McMaster University DOCTOR OF PHILOSOPHY (2022) Hamilton, Ontario (Engineering Physics) TITLE: Development and Evaluation of Polaris CANDU Geometry Modelling and of TRACE_Mac/PARCS_Mac Coupling with RRS for CANDU Analysis AUTHOR: Simon Younan, M.A.Sc. (McMaster University), B.Eng. (McMaster University) SUPERVISOR: Dr. David Novog NUMBER OF PAGES: xiv, 163 / In the field of nuclear safety analysis, as computers have become more powerful, there has been a trend away from low-fidelity models using conservative assumptions, to high-fidelity best-estimate models combined with uncertainty analysis. A number of these tools have been developed in the United States, due to the popularity of light water reactors. These include the SCALE analysis suite developed by ORNL, as well as the PARCS and TRACE tools backed by the USNRC. This work explores adapting the capabilities of these tools to the analysis of CANDU reactors. The Polaris sequence, introduced in SCALE 6.2, was extended in this work to support CANDU geometries and compared to existing SCALE sequences such as TRITON. Emphasis was placed on the Embedded Self-Shielding Method (ESSM), introduced with Polaris. Both Polaris and ESSM were evaluated and found to perform adequately for CANDU geometries. The accuracy of ESSM was found to improve when the precomputed selfshielding factors were updated using a CANDU representation. The PARCS diffusion code and the TRACE system thermalhydraulics code were coupled, using the built-in coupling capability between the two codes. In addition, the Exterior Communications Interface (ECI), used for coupling with TRACE, was utilized. A Python interface to the ECI library was developed in this work and used to couple an RRS model written in Python to the coupled PARCS/TRACE model. A number of code modifications were made to accommodate the required coupling and correct code deficiencies, with the modified versions named PARCS_Mac and TRACE_Mac. The coupled codes were able to simulate multiple transients based on prior studies as well as operational events. The code updates performed in this work may be used for many future studies, particularly for uncertainty propagation through a full set of calculations, from the lattice model to a full coupled system model. / Thesis / Doctor of Philosophy (PhD) / Modern nuclear safety analysis tools offer more accurate predictions for the safety and operation of nuclear reactors, including CANDU reactors. These codes take advantage of modern computer hardware, and also a shift in philosophy from conservative analysis to best estimate plus uncertainty analysis. The goal of this thesis was to adapt a number of modern tools to support CANDU analysis and uncertainty propagation, with a particular emphasis on coupling of multiple interacting models. These tools were then demonstrated, and results analyzed. The simulations performed in this work were successful in producing results comparable to prior studies along with experimental and operational data. This included the simulation of four weeks of reactor operation including “shim mode” operation. Sensitivity and uncertainty analyses were performed over the course of the work to quantify the precision and significance of the results as well as to identify areas of interest for future research.

Über 60 % der Aufträge der Bauindustrie werden heute im Bestand umgesetzt. Bei Umbauten oder Aufstockungen stellt sich für den Tragwerksplaner dabei wiederkehrend die Frage nach der Tragsicherheit der Baukonstruktionen für die aktuellen Lastansätze. Besondere Herausforderungen sind historische Bauwerke, die auf der Grundlage traditioneller, baumeisterlicher Erfahrungen mit zeitgenössisch verfügbaren Materialien errichtet worden sind. Sie lassen sich mangels zuverlässiger Daten über die Baustoffe und den Lastabtrag nur selten rechnerisch zutreffend beurteilen. Dieser Beitrag soll zurückblicken auf die vergangenen 15 Jahre, in denen wir über 180 Decken in fast 60 Bauwerken durch Belastungsversuche getestet haben. Dabei möchten wir von unseren Erfahrungen berichten, Besonderheiten herausheben und grundsätzlich das Potential sowie die Grenzen der experimentellen Tragsicherheitsanalyse bewerten.

<p>Supercritical Water-cooled Reactor (SCWR) is a Generation-IV nuclear reactor design that operates on a direct energy conversion cycle above the thermodynamic critical point of water (374⁰C and 22.1 MPa), and offers higher thermal efficiency and considerable design simplification. As an essential step in the design of SCWR safety systems, the accident behaviour of the reactor is evaluated to ensure that the safety systems can achieve safe shutdown for all the design basis accidents. Unfortunately, the computational tools and computer codes that are currently employed for safety analysis have little application in the supercritical region, and faces significant challenges in simulating the transitions from subcritical to supercritical conditions.</p> <p>This thesis examines the predictive capabilities of Computational Fluid Dynamics (CFD) code STAR-CCM+ by evaluating critical flow (or choked flow) due to accidental release of coolant from supercritical fluid systems. The biggest challenge of this research is that the current version of STAR-CCM+ does not support supercritical simulations because the steam tables included in the package are only limited to the subcritical subset of the thermodynamic fluid properties.</p> <p>The research was carried out in two stages. In the first stage, the CFD code STAR-CCM+ was customized to simulate supercritical conditions by, (i) Generating updated steam tables to include subcritical and supercritical fluid properties and using more pressure and temperature points in the pseudo critical region (22 – 25 MPa, 645 -660 K) to handle the rapid changes in the fluid properties, and (ii) Implementing a multi-dimensional steam table interpolation scheme to access the fluid property data at any thermodynamic state during the simulation. In the second stage, the customized CFD code was extensively evaluated by simulating several accidental release scenarios from supercritical conditions using rounded-edge and sharp-edge nozzles and the model results were validated with experimental data. To overcome the solution stability (or convergence) issues encountered during the supercritical simulations, a fine tuning procedure was proposed that guaranteed convergence for all the case studies considered in this thesis.</p> <p>The simulation results revealed that the CFD model produced results that were in good agreement with experimental data and only about 10% prediction error was noticed for most cases considered in the thesis. Considering the sensitivity of the CFD model for upstream temperatures and pressures, these results appear to be quite reasonable. From the computational experience gained in this research , we believe that the CFD code STAR-CCM+ is a very useful tool to perform thermal hydraulic simulations for supercritical systems. However, an appropriate customization and extensive validation of the code is required before it can be exclusively used for safety analysis.</p> / Master of Applied Science (MASc)

Yes / Fault Tree Analysis (FTA) is a well-established and well-understood technique, widely used for dependability evaluation of a wide range of systems. Although many extensions of fault trees have been proposed, they suffer from a variety of shortcomings. In particular, even where software tool support exists, these analyses require a lot of manual effort. Over the past two decades, research has focused on simplifying dependability analysis by looking at how we can synthesise dependability information from system models automatically. This has led to the field of model-based dependability analysis (MBDA). Different tools and techniques have been developed as part of MBDA to automate the generation of dependability analysis artefacts such as fault trees. Firstly, this paper reviews the standard fault tree with its limitations. Secondly, different extensions of standard fault trees are reviewed. Thirdly, this paper reviews a number of prominent MBDA techniques where fault trees are used as a means for system dependability analysis and provides an insight into their working mechanism, applicability, strengths and challenges. Finally, the future outlook for MBDA is outlined, which includes the prospect of developing expert and intelligent systems for dependability analysis of complex open systems under the conditions of uncertainty.

<p dir="ltr">Lithium-ion (Li-ion) batteries are promising electrochemical energy storage and conversion systems to drive the rechargeable world toward a sustainable future. Following the breakthrough of material innovations, advanced Li-ion batteries have significantly mitigated the range and lifetime anxieties of electric vehicles (EVs) and consumer electronics. Nevertheless, state-of-the-art Li-ion chemistries still suffer from several defects, such as rapid degradations under abusive or fast-charge scenarios and unfavorable high thermal instabilities. Essentially, aging mechanisms and safety hazards of Li-ion cells are strongly coupled events. The cell safety factors are most likely to be deteriorated as degradation progresses, making the cell less safe after a long-term deployment. In this thesis, we comprehensively investigate thermo-electrochemical interactions on the safety of Li-ion batteries. Fundamental principles of Li-ion batteries, basic knowledge about material-level thermal instabilities at electrode-electrolyte interphases, thermal characterization approaches, and thermal runaway mechanisms under abusive scenarios are fully overviewed. Thermally unstable characteristics of key cell components, including inter-electrode crosstalk as a result of oxygen liberation from cathode lattice structures, significant electric energy release from massive internal short circuit due to separator collapse, anode-centric lithium-plating-induced early exotherm, and silicon-dopant-driven thermal risks of composite anodes, are specifically discussed to understand their critical role in accelerating cell-level thermal runaway catastrophes. Aging pathways of Li-ion cells under off-normal conditions, particularly overdischarge and fast charging, are thoroughly elucidated using a promising reference electrode architecture, which effectively deconvolutes the electrode behaviors from the complex full-cell performance for precise identification of the root causes in cell failure. Given the profound revelation of degradation-safety sophistication in various Li-ion chemistries, corresponding mitigation and prevention strategies are proposed to maximize cell lifetime and reliability. This thesis provides new insights into aging and safety diagnostics of cutting-edge Li-ion batteries, taking one step further in the online monitoring of battery state of health to develop adaptive battery management systems.</p>

The standard method for assessing traffic safety is to use the predictive method outlined in the Highway Safety Manual (HSM). This method is site-level, data-intensive, and does not account for interactions between sites, making it difficult to assess larger areas. This dissertation develops a corridor-level approach to traffic safety which uses less data than the HSM predictive method and views roadways holistically rather than combinations of individual, independent sites. First, a corridor definition is developed and applied to 10 urban Florida counties with a history of many crashes, resulting in the identification of 1,048 corridors. These corridors were primarily defined using context classification and lane count, with additional considerations for data availability and minimum length. From 2017–2021, these corridors experienced 459,603 unique crashes. After preliminary modeling and scope refinement, 559 corridors received supplemental data collection. Between the two datasets, a total of 11 models were developed using either negative binomial (NB) or random forest (RF) regression. NB models can be used for network screening purposes or identifying the impacts of potential safety improvements, while RF models can be used to identify variables important to the accuracy of the prediction. Potential safety improvements identified from the NB models include increasing proactive law enforcement patrols for dangerous driving behaviors and installing corridor lighting in corridors without lighting. While both NB and RF models were accurate, NB models were recommended due to resulting in a definite equation and overdispersion parameter that could be used with the empirical Bayes (EB) method to improve prediction accuracy. Overall, the corridor-level NB models outperformed the HSM models in terms of accuracy and statistical reliability. Using a corridor-level approach can help agencies quickly network screen their systems to identify high-risk corridors in need of safety improvements or supplement site-level analyses.

L'aboutissement aux Commandes de Vol Électriques (CDVE) des avions civils actuels s'est fait par étapes, après une longue maturation des différentes technologies mises en place. La prochaine étape est l'utilisation de communications intégralement numériques et d'actionneurs intelligents. Cette thèse propose de nouvelles architectures, en rupture avec l'état de l'art, avec de nouvelles répartitions des fonctions intelligentes entre l'avionique centrale (calculateurs de commandes de vols) et l'avionique déportée (électroniques locales des actionneurs) dont l'avantage est d'exiger moins de ressources par rapport aux architectures conventionnelles tout en satisfaisant les mêmes exigences de sécurité et de disponibilité ainsi que les exigences croissantes en fiabilité opérationnelle de la part des compagnies aériennes. La sûreté de fonctionnement et la robustesse des nouvelles architectures proposées ont été validées respectivement sous OCAS/Altarica et Matlab/Simulink. / The current civil aircraft's electrical flight control has been changed to take benefit of technical improvements. New technologies, when mature, can be incorporated in aircrafts. Evolutions are considered towards a digital communication and intelligent actuators. This thesis is aiming at proposing alternative architectures with distribution of system functionality between flight control computers and actuators with less hardware and software resources. New architectures must meet the same safety and availability requirements with additional operational reliability (required by airlines). Dependability and robustness of new architectures have been validated trough respectively OCAS / AltaRica and Matlab / Simulink

Software Product Line Engineering (SPLE) has been proven to reduce development and maintenance costs, improving the time-to-market, and increasing the quality of product variants developed from a product family via systematic reuse of its core assets. SPLE has been successfully used in the development of safety-critical systems, especially in automotive and aerospace domains. Safety-critical systems have to be developed according to safety standards, which demands safety analysis, Fault Tree Analysis (FTA), and assurance cases safety engineering artefacts. However, performing safety analysis, FTA, and assurance case construction activities from scratch and manually for each product variant is time-consuming and error-prone, whereas variability in safety engineering artefacts can be automatically managed with the support of variant management techniques. As safety is context-dependent, context and design variation directly impact in the safety properties changing hazards, their causes, the risks posed by these hazards to system safety, risk mitigation measures, and FTA results. Therefore, managing variability in safety artefacts from different levels of abstraction increases the complexity of the variability model, even with the support of variant management techniques. To achieve an effective balance between benefits and complexity in adopting an SPLE approach for safety-critical systems it is necessary to distinguish between reusable safety artefacts, whose variability should be managed, and those that should be generated from the reused safety artefacts. On the other hand, both industry and safety standards have recognized the use of model-based techniques to support safety analysis and assurance cases. Compositional safety analysis, design optimization, and model-based assurance cases are examples of techniques that have been used to support the generation of safety artefacts required to achieve safety certification. This thesis aims to propose a model-based approach that integrates model-based development, compositional safety analysis, and variant management techniques to support the systematic reuse and generation of safety artefacts in safety-critical software product line engineering. The approach contributes to reduce the effort and costs of performing safety analysis and assessment for a particular product variant, since such analysis is performed from the reused safety artefacts. Thus, variant-specific fault trees, Failure Modes and Effects Analysis (FMEA), and assurance case artefacts required to achieve safety certification can be automatically generated with the support the model-based safety analysis and assurance case construction techniques. / Engenharia de Linha de Produtos de Software (ELPS) contribui para a redução dos custos de desenvolvimento e de manutenção, a melhoria do time-to-market, e o aumento da qualidade de produtos desenvolvidos a partir de uma família de produtos por meio do reuso sistemático dos ativos principais da linha de produtos. A ELPS vem sendo utilizada com sucesso no desenvolvimento de sistemas embarcados críticos, especificamente nos domínios de sistemas automotivos e aeroespaciais. Sistemas embarcados críticos devem ser desenvolvidos de acordo com os requisitos definidos em padrões de segurança, que demandam a produção de artefatos de análise de segurança, árvores de falhas e casos de segurança. Entretanto, a realização de atividades de análise de segurança, análise de árvores de falhas e construção de casos de segurança de forma manual para cada produto de uma linha de produtos é uma tarefa demorada e propensa a erros. O gerenciamento de variabilidade em artefatos de análise de segurança pode ser automatizado com o apoio de técnicas de gerenciamento de variabilidades. Em virtude de safety ser uma propriedade dependente de contexto, a variabilidade no projeto e contexto inerente uma linha de produtos software impacta na definição de propriedades de segurança do sistema, modificando as ameaças à segurança do sistema, suas causas e riscos, medidas de mitigação aplicáveis, e resultados de análise de árvore de falhas. Dessa forma, gerenciar variabilidades em artefatos relacionados à safety em diferentes níveis de abstração aumenta a complexidade do modelo de variabilidade mesmo com o apoio de técnicas de gerenciamento de variabilidades. Para alcançar o equilíbrio eficaz entre os benefícios e a complexidade da adoção de uma abordagem de ELPS para o desenvolvimento de sistemas embarcados críticos é necessário fazer a distinção entre artefatos de safety reusáveis, em que a variabilidade deve ser gerenciada, e artefatos de safety que devem ser gerados a partir de artefatos reusáveis. Por outro lado, tanto a indústria quanto os padrões de segurança têm reconhecido o uso de técnicas dirigidas a modelos para apoiar a análise segurança e a construção de casos de segurança. Técnicas de análise de segurança composicional e otimização de projeto, e de construção de casos de segurança dirigido a modelos vêm sendo utilizadas para apoiar a geração de artefatos de safety requeridos para certificação. O objetivo desta tese é a proposta de uma abordagem dirigida a modelos que integra técnicas de desenvolvimento dirigido a modelos, análise de segurança composicional e otimização de projeto, e construção de casos de segurança dirigido a modelos para apoiar o reuso sistemático e a geração de artefatos de safety em engenharia de linhas de produtos de sistemas embarcados críticos. A abordagem proposta reduz o esforço e os custos de análise e avaliação de segurança para produtos de uma linha de produtos, uma vez que tal análise é realizada a partir de artefatos de safety reusados. Assim, artefatos como análises de árvores de falhas e de modos de falha e efeitos, e casos de segurança requeridos para certificação podem ser gerados automaticamente com o apoio de técnicas dirigidas a modelos.

Process plants that produce chemical products through pre-designed processes are fundamental in the Chemical Engineering industry. The safety of hazardous processing plants is of paramount importance as an accident could cause major damage to property and/or injury to people. HAZID is a computer system that helps designers and operators of process plants to identify potential design and operation problems given a process plant design. However, there are issues that need to be addressed before such a system will be accepted for common use. This research project considers how to improve the usability and acceptability of such a system by developing tools to test the developed models in order for the users to gain confidence in HAZID s output as HAZID is a model based system with a library of equipment models. The research also investigates the development of computer-aided safety applications and how they can be integrated together to extend HAZID to support different kinds of safety-related reasoning tasks. Three computer-aided tools and one reasoning system have been developed from this project. The first is called Model Test Bed, which is to test the correctness of models that have been built. The second is called Safe Isolation Tool, which is to define isolation boundary and identify potential hazards for isolation work. The third is an Instrument Checker, which lists all the instruments and their connections with process items in a process plant for the engineers to consider whether the instrument and its loop provide safeguards to the equipment during the hazard identification procedure. The fourth is a cause-effect analysis system that can automatically generate cause-effect tables for the control engineers to consider the safety design of the control of a plant as the table shows process events and corresponding process responses designed by the control engineer. The thesis provides a full description of the above four tools and how they are integrated into the HAZID system to perform control safety analysis and hazard identification in process plants.

O presente estudo foi realizado para verificar a possibilidade de redução do núcleo do reator IEA-R1 do IPEN/CNEN-SP. Cálculos neutrônicos foram desenvolvidos para um conjunto de novas configurações para que, a posteriori, a análise termo-hidráulica e de segurança pudessem ser realizadas. As novas configurações analisadas são menores por diversos motivos, como obter uma melhor utilização do combustível, melhor distribuição dos fluxos de nêutrons, dentre outros. Para que se possa atingir tais configurações, a densidade de Urânio no combustível deve ser aumentada. Neste estudo, combustíveis de U3Si2-Al com 4,8gU/cm3 foram testados e novos núcleos para o reator IEA-R1 foram propostos e discutidos. A análise neutrônica não impõe restrições aos núcleos estudados. A análise termohidráulica mostrou que as margens de segurança e os perfis de temperatura ao longo das placas combustíveis não excedem os limites de projeto. Os coeficientes de temperatura obtidos para os novos núcleos, no caso isotérmico, são todos negativos, conforme desejado. A queima mostrou que núcleos supercompactos não apresentam excesso de reatividade suficiente para o funcionamento dos mesmo, ao se utilizar combustíveis com 4,8gU/cm3. Um APR (Acidente de Perda de Refrigerante) foi simulado para os núcleos remanescentes. A ruptura da fronteira do primário se mostrou o acidente mais crítico, devido ao curto tempo para o esvaziamento completo da piscina do reator. As temperaturas atingidas após o descobrimento foram calculadas e não excedem aquelas cujos valores propiciam empolamento nas placas combustíveis (475 °! a 550 °!), uma vez que se obedeça os tempos de esvaziamento seguro da piscina para as novas configurações. / This study was performed considering prospective candidates for the IPEN/CNEN-SP IEA-R1 research reactor core. Some neutronic calculations were developed for a set of new core configurations to push forward the thermal-hydraulic and safety analysis. The new core configurations will be smaller for several reasons (e.g., better fuel utilization, neutron fluxes and so on). To achieve such smaller arrangements, the U-fuel density has to be increased. In the current study, configurations with 4.8gU/cm3 U3Si2- Al fuels were tested using the software MCNP and a set of new core configurations for the IPEN/CNEN-SP IEA-R1 research reactor has been presented and discussed. The Neutronic analysis imposes no restrictions on the new cores. The Thermal- Hydraulic (TH) analysis showed that the safety margins and the temperature profile through the fuel plate dont exceed the design limits. The isothermal temperature coefficients were calculated being all negative, as desired. The burnup concludes that super compact cores dont have enough excess reactivity to keep the reactor working with 4.8gU/cm3 U3Si2-Al fuels. A LOCA (Loss of Cooling Accident) was simulated for the remaining cores. The border rupture of the primary system was the most critical accident, due to the short time for the complete emptying of the reactor pool. The temperatures reached after this accident were calculated and dont exceed the fuel plates limits (475 °C - 550 °C), once the time for safe emptying are taken into account for the IEA-R1 pool.