Risk-informed Design Research Articles

Risk-informed design of debris-flow mitigation at Cheekeye Fan

The Cheekeye Fan, located within the District of Squamish, is prone to debris-flow hazards that pose unacceptable risk to development. This article describes how a debris-flow barrier that would protect existing and proposed development was designed to achieve locally-adopted risk tolerance criteria. A risk assessment showed that the barrier should manage debris flows with volumes up to 2.8 Mm3 (1:10,000-year return-period events) to achieve tolerable risk, and that debris flows with volumes below 0.2 Mm3 (10 to 30-year events) can pass the barrier through an outlet without exceeding risk tolerance thresholds. The local government specifies that tolerable debris-flow risks be reduced ‘As Low As Reasonably Practicable’ (ALARP), defined in this project as the point where the cost of additional mitigation measures is grossly disproportionate to the benefits gained. By estimating the disproportionality ratio for potential auxiliary measures, this study shows that the barrier reduces risk ALARP without additional measures in place. The authors believe that new development approval on Cheekeye fan would not be possible without the risk-informed decision-making process described in this article.

Risk-informed integrated design optimization for offshore wind farm electrical systems

The present paper develops and presents a risk-informed framework for the design of electrical systems of offshore wind farms. The framework provides a consistent theoretical and methodical basis for the treatment of uncertainties affecting service life performances and accounts for both the direct and indirect consequences related to system failure events. The risk of electrical systems is represented through a probabilistic systems modeling approach in which the states (direct failure, available, and unavailable) of the components and the resulting consequences are duly accounted for. The paper further proposes a risk-informed design optimization framework for offshore wind farm electrical systems (collection and transmission systems). Two risk indicators, the scenario-based net present value, and the robustness index, are formulated and quantified to support decision-making. The proposed framework and associated methods are illustrated through an application example considering an OWF comprised of 57 10MW wind turbines with HVAC transmission.

Incorporating failure mode and effects analysis into a novel framework for hydrogen production from solid waste gasification

Gasifying waste represents a sustainable and highly effective approach; however, ensuring rigorous control of hydrogen leakage is paramount to guarantee both safety and long-term sustainability. Due to the distinctive features of these production facilities and the likelihood of their placement in public municipal spaces, it is imperative to prioritize a comprehensive approach to ensuring the safety of these installations. This includes a thorough evaluation of the risks linked to hydrogen and taking proactive measures to prevent accidents, a crucial aspect that has been neglected in prior research endeavors. Therefore, this article introduces an enhanced iteration of the risk management framework based on the failure mode and effects analysis (FMEA) and the evaluation based on distance from average solution (EDAS) methods, implemented in a municipal solid waste gasification system to facilitate hydrogen production. The research employs FMEA to scrutinize potential failure modes, strategically prioritizing them through advancements in the EDAS methodology. Notably, this framework is seamlessly integrated during the conceptual design phase, showcasing its efficacy in bolstering risk-informed design strategies. Through rigorous comparative and sensitivity analyses, the resilience of the framework is underscored. The refined FMEA-EDAS framework holds substantial practical implications for managing hydrogen production facilities by providing a structured approach to resource allocation and ensuring adherence to industry standards. Furthermore, it fosters interdisciplinary collaboration, potentially serving as a knowledge hub to fortify safety measures within the realm of hydrogen production.

Life safety in the Reliability-Based design and assessment of structures

We review the developments in life safety and the incorporation thereof in the design and assessment of structures over the last 50 years. Various measures of life safety are presented that have been developed according to the marginal life saving cost principle based on individual, societal and economic considerations. Target probabilities of failure, or target reliabilities, are central to modern structural design and assessment. These are derived either through back-calibration to existing practice or through life cycle cost minimisation, both of which yield comparable safety levels, and are underpinned by lower bounds from life safety. Life cycle cost minimisation is reviewed here, which considers all direct and indirect costs of failure including loss of life and limb, as well as the costs and efficiency of increasing reliability. We discuss the incorporation of life safety into reliability-based design and assessment through the concept of the Life Quality Index, which uses key societal indicators, namely, the GDP and life expectancy, and health economics as a basis for specifying minimum reliabilities for both new and existing structures. The current state of advancement of reliability- and risk-informed design, and recommendations for future developments in life safety are considered.

Probabilistic Validation: Computational Platform and Application to Fire Probabilistic Risk Assessment of Nuclear Power Plants

Abstract Recently, there has been an increasing use of advanced modeling and simulation in the nuclear domain across academia, industry, and regulatory agencies to improve the realism in capturing complex and highly spatiotemporal phenomena within the probabilistic risk assessment (PRA) of existing nuclear power plants (NPPs). Advanced modeling and simulation have also been used to accelerate the risk-informed design, licensing, and operationalization of advanced nuclear reactors. Validation of simulation models traditionally relies on empirical validation approaches which require enough validation data. Such validation data are, however, usually costly to obtain in the contexts of the nuclear industry. To overcome this challenge and to effectively support the use of simulation models in PRA and risk-informed decision-making applications, a systematic and scientifically justifiable validation methodology, namely, the probabilistic validation (PV) methodology, has been developed. This methodology leverages uncertainty analysis to support the validity assessment of the simulation prediction. The theoretical foundation and methodological platform of the PV methodology have been reported in the first paper of this two-part series. The purpose of this second paper is to computationalize the PV methodology, embedded in an integrated PRA framework, and apply it for a hierarchical fire simulation model used in NPP Fire PRA.

Risk-informed design of advanced nuclear reactor: A target unavailability approach

Incorporating specified safety and production targets during the design phase of an engineered facility can effectively support reductions in construction and operation costs of nuclear power plants. In addition, this supports efforts toward making nuclear power technology more competitive and profitable than other electric power production forms by incorporating operational and design features into the design phase that directly support the increased likelihood of meeting such originating targets. Unavailability is the key parameter to establish plant-level capabilities that cascade down to function, system, and component levels to ensure that all sources of unavailability are addressed in the facility's design phases. In this article, two methods are presented to propose unavailability targets for nuclear reactor systems to risk-inform and optimize the design features, from an availability perspective: the first method is a simple method, and the second is a non-dominated sorting genetic algorithm III (NSGA-III) multi-objective optimization. These iterative methods are demonstrated in this paper for a hypothetical facility with a design maturity such that there is knowing the main components to comply with the engineering and security functions of the systems. With an assumed mature design, it is implied that generic data to execute quantitative reliability, and availability analyses are available at the systems levels that are sufficient to support a design-specific probabilistic risk assessment (PRA). The proposed methods modify the probabilities of basic events within the fault tree structures that model system and component unavailability sources that will be required for the facility’s operating license. The methods provided are applied to visualize the characteristics of the problem and the quantitative results. This work forms the basis for future work in which design alternatives affecting unavailabilities can be estimated and compared to their associated unavailability targets at different levels of granularity.

Risk-informed design and safety assessment of structures in a changing climate: a review of U.S. practice and a path forward

Standards for the design of bridges, buildings and other infrastructure specify design loads for climatic hazards such as temperature, snow, wind, and floods based on return periods presented in maps or tables that account for regional differences. These design loads were developed from statistical analyses of historical hazard data under the assumption that the past is representative of the future. Climate change may affect the frequencies and intensities of environmental hazards which, depending on regional variations, raises questions as to whether structures designed to current specifications will meet minimum safety standards over their future service lives. This paper critically appraises issues related to using historical hazard data for future designs. It reviews basic principles of uniform reliability, that modern design codes use as the basis for ensuring minimum levels of safety, describing the relationship between hazard return periods, structural reliability, risk and the maximum loads expected within a structure’s service life. Simple examples involving wind effects on structures demonstrate how to calibrate structural design hazard maps for climate-related extreme events to meet the minimum standards of safety implied in current specifications. The paper also introduces a possible practical approach to account for climate change when designing new structures and assessing the safety of existing facilities.

Neurophysiological Assessment of An Innovative Maritime Safety System in Terms of Ship Operators' Mental Workload, Stress, and Attention in the Full Mission Bridge Simulator.

The current industrial environment relies heavily on maritime transportation. Despite the continuous technological advances for the development of innovative safety software and hardware systems, there is a consistent gap in the scientific literature regarding the objective evaluation of the performance of maritime operators. The human factor is profoundly affected by changes in human performance or psychological state. The difficulty lies in the fact that the technology, tools, and protocols for investigating human performance are not fully mature or suitable for experimental investigation. The present research aims to integrate these two concepts by (i) objectively characterizing the psychological state of mariners, i.e., mental workload, stress, and attention, through their electroencephalographic (EEG) signal analysis, and (ii) validating an innovative safety framework countermeasure, defined as Human Risk-Informed Design (HURID), through the aforementioned neurophysiological approach. The proposed study involved 26 mariners within a high-fidelity bridge simulator while encountering collision risk in congested waters with and without the HURID. Subjective, behavioral, and neurophysiological data, i.e., EEG, were collected throughout the experimental activities. The results showed that the participants experienced a statistically significant higher mental workload and stress while performing the maritime activities without the HURID, while their attention level was statistically lower compared to the condition in which they performed the experiments with the HURID (all p < 0.05). Therefore, the presented study confirmed the effectiveness of the HURID during maritime operations in critical scenarios and led the way to extend the neurophysiological evaluation of the HFs of maritime operators during the performance of critical and/or standard shipboard tasks.

QUANTIFYING RISKS FOR COASTAL LEVEE DESIGNS ALONG THE U.S. GULF COAST

For all U.S. Army Corps of Engineers (USACE) dam and levee designs for new projects, modifications, improvements, rehabilitation, or repairs, a risk-informed design approach is taken (ECB 2019-15). Risk-informed design ensures that risks and uncertainties are evaluated and estimated to be tolerable. This approach occurs in parallel to the typical design approach, which primarily focuses on ensuring the project is commensurate with available policies, guidance, and criteria as specified in USACE publications (regulations, manuals, etc.) as well as project-specific criteria. These criteria result in designs that achieve adequate factors of safety for levees, floodwalls, or other structural features across a full range of hydraulic, seismic, and other types of hazards. The risk-informed design approach allows for adaptability to identify cases where a lesser factor of safety may still result in tolerable risks, or conversely, where proposed criteria may not be sufficient to reduce risks to an acceptable level. These type of assessments are performed while ensuring that the project holds life safety paramount, and the design and risk teams are open and transparent in their engagement with local partners.

Risk-informed collision avoidance system design for maritime autonomous surface ships

The maritime industry is paving the way towards developing Maritime Autonomous Surface Ships (MASSs) through the adoption of key enabling technologies for safety-critical operations, which are associated with new challenges, especially at their early design phase. This study aims to develop a methodology to conduct the risk-informed design for the Collision Avoidance System (CAS) of MASSs. Pertinent regulatory instruments are reviewed to identify functional and system requirements and develop a baseline CAS configuration at the component level. Quantitative Fault Tree Analysis is performed to derive risk metrics, such as probability of failure, Importance measures, and Minimal Cut Sets, whereas criticality analysis is conducted to recommend risk-reducing measures. A Short Sea Shipping case study is investigated considering four operating modes based on various weather and illumination conditions. Results demonstrate that the developed Fault Tree diagram provides a robust representation of the CAS failure. The most critical components are found to be related to the Intention Communication and Situation Awareness Systems, the redundancy of which leads to 91% reduction of the CAS probability of failure. This study contributes towards the risk-informed design of safety-critical systems required for the development of MASSs.

Risk-informed design optimization method and application in a lead-based research reactor

Risk-informed approach has been widely applied in the safety design, regulation, and operation of nuclear reactors. It has been commonly accepted that risk-informed design optimization should be used in the innovative reactor designs to make nuclear system highly safe and reliable. In spite of the risk-informed approach has been used in some advanced nuclear reactors designs, such as Westinghouse IRIS, Gen-IV sodium fast reactors and lead-based fast reactors, the process of risk-informed design of nuclear reactors is hardly to carry out when passive system reliability should be integrated in the framework. A practical method for new passive safety reactors based on probabilistic safety assessment (PSA) and passive system reliability analyze linking is proposed in this paper. New three-dimension frequency-consequence curve based on risk concept with three variables is used in this method. The proposed method has been applied to the determination optimization of design options selection in a 10 MWth lead-based research reactor(LR) to obtain one optimized system design in conceptual design stage, using the integrated reliability and probabilistic safety assessment program RiskA, and the computation resources and time consumption in this process was demonstrated reasonable and acceptable.

Risk-Informed Design of RCC Dams under Extreme Seismic Loading

The existing Scoggins Dam and reservoir are in Washington County, Oregon, and the title is held by the U.S. Bureau of Reclamation (Reclamation). Reclamation has previously identified dam safety concerns related to the existing embankment dam. Regional project sponsors, including Clean Water Services, have identified the need for expanded storage capacity in the reservoir to meet growing water demands and address water quality issues in the Tualatin River downstream of the dam. As part of efforts to resolve dam safety issues and increase the water storage in the reservoir, a comprehensive feasibility level design of a new 185-foot-high Roller Compacted Concrete (RCC) dam. Extraordinary seismic hazards have been identified in the region associated with the Cascadia Subduction Zone (CSZ). Further, any dam alternative carried forward for funding, final design, and construction will have to meet the Public Protection Guidelines (PPG) of Reclamation that require a formal quantitative risk analysis. A risk-informed design approach was adopted to configure the layout and cross-section properties of the dam. A multi-phase site characterization program and preliminary RCC mix design program were performed to support the design. In addition, models were developed, and an extensive suite of both (two-dimensional) 2D and (three-dimensional) 3D structural analyses were performed for seismic loadings with total durations of over 200 s, strong shaking of over 140 s, and peak ground accelerations of over 2 gravitational accelerations (g) (up to 50,000-year return period event). This paper describes the feasibility design configuration of the dam, including the seismic hazard characterization, structural analysis models, and seismic response modeling results. The expected performance of the dam relative to the risk-informed design criteria and Reclamation PPGs will be generally described.

Development of the Versatile Test Reactor Probabilistic Risk Assessment

The Versatile Test Reactor (VTR) is a fast spectrum test reactor currently being developed in the United States under the direction of the U.S. Department of Energy (DOE), Office of Nuclear Energy (DOE-NE). The mission of the VTR is to enable accelerated testing of advanced reactor fuels and materials required for advanced reactor technologies. The conceptual design of the 300-MW(thermal), sodium-cooled, metallic-fueled, pool-type fast reactor has been led by U.S. national laboratories in collaboration with General Electric-Hitachi and Bechtel National Inc. To facilitate risk-informed design and authorization activities during the conceptual development phase, a conceptual design probabilistic risk assessment (PRA) was performed for the VTR. This paper provides an overview of the development of the VTR conceptual design PRA, including key DOE and industry standards and the PRA analysis approach and structure. In addition, the results of the VTR conceptual design PRA are provided, which include its use within authorization documentation and design decisions, along with important lessons learned during the process. The work reported in the paper is the result of studies supporting a VTR conceptual design, cost, and schedule estimate for DOE-NE to make a decision on procurement. As such, it is preliminary.

Risk-Informed Design Optimization of Vertically Distributed Tuned Liquid Wall Dampers for Multihazard Mitigation

Risk-Informed Design Optimization of Vertically Distributed Tuned Liquid Wall Dampers for Multihazard Mitigation

Spatial correlation in ground motion prediction errors in Central and Eastern North America

Risk analysis and risk-informed design of spatially distributed infrastructure systems for earthquake hazards require an understanding of and ability to model the spatial correlation of ground motion prediction errors. We assess this spatial correlation in Central and Eastern North America (CENA) by calculating ground motion residuals and semivariograms from earthquake recordings in the Next Generation Attenuation (NGA)-East database. Although data limitations prohibit the development of a reliable model to capture this correlation, we have made notable findings relevant to future risk analyses. The spatial correlation of ground motion prediction errors in CENA is larger than those previously published for shallow crustal regions, which agrees with the lower attenuation observed in CENA. Differences in correlation behavior is also observed between tectonic and induced event recordings. This is, in part, due to the characteristics of the system of stations in which they were recorded. In addition, the choice of ground motion model (GMM) used to calculate the predicted ground motions was found to have an impact on the resulting correlation of errors and we recommend that future CENA spatial correlation models be tailored to the specific infrastructure system and location that will be analyzed.

Benchmarking FEMA P-58 repair costs and unsafe placards for the Northridge Earthquake: Implications for performance-based earthquake engineering

Performance-based earthquake engineering organizes the explicit quantification of building seismic performance and risk, facilitating risk-informed design and mitigation decisions. However, little work has been done to benchmark outcomes from these procedures with the available empirical evidence from past earthquakes. In this study, we benchmark the end-to-end outcomes of the FEMA P-58 performance-based engineering methodology against empirical data from California's 1994 Northridge Earthquake. Specifically, we perform a regional scenario assessment for around 2.6 million buildings in the Los Angeles area at the time of the 1994 earthquake to hindcast repair costs and numbers of unsafe placards from the earthquake. Based on the initial comparison with losses from the Northridge earthquake, we find expected values from our FEMA P-58 regional assessment to overpredict repair costs and unsafe placards, especially for wood frame buildings at low-to-moderate levels of shaking. We use this comparison to investigate underlying methodological and modeling assumptions and propose procedures to improve the outcomes, including increasing elastic damping for wood buildings, updating the FEMA P-58 virtual inspection process for unsafe placarding, and adopting truncated fragility functions to define uncertainties in damage. Outcomes from the proposed methodological updates provide a close match to observed losses in terms of repair costs and numbers of unsafe placards from the event for most building types.

Research on level 1 PSA and risk-informed design for ACP100

Advanced China Power 100 (ACP100) is a kind of multi-purpose small modular reactor (SMR) based on the present pressurized water reactor (PWR) technology. It adopts the integrated reactor technology routes, satisfies the current nuclear safety codes and guides issued by National Nuclear Safety Administration (NNSA), and also refers to the safety standards of International Atomic Energy Agency (IAEA). In the design phase, Probabilistic Safety Assessment (PSA) technology plays an important role to demonstrate the total safety level, identify the design vulnerabilities, and provide suggestions for the improvement of ACP100. After the brief summary of the level 1 PSA and its risk-informed design method, the level 1 PSA analysis was carried out for ACP100. The identification of initiating events (IEs), the event tree analysis, fault tree analysis and accident sequence quantification were performed. The main PSA results are shown in the paper, such as core damage frequency (CDF), dominating accident sequences, significant common cause failures (CCF). Finally, different design options and their impacts on risk which can be reflected by risk return were evaluated to avoid using the risk-increased design based on the quantitative risk calculation for the sake of increasing the ACP100’s safety. Consequently, the results show that the point estimated value of the total CDF of level 1 IEs PSA for operations at power of ACP100 is 1.42E-07/ry. After the design improvement proposed in this paper, the CDF (point estimate) of ACP100 can be reduced to 6.78E−08/ry. The risk were obviously reduced and the safety of the ACP100 is significant improved. This research provides a technical reference for future new nuclear reactor design.

Integrated Risk-Informed Design (I-RID) methodological framework and computational application for FLEX equipment storage buildings of Nuclear Power Plants

In this research, an Integrated Risk-Informed Design (I-RID) methodological framework is developed for generating and evaluating design options for Nuclear Power Plant (NPP) structures and for providing plant decision makers with a quantitative comparison among design options based on multiple decision criteria, e.g., safety risk and cost. In the I-RID framework, simulations of underlying failure mechanisms are integrated with Probabilistic Risk Assessment (PRA) (consisting of event trees and fault trees) and a cost assessment model in a unified framework. The failure mechanisms are simulated by conducting Finite Element Analysis (FEA), and a probabilistic interface between FEA and the existing plant PRA is generated using structural reliability techniques. A causal model for cost assessment is developed, which allows for the modeling of multi-layer causal relationships among underlying contributing factors and, therefore, creates an explicit connection between cost and safety risk outputs. This paper applies the I-RID framework to the design of a storage building for the Diverse and Flexible Coping Strategies (FLEX) equipment in an NPP subjected to a potential tornado impact. Over two hundred design options are generated and evaluated, and three suggested design options with the lowest values of safety risk and cost are identified.

Identification of the Postulated Initiating Events of Accidents Occurring in a Toroidal Field Magnet of the EU DEMO

The design of the European Union (EU) DEMO reactor magnet system, currently ongoing within the EUROfusion consortium, will take advantage of the know-how developed during the design and manufacturing of ITER magnets; however, DEMO will suffer some new, more severe challenges, e.g., larger tritium inventory and higher neutron fluence, both having an impact on safety functions accomplished, among the other systems, also by the magnets. For these reasons, and in view of the need to demonstrate a high availability of the reactor (aimed at electricity production), a new, more systematic assessment of the system safety is required. As a contribution in this direction, the initiating events (IEs) of the most critical accident sequences in the EU DEMO magnet system (with special reference to the toroidal field magnets) are identified here, adopting first a functional analysis and then a failure mode, effects, and criticality analysis. In particular, the following are provided: (1) the EU DEMO magnet system is subdivided into functionally independent subsystems and components (e.g., the magnets, their cooling circuits, and their power supply system); (2) the relevant failure modes of each subsystem are systematically identified, together with the corresponding causes and consequences; (3) a list of IEs is compiled, leading to scenarios that may compromise the magnet safety and availability. Finally, the so-called postulated IEs are selected as the most challenging IEs for the safety of the magnet system. This analysis initializes a path leading to a risk-informed design, i.e., the identification of safety issues that could be addressed at the design level instead of introducing expensive mitigation measures after the design completion.

Risk-Informed Mean Recurrence Intervals for Updated Wind Maps in ASCE 7-16.

ASCE 7 is moving toward adopting load requirements that are consistent with risk-informed design goals characteristic of performance-based engineering (PBE). ASCE 7-10 provided wind maps that correspond to return periods of 300, 700, and 1,700 years for Risk Categories I, II, and combined III/IV, respectively. The risk targets for Risk Categories III and IV buildings and other structures (designated as essential facilities) are different in PBE. The reliability analyses reported in this paper were conducted using updated wind load data to (1) confirm that the return periods already in ASCE 7-10 were also appropriate for risk-informed PBE, and (2) to determine a new risk-based return period for Risk Category IV. The use of data for wind directionality factor, Kd , which has become available from recent wind tunnel tests, revealed that reliabilities associated with wind load combinations for Risk Category II structures are, in fact, consistent with the reliabilities associated with the ASCE 7 gravity load combinations. This paper shows that the new wind maps in ASCE 7-16, which are based on return periods of 300, 700, 1,700, and 3,000 years for Risk Categories I, II, III, and IV, respectively), achieve the reliability targets in Section 1.3.1.3 of ASCE 7-16 for nonhurricane wind loads.