Budapesti Műszaki és Gazdaságtudományi EgyetemÉpítőmérnöki Kar - építőmérnök képzés 1782 óta

High-level radioactive waste (HLW) requires sophisticated treatment and management to successfully isolate it from the biosphere. This usually necessitates treatment, followed by a long-term management strategy involving permanent storage, disposal or transformation of the waste into a non-toxic form of material. The radioactivity of the wastes decays with time, so high-level wastes are stored about 50 years before disposal. Storage of used fuel is normally under water for at least five years, often followed by dry storage. The isolation is provided by a combination of engineered and natural barriers. The multi-barrier concept consists of the waste packaging, the engineered repository and the geology, which all providing barriers to prevent the radionuclides from reaching humans and the environment. In addition, deep groundwater is generally devoid of oxygen.

HLW in deep geological formation is deposited in multi-layer containers, between 250m and 1000m under the ground, in isolated area under supervised conditions. The container has layers of steel, glass, ceramics or other materials. The long term deterioration of the waste forms and materials are extensively studied.

The presence of microorganisms in the storage should not be ignored. If a small number of indigenous microorganisms is present in the argillaceous sedimentary rock, an introduction microbial mass is expected during construction, excavation and operation of the storage site. These microorganisms introduced aerobic (such as Thiobacillus) or anaerobic (such as Sulphate Reducing Bacteria, SRB), able to adapt to polluted environments and can develop defences against the extreme conditions of survival in the presence of heavy metals, radioactivity, etc. Activities of different bacteria produce corrosive environment for the containment.

SON68 is an inactive reference nuclear waste glass. It is a High Level Long Lived nuclear Waste (HLLLW) glass, and it is expected to be disposed in a deep geological formation. This glass is poured into stainless steel containers and then placed in an overpack made of iron steel.

A natural corrosion is expected to be happened over this glass in unsaturated conditions upon the closure of the storage galleries during argillite host rock re-saturation in the proposed disposal site. The repository would exist 300 – 500 meters underground in an unsaturated layer where the host rock is argillite. Corrosion of nuclear waste glass in unsaturated conditions is expected to occur upon the closure of the storage galleries during argillite host rock resaturation in the proposed disposal site.

The objectives of the expected work are to determine the alteration kinetics of the SON68 reference waste glass in such conditions. Experiments will be conducted with small polished glass chips, involving accelerated ageing of glass due to environment provided by the microbial activity. The nature and extent of corrosion will be determined by characterizing the reacted glass surface and volume with scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy dispersive x-ray spectroscopy (EDS).