R. Rolli

Size-Dependent Crush Analysis of Lithium Orthosilicate Pebbles

Abstract The crushing strength of the breeder material [lithium orthosilicate (Li4SiO4 or OSi)] in the form of pebbles to be used for EU solid breeder concept is investigated. The pebbles are fabricated using a melt-spray method, and hence, a size variation in the pebbles produced is expected. Knowledge of the mechanical integrity (crush strength) of the pebbles is important for a successful design of a breeder blanket. In this paper, we present the experimental results of the crush (failure) loads for spherical OSi pebbles of different diameters ranging from 250um to 800um. The ultimate failure load for each size shows a Weibull distribution. Furthermore, the mean crush load increases with increase in pebble diameter. It is also observed that the level of opacity of the pebble influences the crush load significantly. The experimental data presented in this paper and the associated analysis could possibly help us to develop a framework for simulating a crushable polydisperse pebble assembly using discrete element method.

Overview of the HCPB Research Activities in EUROfusion

In the framework of the EUROfusion’s Power Plant Physics and Technology, the working package breeding blanket (BB) aims at investigating four different BB concepts for an EU demonstration fusion reactor (DEMO). One of these concepts is the helium-cooled pebble bed (HCPB) BB, which is based on the use of pebble beds of lithiated ternary compounds and Be or beryllides as tritium breeder and multiplier materials, respectively, EUROFER97 as structural steel and He as coolant. This paper aims at giving an overview of the EU HCPB BB Research and Development (R&D) being developed at KIT, in collaboration with Wigner-RCP, BUTE-INT, and CIEMAT. The paper gives an outline of the HCPB BB design evolution, state-of-the-art basic functionalities, requirements and performances, and the associated R&D activities in the areas of design, functional materials, manufacturing, and testing. In addition, attention is given also to the activities dedicated to the development of heat transfer augmentation techniques for the first wall and the corresponding testing. Due to their nature as design drivers, a brief overview in the R&D of key HCPB interfacing areas is given as well, namely, the tritium extraction and recovery system, the primary heat transfer and power conversion systems, and safety topics, as well as some specific activities regarding the integration of in-vessel systems through the BB. As concluding remarks, an outline of the standing challenges and future R&D plans is summarized.

Investigation of Durability of Optical Coatings in Highly Purified Tritium Gas

Abstract Anti-reflection coated windows are part of Raman spectroscopy systems for tritium analytics in the KATRIN experiment and fusion-related applications. Damages of such windows were observed after three months of exposure to highly purified tritium gas in the LOOPINO facility. In this work, the origin of the damages was investigated, identified and eliminated. Coating samples manufactured by various physical vapor deposition methods have been tested for durability by exposure to pure tritium gas and subsequent visual inspection. Electron beam deposited coatings showed indications for damage after 17 days of tritium exposure in contrast to samples manufactured by ion assisted deposition or sputtering. An improved coating layout of the sample cell is presented for reliable long-term monitoring of tritium gas using Raman spectroscopy.