In-Situ Testing of Nuclear Waste Glasses in a Clay Laboratory - Results After Two Years Corrosion
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IN-SITU TESTING OF NUCLEAR WASTE GLASSES IN A CLAY LABORATORY RESULTS AFTER TWO YEARS CORROSION P. VAN ISEGHEM, W. TIMMERMANS AND B. NEERDAEL Department Nuclear Chemistry and the Fuel Cycle, Belgium
S.C.K./C.E.N.,
B-2400 Mol,
ABSTRACT The first retrieval of an in-situ experiment on the interaction waste form - clay host in the underground laboratory under the Mol site has been finished successfully. The test consisted in a two years exposure of various candidate simulated waste glasses at 90°C to Boom clay. The retrieval was done by overcoring. The experimental data showed satisfactorily correspondence between in-situ and laboratory simulation tests both for mass loss and surface analytical data, supporting the validity of the in-situ test as it was performed. The thickness of waste form dissolved within two years varies between 40 and 325 pm (case of the high-level waste glasses), depending on the composition. Matrix dissolution is expected to be the major mechanism of interaction.
INTRODUCTION In the Belgian R&D programme on the disposal of conditioned radioactive waste [I], in-situ experiments on waste forms have been considered already early as a very important means to validate data obtained in laboratory. This philosophy was followed in other countries as well [2,3]. Therefore, extensive use was made of the opportunities offered by the underground laboratory in Boom clay, constructed during the first half of the 1980's. This laboratory at about 220 m below the surface, was built to investigate the feasability to construct an underground disposal site in clay. Also a number of in-situ experiments were elaborated to characterize the clay confinement properties such as heat transfer, migration of radionuclides. In parallel, in-situ experiments were designed to investigate the interaction of candidate waste forms and canister materials with Boom clay [4]. Two experimental test configurations were selected. The first consisted to expose waste forms and canister materials to a humid atmosphere produced by the clay rock (relevant for the initial period after closure of the repository); the second aimed for investigation of long term interaction between waste form and clay host (no other barriers present any longer). Four stainless steel tubes were manufactured [5] for tests at host temperature (five years), 90%C (two and five years) and 170°C (five years). The tested waste forms consist of two categories: (1) candidate high-level waste glasses considered in various European countries (Belgium, France, Italy, FR Germany, United Kingdom); (2) candidate alpha/low level waste glasses developed for the FLK incinerator by the S.C.K./C.E.N. Some HLW glasses were exposed to Boom clay in the presence of candidate canister/overpack materials. In parallel with the in-situ experiments in direct contact with clay, laboratory tests were performed simulating as close as possible the in-situ conditions. The present paper reports the retrieval and examination of the first in-situ experiment after two years exposure at 90=C in cl
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