Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas
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Estimation of the atmospheric boundary layer height by means of machine learning techniques using ground-level meteorological data
No full textAerosols affect air quality, weather and climate through many mechanisms and are dangerous to human health. They are mostly concentrated within the atmospheric boundary layer (ABL) its height is affected by the radiation emitted by the surface, causing turbulence and evolving along the day, influencing the vertical mixing of the air
pollutants generated near the surface and therefore, their ground-level concentration from local sources. Lidars have demonstrated their capabilities to study the aerosol vertical distribution and their spatio-temporal evolution can provide very complete information on the ABL dynamics. In this work, machine learning techniques are
employed to predict the ABL height. The meteorological variables measured at ground-level are used as features of the algorithm and the ABL height estimated by the STRATfinder algorithm using ceilometer profiles, a small lidar instrument with enhanced characteristics for unassisted continuous operation, are considered the truth in the supervised regression algorithm. The machine learning models allow considering combination of features in the regression algorithm and also allow characterizing the importance of each of the predictors to determine the final result. This property is used to study different boundary layer regimes. The ABL is difficult to study in
certain parts of the day due to transitions between atmospheric regimes. In order to improve the performance of the model, each day was divided in four parts (nighttime, morning, daytime and evening). The Madrid ceilometer profile database has been studied for the year 2020, splitting the training datasets for the machine learning algorithm into season and part of the day, and the importance of predictors analyzed. Major influence of temperature and relative humidity is found in most of the situations, but also wind velocity in certain circumstances and pressure. The influence of radiation is small, contrary to expected. The main advantage of the proposed method is that MLHs and ABLHs can be retrieved directly from widely available ground-level meteorological data. Future work will focus on more relevant predictors, as latent heat or turbulence
PEP-39 Update from JET-ILW: Configuration effects on L-H power threshold and H-mode
No full textIn JET-ILW Corner (CC) plasmas the L-H transition power threshold (PLH) is higher than in the Horizontal Target (HT) ones, indicating poorer L-mode confinement in Corner. The ne,min dependence on both plasma configuration and plasma current was shown. In D plasmas, typically ne,min(CC)~0.3 of the Greenwald density (nGW), while ne,min(HT)~0.4 nGW, for various Btor and Ip L-H transition datasets. A reduction in ne,min when Ip is lower was shown. Despite the fact that HT has lower PLH, for the same gas fuelling and input power, the H-mode in HT has poorer confinement than CC. In the CC time-window density is lower and temperatures higher, and steady large ELMs are observed. In the HT time window, pedestal density is higher and temperatures lower, a mixture of small and large ELMs is present. A higher ratio of heating power to PLH threshold does not correlate with good confinement or steady type I ELMy regime. Additional L-H transition experiments investigating the configuration effect and the relationship between Ip and ne,min (at fixed Btor) were requested, even if in Carbon devices
Foaming of aluminium-silicon alloy using concentrated solar energy
No full textSolar energy is used for the work reported here as a nonconventional heating system to produce aluminium foam from Al{single bond}Si alloy precursors produced by powder metallurgy. A commercial precursor in cylindrical bars enclosed in a stainless-steel mould was heated under concentrated solar radiation in a solar furnace with varied heating conditions (heating rate, time, and temperature). Concentrated solar energy close to 300 W/cm2 on the mould is high enough to achieve complete foaming after heating for only 200 s. Under these conditions, the density and pore distribution n the foam change depending on the solar heating parameters and mould design
Optimisation of NaOH texturisation process of silicon wafers for heterojunction solar-cells applications
No full textThe formation of a pyramidal structure on the surface of h100i-oriented monocrystalline-silicon wafers is an effective and well known
method to reduce reflection losses from the front surface of both silicon solar cells and silicon-heterojunction solar cells (SHJs). The con sequence of this texturisation is an important optical gain, with a subsequent increase of the short-circuit current density (Jsc) and thus of
the conversion efficiency of the devices. On the other hand, silicon-heterojunction solar cells are critically affected by the surface quality
of the c-Si substrates, so the right combination of optimum texturisation- and cleaning steps previous to emitter (a-Si:H) deposition are
indispensable in the fabrication process. The main goal of this work has been to perform a systematic and comprehensive analysis aimed
at optimising the texturisation process based on the use of alkali solutions of NaOH with de-ionised water (DIW) and isopropyl alcohol
(IPA) in different types of monocrystalline-silicon wafers for silicon-heterojunction solar-cell (a-Si:H/c-Si) applications. Three types of
h100i silicon substrates have been used: polished float-zone (FZ) wafers and rough- (as-cut) and polished Czochralski (CZ) wafers.
The texturisation process has been evaluated from images obtained by Scanning Electron Microscopy (SEM) and from
hemispherical-reflectance spectra. Different etching times, temperatures and NaOH concentrations of the solutions as well as cleaning
treatments of the wafers prior to the texturisation process have been analysed. Results show different conditions of the optimum texturi sation process for each type of silicon wafers. An effective texturisation of FZ and CZ substrates has been achieved. Finally, SHJ solar
cells have been obtained from FZ and CZ silicon wafers textured by the chemical processes optimised in this wor
In-containment source term predictability of ASTEC-Na: Major insights from data-predictions benchmarking
No full textModeling the containment response to a sodium pool fire is to be one of the key aspects of any comprehensive safety evaluation of the new generation of sodium cooled fast reactors. Through a peer review of
earlier experimental investigations some useful data can be collected and then used for assessing the current
analytical capabilities to model severe accidents or some of their specific aspects. This paper provides
major insights into the in-containment aerosol behavior predictability of ASTEC-Na (CPA???module) during Na-pool fires. By comparing against tests from the ABCOVE (AB1 and AB2) and FAUNA
(F2) programs, it has been shown that experimental trends can be roughly reproduced with a single-cell approach whenever natural convection is effective in making the vessel atmosphere uniform both thermally and in composition. Nonetheless, the present heavy parametrization of ASTEC-Na models
should be avoided or strongly supported by further experimentation that allows setting sound default values, concerning both combustion energy distribution and aerosol formation and distribution.
Anyway, the peer data review has highlighted that a meaningful comparison to predictions is not always feasible due to large data uncertainties, particularly at the beginning of Na burning. As for the particle
ageing, the comparisons set seems to indicate that transformation from oxides to hydroxides is predicted to be too slow; nevertheless, a more extensive benchmarking should be conducted to confirm it
Analysis of the Long-Term Interaction Between Molten Core and Dry Concrete at Fukushima Daiichi Unit 1
No full textVolume 211, 2025 - Issue 10: Selected papers from the 20th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-20)The latest investigations of Fukushima Daiichi Unit 1 have demonstrated that corium attack to the pedestal walls and pedestal floor has occurred in Fukushima Daiichi Unit 1 to a certain extent. The
results of past analytical benchmarks, such as the Organisation for Economic Co-operation and
Development (OECD)/Nuclear Energy Agency (NEA) Benchmark Study of the Accident at the Fukushima
Daiichi Nuclear Power Plant (BSAF project), have agreed with this finding. However, the latest investigation does not show evidence of unlimited molten core???concrete interaction (MCCI), which is one of the
main discrepancies from the BSAF project.
More recently a MCCI benchmark has been launched in the context of the OECD/NEA project ARC-F
(Analysis of Information from Reactor Building and Containment Vessels of Fukushima Daiichi Nuclear Power
Station). In the benchmark, common geometry, boundary, and initial conditions have been selected among all
the participants. The results show an improved agreement among different codes for what concerns overall
erosion, corium temperature, and hydrogen generation, confirming that to some extent, the earlier scatter
found in these variables came from differences in the MCCI scenario modeled by each partner.
However, common unlimited erosion, not observed by onsite visual inspections, is still predicted.
Understanding the origin of this deviation might provide insights into boundary conditions, model drawbacks,
or ill-posed assumptions that might need to be revisited (e.g. interfacial temperature, effective heat
transfer coefficients, concrete heat transfer). In this paper, a summary of the overall results and a discussion
of modeling and boundary conditions is presented to disclose the results of the activity and the future steps
to be taken in the OECD/NEA project FACE (Fukushima Daiichi Nuclear Power Station Accident Information Collection and Evaluation)
Report on S/U analyses in MYRRHA homogenized model v1.8 performed with the MCNP6.2 and SUMMON codes and the JEFF-3.3 library
No full textThis report presents nuclear data sensitivity and uncertainty (S/U) analyses for several safety-related
reactor parameters (keff, ??eff and reactivity coefficients) of the latest design (version 1.8) of the MYRRHA
facility. This work has been performed within the frame of task 5.1 of EU H2020 SANDA project using the
codes MCNP 6.2 and SUMMON, the JEFF-3.3 nuclear data library and an homogenized model of
MYRRHA version 1.8 supplied by SCK CEN. In this report, nominal values for these parameters,
integrated sensitivity coefficients (ISCs), sensitivity profiles for the major nuclear reactions with the highest
contributions to the uncertainty, the total uncertainty due to nuclear data and top reactions contributing to
the uncertainty are provided. As a conclusion, and although major contributors to the uncertainty depend
on the specific parameter, in general, the major reaction contributors are elastic and inelastic reactions in
fuel, coolant and structural materials. Nevertheless, given the slow convergence of sensitivity calculations
with these reactions, more detailed simulations will be required to fully understand these contributions
One Health perspective: an integrated in-silico approach to assess the environmental fate of pesticides, the exposure of aquatic and soil organisms and the risks for human health
No full textWithin the One Health perspective, the health of humans, animals and ecosystems is highly interconnected. This study presents an in silico approach to assess the environmental fate of plant protection products (PPPs) in soil and water, as well organisms and humans exposure and associated risks. The methodology integrates scenarios, models, tools and approaches recognized and used by the European Food Safety Authority and the scientific community for PPP market authorization risk assessments. Three European Member States ???Portugal (PT),
Denmark (DK), and the Netherlands (NL) ???were selected to demonstrate = model applicability, each representing a different EU Regulatory Zone. For each country, real PPP application data and site-specific meteorological and pedological information were collected, and environmental concentrations monitored. Results
showed that the predicted environmental concentration in soil (PECsoil) was lower than the monitored concentrations in PT locations, whereas PECsoil was overestimated in both NL and DK. The toxicity to exposure ratio (TER) indicated low risk to earthworms in all simulations. For surface water (SW), PECSW was below the environmental quality standard (EQSSW) in PT, whereas significant exceedances occurred in NL and DK. However, in DK, PPP concentrations declined below EQSSW within one day post-application. Comparison with reference toxicological endpoints for fish and invertebrates suggested low risks. Estimated PPP concentrations in invertebrates and fish for human consumption indicated intake would not exceed the acceptable daily intake (ADI)
in PT and NL. However, at the DK location, small consumption (>13 g) of a given invertebrate would exceed the ADI for prosulfocarb (5 ??g kg??? 1 ). Despite limited experimental dataset and some constraints in field data collection that influenced models performance and verification, this in-silico approach can serve as a useful screening tool for assessing PPP fate and exposure in soil, aquatic organisms, and humans, supporting the
integrative perspective of the One Health approach
Solar sintering of alumina ceramics: Microstructural development
No full textAlumina powders were lab-synthesized and then sintered on a solar furnace (SF) in order to test the capability of these solar devices to
produce dense ceramic bodies. The special configuration of the SF at Plataforma Solar de Almer????a (PSA-CIEMAT) in Spain, allowed to
perform several experiments using high temperatures (up to 1780 C), fast heating rates (50 and 100 C min 1) and different atmospheres
(air, Ar and 95N2:5H2). For comparison, similar alumina samples were sintered in an electric furnace (EF) using standard conditions
(5 C min 1 at 1600 C during 240 min in air). An exhaustive microstructural characterization by scanning (SEM) and transmission
(TEM) electron microscopies were performed on the sintered materials. Results for SF-samples showed a well-sintered alumina matrix
of polyhedral grains even using shorter dwell times and higher heat-up rates than the conventional sintering. Obtained microstructures
are in agreement with the presence of some impurities (mainly SiO2, CaO, ZrO2 and MgO) which are distributed at grain boundaries,
triple points and matrix voids. For solar treatments, the variations of sintering parameters produced significant changes on matrix grain
size, porosity and distribution of second phases. An important grain growth and density increase was observed after solar sintering on
those tests performed at 1780 C and under N2:H2 sintering atmosphere. The gathered data point out once more the convenience of solar furnace as sintering reactors to obtain ceramic materials with improved grain sizes
