Abstract:The levels of retention in codeposited layers of each of the three ITER materials (C, Be and W) are compared.Scaling laws, based on the conditions during the codeposition process (surface temperature, incident particle energy and ratio of the depositing fluxes), are presented to allow prediction of expected retention under ITER conditions. Retention in carbon codeposits scales inversely with incident particle energy, whereas in the metallic codeposits the retention level scales proportional to increasing particle energy. The differing scaling of retention with incident particle energy provides insight into which material may impact the global retention in ITER depending on where it may form codeposits. In addition to the amount of retention, the release behavior of tritium from codeposits will influence the tritium accumulation rate within ITER. The thermal release behavior of T (or D) from codeposits can be used to evaluate the effectiveness of baking at different temperatures as a means of tritium removal. Finally, the desorption kinetics from Be and W codeposits are contrasted. In the case of W codeposits, the duration of the baking cycle is important in determining the removal efficiency, whereas with Be codeposited layers, the maximum achievable bake temperature plays the leading role in determining removal efficiency.

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Plasmas with peaked radial density profiles have been generated in the world’s largest helicon device, with plasma diameters of over 70 cm. The density profiles can be manipulated by controlling the phase of the current in each strap of two multistrap antenna arrays. Phase settings that excite long axial wavelengths create hollow density profiles, whereas settings that excite short axial wavelengths create peaked density profiles. This change in density profile is consistent with the cold-plasma dispersion relation for helicon modes, which predicts a strong increase in the effective skin depth of the rf fields as the wavelength decreases. Scaling of the density with magnetic field, gas pressure, and rf power is also presented.

Some 60,000 and 46,000 MT of sodium rich nuclear waste are now in storage in the US at Hanford and SRS facilities, respectively. We have developed a technology that uses the high sodium content to advantage: aqueous slurry wastes are first calcined into sodium hydroxide (NaOH) melt slurries, then vaporized and injected into a plasma. The Archimedes Filter separates plasma ions into light and heavy mass groups. For the first time, it is feasible to economically separate large amounts of material in a single-pass plasma device. Such a separation would substantially decontaminate High Level Waste since most radionuclides partition to the heavy fraction. The plasma process is based on setting up fast ExB rotation of a cylindrical plasma. At a certain critical rotational velocity ω E > ω B /2 ions are not confined by axial magnetic field and are lost radially. Because the critical rotational velocity depends on magnetic field the plasma and machine parameters can be set up to separate heavy radionuclides from majority of the light elements in the plasma and, thus, accomplish waste clean up. The paper discusses the Filter process, describes a demonstration device that has been constructed in San Diego, USA, and presents the first experimental results.

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