Realocação do Núcleo do Reator Nuclear após Derretimento e Unidades de Contenção do Núcleo

Nuclear meltdown with the potential human and environmental harm is one of the major accident hazard (MAH) faced by nuclear power plants. Limiting (or entirely avoiding) criticality events are the main design strategies for reactors of generations 3½ and 4 (Gen3½ and Gen4). These include ensuring negative void and negative temperature coefficients (for both moderator and fuel) regardless of operational conditions, which provide a self-regulating mechanism that helps preventing accidents occurrence (i.e., to address safety and reliability aspects of Gen4’s goals). However, in severe accident scenarios (e.g. during loss-of-coolant, LOCA, events) where failure to extract heat from the reactor may lead to core degradation, strategies to mitigate reactor meltdown and relocation are critical in the design of safety protocols. This work aims to numerically investigate core relocation as an integrated multi-fluid and heat dynamics problem in which flow of melted materials (UO2, Zircaloy and graphite) are modelled through interface capturing/tracking methods. Two interface tracking/capturing methods were compared, the level-set volume of fluid method (VOF) in Ansys Fluent, and the compressive advection method (CAM) in Fluidity/ICFERST. Both methods are in good agreement for the core relocation simulation. An in-vessel core catcher (IVCC) of tungsten alloy was also proposed to demonstrate core degradation control strategy through cooling of the melted multi-materials. The IVCC was simulated with a multifluid model in Ansys Fluent, in a specified applied heat flux model. The thickness of the IVCC is 0.20 m and the heat flux used is 600 kW m-2. The tungsten material used was able to withstand both thermal and mechanical loads on the lower plenum by extracting decay heat from the corium.O derretimento nuclear, com potencial danos humanos e ambientais, é um dos principais acidentes graves em usinas nucleares. Limitar (ou mesmo evitar) eventos críticos são as principais estratégias no design de reatores das gerações 3½ e 4 (Gen3½ e Gen4). Isso inclui garantir coeficientes de reatividade (de temperatura e de vazio) negativos (para ambos, moderador e o combustível) independentemente das condições operacionais. Este é um mecanismo de auto- regulação para prevenir a ocorrência de acidentes (ou seja, para abordar aspectos de segurança e confiabilidade dos objetivos do Gen4). No entanto, em cenários de acidentes graves (por exemplo, durante eventos de perda de fluido refrigerante, LOCA), onde a falha na extração de calor do reator pode levar à degradação do núcleo, estratégias para mitigar o derretimento e a realocação do reator são críticas na concepção de protocolos de segurança. Este trabalho visa investigar numericamente a realocação do núcleo como um problema integrado de dinâmica multifluido e térmica em que o fluxo de materiais derretidos (UO2, Zircaloy e grafite) é modelado através de métodos de captura/rastreamento de interface. Dois métodos de rastreamento/captura de interface foram comparados, o método de volume de fluido (VOF, no CFD ANSYS Fluent) e o método de advecção compressiva (CAM, no CFD Fluidity/ICFERST). Ambos os métodos estão em bom acordo para o estudo de caso de realocação do núcleo. Também foi proposto uma unidade de contenção do núcleo (IVCC) composta de uma liga de tungstênio para demonstrar a estratégia de controle da degradação do núcleo através do resfriamento dos materiais. O IVCC foi simulado com um modelo multifluido com fluxo de calor especificado. A espessura do IVCC é de 0.20 m e o fluxo de calor utilizado é de 600 kW m-2. O material de tungstênio utilizado foi capaz de suportar as cargas térmicas e mecânicas no plénum inferior extraindo o calor residual do corium

Corrosion properties of tempered medium carbon steel in 1.0 M HCl and homemade vinegar

ABSTRACT. The consumable palm wine has never been used in heat treatment process of steels. This research therefore focuses on the utilization of the consumable palm wine and other palm tree products as quenchants. The mechanical and physical properties of the samples were also evaluated to determine which of the quenchants that influences the hardness and corrosion rate values of medium carbon steel the most. The corrosion test was performed in 1.0 M of HCl solution and homemade vinegar using potentiodynamic polarization method. The results revealed a hardness value of 431, 351, 359 and 265 HB for the samples quenched in palm wine, palm kernel oil, palm oil and as-received, respectively. The corrosion rates of palm oil tempered samples showed more susceptibity to corrosion in HCl solution with a value of 2.261e+003 mil/year. Vinegar offers the highest corrosion rate with a value of 4.017e+002 mil/year for palm wine tempered. The corrosion rate of the as-received samples pulled the lowest values while on the treated samples, palm kernel oil showed the least corrosion rate values.   KEY WORDS: Consumable palm wine, Palm oil, Hardness, Corrosion rate, Austenitization, Quenching   Bull. Chem. Soc. Ethiop. 2022, 36(4), 893-901.                                                               DOI: https://dx.doi.org/10.4314/bcse.v36i4.14                                                     &nbsp

Nuclear Meltdown Relocation and Core Catcher Analysis

This article is an extended version of the work presented at the Joint XXV ENMC National Meeting on Computational Modeling, XIII ECTMMeeting on Science and Technology of Materials, 9th MCSul South Conference on Computational Modeling and IX SEMENGO Seminar andWorkshop on Ocean Engineering, held in webinar mode, from October 19th to 21th, 2022Peer reviewe