Risk-informed Assessment Research Articles

A KDE-based non-parametric cloud approach for efficient seismic fragility estimation of structures under non-stationary excitation

With the development of performance-based earthquake engineering, the risk-informed assessment framework has received broad recognition over the world, of which the probability seismic fragility analysis is an important step. The classic seismic fragility adopts the lognormal assumption and forms a parametric derivation. With the development of fragility theory, researchers are hoping to seek out non-parametric approaches to express the intrinsic fragility in a pure analytical form without any distribution assumptions. Besides, how to keep the calculation efficiency (e.g., combining with cloud approach) and how to consider the non-stationary stochastic responses (e.g., combining with non-stationary stochastic excitation model) are critical aspects in fragility that deserve further attention of researchers. In this paper, a kernel density estimation (KDE) based non-parametric cloud approach is proposed for efficient seismic fragility estimation of structures under non-stationary excitation. First, the methodology framework of the efficient approach is illustrated. Then, the procedures of non-stationary stochastic seismic response of structures and KDE-based non-parametric cloud approach for efficient seismic fragility are demonstrated. After that, an application example via a three-span-six-story reinforced concrete frame is given for implementation, followed with a parametric analysis of critical factors. During the process, the classic parametric linear-regression based cloud approach (cloud-LR) and benchmark Monte-Carlo-simulation based cloud approach (cloud-MCS) are also incorporated for validation. In general, the analysis verifies the effectiveness of the non-parametric cloud-KDE approach without requiring more computation work (i.e., same as the parametric cloud-LR approach and much less than the benchmark cloud-MCS approach). Meanwhile, the non-parametric cloud-KDE approach indicates a comparable accuracy with the classic fragility approaches (i.e., less deviation than the parametric cloud-LR approach and much closer to the benchmark cloud-MCS approach), and with the increase of stochastic cloud-point number, the corresponding fitting degree of cloud-KDE approach is growing better. The research provides a new sight for the development of non-parametric seismic fragility approach, and the corresponding findings can be further combined with the probabilistic hazard and risk analysis for a non-parametric assessment procedure in performance-based earthquake engineering.

Study on probabilistic safety assessment in decommissioning of nuclear power plant

The decommissioning of Nuclear power plant involves many activities different from the normal operation stage of Nuclear power plant. In the process of decommissioning, there are many new safety problems, which usually require new safety evaluation. The safety management of decommissioning runs through the whole decommissioning stage until the decommissioning of the plant site is completed. The management level depends on the risk level of each stage of decommissioning, especially the decommissioning process of high radioactivity in nuclear power plant, so it is necessary to pay attention to the risk of different stages of decommissioning and improve the decommissioning safety management. At present, probabilistic safety assessment method has become an effective tool to support and supplement deterministic safety assessment, and is used in regulatory activities. The safety risk analysis of nuclear power plant in the decommissioning stage in China is in the initial stage, with little experience. Therefore, it is necessary to study the corresponding technical methods and risk management applications. This paper study on the probabilistic safety assessment in the decommissioning of nuclear power plant, including its scope of application, risk-informed assessment method and safety management application. The probabilistic safety assessment of decommissioning of nuclear power plant is an effective means to evaluate the potential risks related to decommissioning activities and their possible consequences. This method can be used for safety review and safety management in the decommissioning stage of nuclear power plant.

A risk-informed assessment tool to support review of license amendment requests for spent nuclear fuel dry cask storage systems

While risk-informed safety evaluations are common methodologies used by the U.S. Nuclear Regulatory Commission (NRC), their application in the field of commercial spent nuclear fuel (SNF) dry storage has received limited attention. For instance, license amendment requests (LARs) for SNF dry cask storage systems (DCSSs) are evaluated according to U.S. NRC standard review plans (SRPs). However, risk-informed LAR review strategies could improve the understanding of critical system modifications, and lead to more effective, efficient, and consistent LAR review processes.A methodology to develop a risk-informed LAR review tool is presented. Although focused on DCSSs, this methodology can be used to develop similar tools for a broad spectrum of safety-relevant systems. The end product (i.e., the tool) includes a tree diagram to help visualize the review risk significances assigned to a predefined set of system modifications and supporting rationale documentation. Instructions support correct tool application and provide the user with a path to incorporate currently unevaluated modifications in the tool structure.The demonstration of the methodology leads to the conclusion that risk-informed reviews of DCSS LARs are possible, although the tool precision could benefit from additional risk information. Further, the results indicate that many typical LARs involve low-risk or medium-risk modifications.

Simulation-Based and Risk-Informed Assessment of the Effectiveness of Tsunami Evacuation Routes Using Agent-Based Modeling: A Case Study of Seaside, Oregon

Typically, tsunami evacuation routes are marked using signs in the transportation network and the evacuation map is made to educate people on how to follow the evacuation route. However, tsunami evacuation routes are usually identified without the support of evacuation simulation, and the route effectiveness in the reduction of evacuation risk is typically unknown quantitatively. This study proposes a simulation-based and risk-informed framework for quantitative evaluation of the effectiveness of evacuation routes in reducing evacuation risk. An agent-based model is used to simulate the tsunami evacuation, which is then used in a simulation-based risk assessment framework to evaluate the evacuation risk. The route effectiveness in reducing the evacuation risk is evaluated by investigating how the evacuation risk varies with the proportion of the evacuees that use the evacuation route. The impacts of critical risk factors such as evacuation mode (for example, on foot or by car) and population size and distribution on the route effectiveness are also investigated. The evacuation risks under different cases are efficiently calculated using the augmented sample-based approach. The proposed approach is applied to the risk-informed evaluation of the route effectiveness for tsunami evacuation in Seaside, Oregon. The evaluation results show that the route usage is overall effective in reducing the evacuation risk in the study area. The results can be used for evacuation preparedness education and hence effective evacuation.

Image‐based road crack risk‐informed assessment using a convolutional neural network and an unmanned aerial vehicle

Rapid crack assessment is widely thought to be critical for monitoring and maintaining roads in appropriate conditions. In this paper, a novel crack-affected risk-informed assessment framework is proposed for the monitoring and maintenance of roads. The framework includes five steps: data collection, crack detection, crack location extraction, crack real-size calculation, and risk-level assessment. To support the framework, an unmanned aerial vehicle (UAV) is used to monitor roads and collect data. A state-of-the-art semantic segmentation network, DeepLabv3+, is also applied to detect cracks. Based on the height and pixel statistics of the detected crack, the real size of the crack can be calculated using the pixel-physical conversion coefficient equation. This is followed by a risk-informed assessment of the road identifying the location of the crack for maintenance priority determination. Data collection and experiments using a UAV were performed on a real road to verify the feasibility and effectiveness of the proposed method. It was found that the proposed method was not only able to determine the real size of the cracks from the collected images but also able to determine their risk levels. In summary, this method presents a convenient and reliable solution for risk-informed road crack assessment that can be employed in practical applications.

Evaluating flood resilience in rural communities: a case-based assessment of Dyer County, Tennessee

Communities everywhere are being subjected to a variety of natural hazard events that can result in significant disruption to critical functions. As a result, community resilience assessment in these locations is gaining popularity as a means to help better prepare for, respond to, and recover from potentially disruptive events. The objective of this study was to identify key vulnerabilities relevant to addressing rural community resilience through conducting an initial flood impact analysis, with a specific focus on emergency response and transportation network accessibility. It included a use case involving the flooding of a rural community along the US inland waterway system. Special consideration was given to impacts experienced by at-risk populations (e.g., low economic status, youth, and elderly), given their unique vulnerabilities. An important backdrop to this work is recognition that Federal Emergency Management Agency’s Hazus, a free, publicly available tool, is commonly recommended by the agency for counties, particularly those with limited resources (i.e., rural areas), to use in developing their hazard mitigation plans. The case study results, however, demonstrate that Hazus, as currently utilized, has some serious deficiencies in that it: (1) likely underestimates the flood extent boundaries for study regions in a Level 1 analysis (which solely relies upon filling digital elevation models with precipitation), (2) may be incorrectly predicting the number and location of damaged buildings due to its reliance on out-of-date census data and the assumption that buildings are evenly distributed within a census block, and (3) is incomplete in its reporting of the accessibility of socially vulnerable populations and response capabilities of essential facilities. Therefore, if counties base their flood emergency response plans solely on Hazus results, they are likely to be underprepared for future flood events of significant magnitude. An approach in which Hazus results can be augmented with additional data and analyses is proposed to provide a more risk-informed assessment of community-level flood resilience.

Spectrum sharing analysis for unlicensed use in 6 GHz using Risk-Informed Interference Assessment

In October of 2018, the FCC proposed new rules for opening 1.2 GHz of spectrum in the 6 GHz band, from 5925 to 7125 MHz, for unlicensed Wireless Local Area Networks (WLAN) devices. The objective is to allow WLAN in the 6 GHz band while sharing the spectrum with current incumbents. The traditional spectrum sharing approach relies on the worst-case scenario analysis of single events of severe consequences, regardless of their probability of occurrence, which leads to over-conservative use of the spectrum. Risk-Informed Interference Assessment (RIIA) is a quantitative approach that can be successfully applied for spectrum sharing analysis. Based on statistical analysis, RIIA estimates the probability and the consequence of interference. The objective is to allow flexible use of spectrum without being overprotective. It has been applied to a few coexistence studies in the last years and has shown great potential in providing informed insight to spectrum sharing analysis. To date, however, it has not been yet applied to coexistence studies in the 6 GHz band. In this work, we apply RIIA to analyze coexistence between WLAN and each type of incumbent service in this band and propose spectrum sharing mechanisms to reduce the probability of harmful interference. To facilitate sharing in the 6 GHz band, the FCC has divided it into four sub-bands, from U-NII-5 to U-NII-8, and proposed mitigation rules for each of them depending on the incumbents. This band is allocated to Broadcast Auxiliary Service (BAS) and Cable Television Relay Service (CARS) fixed and mobile links, Fixed Satellite Service (FSS) and fixed point-to-point links. These systems use narrow beamwidth antennas located at elevated heights, while WLANs employ low-power transmitters, mostly indoors, and, typically, omnidirectional antennas at few meters above the ground, which suggests the possibility that little energy from the incumbent links is perceptible on the ground and vice versa. To investigate this hypothesis, we apply RIIA to quantify the level of risk and its consequences to both, incumbent links and WLANs devices. Our analysis is based upon a four-step method. First, we make an inventory of all significant harmful interference hazards, in our case, 6 GHz Wi-Fi APs or incumbent links that could cause co-channel interference to the incumbents or Wi-Fi devices, respectively. Second, we define the interference protection criteria for each of them as consequence metrics to characterize the severity of hazards. Third, the likelihood and consequence of each hazard are analyzed. Using Monte Carlo simulations, we calculate the likelihood of downlink and aggregate interference from/to current incumbents to/from future WLANs and, using an interference protection criterion, determine if this interference can be tolerable. Finally, the likelihood-consequence results are aggregated and compared for different scenarios. This approach provides detailed coexistence analysis between WLAN and incumbent services in the 6 GHz band using the RIIA methodology. The results suggest that there is a low risk of harmful interference to terrestrial incumbent links in the U-NII-6 and U-NII-8 bands, which consider low-power indoor APs only. For the U-NII-5 and U-NII-7 bands, considering outdoor APs transmitting at full power, the probability of harmful interference ranges from low to high, depending on the scenario. To reduce this risk, it is suggested to implement a mitigation technique. In the case of a satellite incumbent, coexistence is possible without the need of mitigation techniques. Ultimately, this work will provide decision-makers with information regarding the risks associated with coexistence in the 6 GHz band.

Risk-informed assessment of radionuclide release from dissolution of spent nuclear fuel and high-level waste glass

This paper aims to detail the different parameters to be considered for use in an assessment of radionuclide release. The dissolution of spent nuclear fuel and high-level nuclear waste glass was considered for risk and performance insights in a generic disposal system for more than 100,000years. The probabilistic performance assessment includes the waste form, container, geology, and hydrology. Based on the author’s previous extended work and data from the literature, this paper presents more detailed specific cases of (1) the time dependence of radionuclide release, (2) radionuclide release coupled with container failure (rate-limiting process), (3) radionuclide release through the opening area of the container and cladding, and (4) sequestration of radionuclides in the near field after container failure. These cases are better understood for risk and performance insights. The dissolved amount of waste form is not linear with time but is higher at first. The radionuclide release rate from waste form dissolution can be constrained by container failure time. The partial opening area of the container surface may decrease radionuclide release. Radionuclides sequestered by various chemical reactions in the near field of a failed container may become stable with time as the radiation level decreases with time.

Risk-Informed Interference Assessment for Shared Spectrum Bands: A Wi-Fi/LTE Coexistence Case Study

Interference evaluation is crucial when deciding whether and how wireless technologies should operate. In this paper, we demonstrate the benefit of risk-informed interference assessment to aid spectrum regulators in making decisions, and to readily convey engineering insight. We apply, for the first time, risk assessment to an open question of inter-technology spectrum sharing, i.e., a Wi-Fi/LTE coexistence study in the unlicensed band, and we demonstrate that this method comprehensively quantifies the interference impact. We perform simulations with our newly publicly available tool and we consider throughput degradation and fairness as example metrics to assess the risk for different network densities, numbers of channels, and deployments. The risk assessment study shows that no regulatory intervention is needed to ensure harmonious technical Wi-Fi/LTE coexistence: for the typically large number of channels available in the 5 GHz band, the risk for Wi-Fi from LTE is negligible. As an engineering insight, Wi-Fi coexists better with itself in dense deployments, but better with LTE in sparse deployments. Also, both main LTE-in-unlicensed variants coexist well with Wi-Fi in general. For LTE intra-technology inter-operator coexistence, both variants typically coexist well in the 5 GHz band, but for dense deployments, implementing listen-before-talk causes less interference.

Risk-Informed Interference Assessment: A Quantitative Basis for Spectrum Allocation Decisions

Risk-Informed Interference Assessment: A Quantitative Basis for Spectrum Allocation Decisions

Estimates of Economic Value Generated by Contracting Radio Exclusion Zones in the 1695-1710 MHz Band

This paper estimates the economic value of contracting protection or exclusion zones for three polar weather satellite earth stations in the 1695 MHz–1710 MHz band located in Suitland, MD; Miami, FL; and San Francisco, CA.In 2010 President Obama directed the Secretary of Commerce and the National Telecommunications and Information Administration (NTIA) to make 500 MHz of spectrum available within the next decade for wireless broadband use. As part of its “fast track report” responding to the President’s request, the NTIA identified 1695–1710 MHz as one a number of candidate bands. The fast track report calculated exclusion zones – radii surrounding satellite earth stations in which commercial operation would be disallowed. Subsequently a working group within the NTIA’s Commerce Spectrum Management Advisory Committee (CSMAC) conducted more detailed work on the exclusion zones. The CSMAC working group refined the analysis whereby the radii were calculated, shrinking those radii in the process. It also recommended converting the exclusion zones to protection zones in which certain commercial activities could be permitted if they were coordinated beforehand with federal uses. The purpose of this paper is to estimate the economic value of the reduction of the radii, treating the smaller protection zones as if they were exclusion zones to simplify the analysis.This paper uses a rough population-based methodology, under which the value of a given spectrum license is assumed to be directly proportional to the number of people who can be served by that license. Population is assumed to be evenly distributed across the given area. Though this approach is obviously imprecise, it suffices to give an order-of-magnitude estimate of the economic value that would be created by shrinking exclusion zones and converting them to protection zones. It also treats exclusion zones and protection zones as functionally identical because it does not seek to generate precise dollar figures that would entail valuing the option of operating inside a protection zone.This paper’s findings may contribute to the deliberations of the Federal Communications Commission Technological Advisory Council (FCC TAC) working group exploring how risk-informed interference assessment, and particularly quantitative risk assessment rather than worst-case analysis, can inform spectrum sharing or spectrum allocation questions. The calculations contained in the NTIA’s fast track report were based on worst-case or at least very conservative assumptions. CSMAC’s assumptions were less conservative, for example using a realistic distribution of transmit power values for interfering mobiles rather than the maximum in all cases. This paper thus estimates the economic value generated by the change in method.

Risk-Informed Interference Assessment: A Quantitative Basis for Spectrum Allocation Decisions

The trade-off between the benefits of a new radio service allocation and its risk to incumbents has to date been based on “worst case” analyses that focus on the single scenario with the most severe negative consequence, regardless of its likelihood. This is no longer a tenable approach since it leads to over-conservative allocations that limit the social benefits of new services while giving incumbents more protection than they need.This paper describes an alternative to worst case reasoning: the use of quantitative risk assessment (QRA) to analyze the harm that may be caused by changes in radio service rules. QRA considers both the likelihood and the consequences for multiple hazard scenarios, not just the most severe consequence, regardless of likelihood, as in worst case. While quantitative risk assessment has been used for decades in many regulated industries it has not yet been applied to spectrum management. This paper identifies four key elements of a systematic, quantitative analysis of radio interference hazards, and illustrates them with examples: (1) make an inventory of all significant harmful interference hazard modes; (2) define a consequence metric to characterize the severity of hazards; (3) assess the likelihood and consequence of each hazard mode; and (4) aggregate them into a basis for decision making. The four elements are illustrated by examples from spectrum policy questions past and present; the focal case study is the determination of geographic exclusion zones to protect weather satellite earth stations from co-channel cellular mobile transmitters.In order to reap the benefits of risk-informed interference analysis, the paper rec-ommends that regulators (1) develop know-how through a variety of educational initiatives; (2) use quantitative risk assessment in their analysis of harmful interference, and publish the results; and (3) pilot this approach in proceedings with limited scope, like selected site-specific license waiver proceedings. There is also a role for legislators and the executive branch: (1) they can require risk-informed assessments as part of their spectrum oversight activities; (2) when presented with politically charged claims of harmful interference, they can avoid the temptation of nightmare scenarios and instead make assessments that consider both the likelihood and consequences of interference harms; and (3) they can support regulators that use risk-informed interference assessments rather than basing decisions on worst case analysis.

An Outline of Risk-Informed Interference Assessment

In judging whether to allow new service rules, a regulator has to balance the interests of incumbents, new entrants and the public. The trade-off between the benefits of a new service and the risks to incumbents has to date been essentially qualitative. This short paper proposes the use of quantitative risk analysis to assess the harm that may be caused by changes in radio service rules. Risk analysis considers the likelihood-consequence combinations for multiple hazard scenarios, and complements a “worst case” analysis that considers the single scenario with the most severe consequence, regardless of its likelihood. Risk-informed interference assessment is the systematic, quantitative analysis of interference hazards caused by the interaction between radio systems. Such an assessment has three major steps: 1. Make an inventory of all significant harmful interference hazard modes. 2. Define a consequence metric to characterize the severity of hazards. 3. Assess the likelihood and consequence of each hazard mode. Quantitative risk assessment can: • provide a common currency for comparing different interference scenarios and assessments; • enhance the completeness of analysis and increase the chances of identifying unexpected harmful interference mechanisms; • provide objective information to policy decision makers balancing the benefits of a new service and its adverse technical impact on incumbents. Implementing quantitative risk assessment requires a change in culture, and will take time. A regulator should therefore start small, but start soon: • Develop know-how in the agency and the wider community, for example through a lecture series on modern risk management, and — if there is an on-going education facility like the FCC University — by offering courses to staff on statistics and risk-management. • Use quantitative risk assessment in its own work, and publish the analyses and results. • Provide quantitative guidelines on unquestionably acceptable and unacceptable interference risks, respectively, e.g. as likelihood-consequence regions on a risk chart. • Pilot this approach in selected site-specific license waiver proceedings.

Piloting Risk-Informed Interference Assessment Using Waivers

This working paper investigates whether there are Federal Communications Commission actions that would be well suited to serve as pilots of risk-informed interference assessment (“RIIA”). It investigates the record of petitions for spectrum-related waivers, experimental licenses and special temporary authority over the last five years.It concludes that waivers — rulings by the FCC that excuse compliance, in whole or part, with its rules following a petition by a licensee — seem to be the well suited for RIIA pilots because they are narrower than larger-scale rulemakings, reducing the risk of unexpected adverse impacts. We expect that waivers will accommodate RIIA with minimal disruption to the existing process. Site-specific waivers may be best suited for initial trials because they involve a smaller number variables than nationwide or device waivers.

Probabilistic ship collision risk and sustainability assessment considering risk attitudes

The disastrous consequences of ship collision necessitate the development of a collision risk-informed assessment procedure that ensures safety and functionality of maritime transportation systems. In this paper, an approach to assess the risk and sustainability associated with ship collision accidents is presented. The probability of ship collision is computed by taking into account traffic data and operational conditions. In this paper, sustainability is quantified considering the detrimental economic, social, and environmental consequences associated with ship collision. The economic, social and environmental metrics are evaluated separately and then social and environmental metrics are converted into an economic metric considering their associated monetary values. Epistemic and aleatory uncertainties associated with damage conditions of ships and consequences are incorporated in this methodology in order to provide a rational assessment of risk and sustainability. Risk attitudes are incorporated within risk analysis by utilizing utility functions. The approach is illustrated on a maritime transportation system in the Delaware River area considering the properties of damaged ships and maritime traffic in this specific region. Ultimately, this approach can aid the decision maker to make informed choices based on risk and sustainability considering risk attitudes.

Defining resilience within a risk-informed assessment framework

The concept of resilience is the subject of considerable discussion in academic, business, and governmental circles. It is complex, multidimensional, and defined differently by different stakeholders. The authors contend that there is a benefit in moving from discussing resilience as an abstraction to defining resilience as a measurable characteristic of a system. This paper proposes defining resilience measures using elements of a traditional risk assessment framework to help clarify the concept of resilience and as a way to provide non-traditional risk information. The authors show various, diverse dimensions of resilience can be quantitatively defined in a common risk assessment framework based on the concept of loss of service. This allows the comparison of options for improving the resilience of infrastructure and presents a means to perform cost-benefit analysis.

Risk-informed assessment of regional preparedness: A case study of emergency potable water for hurricane response in Southeast Virginia

Decisionmakers need to understand the degree to which information-based decision processes affect the capabilities of a region to absorb the impact of a disaster and to respond and recover within an acceptable envelope of time and cost. This paper explores the modeling of a region as a system that has imperfect information about itself and an imperfect ability to discern its future infrastructure conditions. The paper illustrates this system-modeling paradigm with a data-based example of how emergency potable water was supplied as part of hurricane response in Southeastern Virginia. In this example, results indicate that prepositioning potable water supplies can result in savings in excess of one million dollars per forecast and can affect as much as one-third of the regional population. Moreover, the capacity of the region to respond to imperfect information and to reduce risk of both response costs and persons impacted can be achieved through strategic preparedness methods that change the decision-processing capability of the region. The major purpose of this paper is to demonstrate the importance of information and information processes in evaluating regional risk and capability and to emphasize the need for simultaneous evaluation of response and preparedness.

Risk-informed assessment of degraded containment vessels

This study couples structural analyses of four typical U.S. nuclear power plant containments with existing probabilistic risk assessment (PRA) models to assess the effects of degradation. This method is used to determine the increase in the early release frequencies (risk) due to postulated cases of corrosion in the steel liners and shells, as well as other forms of degradation.

Risk-Informed Assessment of the Technical Specifications of PWR RPS Instrumentation

A special Markov reliability model is used to simulate the effects of frequency of testing and allowable bypass time of the analog channels and logic trains on the performance of a pressurized water reactor, reactor protection system (RPS). The effects of these technical specifications (TSs) on the unavailability of the RPS and on the frequencies of spurious scrams, core damage, anticipated transients without scram, and large early releases are assessed. The use of these results to support decision making concerning changing the TSs in light of the relevant policy statement by the U.S. Nuclear Regulatory Commission on risk-informed decision making is demonstrated. The analysis includes point-value calculations sensitivity and uncertainty analysis.