Equatorial Module Research Articles

Tritium Transport in WCLL Outboard Breeding Blanket of EU-DEMO Reactor Under Pulsed Plasma Operation

The accurate prediction of the tritium inventory and permeation fluxes in the water-cooled lithium-lead (WCLL) breeding blanket of the European DEMO fusion reactor is a key aspect for future thermonuclear power plant licensing. In this context, a tritium transport analysis is essential for the evaluation of the tritium retention in LiPb (15.7 at. % Li) and in the structural components and tritium permeation fluxes into the cooling water. This study presents a COMSOL Multiphysics model of a portion of the minimum functional unit of the outboard equatorial module of the WCLL. The neutronics analysis, performed with the MCNP Monte Carlo transport code, allows for the assessment of the tritium generation rate and the volumetric power deposition in the lithium-lead, both of which are used as an input for tritium transport modeling. Moreover, the buoyancy forces and the magnetohydrodynamic effect are also included. In order to take into account a pulsed operation for the DEMO reactor, a suitable algorithm was developed. The results show peak velocities in LiPb up to 24.1 mm with a maximum temperature at the first wall (FW) of 441°C. Most of the tritium is concentrated between the FW and the baffle plate, with partial pressures between 0.15 and 0.4 Pa considering Aiello’s correlation and in-house measurements of Sieverts’ constant on the HyPer-QuarCh II (HQ-II) device, whereas from 70 to 180 Pa adopting Reiter’s correlation. This has an impact also on the inventory in the Eurofer and in permeation fluxes to the water pipes. For Reiter’s correlation, the inventories in the Eurofer are about one order of magnitude lower with respect to LiPb, and the inventory in water is five orders of magnitude higher with respect to HQ-II and Aiello’s correlation.

A novel approach to the study of magnetohydrodynamic effect on tritium transport in WCLL breeding blanket of DEMO

The Water-Cooled Lithium Lead (WCLL) breeding blanket is one of the European blanket designs proposed for DEMO reactor. Tritium can permeate into the different structural materials, arising potential issues concerning the fuel self-sufficiency and can be lost into the environment with consequent radiological hazard for the population. Within this frame, a tritium transport analysis is fundamental to evaluate tritium retention in LiPb (15.7 at. % Li) and in the structures and tritium permeation fluxes into the cooling water. To assess this study, a portion of the breeder unit of the outboard equatorial module of the WCLL was modelled. The buoyancy forces and the magnetohydrodynamic (MHD) effect were also included. The final system of partial differential equations was solved with a novel approach through COMSOL Multiphysics. The coupled MHD and heat transfer system of equations was solved performing a transient simulation, that was stopped when the main average variables, temperature and velocity, reached a stable condition. In this way, it was possible to determine the lithium-lead velocity field and to use it as an input for the transport analysis. Tritium transport was modelled by using the input data of tritium generation rate and volumetric power deposition coming from an ad-hoc Monte Carlo simulation realized with MCNP software. Moreover, the transport analysis included advection-diffusion of tritium into the LiPb, transfer of tritium from the liquid interface towards the steel, diffusion of tritium inside the steel, transfer of tritium from the steel towards the coolant, advection-diffusion of diatomic tritium into the coolant.

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.

Tritium transport model at breeder unit level for WCLL breeding blanket

In a fusion power demonstration plant (DEMO), the development of a tritium transport model is mandatory in order to correctly predict the tritium concentration inside the liquid metal, the permeated flux through the structural materials and into the coolant, playing a fundamental role in guaranteeing tritium self-sufficiency in the fusion reactor and safety both for the workers and for the external environment. In the present work, a multi-physics 3D tritium transport model has been assessed for a single breeder unit located in the outboard equatorial module of the Water-Cooled Lithium Lead (WCLL) breeding blanket of DEMO, adopting an approach that permits to have a modelling tool able to be adaptive within certain margins to changes in operating parameters and geometry. 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/dissociation), advection-diffusion of diatomic tritium into the coolant. The effect of buoyancy forces, which arise due to temperature variation, has been also considered. Under the above-specified phenomena, tritium concentrations, inventories and losses have been derived.

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.

Numerical assessment of the thermomechanical behaviour of the DEMO Water-Cooled Lithium Lead inboard blanket equatorial module

Within the framework of EUROfusion R&D activity, a research campaign has been carried out at the University of Palermo, in close cooperation with ENEA labs, in order to assess the thermo-mechanical performances of the DEMO Water-Cooled Lithium Lead (WCLL) inboard blanket equatorial module, whether properly integrated within its whole inboard segment. In particular, a detailed 3D model of this segment, including all the other modules, the back-supporting structure and the attachment system, has been considered in order to realistically simulate the boundary conditions affecting the equatorial module behaviour.The study has been focused on the investigation of the module thermo-mechanical performances under the Over Pressurization (Level D) loading scenario envisaged for the DEMO WCLL breeding blanket as a consequence of a small in-box Loss Of Coolant Accident (LOCA) accident.A theoretical-numerical approach, based on the Finite Element Method (FEM), has been followed and the qualified ABAQUS v. 6.14 commercial FEM code has been adopted.The obtained thermo-mechanical results have been assessed in order to verify their compliance with the design criteria foreseen for the structural material. To this purpose, a stress linearization procedure has been performed along the most critical paths located within the inboard equatorial module structure, in order to check the fulfilment of Level D rules prescribed by the SDC-IC structural design code. The obtained results are herewith presented and critically discussed.

On the thermo-mechanical behaviour of DEMO water-cooled lithium lead equatorial outboard blanket module

Within the framework of EUROfusion R&D activities an intense research campaign has been carried out at the University of Palermo, in close cooperation with ENEA Brasimone, in order to investigate the thermo-mechanical performances of the DEMO water-cooled lithium lead breeding blanket (WCLL). In particular, attention has been paid to the most recent geometric configuration of the DEMO WCLL outboard equatorial module, as designed by WCLL project team during 2015, endowed with an attachment system based on the use of radial pins, purposely outlined to connect the module back-plate to its back-supporting structure, that have been properly considered to simulate more realistically the module thermo-mechanical behaviour.The research campaign has been mainly focused on the investigation of the module thermo-mechanical performances under the Normal Operation (Level A) and Over Pressurization (Level D) steady state loading scenarios envisaged for the DEMO WCLL.A theoretical-numerical approach, based on the Finite Element Method (FEM), has been followed and the qualified ABAQUS v. 6.14 commercial FEM code has been adopted.Thermo-mechanical results obtained have been assessed in order to verify their compliance with the design criteria foreseen for the structural material. To this purpose, a stress linearization procedure has been performed along the most critical paths located within the module structure, in order to check the fulfilment of both Level A and Level D rules prescribed by the SDC-IC structural design code. Results obtained are herewith presented and critically discussed, highlighting the open issues and suggesting the pertinent modifications to DEMO WCLL outboard equatorial module design aimed to obtain the complete fulfilment of the prescribed design criteria.

On the optimization of the first wall of the DEMO water-cooled lithium lead outboard breeding blanket equatorial module

Within the framework of EUROfusion R&D activities a research campaign has been carried out at the University of Palermo in order to investigate the thermo-mechanical performances of the DEMO water-cooled lithium lead (WCLL) breeding blanket first wall (FW). The research campaign has been mainly focused on the optimization of the FW geometric configuration in order to maximize the heat flux it may safely withstand fulfilling all the thermal, hydraulic and mechanical requirements foreseen by safety codes. Attention has been focused on the FW flat concept endowed with square cooling channels and the potential influence of its four main geometrical parameters on its thermo-mechanical performances has been assessed performing a parametric analysis by means of a qualified commercial finite element method code. A set of 5929 different FW geometric configurations has been considered and the thermal performances of each one of them have been numerically assessed in case it undergoes 26 different values of heat flux on its plasma-facing surface. The resulting 154154 thermal analyses have allowed to select those cases fulfilling the adopted thermal-hydraulic requirements, whose thermo-mechanical performances have been numerically assessed under both normal operation and over-pressurization steady state loading scenarios to check whether they met the mechanical requirements prescribed by the pertaining SDC-IC safety rules. Four optimized FW configurations have been found to safely withstand a heat flux up to 2MW/m2 fulfilling all the rules prescribed by safety codes. Finally, the thermo-mechanical performances of these FW optimal configurations have been further investigated under both normal operation and over-pressurization steady state loading scenarios setting-up more realistic 3D FEM models. Results obtained, herewith presented and critically discussed, have allowed to select one promising FW geometrical configuration.

Optimization of the breeder zone cooling tubes of the DEMO Water-Cooled Lithium Lead breeding blanket

The determination of an optimal configuration for the breeder zone (BZ) cooling tubes is one of the most important issues in the DEMO Water-Cooled Lithium Lead (WCLL) breeding blanket R&D activities, since BZ cooling tubes spatial distribution should ensure an efficient heat power removal from the breeder, avoiding hotspots occurrence in the thermal field. Within the framework of R&D activities supported by the HORIZON 2020 EUROfusion Consortium action on the DEMO WCLL breeding blanket design, a campaign of parametric analyses has been launched at the Department of Energy, Information Engineering and Mathematical Models of the University of Palermo (DEIM), in close cooperation with ENEA-Brasimone, in order to assess the potential influence of BZ cooling tubes number on the thermal performances of the DEMO WCLL outboard breeding blanket equatorial module under the nominal steady state operative conditions envisaged for it, optimizing their geometric configuration and taking also into account that a large number of cooling pipes can deteriorate the tritium breeding performances of the module. In particular, attention has been focused on the toroidal-radial option for the BZ tube bundles lay-out and a parametric study has been carried out taking into account different tube bundles arrangement within the module. The study has been carried out following a numerical approach, based on the finite element method (FEM), and adopting a qualified commercial FEM code. Results obtained are herewith presented and critically discussed.

Analysis of the thermo-mechanical behaviour of the DEMO Water-Cooled Lithium Lead breeding blanket module under normal operation steady state conditions

Within the framework of DEMO R&D activities, a research cooperation has been launched between ENEA, the University of Palermo and CEA to investigate the thermo-mechanical behaviour of the outboard equatorial module of the DEMO1 Water-Cooled Lithium Lead (WCLL) blanket under normal operation steady state scenario. The research campaign has been carried out following a theoretical–computational approach based on the Finite Element Method (FEM) and adopting a qualified commercial FEM code. In particular, two different 3D FEM models (Model 1 and Model 2), reproducing respectively the central and the lateral poloidal–radial slices of the WCLL blanket module, have been set up. A particular attention has been paid to the modelling of water flow domain, within both the segment box channels and the breeder zone tubes, to simulate realistically the coolant-box thermal coupling. Results obtained are herewith reported and critically discussed.

Assessment of the Thermo-mechanical Performances of a DEMO Water-Cooled Liquid Metal Blanket Module

Within the framework of DEMO R&D activities, a research cooperation has been launched between ENEA-Brasimone, CEA-Saclay and the University of Palermo to investigate the thermo-mechanical behaviour of the outboard equatorial module of the DEMO1 Water-Cooled Lithium Lead (WCLL) blanket, both under normal operation and over-pressurization steady state scenarios. The research campaign has been carried out following a theoretical-computational approach based on the finite element method (FEM) and adopting a qualified commercial FEM code. In particular, two different three-dimensional FEM models of the WCLL blanket module have been set-up to be used for normal operation and over-pressurization analysis, respectively. The former reproduces realistically the WCLL blanket module central poloidal–radial region, including one breeder cell in the toroidal direction and all the five cells in the radial one. The latter simulates the entire module segment box, without including the breeder and its cooling tubes. Two set of uncoupled steady state thermo-mechanical analyses have been carried out with reference to the investigated loading scenarios. In particular, under normal operation scenario (level A) the module has been supposed to undergo both 15.5 MPa coolant pressure on its cooling channels walls and thermal deformations due to the flat-top plasma operational state thermal field, while under over-pressurization scenario (level D) it has been assumed to experience 15.5 MPa coolant pressure on its segment box internal walls while operating at normal operation thermal level. Results obtained are presented and critically discussed according to the SDC IC code.

Equatorial modulation and north-south asymmetry of galactic cosmic rays due to the interplanetary magnetic field

Measurements of galactic cosmic rays made in 1967 on a low-altitude polar satellite exhibited two kinds of quasi-periodic variations which were synchronous with the changes in sector polarity of the interplanetary magnetic field (IMF). A modulation of 30% in the equatorial flux and a north-south asymmetry of roughly the same magnitude were observed. Both effects have been found in the records of surface neutron monitors. Relevance of the equatorial modulation to IMF structure is discussed briefly. It is suggested that the north-south asymmetry is due to intermittent connection between the IMF and GMF (geomagnetic field) and that magnetospheric trapping of charged particles takes place at those times. Evidence is presented that connection occurs on the dayside of the earth.

Equatorial modulation of electrons in a pulsating aurora

Electron intensities at 4, 6 and > 22 keV were measured on the ESRO Skylark rocket S29 2 launched into a pulsating aurora from Kiruna, Sweden at 2326:40 LT on 17 October 1969. The similarity of pulsations in electron intensity at the rocket and optical intensity seen from the ground shows that the pulsations were true temporal changes over part of the flight. The time dispersion between the pulsations at different electron energies places the source of the modulation at a distance of (4 ± 1) × 10 4km from the ionosphere, i.e. within about 10 4 km of the geomagnetic equator on the L = 5.4 magnetic shell. The modulation process was found to be coherent to within 1 sec over a radial distance at the Equator of at least 500 km.