Tritium retention in W plasma-facing materials : Impact of the material structure and helium irradiation

This article has an erratum: DOI 10.1016/j.nme.2020.100729Plasma-facing materials for next generation fusion devices, like ITER and DEMO, will be submitted to intense fluxes of light elements, notably He and H isotopes (HI). Our study focuses on tritium (T) retention on a wide range of W samples: first, different types of W materials were investigated to distinguish the impact of the pristine original structure on the retention, from W-coated samples to ITER-grade pure W samples submitted to various annealing and manufacturing procedures, along with monocrystalline W for reference. Then, He and He-D irradiated W samples were studied to investigate the impact on He-damages such as nano-bubbles (exposures in LHD or PSI-2) on T retention. We exposed all the samples to tritium gas-loading using a gentle technique preventing any introduction of new damage in the material. Tritium desorption is measured by Liquid Scintillation counting (LSC) at ambient and high temperatures (800 degrees C). The remaining T inventory is then measured by sample full dissolution and LSC. Results on T inventory on He exposed samples highlighted that in all cases, tritium desorption as a gas (HT) increases significantly due to the formation of He damages. Up to 1.8 times more T can be trapped in the material through a competition of various mechanisms, but the major part of the inventory desorbs at room temperature, and so will most likely not take part to the long-term trapped inventory for safety and operational perspectives. Unfortunately, investigation of "as received" industrial W (used for the making of plasma-facing materials) highlighted a strong impact of the pre existing defects on T retention: up to 2.5 times more T is trapped in "as received W" compared to annealed and polish W, and desorbs only at 800 degrees C, meaning ideal W material studies may underestimate T inventory for tokamak relevant conditions.Peer reviewe

A 3D In Vitro Model of the Human Airway Epithelium Exposed to Tritiated Water: Dosimetric Estimate and Cytotoxic Effects

International audienceTritium has been receiving worldwide attention, particularly because of its production and use in existing fission reactors and future nuclear fusion technologies, leading to an increased risk of release in the environment. Linking human health effects to low-dose tritium exposures presents a challenge for many reasons. Among these: biological effects strongly depend on the speciation of tritiated products and exposure pathway; large dosimetric uncertainties may exist; measurements using in vitro cell cultures generally lack a description of effects at the tissue level, while large-scale animal studies might be ethically questionable and too highly demanding in terms of resources. In this context, threedimensional models of the human airway epithelium are a powerful tool to investigate potential toxicity induced upon inhalation of radioactive products in controlled physiological conditions. In this study we exposed such a model to tritiated water (HTO) for 24 h, with a range of activity levels (up to ;33 kBq ll–1 cm–2). After the exposures, we measured cell viability, integrity of epithelial layer and pro-inflammatoryresponse at different post-exposure time-points. We also quantified tritium absorption and performed dosimetric estimates considering HTO passage through the epithelial layer, leading to reconstructed upper limits for the dose to the tissue of less than 50 cGy cumulative dose for the highest activity. Upon exposure to the highest activity, cell viability was not decreased; however, we observed a small effect on epithelial integrity and an inflammatory response persisting after seven days. These results represent a reference condition and will guide future experiments using human airway epithelium to investigate the effects of other peculiar tritiated products

Training in crisis communication and volcanic eruption forecasting:Design and evaluation of an authentic role-play simulation

We present an interactive, immersive, authentic role-play simulation designed to teach tertiary geoscience students in New Zealand to forecast and mitigate a volcanic crisis. Half of the participating group (i.e., the Geoscience Team) focuses on interpreting real volcano monitoring data (e.g., seismographs, gas output etc.) while the other half of the group (i.e., the Emergency Management Team) forecasts and manages likely impacts, and communicates emergency response decisions and advice to local communities. These authentic learning experiences were aimed at enhancing upper-year undergraduate students’ transferable and geologic reasoning skills. An important goal of the simulation was specifically to improve students’ science communication through interdisciplinary team discussions, jointly prepared, and delivered media releases, and real-time, high-pressure, press conferences. By playing roles, students experienced the specific responsibilities of a professional within authentic organisational structures. A qualitative, design-based educational research study was carried out to assess the overall student experience and self-reported learning of skills. A pilot and four subsequent iterations were investigated. Results from this study indicate that students found these role-plays to be a highly challenging and engaging learning experience and reported improved skills. Data from classroom observations and interviews indicate that the students valued the authenticity and challenging nature of the role-play although personal experiences and team dynamics (within, and between the teams) varied depending on the students’ background, preparedness, and personality. During early iterations, observation and interviews from students and instructors indicate that some of the goals of the simulation were not fully achieved due to: A) lack of preparedness, B) insufficient time to respond appropriately, C) appropriateness of roles and team structure, and D) poor communication skills. Small modifications to the design of Iterations 3 and 4 showed an overall improvement in the students’ skills and goals being reached. A communication skills instrument (SPCC) was used to measure self-reported pre- and post- communication competence in the last two iterations. Results showed that this instrument recorded positive shifts in all categories of self-perceived abilities, the largest shifts seen in students who participated in press conferences. Future research will be aimed at adapting this curricula to new volcanic and earthquake scenarios

Development of the WAter-interface Permeation In Tritium-exposed materIals (Wapiti) tritium experiment and preliminary Eurofer97 results

The control of tritium inventory and permeation is crucial for the safe operation of fusion reactors. To measure these phenomena, a novel tritium experiment is introduced and used to measure tritium permeation through Eurofer97 at room temperature, with several possibilities for the downstream conditions: air or water and overhead air. A pre-loading condition was shown to be required for this experiment. This direct comparison revealed that tritium is preferentially found in the water phase and secondarily in the air phase

Dust sampling in WEST and tritium retention in tokamak-relevant tungsten particles

International audienceThe paper presents complementary approaches based on experimental and numerical works to address the behavior of tokamak-relevant tungsten particles loaded with tritium. Sampling of particles inside the WEST tokamak have been realized thanks to an in situ particle collection system called Duster Box. This method allowed to identify various types of tungsten particles among them spherical shaped micro-particles between 5 µm and 30 µm in diameter. Based on these results a surrogate tungsten powder has been provided by means of spheroidization process and sieving method. Moreover, the powder tritium retention capacity was measured and specific activities of 90 MBq.g−1 and 280 MBq.g−1 were obtained for particles with 17 µm and 11.5 µm median diameters, respectively. Considering such tritium activities trapped in the particles, Monte-Carlo simulation were performed to estimate the electrostatic self-charging rates and the corresponding electrical charge carried by the radioactive tungsten dust. The results of these experiments provide robust data for the assessment of the dispersion of toxic/radioactive material in the environment that could follow a loss of containment

Tritium absorption/desorption in ITER-like tungsten particles

International audienceTritium retention in plasma facing materials such as tungsten is a major concern for future fusion reactors. During ITER operating mode, the reactor could generate tritiated tungsten dust-like particles which need to be characterized in terms of amount of trapped tritium, tritium source and radiotoxicity. This study is focused on the preparation and characterization of tungsten particles and on a comparative analysis of tritium absorption/ desorption kinetics in these particles and in massive samples. An original gas phase thermal charging procedure was used successfully for tritium incorporation in tungsten powders and massive samples. Much larger tritium amounts are incorporated in W particles than in massive samples indicating important surface effects on tritium absorption, desorption and trapping in W. Tritium desorption from particles occurred at different temperatures related with different interactions on the particles surface and in the bulk; the tritium behavior in massive samples was also shown to depend on the metal microstructure. According to these experimental results tritium absorption/desorption in W particles may have important implications on tritium management in ITER reactor

Tungsten as a plasma-facing material in fusion devices: impact of helium high-temperature irradiation on hydrogen retention and damages in the material

International audienc

The Need for Improved Integration between PLM and KM: A PLM Services Provider Point of View

Part 1: Knowledge ManagementInternational audienceWith widespread use of digital tools in industry, an increasing amount of data and knowledge can be edited, shared and made accessible throughout the product lifecycle. As such, new technologies, that provide a formal framework for managing and organizing the intellectual assets of a business, can significantly influence the application of knowledge and the extent to which this knowledge will serve as a source of sustainable differentiation. Similarly, much suggests that the management of knowledge can positively influence and support the links between individual activities in the value stream, hence enabling the product-centered approach, which is fundamental to product lifecycle management (PLM). This paper draws on our experiences as a PLM and Knowledge Management (KM) supplier and highlights industry examples in aeronautics. It explores the potential application of a combined approach that utilizes digital support to encourage the effective use of KM throughout the product lifecycle