Quality Control Procedures for HTGR Fuel Element Components

The growing use of nuclear reactors for the production of electric power throughout the world, and the consequent increase in the number of nuclear fuel manufacturers, is giving enhanced importance to the consideration of quality assurance in the production of nuclear fuels. The fuel is the place, where the radioactive fission products are produced in the reactor and, therefore, the integrity of the fuel is of utmost importance. The first and most fundamental means of insuring that integrity is through the exercise of properly designed quality assurance programmes during the manufacture of the fuel and other fuel element components. The International Atomic Energy Agency therefore conducted an International Seminar on Nuclear Fuel Quality Assurance in Oslo, Norway from 24 till 28 May, 1976. The seminar was addressed to a wider audience and was, with its educational content, of interest in those countries newly entering the field as well as in those with established nuclear fuel fabrication capabilities. This KFA report contains a paper which was distributed preliminary during the seminar'and - in the second part - the text of the oral presentation. The tables and figures were presented as slides. The paper gives a summary of the procedures available in the present state for the production control of HTGR core materials and of the meaning of the particular properties for reactor operation. The work was partly sponsored by the Bundesministerium für Forschung und Technologie of the Federal Republic of Germany as well as by the Government of North-Rhine-Westfalia

Contributions for the International Carbon Conference : CARBONE 84

This report is the compilation of some papers prepared by KFA Jülich GmbH for the International Carbon Conference CARBONE 84, which will be held at Bordeaux/France. The presentations deal with objectives of manufacture as well as technical and nuclear applications of carbeneous materials

Oxydationsverhalten von Coat-Mix-Materialien in Luft bei Temperaturen um 800 K

Coat-Mix materials were oxidized in a flowing gas mixture of nitrogen and oxygen (N$_{2}$/O$_{2}$ = 4/1) at about 800 K and under a pressure of 50 kPa. The reaction rate was measured by means of thermal gravimetry and was compared to the changes of specific surface area, porosity, density and compressive strength in dependence on carbon burn-off. The suitability of Coat-Mix materials as a model substance for studying the oxidation behaviour of binder coke and filler separately was proved. The oxidation behaviour of the binder coke was understood only assuming two different components to exist in binder coke. This assumption could be proved by means of a hypothesis on the interaction between the binder and the filler grains during the coking process of the Coat-Mix materials

Statische Pyrokohlenstoffabscheidung im Temperaturbereich von 1900 °C - 2200 °C : Untersuchungen unter Verwendung eines statistischen Versuchsprogramms : Optische Bestimmungen der Abscheidungszonen

By means of static pyrocarbon-depositions, it was the aim to contribute to the understanding of the formation and the deposition of pyrocarbon. To achieve this target, a statistical test programme was applied, which enabled the reduction of the necessary individual trials to only 10 with coincident variation of three independant test-variables. The boundary layer over heated substrates in gaseous atmospheres, the Langmuirzone, was evaluated in various gases by optical means; the structure of the Langmuirzone could be defined. The combination of the results from structure evaluations and evaluations from the Langmuirzone led to a better understanding of the pyrolysis procedure; a hypothesis on this subject could be confirmed. A proposal was made to describe the structure of high density pyrocarbon completely. A method for planimetric evaluation of single film exposures was developed and applied. A procedure was also developed for coincident determination of the temperatures of two heated objects, and this method could be mathematically verified

Der Einfluss der thermischen Behandlung auf den Binderkoks von Coat- Mix- Material mit Sic- Füller für unterschiedliche Rezepturen und Herstellungsbedingungen

The effects of the composition and production parameters on porosity, texture and structure of Coat- Mix(CM) materials have been investigated. In particular, CM binder coke was compared with pure binder coke and a conventionally produced material. As filler material which is incompressible, chemically inert and porosity-free, two silicon carbide powders of different grain size were used. The heat treatment of specimens was carried out in stages at temperatures between 400 and 1700°C. The porosity and texture formed during heat treatment by release of gases and shrinkage were characterized using a number of different methods. The volume of open macro- and mesopores was measured using mercury porosimetry and by determination of the real density and air permeability. Meso- and micropore volumes were also measured using helium pycnometer and small angle X-ray scattering. Textures were investigated using scanning and transmission electron microscopy and X-ray diffraction measurements. The cyclic temperature resistance of the specimens produced in the course of this study was examinated by exposure in a high energy electron beam. The surfaces of exposed specimens were examined by optical micro-scopy, scanning electron microscopy, Auger spectroscopy and EDAX. The damage was correlated with the material parameters. The CM material exhibited a significantly better resistance to the high energy electron beam exposure than other ceramic materials tested to date

Untersuchungen zur Erhöhung der Festigkeit und Oxidationsbeständigkeit von Coat-Mix-Formenmaterial

In a study to increase the oxidation resistance of coat-mix(CM)- material, several experiments for SiC-coatings were performed using different initial materials. The wetting angle between the binder coke and the used liquids was measured by the "drop"-method, for which an apparatus was designed and built. All of the liquids used wetted the binder coke and were usable for the infiltration of CM-material. Information from Japan states that successful SiC-coatings on porous materials were obtained by infiltration of a SiC-dispersion. Experiments to infiltrate CM-materials using this method were not successful. An infiltration depth of only severalmicrometers was reached and the pores were partly closed. A simulation of an ideal layer showed that the porosity of the material would be highly decreased, even by a thin layer. In an other case, CM-material was infiltrated by heating the sample in a mixture of SiC and Si powder in which no melt was formed. The silicon was vaporized into the sample and reacted with the carbon of the material .With a high fraction of silicon in the mixture, only the outer surface of the sample was siliconized. In that case, the structure of the material was destroyed and the edges broke. In a mixture with less Si, a higher infiltration depth was reached and the oxidation resistance was increased by 33 %. As a third infiltration method, the CM-material was infiltrated by different Tetraethoxisilan solutions, which formed a SiO$_{2}$-framework through gelation and drying . The SiO$_{2}$ coated CM-samples were heated up thereafter. The SiO${2}$ reacted to form SiC with the carbon of the material. A good solution for coating the CM-material was attempted by evaluation of literature results and characterisation of the gels by examination of the formed glass by measuring small angle x-ray scattering and viscosity. Samples 8 cm in diameter were completly infiltrated in vacuum. After complete gelation, the gel was dried at 850°C. Afterwards, the SiO$_{2}$-layer was converted to SiC at 1650°C. These layers had no influence on the density, porosity, permeability, heat conductivity and strength of the material. The influence of different temperatures, TEOS-solutions and multiple infiltration on the oxidation behavior was characterized by the loss of mass during oxidation. The oxidation resistance was increased up to 30 %. Extensive SEM-examinations showed that $\beta$-SiC-layers about 0,1 $\mu$m thickness were created on the CM-material. Contrary to the layers on binder coke materials, they were not porous and had a good adherence to the CM-material. It could not be proved whether the layer was complete. The surface microstructures of uncoated and coated samples were examined by SEM during the oxidation. The coated sample had a lower edge resistance than the uncoated samples. Complete infiltration and conversion to SiC, an absence of porosity in the layer, good adherence between layer and binder coke and increasing of the oxidation resistance have been achieved. However, the edge resistance and the accuracy of shape of the CM-mold material were decreased by the coating. Therefore the sol-gel method is not usable for coating the CM-material with SiC