Parametrization of embedded-atom method potential for liquid lithium and lead-lithium eutectic alloy

Liquid lead-lithium eutectic remains as a promising candidate for various breeding-blanket designs in future nuclear-fusion technologies. The lack of a generalized theory of interatomic forces in the liquid state is reflected on the wide variety of proposed functional forms to describe interatomic interactions even in simple liquids. Computer simulations facilitate the study of liquid metal properties, due to mathematical and experimental challenges. A classical-MD EAM potential is parametrized using mechanical and non-mechanical (melting-point) properties to minimize the arbitrariness of functional forms, where the employed pair potential stems from the liquid-state theory to avoid the issue of the uniqueness of the potential. Enhanced performance is obtained for liquid density, energy, structure, diffusivity and shear viscosity of Li, and their temperature-dependencies. In a similar manner, reference experimental and ab initio MD data are used to parametrize a functional to describe Pb-Li pairwise interactions in liquid Pb-Li alloy, which is used with the derived EAM of liquid Li and a reference EAM of liquid Pb to investigate properties of liquid Pb-Li alloy. Enhanced transferability characteristics are obtained for low-in-lithium liquid Pb-Li melts, where Coulombic interactions are negligible. In specific, the exhibited behaviour of Li in liquid lead-lithium eutectic is consistent with findings from ab initio MD methods, and drastically different from predictions of previous C-MD studies which suggested a substantial segregation of Li atoms instead of dispersion. It is concluded that the functional form of the pair potential and its uniqueness influence both the pure liquid-metal properties and the validity of the potential transferability in multi-component systems, where a theoretical functional results in enhanced performance in pure and alloyed liquid systems.The first author is a holder of FI AGAUR doctoral fellowship, provided by Generalitat de Catalunya and European Social Plus Fund. This work is partially funded by the EUROfusion project (Grant Agreement No. 101052200) under the Horizon Europe programme.Peer ReviewedObjectius de Desenvolupament Sostenible::7 - Energia Assequible i No ContaminantObjectius de Desenvolupament Sostenible::9 - Indústria, Innovació i InfraestructuraObjectius de Desenvolupament Sostenible::13 - Acció per al ClimaPostprint (published version

Advanced tools for ITER Tritium Plant System Modeling & Design

Chemical plant system modeling experience based on the use of largely validated commercial modeling tools such as the Aspen HYSYS is adapted and exploited to develop numeric routines for unitary isotopic operations, including permeation, cold trapping, reversible absorption, and cryogenic distillation, for the ITER tritium plant systems. Model prediction capabilities and isotopic database inputs for first-principle models are discussed. Numeric implementation of the Aspen HYSYS routines are presentedPeer ReviewedPostprint (author's final draft

The solubility of helium in lead–lithium eutectic alloy

The helium production rates in liquid metals (Pb-Li eutectic alloy, LLE and others) Blanket Breeders (BB) are nearly mol-to-mol linked to tritium and intimately associated with the compulsory requirement of high tritium self-sufficiency of next fusion reactors. When LLE is oversaturated and the helium solubility limit is exceeded, helium atoms can nucleate in the form of bubbles. The presence of helium bubbles within LLE channels could have severe impact on the diverse BB designs, in particular on tritium transport permeation and its recovery. Even though He is an inert gas assumed to be insoluble, the helium Henry’s constant (KH) in a liquid metal is not zero. The very low KH and difficulties to measure it has historically driven to the absence of basic data. A semi-empirical correlation is proposed providing the helium solubility (i.e.: the helium Henry’s constant) based on Kumar’s cohesion model using the available thermo-physical experimental solubility data for lithium, sodium, potassium, mercury. The proposed expression for eutectic lead–lithium is: being KH the Henry’s constant; T [K], R [8.314 10-3 kJ mol-1 K-1] and dk the Kumar’s cohesive parameter. From a dk justified value of 18.2 MPa1/2 in LLE the values for KH range from 1.14·10-17 to 1.35·10 -15 at.fr.Pa-1 for temperatures between 350 and 870C. The helium solubility should integrate the lead–lithium eutectic nuclear material database for fusion systems design.Peer ReviewedPostprint (published version

Association Between Preexisting Versus Newly Identified Atrial Fibrillation and Outcomes of Patients With Acute Pulmonary Embolism

Background Atrial fibrillation (AF) may exist before or occur early in the course of pulmonary embolism (PE). We determined the PE outcomes based on the presence and timing of AF. Methods and Results Using the data from a multicenter PE registry, we identified 3 groups: (1) those with preexisting AF, (2) patients with new AF within 2 days from acute PE (incident AF), and (3) patients without AF. We assessed the 90-day and 1-year risk of mortality and stroke in patients with AF, compared with those without AF (reference group). Among 16 497 patients with PE, 792 had preexisting AF. These patients had increased odds of 90-day all-cause (odds ratio [OR], 2.81; 95% CI, 2.33-3.38) and PE-related mortality (OR, 2.38; 95% CI, 1.37-4.14) and increased 1-year hazard for ischemic stroke (hazard ratio, 5.48; 95% CI, 3.10-9.69) compared with those without AF. After multivariable adjustment, preexisting AF was associated with significantly increased odds of all-cause mortality (OR, 1.91; 95% CI, 1.57-2.32) but not PE-related mortality (OR, 1.50; 95% CI, 0.85-2.66). Among 16 497 patients with PE, 445 developed new incident AF within 2 days of acute PE. Incident AF was associated with increased odds of 90-day all-cause (OR, 2.28; 95% CI, 1.75-2.97) and PE-related (OR, 3.64; 95% CI, 2.01-6.59) mortality but not stroke. Findings were similar in multivariable analyses. Conclusions In patients with acute symptomatic PE, both preexisting AF and incident AF predict adverse clinical outcomes. The type of adverse outcomes may differ depending on the timing of AF onset.info:eu-repo/semantics/publishedVersio

Atomistic simulations and theoretical predictions of helium nucleation in liquid Pb-Li eutectic alloy

Liquid Lead-Lithium Eutectic (LLE) alloy is a promising candidate coolant and/or breeder to attain tritium self-sufficiency in the EU DEMO breeding blanket design. Liquid metals are characterized with excellent heat-transport properties, and a wide range of densities, melting points and low viscosities. More than 20 years ago, a potential helium nucleation issue in LLE was raised based on experimental observations, since helium is produced in a one-to-one mole ratio with tritium through nuclear breeding reactions of Li isotopes. Theoretical and numerical modelling investigations remained inconclusive due to the complexity of the system, i.e., multi-component system of liquid metal and a noble gas with extremely low solubility, thus challenging the validity of the relevant theories. In this study, ab initio and classical Molecular Dynamics methods are used to investigate the helium bubble formation in LLE. An Embedded Atom Method potential is developed to model liquid Li with enhanced performance and transferability to reproduced LLE characteristics. The nucleation phenomenon of helium is investigated by implementing the Mean First-Passage Time atomistic technique, and nucleation curves are produced for a variety of thermodynamic states. It is found that helium is in the regime of kinetic spinodal, which suggests that nucleation of small clusters is imminent, and bubble growth to a macroscopic-size is only a function of time.Peer ReviewedPostprint (published version

Mathematical models for tritium permeation analysis in liquid metal flows with helium bubbles

In LIBRETTO-2 test, evidence was obtained that helium bubbles nucleated and grew in the neutron irradiated PbLi probes. If such phenomenon occurs inside liquid metal (LM) breeding blanket channels, the study of its effect on tritium permeation and heat transfer in the near wall region will acquire utmost importance. The T4F research group has developed in the past a nucleation, growth and transport model for helium bubbles in LM flows, as well as a tritium transport model in such a multi-fluid system. In the present study, we are focused on the near-wall region analysis in order to obtain a wall function that allow reproducing the tritium permeation with coarse meshes and, hence, reduce the computational time. First, we perform some detailed CFD simulations of the near-wall region where bubbles might be attached. In these simulations, tritium diffusion processes as well as tritium recombination and dissociation are modelled. The analysis of such simulations allows us to further understand the complex phenomena and justify the use of simplified models. As a result, a new model for tritium transport across a LM-solid interface partially covered by helium bubbles is developed, implemented and validated. This simplified model can be seen as a wall function for the CFD simulation which substantially reduces computational time. © 2014 Elsevier B.V.Postprint (published version

Desarrollo e implementación de un modelo de permeación de tritio en presencia de burbujas de helio para envolturas tritigénicas de metal líquido

En los canales de metal líquido (ML) de las envolturas regeneradoras de un reactor de fusión la posibilidad de formación de burbujas de helio no es remota. La presencia de burbujas adheridas a la pared de los canales de ML afectaría a la transferencia de calor y a la permeación de tritio. Se han efectuado análisis de detalle (mallado fino), mediante OpenFOAM, del entorno de una burbuja adherida a la pared y se ha desarrollado un modelo para la permeación de tritio a través de una superficie de contacto ML-sólido parcialmente recubierta con burbujas de helio. El modelo desarrollado se ha implementado como “wall function” en OpenFOAM, se ha validado y se ha aplicado a un caso práctico, utilizando un mallado relativamente grueso. El modelo desarrollado reduce substancialmente la necesidad de potencia de cálculo respecto del cálculo detallado.Postprint (published version

Hacia la monitorización dinámica del inventario de tritio en los sistemas auxiliares de un reactor de fusión

La sostenibilidad de la fusión nuclear depende, entre otros condicionantes, de la capacidad de regeneración de tritio. Los requisitos de protección radiológica imponen severas limitaciones a las emisiones ambientales de tritio, lo que a su vez obliga a un control muy preciso del inventario.En esteartículose proponeuna estrategia de control dinámico de inventario, en contraposición al control estático planteado para ITER. Para que dicha estrategia sea robusta, se necesita: 1) una capacidad de monitoreo continuo de concentraciones en conductos y atmósferas con precisión suficiente; 2) suficiente capacidad predictiva de las herramientas numéricas disponibles; y 3) el desarrollo de un sistema adecuado de control, adquisición de datos y comunicación.Se presentan aquí las actividades encaminadas a la obtención de un modelo numérico predictivo, en el contexto de proyectos de I+D Industrial en curso, que incluyen el desarrollo de modelos de migración de especies hidrogenoidesy laimplementación de los mismos en herramientas de cálculo (códigos CFD, códigos unidimensionalesad-hoc y Aspen HYSYS). Se discute la capacidad predictiva de los modelos paramétricos simplificados.Postprint (published version

Dynamic simulation tools for isotopic separation system modeling and design

Cryogenic distillation is the best candidate for hydrogen isotopic separation in fusion power plants. The design of the ITER's Isotope Separation System can still undergo major changes due to its close contact with the Water Detritiation System and this will be decisive in the design of future DEMO detritiation facilities. Dynamic simulation tools are key in the analysis and design of tritium processing systems and the use of commercial simulators can be especially valuable to this end and may add capabilities in terms of standardization of industrial-scale fusion plant modeling and conjunction of operator training systems, human-machine interface and process monitoring and control. The present work proposes the use of a commercial dynamic process simulator such as Aspen HYSYS given its abilities to overcome the challenges described. This document presents the implementation of a cryogenic distillation column in Aspen HYSYS by setting the thermodynamic principles upon which the simulation is founded and verifying isotopic separation models with experimental data available in the literature.Peer ReviewedPostprint (author's final draft