This study examines the biocorrosion of cement and bitumen which occurs through the production of mineral or organic acids by alkalitolerance micro-organisms to determine the gas production and the physico-chemical modification of the materials.
The knowledge of possible evolution of conditioned wastes during intermediate storage, handling and deep repository is necessary to warrant the safety of workers and to define the conditions for storage and disposal. These conditions can depend on production of gases and of chemical compounds able to promote degradation or biodeterioration phenomena. The origin of gas production can be:
the waste itself, producing radon and gases from alpha and gamma radiolysis;
the chemical or microbiological corrosion of coating matrix and structural material;
the radiolysis of organic compounds included in the waste.
Living microorganisms can also produce complexing agents and organic or mineral acids able to promote corrosion and modifying the redox conditions and the pH of the repository.
The biodeterioration of bitumen studies will be done under low oxygen content conditions because strict anaerobic conditions will not be present in a deep repository on account of gas production by radiolysis. 2 kinds of microorganisms have been chosen: heterotrophic microoganisms that produce organic acids and autotrophic microorganisms producing mineral acids.
The qualitative and quantitative evaluation of gaseous production from waste package allows the determination of their storage conditions. Two packages have been selected: a cementitious embedded alpha wastes one (sludges from liquid waste filtration, containing alpha emiters) and a radifere one.
Conditions have also been selected for an underground repository in which organic solid waste is packaged in containers held in a cementitious matrix.
Microbial growth in bitumen samples is evaluated qualitatively by measuring the gas produced (CO2, N2O and N2 for denitrifying microbes, CO2 and H2S for sulphate reducing bacteria, CO2 for fermentative micro-organisms), decrease of nitrates or sulphate concentrations and microscopic observation.
Cement samples are completely immersed in a mineral media inoculated by:
- a mixed culture of funge (Trichoderma irride and Aspergillus niger) using gluose (an intermediate product of cellulose degradation) and producing several organic acids,
- a mixed culture of Thiobacillus strains, growing on thiosulphate (a soluble reduced sulphur source) and producing sulphuric acid.
Another part of the study will determine the radon quantity in the gaseous phase using special flasks whose inner walls are coated by Zinc sulphur activated with Silver.
Also as part of the study on gas production, the amount of gas produced by external gamma radiolysis will be determined for bitumen containing organic complexing agents such as TBP and for cement containing EDTA.
Lastly a post of the project is concerned with the growth of micro-organisms on and within cement based matrices typical of those to be used in the disposal of low and intermediate level waste (ILW/LLW).
Funding SchemeCSC - Cost-sharing contracts
OX11 0RA Didcot - Oxfordshire