• Energy Research

This paper describes six projects, most of which are part of the research portfolio of the EERA JPNM, devoted to qualification, modelling and development of structural and fuel materials for advanced and innovative nuclear systems, with also two examples of projects addressing issues of cross-cutting interest through fusion and fission. The main conclusion is that the benefit of the coordination under the umbrella of, in this case, the EERA JPNM, is clearly felt in terms of better alignment of national programmes and subsequent leveraging of institutional funding, to integrate Euratom support. Likewise, the benefit of addressing specific issues of common interest for fusion and fission is not only beneficial because of cross-fertilisation, but also because it allows more rational use of human and infrastructural resources, avoiding duplications.

Post mortem analyses of dust collected in Alcator C-Mod have highlighted a production of large size dust particles. The quantities of such large particles are higher than in any other tokamak. They are divided in two classes as a function of their shape and consequently, their origin. Rounded dust particles such as spheres and splashes constitute the first class. These particles are the result of high heat loads on various leading edges of plasma facing components and possibly, their melting during plasma operation. The heated or already molten material can be destabilized during disruptions and droplets are emitted across the vacuum chamber. After solidification, the resulting rounded particles are either in pure elements or in alloys. Flake-like dust particles, which are mainly due to light material coating delamination, constitute the second class of dust particles.

In this paper, we describe a method to synthesize beryllium (Be) nanoparticles (NPs) by laser ablation of a solid target immersed in a liquid medium. Beryllium dust was successfully synthesized following the irradiation of a Be bulk target, which was immersed in water, acetone or heavy water, respectively, using the first and second harmonic (1064 and 532 nm) of a Nd: YAG laser source providing ns pulses, with a repetition rate of 10 Hz. The laser fluences used for Be target ablation were 8 and 15 J/cm2. In order to argue the successful obtaining of Be dust, scanning electron microscopy (SEM) was used for surface analysis. Colloidal solutions analysis by dynamic light scattering (DLS) supports the SEM analysis in terms of NPs size, whereas chemical analysis by X-ray photoelectron spectroscopy (XPS) was used in order to investigate the chemical composition. Moreover, thermal desorption spectroscopy (TDS) was performed on Be dust synthesized in heavy water to study the retention of deuterium (D). The key parameters for obtaining much sharper and regular size distribution were identified as being the liquid medium, laser fluence, and wavelength.

The adhesion of tungsten (W) dust particles on W tokamak plasma-facing surfaces is investigated. When spherical dust hits the tokamak walls, its shape is altered as a contact area is created by the adhesion work and irreversible plastic deformation. The van der Waals adhesion force between such a deformed grain and a flat surface is estimated, and the link between the force and the impact velocity is determined. We show that adhesion can be increased by several orders of magnitude when the impact velocity approaches the adhesion velocity. Finally, the effects of surface roughness are incorporated.

Fusion energy has the potential to provide sustainable solutions to global energy needs for the next generations. However, despite decades of intense international efforts many scientific and technological breakthroughs need to be achieved before fusion become available and economically viable. In addition, and prior to industrial development of the fusion technology, it is worth addressing possible negative environmental and health impacts. For instance, the interactions between the plasma and refractory materials called plasma facing components (PFC) like tungsten, will generate tritiated dust. The aim of the study is to address the fate in water and biological media of W nanoparticles that might be released in case of Lost Of Vacuum Accident (LOVA). The dilution of particles in TRIS, LHC9 and pulmonary media did not strongly affect the average size of the particles while the dilution in Saline medium lead to substantial aggregation. The results proved that oxidative dissolution of W nanoparticles occurred in several aqueous/biological media (TRIS, LHC9 and Lung media) with increasing time. From the different dissolution rates as a function of the tested media, it seems that the oxidative dissolutions are rate limited by diffusion in the oxidized layer surrounding the metallic core of particles. The mechanisms of dissolution involved $\mathrm{W}^{4+}$ and $\mathrm{W}^{6+}$ corroded layers prior to $\mathrm{W}^{6+}$ dissolution. Knowledge provided by these dispersion–dissolution experiments helped to determine the environmental mobility and persistence as well as the bio-durability of these tungsten nanoparticles. As dissolution has potential to influence the toxicity of particles, it is a crucial parameter to consider in the risk assessment of particles.