Safety Analysis Methodology Research Articles

Coupled simulation for pin-wise reactor core analysis using subchannel analysis code CUPID and fuel performance code GIFT

Recent efforts to develop high-fidelity, multi-physics safety analysis methodologies aim to assess realistic safety margins. However, they remain conservative using initial conditions based on the hot rod with maximum power for the whole reactor core. This study presents the development and verification of a coupled code for pin-wise reactor core analysis using the subchannel analysis code CUPID and the fuel performance code GIFT. The goal was to generate accurate pin-wise fuel rod conditions during normal operation for safety analysis. CUPID was applied for thermal–hydraulic analysis considering fuel behavior, and GIFT was extended to multiple fuel rods. The coupled code was verified for a single assembly to examine subchannel geometry deformation, followed by a practical simulation for a quarter reactor core during the first cycle. Key parameters for safety analysis were examined, revealing that maximum stored energy occurred in a specific fuel rod rather than the hot rod with maximum power.

Assessment of the Choked Flow Model of RELAP5 for Application of Inverse Quantification Methods

In the framework of deterministic safety analysis, best estimate plus uncertainty methodologies can provide a more informative detailed analysis of transients than conservative approaches. However, one important step in the application of such methodologies is derivation of uncertainty of the physical models. Probability density functions of the physical model parameters are obtained by applying inverse uncertainty quantification (IUQ) methods to experimental data. The present work deals with evaluation of the experimental database and assessment of the simulation model, which are required steps prior to the application of IUQ methods. The U.S. Nuclear Regulatory Commission system code RELAP5 has been applied for simulation of three experimental databases on choked/critical flow: Sozzi-Sutherland, Super MobyDick, and Marviken Critical Flow Tests. First, the adequacy of the experimental data to the specific target domain is carried out, to then proceed to calibration of the input model parameters by combining the use of Gaussian Process metamodels and optimization schemes. The assessment of the simulation models is performed by evaluating independently accuracy, precision, and consistency through four statistical indicators, including a novel indicator to evaluate the consistency of the results. The final results indicate that the model is capable of reproducing the selected experimental database and overall average accuracy, precision, and consistency below the 10% threshold and can be used for application of IUQ methods.

The application study of conservative best-estimated approach for steam line break accident

The most important characteristic of main Steam Line Break (SLB) accident is the asymmetry cooldown between loops due to secondary break spurting, which results non-uniform reactivity feedback in different reactor core sections. The fuel rod DNBR limit would be more challenged in the core section with peak power. The SLB safety analysis methodologies in Administration License Application for typical PWR in China are investigated in this paper. Based on the conservative universal methodology, the best-estimated code RELAP5/MOD3 is used to perform the SLB thermal-hydraulic calculation for a three-loop PWR. In this analysis, the critical conservative models submitted for Licensing process are implemented in RELAP5/MOD3 specified modeling, which includes the Three-Channel Core Model, core inlet mixture array, core outlet mixture, vessel upper head flow and the more realistic SG model. The “second pressurizer” phenomenon in vessel upper head flashing is studied, which affects the system pressure response and mitigation. The effect of SG spouting during the transient is also studied in this paper, which is different with lumped parameter SG model. The combined approach for Deterministic safety analysis is validated in this paper, which is composed with best-estimated code, Conservative assumptions and Conservative initial & boundary conditions. Because of the flexibility and adequate conservatism, it can be spread for design optimization and independent safety assessment from the third party.

Geomechanical Characterization of a Brazilian Experimental Site: Testing, Interpretation, and Material Properties

Clarity in monitoring existing foundation structures demands innovative safety analysis methodologies for deep foundations, necessitating advanced models calibrated with real-world field parameters. Understanding controlled conditions, including geotechnical profiles, seismic attributes, and soil mechanics, is crucial. A dedicated research group at the University of São Paulo spent three years refining these conditions, characterizing an experimental field along a canal in São Paulo. This study pioneers geotechnical and geomechanical characterization of the region’s tertiary sediments in São Paulo, offering valuable insights for current and future applications. Standard penetration tests with torque (SPT-Torque), piezocone tests (CPTu), and measurement of wave velocity (Vs) with piezocone tests (S-CPTu) were carried out. The exploration of the subsoil shows that in up to 2 m of excavation, there are clays and silts, and in up to 25 m, there is a significant layer of compact fine sand that has high values of tip resistance and wave velocities more significant than 100 m/s. In the electric cone tests, the abacus used displayed a reasonable classification. All propositions identified the transition from the surface soil to the sandy soil at between 3 and 25 m. The soil classification values were obtained with the data of the field parameters, and the geotechnical and mechanical parameters were estimated. No differences were detected among the values found in the SPT-T and CPTu tests for the values obtained via cone resistance. This demonstrates the reliability of both methods. In addition, using the CPTu test to identify the stratigraphic profile horizons employing the soil’s mechanical behavior when the cone is driven proved appropriate.

Integrated methodology for safety analysis based on a system-theoretic approach and numerical simulation

The System-Theoretic Process Analysis (STPA) method is a recognized approach to system safety analysis. However, it still has inadequate capabilities for quantitative safety analysis. To overcome this limitation, an integrated methodology was investigated for quantitative safety analysis of the complex socio-technical system that combines a system-theoretic approach and numerical simulation. In the proposed methodology, STPA method is utilized to reveal potential unsafe control actions (UCAs) and corresponding causes based on the operational principle of the target system from systemic perspective. Moreover, the consequences of identified UCAs can be quantified and safety constraints also can be improved to prevent UCAs using numerical simulations. As a complex system, the blind shear ram preventers (BSRPs) in deepwater drilling activities, with tightly interacting diverse subsystems or components, is employed to illustrate the applicability of the methodology. The results verified that the proposed methodology could evaluate potential hazards and quantify the analysis results. These results will be helpful for the design and safe operations of the BSRP system. The developed methodology has the potential to be used for safety analyses in other process industries.

Safety Analysis of Lithium-Ion Cylindrical Batteries Using Design and Process Failure Mode and Effect Analysis

Cylindrical lithium-ion batteries are widely used in consumer electronics, electric vehicles, and energy storage applications. However, safety risks due to thermal runaway-induced fire and explosions have prompted the need for safety analysis methodologies. Though cylindrical batteries often incorporate safety devices, the safety of the battery also depends on its design and manufacturing processes. This study conducts a design and process failure mode and effect analysis (DFMEA and PFMEA) for the design and manufacturing of cylindrical lithium-ion batteries, with a focus on battery safety.

Recovery policies for safe exploration of lunar permanently shadowed regions by a solar-powered rover

The success of a multi-kilometre drive by a solar-powered rover at the lunar south pole depends upon careful planning in space and time due to highly dynamic solar illumination conditions. An additional challenge is that the rover may be subject to random faults that can temporarily delay long-range traverses. The majority of existing global spatiotemporal planners assume a deterministic rover-environment model and do not account for random faults. In this paper, we consider a random fault profile with a known, average spatial fault rate. We introduce a methodology to compute recovery policies that maximize the probability of survival of a solar-powered rover from different start states. A recovery policy defines a set of recourse actions to reach a safe location with sufficient battery energy remaining, given the local solar illumination conditions. We solve a stochastic reach-avoid problem using dynamic programming to find an optimal recovery policy. Our focus, in part, is on the implications of state space discretization, which is required in practical implementations. We propose a modified dynamic programming algorithm that conservatively accounts for approximation errors. To demonstrate the benefits of our approach, we compare against existing methods in scenarios where a solar-powered rover seeks to safely exit from permanently shadowed regions in the Cabeus area at the lunar south pole. We also highlight the relevance of our methodology for mission formulation and trade safety analysis by comparing different rover mobility models in simulated recovery drives from the LCROSS impact region.

A Timing-Based Framework for Designing Resilient Cyber-Physical Systems under Safety Constraint

Cyber-physical systems (CPS) are required to satisfy safety constraints in various application domains such as robotics, industrial manufacturing systems, and power systems. Faults and cyber attacks have been shown to cause safety violations, which can damage the system and endanger human lives. Resilient architectures have been proposed to ensure safety of CPS under such faults and attacks via methodologies including redundancy and restarting from safe operating conditions. The existing resilient architectures for CPS utilize different mechanisms to guarantee safety, and currently, there is no common framework to compare them. Moreover, the analysis and design undertaken for CPS employing one architecture is not readily extendable to another. In this article, we propose a timing-based framework for CPS employing various resilient architectures and develop a common methodology for safety analysis and computation of control policies and design parameters. Using the insight that the cyber subsystem operates in one out of a finite number of statuses, we first develop a hybrid system model that captures CPS adopting any of these architectures. Based on the hybrid system, we formulate the problem of joint computation of control policies and associated timing parameters for CPS to satisfy a given safety constraint and derive sufficient conditions for the solution. Utilizing the derived conditions, we provide an algorithm to compute control policies and timing parameters relevant to the employed architecture. We also note that our solution can be applied to a wide class of CPS with polynomial dynamics and also allows incorporation of new architectures. We verify our proposed framework by performing a case study on adaptive cruise control of vehicles.

Rigorous dynamic simulation methodology for scenario-based safety analysis of pressure-swing distillation considering independent protections

Process engineers often assess process safety performance early in the design stage to reduce or eliminate potential hazards cost-effectively. Process simulation tools widely used in design can provide fast and precise hazard evaluation using limited design information. However, there is a knowledge gap on how to build rigorous dynamic process models and how model configurations can affect safety analysis results. This study applied commercial dynamic simulation software, Aspen Dynamics, to address these issues through rigorous dynamic simulations and safety analysis of a two-column pressure-swing distillation with top recycling. The study implements and simulates various layers of protection, including basic process controls, alarms, safety instrumented systems, and pressure relief systems, and evaluates their impact on accident prevention. The hazardous scenarios considered are overpressure and flooding in the distillation columns, and the dynamic responses to a set of deviations such as coolant and steam utility failures and undesired throughput and composition disturbances are investigated. A scenario-based safety analysis is performed to assess the dynamic safety performance and the effectiveness of protection layers. The results indicate that the presented scenario-based dynamic safety analysis methodology is essential for accurately determining dynamic column behaviors, thereby better assisting in determining process safety time and designing effective safety systems.

Safety and security collaborative analysis framework for high-performance embedded computing devices

Next generation dependable embedded systems are facing a dramatic increase of functionalities and software complexity, requiring heterogeneous high-performance embedded computing devices. The increased software and hardware complexity of such emerging systems, together with the novelty of the technology, poses serious concerns regarding system’s safety certification. Moreover, driven by the increased connectivity features, security has become a crucial aspect that shall be considered alongside safety. This article aims to define a safety and security collaborative analysis framework for the systematic analysis of heterogeneous high-performance embedded computing devices. In this direction, a safety and security collaborative analysis methodology is proposed, which is implemented following an incremental top-down strategy. Following this methodology, a generic safety–security model is built first, which is then tailored to a case study for the Zynq UltraScale+ Multi-Processor System-on-Chip (MPSoC) device.

Methodology for a combined Safety and Security Analysis based on classic HAZOPs for Operational Technology Insert

Methodology for a combined Safety and Security Analysis based on classic HAZOPs for Operational Technology Insert

Comparison of Blind and Open Calculation Results for Top-Slot Break LOCA in Fourth ATLAS Domestic Standard Problem

The advanced thermal-hydraulic test loop for accident simulation (ATLAS) was developed and operated at The Korea Atomic Energy Research Institute. The ATLAS is operated to simulate accidents in pressurized water reactors (PWRs). A domestic standard problem (DSP) using the ATLAS was proposed for transferring the database of the integral effect test to Korean nuclear researchers and developing the safety analysis methodology of PWRs. The fourth DSP (DSP-04) exercise was performed during 2015–2017 with 15 participants (13 organizations), that are universities, government, and nuclear industries. In DSP-04, a top-slot break at the cold leg was chosen as the target scenario to resolve an issue about the effect of loop seal clearing and the reformation on the peak cladding temperature during the cold leg top-slot break LOCA for APR1400. The participants performed a code calculation for the experimental simulation and sensitivity studies for the enhancement of the code. This paper includes brief information about the experimental and major code assessment results.

Energy performance and indoor airflow analysis of a healthcare ward designed with resource conservation objectives

With the outbreak of COVID-19, the urgency of wide-scale healthcare infrastructure development has been felt globally for human survival. To accommodate a large infected population, copious wards are to be built within the prevalent constraints of land, power and material availability. This study designs a two-bed modular healthcare ward which is shrunk in size to minimize the requirement of space and other construction commodities such as materials, labour and power. Additionally, HVAC energy usage is accounted for conservation. The health safety and thermal comfort of occupants are regulated by monitoring indoor environment attributes while pushing towards a resource-efficient structure. Two popular envelope thermal retrofits viz. phase change material and thermal insulation are tested to conceive gains in terms of improved energy performance of the ward. Various ward designs contest with their energy performance and occupant's health safety and comfort characteristics in a multicriteria decision making process for delivering the most favourable solution. Subsequently, the most suitable solution is offered by a design involving thermal insulation retrofit with 8 ACH fresh air supply rate and 26°C inlet air temperature. The proposed design can support developing nations to contrive quick response to pandemic outbreaks with reduced construction (cost, time) and energy loads.

Overview of the seismic probabilistic safety assessment applied to a nuclear installation located in a low seismicity zone

Deterministic and probabilistic nuclear safety analysis methodologies have been developed and updated based on operational experience, investigation of past incidents or accidents, and analysis of postulated initiating events in order to maintain the protection of workers, the public and the environment. The evaluation of accident sequences and the total radiological risk resulting from off-site releases are general objectives addressed by these methodologies. There are hazards that continually challenge the safety of a nuclear facility or its nearby area. In particular, seismic events represent a major contributor to the risk of a nuclear facility. Different levels of ground motion induced by earthquakes may be experienced by the structures, systems and components (SSCs) of the installation. In this context, a seismic hazard analysis, seismic demand analysis and seismic fragility analysis must be carried out in order to characterize the local seismic hazard and what are the seismic demands on SSCs, allowing an adequate seismic classification of SSCs, even in installations located in sites with low seismicity. In this article, a general description of the Seismic Probabilistic Safety Assessment (Seismic PSA) methodology is presented, with emphasis on their support studies, aiming at applying the methodology described in this article to an experimental nuclear installation containing a PWR reactor designed for naval propulsion to be installed in a low seismicity zone in Brazil.

Safety Assessment Review of a Dressing Assistance Robot.

Hazard analysis methods such as HAZOP and STPA have proven to be effective methods for assurance of system safety for years. However, the dimensionality and human factors uncertainty of many assistive robotic applications challenges the capability of these methods to provide comprehensive coverage of safety issues from interdisciplinary perspectives in a timely and cost-effective manner. Physically assistive tasks in which a range of dynamic contexts require continuous human–robot physical interaction such as e.g., robot-assisted dressing or sit-to-stand pose a new paradigm for safe design and safety analysis methodology. For these types of tasks, considerations have to be made for a range of dynamic contexts where the robot-assistance requires close and continuous physical contact with users. Current regulations mainly cover industrial collaborative robotics regarding physical human–robot interaction (pHRI) but largely neglects direct and continuous physical human contact. In this paper, we explore limitations of commonly used safety analysis techniques when applied to robot-assisted dressing scenarios. We provide a detailed analysis of the system requirements from the user perspective and consider user-bounded hazards that can compromise safety of this complex pHRI.

Safety Method for the Pre-conceptual Phase of Sodium-cooled Fast Reactors

Abstract The ESFR-SMART European project (Contract number: 754501) focuses on the development of innovative safety design options for future Sodium-cooled Fast Reactors (SFRs). The goal of this paper is to show how the Objective Provision Tree (OPT) method, which is part of the Integrated Safety Analysis Methodology (ISAM) developed by Generation IV Forum (GIF), can help in defining safety guidelines for the definition and the study of ESFR-SMART innovative design options. The OPT method provides a view of the implementation of main safety functions in accordance with defence-in-depth principle and has been adapted to ESFR-SMART needs. Guidance for a consistent and homogeneous application has been developed. The method is applied to each safety function with a specific adaptation for the confinement function. Beyond the allocation of the main equipment ensuring the safety functions to the different levels of defence-in-depth, the adapted method proposes a systematic identification of the mechanisms likely to degrade them. Then, safety features to cope with these mechanisms are investigated as well as the potential common cause failures of main equipment belonging to different levels of defence-in-depth. This adapted method allows to study and then to improve the independence between the levels of defence-in-depth as required for future reactors in Europe by Western European Nuclear Regulators' Association (WENRA). The paper provides the outline of guidance for OPT method adaptation to ESFR-SMART project needs, examples of application and main outcomes of the use of the method.

Development of phenomena identification and ranking table for Westinghouse lead fast reactor's safety

The Westinghouse Lead-cooled Fast Reactor (LFR) is a medium-size, passively safe, economic, Gen-IV nuclear reactor. An important effort within the Westinghouse LFR program is the development of the safety analysis methodology, which comprises computer code development, model development, and experimental testing. A key initial task associated with the development of the safety analysis methodology is the identification of processes and phenomena that affect the plant's capability to meet selected safety performance indicators. This is accomplished through the development of a Phenomena Identification and Ranking Table (PIRT) for selected accident scenarios which, for this specific PIRT effort, included selected postulated design basis accidents and hypothetical beyond design basis accidents in LFRs.This paper describes the role of PIRT in the development of the Westinghouse LFR safety analysis methodology and the process used in the PIRT development. Specifically, the Westinghouse LFR PIRT assessed importance of pertinent phenomena and identified gaps in their knowledge-base by evaluating current modeling capabilities and data available for validation. The ultimate goal was to provide guidance on computer code development and validation efforts and to prioritize testing to support LFR design and licensing. The key phenomena and processes that are deemed highly important for the safety performance indicators, but for which the state of knowledge is low, are presented. The testing program and analyses development are planned to address significant phenomena in the PIRT.

Preliminary safety evaluation of a supercritical carbon dioxide Brayton cycle cooled reactor system under loss-of-flow accident

Reactor system which applies supercritical carbon dioxide(s-CO2) Brayton Cycle as its direct power conversion system has advantages of high thermal efficiency and high compactness. Due to the high coolant outlet temperature (around 500 °C) and the less effective heat transfer capacity of S-CO2 compared to water or metal liquid, which are commonly used in GEN IV reactor concepts, the safety performance of this kind of newly developed reactor system needs to be carefully evaluated. Preliminary safety assessment of loss-of-flow accident (LOFA) for a s-CO2 Brayton cycle cooled reactor system is carried out in this paper. The safety analysis methodology is proposed firstly and three types of LOFA are investigated to clarify the unique safety characteristics of s-CO2 Brayton cycle cooled reactor system, including partial LOFA with reactor scram, partial LOFA without reactor scram and total LOFA. The short term analysis results demonstrate that the reactor core can survive these three types of LOFA without safety system in the very first 10 to 20 s. A hybrid passive/active emergency core cooling system is designed to remove the decay heat for a long time. Results indicate that the hybrid passive/active emergency core cooling system designed in this paper can help the reactor system safely go through these three types of LOFA. This study will be benefit for the core design and safety system design for s-CO2 direct cooled rector system.

Análisis probabilístico de seguridad para laboratorio secundario de calibración dosimétrica

Se aplicó la metodología análisis probabilístico de seguridad para la cuantificación del riesgo radiológico asociado a la operación del irradiador del fabricante HopeWell modelo G-100 en el Laboratorio Secundario de Calibración Dosimétrica del Servicio Geológico Colombiano. El irradiador cuenta con una fuente radiactiva de 60Co con actividad nominal de 185 TBq, considerada una fuente extremadamente peligrosa para las personas, según el Organismo Internacional de Energía Atómica. El análisis contempló la identificación de los sucesos iniciadores mediante la metodología de diagramas lógicos maestros, la determinación de las secuencias accidentales y su frecuencia mediante árboles de fallo y la estimación de la magnitud de la consecuencia de cada secuencia accidental en función de la probabilidad de causar la muerte de un individuo asociada al escenario de exposición planteado. El riesgo cuantificado fue de 1,6 x 10–5 por año para una exposición mortal, que es inferior a la restricción establecida de 1,44 x 10–4 por año. Finalmente, se encontró que las disposiciones de protección y seguridad más críticas son las relacionas con la capacitación sobre el significado de las señales de advertencia del inicio de las secuencias de último hombre afuera (LMO, por su sigla en inglés) y de inicio de irradiación, seguidas por estas señales de advertencia.

Preliminary study of system design and safety analysis methodology for supercritical carbon dioxide Brayton cycle direct-cooled reactor system

Due to advantage of compact component and simply layout, supercritical CO2 (s-CO2) Brayton cycle is considered as power conversion system for small modular reactors (SMRs). The safety performance of SMRs coupling with s-CO2 Brayton cycle, especially for s-CO2 Brayton cycle direct cooled reactor, is quite different from that of conventional reactor systems. Safety analysis is essential work before the system design of a newly proposed reactor system is finalized. In this paper, preliminary system design and safety analysis methodology is proposed for a direct cooled reactor system (SCFR-300). System characteristic is clarified through simulation and analysis. Conceptual design of overall plant system is developed based on its unique characteristics. 35 initial accident events are obtained through main logic diagram. The system design and protection logic, and safety analysis methodology determined in this study will be used in further safety analysis. This work will provide helpful implications for safety performance evaluation for s-CO2 direct cooled reactor systems.