Radiation Effects in Radwaste Glasses: A Reappraisal of Alpha-Recoil Aging as Simulated by Ion Implantation
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RADIATION EFFECTS IN RADWASTE GLASSES : A REAPPRAISAL OF ALPHA-RECOIL AGING AS SIMULATED BY ION IMPLANTATION.
J.C. DRAN, Y. LANGEVIN, M. MAURETTE, J.C. PETIT Laboratoire Rend Bernas, B.P. 1, 91406 Orsay, France. ABSTRACT New results on the etchability of lead implanted silicate glasses are presented which are satisfactorily accounted for by a Monte Carlo Model of etching. These results strongly support the radiation damage origin of the ion-induced modification of the chemical reactivity of glass. Major artefacts of ion implantation are then discarded as possible causes of the observed effects and consequently this technique is shown to be a valuable tool for the study of c-recoil aging in H.L.W. glasses. INTRODUCTION The radiation stability of HLW glasses could be of particular concern for the long-term isolation of their radioactivity from the biosphere. It is now widely agreed that the most damaging particles which could affect the etchability of these glasses when exposed to ground waters,would be the recoil nuclei emitted during the c-decay of actinides. In order to investigate such effects we have developed an experimental procedure which has been already extensively described [1]. This procedure is based on an external implantation of lkeV/amu lead ions, coupled with leach tests in simulated natural waters and profilimetric measurements with a stylus instrument. Our main result was the observation of a threshold effect on the _tchability of the irradiated glass above a critical ion dose ý 5.1012 ions.cm . For some glasses which are not directly relevant to waste glass composition, the aqueous corrosion could be significantly enhanced by ion implantation above 4 [2]. However we have already shown [3] that such enhancement strongly depends on the glass and etchant compositionsand in particular, for a representative simulated radwaste glass it could not be detected in accordance to results obtained by other authors. By considering that silicate glasses are in fact solid state track detectors, we interpreted the observed threshold effect as resulting from the overlapping of islands of damaged material (planar track) of increased chemical reactivity produced by the registration of individual low energy lead ions which can be visualized in the case of mica as shallow etch pits. However the relevance of this approach was questionable mainly because such radiation effects have never been observed previously by using short-lived actinide doping techniques [4] and thus could be attributed to various possible ion implantation artefacts. This paper is only intended to demonstrate on a much firmer basis the radiation damage origin of the alteration of etchability in ion implanted glasses with no reference to a-recoil aged HLW glasses. In a companion paper we will report on results obtained with a larger sampling of simulated radwaste glasses which we compare with those of actinide doping techniques.We first present here new experimental and theoretical data on the etching properties of glasseý and d6 insulati
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