JRP CALL information
Supported By

European Commission

Short description of the work
This JRP's aim is a fundamental study of the interaction of Am with stainless steels encountered in repository and waste separations, treatment and storage. The specific objectives are:
To determine whether and in what form Am incorporates into passivating layers on Cr/Ni rich low carbon steels in acid and neutral media (relevant to waste separation processes and repository).
To determine whether and in what form Am incorporates into corrosion products formed in carbon steels under alkaline conditions (of relevance to waste storage) and on low carbon steels under acid conditions (of relevance to HAL evaporators)
To determine whether Am affects steel corrosion, either as a corrosion accelerator or by changing the corrosion product (as per U uptake in iron oxyhydroxides)
A large amount of cyclic voltammograms have been generated in the various nitric acid concentrations using the glassy carbon and various sized gold microelectrodes. Active and inactive experiments have been carried to isolate carbon/gold electrochemistry from Am electrochemistry. Background subtract experiments were carried out in order to deconvulate Am peaks. A 8 M perchloric acid solution has been made up to be used with the glassy carbon electrode to widen the potential window and separate out any oxygen evolution that has been seen in nitric acid media.

 

Short description of the work
This JRP's aim is a fundamental study of the interaction of Am with stainless steels encountered in repository and waste separations, treatment and storage. The specific objectives are:
To determine whether and in what form Am incorporates into passivating layers on Cr/Ni rich low carbon steels in acid and neutral media (relevant to waste separation processes and repository).
To determine whether and in what form Am incorporates into corrosion products formed in carbon steels under alkaline conditions (of relevance to waste storage) and on low carbon steels under acid conditions (of relevance to HAL evaporators)
To determine whether Am affects steel corrosion, either as a corrosion accelerator or by changing the corrosion product (as per U uptake in iron oxyhydroxides)
Various cyclic voltammetries and open circuit potential measurements were carried out using the glassy carbon and various sized gold microelectrdoes.
The following peak assignments in 1 M HNO3 with glassy carbon were made:
Oxidation wave observed during forward sweep assigned to conversion of Am(III) to Am(VI)
Reductive peak at 1.2 V has been assigned to carbon electrochemistry
Am reduction peak observed at ~ 0.7 V
Am reduction peak observed at ~ 0.7 V - corresponding to Am(V) to Am(IV) reduction. Randle-Sevcik analysis reveals this to be the reduction of a solution phase species. It also reveals that this peak corresponds to the reduction of Am(V) derived from the stoichiometric oxidation of Am(III).

 

Short description of the work
This JRP's aim is a fundamental study of the interaction of Am with stainless steels encountered in repository and waste separations, treatment and storage. The specific objectives are:
To determine whether and in what form Am incorporates into passivating layers on Cr/Ni rich low carbon steels in acid and neutral media (relevant to waste separation processes and repository).
To determine whether and in what form Am incorporates into corrosion products formed in carbon steels under alkaline conditions (of relevance to waste storage) and on low carbon steels under acid conditions (of relevance to HAL evaporators)
To determine whether Am affects steel corrosion, either as a corrosion accelerator or by changing the corrosion product (as per U uptake in iron oxyhydroxides)
A 150 ppm (concentration of PUREX raffinates) stock solution of Am was prepared to study Am(III) electrochemistry in acid, neutral and basic media on inert noble metal microelectrodes to establish baseline behaviour. The following electrolytes were made up containing 6.2 x 10-4 M Am:
1, 3 & 5 M HNO3
0.1 M KNO3
0.01 mM KCl
Modified simplified groundwater (0.01 M NaCl & 0.002 M NaHCO3)
'Pondwater' – representative of interim storage ponds, Na2SO4 electrolyte adjusted to pH 11 with NaOH
Electrodes used were: 10, 50 100, 250 & 500 um Gold microelectrodes, Graphene ring nanoelectrode, glassy carbon electrode and 100 um platinum microelectrode.
It was found that only the glassy carbon and various gold microelectrodes yielded useful results, therefore only these electrodes have been used in subsequent experiments. It was not possible to use the pondwater in these experiments as the americium precipitated out of the solution due to the basic nature of the electrolyte.

 

Short description of the work

This research project focuses on the sorption of the redox sensitive element neptunium by montmorillonite under geochemical conditions relevant for radioactive waste repositories. In the near-field, corrosion of steel containers produces large amounts of Fe(II), which may influence Np sorption by the engineered barrier system. The sorption of the reduced Np(IV) in the absence Fe(II) will be studied by batch sorption experiments to verify the chemical analogy with Th(IV) and to provide Kd values for the performance assessment. For the oxidized Np(V), we will measure sorption edges and isotherms in the presence and absence of dissolved Fe(II). These experiments aim at elucidating the sorption mechanism in the presence of dissolved Fe(II), i.e. competitive sorption as well as surface mediated redox reactions between sorbed Fe(II) and Np(V). The 2SPNE SC/CE sorption model is complemented with the derived surface complexation reactions and associated thermodynamic constants for Np(IV/V) and with redox reactions. X-ray absorption spectroscopy (XAS) is carried out on the Np(V)-Fe(II)-montmorillonite system to derive structural information on the surface complexes. The results provide hitherto neglected data for the performance system of anoxic radioactive waste repositories.

 

Short description of the work
Heavy ion irradiation of U-Mo/Al fuel simulates in-pile irradiation; the interdiffusion layer (IDL) found after both kind of irradiations is similar in composition and microstructure. This similarity implies that the major contribution to the diffusion reaction comes from collisions of fission fragments. Based on this finding, studying the heavy ion induced diffusion behaviour will lead us to the diffusion mechanism of U-Mo/Al fuel. Atomic mixing at interfaces after irradiation is observed. This atomic mixing implies either the formation of solid solutions or of irradiation-induced new phases at the interfaces. Several parameters have been used in this study to provide overall understandings: U-Mo thickness, different protection layers and irradiation temperature. Different thickness of U-Mo layer induces different ion beam energy at interfaces. Application of different irradiation temperatures gives different amount of thermal energy contribution to the diffusion reaction. Up to now we have investigated the ion beam mixing effect (IBM) induced by heavy ion irradiation by means of SEM, EDX and RBS. Further understanding of the diffusion mechanism of U-Mo/Al fuels is currently limited by the resolution of these methods. First TEM measurements have indicated that “better” information can be gained by TEM. TEM measurements are able to clarify the compositions of intermixing. Selected area diffraction pattern (SADP) provide precise phase identifications and crystal structures. For instance it is important to know whether the IDL is amorphous or crystalline. Nano-EDX line-scan will be able to provide the elemental distributions across the interfaces. This line-scan can clarify the possible ion beam mixing model which cannot be achieved with limited resolution. The information at interfaces is important to evaluate the stability of the diffusion barrier and the adequacy.

 
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