kWh/(m2·year), it was obtained that the system efficiencies are respectively 41.1 %, 51.6 %, and 51.5 %. To assess the differences between the 3-SWHS, the energy balances for the considered period are built. Also, even the economic estimation based on DPBP and NPV is carried out. • An experimental study of three SWHS (2-active and 1-passive) is performed. • The annual energy balances and system efficiencies of 3-SWHS are analyzed. • By employing HP-ETC, annual efficiency of active and passive SWHS is quasi equal. • Fluctuations of efficiency in active SWHS with ETC are lower than in passive ones. • The passive SWHS with HP-ETC is the most economically feasible for the region. [ABSTRACT FROM AUTHOR]

A hybrid safety injection tank (H-SIT) is designed to passively inject coolant into a reactor coolant system under any pressure condition without depressurization, enabling it to be applied in various accident types. In certain accident conditions, if long-term cooling is not achievable because the required active mitigation components are unavailable, the H-SIT can replace the function of the failed components for at least a certain period. Since the H-SIT has limited inventory, related mitigation strategies need to be carefully developed to effectively enhance accident mitigation strategies and contribute to overall plant safety. This study focuses on the risk effect of the H-SIT system under a steam generator tube rupture (SGTR) accident with safety injection system (SIS) failure, a case typically considered to cause core damage. In such cases, the use of the H-SIT provides for a greater diversity of mitigation options and allows more time to repair the failed components. In order to address plant dynamics in a realistic manner, this study considers a variety of secondary-side cooling performances with corresponding repair probabilities. Multiple-tube rupture cases are also considered. The analysis results demonstrate that the H-SIT provides preferred strategies for managing the risks of both SGTR and MSGTR events. [ABSTRACT FROM AUTHOR]

We present two linked theorems on passivity: the passive behavior theorem, parts 1 and 2. Part 1 provides necessary and sufficient conditions for a general linear system, described by a set of high order differential equations, to be passive. Part 2 extends the positive-real lemma to include uncontrollable and unobservable state-space systems. [ABSTRACT FROM AUTHOR]

Phase change material (PCM) used in buildings can increase building energy efficiency and decrease indoor temperature fluctuation. In this study, composite PCM was composed of paraffin and expanded perlite (EP) (60 wt%, 40 wt%) and was prepared through a self-made vacuum absorption roller. A phase change material wallboard (PCMW) was fabricated by the prepared composite PCM through the mould forming method. A plate-type heat accumulator (HAR) with embedded copper tubes was connected to a solar thermal heating system. HAR is fully filled with paraffin, which can store or release the heat gained by the solar thermal heating system. Therefore, PCM active and passive combination is realised through the PCMW incorporated in the building wall and the HAR connected to the solar thermal heating system in the same building. In order to analyze the performance of PCM active and passive combination, two same cubes were used to conduct a contrastive experimental study using different strategies under the winter conditions. The experimental result has indicated that (1) PCMW with melting point of 24.88 °C and latent heat of 59.68 J/g was incorporated in the walls, passively enhancing the thermal inertia of building envelope; (2) HAR with PCM extended the service period of solar thermal heating system; (3) PCM active and passive combination further enhanced the thermal performance of building envelope, indoor thermal comfort and building energy efficiency. [ABSTRACT FROM AUTHOR]

Windows have been under study for the last decade due to their improvements and for being the lowest thermal resistance component of the facades. Amongst this component, the building also loses heat as a result of airing needs. Thermal losses through windows and ventilation may represent a large percentage of the whole thermal losses of the building. The double ventilated window is one of several construction systems that preheat the incoming air. It also reduces thermal losses through windows, reducing the heating load of the building. Several studies have shown the performance of the ventilated double window under different climatic conditions as well as the influence of different inputs. This paper shows how this passive air heating system can be improved in order to collect more solar heat. Thermal balance was improved by 8.4% and 12.5% in Bragança and Évora, respectively, while the delivered air temperature increased from 9.8 °C to 11.9 °C and from 13.5 °C to 17.4 °C in Bragança end Evora, respectively. [ABSTRACT FROM AUTHOR]

Extensive green roofs have been consolidated as good tools for passive energy savingsystems in buildings, providing a more sustainable trend in the building field. However, as the growth of vegetation is variable depending on external factors such as weather conditions, disease, etc. the coverage of plants cannot ensure uniformity and consequently the “shadow effect” cannot be considered as a constant parameter. On the other hand, materials used in substrate and drainage layers should provide a constant “insulation effect” depending only on their physical properties and water content. In spite of this, the complexity of disaggregated materials used in internal layers of extensive green roofs implies a lack of real data about their thermal properties. The main objective of this study is to determine experimentally the physical properties of different disaggregated materials from the internal layers of extensive green roofs commonly used in Mediterranean climates. The experimentation presented in this paper allows to calculate the thermal transmittance in steady-state (U-value), the heat storage capacity (C p ), and the dynamic thermal response under a daily thermal oscillation. [ABSTRACT FROM AUTHOR]

The objective of the research is the definition of a new set of parameters to evaluate the effective dynamic thermal behavior of a layer subject to phase change (PCM) that, for the effect of non-sinusoidal periodic boundary conditions, characterizing the external walls of air-conditioned buildings, give rise to the formation of one or more melting or solidification bi-phase interfaces. Such bi-phase interfaces originate on the boundary surfaces, or are always present and fluctuate within the layer. Defined parameters are to be used for the thermal design of innovative walls containing a PCM layer, targeting the reduction of power peaks entering the environment, in order to reduce the energy requirements and even to improve the indoor thermal comfort. The study has been developed by a finite difference numeric calculation model, which explicitly determines, the number and the position of the bi-phase interfaces that originate in the layer and the temperature and the heat flux fields. The methodology developed allowed us to determine the dynamic characteristics, for each month of the year, of PCM layers with different melting temperatures and thermophysical properties and subject to climatic conditions of two locations, one with a continental climate and the second one with a Mediterranean climate. In particular, it was found that all defined dynamic parameters, irrespective of locality and of PCM type, are related to the latent storage efficiency and, furthermore, some calculation correlations between the dynamic parameters were obtained. Finally, the results show that it was sufficient to reach the phase change in a portion of the layer of about 35% to obtain excellent dynamic thermal performance. [ABSTRACT FROM AUTHOR]

While safety functions in current nuclear power plants are mainly provided by active safety systems, recently passive safety systems are being combined with the active systems to strengthen accident mitigation capability and therefore enhance overall plant safety. To this end, securing long-term cooling of the core is of particular importance. This study considers the hybrid safety injection tank (H-SIT), a passive injection system, as a target component to develop a long-term cooling strategy using active and passive systems concurrently. In the feed-and-bleed (F&B) operation, one of the important long-term cooling strategies to maintain core safety in pressurized water reactors, low pressure safety injection (LPSI) pumps are typically considered inoperable as depressurization is first required, which leads to core dry-out before reaching LPSI operable pressure. This study investigates whether H-SITs, with the important design feature of passive coolant injection under any pressure condition of the primary coolant system, can make up the core during depressurization thereby allowing LPSI pumps to be used in F&B operation as an additional means of long-term cooling. The effectiveness of the H-SITs is verified using thermal-hydraulic simulations, and based on the results a novel F&B operation strategy with H-SITs and LPSI pumps is developed. A probabilistic safety assessment (PSA) model is then developed in order to assess the risk effect of the suggested strategy. PSA results demonstrate that the proposed strategy lowers core damage frequency in the target plant by 5.0 percent in the case of a small break loss of coolant accident. Total core damage frequency of the plant decreases by 4.8 percent compared to the reference model, and also lowers the number of cutsets by around 13 percent from the original value. [ABSTRACT FROM AUTHOR]

Passive safety systems are being increasingly used in innovative reactor designs due to its inherent safety characteristics. The passive safety system failure can occur due to process uncertainties and changes in system hardware state with time. The failure probability contribution due to process uncertainties of a passive decay heat removal system of a fast breeder reactor are quantified through functional reliability analysis. The probability density of the peak hot pool temperature obtained from functional reliability analysis is combined with system hardware reliability through Monte Carlo simulation. The probabilities of crossing the various design safety limits on hot pool temperature are evaluated. The failure probabilities are estimated for different standard deviation values of the peak hot pool temperature probability density. This leads to a linear relationship between failure probability and standard deviation having two distinct regions. The results from the present analysis are compared with the results from two other methods. The results from the three methods converge when the process uncertainty contribution to total failure probability is dominant. The results are significantly different from the three methods when the process uncertainty contribution to total failure probability is not dominant. The difference or the convergence of results by different methods is governed by the extent of process uncertainty contribution to the total failure probability. The proposed method reduces the conservatism as compared to the functional reliability analysis combined with fault tree approach. [ABSTRACT FROM AUTHOR]

Improving energy efficiency is one of the most reliable ways toward carbon neutrality. Most previous studies have focused on how to reduce energy intensity; however, it is not enough to provide an overview of how many carbon emissions can be reduced by technical efficiency improvements underlying energy systems. To fill this gap, this study extended the common Kaya identity to systematically evaluate the carbon reduction potential from technical efficiency improvements of various technical conversion components within the energy system at a granular level. The extended Kaya identity includes technical efficiency factors of electricity efficiency, conversion efficiency, and passive efficiency. It provides a comprehensive framework to evaluate current performance, historical contributions, and future potential of technical efficiency improvements. The case of China reveals that: Currently, only around 5% of energy sources were delivered to final services. By improving technical efficiency to high levels, 59% carbon reduction can be achieved during the future energy transition, even when the economy is still growing. In the past, electricity efficiency and conversion efficiency have significantly reduced carbon emissions. Future policymakers should pay more attention to passive systems to provide more final services, such as improved room insulation, streamlined vehicle designs, and smart energy management. • Proposed an extended Kaya identity framework for the systematic evaluation. • Evaluated the role of technical efficiency improvements at the most granular level. • 59% carbon reduction by improving technical efficiency during energy transition. • Passive systems highlighted for more carbon reduction potential. • Strongly promoting technical efficiency improvements in China's carbon neutrality. [ABSTRACT FROM AUTHOR]

Heavy lift vessels are used to install offshore infrastructure. For floating vessels, roll responses can significantly limit their operability, especially for offshore sites where multimodal wave spectra are expected. This paper deals with a numerical study of a heavy lift vessel equipped with submerged flopper stopper (FS) templates suspended from the sides of the vessel. Dynamic analyses for various sizes and numbers of FS templates were conducted. A medium-size (28 m × 14 m) template can increase operational limits by shifting the roll's natural frequency towards lower values and dampening the responses through drag forces. The operability can increase by about 500% when compared with a vessel without FS templates. A preliminary structural design of a critical beam shows an ultimate limit state design safety factor of 1.5 and fatigue damage of 0.32 for 20 years of service. The cost of construction per template is about $1.75 million (U.S. dollars); the total cost of 4 templates could be recovered in a single wind farm installation project. The system is shown to be feasible for construction vessels used in the execution of marine operations, especially heavy lifting. • A passive roll compensation system using flopper stoppers for offshore construction vessels. • The proposed concept is shown to be technically and economically feasible. • The proposed concept is suitable for crane vessels that operate in combined wind sea and swells. • Four medium size flopper stoppers can increase the operability of a vessel in 500%. • Construction costs can be recovered in a single large offshore wind farm project. [ABSTRACT FROM AUTHOR]

Sustainability trends for buildings require new construction systems to foster energy efficiency and environmentally friendly buildings. Green roofs are interesting construction systems because they provide both aesthetic and environmental benefits. This paper continues a long-term research in order to evaluate and improve the thermal behaviour and sustainability of extensive green roofs. Simultaneously this research provides experimental data for specific Mediterranean continental climate conditions. The experiment consists in evaluating the energy consumption and thermal behaviour of three identical house-like cubicles located in Puigverd de Lleida (Spain), where the only difference is the roof construction system. The roof consists of a conventional flat roof with insulation in the reference case, while in the other two cubicles the insulation layer has been replaced by a 9 cm depth extensive green roof (comparing recycled rubber crumbs and pozzolana as drainage layer materials). The electrical energy consumption of a heat pump system was measured for each cubicle during 2012 and part of 2013. Both extensive green roof cubicles show less energy consumption (16.7% and 2.2%, respectively) than the reference one during warm periods, whereas both extensive green roof systems present a higher energy consumption (6.1% and 11.1%, respectively) compared to the reference cubicle during heating periods. [ABSTRACT FROM AUTHOR]

Energy consumption trends in residential and commercial buildings show a significant increase in recent decades. One of the key points for reducing energy consumption in buildings is to decrease the energy demand. Buildings envelopes are not just a structure they also provide protection from outdoor weather conditions always taking into account the local climate. Thermal energy storage has been used and applied to the building structure by taking advantage of sensible heat storage of materials with high thermal mass. But in recent years, researchers have focused their studies on the implementation of latent heat storage materials that if well incorporated could have high potential in energy demand reduction without occupying the space required by sensible storage. The aim of this study is to review the thermal energy storage passive systems that have been integrated in building components such as walls, ceilings or floors, and to classify them depending on their component integration. [ABSTRACT FROM AUTHOR]

This review paper organizes and summarizes the literature on Vertical Greenery Systems (VGS) when used as passive tool for energy savings in buildings. First, with the information obtained in the reviewed literature some key aspects to consider when working with VGS are clarified, such as the classification systems, the climate influence, the plant species used and the different operating mechanisms. Then, the main conclusions of this literature, sorted by construction system (Green Walls or Green Façades) and climatic situation, are summarized. In general, it can be concluded that VGS provide great potential in reducing energy consumption in buildings, especially in the cooling periods. However, a lack of data on operation during the heating period as well as during the whole year has been found. On the other hand, results show that the investigations of VGS are not equally distributed around the world, being basically concentrated in Europe and Asia. Moreover, the review concludes that some aspects must be studied in depth, such as which species are the most suitable for each climate, influence on energy savings of the façade orientation, foliage thickness, presence of air layers, and finally, substrate layer composition and thickness in the case of green walls. [ABSTRACT FROM AUTHOR]

During research of new possible sources of energy, hydrogen was identified as a very promising potential energy carrier. Because of its very good energy characteristics, it has received a lot of research attention while its safety features are the ones that were its drawback for potential use. Before it can be put in general use in transportation industry, there were safety problems identified as hazard which has to be further analysed. The main problem in the transport is the safe use of hydrogen in road tunnels where it should be safe in case of possible accidents where its release could end up in fire, deflagration and even detonation. In the article, concept of hydrogen trap on the ceiling is developed and described based on the available data and research results from which passive safety approach is suggested to be used in future designs of the road tunnels. [ABSTRACT FROM AUTHOR]

Abstract: The design and test of a 9.5 kWe proton exchange membrane fuel cell passively coupled with a 33 × 1500 F supercapacitor pack is presented. Experimental results showed that the system reduced dynamic loads on the fuel cell without the need for additional DC/DC converters. Fuel efficiency gains of approximately 5% were achieved by passive hybridisation in addition to addressing two main operational degradation mechanisms: no-load idling and rapid load cycling. Electrochemical Impedance Spectroscopy measurements indicated that the supercapacitor capacitance dropped with decreasing cell voltage and suggested that operation below 1.3 V is not recommended. Knee-frequency measurements suggested little benefit was gained in using passive systems with load cycles that have frequency components above 0.19 Hz. Analysis of system sizing suggested using the minimum number of supercapacitors to match the open circuit voltage of the fuel cell to maximise load buffering. [Copyright &y& Elsevier]

Abstract: This paper presents an inspection-based maintenance optimisation model where the inspections are imperfect and potentially failure-inducing. The model is based on the basic delay-time model in which a system has three states: perfectly functioning, defective and failed. The system is deteriorating through these states and to reveal defective systems, inspections are performed periodically using a procedure by which the system fails with a fixed state-dependent probability; otherwise, an inspection identifies a functioning system as defective (false positive) with a fixed probability and a defective system as functioning (false negative) with a fixed probability. The system is correctively replaced upon failure or preventively replaced either at the N'th inspection time or when an inspection reveals the system as defective, whichever occurs first. Replacement durations are assumed to be negligible and costs are associated with inspections, replacements and failures. The problem is to determine the optimal inspection interval T and preventive age replacement limit N that jointly minimise the long run expected cost per unit of time. The system may also be thought of as a passive two-state system subject to random demands; the three states of the model are then functioning, undetected failed and detected failed; and to ensure the renewal property of replacement cycles the demand process generating the ‘delay time’ is then restricted to the Poisson process. The inspiration for the presented model has been passive safety critical valves as used in (offshore) oil and gas production and transportation systems. In light of this the passive system interpretation is highlighted, as well as the possibility that inspection-induced failures are associated with accidents. Two numerical examples are included, and some potential extensions of the model are indicated. [Copyright &y& Elsevier]

Highlights: [•] The decrease in concentration of fluoride depends on initial feed concentration. [•] The removal of fluoride was found to be effective in the pH range 6–7. [•] The increase in quantity of adsorbent showed increased rate of fluoride removal. [•] Eco-friendly method with easy operation and maintenance. [•] Easy to reduce fluoride levels below 1.5mg/L using optimized parameters. [Copyright &y& Elsevier]

Abstract: In this paper a four-dimensional hyperchaotic system with only one equilibrium is considered and it is shown how the control and the synchronization of this system can be realized via two different control techniques. Firstly, we propose a periodically intermittent controller to stabilize the system states to the equilibrium and to achieve the projective synchronization of the system both in its periodic and hyperchaotic regime. Then, based on the stability properties of a passive system, we design a linear passive controller, which only requires the knowledge of the system output, to drive the system trajectories asymptotically to the origin. Using the same passivity-based method, the complete synchronization of the hyperchaotic system is also obtained. Both the intermittent and the passive controllers are feedback, global and easy to implement. Numerical simulations are included to show the effectiveness of the designed controllers in realizing the stabilization and the synchronization of the hyperchaotic system. [Copyright &y& Elsevier]

Abstract: Nowadays, European policies are promoting low energy buildings because of the high amount of energy consumption of the building sector. Phase change materials (PCM) have been studied in building implementation as a passive system to reduce the energy demand. Based in the experience obtained in the experimental set-up of Puigverd de Lleida (Spain), this paper pretends to analyze experimentally the PCM performance in a scenario with internal thermal gains. The experiments were done in three different cubicles with the same internal dimensions. The selection of the constructive systems used in these three cubicles allows the authors to evaluate the impact of using PCM in a typical Mediterranean building. A domestic heat pump for summer and an electric radiator for winter were installed to control the internal temperature of the cubicles. The results of summer period experiments show that the PCM cubicle stored the heat produced by the internal loads limiting the heat dissipation to the outer environment. Therefore, the energy consumed by the HVAC system of the PCM cubicle during the cooling period is higher than that of the other cubicles that dissipated the thermal loads according to the thermal resistance of their envelopes. Therefore, the PCM selection should take into account not only the comfort temperature but also the activity and functionality of the building. [Copyright &y& Elsevier]

Abstract: Today, green roofs are a building system which provides interesting benefits over traditional roof solutions. The most important advantages are the reduction of surface runoff in cities, improvement of the urban climate, biodiversity support, improvement of the durability of roofing materials, and, especially, energy savings. This paper has the aim of studying the performance of green roofs as a passive system for energy savings, within a wider objective of seeking constructive solutions suitable for sustainable and environmentally friendly architecture. This idea is tested at an experimental installation available at the University of Lleida, with several cubicles testing the energy performance of different construction solutions. This work raises the possibility of using recycled rubber from tires as a drainage layer in green roofs, substituting the porous stone materials currently used (such as expanded clay, expanded shale, pumice, and natural puzolana). This solution would reduce the consumption of these natural materials, which also require large amounts of energy in its transformation process to obtain their properties. Moreover it would provide a solution to the problem of waste rubber from the tires, known as rubber crumbs. Since the purpose of the drainage layer is the optimum balance between air and water in the green roof system, first the ability for draining of recycled rubber granules was studied and was compared with the offered by stone materials. The new solution using rubber crumbs is also studied to test if it would keep the same insulating properties that the green roof with stone materials presented in previous studies. Early results show that this extensive green roof system can be a good passive energy savings tool in Continental Mediterranean climate in summer, and that rubber crumbs can be an interesting substitute for stone materials used as drainage layer in this type of green roofs. [Copyright &y& Elsevier]

An exergy analysis has been conducted to show the effect of a small fan on the exergy efficiency in a pyramid-shaped solar still. The tests were carried out in Mashhad (36° 36′ N), for two solar still systems. One of them was equipped with a small fan (active system), to enhance the evaporation rate while the other one was tested in passive condition (no fan). To examine the effects of radiation and water depth on exergy efficiency, experiments in two seasons and two different depths of water in the solar still basin were performed. The results show that during summer, active unit has higher exergy efficiency than passive one while in winter there is no considerable difference between the exergy efficiency of the units. Results also reveal that the exergy efficiency is higher when the water depth in the basin is lower. Finally, the economic analysis shows a considerable reduction in production cost of the water (8–9%) when the active system is used. [Copyright &y& Elsevier]

Abstract: The quantitative reliability assessment of a thermal–hydraulic (T–H) passive safety system of a nuclear power plant can be obtained by (i) Monte Carlo (MC) sampling the uncertainties of the system model and parameters, (ii) computing, for each sample, the system response by a mechanistic T–H code and (iii) comparing the system response with pre-established safety thresholds, which define the success or failure of the safety function. The computational effort involved can be prohibitive because of the large number of (typically long) T–H code simulations that must be performed (one for each sample) for the statistical estimation of the probability of success or failure. In this work, Line Sampling (LS) is adopted for efficient MC sampling. In the LS method, an “important direction” pointing towards the failure domain of interest is determined and a number of conditional one-dimensional problems are solved along such direction; this allows for a significant reduction of the variance of the failure probability estimator, with respect, for example, to standard random sampling. Two issues are still open with respect to LS: first, the method relies on the determination of the “important direction”, which requires additional runs of the T–H code; second, although the method has been shown to improve the computational efficiency by reducing the variance of the failure probability estimator, no evidence has been given yet that accurate and precise failure probability estimates can be obtained with a number of samples reduced to below a few hundreds, which may be required in case of long-running models. The work presented in this paper addresses the first issue by (i) quantitatively comparing the efficiency of the methods proposed in the literature to determine the LS important direction; (ii) employing artificial neural network (ANN) regression models as fast-running surrogates of the original, long-running T–H code to reduce the computational cost associated to the determination of the LS “important direction” and (iii) proposing a new technique for identifying the LS “important direction”, based on the genetic algorithm (GA) minimization of the variance of the LS failure probability estimator. In addition, this work addresses the second issue by assessing the performance of the LS method in estimating small failure probabilities with a reduced (e.g., lower than one hundred) number of samples. The issues are investigated within two case studies: the first one deals with the estimation of the failure probability of a nonlinear structural system subject to creep and fatigue damages ; the second one regards a passive decay heat removal system in a gas-cooled fast reactor (GFR) of literature, . [Copyright &y& Elsevier]

Abstract: The probabilistic safety assessment (PSA) has been investigated for the very high temperature reactor (VHTR). It is difficult to make the quantification of the PSA because the operation and experience data are deficient. Therefore, the necessity of the statistical data usage is considered for the basic event. The physical data using the non-linear fuzzy set algorithm are applied to quantification of the designed case. The main model of this study is the mass flow rate in natural circulation. Furthermore, the potential energy in the gravity, the temperature and pressure in the heat conduction, and the heat transfer rate in the internal stored energy are also investigated. For the failure analysis, the values in the probability set and the fuzzy set are compared. In the results, how to use the newly made failure frequency in the propagations is found. It is concluded the artificial intelligence analysis of the fuzzy set could enhance the reliability method than the probabilistic analysis. [Copyright &y& Elsevier]

Abstract: In this paper, a new adaptive controller is proposed to ensure the stability and good performance of a teleoperation system while a wide range of time delays is considered. For this means, a feedforward compensator is designed to ensure system passivity and then a new model reference adaptive controller (MRAC) is developed to provide good performance. The developed system demonstrates good stability and force tracking capabilities. A command generator tracker (CGT) is designed for a sample teleoperation system and the results are compared with the proposed system. [Copyright &y& Elsevier]

Abstract: The probabilistic safety assessment (PSA) for gas-cooled nuclear power plants has been investigated where the operational data are deficient, because there is not any commercial gas-cooled nuclear power plant. Therefore, it is necessary to use the statistical data for the basic event constructions. Several estimations for the safety margin are introduced for the quantification of the failure frequency in the basic event, which is made by the concept of the impact and affordability. Trend of probability of failure (TPF) and fuzzy converter (FC) are introduced using the safety margin, which shows the simplified and easy configurations for the event characteristics. The mass flow rate in the natural circulation is studied for the modeling. The potential energy in the gravity, the temperature and pressure in the heat conduction, and the heat transfer rate in the internal stored energy are also investigated. The values in the probability set are compared with those of the fuzzy set modeling. Non-linearity of the safety margin is expressed by the fuzziness of the membership function. This artificial intelligence analysis of the fuzzy set could enhance the reliability of the system comparing to the probabilistic analysis. [Copyright &y& Elsevier]

Abstract: Reliability analysis of passive systems mainly involves quantification of the margin to safety limits in probabilistic terms. For systems represented by complex models, propagating input uncertainty to get the response uncertainty and hence probability information requires intensive computational effort. Here a computationally efficient method for the functional reliability analysis of passive fluid dynamical systems is presented. The approach is based on continuous adjoint operator technique to generate a response surface approximating the given system model from the sensitivity coefficients. A numerical application of this method to the reliability analysis of heat transport in an asymmetrical natural convection loop is demonstrated. Computational efficiency and accuracy compared with the direct Monte-Carlo and forward response surface methods. [Copyright &y& Elsevier]

After the FUKUSHIMA accident, passive systems become an important issue for the new projects of Pressurized Water Reactor (PWR). In response to the demands of its partners, the CEA (French Commission for the Atomic Energy and Alternative Energy) has proposed suitable systems to deal with different accidental sequences. Then, it has dimensioned their components and modelled their integration in the reactor using the CATHARE system code. In particular, the CEA has worked on the ADS system (Automatic Depressurization System) devised to tackle with the well-known LOCA accident (Loss of Coolant Accident), resulting from a breach in the pipes of the primary circuit. Concretely, the ADS system is made up of a tank called IRWST (In-Containment Refueling Water Storage Tank), placed high in the containment, which has the role of achieving a safety passive injection to replace the conventional one using low-pressure pumps, during a LOCA accident. The ADS is in fact already present on the AP1000 reactor, the US PWR designed to be totally passive. The CEA has proposed to improve it by adding a LPWT tank (Low-Pressure Water Tank) pressurisable by steam issued from the pressurizer on the last line of the ADS system. It should allow a better core cooling by the additional water injection in the reactor core, anticipated in time compared to that of the IRWST. The CFD application in reactor safety studies, due to its high-level of accuracy, is now widespread. The CFD calculation is used to predict local fluid temperature in the different regions of a nuclear reactor in nominal conditions and transient situations. Local CFD calculation coupled with a component system code for the whole domain of the reactor is also a current approach (Guelfi et al.). The study presented here exclusively focuses on the LPWT water pressurization phase prior to its injection into the reactor core. Three approaches are exposed: - An analytical approach, in which one considers the pressurization of the volume of gas present in the tank without taking into account the liquid phase; - A system approach with the CATHARE thermal–hydraulic code which allows to describe at the same time the volume of gas and the volume of liquid contained in the tank; - A CFD approach using the NEPTUNE_CFD code to determine the local evolution of the quantities that characterize the system. This approach will notably make it possible to describe the movement of the interface and the velocity profile of the water vapor. It will also help to bring a better understanding of the physical phenomena involved during the LPWT water pressurization phase. At the end, these different approaches show that the increase in pressure by the steam injection is an interesting option to pressurize the water tank. On the other hand, the results of the pressure evolution obtained by the system approach are very close to those obtained analytically, in the absence of liquid phase. However, they are overestimated compared to the CFD approach, which, thanks to a better modeling of the condensation of the injected vapor, leads to a more realistic evaluation. [ABSTRACT FROM AUTHOR]

Abstract: This study addresses the time-variant reliability assessment in relation to systems presenting a non-stationary random process during their operation, such as thermal-hydraulic passive systems for advanced reactors, resting on natural circulation. The reliability assessment efforts conducted so far do not address this specific aspect: the dependence upon time is usually ignored, or at most the system unavailability is intended to be assessed per mission time, during which the parameter values, as t–h parameters for instance, are assumed as constant quantities. The study endeavours to present a consistent approach to model the natural circulation passive systems, in terms of time-variant performance parameters, as for instance mass flow-rate and thermal power, to cite any. [Copyright &y& Elsevier]

Abstract: In this paper, we solve the tracking and disturbance rejection problem for fully actuated passive mechanical systems. We assume that the reference signal and its first two derivatives are available to the controller and the disturbance signal can be decomposed into a finite superposition of sine waves of arbitrary but known frequencies and an arbitrary signal. We combine the internal model principle with the ideas behind the Slotine–Li adaptive controller. The internal model-based adaptive controller that we propose causes the closed-loop state trajectories to be bounded, and the tracking error and its derivative to converge to zero, without any prior knowledge of the plant parameters. An important part of our results is that we prove the existence and uniqueness of the state trajectories of the closed-loop system. [Copyright &y& Elsevier]

Abstract: Uncertainties involved in passive system operation play a crucial role in the relative reliability assessment endeavor. These uncertainties concern the deviations of the underlying physical principles from the expected behavior and are related to the onset of physical phenomena infringing the system performance or to the changes in the initial/boundary conditions. This issue is addressed by the development of subjective probability distributions relative to the physical modes of failure for a typical passive system for reactor decay heat removal, operating in natural circulation. Because of the limited availability of data, both experimental and operational, expert judgment and engineering assessment are used to characterize the present status of uncertainty with regard to a set of critical parameters driving the failure modes. This allows deriving a set of natural circulation failure probability distributions to quantitatively get information on system reliability. [Copyright &y& Elsevier]

The seawater extracted from a depth of 30 m has a constant temperature of about 18°C. This water can be used as cold source for the conditioning of Salammbô Museum aquariums (Tunisia). With this intention a passive system, [Copyright &y& Elsevier]

In the paper we develop methods for stability analysis and control design for single phase, distributed chemical processes in one spatial dimension. The physical phenomena we model include reaction, diffusion, heat transfer and convection. The approach is motivated by the formalism of non-equilibrium thermodynamics, the energy methods of fluid mechanics and the passivity theory of non-linear control. We provide two distinct contributions. First, we give a tutorial overview of background material and examples to illustrate. Second, we introduce a new approach for stabilization of non-equilibrium, fluid flow systems. Some applications to systems of conservation laws are presented and connected with boundary and inventory control. We also develop an approach to study the classical problem of minimum entropy production in stationary flow. [Copyright &y& Elsevier]

• ET was increased when outdoor temperature, wind speed and solar radiation rose. • ET was influenced by the volumetric water content of the substrate. • The irrigation management affected ET and the heat flux of the eco-roof. • A proper irrigation strategy allowed a significant reduction of energy demand. • Eco-roofs can be used in the rehabilitation of old buildings. A passive system widely used to reduce the energy consumption of a building is the green roof. The main objective of this work was to determine the reduction of energy demand of a building with a green roof without plants, eco-roof, under 20 different irrigation strategies, compared to a traditional gravel ballasted roof, in southern Europe. Experimental data of heat flux collected during one year were used to calibrate two numerical models developed with DesignBuilder software. Evapotranspiration and volumetric water content were demonstrated to have a great impact on the heat flux reduction of the eco-roof. Moreover, evapotranspiration strongly depended on the climatic conditions. The annual heat flux results showed that the eco-roof improved the thermal performance of the building compared to the traditional roof, achieving a high reduction of annual energy demand, ED, up to 78.7%. The strategy that had the highest ratio between the annual ED to the lowest use of water was watering in alternate days for 20 min in the morning, obtaining an ED value of 46.7%. These results indicate that eco-roofs with a proper irrigation strategy could be used as an efficient passive system for the rehabilitation of old buildings. [ABSTRACT FROM AUTHOR]