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

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

Modeling the Tokamak exhaust processing system in a commercial simulator for process monitoring purposes

Nuclear fusion depends on tritium breeding and self-sufficiency. Tritium represents a hazard due to its radioactivity and migration properties. Because of these difficulties, ITER, the largest fusion experiment so far, relies on a conservative static procedure to monitor the tritium inventory. Future commercial fusion plants can avoid operation halts if a dynamic monitoring strategy proves itself valid. Tritium plant models have been developed for this kind of monitoring and analysis task, but sensor accuracy and reliability are an issue still to be addressed, and the path to dynamic monitoring remains unclear. The present work shows the modeling procedure of the Tokamak Exhaust Processing system in a commercial simulator, Aspen HYSYS, to reproduce the inventories, streams, process conditions, and compositions of this subsystem during operation. The model is verified in a steady-state scenario using data from the available literature. A demonstration of such a tritium plant subsystem shows meaningful value for several reasons. First, this process has not been modeled before in commercial dynamic simulators, which are typically used in the process industry. It will also allow new stakeholders to participate in future fusion-related projects. Second, it will play a key role in industry-like tritium process monitoring, in which the new model will act as a digital twin of the plant. Data-driven diagnostics can be fueled by model data, helping engineers to generate additional data that could otherwise be expensive to get directly from the plant. For these reasons, models will represent an essential part of a dynamic monitoring system, necessary for feasible fusion projects.Peer ReviewedPostprint (author's final draft

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

Liquid metal MHD flow influence on heat transfer phenomena in fusion reactor blankets

DEMO reactor is projected as a technological demonstrator and a component test reactor for several key systems such as the breeding blanket. The dual coolant lithium lead (DCLL) is one promising breeding blanket candidate that performs the functions of shielding, part of the cooling and breeding with the same liquid metal fluid. PbLi is also in charge of transporting the bred tritium to the Tritium Extraction System. Structural cooling of the blanket walls is performed by pressurized helium flow which also transfers heat to the balance of plant. Keeping a proper distribution of thermal loads between the two coolants is a key aspect to reach a plant high efficiency. The thermal power transferred from the liquid metal to the helium channels depends on the flow regime. While liquid metal flows under the magnetic field, the magnetohydrodynamic (MHD) phenomena will occur, influencing the flow regime and the velocity profile. The heat is volumetrically deposited in the liquid metal coolant due to the interaction between the highly energetic neutrons originated in the plasma and the coolant. The heat deposition profile is roughly exponential causing temperature differences across the same channel cross section. Temperature gradients induce buoyant effects altering the expected MHD profile and affecting the heat transfer rate from the liquid metal to the surrounding walls cooled with helium. It is of utmost interest to identify the effects of the main flow parameters on the heat transfer coefficient under such complex conditions. The work studies computationally a domain consisting of a liquid region and a surrounding solid region electrically and thermally coupled using latest EU DCLL design characteristics. A fully developed flow is assumed where buoyancy is modelled under the Boussinesq approximation. Joule effect has been considered negligible compared to the neutron deposition. The influence of the buoyant MHD phenomena to the heat transfer coefficient is analysed parametrically with a CFD solver implemented in OpenFOAM®. The parameters investigated here are the Reynolds, Hartmann and Grashof numbers, the Grashof ratio, and the wall conductance ratio (cw).Peer ReviewedPostprint (published version

SMART_TC: an R&D Programme on uses of artificial intelligence techniques for tritium monitoring in complex ITER-like tritium plant systems

The realization of nuclear fusion energy is nowadays based on the concept of tritium breeding and the success of the ITER experiment. The latter relies today on a static monitoring approach to fulfill the emission limits imposed by the regulatory institutions. Artificial intelligence applications for fault diagnosis and process monitoring anticipate potential for the dynamic management of tritium in complex plant systems. This paper explores the dynamic tritium inventory management issue in complex systems, reviews the diverse artificial intelligence techniques and discusses the most promising approaches for ITER-like plant system match balance monitoring.Peer ReviewedPostprint (author's final draft

Validation and verification of a quasi two-dimensional turbulence model and an eddy detection method for liquid metal magnetohydrodynamics flows

The flow of liquid metals in straight rectangular channels with an externally applied transverse magnetic field is considered for breeding blankets in tokamak fusion reactors. Under the tokamak magnetic field, the liquid metal experiences the magnetohydrodynamic (MHD) effect that enhances the laminarization of the flow. In geometric singularities, or under certain flow conditions, the combination of Lorentz forces, momentum, and buoyant forces may trigger the formation of vortical structures. The generated vortices will align with the direction of the magnetic field, and therefore the use of a quasi-two-dimensional (Q2D) model is convenient to study them assuming that the walls are electrically insulating and the Hartmann number $\textbf{Ha} = B L \sqrt{\sigma/\mu}$ is high enough. Using this model is computationally affordable, allowing extensive parametric analyses. To identify the presence of eddies in the two-dimensional domain, the application of the bi-dimensional fast Fourier transform (FFT2) is foreseen as an adequate detection method. This work presents a methodology to systematically calculate liquid metal MHD flows with a Q2D model and evaluate the formation of eddies in the flow domain. The work includes a description of the validation and verification of the Q2D MHD model and of the FFT2 method proposed to automatically identify eddies. The sensitivity of the detection method is analyzed to subsequently apply it in parametric analyses.Peer ReviewedPostprint (published version