Method for the detection of labelled test, or measuring spheres in a bed of spherical reaction substances and appropriate test or measuring spheres

For studying the yielding behaviour of the pebble bed of a HTGR, labelled spheres are used. The label consists of an enclosure or coating determining resp. changing the electric conductivity of the test spheres. The electric conductivity of the test spheresas well as the other spheres is determined electromagnetically at a fixed measuring point. As enclosures or coatings, layers, networks, or loops from electrically well-conducting metal with a high melting point, as e.g. silicon, tungsten, tantalum, zirconium, titanium, their carbides, iridium, osmium and/or rhenium may be used. The enclosures or coatings are precipitated chemically from the steam phase or currentless resp. electrolytically. (DG)