Corrosion-induced changes in pore-size distributions of fuel-matrix material

In order to understand the mechanism of metallic fission-product adsorption and desorption as well as diffusion in graphitic materials, a detailed knowledge of the material microstructure is essential. Different types of grahitic matrix material used or to be used in fuel elements of the German HTR Program were measured at ORNL in cooperation with the Hahn-Meitner-Institut Berlin. Actual measurements of fission product diffusion and adsorption/desorption were performed at HMI Berlin

Über die röntgenographisch bestimmte Mikroporosität: Untersuchung ihres Einflusses auf die Materialeigenschaften und das Bestrahlungsverhalten von Brennstoffteilchen-Hüllschichten

This paper is concerned with the application of small angle x-ray scattering to the investigation of the microporosity of pyrocarbon coatings. Unambiguous correlation between the deposition parameters and the pore size distribution of the pyrocarbon is shown. The change of the pore spectrum during heat treatment and neutron irradiation and the relationship of the porosity to the microstructure, fracture stress, and the relative oxidation rate of the coatings is discussed. The properties of the pyrocarbons can be interpreted in terms of three microstructural components which can be differentiated by their pore size distribution, inner surface area, and local density fluctuation, each of which is deduced from the scattering curve. The microstructure and, as a consequence, the irradiation behaviour can therefore be estimated from the x-ray scattering data

Entwicklung, Fertigung und Erprobung von Uran Targetelementen für eine Spallationsneutronenquelle 1 : Entwicklung und Fertigung von Uran-Targetelementen

Bei den Arbeiten zur Herstellung von umhüllten Protonen-Targetelementen auf Uranbasis wurde der Einflup des Giepvorgänges auf die Stabilität der $\gamma$-Phase der Uranlegierung (UMo10) untersucht, Material und Dicke von Bondingschichten (Nickel, Aluminium, . Zinn, Zink) sowie die Art des Hüllmaterials (Zirkaloy 2, AlMg3 . AlMgSiO,5) variiert. Gleichzeitig wurden verschiedene Herstellungsverfahren für das Bonding (galvanische Abscheidung, Aufdampfen) und Fügetechniken für das Cladding (Heiß-Isostatisches-Pressen, Aufschrumpfen, Aufziehen, Verldten) erprobt. Sowohl von der Produktqualität als auch aus verfahrenstechnischen Gründen hat sich bei der Herstellung von Uran-Targetelementen folgendes Design als günstig erwiesen: UMo10 ($\gamma$-Phase) als Spallationsmaterial kein Bonding Zirkaloy 2 als Hüllwerkstoff Heiß-Isostatisches -Pressen des UMo10-Zry2-Verbunde

Prediction of irradiation behavior of HTGR fuel particle coatings by structural characterization of LTI pyrocarbons

In order to retain the fission products within the coated fuel particles, the coatings which act as fission product barrier have to remain mechanically intact during irradiation. As the mechanical stability of well designed pyrocarbon (PyC) coatings is mainly governed by their microstructure, this paper discusses the influence of PyC microstructure on the irradiation performance of the coatings

Das Gefüge von Pyrokohlenstoff-Hüllschichten nach der Abscheidung im Fließbett und seine Änderungen durch Bestrahlung

The introducing review of literature is followed by a discussion of some equations to explain image contrast of TEM micrographs of pyrocarbon (PyC). Subsequently methods are described, which allow quantitative measurements of defined properties of the texture of PyC-coatings. The results show that PyC consists of three types of microstructure called components differing by density and/or crystallite size. The gross properties of the coatings such as density or porosity are due to the relative volume-fraction and the arrangement of the components within the coatings. Deposition of the components may be assigned to certain regions of the fluidized bed. This allows to explain how some properties of the coatings depend on deposition conditions. Partially the results are consistent with attempts to describe the deposition process theoretically. After fast neutron irradiation microcracks are found within each of the three components. The quantity of microcracks per unit area of any plane through the PyC-coating is described by a specific crack-length. The specific crack-length increases with fast neutron fluence and is due to the as-deposited properties of the coatings. The results suggest that gaseous fission products are released by these microcracks