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The Corrosion of Nuclear Waste Glasses in a Clay Environment: Mechanisms and Modelling

Objective

The objective of the present project is to enlarge the already existing database on the performance of various simulated HLW-glasses in one of the reference repository environments, the Boom clay, with the aim to elucidate corrosion mechanisms in clay media and to propose a source term for the radionuclide release into the near field by the use of corrosion accelerating conditions (accelerated tests) and more complex media (integrated tests) and to model the long term interaction between glass and clay environment, which is the final goal of the project.
This programme studies the performance of various simulated high level radioactive waste (HLW) glasses in one of the reference repository environments, the Belgian Boom clay, with the aim to elucidate corrosion mechanisms in clay media and to propose a source term for the radionuclide release into the nearfield. The objective of the present project is to enlarge the already existing database by the use of corrosion accelerating conditions (accelerated tests) and more complex media (integrated tests) and to model the long term interaction between glass and clay environment, which is the final goal of the project. In the accelerated tests, surface area to solution volume and temperature are used as the corrosion accelerating parameters. To obtain a high surface area to solution volume the glass is powdered. In the integrated tests glass corrosion is studied in the presence of canister and overpack corrosion products and backfill.

All attention has been focussed on the starting up of the experiments. By the end of 1991 the inactive accelerated tests were partly started. The remaining accelerated tests, the inactive integrated tests and the tracered meltings were in preparation. The modelling effort will commence at a later stage.
Work programme:

Accelerated tests, inactive: powdered samples of glasses SON68 and SM539 are exposed to distilled water (DW), synthetic interstitial claywater (SIC) and a mixture of 500 g Boom clay and 25 g Fe2O3 per litre synthetic interstitial claywater (called "CCSICM + CP"). The SA/V values are 500, 2500 and 10000 m{-1}, the experimental temperatures are 40, 90 and 150 C. The maximum test duration is 720 days.
Accelerated tests, active: grains of glasses SON68 and SM539 are exposed to the same media as sub. The glasses are doped with either Pu/134Cs/90Sr or 237Np/99Tc/55Fe/241Am. The SA/V value is approximately 400 m{-1}. The experimental temperature is 90 C. The maximum test duration is 360 days.
Integrated tests, inactive: a first series of powdered samples of glasses SON68 and SM539 is exposed to a mixture of 250 g Ca-bentonite, 250 g Boom clay and 25 g Fe2O3 per litre synthetic interstitial claywater. A second series of powdered glasses is exposed to a mixture of 475 g Boom clay, 25 g Cibercor P40 cement and 25 g Fe2O3 per litre synthetic interstitial claywater. The SA/V values are 500 and 2500 m{-1}. The experimental temperatures are 40, 90 and 150 C. The maximum test duration is 720 days.
Integrated tests, active: grains of glasses SON68 and SM539 are exposed to a mixture of 250 g Ca-bentonite, 250 g Boom clay and 25 g Fe2O3 per litre synthetic interstitial claywater. The glasses are doped with the same radionuclides as for the active accelerated tests. SA/V, temperature and test durations are also the same as sub.
Modelling of the dissolution behaviour of the glass matrices in the studied clay disposal surroundings.

Funding Scheme

CSC - Cost-sharing contracts

Coordinator

Organisme National des Déchets Radioactifs et des Matières Fissiles enrichies
Address
1,Place Madou - Boites 24/25
1030 Bruxelles
Belgium

Participants (1)

Centre d'Etudes de l'Energie Nucléaire-Studiecentrum voor Kernenergie CEN/SCK
Belgium
Address
200,Boeretang
2400 Mol