The development of tritium transport models for the dual coolant lithium lead breeding blanket concept: the effect of magnetohydrodynamics on tritium behavior

Tesis doctoral inédita leída en la Universidad Autónoma de Madrid, Facultad de Ciencias, Departamento de Física Teórica, Fecha de lectura: 09-01-2018El tritio es uno de los combustibles necesarios para los futuros reactores de fusión por confinamiento magnético. Se trata de un elemento inestable y muy escaso en la naturaleza, lo que lo convierte en un recurso valioso y estratégico para la sociedad. Es por ello que, desde hace varias décadas, se están desarrollando distintos diseños de envolturas regeneradoras (breeding blankets), cuya función es regenerar el tritio quemado en el reactor. De esta manera, se pretende desarrollar una tecnología de fusión autosuficiente respecto al tritio, es decir, que no dependa de la inyección constante de tritio proveniente de fuentes externas. Al igual que los demás isótopos de hidrógeno, el tritio no puede confinarse fácilmente debido a su capacidad de permear a través de las estructuras sólidas conforme a las leyes de la difusión. Por ello, la creación de herramientas computacionales predictivas rápidas y de suficiente precisión resulta fundamental para el diseño de la envoltura. En concreto, el objetivo principal de este proyecto de investigación es desarrollar modelos de transporte de tritio optimizados para el concepto de envoltura regeneradora de doble refrigerante DCLL (Dual Coolant Lithium Lead). Para cumplir este objetivo, se ha empleado una metodología nueva basada en el uso recursivo de modelos a nivel de sistema y de modelos tridimensionales de elementos finitos. Los primeros son rápidos y consumen pocos recursos, sin embargo, su precisión está sumamente limitada por su baja dimensionalidad. Por el contrario, los modelos de elementos finitos ofrecen una gran precisión pero requieren una cantidad muy considerable de tiempo y recursos. El uso combinado de ambos tipos de modelos ha permitido realizar una optimización de los modelos a nivel de sistema y, así, incrementar enormemente su precisión en comparación con otros modelos desarrollados en el pasado. El desarrollo de modelos de transporte de tritio tridimensionales requiere de un estudio fluidodinámico previo de la envoltura. En efecto, la envoltura DCLL está basada en una aleación líquida de litio-plomo que fluye en torno al plasma del reactor. La dinámica del metal líquido está dominada por los efectos magnetohidrodinámicos: potentes fuerzas de Lorentz causadas por el campo magnético del reactor. Estas fuerzas modifican el perfil de velocidades del metal líquido, lo que repercute muy significativamente en el transporte de tritio. En el presente trabajo se han realizado los primeros estudios en los que se analiza el efecto de las fuerzas MHD en la evolución del tritio. Gracias a los resultados obtenidos, se ha logrado reducir notablemente la incertidumbre asociada a los modelos de transporte del DCLL a nivel de sistema

3D MHD analysis of prototypical manifold for liquid metal blankets

The water-cooled lead lithium (WCLL) and the dual-cooled lead lithium (DCLL) are two of the breeding blanket (BB) concepts that the EUROfusion consortium is pursuing in the framework of the development of the fusion reactor industrial demonstrator DEMO. Both involve the use of a liquid metal (LM) as working fluid, the lead-lithium eutectic alloy (PbLi), due to its excellent thermal properties and the possibility to serve as both the blanket coolant and tritium breeder and carrier. Unfortunately, due to the high electrical conductivity of LMs, their motion is influenced by the magnetic field used in the reactor to confine the plasma, generating a complex phenomenology which is studied by magnetohydrodynamics (MHD). In this work, a representative prototypical manifold of a BB bottom feeder is investigated for different configurations with the custom phiFoam solver, capable of simulating unsteady, incompressible and isothermal MHD flow. The aim of this study is to investigate which configuration minimizes the flow imbalance in the manifold for the WCLL or in the poloidal breeding zone channels for the DCLL. The distribution of the flow rate among the channels is strongly influenced by the position of the feeding pipe (FP) and by the development of the MHD internal layer near the expansion, which generates important jets close to the lower plate and the upper one, where the channels are attached. The channel aligned with the FP is the one carrying most of the flow, from 55% to 82%, while in the more distant one the flow is almost stagnant, carrying from 17% to 6% of the total flow rate. The total pressure loss is also estimated and its functional dependence on the manifold configuration is discussed

Code-to-code comparison for a PbLi mixed-convection MHD Flow

In “An Approach to Verification and Validation of MHD Codes for Fusion Applications” [S. Smolentsev et al., Fusion Eng. Des., Vol. 100, p. 65 (2015)], an effort for verification and validation of computer codes for liquid metal flows in a magnetic field for fusion cooling/breeding applications was initiated. The current study continues that effort. A group of experts in computational magnetohydrodynamics from several institutions in the United States and Europe performed a code-to-code comparison for the selected reference case of a mixed-convection buoyancy-opposed magnetohydrodynamic flow of eutectic lead-lithium (PbLi) alloy in a thin-wall conducting square duct at Hartmann number Ha = 220, Reynolds number Re = 3040, and Grashof number Gr = 2.88 × 107. As shown, the reference flow demonstrates a boundary layer separation in the heated region and formation of a reversed flow zone. The results of the comparison suggest that all five solvers predict well the key flow features but have moderate quantitative differences, in particular, in the location of the separation point. Also, two of the codes are more computationally dissipative, showing no velocity and temperature oscillations

MHD and heat transfer analyses in PbLi radial channels for the EUROfusion WCLL breeding blanket

The Water Cooled Lithium Lead (WCLL) breeding blanket concept is the one of the PbLi-based concepts under development within the framework of the EUROfusion project. This concept is characterized by cooling the PbLi using water tubes embedded in the PbLi flow. In this work, the MHD coupling between the conductive tubes walls and the PbLi flow is studied for the geometrical and operational configuration of the WCLL. Velocity profiles are computed first considering a toroidal magnetic field using a fully developed flow approach. The obtained MHD velocity profiles are then used as an input for a 3D thermal-hydraulic computation of a WCLL channel. This includes the volumetric heat generation in PbLi and solid materials caused by the neutron flux

The DEMO Water-Cooled Lead–Lithium Breeding Blanket: Design Status at the End of the Pre-Conceptual Design Phase

The Water-Cooled Lead–Lithium Breeding Blanket (WCLL BB) is one of the two blanket concept candidates to become the driver blanket of the EU-DEMO reactor. The design was enacted with a holistic approach. The influence that neutronics, thermal-hydraulics (TH), thermo-mechanics (TM) and magneto-hydro-dynamics (MHD) may have on the design were considered at the same time. This new approach allowed for the design team to create a WCLL BB layout that is able to comply with different foreseen requirements in terms of integration, tritium self-sufficiency, and TH and TM needs. In this paper, the rationale behind the design choices and the main characteristics of the WCLL BB needed for the EU-DEMO are reported and discussed. Finally, the main achievements reached during the pre-conceptual design phase and some remaining open issues to be further investigated in the upcoming conceptual design phase are reported as well