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An Experimental Loess-cement is Being Built at NDF Site

10.06.2015

At the end of May the implementation of an interesting scientific practical project started at Radiana site – it is a part of the preliminary preparation for the construction of the future storage facility. The project will be realised by the Department of Environmental Geotechnics at the Geological Institute of the Bulgarian Academy of Sciences. Prof. Doncho Karastanev told us more about the nature of the project and its meaning with regards to the safety of the facility.

A loess-cement cushion is planned to be built with the same technology and proportion of cement with which the loess-cement cushion under the NDF storage modules will be made. This cushion will stay as a reference object from which, after long aging period, samples could be taken for studying the stability and the condition of the loess-cement cushion. The experimental site will be an area of 100 sq. m. area and 1 m thick layer.

Till now the scientific team has conducted large-scale laboratory analyses and defined the optimal content of cement, water content and the maximum density which have to be achieved. All these analyses will be conducted and their results will be verified with the construction of this cushion on site. The whole disposal facility foundations will be built on such cushion. It will be done not only to increase the bearing capacity of the soil basis, but mainly as a barrier towards eventual distribution of radionuclides.

In the beginning of our work on the site now we made three drillings with which we will estimate the thickness of the soil layer. It will be excavated and under it about 1-1.2 m loess will be dug. These earth mass will be used for the loess-cement mixture for the experimental cushion. We will take samples from the loess in order to check its natural moisture, whether it is close to the optimal, what is its grains composition and plasticity in order to estimate whether it corresponds to the one, used for the laboratory tests. The tests were made with an average sample, taken from 18 drillings, situated along the axis of the disposal modules. We have been working on these analyses since August last year. More than 200 laboratory samples were made, which after 28 and 90 days aging were tested in various tests – compressive strength, shear strength, tensile strength in bending, water tightness. The laboratory tests were finalised and based on the results from them this on site experiment was planned. After this experiment we will finally specify the design characteristics of the loess-cement cushion.

The method of foundation-building on loess-cement cushions has been applied in Bulgaria in the construction of all the facilities of Kozloduy NPP, in the construction of several tv towers in Northern Bulgaria (Silistra, Ruse and Pleven) and more than 100 apartment buildings, built in the towns which are on loess terrains.

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