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Posiva publishes Working Reports and Posiva Reports. From the year 2006 nearly all the reports have been published on our webpage and they can be found in the databank. In the databank you can also find our Annual Reviews and some other publications as well. You can also find print-quality pictures and useful links in the databank.

Recent publications


POSIVA Report 2010-6

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Name:

Laboratory Studies on the Effect of Freezing and Thawing Exposure on Bentonite Buffer Performance: Closed-System Tests

Writer:

Schatz, T. & Martikainen, J.

Language:

English

Page count:

58

ISBN:

978-951-652-177-3

Summary:

This report presents a set of results from laboratory studies on the effect of freezing and thawing on compacted bentonite buffer material.

In order to evaluate the effect of freezing and thawing on compacted bentonite buffer performance a series of experiments were conducted using closed, constant-volume cells as follows:
-    Pre- and post-freezing swelling pressure measurements were performed on fully saturated MX-80 and Deponit CA-N bentonite samples, at dry density values of approximately 1.6 g/cm3, over five freeze/thaw cycles from room temperature to -18 °C with rapid (instantaneous) temperature exposure.
-    Pressure measurements were performed on fully saturated MX-80 bentonite samples, at dry density values of 1.470 and 1.501 g/cm3, during a temperature run from room temperature to -10 °C with step-change temperature exposure and back from -10 °C to room temperature under continuous temperature change exposure at 0.1 °C/h.
-    Pressure measurements were performed on fully saturated MX-80 bentonite samples, encompassing a range of dry density values from 0.940 to 1.534 g/cm3, during repeated temperature runs from room temperature to -10 °C and back with continuous temperature change exposure at 0.1 °C/h.
-    Pressure measurements were performed on a fully saturated Deponit CA-N bentonite sample, at a dry density of 1.484 g/cm3, during a temperature run from room temperature to -10 °C and back with continuous temperature change exposure at 0.1 °C/h.
-    In some cases, hydraulic conductivity measurements were performed before and after freeze/thaw exposure.
In general, exposure to freezing temperatures, down to an average temperature of -10 °C, results in the development of significant internal pressures in compacted bentonite samples, which is attributed to the formation of ice. The specific test results are summarised as follows:
-    Increases in pressure by factors of 1.5 to 2.2 were observed for MX-80 samples at dry densities between 1.470 and 1.534 g/cm3.
-    An increase in pressure by a factor greater than 8 was observed for MX-80 at a dry density of 1.267 g/cm3.
-    An increase in pressure by a factor greater than 30 was observed for MX-80 at a dry density of 0.940 g/cm3.
-    An increase in pressure by a factor of 1.8 was observed for Deponit CA-N at a dry density value of 1.484 g/cm3.
-    The observed pressure increases fall below a pressure limit described by the standard Clapeyron equation.
-    Sample hydraulic conductivities are likely not affected by freezing and thawing exposure.
-    Some loss of swelling pressure was observed during step-change temperature exposure for MX-80 bentonite samples between 0 and -5 °C.
-    On average, over every individual freezing and thawing run reported here, for MX-80 and Deponit CA-N bentonites compacted to a dry density close to 1.6 g/cm3, swelling pressures are completely recovered after any freezing and thawing exposure.
-    No significant differences in behaviour resulting specifically from freezing and thawing exposure were observed between MX-80 and Deponit CA-N bentonites.

Keywords:

Bentonite buffer, freezing, thawing, permafrost, long-term safety, performance

File(s):

Laboratory Studies on the Effect of Freezing and Thawing Exposure on Bentonite Buffer Performance: Closed-System Tests (pdf) (2.4 MB)


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