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The neutron irradiation response of a novel hot isostatically pressed SA508 Grade3 steel was studied, such to deduce any influence this unconventional RPV microstructure has on radiation response. In particular, the role of elevated ferrite fraction was investigated. Neutron irradiation was conducted at 155 ± 10˚C to induce 0.1dpa of damage, this corresponded 2.53 ± 0.63GPa hardening for the ferrite and 1.94 ± 0.57GPa for the bainite as measured by nanoindentation. Atom probe tomography detected the presence of Mn-Ni-Si type clusters in both microconstituent phases. The ferrite microstructure showed a greater percentage of solute atoms available to form clusters than bainite, but it also contained a lower cluster volume fraction and number density compared to the bainite.

Activated corrosion products generation in primary heat transfer systems of nuclear fusion facilities is a relevant radiological source term for occupation dose assessments. The formation of the Chalk River Undefined Deposit, already well known in nuclear fission power plants, represents a significant safety issue in fusion applications due to the intense high energy neutron fluences (about 14 MeV in Deuterium-Tritium operation). The activated corrosion products formation is a multi-physical problem. The combined synergy of activation, corrosion, dissolution, erosion, ejection, precipitation, and transport phenomena induces the contamination of coolant loop regions located outside the bio-shield, where scheduled worker operation might take place. The following manuscript shows how activated corrosion products are evaluated for the nuclear fusion power plant design under investigation by the Safety and Environment Work Package (WPSAE) of the Eurofusion Consortium (i.e., the European Demonstration power plant, EU-DEMO). The major issues in activated corrosion products estimations are here exposed and the main results for mass and activity inventories are briefly shown for some main Primary Heat Transfer Systems of EU-DEMO.

To reach fusion conditions and control the plasma configuration in ITER, the next step in tokamak fusion research, two neutral beam injectors (NBIs) will supply 16.5 MW each, by neutralizing accelerated negative hydrogen or deuterium ions. The requirements of ITER NBIs (40A/1 MeV D- ions for ≤1 h, 46A/870 keV H- ions for ≤1000 s) have never been simultaneously attained. So in the Neutral Beam Test Facility (NBTF, Consorzio RFX, Italy) the operation of the full-scale ITER NBI prototype (MITICA) will be tested and optimised up to full performances, focussing on accelerator (including voltage holding), beam optics, neutralisation, residual ion removal. The NBTF includes also the full-scale prototype of the ITER NBI source with 100 keV particle energy (SPIDER), for early investigation of: negative ion production and extraction, source uniformity, negative ion current density and beam optics. This paper will describe the main results of the first two years of SPIDER operation, devoted to characterizing plasma and beam parameters, including investigation of RF-plasma coupling efficiency and magnetic filter field effectiveness in reducing co-extracted electrons. SPIDER is progressing towards the first caesium injection, which aims at increasing the negative ion density. A major shutdown, planned for 2021, to solve the issues identified during the operation and to carry out programmed modifications, will be outlined. The installation of each MITICA power supply and auxiliary system is completed; in-vessel mechanical components are under procurement by Fusion for Energy (F4E). Integration, commissioning and test of the power supplies, procured by F4E and QST, as the Japanese Domestic Agency (JADA), will be presented. In particular, 1.0MV insulating tests were carried out step-by-step and successfully completed. In 2020 integrated tests of the power supplies on the accelerator dummy load started, including the assessment of their resilience to accelerator grid breakdowns using a short-circuit device located in vacuum. The aggressive programme, to validate the NBI design at NBTF and to meet ITER schedule (requiring NBIs in operation in 2032), will be outlined. Unfortunately, in 2020 the coronavirus disease infection affected the NBTF activities. A solution to proceed with integrated power tests despite the coronavirus is presented.

Corrosion-erosion phenomena occurred in the cooling circuits of primary heat transfer systems of the prototype of the ITER-like ion source named SPIDER, in particular during the first phase of the experiment activity which began in May 2018. Demineralised water circulating in cooling channels of components subjected to high heat loads reacts with inner channel surfaces made of copper alloys, aluminium, and stainless steel thus producing thinning of cooling channel walls. Then, resistivity degradation phenomenon of the demineralised water occurred and resistivity was measured before and after a working cycle to plan water treatment operations in order to maintain maximum availability of the SPIDER plants. This degradation was observed to be particularly fast during experimental campaigns: despite predictions, this effect is more significant in the less complex cooling circuit linked to Ion Source and Extraction Power Supply (ISEPS), feeding the Ion Source polarized to ground at -100 kV dc. Corrosion-erosion phenomena were investigated considering dissolved O2 and CO2, pH, flow velocity and turbulence, galvanic corrosion at dissimilar metal junctions, leakage current through high voltage cooling breaks, temperature, and water conductivity. This paper presents the first data of water parameters, monitored during experimental sessions by using the Cooling Plant and ISEPS Local Control Systems. Basing on collected data, some hypotheses were put forward on the behaviour of circuits and components, in order to propose possible mitigation actions and to reduce the frequency at which the cooling water should be renewed to keep the resistivity value in the required operative range.

The determination of the water chemistry for cooling systems of nuclear fusion plants is under debate. It should be tailored for different types of fusion reactors: either experimental, e.g., ITER, JT-60SA, and DTT, or aimed at power generation, e.g., DEMO, given the different operation requirements. This paper presents the dual approach involving experiments and computer simulations chosen for the definition of DEMO water chemistry. Experimental work was performed to assess the corrosion susceptibility of reduced activation ferritic martensitic EUROFER 97 and AISI 316L in different water chemistry regimes. At the same time, the low corrosivity requirement brings an additional safety aspect for the radiation protection since some neutron-activated corrosion products (ACPs) create a gamma radiation when deposited outside the plasma chamber in components accessible to operators and these must be minimized. To evaluate the ACP inventory for DEMO, assessments were carried out using a reference computer code. Preliminary experimental activities to define the water chemistry of DTT under construction at ENEA were also conducted. The comparison of code results with experiments is two-fold important: for the validation of the computer code models and to determine data that are necessary to perform calculations.

The dependencies of the enhanced thermomechanical properties of zirconium carbide (ZrCx) with sample purity and stoichiometry are still not understood due to discrepancies in the literature. Multiple researchers have recently reported a linear relation between the carbon to zirconium atomic ratio (C/Zr) and the lattice parameter, in contrast with a more established relationship that suggests that the lattice parameter value attains a maximum value at a C/Zr ~ 0.83. In this study, the relationship between C/Zr atomic ratio and the lattice parameter is critically assessed: it is found that recent studies reporting the thermophysical properties of ZrCx have unintentionally produced and characterised samples containing zirconium oxycarbide. To avoid such erroneous characterization of ZrCx thermophysical properties in the future, we propose a method for the accurate measurement of the stoichiometry of ZrCx using three independent experimental techniques, namely: elemental analysis, thermogravimetric analysis and nuclear magnetic resonance spectroscopy. Although a large scatter in the results (ΔC/Zr = 0.07) from these different techniques was found when used independently, when combining the techniques together consistent values of x in ZrCx were obtained.

In this paper, microtensile testing is demonstrated to be a viable technique for measuring irradiation hardening and reduction of ductility of ion irradiated hot isostatic pressed SA508 ferritic/bainitic steel. Ion irradiation with He2+ was used as a surrogate for neutron irradiation to reach a damage level of 0.6 dpa (Kinchin-Pease). The mechanical properties of four unirradiated microtensile steel specimens were measured and compared to the bulk properties: when averaged the 0.2% proof stress was 501.6 ± 56.0 MPa, in good agreement with the macrotensile 0.2% proof stress of 456.2 ± 1.7 MPa. On the basis of the agreement between microtensile and standard tensile 0.2% proof stress in the unirradiated material, it was possible to directly measure irradiation induced hardening from ion irradiation performed with He2+ ions to a dose of 0.6 dpa. Microtensile testing of the ion irradiated steel revealed an increase in 0.2% proof stress of approximately 730 MPa. The irradiation hardening measured by nanoindentation was 3.22 ± 0.29 GPa. Irradiation hardening was higher than that previously observed in neutron irradiated low alloy steels exposed to similar doses at low temperatures (

Oxidation of dense hot pressed ZrC specimens from 10 73 – 1473 K was investigated using an in - situ technique: HT - ESEM. Cuboid specimens were monitored on the surface and on edges and corners durin g oxidation in order to understand the influence of crack formation and propagation on the Maltese c ross shape development of the oxide . The oxidation mechanism comprised three steps: (1) delamination of sample edges , (2) crack formation at corners and (3) crack propagation towards the inner core and formation of microcracks parallel to the interface that increase the accessible surface area followed by a drastic volume expansion . The m icrocrack pattern is found to be repetitive as if a cyclic deb on ding of the interface occurred . Characterization of the interface by TEM and HRTEM revealed the interface between ZrC and ZrO 2 to comprise a 2 μm thick amorphous carbon matrix with ZrO 2 nanocrystals embedded in it.

International audience; Oxidation of UC was studied from 873 to 1173 K in air and in 10 Pa oxygen using a High Temperature Environmental SEM (HT-ESEM). Conversion to U3O8 improved when using 873 K as the oxide product was a fine powder. At higher temperatures (973 K to 1173 K) oxidation slowed due to a densification process with formation of coarse fragments. The oxide fragmentation at 973 K and 1073 K and oxide pulverisation at 873 K were observed in situ in a HT-ESEM. Cracking induced fragmentation and pulverisation was linked to stresses generated from the volumetric transformation from UC to U3O8.

The oxidation mechanism and products of U3Si2 accident tolerant nuclear fuel in flowing air up to 750 °C is reported. Differences between observed and theoretical mass gains for complete oxidation is due to un-oxidised Si that forms nano-crystalline regions of Si. Some Si rich regions are protected by the formation of UO2, which is thermodynamically preferential to oxidise before Si. The UO2 is further kinetically oxidised to form nano-crystalline U3O8. The nanostructure formed, accompanied by large volumetric expansions during oxidation produces pulverisation of fragments into powder, which may have serious consequences for fuel integrity if exposed to oxidative atmospheres.

International audience; Oxidation of hot-pressed ZrC was investigated in air in the 1073-1373 K range. The kinetics were linear at 1073 K, whereas at higher temperature samples initially followed linear kinetics before undergoing rapid oxidation leading to a Maltese cross shape of the oxide. The linear kinetics at 1073 K was governed by inward oxygen diffusion through an intermediate layer of constant thickness between ZrC and ZrO 2 which was comprised of amorphous carbon and ZrO 2 nanocrystals. Diffusion of oxygen through the intermediate layer was measured to be 9 9 10 À10 cm 2 s À1 using 18 O as a tracer in a double oxidation experiment in 16 O/ 18 O. Oxidation at 1073 and 1173 K produced samples made of m-ZrO 2 and either t-or c-ZrO 2 with an adherent intermediate layer made of amorphous carbon and ZrO 2 , whereas oxidation at 1273 and 1373 K produced samples with a voluminous oxide made of m-ZrO 2 showing a gap between ZrC and the oxide. A sub-stoichiometric zirconia layer was found at the gap at 1273 K and no carbon uptake was detected in this layer when compared with the top oxide layer. The loss of the intermediate layer and the slowdown of the linear rate constant (g m À2 s À1) at 1273 K compared to 1173 K was correlated with the preferential oxidation of carbon at the intermediate layer which would leave as CO and/or CO 2 leaving a gap between ZrC and substoichiometric zirconia.

One of the main challenges for the nuclear power industry today is the disposal of spent nuclear fuel. One of the most developed methods for its long term storage is the Swedish KBS-3 concept where the spent fuel is sealed inside copper canisters and placed 500 meters down in the bedrock. Gamma radiation will penetrate the canisters and be absorbed by groundwater thereby creating oxidative radiolysis products such as hydrogen peroxide (H2O2) and hydroxyl radicals (HO˙). Both H2O2 and HO˙ are able to initiate corrosion of the copper canisters. In this work the kinetics and mechanism of reactions between the stable radiolysis product, H2O2, and copper and copper oxides were studied. Also the dissolution of copper into solution after reaction with H2O2 was monitored by ICP-OES. The experiments show that both H2O2 and HO˙ are present in the systems with copper and copper oxides. Nevertheless, these species do not appear to influence the dissolution of copper to the same extent as observed in recent studies in irradiated systems. This strongly suggests that aqueous radiolysis can only account for a very minor part of the observed radiation induced corrosion of copper.

International audience; $In\ situ$ HT-ESEM oxidation of sintered UC fragments revealed the morphological changes occurring during the transformation between UC to UO$_2$ and UO$_2$ to U$_3$O$_8$ at 723 to 848 K and in an atmosphere of 10 to 100 Pa O$_2$. Two main oxidation pathways were revealed. Oxidation at 723 K in atmospheres ≤ 25 Pa O$_2$ showed the transformation from UC to UO$_{2+x}$, as confirmed by $post\ mortem$ HRTEM analysis. This oxidation pathway was comprised of three steps: (i) an induction period, where only surface UC particles oxidised, (ii) a sample area expansion accompanied by crack formation and propagation, (iii) a stabilisation of the total crack length inferring that crack propagation had stopped. Samples oxidised under 50 Pa O$_2$ at 723 K and at 773-848 K for 10 to 100 Pa O$_2$ showed an "explosive" oxidation pathway: (i) sample area expansion occurred as soon as oxygen was inserted into the chamber and crack propagation and crack length followed an exponential law; (ii) cracks propagated as a network and the oxide layer fragmented, (iii) an "explosion" occurred causing a popcorn-like transformation, typical for oxidation from UO$_2$ to U$_3$O$_8$. HRTEM characterisation revealed U$_3$O$_8$ preferentially grow in the [001] direction. The explosive growth, triggered by ignition of UC, proceeded as a self-propagating high-temperature synthesis reaction, with a propagation speed of 150-500 ± 50 $\mu$m/s.

Instruments and techniques for the study of gold and other precious metals in their ores are available. Nobody ever denies the importance of the knowledge of the microcomposition of the ore for proper recovery planning. Yet it seems as if generally very little is done towards the use of systematic studies before separation is attempted. Let us discuss in some more detail how some metallurgists and mineralogists function and try to understand why their way of operating is largely responsible for such an apparent contradiction.

The variables discussed in the previous chapter are found in the literature or are determined experimentally.

During the past 30 years and largely following the advent and development of computers, an incredible advance has taken place in many sectors of modern technology, for example medicine, dentistry, the automobile industry, the TV and stereo, the appliances industries. This advance has happened so quickly that a wide intellectual gap has developed between the older and younger generations. Many people over 40 cannot believe that a child under 10 understands and operates computers better than they can, if they can at all.

There are many differences between gold and silver and several affect the decisions regarding ore exploitability first, then the choice of recovery agents and techniques. In order to understand these differences (listed in table 12), we need to go back to the variables discussed in chapter 3.

So precious metal deposits are more complex than metallurgists believe. Let us examine what makes the applied study and understanding of these deposits complex.

Metallurgy, the study of the physical and chemical properties of metals, is a relatively new science. Many of the elements in the periodic table were discovered during the past 250 years (see chapter on base metals and table 17). Their systematic study has been carried out for less than a century.

Platinum group elements are ruthenium, rhodium and palladium (of similar weight as, but lighter than silver, the next element in the periodic table by atomic number) and osmium, iridium and platinum (of similar weight as, but lighter than gold, the next element in the periodic table by atomic number). As opposed to gold and silver, known probably since the stone age, the first certain discovery of platinum, in the alluvial deposits of the Rio Pinto – Columbia, is as recent as 1741. Platinum was introduced to Europe by Sir Charles Wood who brought it to England during that same year. Osmium and iridium were isolated together from the residues of platinum ores in aqua regia in 1803 or 1804 by English chemist Smithson Tennant. The existence of rhodium and palladium was established in 1803 by English doctor W. Hyde Wollaston. Ruthenium was recognized as an element in 1844 or 1845 by Russian chemist C.E. Claus.

SPIDER is the 100 keV full-size Negative Ion Source prototype of the ITER Neutral Beam Injector, operating at Consorzio RFX in Padova, Italy. The largest Negative Ion Source in the world, SPIDER generates an RF driven plasma from which Deuterium or Hydrogen negative ions are produced and extracted. At the end of 2021, a scheduled long-term shutdown started to introduce major modifications and improvements aiming to solve issues and drawbacks identified during the first three years of SPIDER operations. The first action of the shutdown period was the disassembly and characterization of the SPIDER beam source after removal from the vacuum vessel and its placement inside the clean room. Each component was carefully assessed and catalogued, following a documented procedure. Some source components, i.e., the Plasma Grid, Extraction Grid and Bias Plate, revealed the presence of different and non-uniform red, white and green coatings that might be correlated to back-streaming positive ions impinging on grid surfaces, electrical discharges and caesium evaporation. Thus, several analyses have been carried out to understand the nature of such coatings, with the study still ongoing. The evidence of caesium evaporation and deposition on molybdenum-coated SPIDER components, such as the formation of oxides and hydroxides, is demonstrated through surface characterization analyses with the use of the Scanning Electron Microscope (SEM), X-ray Diffraction (XRD) and X-ray Photoelectron Spectroscopy (XPS).