Adrien Couet

University of Wisconsin–Madison | UW · Department of Nuclear Engineering

The multi-megawatt proton beams that will be employed at future accelerator complexes introduce many new challenges for next-generation targetry systems, primarily due to the increased levels of beam-induced radiation damage combined with thermal shock effects during a beam pulse. Novel material classes, such as high-entropy alloys and electro-spun...

In the study, we report an in situ corrosion and mass transport monitoring method developed using a radionuclide tracing technique for the corrosion study of 316L stainless steel (316L SS) in a NaCl-MgCl 2 eutectic molten salt natural circulation loop. This novel method involved cyclotron irradiation of a small tube section with 16 MeV protons, lat...

Silicon carbide nanowires (SiC NWs) exhibit promising features to allow solution-processable electronics to be deployed in harsh environments. By utilizing a nanoscale form of SiC, we were able to disperse the material into liquid solvents, while maintaining the resilience of bulk SiC. This letter reports the fabrication of SiC NW Schottky diodes....

Electrochemistry has been used for decades to study materials' degradation in situ in corrosive environments, whether it is in room-temperature chemically aggressive solutions containing halide ions or in high-temperature oxidizing media such as pressurized water, liquid metals, or molten salts. Thus, following the recent surge in high-throughput t...

Nuclear materials are often demanded to function for extended time in extreme environments, including high radiation fluxes and transmutation, high temperature and temperature gradients, stresses, and corrosive coolants. They also have a wide range of microstructural and chemical makeup, with multifaceted and often out-of-equilibrium interactions....

A nanoscale characterization study was carried out on SRA ZIRLOTM at various cycles, aiming to highlight the effect of irradiation-induced alloying element (Sn, Nb, Fe) redistribution on the in-reactor corrosion kinetics. Using a combination of scanning transmission electron microscopy (STEM), energy dispersive X-ray spectroscopy (EDS), and atom pr...

The choice of a material and the engineering design that is intended to lead to a beam exit window capable of sustaining mechanical and thermal loads in a high-radiation environment, while minimizing the beam loss and maximizing the window lifetime is discussed. Thin titanium windows have been typically used in industrial accelerators in the tens o...

ASME Sec(III) Div(5) code-certified structural alloys for Molten (halide) Salt Reactors (MSRs) such as 800H, SS316, and IN617 have significant Cr content. This makes them readily-degradable in molten halide salts due to the thermodynamic favorability of soluble chromium halide formation. It is therefore imperative to discover alloys with corrosion...

Porosity throughout the zirconium oxide films plays a crucial role in the corrosion behavior and oxidation kinetics of Zr alloys, as it likely provides pathways for oxidizing and hydriding species through the oxide. In addition, it is known that substrate texture can affect the corrosion rate, although the detailed mechanisms are unclear. In this w...

The potentiodynamic polarization method using the K/K+ dynamic reference electrode was used to understand the corrosion behavior of Ni, Fe, Cr, the Ni-20Cr binary alloy, and 316L stainless steel in molten 46.5LiF 11.5NaF-42KF (FLiNaK, composition in mol %) salt at 700˚C. Exposure of the materials without an applied potential revealed that Ni and Fe...

Insufficient availability of molten salt corrosion‐resistant alloys severely limits the fruition of a variety of promising molten salt technologies that could otherwise have significant societal impacts. To accelerate alloy development for molten salt applications and develop fundamental understanding of corrosion in these environments, here an int...

High temperature gas-cooled reactors (HTRs) are intentionally tall and thin to enable passive decay heat removal through conduction, with a core height of 8 m being typical. Units are typically embedded in the ground, which has numerous safety advantages but requires excavating a deep silo, the cost of which grows super-linearly with depth. HTRs co...

Nuclear materials are often demanded to function for extended time in extreme environments, including high radiation fluxes with associated transmutations, high temperature and temperature gradients, mechanical stresses, and corrosive coolants. They also have a wide range of microstructural and chemical makeups, resulting in multifaceted and often...

Two CrFeMnNi face-centered cubic complex concentrated solid-solution alloys (CSA) have been evaluated for phase stability, mechanical properties, and radiation damage effects from heavy ions. Cr18Fe27Mn27Ni28 and Cr15Fe35Mn15Ni35 were predicted by thermodynamic calculations to phase separate and maintain a single phase at 700°C, respectively. Aging...

The molten salt-cooled reactor concept has garnered significant interest and one of the current challenges limiting the deployment of these reactor concepts is the complex corrosion phenomenon observed in molten salt environments. One of these phenomena is activity gradient mass transport, which has been shown to affect dissimilar materials submerg...

Novel beam-intercepting materials and targetry concepts are essential to improve the performance, reliability and operation lifetimes of next generation multi-megawatt (multi-MW) accelerator target facilities. The beam-intercepting materials and components must sustain an order-of-magnitude increase in particle beam intensities and are beyond the c...

High Power Target systems are key elements in future neutrino and other rare particle production in accelerators. These systems transform an intense source of protons into secondary particles of interest to enable new scientific discoveries. As beam intensity and energies increase, target systems face significant challenges. Radiation damages and t...

Laser-based directed energy deposition (DED) additive manufacturing (AM) of the alloying process is performed using mixtures of Mo, Nb, Ti, and V powders and directly observed through in situ high-speed synchrotron X-ray imaging. The investigation on the integration of dissimilar powders into a single melt pool will narrow the gaps between the appl...

In 2016, an Editorial in ACS Nano, entitled “The Rising and Receding Fortunes of Electrochemists”, (1) reflected the growing scientific consensus that existing initiatives in fundamental research were undermatched to the fact that electrochemistry was becoming ubiquitous in applications in energy, thus handicapping progress toward social impact. Th...

Arguably one of the most important factors in the fast deployment of advanced nuclear reactors, with major improvements in safety, is the development and qualification of radiation and corrosion tolerant materials, that serve as the structural components in reactor cores. However, the discovery, improvement, and assessment of materials resistant to...

Oxidation kinetics and scale formation were examined in 21-2 N Stainless Steel alloys in a CO2 environment at 700 °C. Several characterization techniques were used to identify the morphology, crystallographic structure, and chemical composition of the oxide scale formation during exposures up to 1925 hours. High manganese content played an importan...

Ion irradiation has long been used as a surrogate for neutron irradiation experiments which are comparatively slower, more expensive, and often can leave materials activated and difficult to handle post-irradiation. However, with the growing use of combinatorial synthesis methods and high-throughput, automated characterization techniques, ion irrad...

MoNbTiV high-entropy alloy was in situ alloyed with laser power-blown directed energy deposition additive manufacturing from a mixture of four elemental powders of Mo, Nb, Ti, and V. This study provides a fundamental understanding of the alloying process through in situ high-speed synchrotron X-ray imaging and infrared imaging. High-speed X-ray ima...

Molten lithium tetrafluoroberyllate (Li2BeF4) salt, also known as FLiBe, with a 2:1 mixture of LiF and BeF2 is being proposed as a coolant and solvent in advanced nuclear reactor designs, such as the molten salt reactor or the fluoride salt cooled high-temperature reactor. We present the results on the structure and properties of FLiBe over a wide...

Although zirconium-niobium (Zr-Nb) alloys are commonly used over Zircaloys as fuel claddings in light-water reactors, the fundamental understanding of Nb effects on oxidation and hydrogen pickup mechanisms, especially under irradiation, is still lacking. This study aims at filling this knowledge gap by coupling state-of-the-art experimental and mod...

Corrosion of nickel and copper electroplated coatings on SS316H in molten FLiNaK salt was studied. 500- and 1000-hour static corrosion tests were performed in molten FLiNaK at 700 degrees Celsius. Characterization of the coatings following corrosion indicated that they did not degrade in the molten salt during the corrosion experiment and fully pro...

A comprehensive characterization study was carried out on 1 and 4 cycles X2®, aiming to reveal effect of irradiation-induced alloying element redistribution on the in-reactor corrosion kinetics. Using a combination of (scanning) transmission electron microscopy ((S)/TEM) and atom probe tomography (APT), the results strongly evidenced the existence...

Oxidation modeling in modern nuclear fuel performance codes is currently limited by the lack of coupling with mechanics, thus preventing proper description of how high-temperature oxidation impacts mechanical properties. This is mostly due to the fact that the finite difference formalism adopted in corrosion models is incompatible with the direct c...

The design of corrosion-resistant high entropy alloys (CR-HEAs) is challenging due to the alloys' virtually astrological composition space. To facilitate this, efficient and reliable high-throughput exploratory approaches are needed. Toward this end, the current work reports a first-principles-based approach exploiting the correlations between work...

Insufficient availability of molten salt corrosion-resistant alloys severely limits the fruition of a variety of promising molten salt technologies that could otherwise have significant societal impacts. To accelerate alloy development for molten salt applications and develop fundamental understanding of corrosion in these environments, here we pre...

Several advanced nuclear reactor designs promise efficiency and safety improvements over the current reactor fleet but are limited by the current set of ASME code-qualified materials. Novel alloys including high-entropy alloys (HEAs), and more broadly compositionally complex alloys (CCAs), have shown promising irradiation-tolerance. However, the va...

We have investigated microstructure and microchemistry of precipitates and dislocation loops in high-burnup M5® using (scanning) transmission electron microscopy ((S)TEM) equipped with energy dispersive X-ray spectroscopy (EDS). Two (S)TEM lamellae were made by cryo-FIB from the same cladding sample. The Nb-rich native precipitates were found in th...

Irradiation often deteriorates cladding properties in the reactors and poses significant challenges, such as irradiation-induced growth and accelerated in-reactor corrosion kinetics. On the other hand, we are reporting that the irradiated area of 1 dpa proton irradiated Zr-xNb alloys (x=0.5/1.0wt%) have lower corrosion rate in pure water at 320 °C...

ZrNb alloys have significant advantages over Zircaloys due to the reduced irradiation-induced-growth and corrosion kinetics. Such enhancements have been related to the redistribution of alloying elements in the Zr matrix upon irradiation. Indeed, many studies have shown the precipitation of Nb-rich irradiation induced platelets (IIPs) / nanocluster...

Structural material corrosion is a significant concern for the development of molten salt-cooled reactors (MSR) and redox control was proposed to mitigate the corrosion. This study presents an efficient approach to identify the partial pressure of F2 gas for fluorine driven corrosion, the concentration ratios of UF4/UF3 and ZrF4/ZrF2, and the parti...

This study characterizes the microstructural evolution of single-phase complex concentrated solid-solution alloy (CSA) compositions under heavy ion irradiation with the goal of evaluating mechanisms for CSA radiation tolerance in advanced fission systems. Three such alloys, Cr18Fe27Mn27Ni28, Cr15Fe35Mn15Ni35, and equimolar NbTaTiV, along with refer...

Mass transport of corrosion products between Ni-201 test samples and 316L capsules in a 500-hour FLiNaK corrosion experiment has been investigated. In one experiment, the capsule and samples were electrically connected for galvanic coupling, while in the other they were electrically isolated using boron-nitride. Post-corrosion characterization of N...

The effect of proton irradiation on corrosion rate of α-annealed and β-quenched Zr-0.5Nb alloys is investigated. The major focuses of this study are to understand i) if the nucleation of irradiation-induced platelets (IIPs)/nanoclusters requires dissolution of Nb-rich native precipitates, ii) if the irradiated native precipitates and interlaths are...

A 1000 -h corrosion experiment of 316H stainless steel at 700 °C investigated the role of metal fluoride impurities CrF2 and FeF2 in LiF-BeF2 (66-34 mole %) (FLiBe) salt. Inductively coupled plasma-optical emission spectroscopy (ICP-OES) demonstrated the ability to measure changes in the concentration of these fluorides in FLiBe salt. Cyclic voltam...

The electrochemical characteristics of a Zr-Nb-Sn zirconium alloy have been investigated at 360 ℃ in simulated primary water condition of pressurized water reactor with two different dissolved hydrogen contents. In-situ electrochemical impedance spectroscopy experiment was performed for 100 d, and the thickness and resistivity of the zirconium oxid...

When zirconium alloys are used in water-cooled reactors, they are subjected to waterside corrosion. As a result, an oxide thickness forms at the interface and hydrogen is being picked up by the substrate. The emphasis of this article is on uniform oxidation and hydrogen embrittlement and how environmental factors such as irradiation may affect them...

The corrosion behavior of the FCC Cr18Mn27Fe27.5Ni27.5 high entropy alloy (HEA) after exposure to molten FLiBe salt at 700 °C for 1000 hours, has been investigated. Results show that the HEA lost a higher mass compared to the reference 316 H stainless steel due to the dissolution of Mn into the molten salt. The loss of Mn from the alloy appeared to...

High-entropy alloys (HEAs) are a class of alloys that can exhibit promising properties including enhanced irradiation resistance, high-temperature strength, and corrosion resistance. However, they exist in a relatively unexplored region of quasi-limitless composition space. Thus, to enable the development of promising compositionally complex alloys...

The influence of 9Cr-1Mo sample thickness on oxidation and carburization kinetics was investigated. State of the art characterization and modeling techniques were employed to investigate the oxidation and carburization behavior. Within the tested exposure times, the sample thickness did not affect oxidation kinetics, products, or the carburized mic...

Two new, low activation high entropy alloys (HEAs) TiVZrTa and TiVCrTa are studied for use as in-core, structural nuclear materials for in-core nuclear applications. Low-activation is a desirable property for nuclear reactors, in an attempt to reduce the amount of high level radioactive waste upon decommissioning, and for consideration in fusion ap...

The effect of UV irradiation on the oxidized zirconium surface during high temperature water corrosion was investigated in both static and flowing conditions. Iron oxide deposits were found to form only on the UV irradiated surfaces. The formation of these deposits resulted from the UV illumination, which induces photo-electrochemical processes at...

Hydrogen pick-up during corrosion of nuclear fuel cladding is a critical life-limiting degradation mechanism in Light Water Reactors. In this study, the oxidation kinetics and hydrogen pickup of a Zr-0.5Nb and an annealed Zr-1.0Nb alloys are being measured during corrosion in pure water autoclave (360 C, 18 MPa). Both the oxidation and hydriding ki...

Two new, low activation high entropy alloys (HEAs) TiVZrTa and TiVCrTa are studied for use as in-core, structural nuclear materials for in-core nuclear applications. Low-activation is a desirable property for nuclear reactors, in an attempt to reduce the amount of high level radioactive waste upon decommissioning, and for consideration in fusion ap...

Proton irradiation induced Nb redistribution in Zr-xNb alloys (x = 0.4, 0.5, 1.0 wt%) has been investigated using scanning transmission electron microscopy/energy dispersive X-ray spectroscopy (STEM/EDS). Zr-xNb alloys are mainly composed of Zr matrix, native Zr–Nb–Fe phases, and β-Nb precipitates. After 2 MeV proton irradiation at 350 °C, a decrea...

Presentation and transaction paper of "Nb redistribution in proton irradiated Zr1.0Nb". paper link: http://epubs.ans.org/?a=45372

The corrosion behavior of zirconium alloy was investigated using synchrotron scanning transmission X-ray microscopy and X-ray absorption spectroscopy. Scanning transmission X-ray micrographs showed different electronic structures at the oxide/metal interface of Zr–Nb–Sn alloy after exposure to high-temperature hydrogenated water. The orbital hybrid...

Waterside corrosion of zirconium alloys is currently the life-limiting degradation mechanism of fuel elements in pressurized-water reactor (PWR) systems. Today, PWRs use Zr-Nb fuel cladding designed to limit oxidation and hydrogen pickup. However, oxidation kinetics of Zr-Nb alloys can vary substantially depending on the Nb content and distribution...

We have investigated proton irradiation induced Nb redistribution in Zr-xNb alloy (x = 0.4, 0.5, 1.0) by using Scanning Transmission Electron Microscopy (STEM) and Atom Probe Tomography (APT). Initially without an irradiation effect, the Zr matrix only contains βNb and native Laves phase native precipitates. However, after 2 MeV proton irradiation...

The data presented here is complementary to the publication entitled “High temperature, low neutron cross-section high-entropy alloys in the Nb-Ti-V-Zr system” [1]. A homogenization methodology with slower cooling rate (∼2 °C/min) was performed. X-ray diffraction and scanning electron microscopy (backscattered electron and energy dispersive spectro...

ZrNb alloys under in-reactor service has been well to known to contain irradiation induced Nb-rich nano-precipitates in the í µí»¼-Zr matrix. However, it is unclear that the formation mechanism is either due to irradiation enhanced diffusivity of Nb in solid solution or irradiation induced segregation of Nb atoms to sinks. To understand the mechani...

High-entropy alloys (HEAs) with high melting points and low thermal neutron cross-section are promising new cladding materials for generation III+ and IV power reactors. In this study a recently developed high throughput computational screening tool Alloy Search and Predict (ASAP) has been used to identify the most likely candidate single-phase HEA...

The corrosion and hydrogen pickup of in-reactor zirconium-based cladding is currently limiting the maximum fuel burnup in light-water reactors. Since the oxidation rate and hydrogen pickup fraction of zirconium alloys vary significantly as a function of exposure time, burnup, and alloy composition, it is critical to better understand the underlying...

The nuclear incident at the Fukushima Daiichi nuclear power plant has created a strong push for accident-tolerant fuel cladding to replace current zirconium-based cladding. A current near-term focus on iron-chromium-aluminum (FeCrAl) alloys. Laser-welded FeCrAl samples (C35MN, C37M, and C35M10 TC) were subjected to three different post-weld heat tr...

Due to the absence of significant in-reactor corrosion acceleration, commercial ZrNb alloys such as ZIRLO, M5, and E110 have replaced Zircaloy-4 as the fuel cladding in Light Water Reactors. Although the enhanced corrosion resistance, resulting in lower hydrogen uptake, of ZrNb alloys has allowed significant increase in fuel burnup over the recent...