A Transmission Electron Microscopy Study of the Structure and Annealing Behavior of Copper-Krypton Deposits

A combined implantation and sputtering method has been developed at Harwell to entrap high (5%) atomic concentrations of krypton in a metal matrix. The work has been aimed at providing a safe and effective method for storing the active krypton-85 resulting from fuel reprocessing. In the present paper, the results of a transmission electron microscopy investigation into the structures of copper-krypton deposits will be presented together with the effects of annealing behavior. The overall impression of the as-deposited material is one of a very fine grain size, high dislocation density, and an extremely large concentration of small bubbles in the range 1.5 to 2.0 nm diameter. Taking into account additional results of macroscopic density and lattice parameter measurements, it is argued that the bubbles contain krypton at very high pressures; nevertheless, an appreciable fraction of krypton must be present in bubbles that are submicroscopic in size.

On annealing, large changes in bubble substructures became apparent at temperatures greater than half the melting point when the main effect was one of bubble coarsening as a result of coalescence and grain boundary bubble growth. These effects were reflected in the specimen surface structure as observed by scanning electron microscopy. The observations of the as-deposited material and its evolution with temperature should provide a useful background to the understanding of the material stability and high temperature gas release behavior.