Arjen van Veelen

Los Alamos National Laboratory | LANL · Materials Science in Radiation and Dynamics Group

The defect chemistry and thermal oxidation of lanthanide (Ln) incorporated-UO2 are critical for understanding and predicting their behavior as enhanced fuels, mixed oxide (MOX) fuels, spent nuclear fuels (SNF), and particles for safeguard purposes. In this study, we independently controlled the Ln type (Ce4+, Nd3+, and Gd3+) and the preparation con...

Mobilization of naturally-occurring uranium(U) has been recognized to give rise to geogenic U groundwater contamination in aquifers. In addition to carbonate ligand complexation, nitrate has been demonstrated to play a role in controlling U mobility by altering uranium solubility through redox reactions. Nitrate is a common anthropogenic contaminan...

To enable better implementation of uranium monocarbide (UC) as an advanced nuclear fuel for future high-temperature reactors, it is essential to have a thorough knowledge of its thermal and thermodynamic properties under reactor operational conditions. In this work, we studied thermal bulk oxidation of UC by simultaneous thermal analysis consisting...

Uranium mononitride (UN) is a promising nuclear fuel that combines the advantageous properties of readily used UO and uranium alloys, such as high melting temperature and high uranium density, and thermal conductivity, respectively. A better understanding of UN behavior at operating temperatures can be obtained from finite temperature data, such as...

Uranium mononitride (UN) is an advanced nuclear fuel currently being considered for use in several generation IV fast and thermal neutron spectrum core designs, with additional applications to thermal and electric nuclear propulsion reactors. To better understand the thermal behavior and thermodynamic stability of UN, we investigated the bulk therm...

Here, we describe a new synchrotron X-ray Fluorescence (XRF) imaging instrument with an integrated High Energy Fluorescence Detection X-ray Absorption Spectroscopy (HERFD-XAS) spectrometer at the Stanford Synchrotron Radiation Lightsource at beamline 6-2. The X-ray beam size on the sample can be defined via a range of pinhole apertures or focusing...

Small-particle analysis is a highly promising emerging forensic tool for analysis of interdicted special nuclear materials. Integration of microstructural, morphological, compositional, and molecular impurity signatures could provide significant advancements in forensic capabilities. We have applied rapid, high-sensitivity, hard X-ray synchrotron c...

Phosphorus (P) is essential for plant growth. Arbuscular mycorrhizal fungi (AMF) aid its uptake by acquiring P from sources distant from roots in return for carbon. Little is known about how AMF colonise soil pore‐space, and models of AMF‐enhanced P‐uptake are poorly validated. We used synchrotron X‐ray computed tomography to visualize mycorrhizas...

In order to provide important details concerning the adsorption reactions of Sr, batch reactions and a set of both ex situ and in situ Grazing Incidence X-ray Absorption Fine Structure (GIXAFS) adsorption experiments were completed on powdered TiO2 and on rutile(110), both reacted with either SrCl2 or SrCO3 solutions. TiO2 sorption capacity for str...

Portlandite [Ca(OH)2] is a potentially dominant solid phase in the high pH fluids expected within the cementitious engineered barriers of Geological Disposal Facilities (GDF). This study combined X-Ray Absorption Spectroscopy with computational modelling in order to provide atomic-scale data which improves our understanding of how a critically impo...

Aims: Organic acid exudation by plant roots is thought to promote phosphate (P) solubilisation and bioavailability in soils with poorly available nutrients. Here we describe a new combined experimental (microdialysis) and modelling approach to quantify citrate-enhanced P desorption and its importance for root P uptake. Methods: To mimic the rhizosp...

Aims We sought to develop a novel experimental system which enabled application of iodinated contrast media to in vivo plant roots intact in soil and was compatible with time-resolved synchrotron X-ray computed tomography imaging. The system was developed to overcome issues of low contrast to noise within X-ray computed tomography images of plant r...

The good biocompatibility and corrosion resistance of the bulk CoCrMo alloy has resulted in it being used in the manufacture of implants and load bearing medical devices. These devices, however, can release wear and corrosion products which differ from the composition of the bulk CoCrMo alloy. The physicochemical characteristics of the particles an...

Mass transport by aqueous fluids is a dynamic process in shallow crustal systems, redistributing nutrients as well as contaminants. Rock matrix diffusion into fractures (void space) within crystalline rock has been postulated to play an important role in the transient storage of solutes. The reacted volume of host rock involved, however, will be co...

Rhizosphere soil has distinct physical and chemical properties from bulk soil. However, besides root‐induced physical changes, chemical changes have not been extensively measured in situ on the pore scale. In this study, we couple structural information, previously obtained using synchrotron X‐ray computed tomography (XCT), with synchrotron X‐ray f...

This investigation establishes a system of gold nanoparticles that show good colloidal stability as an X-ray computed tomography (XCT) contrast agent under soil conditions. Gold nanoparticles offer numerous beneficial traits for experiments in biology including: comparatively minimal phytotoxicity, X-ray attenuation of the material and the capacity...

Recent progress has been made in paleontology with respect to resolving pigmentation in fossil material. Morphological identification of fossilized melanosomes has been one approach, while a second methodology using chemical imaging and spectroscopy has also provided critical information particularly concerning eumelanin (black pigment) residue. In...

Neptunium and uranium are important radionuclides in many aspects of the nuclear fuel cycle and are often present in radioactive wastes which require long term management. Understanding the environmental behaviour and mobility of these actinides is essential in underpinning remediation strategies and safety assessments for wastes containing these r...

Trace element inventories are known to correlate with specific histological structures in bone, reflecting organismal physiology and life histories. By studying trace elements in fossilised bone, particularly in individuals with cyclic bone growth (alternating fast/slow bone deposition), we can improve our understanding of the physiology of extinct...

Root exudates are a crucial component of the rhizosphere. Often, they take a form of a gel exuded by the plant roots and are thought to influence the soil aggregation, root penetration into soil, soil nutrient availability, immobilization of toxic cations, and microbial activity amongst other things. In addition, the capacity of exudates to store w...

INTRODUCTION: A major problem with metal-on-metal (MoM) hip replacements results from their potential to release wear and corrosion products in the body. The clinical implications of metal debris cover a wide spectrum of adverse local tissue reactions (ALTRs) and systemic manifestations, which can occur even in the absence of MoM bearing surfaces w...

Here, we reveal the size, morphology, composition and speciation of debris released from CoCrMo tapers, mixed CoCrMo/Ti tapers and cement-stem ibterface, and compare the physico-chemical characteristics of the particles in relation to the origin. The comprehensive structural and chemical characterisation was performed with a high-resolution STEM (C...

This study applied time lapse (4D) synchrotron X-ray computed tomography (SRXCT) to observe micro-scale interactions between plant roots and soil. Functionally contrasting maize root tips were repeatedly imaged during ingress into soil columns of varying water content and compaction. This yielded sequences of 3D densiometric data, representing time...

We review the recent progress in the use of image based modelling to describe water dynamics in the rhizosphere. In addition, we describe traditional modelling and experimental methods, and how images obtained from X-ray Computed Tomography can be used in combination with direct pore-scale modelling to answer questions on water movement in the rhiz...

Endochondral ossification is the process by which bone is deposited during development, growth and repair of the skeleton. The regulation of endochondral ossification is extremely important as developmental flaws can result in severe skeletal abnormalities. However, until recently the limitations of available methodologies have restricted our under...

Melanin is a critical component of biological systems, but the exact chemistry of melanin is still imprecisely known. This is partly due to melanin’s complex heterogeneous nature and partly because many studies use synthetic analogues and/or pigments extracted from their natural biological setting, which may display important differences from endog...

Polarization-dependent grazing incidence X-ray absorption spectroscopy (XAS) measurements were completed on oriented single crystals of magnesite [MgCO3] and brucite [Mg(OH)2] reacted with aqueous uranyl chloride above and below the solubility boundaries of schoepite (500, 50, and 5 ppm) at pH 8.3 and at ambient (PCO2 = 10(-3.5)) or reduced partial...

Bone remodelling is a crucial biological process needed to maintain elemental homeostasis. It is important to understand the trace elemental inventories that govern these processes as malfunctions in bone remodelling can have devastating effects on an organism. In this study, we use a combination of X-ray techniques to map, quantify, and characteri...

The preservation of fossils reflects the interplay of inorganic and organic chemical processes, which should be clearly differentiated to make interpretations about the biology of extinct organisms. A new coliiformes bird (mouse bird) from the 50 million year old Green River Formation (Wyoming, USA) has here been analysed using synchrotron X-ray fl...

Iron oxides resulting from the corrosion of large quantities of steel that are planned to be installed throughout a deep geological disposal facility (GDF) are expected to be one of the key surfaces of interest for controlling radionuclide behaviour under disposal conditions. Over the lengthy timescales associated with a GDF, the system is expected...

Current understanding of bone healing and remodelling strategies in vertebrates has traditionally relied on morphological observations through the histological analysis of thin sections. However, chemical analysis may also be used in such interpretations, as different elements are known to be absorbed and used by bone for different physiological pu...

Large-scale Synchrotron Rapid Scanning X-ray Fluorescence (SRS-XRF) elemental mapping and X-ray absorption spectroscopy are applied here to fossil leaf material from the 50 Mya Green River Formation (USA) in order to improve our understanding of the chemistry of fossilized plant remains. SRS-XRF of fossilized animals has previously shown that bioac...

Many exceptionally preserved fossils have long been thought the product of preservation by bacterial autolithification, based largely upon the presence of, micron-sized, spherical or elongate bodies on their surface. This has recently been challenged by studies of similar fossils which cite morphological and geochemical evidence that these structur...

Around the world large quantities of sludge wastes derived from nuclear energy production are currently kept in storage facilities. In the UK, the British government has marked sludge removal as a top priority as these facilities are nearing the end of their operational lifetimes. Therefore chemical understanding of uranium uptake in Mg-rich sludge...