Safety Design Approach Research Articles

Experiment on distributed dynamic simulation for safety design of chemical plants

To meet the market challenges, chemical plants need to provide safer plant operation. Safety design approach is used to ensure the safety during the design stage, which satisfies the safety during the plant operation. In such approach, simulation practices are widely used to provide quantitative measures to assess the fault propagation and abnormal situations. As most of the chemical plants are becoming more complex, simulation tools need to provide more intelligent and distributed environment to meet the performance requirements. This research work proposes a distributed simulation environment to support safety design activities of complex chemical plants using intelligent agents. The proposed approach is based on dividing the complex plant design model into smaller and controlled sub-processes called control group units (CGUs). The design and simulation activities of each CGU will be carried out independently on a set of computation resources. Intelligent agents are developed to integrate the plant partitions where simulation results are exchanged among the different simulation sessions. The proposed distributed simulation environment is used to assess the fault propagation within each plant segment (i.e. CGU) and between the adjacent CGUs. The proposed solution is used during the design of a case study HDS chemical plant.

Overview of tritium safety studies in Japan

Tritium safety is one of the most important R&D subjects for developing International Thermonuclear Experimental Reactor (ITER) and fusion reactor. In Japan, tritium safety studies are being conducted in JAERI (Japan Atomic Energy Research Institute), NIRS (National Institute of Radiological Sciences), and universities. In JAERI, experiments and experiences in Tritium Process Laboratory (TPL) are most important. Here, a few kilograms of tritium have been safely used from its start of operation in 1988. Recent important research subject is elucidation of tritium behavior in the tritium confinement system using a caisson (12 m 5) combined with tritium removal system. JAREI is also conducting safety related studies such as, tritium confinement, tritium decontamination, tritium permeation, off-normal events, and tritium accountancy. In universities, various fundamental researches have been conducted, including tritium permeation, simulation of tritium behavior in the fusion reactor system, tritium contamination and decontamination, tritium measurement, tritium interaction with materials, and tritium trapping on the surface of various fusion reactor components. Tritium environmental behavior and biological effect are important subjects to evaluate the consequences of released tritium and to provide an appropriate information to receive good public acceptance for fusion reactor. Fundamental and code development studies related to them are being conducted in universities, JAERI, and NIRS. Licensing preparation for ITER is being conducted at the Government in the collaboration with JAERI. This includes safety features, fundamental approach for safety design, assessment of safety design features, and evaluation of the consequences of off-normal events.

Three-dimensional analysis of water–vapor void fraction in a fusion experimental reactor under water ingress

An integrated Ingress-of-Coolant Event (ICE) test facility was constructed to demonstrate that the International Thermonuclear Experimental Reactor (ITER) safety design approach and design parameters for the ICE are adequate. The integrated ICE test facility simulates the actual ITER components with a scaling factor of 1/1600. Before the integrated ICE experiments the water–vapor two-phase flow characteristics inside the test facility during the ICE were predicted by the three-dimensional numerical simulations using the modified Transient Reactor Analysis Code (TRAC). From the present study it was clarified numerically that the actual ITER safety approach during the ICE is adequate and the present numerical method is very effective to predict the water–vapor void fraction during the ICE.

Experimental verification of effectiveness of integrated pressure suppression systems in fusion reactors during in-vessel loss of coolant events

An integrated ingress of coolant event (ICE) test facility was constructed to demonstrate that the ITER safety design approach and design parameters for ICEs are adequate. The major objectives of the integrated ICE test facility are: to estimate the performance of an integrated pressure suppression system; to obtain validation data for safety analysis codes; and to clarify the effects of two phase pressure drops at the divertor and condensation in the suppression tank. The integrated ICE test facility simulates the current ITER components with a scaling factor of 1/1600. The TRAC-PF1 code is used to verify the integrated ICE experimental results. From the present study the effectiveness of the ITER pressure suppression system was verified experimentally and analytically, and then it was clarified quantitatively that the prediction accuracy of the TRAC-PF1 code is very high.

Safety activities in JAERI related to ITER

Safety design approach, design codes and safety-related technology development for construction of the international thermonuclear experimental reactor (ITER) initiated in Japan Atomic Energy Research Institute (JAERI) has been reviewed. Safety design approach and implementation are focused on inherent and high-level passive safety features of the ITER-FEAT. By such features, escalation of abnormal condition to accident can be prevented without any special countermeasures such as emergency plasma shutdown system. As a result, the primary containment system and the secondary confinement one are proposed to achieve the ITER safety objectives. To establish the structural design codes for unique ITER components, an ad-hoc technical committee has been organized. The designs of the vacuum vessel and tritium process components have been reviewed and discussed. Recommendations including some attractive methodologies for structural design and components examinations, taking into account a low level of hazard potential and unique safety features of ITER was given by the committee. Another ad-hoc technical committee under JAERI Construction Division is discussing the design codes for ITER seismic isolation. The current status of R&D activities ongoing in JAERI for accumulation of experimental data required for assurance of the safety analysis and design codes for ITER are also reviewed.

Results of two-phase flow experiments with an integrated Ingress-of-Coolant Event (ICE) test facility for ITER safety

An integrated ICE (Ingress-of-Coolant Event) test facility was constructed in order to demonstrate the adequacy of the ITER (International Thermonuclear Experimental Reactor) safety design approach and investigate two-phase flow behavior during an ICE event. The integrated ICE test facility corresponds to approximately 1/1600 of the ITER components. In the experiments the fluid flow configurations inside the vacuum vessel at the ICE events were observed visually and pressure transients were measured quantitatively. Two-phase flow analyses were carried out with the TRAC code and the experimental results were validated numerically. From the present study it was clarified that the ITER pressure suppression system is very effective in reducing the pressure rise in case of the ICE event and the water–vapor two-phase flow characteristics in ITER can be predicted numerically with sufficient accuracy.

Analysis of Pressure Rise in an ITER-Like Fusion Reactor During In-Vessel LOCA by A Modified TRAC-PF1 Code

Damage of cooling tubes of plasma facing components (PFCs) results in water discharge into a vacuum vessel (W) of a fusion reactor. Flashing in vacuum, water pool boiling and impingement-jet on a surface of the PFC are the main heat transfer phenomena responsible for steam production that causes a rapid pressurization of the W. This is called an in-vessel loss-of-coolant accident (LOCA) event or ingress-of-coolant event (ICE). The ICE event is one of the most severe accidents in the fusion reactors.The integrated ICE test facility was constructed to demonstrate the safety design approach of International Thermonuclear Experimental Reactor (ITER) and obtain validation data for the ITER safety analysis codes. Then, an experimental study was performed using the integrated ICE test facility and at the same time the code validation study with the TRAC code was carried out. The pressure rise characteristics in the current ITER machine during the ICE event were analyzed numerically using the verified TRAC-PF1 code and the effects of the relief pipe diameter and suppression tank volume regarding to the pressure rise due to the ICE events were clarified quantitatively from the present analytical results.

Numerical study on pressure rise characteristics in simulated ITER structural components during ingress-of-coolant events

A numerical study was performed to predict the pressure rise characteristics during ingress-of-coolant events (ICE) in an integrated test facility which simulated structural components of International Thermonuclear Experimental Reactor (ITER). The integrated ICE tests were planned to clarify the two-phase flow characteristics from the plasma chamber through the divertor and vacuum vessel to the suppression tank during the ICE events and demonstrate adequacy of the ITER safety design approach, and obtain validation data for safety analysis codes for fusion experimental reactors. The TRAC code, which was originally developed for the accident analysis in light water reactors, was used in the present study. It was clarified quantitatively from the numerical predictions that the pressure inside the vacuum enclosure in ITER during the ICE events receives the injected water flow rate, orifice size and pitches, and wall and water temperatures, and then, the suppression tank is very effective to reduce the pressure rise.

Accommodating perceptions of risk in performance-based building fire safety code development

Differing perceptions of risk by various stakeholders have long played a role in influencing the development of prescriptive-based building fire safety codes. As performance-based building fire safety codes are developed, differing perceptions of risk will continue to be a significant influence. In this paper, the concepts of revealed preference, risk factors, risk adjustment factors and risk conversion factors are discussed, and two methods to address risk perceptions in a performance-based building fire safety code are introduced. The first method proposes the use of risk factors to classify buildings in terms such as low, medium, and high risk. Each class of building would be assigned a risk adjustment factor. Similar to safety factors, risk adjustment factors would be applied during deterministic building fire safety design to provide an increased level of safety in buildings where the risk perceptions would mandate greater safety. The second method would be used with a probabilistic-based building fire safety design approach, and uses risk factors to develop risk conversion factors (RCFs). In the probabilistic approach, a maximum expected-risk-to-life (ERL) value would be established by the code, with appropriate RCFs being applied to adjust maximum ERL values depending on how the building's fire safety risk is perceived.

Performance-based Fire Engineering Design And Its Application In Australia

In the international context there have been considerable advances recently towards the development of a performance-based approach for fire safety design. For the consideration of others involved in planning or implementing a performance-based approach, an examination is given of the experiences gained in Australia. This paper outlines those developments that have led to the implementation of a performance-based approach to fire safety design in Australia. It is noted that several factors must be in existence for there to be a successful implementation of a performance-based approach. Some important issues that need to be resolved are noted also. A brief description is given of some research which is currently in progress to further develop a risk-assessment model. Finally, some challenges and issues surrounding the future international application of a performance based approach to fire safety design are presented.

Approaches to safety, environment and regulatory approval for ITER

International Thermonuclear Experimental Reactor (ITER) Engineering Design Activities (EDA) in safety and environment are approaching the point where conceptual safety design, topic studies and research will give way to project oriented engineering design activities. The Joint Central Team (JCT) is promoting safety design and analysis necessary for siting and regulatory approval. Scoping studies are underway at the general level, in terms of laying out the safety and environmental design framework for ITER. ITER must follow the nuclear regulations of the host country as the future construction site of ITER. That is, regulatory approval is required before construction of ITER. Thus, during the EDA, some preparations are necessary for the future application for regulatory approval. Notwithstanding the future host country's jurisdictional framework of nuclear regulations, the primary responsibility for safety and reliability of ITER rests with the legally responsible body which will operate ITER. Since scientific utilization of ITER and protection of the large investment depends on safe and reliable operation of ITER, we are highly motivated to achieve maximum levels of operability, maintainability, and safety. ITER will be the first fusion facility in which overall ‘nuclear safety’ provisions need to be integrated into the facility. For example, it will be the first fusion facility with significant decay heat and structural radiational damage. Since ITER is an experimental facility, it is also important that necessary experiments can be performed within some safety design limits without requiring extensive regulatory procedures. ITER will be designed with such a robust safety envelope compatible with the fusion power and the energy inventories. The basic approach to safety will be realized by ‘defense-in-depth’. The first priority will be in the prevention of accidents through the intrinsic features of the facility, quality assurance throughout, in design, construction, operation and maintenance, and appropriate provisions for human factors. Nevertheless, the plant will be designed to be ready for anomalous events. In addition, public will be protected with appropriate mitigative features, even for extremely unlikely and unforeseen hypothetical accidents to add safety margins as appropriate. Current safety design approaches are introduced in this paper, including a global methodology, off-normal plasma termination, decay heat removal, and containment and confinement strategies.

Progress in design and verification of the AMPS nuclear-electric plant

While nuclear plants of reduced scale and output specification supported by various degrees of inherent safety are being advanced for land-based applications, the AMPS development seeks to introduce nuclear plants with inherent safety to the marine industry, and in particular to small, highly mobile submersibles for commercial, oceanographic and coast-guard service. The AMPS development is rooted in an inherent safety design approach, as a matter of both practical necessity and opportunity. Verification of the AMPS concepts and design analyses is in progress using a full-scale thermalhydraulic facility and an organic Rankine engine representing the 100-kWe AMPS Prototype plant. Also, the design of an AMPS unit of over 1000 kWe and using a low-pressure steam cycle is subjected to analytical studies of accident scenarios.