A new kind of nonresonant optical recirculator, dedicated to the production of γ rays by means of Compton backscattering, is described. This novel instrument, inspired by optical multipass systems, ...has its design focused on high flux and very small spectral bandwidth of the γ -ray beam. It has been developed to fulfill the project specifications of the European Extreme Light Infrastructure “Nuclear Pillar,” i.e., the Gamma Beam System. Our system allows a single high power laser pulse to recirculate 32 times synchronized on the radio frequency driving accelerating cavities for the electron beam. Namely, the polarization of the laser beam and crossing angle between laser and electrons are preserved all along the 32 passes. Moreover, optical aberrations are kept at a negligible level. The general tools developed for designing, optimizing, and aligning the system are described. A detailed simulation demonstrates the high efficiency of the device.
The machine described in this document is an advanced Source of up to 20 MeV Gamma Rays based on Compton back-scattering, i.e. collision of an intense high power laser beam and a high brightness ...electron beam with maximum kinetic energy of about 720 MeV. Fully equipped with collimation and characterization systems, in order to generate, form and fully measure the physical characteristics of the produced Gamma Ray beam. The quality, i.e. phase space density, of the two colliding beams will be such that the emitted Gamma ray beam is characterized by energy tunability, spectral density, bandwidth, polarization, divergence and brilliance compatible with the requested performances of the ELI-NP user facility, to be built in Romania as the Nuclear Physics oriented Pillar of the European Extreme Light Infrastructure. This document illustrates the Technical Design finally produced by the EuroGammaS Collaboration, after a thorough investigation of the machine expected performances within the constraints imposed by the ELI-NP tender for the Gamma Beam System (ELI-NP-GBS), in terms of available budget, deadlines for machine completion and performance achievement, compatibility with lay-out and characteristics of the planned civil engineering.
The use of optical proxies is essential to the sustained monitoring of dissolved organic carbon (DOC) in estuaries and coastal wetlands, where dynamics occur on subhour time scales. In situ dissolved ...organic matter (DOM) fluorescence, or FDOM, is now routinely measured along with ancillary water-quality indicators by commercial sondes. However, its reliability as an optical proxy of DOC concentration is often limited by uncertainties caused by in situ interferences and by variability in DOM composition and water matrix (ionic strength, pH) that are typical at the land-ocean interface. Although corrections for in situ interferences already exist, validated strategies to account for changes in the DOM composition and water matrix in these systems are still lacking. The transferability of methods across systems is also poorly known. Here, we used a comprehensive data set of laboratory-based excitation–emission matrix fluorescence and DOC concentration matched to in situ sonde measurements to develop and compare approaches that leverage ancillary water-quality indicators to improve estimates of DOC concentration from FDOM. Our analyses demonstrated the validity of in situ interference correction schemes, the importance of ancillary water-quality indicators to account for DOM composition and water matrix change, and the good transferability of the proposed methods.
The global budget of tropospheric carbonyl sulfide (OCS) is believed to be at equilibrium because background air concentrations have remained roughly stable over at least the last decade. Since the ...uptake of OCS by leaves (associated with photosynthesis) and soils have been revised significantly upwards recently, an equilibrated budget can only be obtained with a compensatory source of OCS. It has been assumed that the missing source of OCS comes from the low-latitude ocean, following the incident solar flux. The present work uses parameterizations of major production and removal processes of organic compounds in the NEMO-PISCES (Nucleus for European Modelling of the Ocean, Pelagic Interaction Scheme for Carbon and Ecosystem Studies) ocean general circulation and biogeochemistry model to assess the marine source of OCS. In addition, the OCS photo-production rates computed with the NEMO-PISCES model~were evaluated independently using the UV absorption coefficient of chromophoric dissolved organic matter (derived from satellite ocean color data) and apparent quantum yields available in the literature. Our simulations show global direct marine emissions of OCS in the range of 573-3997 GgS yr-1, depending mostly on the quantification of the absorption rate of chromophoric dissolved organic matter. The high estimates of that range are unlikely, as they correspond to a formulation that most likely overestimate photo-production process. Low and medium (813 GgS yr-1) estimates derived from the NEMO-PISCES model are however consistent spatially and temporally~with the suggested missing source of Berry et al. (2013), allowing us thus to close the global budget of OCS given the recent estimates of leaf and soil OCS uptake.
Coastal marsh survival relies on the ability to increase elevation and offset sea level rise. It is therefore important to realistically model sediment fluxes between marshes, tidal channels, and ...bays as sediment availability controls accretion. Traditionally, numerical models have been calibrated and validated using in situ measurements at a few locations within the domain of interest. These datasets typically provide temporal information but lack spatial variability. This paper explores the potential of coupling numerical models with high-resolution remote sensing imagery. Products from three sensors from the NASA Delta-X airborne mission are used. Uninhabited Aerial Vehicle Synthetic Aperture Radar (UAVSAR) provides vertical water level change on the marshland and was used to adjust the bathymetry and calibrate water fluxes over the marsh. AirSWOT yields water surface elevation within bays, lakes, and channels, and was used to calibrate the Chezy bottom friction coefficient. Finally, imagery from AVIRIS-NG provides maps of total suspended solids (TSS) concentration that were used to calibrate sediment parameters of settling velocity and critical shear stress for erosion. Three numerical models were developed at different locations along coastal Louisiana using Delft3D. The coupling enabled a spatial evaluation of model performance that was not possible using simple point measurements. Overall, the study shows that calibration of numerical models and their general performance will greatly benefit from remote sensing.
The photochemical degradation of chromophoric dissolved organic matter (CDOM) upon solar exposure, known as photobleaching, can significantly alter the optical properties of the surface ocean. By ...leading to the breakdown of UV- and visible-radiation-absorbing moieties within dissolved organic matter, photobleaching regulates solar heating, the vertical distribution of photochemical processes, and UV exposure and light availability to the biota in surface waters. Despite its biogeochemical and ecological relevance, this sink of CDOM remains poorly quantified. Efforts to quantify photobleaching globally have long been hampered by the inherent challenge of determining representative apparent quantum yields (AQYs) for this process, and by the resulting lack of understanding of their variability in natural waters. Measuring photobleaching AQY is made challenging by the need to determine AQY matrices (AQY-M) that capture the dual spectral dependency of this process (i.e., magnitude varies with both excitation wavelength and response wavelength). A new experimental approach now greatly facilitates the quantification of AQY-M for natural waters, and can help address this problem. Here, we conducted controlled photochemical experiments and applied this new approach to determine the AQY-M of 27 contrasting water samples collected globally along the land-ocean aquatic continuum (i.e., rivers, estuaries, coastal ocean, and open ocean). The experiments and analyses revealed considerable variability in the magnitude and spectral characteristics of the AQY-M among samples, with strong dependencies on CDOM composition/origin (as indicated by the CDOM 275–295-nm spectral slope coefficient, S275–295), solar exposure duration, and water temperature. The experimental data facilitated the development and validation of a statistical model capable of accurately predicting the AQY-M from three simple predictor variables: 1) S275–295, 2) water temperature, and 3) a standardized measure of solar exposure. The model will help constrain the variability of the AQY-M when modeling photobleaching rates on regional and global scales.
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•New method was applied to assess natural variability in CDOM photobleaching AQY-M.•AQY-M varies with CDOM composition/origin across land-ocean aquatic continuum.•AQY-M also depends on water temperature and extent of solar exposure.•S275–295, water temperature, and solar exposure together can predict accurate AQY-M.•New predictive AQY-M model can help calculate photobleaching rates on large scales.
Seagrass meadows worldwide provide valuable ecosystem services but have experienced sharp declines in recent decades. This rapid loss has prompted numerous restoration efforts with variable levels of ...success, often depending on the suitability of the restoration sites. The selection of sites can be guided by simple habitat suitability models driven with environmental variables deemed critical to the successful growth of new transplants. Habitat suitability models typically consider the influence of bathymetry, sediment type, salinity, wave exposure, and water quality. However, they typically do not explicitly include benthic exposure to ultraviolet (UV) and commonly use depth as a coarse proxy for photosynthetically active radiation (PAR). Benthic exposure to UV and PAR are both key parameters for habitat suitability but can be challenging to determine, especially in coastal environments influenced by rivers and tides where they are extremely variable. Here, we demonstrate the development of a simple but effective model of spectrally-resolved benthic solar irradiance for a dynamic marsh-influenced mesotidal estuary in Massachusetts. In-situ measurements were used to develop and validate an empirical model predicting the UV–visible vertical diffuse attenuation coefficient spectra of downwelling irradiance, Kd(λ), from simple physical parameters about tides, river discharge and location. Spectral benthic solar irradiances (280–700 nm) were calculated hourly for 3 years (2017–2019) using modeled and validated cloud-corrected surface downwelling irradiances, estimates of water depth, and the modeled Kd(λ) spectra. The mapped irradiances were used to provide improved seagrass habitat suitability maps that will guide future restoration efforts in the estuary. We expect the approach presented here can be adapted to other dynamic coastal environments influenced by tides and rivers and/or applied to other light-dependent organisms and biogeochemical processes.
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•Vertical light attenuation spectra (Kd) modeled from simple physical parameters.•Kd facilitated calculation of benthic irradiance spectra in dynamic, tidal estuary.•Modeled benthic irradiance spectra improved seagrass habitat suitability model.•Better seagrass habitat suitability maps facilitate selection of restoration sites.•Approach is adaptable to other dynamic coastal systems and for other applications.
•Chemical interactions between (U-Zr-O) molten corium and molten steel are performed to study the impact of temperature difference and presence of crust between stratified phases.•The existence of a ...crust between stratified oxide and metal phases does not prevent mass transfers and a possible inversion of stratification due to changes in metal composition.•Under oxidizing atmosphere, two main processes may limit the rate of oxidation: the presence of a top crust or the oxidant starvation.•Chemical interactions between (U-Zr-O) porous debris bed and molten steel are performed to study the impact of temperature and oxidizing atmosphere on the progression of molten metal.•Under non-oxidizing atmosphere, an eutectic metallic mixture is formed around 900 °C and progresses easily through the oxide particle bed. Under oxidizing atmosphere, metal wettability is reduced and progression is stopped.
One of the strategies to mitigate the consequences of a severe accident is to stop the progression of molten materials (corium) within the vessel by external cooling of the vessel. This strategy is called in-vessel retention (IVR). The safety demonstration of IVR requires the accurate evaluation of the thermal load imposed on the internal surface of the vessel by the corium debris. During the progression of the accident, solid debris may be generated initially in the lower plenum because of fragmentation in water and, after melting of those debris, a (possibly stratified) molten pool would be formed. The consequences of the thermal and chemical interactions of the corium with the vessel are difficult to predict because there are still uncertainties on the application of existing results to models for reactor cases. These include scaling effects of course, but also the influence of transient processes occurring simultaneously: oxidation, dissolution, melt progression and/or stratification. In order to be able to predict the heat fluxes through the RPV wall, it is necessary to establish an overall view of the possible transient evolutions of corium and determine which are the most probable ’steady-state’ corium configurations after debris melting. The CORDEB program studies corium phenomena taking place at different stages of molten pool formation in the reactor vessel. It may be considered as an investigation of corium configurations that were not considered in previous programs such as the OECD RASPLAV and MASCA programs. All experiments within the program are carried out in the Rasplav tests facility of NITI, using the technology of induction melting in a cold crucible. This program is co-funded by IRSN, EDF, AREVA and CEA in the frame of the CPSIN agreement. This paper presents the main conclusions drawn from CORDEB tests, both for phenomenological knowledge and for transposition to reactor situations. Quantitative elements are provided for a clearer picture of kinetic effects. CORDEB tests have shown the importance of chemical interactions between molten steel and solid sub-oxidized (U-Zr- O) corium which lead to penetration of steel inside the solid oxide (crust or debris) and to the partial dissolution of the solid. As a consequence, the crust surrounding a molten pool cannot be considered as a barrier to mass transfer. CORDEB tests also made it possible to assess the oxidation kinetics of a molten pool: in the presence of surface crust, this is a rather slow process and it does not have a significant effect on the deterioration of accident scenario. The gaseous atmosphere above the pool plays an important role in several processes, in particular in the evaporation of molten steel.
Suspended particle concentration (Total Suspended Solids or TSS) determines sediment availability for deposition, whereas particle physico-chemical properties (e.g. composition and size) can ...influence sediment transport and accretion. These variables are critical to modeling and understanding nearshore sediment dynamics and coastal soil accretion and erosion. Upcoming satellite imaging spectrometers (e.g., GLIMR, SBG) have the potential to improve the detailed mapping and characterization of suspended particles in nearshore areas. Here, we conducted a detailed feasibility study assessing the capacity of imaging spectroscopy to accurately map suspended particle concentrations and physico-chemical properties in the Mississippi River Deltaic Plain (Louisiana, USA), a nearshore system with extreme coastline vulnerability. To that end, a large dataset of in situ TSS, Particulate Organic Carbon (POC) concentration, particle size, inherent optical properties (IOPs), and hyperspectral remote sensing reflectance (Rrs) was collected during the 2021 NASA Delta-X field campaigns in coastal Louisiana. Analyses of the data revealed that the enhanced spectral information provided by imaging spectroscopy (hyperspectral Rrs) improved the retrieval of TSS and POC/TSS (% organic carbon content), but highlighted the challenge of retrieving particle size in this system. Partial-least-squares-regression (PLSR) algorithms for TSS performed better than existing state-of-the-art algorithms and confirmed the importance of using local measurements and near-infrared Rrs. Implementation on Airborne Visible Infrared Imaging Spectrometer-Next Generation (AVIRIS-NG) imagery generated high-resolution (< 5 m), high-quality maps of TSS and POC/TSS in contrasted areas with a wide range of TSS concentrations from (0.1 to 100 mg L−1), and demonstrated the enhanced potential of upcoming missions such as SBG and GLIMR to inform studies of nearshore sediment dynamics and coastal vulnerability/resilience.
•Accurate TSS and POC/TSS retrieved from nearshore airborne imaging spectroscopy.•Algorithm performs well in nearshore coastal waters with 10−1–102 mg L−1 TSS.•Vis-NIR PLS algorithm outperforms existing empirical/semi-analytical TSS algorithms.•Mapped TSS and POC/TSS distributions indicate hydrology and particle dynamics.•Modeling suggests bottom reflectance was not an issue in waters deeper than 0.5 m.
•A new method was developed for measuring the void fraction for two-phase flows in debris beds.•This technology, based on the use of a capacitance probe, was validated by comparison to a weighing ...method.•Integral tests have been performed subsequently on single-size debris beds made of 4mm and 8mm glass beads.•The data demonstrate the strong impact of interfacial friction phenomena.
The modeling of pressure drop for two-phase flows through porous media is a key point to assess the coolability of debris beds resulting from nuclear severe accidents. Models involve several parameters which are non-linear functions of the void fraction, e.g. relative permeabilities. Their identification requires that experimental data include the measurement of void fraction. This paper presents a new technique developed to reach this objective. The method is based on the use of a capacitance probe and has been validated by comparison with a weighing method. The validation has shown that the accuracy is better than 10%. The measurement device has been implemented in the CALIDE facility, at IRSN, which has been designed to perform air–water flow through debris bed. Tests have been carried out with beds made of single size 4mm and 8mm beads. Measurements of pressure drop and average void fraction are reported in the paper, for air and water flow rates representative of flows that would result of either the reflooding of the damaged core or the cooling of corium debris in a stagnant pool of water. Finally, the pressure drop models used in severe accident simulation codes, based on generalizations of the single-phase Ergun law, have been assessed against the new data. It has been observed that generalized Ergun laws including an interfacial drag term accurately predict the pressure drop and the void fraction for flows with a zero net water velocity.
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