Helium-Cooled Lithium Lead Breeding Blanket Research Articles

Tritium transport model at breeder unit level for HCLL breeding blanket

The Helium-Cooled Lithium Lead (HCLL) breeding blanket is one of the European blanket designs proposed for DEMO reactor. A tritium transport model is fundamental for the correct assessment of both design and safety, in order to guarantee tritium self-sufficiency and to characterize tritium concentrations, inventories and losses. The present 2D transport model takes into account a single breeder unit located in the outboard equatorial module of the HCLL breeding blanket, which is one of the most loaded modules in normal operating conditions. A multi-physics approach has been adopted considering several physics phenomena, providing for buoyancy effect, temperature fields, tritium generation rate and velocity profile of lead-lithium and coolant. The transport has been modelled considering advection-diffusion of tritium into the lead-lithium eutectic alloy, transfer of tritium from the liquid interface towards the steel (adsorption/desorption), diffusion of tritium inside the steel, transfer of tritium from the steel towards the coolant (recombination/desorption), advection-diffusion of diatomic tritium into the coolant. Tritium concentrations, inventories and losses have been derived under the above specified phenomena. In particular, the effect of buoyancy forces on the tritium transport has been implemented and compared with the condition without buoyancy.

On the thermal and thermomechanical assessment of the “Optimized Conservative” helium-cooled lithium lead breeding blanket concept for DEMO

Within the framework of EUROfusion R&D activities a research campaign has been performed at CEA-Saclay, in close collaboration with the University of Palermo, in order to investigate thermal and thermomechanical performances of the “Optimized Conservative” concept of DEMO Helium-Cooled Lithium Lead breeding blanket (HCLL). Attention has been paid to the HCLL outboard equatorial module (OEM) when subjected to the steady state nominal loading scenario. To this purpose three simplified 3D models, characterized by an increasing level of detail, have been set-up taking into account, firstly, a single radial-toroidal slice, then a basic module geometric unity composed by two adjacent slices and adding, lastly, the peripheral poloidal region. This latter 3D model has allowed the assessment of the Caps potential influence on the module thermal and thermomechanical behaviour. For each investigated 3D model, thermal and thermomechanical analyses have been performed and a stress linearization procedure has been carried out in order to verify the fulfilment of the criteria prescribed by the RCC-MRx 2015 code. The study has been performed adopting a numerical approach, based on the Finite Element Method (FEM), and adopting the Siemens NX v. 10.0 software in order to discretize the geometric domain, whereas thermal and thermomechanical calculations have been carried out using the Cast3 M 2015 FEM code.The obtained results, herewith reported and critically discussed, allow predicting a good thermal and mechanical behaviour of the “Optimized Conservative” concept of DEMO HCLL OEM, even if some small modifications to the module cooling scheme should be performed in order to avoid the insurgence of hotspots where temperature is slightly above the Eurofer limit temperature (550 °C). This will entail, from the mechanical point of view, a reduction of the secondary stress amount which is the main responsible of the failure in RCC-MRx criteria verification within First Wall-Side Wall bend region.

Status of the EU DEMO HCLL breeding blanket design development

In the framework of the European “HORIZON 2020” innovation and research programme, the EUROfusion Consortium develops a design of a fusion power demonstrator (DEMO). One of the key components in the fusion reactor is the Breeding Blanket (BB) surrounding the plasma, ensuring tritium self-sufficiency, heat removal for conversion into electricity, and neutron shielding. CEA-Saclay, with the support of Wigner-RCP and Centrum výzkumu Řež, is in charge of the development of one of the four BB concepts investigated in Europe for DEMO: the Helium Cooled Lithium Lead (HCLL) BB. The rationales of the HCLL are the use of Eurofer as structural material, eutectic liquid lithium-lead (PbLi) as tritium breeder and neutron multiplier, and helium gas as coolant.This paper shows the basic description of the DEMO HCLL BB concept and its design evolution during the past years, from a design based on the ITER Test Blanket Module (TBM) concept to a more advanced design called “Advanced-Plus” concept. This new HCLL BB concept that has been designed in order to improve Tritium Breeding Ratio (TBR) and shielding performances is presented. This new reference HCLL BB design has been analyzed and show very promising nuclear performances. Nevertheless, the “Optimized Conservative” concept, based on ITER TBM, is still considered as a robust back-up solution since structural improvements are still necessary on the “Advanced-Plus” concept. Moreover, a new Back Supporting Structure (BSS) is presented in this paper, designed to support the BB modules, with the aim to reduce pressure drops and thermal stresses.

Investigation on the “advanced-plus” Helium Cooled Lithium Lead Breeding Blanket design concept for TBR enhancement regarding thermal and mechanical behavior

In the framework of the European “HORIZON 2020” research program, the EUROfusion Consortium develops a design of a fusion demonstrator (DEMO). The Breeding Blanket (BB) directly surrounding the plasma is a major component ensuring tritium self-sufficiency, shielding against neutrons from D-T plasmas and heat extraction for electricity conversion. CEA-Saclay, with the support of Wigner-RCP and IPP-CR is responsible of developing the Helium Cooled Lithium Lead (HCLL) BB concept. In order to enhance Tritium Breeding Ratio (TBR), an alternative HCLL BB design, called “Advanced-Plus” concept, has been investigated, with the aim to reduce the amount of steel, while ensuring good thermal and mechanical behavior. The thermal behaviors of the horizontal Stiffening Plates (hSPs) with various channels designs in terms of dimensions and layout have been parsed on simplified FE models for verifying and optimizing the HCLL Breeding Zone (BZ) before analyzing a HCLL BB ¼ model. Moreover, sensitive analyses have been carried out for testing various hSPs pitches, alternative Helium hydraulic schemes inside the hSPs as well as the detachable FW option in applying a zero Heat Flux (HF) on the FW. Furthermore, mechanical calculations have also been performed to assess the behavior of the module in faulted condition. The results obtained with the Cast3M-qualified-FEM code are presented and discussed.

Optimization of the pressure drops in the helium in-module manifolds of the EU DEMO “Optimized Conservative” HCLL Breeding Blanket

In Europe the technology to develop DEMO is being supported by HORIZON 2020 research programme under EUROfusion Consortium. One of the key components that DEMO relies on is a working Breeding Blanket (BB). There are currently four Breeding Blanket concepts being developed in Europe, whose primary purpose is to convert kinetic energy of the neutrons into heat and to transfer this converted heat to a coolant, breed tritium to make plant self-sufficient of fuel and to shield magnets from radiation. This paper describes helium distribution system in the “Optimized Conservative” concept of Helium Cooled Lithium Lead (HCLL) BB, according to the HCLL 2014 Design Description Document. This contains three manifolds to distribute the helium in to several parts of the BB namely the First Wall, Cooling Plates, horizontal Stiffening Plates and the vertical Stiffening Plates. The work mainly focuses on optimization study and reduction of the pressure drops in the helium manifolds. The same is achieved by changing several geometrical parameters to keep the pressure drops under the limit. To achieve the results ANSYS-FLUENT commercial Computational fluid dynamic code is used. The final results include the modified geometry which gives lowest pressure drops for the given mass flow rate.

Thermal optimization of the Helium-Cooled Lithium Lead breeding zone layout design regarding TBR enhancement

Within the framework of EUROfusion R&D activities, CEA-Saclay has carried out an investigation of the thermal and mechanical performances of alternative designs intended to enhance the Tritium Breeding Ratio (TBR) of the Helium-Cooled Lithium Lead (HCLL) Breeding Blanket (BB) for DEMO. Neutronic calculations performed on the 2014 DEMO HCLL baseline predicted a value of TBR equal to 1.07, lower than the required value of 1.1, necessary to ensure the tritium self-sufficiency of the breeding blanket taking into account uncertainties. In order to reach the TBR target, the strategy of the steel amount reduction inside the HCLL module breeding zone (BZ) has been followed by suppressing some stiffening/cooling plates inside the BZ, leading to this “advanced” concept. Since all the plates inside the BZ are actively cooled by helium, each change in their geometric layout has a strong impact on the thermal response of the module. Moreover, the removal of stiffening plate may impact the resistance of the box in case of in-module loss of coolant accident (LOCA).A thermal and mechanical campaign of analyses has been carried out in order to assess a potentially optimized layout of the module which could comply with the whole set of rules foreseen for the HCLL BB design. To perform this research campaign, a theoretical-numerical approach, based on the Finite Element Method (FEM), has been followed and the qualified Cast3M and NX FEM codes have been adopted.Results obtained are herewith reported and critically discussed, highlighting the open issues and suggesting the pertinent modifications to DEMO HCLL module design.

Status on DEMO Helium Cooled Lithium Lead breeding blanket thermo-mechanical analyses

The EUROfusion Consortium develops a design of a fusion power demonstrator (DEMO) in the framework of the European “Horizon 2020” innovation and research program. One of the key components in the fusion reactor is the breeding blanket surrounding the plasma, ensuring tritium self-sufficiency, heat removal for conversion into electricity, and neutron shielding. The Helium Cooled Lithium Lead (HCLL) blanket is one of the concepts which is investigated for DEMO. It is made of a Eurofer structure and uses the eutectic liquid lithium–lead as tritium breeder and neutron multiplier, and helium gas as coolant. Within the EUROfusion organization, CEA with the support of Wigner-RCP and IPP-CR, is in charge of the design of the HCLL blanket for DEMO.This paper presents the status of the thermal and mechanical analyses carried out on the HCLL breeding blanket in order to justify the design. CFD thermal analyses on generic breeding unit including stiffening plates and cooling plates have been performed with ANSYS in order to consolidate results obtained with previous FEM design analyses. Moreover in order to expand the justification of the HCLL Breeding blanket design, the most loaded area of the equatorial outboard module has been analyzed with CAST3M in case of accident, according to RCC-MRx, resulting in relatively good behavior of the box. Additionally analyses have been performed in order to check the good behavior of the tie rods modules’ attachments system in normal condition showing promising results.

Numeric implementation of a nucleation, growth and transport model for helium bubbles in lead–lithium HCLL breeding blanket channels: Theory and code development

Large helium (He) production rates in liquid metal breeding blankets of a DT fusion reactor might have a significant influence in the system design. Low He solubility together with high local concentrations may create the conditions for He cavitation, which would have an impact in the components performance. The paper states that such a possibility is not remote in a helium cooled lithium–lead breeding blanket design. A model based on the Classical Nucleation Theory (CNT) has been developed and implemented in order to have a specific tool able to simulate HCLL systems and identify the key parameters and sensitivities. The nucleation and growth model has been implemented in the open source CFD code OpenFOAM so that transport of dissolved atomic He and nucleated He bubbles can be simulated. At the current level of development it is assumed that void fraction is small enough not to affect either the hydrodynamics or the properties of the liquid metal; thus, bubbles can be represented by means of a passive scalar. He growth and transport has been implemented using the mean radius approach in order to save computational time. Limitations and capabilities of the model are shown by means of zero-dimensional simulation and sensitivity analysis under HCLL breeding unit conditions.

Thermal–hydraulic analysis of the HCLL DEMO blanket

The present design of the helium-cooled lithium-lead (HCLL) blanket foresees the successive cooling of three sub-components (the first wall, the stiffening grid, and the breeder cooling plates) by parallel He-cooling channels. The optimisation of the coolant flow is complicated by the fact that the heat recovered by the cooling elements depends on the coolant parameters (temperature, velocity, heat exchange coefficient). Since all these parameters are intrinsically related, the classical approach of obtaining the coolant temperature distribution by enthalpy balance and using this distribution as an input for finite element analyses cannot be used. In this paper we present new finite elements models of the blanket that allow to obtain the temperature distribution in the coolant on the basis of the detailed power density distribution in the surrounding structures. At the same time, the models allow to improve the description of the heat transfer between the solid walls and the coolant. A review of the most used correlations available in literature to estimate the heat transfer coefficient has then been performed and the most appropriate one has been selected. The new models have been used to carry out a thermal–hydraulic analysis of the cooling system of the HCLL breeding blanket. Moreover, an estimation of the pressure drops in the different cooling elements has been made. The obtained results are discussed in terms of differences with those obtained in previous analyses and of the consequences on the blanket design.