Risk-informed Approach Research Articles

A Demonstration of the Risk-Informed NEI 18-04 Design Evaluation Model for the Modular High-Temperature Gas Reactor

Several advanced reactor designs are now under active development in the United States and elsewhere, promising sustainable solutions to the growing world energy needs. The designs currently being considered are quite diverse and different from the more established light water reactor technology that has dominated the operating commercial nuclear landscape. While advanced reactor concepts were first explored in the dawn of the nuclear age, they are now being reconsidered under the light of modern needs, and specifically, for their flexible operating conditions and inherent safety characteristics. In response, the U.S. Nuclear Regulatory Commission staff is moving forward with development of 10 CFR Part 53 rulemaking, which is a more risk-informed, technology-agnostic framework for licensing and regulating such new designs. The nuclear industry response to this regulatory initiative resulted in the technical report by the Nuclear Energy Institute, NEI 18-04 Revision 1, which provides an implementation roadmap of the risk-informed approach when defining the safety case for a new plant design. The implementation of this safety case may be a nontrivial exercise for an actual reactor design. This paper provides a demonstration of performing such an analysis for a representative advanced reactor. Public information from the General Atomics high-temperature gas reactor design was considered in this demonstration. The analysis workflow was facilitated with the FPoliSolutions’ proprietary Risk-Informed System Engineering (RISE) digital platform, a product that was presented in previous publications. RISE is one application of FPoli’s enterprise digital platform, which was created to facilitate orchestration of complex workflows leveraging recent technologies developed at national laboratories, such as Idaho National Laboratory’s RAVEN and EMRALD frameworks. The analysis described in the paper includes the selection and classifications of events, the integration of probabilistic risk analysis artifacts, and event modeling simulations for consequence evaluations. The results are then used for system, structures, and components safety classification and a synthesis of the safety case for the design in line with the frequency-consequence targets presented in NEI 18-04. The purpose of the analysis, as framed in RISE, is to readily produce outputs and views that can aid users and regulators in making risk-informed decisions to demonstrate their plant safety case.

Mitigating uncertainty: A risk informed approach for deploying hydrogen refueling stations

Regulatory gaps and safety concerns induce uncertainty amongst stakeholders, increases investment risk and impedes the deployment of hydrogen refueling stations (HRS). In this study, a risk-informed approach was employed on a potential HRS in Canada, to optimize separation distances, and identify regulatory gaps. This risk assessment improves upon previous ones that assumed uniform hydrogen leak sizes throughout the entire HRS. This analysis considers variable leak sizes based on the varying pipe flow area in different parts of the HRS like the tube-trailer area, hydrogen system area and the dispenser area. For each area, the potential leak sizes of 0.1%, 1%, 10%, and 100% of the pipe flow area were evaluated to cover a range of possible leaks. Leak frequency for 1% and 10% leak sizes were found to be 2.38E-02/year and 2.68E-03/year indicating relatively smaller difference as compared to other leak sizes. Leak frequency and consequence distances were assessed using HyRAM+ (V5.0) and Safeti (V8.9) respectively. Separation distances, which refer to the required spacing measured from the hydrogen process areas beyond which the risks are considered tolerable, were assessed for the tube-trailer area, storage area, and dispenser area at 350 bar and 700 bar dispensing pressures. Results indicated that 700 bar scenario requires substantially larger separation distances up to 39.1 m due to extended harm distances at lower temperatures. This study proposes safety barriers which reduced jet and flash fire frequencies by 100 and 20 events/year, respectively, that enables decreasing separation distances for each area. The comprehensive evaluation of separation distances generates important insights into separation distance criteria and guidelines, addressing the identified gap in existing codes and standards. While the study focuses on a potential HRS in Canada, the methodology, approach, and results presented are broadly applicable and transferable to similar contexts globally.

Risk-Informing Nuclear Reactor Safety: The Prediction of the Probability of Core Damage Due to Loss of Power and Cooling

Abstract The modern idea of risk-informed decision-making (RIDM) is here critically examined for all existing, advanced and, generation-IV nuclear reactor systems. Motivated by the predictive difficulties of probabilistic risk assessment (PRA) in regard to occurred accidents, it is evident that the real (not hypothetical) consequences of nuclear core damage accidents that must be considered and quantified are the financial losses, infrastructure damages, societal disruptions, and adverse political policies, and not solely the traditional exceedance of regulated radiation release or public exposure limits. With this perspective, a new dynamic analysis is presented for estimating the probability of core damage due to extended loss of power and cooling in a modern nuclear reactor, giving results different from current standardized PRA/PSA analyses. Using existing data, we approach the multitude of different events in a new way: whatever the initial event in the finite event set {external flood, fire, hurricane, ice storm, typhoon, earthquake, cyber attack…}, the fundamental concerns are the consequent loss and nonrestoration of power, and the inadequate cooling of the core. The present proposed quantitative evaluation uses applicable and fully “exchangeable” severe event data for nuclear and nonnuclear systems, including active and passive emergency back-up systems for a wide range of power losses that lead to widespread damage and societal disruption. While not design-specific, this new independent “order-of-magnitude” estimate for the probability of core damage is some two to two hundred times larger than that shown or reported in recent modern and formal PSA/PRA for licensing submissions using generic failure rate data rather than actual severe event data. This new finding suggests greater uncertainties exist than presently assumed for risk-informed decision-making (RIDM), and points to the need for a major reconsideration and updating of risk assessment and regulatory risk-informed approaches for nuclear plant safety evaluation.

Methods for Risk Reduction: Training and Exercises to Pursue the Planned Evacuation

Natural and anthropic disasters produce relevant economic and environmental losses at a global level. Many countries have adopted a risk management cycle to limit these losses. Agenda 2030 defined specific Sustainable Development Goals (SDGs) and relative targets dedicated to disaster risk reduction. Planned actions can pertain to the context “before” or “after” a disastrous event. The United Nations recommend a risk-informed approach for achieving the SDGs by working on anticipation and prevention. Planning with training and exercises, referring to transport systems in emergency conditions, can limit disaster impacts and strongly support the pursuit of sustainability. This research focuses on actions and methodologies for increasing preparedness levels “before” a disastrous event, to improve the capabilities of managers and people by increasing awareness of the effects of planned actions. Transport system models (TSMs) play an important role in simulating the evacuation of people to reduce theoretical risk, thereby reducing theoretical exposure. In this work, a method is presented that allows us to investigate how this theoretical reduction can become effective, through training and exercises. The paper proposes a general framework of training and exercises for risk reduction based on a given transportation planning model. The framework supports ex ante evaluations of exposure reduction produced by an evacuation plan. The obtained results show that the effectiveness of the planned actions increases with different levels of exercise implementation. The progressive implementation of exercises contributes to achieving the risk reductions estimated at the evacuation planning stage. The TSM in the mitigation phase is the basis for the development of specific quantitative evacuation plans, that must be implemented in the preparedness phase by means of training and exercises to test the planned actions in terms of reducing the exposure risk component. Some exercises implemented worldwide verify the proposed framework by means of some empirical evidence. The results and discussions reported in this paper can be useful for researchers, decisionmakers, and society by offering a contribution to the growing knowledge about risk and the potential actions and their relative effects on reducing it.

The role of risk-informed approaches for advanced reactors in Korea

Currently, various types of advanced reactors are being developed in the Republic of Korea, including (1) advanced large power reactors, (2) light water–based small and modular reactors, and (3) Generation IV reactors. While Probabilistic Safety Assessments (PSAs) have been performed for these advanced reactors in Korea, the PSAs were not conducted in detail since they were not regulatory requirements in many cases. However, the role of PSA is changing in Korea nowadays, and qualified PSA models have recently become an essential element in the licensing of operating and new reactors. In addition, PSAs for advanced reactors are essential not only to meet regulatory requirements but also to improve the safety and performance of advanced reactors. It can be said that the success of advanced reactors depends on how their safety and economics can be secured effectively and efficiently. The PSA will play an essential role in this aspect. Various risk-informed approaches (RIAs) based on PSAs are used in many countries worldwide for this purpose. A few issues remain to be resolved for the success of PSAs and RIAs for advanced reactors, such as the development of licensing frameworks for advanced reactors, the reliability assessments of passive safety systems, and so on. In this paper, we introduce the current status of PSAs and RIAs for advanced reactors, including descriptions regarding the characteristics of advanced reactors currently being developed in Korea. We also discuss some important issues to be resolved for the success of RIAs for advanced reactors. We also briefly introduce some research performed to resolve those issues.

Induced seismicity traffic light protocol at the Alberta No. 1 geothermal project site

The Alberta No. 1 Geothermal Project (ABNo1) is a renewable energy project in Canada; it will use deep geothermal energy for electrical power generation and direct-use thermal power. However, concerns regarding induced seismicity must be addressed. This study proposes implementing the Traffic Light Protocol (TLP) as a risk management tool for conventional geothermal projects in Alberta. We focus on determining an appropriate TLP red-light threshold, employing a risk-informed approach for the Leduc Formation - one of the geothermal reservoirs proposed for development by ABNo.1. The recommended red-light threshold of ML 3.5 signifies the level at which operations must be halted (i.e., the red light) to mitigate nuisance impact, damage, and personal risk. The recommended yellow light threshold of ML 1.5 signifies the level at which assessment of injection operations must be re-assessed, the regulator must be informed, and a risk mitigation analysis must be undertaken to re-evaluate operations to keep induced seismicity at a low magnitude. Comparison to induced seismicity near the project site highlights key factors requiring consideration during the project's design phase: injection volume, chances of basement fault reactivation, and delayed seismic activity onset. Effective mitigation entails controlling injection rate, continuous fluid balance monitoring, allowing gradual and appropriate pressure dissipation rates, and potentially the use of tracer tests to deconvolve pathways. This study provides insights for stakeholders involved in injection projects, aiding risk mitigation and ensuring safe, sustainable energy extraction while also prioritizing the local community's well-being.

Risk-informed Emergency Response Training for Backdraft in Nuclear Power Plants

Research has been conducted for developing fire evacuation and response training programs for nuclear power plant (NPP) application. Among numerous fire scenarios that may occur in an NPP environment, three different points of origin for a fire were selected for the program based on a risk-informed approach: switchgear room, main control room, and safety injection pump room. Fire outcomes were predicted for these scenarios via numerical modeling and the results were incorporated into the newly developed fire evacuation and response training program for the APR1400, Korea’s next-generation NPP model. The switchgear room fire scenario was found to have the most potential for backdraft to occur during manual fire response following automatic gaseous fire suppression system activation. The emergency response manual does discuss this possible backdraft occurrence; however, the guidance to avoid injuries is qualitative, such as to be cautious of backdrafts and wait a sufficient amount of time after opening a door before entering the. In this study, backdraft phenomenon that may occur from a switchgear room fire was numerically examined using the recent version of the Fire Dynamics Simulator to develop an appropriate timeline to be implemented in the fire evacuation and response training program. Based on the findings, the following guidance is provided: (1) backdraft can only occur when the fire originates in the space near the door; (2) wait at least 10 minutes after opening the door before entering the room; (3) watch for rapid smoke production, as this may be an antecedent phenomenon of backdraft; and (4) when smoke production increases rapidly, leave the room as soon as possible to avoid being caught within the deflagrating flames from a backdraft.

Risk-informed coordinated generation and transmission system expansion planning: A net-zero scenario of Switzerland in the European context

Power systems around the world are changing due to the rapid transformation of the generation mix. Unprecedented configurations of the power system may increase the exposure to failures, and thus, lower security of supply. At the same time, the secure development of the system cannot neglect cost considerations. This demands for adequate tools to assess and prepare for future scenarios of the energy transition. In this paper, a risk-informed approach for generation and transmission expansion planning is developed. The approach integrates cost-based generation and transmission expansion planning and risk-based transmission expansion planning. Interfacing these two models to perform coordinated generation and transmission expansion planning results in solutions that are cost-effective, account for the risk implications of the systemic changes, and guarantee system security. The risk-informed coordinated generation and transmission system expansion planning is performed for the Swiss power system which is modeled in full detail for the year 2050. To account for electricity exports and imports, the four surrounding countries are considered in an aggregated manner and their 2050 capacities are projected assuming a net-zero scenario. The results of the risk-informed coordinated expansion planning show that the pure cost-minimization approach applied to either generation or combined generation and transmission expansion planning does not necessarily lead to a reliable power supply in Switzerland. In fact, not accounting for reliability leads to expansion solutions that may incur up to 16 times higher demand not served compared to the reference year 2018. This highlights the importance of considering in-depth system security analyses in power system expansion planning.

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.

Quantitative and qualitative risk-informed energy investment for industrial companies

In the ongoing energy transition, small and medium-sized industrial companies are making energy equipment investments due to the obsolescence of their current equipment as well as social, political and market pressures. These firms typically choose investments with low risk exposure based on a combination of criteria that are not always quantifiable. However, published studies on energy investment to date have not been suitable for industrial SMEs because they do not assess the value of the investment over time, ignore the qualitative aspects of decision-making, and do not consider uncertainties. To fill this gap in the literature, this paper proposes a methodology that considers both quantitative and qualitative parameters and risks over time through an extended two-stage risk-informed approach. The proposed methodology includes fuzzy and statistical techniques for evaluating both qualitative and quantitative parameters, as well as their uncertainties, at the time of decision-making and over the investment lifetime. Fuzzy logic is used in the first stage of the optimisation process to measure qualitative parameters and their uncertainty, while quantitative parameters are expressed using probability density functions to account for their uncertainty and measure the quantitative risk assumed by the investor. This methodology is applied to a case study involving a real industrial SME, and the results show that considering both quantitative and qualitative parameters and uncertainties in the optimisation process leads to a more balanced consideration of economic, environmental and social criteria and reduces the variability of the outcome compared to economic-only approaches that do not account for risks. Specifically, the case study shows that considering these parameters and uncertainties resulted in a 15.7% reduction in the size of the cogeneration system due to its environmental and social impacts, and 4.2% reduction in the variability of the economic result.

Towards Co-Design in Delivering Assistive Technology Interventions: Reconsidering Roles for Consumers, Allied Health Practitioners, and the Support Workforce.

A complexity of factors, from health and technology innovations to policy redesign to achieve consumer-directed care, are impacting traditional roles for Australian allied health practitioners (AHPs). This pilot study considers roles for AHPs in relation to assistive technology (AT) interventions. Articulating 'who does what' may serve a number of purposes including de-professionalization of the discourse; better utilization of support networks and workforces; and alignment with contemporary policy. Yet, a suitable framework to assist with collaborative AT implementation between relevant stakeholders was not identified within the existing literature. This research aimed to develop and pilot an AT collaboration tool which enables AHPs, consumers, their support networks and the support workforce, to navigate policy redesign toward ethical consumer-directed implementation of AT interventions. An AT collaboration tool was developed based upon practice-based knowledge, relevant regulatory and practice evidence and identifies relevant stakeholders, AT service steps and roles, and quality indicators to support competent practice. The tool was piloted in four separate and diverse practice analyses of AT interventions (custom prosthetics, home enteral nutrition, communication devices, and vehicle modifications) considering four allied health professions (prosthetics and orthotics, dietetics, speech pathology, occupational therapy). Pilot testing of the tool supports the feasibility of re-framing AT provision using competency-based and risk-informed approaches and enabling more inclusive roles for consumers and the support workforce. Further testing of the tool is indicated, followed by strategic actions for uptake by individuals, professions and policymakers. The AT collaboration tool has potential to enable AHPs to fulfil ethical obligations for consumer-centered practice, and to facilitate consumer choice, both in Australia and internationally.

Computing Physical Security System Effectiveness at Commercial Reactors

The use of advanced security technologies, such as modeling and simulation in support of vulnerability assessment, has continued to find acceptance in both the operator and the regulatory realms. A critical component to gaining acceptance for modeling and simulation is employing a proven analysis process using best practices and proven tools. These processes and tools allow security managers to be responsive to changing threats and management/financial constraints by quantifying a site’s level of security under different attack scenarios and defensive configurations. Based on best practices and performance data from government agencies, modeling and simulation experts have proposed a process to compute security system effectiveness for commercial nuclear sites. This process will allow decision makers to use a risk-informed approach to quantify security risk at their sites. This also includes a formal accreditation and review process that will provide decision makers and regulators confidence into the development of the defense strategy. Providing a consistent means to assess security, using government-provided or other agreed-upon performance data, will allow sites to compare new and more cost-effective strategies directly with existing/approved strategies to perform a cost-benefit analysis and return on investment estimate.

On the use of time-dependent success criteria within risk-informed analyses. Application to LONF-ATWS sequences in PWR reactors

The classical Probabilistic Safety Analysis (PSA) does not include any time dependence explicitly. However, the success criteria (SC) could evolve during the cycle for some initiating events. In that sense, there is a type of sequence in which this time-dependency is quite important, the family of Anticipated Transient without Scram (ATWS) sequences in Pressurized Water Reactors. Therefore, a new risk-informed approach is proposed in this paper, which makes it possible to obtain the time-dependent SC evolution of the safety functions affected by the Moderator Temperature Coefficient (MTC) value. Then, the evolution of the ATWS conditional core damage probability (CCDP) could be obtained using a PSA model. To quantify the CCDP, the average values of the time-dependent failure probabilities must be computed. Finally, the comparison between the CCDP obtained through the application of the classical PSA approach and the new one makes it possible to quantify the impact of time-dependence on the SC of the headers that this new risk-informed ATWS approach can provide.

Emulating loss of coolant simulations in a pressurized heavy water reactor

In an ideal risk-informed approach to safety analysis, all possible operational states of the system and all sources of uncertainty would be factored. Brute force approaches are cost-prohibitive if high-fidelity multiphysics simulation systems are used. To address this barrier, we present a first attempt to develop emulators for coupled neutronics/thermalhydraulics simulations of large break loss-of-coolant accidents in a generic pressurized heavy water reactor. The emulators are based on a linear mean function coupled with a locally approximate Gaussian process model.The emulators are capable of predicting the power pulse amplitude and the maximum bundle enthalpy within mean absolute relative errors of 0.75 and 0.36%, and mean relative margins of error of 1.9 and 1.0%, respectively. In relation to the simulator, the evaluation time is reduced by a factor of nearly 1800. The paper covers the simulation system, training data generation framework, statistical models and uncertainties, and results.

Basic Relation between RAW and RRW and Some of Its Implications on Risk Reduction Strategies

In using risk-informed approaches for ensuring safety of operating nuclear power plants (NPPs), risk importance measures obtained from probabilistic safety assessments (PSAs) of the plants are integral elements of consideration in many cases. In PSA models and applications associated with NPPs the risk importance of a particular feature (e.g. function, system, component, failure mode or operator action) can be, most generally, divided into two categories: importance with respect to risk increase potential and importance with respect to risk decrease potential. The representative of the first category, as used for practical purposes, is Risk Achievement Worth (RAW). Representative of the second category, as mentioned in consideration of risk importance, is Risk Reduction Worth (RRW). It can be shown that the two risk importance measures, RAW and RRW, are dependent on each other. The only parameter in this mutual dependency is probability of failure of the considered feature. The paper discusses the relation between RAW and RRW and some of its implications, including those on the general strategies for the reduction of risk imposed for the operation of the considered facility. Two general risk reduction strategies which are considered in the discussion are: a) risk reduction by decreasing the failure probability of the considered feature; and b) risk reduction while keeping the failure probability of the considered feature at the same level. Simple examples are provided to illustrate the differences between two strategies and point to main issues and conclusions.

Application of Risk-Informed Approaches in Significance Determination of Armenian NPP Inspection Findings

Risk-informed decision-making approaches in the field of regulatory inspections performed at the NPPs aim at supporting the regulatory body in better organization of inspections. The paper describes the Armenian national experience of inspection activities by focusing on the process of significance assessment of inspection findings and demonstrates its applicability on practical examples. To demonstrate the applicability of the proposed process, various hypothetic inspection findings are defined for further assessment. Approaches are proposed for the significance determination of single and multiple findings. Several cases of single hypothetic findings and their combinations are considered. The paper summarizes the results for the considered cases, which reveal the applicability of the process by demonstrating the significance of hypothetic findings and the cumulative effects of multiple simultaneous hypothetic findings on plant safety.

Comparing physical protection strategies against insider threats using probabilistic risk assessment

Insiders pose a unique challenge to the safety and security of a nuclear facility. They can take advantage of their access rights and knowledge of the plant to bypass, e.g., physical protection elements. In this paper, we present a risk-informed approach to analyze the most plausible ways for an intelligent insider to cause an unwanted outcome (e.g., plant disturbance) by accessing critical locations and preventing the functioning of critical systems. The strength of different protection strategies can be compared using security risk metrics. The starting point of the method is the logical model of a probabilistic risk assessment. The logic model, in the form of minimal cut sets, identifies critical failure combinations that need to be prevented. The case study we performed demonstrated that the approach is usable and should be applicable to realistic facilities. In the analyses, the unwanted outcome to be protected can be basically any outcome that can be represented by minimal cut sets.

Disaster risk reduction and climate policy implementation challenges in Canada and Australia

ABSTRACT Disaster risk reduction is central to managing the risks of climate change at global, national, and sub-national levels. The operationalization of disaster risk reduction, however, has been met with challenges that have restricted successful policy implementation. Drawing from document analyses and Delphi studies with government practitioners, this article examines the policy context for disaster risk reduction in Canada and Australia and investigates the state of flood and drought planning and preparedness. Results are organized around two central themes: risk (ownership and sensitivity) and engagement (stakeholder involvement and capacity-building). The findings show that public policies on disaster risk reduction in Canada and Australia reflect international discourse that advocates for a whole-of-society, risk-sensitive, and risk-informed approach. However, implementing this approach in household planning and preparedness, cross-sector planning and policy integration, terminology, and socio-cultural representation, has been hampered by several factors. Government practitioners in both countries argued that while disaster risk reduction and climate risk management continue to evolve in multi-level governance, policy implementation is constrained by the legacies of past governance arrangements that have enabled disaster risk creation and accumulation. The results presented herein suggest a need for institutional reform that better reflects the holistic and systemic relationships between disaster risk, climate change, and other policy problems. We argue that disaster risk reduction and climate risk management policies require bridging governance arrangements between these and related policy domains to foster effective multi-level implementation. Key policy insights Implementing disaster risk reduction has been inconsistent, exacerbating exposure to climate change and increasing socio-economic vulnerabilities to disaster impacts. Managing climate and disaster risk requires a holistic approach that targets vulnerable groups, tackles underlying drivers of risk, and builds capacities to support disaster risk reduction. Although disaster risk reduction and climate risk management policies continue to evolve, implementation is hindered by legacy governance arrangements that favour economic growth over sustainable, climate-sensitive disaster risk management. Transformation through the integration of disaster risk reduction and human development offers potential pathways to reduce vulnerabilities via a holistic disaster risk and climate policy approach.

A risk-informed decision support tool for the strategic asset management of railway track infrastructure

The provision of safe, efficient, reliable and affordable railway transport requires the railway track infrastructure to be maintained to an appropriate condition. Given the constrained budgets under which the infrastructure is managed, maintenance needs to be predicted in advance of track failure, prioritized and identified risks and uncertainties need to be considered within the decision-making process. This paper describes a risk-informed approach that can be used to economically justify railway track infrastructure conditions by comparing on a life-cycle basis infrastructure maintenance costs, train operating costs, travel time costs, safety, social and environmental impacts. The approach represents a step-change for the railway industry as it will enable economic maintenance standards to be derived which considers the needs of the infrastructure operator, but also those of users, train operating companies and the environment. Further, the risk-informed capability of the tool enables asset managers to deal with uncertainties associated with forecasting costs and the effects of track maintenance, and unavailability of data. The Monte Carlo simulation technique and a Fuzzy reasoning approach are used to address safety data uncertainties through probabilistic risk assessment allied to expert opinion. The approach is illustrated using data from three routes on the UK mainline railway network. The results demonstrate that the approach can be used to support strategic and tactical levels of railway asset management to inform plausible design and maintenance strategies that realise the maximum benefit for the available budget.

Using Probabilistic Fault Tree Analysis and Monte Carlo Simulation to Examine the Likelihood of Risks Associated with Ballasted Railway Drainage Failure

Inadequate track drainage can lead to a variety of issues, including flooding, accelerated track degradation, and progressive or sudden failure of railway track, slope, or embankment. These can result in unplanned track maintenance, additional passenger travel costs, and damage to third party property. However, railway drainage asset management is challenging because it involves the consideration of large interconnected assets, limited maintenance budgets, and unknown failure probabilities. To address this issue, this paper introduces a risk-informed approach for railway drainage asset management that uses fault tree analysis to identify the factors that contribute to railway drainage flood risk and quantifies the likelihood of the occurrence of these factors using Monte Carlo simulation. This rational approach enables drainage asset managers to evaluate easily the factors that affect the likelihood of railway track drainage failure, thereby facilitating the prioritization of appropriate mitigation measures and in so doing improve the allocation of scarce maintenance resources. The analysis identified 46 basic and 49 intermediate contributing factors associated with drainage failure of ballasted railway track (undesired event). The usefulness of the approach is demonstrated for three sites on the UK railway network, namely, Ardsley Tunnel, Clay Cross Tunnel, and Draycott. The analysis shows that the Clay Cross Tunnel had the highest probability of drainage failure and should be prioritized for maintenance over the other two sites. The maintenance required should focus on blockages because of vegetation overgrowth or debris accumulation.