This study establishes an in-situ synchrotron approach to directly link molten-salt chemistry, redox-buffer speciation, and alloy corrosion in chloride melts. Using a first-of-its-kind corrosion cell coupled to simultaneous X-ray absorption spectroscopy (XAS) and X-ray fluorescence (XRF), we monitor europium redox-buffer speciation and chromium dissolution during corrosion of Ni-20Cr in molten LiCl-KCl and KCl-MgCl 2 salts. To build a mechanistic framework, we combine UV-Vis optical basicity measurements, in-situ electrochemistry, and molecular dynamics simulations to quantify how salt chlorobasicity reshapes europium solvation and shifts the Eu(III)/Eu(II) apparent potential. Increasing MgCl 2 content drives the apparent potential of the Eu(III)/Eu(II) couple +0.45 V relative to LiCl-KCl and stabilizes Eu(II)-compatible solvation environments. In-situ, time-resolved Eu L3-edge XANES reveals progressive Eu(III) reduction in KCl-MgCl 2 melts, while Eu(III) remains predominantly stable in LiCl-KCl. This behavior is consistent with a chlorobasicity-activated reaction with boron nitride (BN) cell components. In less chlorobasic melts, salt redox chemistry enables BN chlorination, allowing BN to act as a sacrificial reductant and chlorinating agent that promotes Eu(III) to Eu(II) conversion, whereas this pathway is not thermodynamically favored in LiCl-KCl. During active corrosion of Ni-20Cr, coupled Eu XANES and Cr XRF measurements show concurrent Eu(III) to Eu(II) conversion and Cr dissolution, confirming that Eu(III) is the oxidizing species driving chromium oxidation. Together, these results demonstrate that chlorobasicity is a central control variable for redox-buffer speciation and corrosion thermodynamics, and more broadly that chlorobasicity can enable or suppress reactive pathways with structural materials in high-temperature molten salts.

This study focuses on mitigating corrosion in the molten chloride salt NaCl-MgCl2 by stabilizing the salt redox potential at similar or equal to-2 vs (Cl2/Cl-)/V through the use of the SmCl3/SmCl2 redox couple, combined with oxoacidity regulation via AlCl3. The reversible, thermally stable and soluble/soluble SmCl3/SmCl2 system effectively imposes a stable potential of-2 V at 700 degrees C. Aluminum plays a dual role: it reduces SmCl3 to SmCl2 and regulates oxoacidity, preventing samarium precipitation and ensuring stability of the x(SmCl3)/x(SmCl2) (ratio 1:5), and consequently the redox potential. Corrosion tests were conducted on Ni-based (Alloy 625) and Fe-based (316 L stainless steel) alloys immersed in NaCl-MgCl2 at 700 degrees C for 13 days. The salt chemistry was controlled by fixing both the oxoacidity and the redox potential. The results demonstrate the effectiveness of this approach by positioning metallic materials within their immunity domain. Alloy 625 exhibited no intergranular neither micrometric-scale corrosion, whereas 316 L stainless steel showed only a 1 & micro;m corrosion layer. This is a significant improvement compared to the loss of 100 & micro;m of material observed when the salt chemistry was not controlled. The redox potential remained stable at-1.96 vs (Cl2/Cl-)/V, confirming the robustness of the redox potential and oxoacidity control approach.

This study examines a thermodynamic approach to mitigating metal corrosion in molten chloride salts, focusing on lowering the salt's potential to protect structural materials. Thermodynamic diagrams show that the constituents of stainless steel and Ni-based alloys, i.e. Fe, Ni, and Cr, are susceptible to oxidation due to their open circuit potential (OCP) relative to the potential of the salt. Mo is an exception, as it is inert. The addition of TiCl2 to the molten salt effectively reduces its potential, buffering it at- 1.07 V, below the oxidation threshold of Cr. This reduction is achieved by in situ synthesis of TiCl2 by ZnCl2, which prevents excessive oxidation of Ti to higher states, and maintains the stability of the salt potential over time. Corrosion tests on 304 L stainless steel and Inconel (R) 600 show significant corrosion without TiCl2, as the unbuffered salt potential exceed the immunity domain of these alloys. However, the addition of TiCl2 shifts the salt potential into the immunity domain of Fe, Ni, and Cr, preventing corrosion. The results that a controlled, lower salt potential is crucial for ensuring material stability in molten chloride environments. The results highlight the importance of maintaining a zero redox potential difference between the salt and the metals to achieve inertness. Therefore, controlling the molten salt potential appears to be essential when considering structural integrity in harsh molten salt environments.

Metallic beryllium is an attractive material for nuclear applications, e.g. thermal reactor and fusion reactors. After use, activated beryllium waste will need to be disposed of in a geological disposal repository. One option for the treatment and conditioning of the beryllium waste could be the direct emplacement of pieces of beryllium in a cementitious matrix. In these conditions, beryllium corrodes due to reaction with water to produce hydrogen, and beryllium hydroxide, leading to possible loss of the waste containment. To gain more information on the anaerobic corrosion of beryllium, Electrochemical Impedance Spectroscopy and hydrogen measurement by gas chromatography were used, while beryllium samples were immersed in solutions representative of promising matrices (Portland cement (OPC, pH 13.5) and magnesium phosphate cement (MPC, pH 8.1)) for maximum one year. At the beginning of the test (< 180 days), both techniques showed that the beryllium corrosion rate was lower in OPC solution than in MPC solution. At longer term (> 180 days), the corrosion rate decreased sharply in MPC solution, while the corrosion rate in OPC solution remained stable. Therefore, at longer term, the lower corrosion rate was observed in MPC solution. The reason of this corrosion rate decrease comes from the formation of a passive layer composed of Be(OH)(2) (inner part) and KBePO4H2O crystals (outer part) at the surface of beryllium in MPC solution, while no protective corrosion product layer was present on the metal surface in OPC solution. In that later case, pitting corrosion was observed in addition to the dissolution of beryllium species in solution probably in the form of Be(OH)(4)(2-).

Magnesium potassium phosphate cement (MKPC) is a promising material for encapsulating low-to intermediate-level radioactive metallic wastes, including aluminium. This study investigates the influence of magnesium oxide (MgO) type and chemical retarders-boric acid and sodium thiosulfate-on the passivation of aluminium A1050 alloy. Corrosion behaviour and hydrogen evolution were monitored over 25 days in aqueous solutions and 230 days in mortars using electrochemical impedance spectroscopy and linear polarisation resistance. In aqueous solutions, boric acid improved passivation by shifting the corrosion potential to more anodic values, while thiosulfate promoted rapid passivation through adsorption, leading to slightly lower anodic potentials. In mortars, the near-neutral pH facilitated passivation, though variations were observed depending on the MgO type and retarder composition. Soft-burnt MgO combined with thiosulfate accelerated the formation of the alumina layer, enhancing passivation and reducing corrosion kinetics due to its higher reactivity and refined pore structure. In contrast, hard-burnt MgO with boric acid resulted in slower passivation and more cathodic potentials, likely due to its lower reactivity and heterogeneous pore network. When both retarders were used together, a competitive effect was observed, reducing passivation efficiency and increasing hydrogen evolution despite anodic potential shifts. These findings underscore the critical role of MgO type and retarder selection in optimising aluminium passivation within MKPC systems.

Beryllium metal is used as neutron moderator and reflector or multiplier in certain types of fission or fusion reactors. Dismantling of these reactors will produce radioactive beryllium waste, classified as low- or intermediate-level waste, that will need to be stabilised and solidified before being sent to disposal. The cementation process is under consideration because it may offer a good compromise between simplicity of implementation, cost, and quality of the final cemented wasteform. Nevertheless, knowledge of the corrosion behaviour of Be metal in a cement-based matrix is still limited, partly due to the high toxicity of Be that complicates testing. This study thus investigates Be corrosion in cement suspensions using potentiometry, voltammetry, and electrochemical impedance spectroscopy. Among the five different investigated systems (Portland cement blended without or with 40 wt.% silica fume, calcium sulfoaluminate clinker blended without or with 15% anhydrite, and calcium aluminate cement), Portland cement blended with 40% silica fume and calcium sulfoaluminate cement comprising 15% anhydrite are the most effective in mitigating beryllium corrosion. They allow reduction in the corrosion current by factors of 4 and 50, respectively, as compared to Portland cement.

The aim of this paper is to present methods for corrosion mitigation in molten salt environments. The corrosion of structural materials depends directly on the redox potential of the salt. When the redox potential of the salt is higher than the standard potentials of the elements constituting the structural materials, corrosion occurs. If the reverse is true, no corrosion is observed. Herein, a methodology for calculating the theoretical potential of a molten salt is provided and compared with experimental measurements. Three ways to mitigate corrosion by modifying the salt redox potential are proposed: (i) using a soluble/soluble redox system; (ii) using a potentiostatic method; and (iii) using an amphoteric compound such as UCl3, TiCl2, or TiCl3. Immersion tests were conducted under the above conditions to validate the methodology.

Portland cement is extensively used for the conditioning of radioactive waste. However, its high alkalinity is a serious obstacle to the stabilization of waste containing aluminum metal since aluminum is oxidized by the pore solution with the production of dihydrogen. This work investigates the potential of an alternative binder, magnesium potassium phosphate (MKP) cement, for the stabilization of Al-Mg alloys comprising 2 to 4.5 wt% of Mg and other metallic impurities. The objective is to assess the influence of the alloy composition on its reactivity in the cementitious matrix at earlier ages, as well as at later ages, when the cement has reached a significant reaction degree. Two complementary techniques are used. Gas chromatography shows that the dihydrogen release, resulting from the corrosion process, is not influenced by the magnesium content in the alloy. Electrochemical impedance spectroscopy provides qualitative information about the corrosion but also makes it possible to assess the corrosion current using an equivalent electrical circuit linked to the kinetic parameters of the postulated corrosion mechanism. Over a one-year period, the corrosion current of the alloys, regardless of their Mg content, is reduced by almost three orders of magnitude in MKP mortar as compared to Portland-cement-based mortar.

Beryllium wastes produced by nuclear industry could be managed by encapsulation in cements. The main risk is the aqueous corrosion, which leads to the hydrogen production and cracks causing a loss of radioactivity confinement. However, the corrosion can be limited by the formation of the hydroxide solid phase Be(OH)(2(s)). A study on the influence of the pH on the reactivity of beryllium was carried out in aqueous solution. The solubility diagram was drawn and showed that the hydroxide solid phase is stable until very high basic pH of 14. The pH variation of solution at different initial pH was measured after immersion of metallic beryllium. The results are in good agreement with the calculated solubility diagram. The open circuit potential (OPC) and the electrochemical impedance spectra (EIS) were recorded at a beryllium electrode from pH 2 to 15. The simulation of the EIS by using an electric equivalent circuit allowed to evaluate the Be reactivity by measuring the charge transfer resistance as a function of the pH. The experimental results confirm that the corrosion of beryllium is limited at neutral to basic pH and this low reactivity was attributed to the formation of the hydroxide solid phase Be(OH)(2). The OCP and EIS measurements put also in evidence that the corrosion of beryllium is the lowest in solution having pH around 12. In this pH range, the Be metal would be protected against the corrosion both by the formation of the hydroxide solid Be(OH)(2) and by the adsorption of hydroxide ions (OH-) at the metal surface.

Beryllium wastes are produced by nuclear industry. One way to manage them is their encapsulation in cements. The main risk of this conditioning is the aqueous corrosion, which leads to the hydrogen production and cracks causing a loss of radioactivity confinement. The corrosion can be limited by the formation of the hydroxide solid phase Be(OH)(2(s)). The stability domain of this phase was calculated in water as a function of the pH: M. Pourbaix has calculated a stability domain from 2.9 to 11.7 for a 10(-4) M beryllium concentration, while according to our calculation with more recent thermodynamic data, it is stable from 5.3 to 13.5. Based on Pourbaix results, beryllium cannot be conditioned in the mainly used cement for nuclear waste, Portland cement, while it is possible according to our calculations. Experimental measurements were achieved to select the data set most in agreement with the experimental observations. The beryllium reactivity has been examined in matrices having different pH pore solution: brushite cement (pH 1.75-6.44), magnesium phosphate cement (pH 5.6-8.4), calcium-sulfoaluminate cement (pH 10.9-12.3), Portland cement (pH 12.5-12.9) cements and activated slag (pH 12.9-13.8), by measuring the open circuit potential and by electrochemical impedance spectroscopy. The experimental results agree with the more recent thermodynamic data. Beryllium corrosion is too high in the brushite cement, leading to a high hydrogen production. This matrix can then not be envisaged for the conditioning of Be waste. If the beryllium is encapsulated in the activated slag, the highly alkalinity is too high in the early age, leading to a high aqueous corrosion. Activated slag are also not suitable for Be conditioning. The main conclusion of this paper is that beryllium can be encapsulated in safe conditions in Portland, magnesium phosphate and calcium sulfoaluminate cements. (C) 2021 Elsevier B.V. All rights reserved.

The objective of this work is to study the Li2CO3-Na2CO3-K2CO3 (29.5-31.1-39.4 mol%) molten salt and the behaviour of several metals (Au, Pt, C, Ni and W) by electrochemical measurements in the salt under three atmospheres (Ar, CO2 and O-2/N-2). Thermodynamic calculations show that the molten salt anodic and cathodic limits correspond to the carbonate ions oxidation and reduction to dioxygen and carbon respectively. An internal reference electrode has been defined based on the redox system Na+/Au2Na, which is independent of the lithium oxide activity. The widths of the electroactivity domain have been measured on gold working electrode by cyclic voltammetry: 2.21 V under Ar and O-2/N-2 and 2.41 V under CO2, which are larger than the values obtained by thermodynamic calculations (1.280 V and 1.025 V respectively). Gas chromatographic (GC) analysis during electrolysis at potentials ranging in the anodic limit allowed to conclude that the electrochemical domain of the carbonate molten salt is limited anodically by the oxidation of carbonate ions to dioxygen, possibly peroxide ions, and carbon dioxide. The characterisation by XRD of a platinum electrode after electrolysis at the cathodic limit has shown that the electroactivity domain of the molten salt is defined by the carbonate ions reduction into carbon, indicating that CO32-/C is an irreversible system. A carbonate ions decomposition rate of 1 x 10(-3) mmol.h(-1).cm(-2) has been determined by GC and thermogravimetric analysis (TGA) under inert gas. A stabilization of the CO2 pressure is observed after the melting of the salt. (c) 2021 Elsevier Ltd. All rights reserved.

Reliable neutron-induced-reaction cross sections of unstable nuclei are essential for nuclear astrophysics and applications but their direct measurement is often impossible. The surrogate-reaction method is one of the most promising alternatives to access these cross sections. In this work, we successfully applied the surrogate-reaction method to infer for the first time both the neutron-induced fission and radiative capture cross sections of ^{239}Pu in a consistent manner from a single measurement. This was achieved by combining simultaneously measured fission and γ-emission probabilities for the ^{240}Pu(^{4}He,^{4}He^{'}) surrogate reaction with a calculation of the angular-momentum and parity distributions populated in this reaction. While other experiments measure the probabilities for some selected γ-ray transitions, we measure the γ-emission probability. This enlarges the applicability of the surrogate-reaction method.

Cobalt-Salen mediated electroreductive and regioselective alkylation of electron deficient olefins is reported in one step in an undivided electrochemical cell, in the presence of an iron rod as sacrificial anode. Although the reactivity depends on the class of alkyl halides, the reported study offers a green and expeditious electrosynthetic route for Csp3-Csp3 bond formation in mild conditions. This study also confirms the possible formation of the heterobinuclear cobalt-Salen-iron complex previously reported as the effective catalyst.

To evaluate the feasibility of developing an efficient electrochemical separation process for rare earth elements (REE) at room temperature, the electrochemical behavior of some representative REE was evaluated in butyl methylpyrrolidinium dicyanamide (BMPyr-DCA), a room temperature ionic liquid.Because of their chemical properties, their commercial availability and their technological applications, yttrium, lanthanum, neodymium and samarium were selected for this study.The differences in the electrochemical properties of these elements as trivalent salts in BMDCA solutions were evaluated by cyclic voltammetry using a Pt electrode under an Ar atmosphere.For the elements with chemical properties that predict only the reduction in one stage (Y, La and Nd), the results exhibited the simultaneous reduction of BMPyr-DCA and the REE cation and the corresponding oxidation of the reduced REE at anodic potentials that were dependent on the REE cation.For Sm, a two-step reduction process from Sm(III) to Sm(II) and from Sm(II) to Sm(0) was observed, and a clear cathodic peak was observed far from the cathodic electrochemical window limit (-1.38 and -2.25 V vs Fc/Fc + ); only one anodic peak was observed at -0.93 V, a more negative potential than for the other studied REE.The results show the same behavior as observed in other media (aqueous and molecular media and molten salts) and allow for the evaluation of the possibility of selectively identifying the studied REE in the context of their differing electrochemical responses.

The U reactivity has been examined in three geopolymer (GP) formulations: GP, GP containing 1.25 M of NaF (GP-NaF) and GP containing 1.25 M of NaF and a double concentration of NaOH (GP-NaF-NaOH). In a previous study, two mechanisms representative of uranium oxidation in basic aqueous solutions have been proposed, depending on the ratio of the fluoride and hydroxide ions concentrations (RF/OH). For RF/OH < 1, U is protected by the oxides layer UO2+x (mechanism A), while for RF/OH > 1, U is continuously corroded (mechanism B). We have exploited the results on the GP pH evolution to understand the uranium behavior in geopolymers. With NaF at the saturated concentration in the geopolymers, if pH > 13.8, RF/OH is lower than 1, while for pH < 13.8, this ratio is higher than 1. Moreover, the pH would be stabilized at 13.4 for GP and GP-NaF and 14.1 for GP-NaF-NaOH. The ratio RF/OH can thus reach values higher than 1 in GP-NaF but not in GP-NaF-NaOH. Consequently, mechanism A can be applied for the U behavior in GP and GP-NaF-NaOH and mechanism B can occur in GP-NaF because of the pH decrease. The open circuit potential measurements confirm that in GP and GP-NaF-NaOH, U is protected by the oxides layer UO2+x while in GP-NaF, corrosion is observed after 10 days. In GP and GP-NaF-NaOH, the presence of the redox couple UO2+x/UO2 has been put in evidence by electrochemical impedance spectroscopy. This technique confirms a different behavior of uranium in GP-NaF. In the presence of fluoride ions, cracks in the GP have been observed and a great quantity of uranium oxide has been produced.

This research is focused on understanding uranium oxidation to predict the behavior of uranium contaminated Mg alloy waste in confinement matrices. The environment of the matrix proposed for the magnesium encapsulation, based on geopolymer material, imposes basic conditions and the presence of fluoride ions (corrosion inhibitor of the Mg alloy). This work demonstrates the opposite behavior of the hydroxide and fluoride ions on the uranium oxidation: the fluoride ions induce the corrosion of uranium, whereas the hydroxide ions protect the metal against corrosion by making an anionic barrier at the uranium/solution interface. Two mechanisms are proposed, depending on the [OH-]/[F-] ratio. In absence of fluoride ions, or if [OH-]/[F-] > 1, the mechanism corresponds to a single step, the charge transfer characteristic of the UO2/UO2+x system. Uranium metal is thus protected from corrosion by the oxides layer. By contrast, if [OH-]/[F-] < 1, uranium is corroded, the fluoride ions diffuse through the oxides layer and cause its desquamation. This phenomenon has to be taken into account for the confinement of uranium contaminated Mg waste in geopolymers matrices containing fluoride ions. (C) 2018 Elsevier Ltd. All rights reserved.

Complexation of Pa(v) with nitrilotriacetic acid (NTA) in aqueous solution (1 M (Na,H)ClO4) was studied by solvent extraction at different acidities (pcH = 0.6; 1.0; 2.0 and 2.5) with the element at the tracer scale (CPa< 10−10M).

Magnesium potassium phosphate cements (MKPCs) are prepared using calcined magnesia (MgO) and an acidic solution of potassium dihydrogen phosphate (KH2PO4). Their fast setting and high heat of hydration can be problematic when large volumes of materials are produced. Boric acid (B(OH)(3)) is thus commonly added as a set retarder. This work investigates MKPC hydration in paste (water-to-cement ratio w/c = 1) and its retardation by B(OH)(3). The precipitation of K-struvite (MgKPO4 center dot 6H(2)O) is preceded by that of phosphorosslerite (MgHPO4 center dot 7H(2)O) and Mg2KH(PO4)(2)center dot 15H(2)O. Cattiite (Mg-3(PO4)(2)center dot 22H(2)O), an end-product in diluted suspension (w/c = 100), is not observed. B(OH)3 slows down the formation of hydrates in two ways: (i) by stabilizing in solution the cations that outbalance the negative charges of the polyborates formed at pH above 6, and (ii) through the precipitation of an amorphous mineral containing borate and orthophosphate. The first process occurs both in diluted suspensions and pastes, the second is specific to pastes.

Aluminum reactivity in cement-based matrices, generally used for conditioning low- and intermediate-level radioactive wastes, is a problem due to dihydrogen produced by the corrosion reaction which depends on the pH of the pore solution. Electrochemical impedance spectroscopy has been used to propose a mechanism for aluminum corrosion in cementitious matrices based on ordinary Portland cement (OPC, pH ≈ 13) or magnesium phosphate cement (MKP, pH ranging between 4 and 9) containing or not LiNO 3 as a corrosion inhibitor. The fit of impedance diagrams recorded on aluminum electrode as a function of time has been realized using electrical parameters to model the cement and kinetic constants for the faradaic impedance. The so determined kinetic constants are used to calculate the corrosion current and the dihydrogen production as a function of time. Comparison of these results with experimental measurements of dihydrogen release obtained by gas chromatography shows a very good agreement except in the MKP matrix containing LiNO 3 . In the OPC matrix, dihydrogen production is between 500 and 1000 times higher than in the MKP matrix, which put in evidence the significant benefit in using MKP cements for aluminum encapsulation.