The pebble bed reactor is one of the most promising concepts for (V)HTR. Nevertheless recent re-evaluation of AVR and THTR results emphasizes once more that claimed advantages strongly depend on the properties of the fuel elements and their behavior under operational conditions. Additionally safeguards, waste management and disposal aspects gain increasing importance today. The conventional uncoated graphite pebbles meet only inadequately the requirements of Generation IV facilities. Since long experts agree, that corrosionresistant pebbles with high retention capability for fission products would considerably improve the chances of the pebble bed reactor concept. With laser beam joining of ceramics the key technology is now available for the silicon carbide (SiC) encapsulation of (V)HTR components. The envisaged innovative fuel element consists of a robust SiC hollow sphere filled with moderator and TRISO coated particles. The positive assessment according to Gen IV criteria should justify necessary R&D efforts to obtain qualified fuel elements and demonstrate their superiority under operational conditions. Verbesserung der (V)HTR Brennelemente gemäß Generation IV-Zielen durch SiC-Einkapselung. Der Kugelhaufenreaktor ist eines der vielversprechendsten Konzepte für den (V)HTR. Nichtsdestotrotz zeigen neuere Einschätzungen der AVR-und THTR-Ergebnisse einmal mehr, dass die reklamierten Vorteile stark von den Eigenschaften der Brennelemente und ihrem Verhalten unter Betriebsbedingungen abhängen. Zusätzlich gewinnen heute Aspekte von Safeguards, Abfall-Management und Endlagerung eine wachsende Bedeutung. Die konventionellen, unbeschichteten Graphit-Kugeln erfüllen die Anforderungen an Generation IV-Anlagen nur ungenügend. Seit langen ist man sich in Fachkreisen einig, dass korrosionsresistente Brennelemente mit hoher Rückhal-tefähigkeit für Spaltprodukte die Zukunftschancen des Kugelhaufenreaktor-Konzepts erheblich verbessern würden. Mit dem Laser-Fügeverfahren für Keramik ist nun die Schlüssel-technologie für eine Siliziumkarbid (SiC)-Kapselung von (V)HTR-Komponenten verfügbar. Das vorgestellte innovative Brennelement soll aus einer robusten SiC-Hohlkugel bestehen, die mit dem Moderatormaterial und TRISO Coated Particles gefüllt wird. Die positive Einschätzung der erwarteten Eigenschaften gemäß den Gen IV-Kriterien sollte verstärkte F&E-Anstrengungen rechtfertigen, um qualifizierte Brennelemente herzustellen und ihre Überlegenheit unter Betriebsbedingungen nachzuweisen.
The synthesis of silicon nitride powder by the reaction between silica, carbon and nitrogen is the economically most interesting route. Only this route makes possible the use of very cheap raw materials as well as the use of a simple production process. On the other side, the properties of the powders are within the limit of the technical requirements of the ceramic part manufacturer. The aim of this paper is to show that an optimized carbothermal Si3N4 powder synthesis leads to a product which fulfills the economical (low price) as well as the technical requirements. After a short introduction regarding the economical requirements, an overview of the carbothermal synthesis will be given. The influence of raw material, conditions of synthesis and removal of excess carbon on the powder properties will be discussed. Also, the properties of the powder as well as the sintering behaviour of Si3Ns4 powders, produced by Si-direct nitridation, Si-diimide process and the carbothermal route, will be compared in detail.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.