Characterization of Highly Active Waste Glasses Produced in a Hot Vitrification Pilot Plant
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CHARACTERIZATION OF HIGHLY ACTIVE WASTE GLASSES PRODUCED IN A HOT VITRIFICATION PILOT PLANT C.Cantale +, J-P.Glatz*, E.H.Toscano*, A. Donato +, M.Coquerelle* and J.Fuger* + ENEA-Casaccia, Fuel Cycle Division, 00060-S.M. di Galeria, Rome, Italy. * Commission of the European Communities, Joint Research Centre Karlsruhe, European Institute for Transuranium Elements, P.O. Box 2340, 7500-Karlsruhe, Federal Republic of Germany.
ABSTRACT Fully radioactive waste glasses produced in a hot vitrification pilot plant were characterized in the hot cells at the JRC-Karlsruhe. The work includes microstructural analysis before and after leaching by SOXHLET extractors (MCC-5S), as well as leachate and gel-layer chemical analysis. Partial devitrification, with phases enriched in metals and rare earths, was observed in one of the products. In the gel layers formed during the dissolution tests, enrichment in some elements (Fe,Ti,Gd,Nd,Ce) and depletion in glass constituents (Si,B,K,Ba,Ca,Na) as well as in Mo and Cs, were determined. This was in good qualitative agreement with the leachate chemical analysis.
INTRODUCTION Leaching of radionuclides from high-level waste forms represents a major item in assessing the performance of any waste disposal strategy. In the past, a great amount of information has been collected on simulated waste forms or those doped with single radionuclides to determine individual release rates and, at the present time, information concerning fully radioactive waste is relatively scarce (see for example [1-41). The usefulness of information about actual waste products can be summarized in three main points: 1) to determine whether there is an influence of the simultaneous presence of several radionuclides on the leaching rate of the bulk and of individual species; 2) to establish the effect of radiolysis on the leaching behaviour of waste forms; and, 3) to compare the performance of fully radioactive products with corresponding simulated products. In the hot vitrification pilot plant, built and operated by ENEA at JRC-Ispra, several highlevel waste borosilicate glasses were produced [51 and three of these were delivered to the hot cell laboratory at JRC-Karlsruhe for characterization. The work reported herein includes the microstructure analysis before and after corrosion tests (using a modified SOXHLET MCC-5S procedure [61), chemical analysis of the leachates by ICP-MS and ICP-OES and electron microprobe chemical analysis (EMPA) of the gel layers. Mat. Res. Soc. Symp. Proc. Vol. 176. ©1990 Materials Research Society
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EXPERIMENTAL AND RESULTS
The compositions of the glass matrix, waste loading, gamma-activity and canister material are reported in Table I. In the case of Crucible 4, an active solution containing Cs-137, Eu-154, Ce144, Ru-106 and Sb-125, was added to the simulated waste used in previous inactive tests [71, having the total activity indicated in Table I. The axial distribution of mass and fission products was checked by radiography and gammascanning. Two isotopes, Cs-137 (662 keV) and Eu
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