THERMAL CONDUCTIVITY AND VOLUMETRIC HEAT CAPACITY OF AIR-DRIED GRANULATED BENTONITE MIXTURES (GBMS) UNDER DIFFERENT PACKING CONDITIONS

Abstract

Granulated bentonite mixtures (GBMs), crushed pellets mixed with powder to have a specific particle size distribution, have been validated as effective buffer materials for the geological disposal of radioactive waste due to their ease of transportation, in-situ placement and backfilling. The evaluation of heat transport parameters such as thermal conductivity (l) and volumetric heat capacity (C) of GBMs is essential to assess the temperature distribution and its evolution with time and subsequent heat generated by the waste. Despite a large volume of studies on compacted bentonite including blocks, limited studies have been done for measuring l and C of GBMs as well as examining the predictive models that are applicable to characterize those parameters under different packed conditions. In this study, therefore, the l and C values of two GBM samples, FE-GBM used in the full-scale in-situ experiments in Switzerland and OK-GBM in Japan, packed with loose to dense conditions by controlling dry bulk density (DD), were measured at air-dried condition in the laboratory and the applicability of predictive existing models for l and C has been tested. The results showed that the measured l of FE-GBM gave slightly smaller values than those of OK-GBM at the same DD while there was no significant difference in the measured C values between two GBMs. The measured l and C values for both GBMs increased linearly with increasing of DD, indicating simple linear regressions were applicable to represent the DD-dependence l and C of GBMs in this study. These findings could be supported by the application of linear correlation models for both l and C as a function of DD.