THM COLUMN CELL WITH MX-80 PELLETS SIMULATING THE HE-E IN SITU EXPERIMENT FOR 10 YEARS: ONLINE RESULTS AND FINAL PHYSICAL STAT

Abstract

To simulate in the laboratory the conditions in the HE-E in situ test, a 50-cm long column of MX-80 bentonite pellets was heated on its base to 140 °C while Pearson water was supplied through its upper surface. The test consisted of a 7-month heating phase and a heating+hydration phase that went on for more than nine years. The initial dry density of the material was 1.53-1.54 g/cm3 and its water content 6 %. The thermal gradient was quickly established and remained constant during the test. Because of the low water permeability of the pellets’ mixture it took long time for the relative humidity inside the column to increase. Upon dismantling it was checked that the upper half of the column had water contents around 30% (corresponding to degrees of saturation 92-99 %), which only increased above this value in the 5 cm closest to the hydration surface. The bentonite in this area was compact and dark, with a smooth appearance in which no pellets could be told apart. In contrast, the water content and degree of saturation sharply decreased towards the heater in the bottom half of the column, with values close to 0 % in the 5 cm closest to the heater. The bentonite in this area was lighter in colour and was loose. The average final water content of the column was 22.0 %, corresponding to a degree of saturation of 75 %. Vapour leaking via the sensors’ inlets likely took place during operation.