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Working reports


Posiva's working reports are used to publish research results related to the practical aspects of the final disposal of spent nuclear fuel. Approximately one hundred working reports are published every year, usually in Finnish or English. The reports are written by Posiva employees or specialists from third party organisations. The working reports are an important tool for distributing the results of research work. All working reports are published on the Posiva website.



Workreport 2009-37

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Name:

Bentonite-Cement Interaction – Preliminary Results from Model Calculations

Writer:

Lehikoinen, J.

Language:

English

Page count:

35

Summary:

The interaction between the bentonite buffer and alkaline plume from degrading cementitious material used in the construction and operation of the repository is envisaged to constitute a risk to the long-term chemical stability of bentonite. In this report, first model calculations to shed light on the possible extent of mineralogical alteration of bentonite due to the plume have been carried out.

A common feature of the model outcome for every case is the clogging of the pore space at the interface between the buffer and the rock fracture carrying the plume. Depending on the pH considered in the calculations for the plume (12.17, 11.60 and 9.70), this clogging will occur after 10, 18 and 5,900 years after the onset on interaction, respectively. For each case, the heavily altered zone in bentonite is confined very close to the interface.

There are uncertainties related to the present calculations, the greatest ones pertaining to the poor knowledge of mineral dissolution/precipitation kinetics and to constraining the set of secondary minerals possible to form. The effects of the latter were clearly illustrated in two model cases (pH 11.60 and 9.70), where initially supersaturated secondary mineral phases were omitted; the pore clogging did not take place at the fracture-buffer interface and the buffer was continuously exposed to the alkaline plume. According to the present model calculations, it seems that the evolution of the interfacial porosity in the model system with pH 12.17 is not very sensitive to the selection of the secondary minerals as the pore space was clogged regardless.

Keywords:

Bentonite, cement, low-pH cement, grouting, hyperalkaline, leachate, chemical interaction, alteration, reactive transport, modelling

File(s):

Bentonite-Cement Interaction – Preliminary Results from Model Calculations (pdf) (2 MB)


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