Probabilistic hazard assessment of volcanic fallout

Treballs Finals de Grau de Física, Facultat de Física, Universitat de Barcelona, Curs: 2022, Tutors: Pilar Queralt, Arnau FolchThis work uses the tephra dispersal model HAZMAP to merge thousands of numerical simulations into probabilistic tephra fallout hazard maps of the Teide volcano in the Canary Islands. Based on historical and meteorological geological data, 7,306 individual scenarios are created to produce these probabilistic hazard maps. These maps give the probability of exceeding a certain threshold value of the ground load and allow us to study how the Teide explosion would affect the Canary archipelago

Development of a simulation tool for MHD flows under nuclear fusion conditions

In Nuclear Fusion Technology, MHD flows can be encountered in liquid metal (LM) breeding blankets, the part of a fusion reactor where tritium, one of the fusion fuels, is to be produced. There are several types of LM breeding blankets, which can be classified according to the fraction of the thermal load extracted by the LM. Such classification provides valuable information on liquid metal flow properties. For instance, if no heat removal is carried out by the LM, its velocity can be quite low, what makes buoyancy the predominant force in front of inertia. The flow inside breeding blanket channels can be very complex, particularly in those blanket types where buoyancy plays a relevant role. The understanding of the flow nature, including the possible instabilities that might appear, the exact knowledge of flow profiles for tritium control purposes, and the prediction of thermal fluxes for thermal efficiency analysis are of great interest for blanket design optimization. In this direction, a thermal-MHD coupled simulation tool has been implemented in the OpenFOAM toolkit. The resultant code can be understood as a preliminary predictive tool for liquid metal breeding blanket channel design. The developed code is a transient 3D tool that accounts for thermal-MHD coupling and can deal with several layers of materials. Various MHD modeling strategies have been studied, starting with the implementation of an induced magnetic field formulation and continuing with an electric potential formulation based on the low magnetic Reynolds approximation, in this case using the conservative formula of the Lorentz force proposed by Ni et al. (2007). Two pressure-velocity couplings have been analyzed. The first one is based on a projection method whereas the second one, which has proved to be more robust, follows a PISO-like algorithm (Weller et al. 1998). The thermal coupling has been achieved by means of the Boussinesq hypothesis. The developed tool accounts for the linear wall function for Hartmann boundary layers from Leboucher (1999), which reduces substantially the CPU time of the simulations. The code also accounts for fluid-solid thermal and electrical coupling by means of implicit coupling of fluid and solid grids. Special attention has been placed in correctly coupling liquid-solid energy transport equations by means of the conservative form of the equations in both domains. All along the development process, validation steps have been carried out with successful results. An alternative thermal-MHD tool has also been implemented following the 2D approach from Sommeria and Moreau (1982). Such code accounts for the 0-equation Q2D turbulence RANS model from Smolentsev and Moreau (2006). Three application cases are considered. In the first case, the integrated effect of volumetric heating and magnetic field on tritium transport in a U-bend flow, as applied to the EU HCLL blanket concept, is studied. The second application case corresponds to the thermal analysis of the blanket design that is being developed in the framework of the Spanish National Project on Breeding Blanket Technologies TECNO_FUS (through CONSOLIDER-INGENIO 2010 Programme). The third and last case includes the instability analysis of a pressure-driven MHD flow in a horizontal channel with a constant thermal load. The application cases have not only shown the code capabilities to simulate liquid metal channels in breeding blankets but, also, have provided a useful know-how on flow properties inside those channels.En Tecnologia de Fusió Nuclear, per descriure la circulació de fluids dins dels embolcalls regeneradors de metall líquid (ML) cal recórrer a la magnetohidrodinàmica (MHD). Un embolcall regenerador (o tritigeni) és la zona d'un reactor de fusió on es produeix triti, un dels combustibles de fusió. Els embolcalls regeneradors de ML poden classificar-se atenent a la fracció de la càrrega tèrmica extreta pel ML. Aquesta classificació proporciona informació valuosa sobre les propietats del flux de metall líquid. Per exemple, si el ML no extreu potència tèrmica, la seva velocitat pot ser bastant baixa, el que implica que la força dominant sigui la flotació en front de la inèrcia. El flux dins dels canals d’un embolcall regenerador pot ser molt complex, especialment en aquells tipus d’embolcall on la flotació juga un paper rellevant. La comprensió de la naturalesa del flux, incloent les inestabilitats que podrien aparèixer, el coneixement exacte dels perfils de flux per al control de triti, i la predicció de fluxos tèrmics per a l’anàlisi de l’eficiència tèrmica són de gran interès per a l’optimització del disseny. En aquest sentit, s’ha implementat un codi de simulació acoblada tèrmica-MHD en l’eina de codi lliure OpenFOAM. El codi resultant pot ser entès com una eina predictiva preliminar per al disseny dels canals de ML dels embolcalls regeneradors. El codi desenvolupat permet el càlcul transitori en 3D amb acoblament tèrmic-MHD i pot tractar amb diverses capes de materials. S’ha estudiat diferents models MHD, començant per la implementació d’una formulació basada en el camp magnètic induït i continuant amb una formulació basada en el potencial elèctric mitjançant l’aproximació per a Reynolds magnètics baixos, en aquest darrer cas utilitzant la fórmula conservativa de la força de Lorentz proposada per Ni et al. (2007). S’han analitzat dos acoblaments pressió-velocitat. El primer acoblament es basa en un mètode de projecció, mentre que el segon, que ha demostrat ser més robust, segueix un algorisme tipus PISO (Weller et al. 1998). L’acoblament tèrmic s'ha modelat per mitjà de la hipòtesi de Boussinesq. El codi desenvolupat compta amb la funció de paret lineal de Leboucher (1999) per a les capes límit de Hartmann, cosa que redueix substancialment el temps de CPU de les simulacions. El codi també inclou acoblament tèrmic i magnètic líquid-sòlid mitjançant l'acoblament implícit de les malles del fluid i del sòlid. S’ha tingut una cura especial en realitzar correctament aquest acoblament fluid-sòlid fent ús de la forma conservativa de l’equació d’energia en ambdós dominis. Al llarg del procés de desenvolupament, s’han dut a terme les corresponents validacions amb resultats satisfactoris. També s'ha implementat un codi tèrmic-MHD alternatiu basat en el model MHD 2D de Sommeria i Moreau (1982). Aquest segon codi té implementat el model RANS de 0-equacions de Smolentsev i Moreau (2006) per a la turbulència Q2D. Els codis desenvolupats s’han emprat en tres casos d’interès. En el primer cas, s’ha estudiat l’efecte integrat de l’escalfament volumètric i el camp magnètic en el transport de triti en un canal en U, com el que es pot trobar en el disseny d’embolcall regenerador UE HCLL. En el segon cas, s’ha realitzat una anàlisi tèrmica del disseny d’embolcall que s’està definint dins del Programa Nacional Espanyol en Tecnologia d’Embolcalls Regeneradors TECNO_FUS (a través del Programa CONSOLIDER-INGENIO 2010). En el tercer i últim cas, s’han analitzat les inestabilitats que tenen lloc en fluxos MHD en canals horitzontals amb gradient de pressió extern, amb camp magnètic transversal i amb una càrrega tèrmica uniforme. Els casos d’aplicació no només han demostrat la capacitat del codi per simular canals de metall líquid en embolcalls regeneradors; també han permès caracteritzar el flux a l’interior d’aquests canals.Postprint (published version

Cellulose oxidation by Laccase-TEMPO treatments

In this work, laccase-TEMPO (Lac-T) treatments were applied to bleached commercial dissolving pulp in order to introduce carbonyl and carboxyl groups, which were found to improve dry and wet strength-related properties. Also the solubility behavior towards xanthate reactions was assessed. The effect of a refining step (R) before the oxidative treatment, the absence or presence of oxygen pressure, TEMPO dose (2 or 8% oven dried pulp) and reaction time (8 or 20 h) were thoroughly examined. Treatments conducted in the presence of oxygen pressure exhibited greater amount of functional groups. Introducing a pre-refining treatment resulted in similar functional groups but higher wet strength was achieved. Specifically, a high W/D strength ratio was observed, indicating that wet strength-related property was satisfactorily developed. Besides the fact that all Lac-T treatments caused severe cellulose degradation, no fiber strength loss was detected. In fact, all oxidized samples presented higher Wet Zero-Span Tensile Strength, mainly in R+ Lac-T (O2) sample, which suggested the formation of hemiacetal linkages between the new introduced aldehyde groups and available free hydroxyl groups resulting from fibrillationPostprint (author's final draft

Dissolving-grade pulp: a sustainable source for fiber production

The global textile fiber output increased five times from 1975 to 2020. Also, in 2010, the combined demand for man-made and natural fibers was projected to increase by 84% within 20 years. Clothing materials are largely made from cotton or petroleum-based synthetic fibers; both sources, however, have adverse environmental impacts. Thus, cotton requires vast amounts of land, water, fertilizers and pesticides, and synthetic fibers are not biodegradable. This scenario has raised the need for further exploration of cellulose polymers as sustainable sources for the textile industry. Cellulose, the most abundant renewable organic material on earth, is an outstanding polymer that by chemical derivatization or modification can offer a broad range of applications. Dissolving-grade pulp (DGP), which consists of highly pure cellulose, is the most suitable material for manufacturing cellulose derivatives and regenerated fibers. The latter are typically obtained by using the viscose process, which has considerable adverse environmental impacts. Although the textile industry has progressed substantially, further efforts are still needed to make its entire production chain more sustainable. This article provides an in-depth introduction to the potential of fibers with a high cellulose content, known as dissolving-grade pulps. It reviews the properties of DGP, the cooking and purifying methods typically used to obtain it, and the process by which paper-grade pulp can be converted into dissolving-grade pulp. Also, it discusses traditional and recently developed technologies for producing regenerated cellulose fibers. Finally, it examines the potential for recovering cellulose from textile waste as a novel sustainable practice.This publication is part of Project PID2020-114070RB-I00 (CELLECOPROD), funded by MCIN / AEI / 10.13039 / 501100011033. The author Elisabet Quintana is a Serra Húnter Fellow.Peer ReviewedPostprint (published version

Conceptual design of the EU-DEMO dual coolant lithium lead equatorial module

© 20xx IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.Within the framework of EUROfusion Program, the Dual Coolant Lithium Lead (DCLL) is one of the four EU breeder blanket concepts that are being investigated as candidates for DEMO. DCLL uses PbLi as the main coolant, tritium breeder, tritium carrier, and neutron multiplier. The main structures, including the first wall, are cooled with helium. The EU program proposed for the next years will consider a DCLL version limited to 550 °C in order to allow the use of conventional materials and technologies. During the first year of EUROfusion activities, a draft design of the DCLL has been proposed. The main blanket performances were adapted to the new specifications and the CAD model of DEMO. The breeder zone has been toroidally divided into four parallel PbLi circuits, separated through stiffening grid radial walls. The PbLi flow routing has been designed to maximize the amount of thermal power extracted by flowing PbLi and to avoid the occurrence of reverse flows due to volumetric heating. Thermal hydraulics, magnetohydrodynamic and neutronics calculations have been performed for the first draft design. The new DCLL design employs Eurofer-alumina-Eurofer sandwich as flow channel insert (FCI).Postprint (published version

Flow analysis in the HCLL-TBM ITER channels including MHD and heat transfer

One of the key components regarding heat transfer and tritium inventories in deuterium-tritium nuclear fusion reactors is the (tritium) Breeding Blanket, called Test Blanket Module or TBM in ITER experiment. Several designs are going to be tested in ITER, one of those is the HCLL (Helium Cooled Lithium Lead) design. Before being tested, it is of major interest to predict in detail several ow parameters such as pressure drop, tritium inventories and tritium permeation rates through walls. The goal of the present study is to analyze the ow near the gap region (close to the rst wall) in the HCLL-TBM so as to quantify tritium inventories and permeation uxes. To do so, simpli ed C-shaped channels are simulated under ITER speci cations. The ow appears to be very complex and, in order to get the origin of this complexity, the phe- nomenon physics are decoupled. First, the pure hydrodynamic case is simulated; obtaining that the critical Reynolds number is around TBM/ITER speci cations. Second, the MHD ow with perfectly insulating walls is studied and, as expected due to the high Hartmann number, hydrodynamic instabilities disappear. Finally, when heat transfer is introduced, vorticity is generated due to Rayleigh-B enard instabilities at the channel inlet and, as the ow travels through the channel, faster vortices appear in the gap region and in the outlet channel. These vortices originate high tritium concentration zones. Hence, the existence of vortices is of crucial interest for tritium inventories prediction and HCLL design.Postprint (published version

Comparative evaluation of the action of two different endoglucanases. Part I: on a fully bleached, commercial acid sulfite dissolving pulp

A fully bleached commercial acid dissolving pulp was treated with two endoglucanases, one obtained from Paenibacillus barcinonensis (B) and the other one produced from Cerrena unicolor (F) with the intention to improve cellulose reactivity and processability in the viscose process. B cellulose was tested under 120 U/g oven dry pulp (odp) and the F cellulase under two conditions, 12 and 60 U/g odp. In addition, a purification stage, consisting in a cold caustic extraction (CCE) of 9 % w/v NaOH, was applied before or after the enzymatic treatment in order to reduce the amount of hemicellulose and improve the action of enzymes. The treated pulps were evaluated in terms of brightness, viscosity, water retention value, fibre morphology, carbohydrate composition, Fock solubility and NMR. In general, results revealed that both endoglucanases improved cellulose reactivity, albeit in a different way; thus, B caused no scissions in the cellulose chain and no significant reduction in fibre length, whereas F strongly decreased viscosity, shortened fibre length and increased considerably the amount of fines. The result of applying two different doses of F cellulase was reflected on Fock solubility and fibre morphology. F60 treatment was found to give the highest value of Fock solubility and the biggest reduction of fibre length. The effect of both endoglucanases on Fock solubility was increased by introducing an earlier CCE stage. Finally, a CCE_B120 pulp with 3 % of hemicellulose and 69 % of Fock solubility was obtainedPostprint (author’s final draft

Spectral radiance of blue light filters on ophthalmic lenses

As a result of the recent improvement in light-emitting diode (LED) technology, the displays of the vast majority of electronic devices are now illuminated by LEDs. There are several advantages of this type of light source over its predecessors; however, recent research is giving support to the fact that prolonged exposition to the white LEDs emission in the blue spectrum may have a negative impact on visual health, as well as, on biological rhythms (circadian rhythms). As a consequence, ophthalmic lens manufacturers have recently introduced in the market innovative lenses that incorporate blue light filters, especially designed for electronic device users. In this work, the performance of different blue light filters present on commercially available ophthalmic lenses was tested and compared. Lenses were placed in front of a LED-based backlight tablet, in a similar way a common user would be reading a text on the electronic device. The absorption characteristics of the various samples from four different ophthalmic lens manufacturers were measured. Analysis of the different samples from the same manufacturer was conducted and blue light filters from different manufacturers were compared. © Sociedad Española de Óptica.Postprint (published version

New strategies to bleach dissolving pulps using enzymatic treatments

A biobleaching sequence was applied to sulphite pulp in order to explore new bleaching possibilities using enzymatic treatments. Therefore, the well-known laccase-mediator system was used with the aim to achieve dissolving pulp characteristics. The enzymatic sequence was compared with a conventional hydrogen peroxide treatment in order to elucidate the effect of a laccase stage (L) for a potential industrial application. The treated pulps showed satisfactory results: high cellulose reactivity, high brightness and low content of hemicellulosesPostprint (published version