Benefits of applying X-ray computed tomography in bentonite based material research focussed on geological disposal of radioactive waste

Heini Maria Reijonen,Pasi Heikkilä,Jukka Kuva

doi:10.1007/s11356-020-08151-2

Abstract

Bentonite-based geomaterials are included in the designs of geological repository planning in most countries, especially in high-level radioactive waste disposal. Physical integrity of the bentonite sealant is key in assuring its hydraulic and retention properties, which affect the long-term performance of the repositories. Examination of the internal textures and structures of bentonite has been challenging until recently. Here, X-ray computed tomography (XCT) is applied to improve the textural and structural characterization of natural and man-made bentonite samples. Based on these initial analyses, clear benefits have been identified compared with conventional bentonite research methods. First, applying XCT prior to destructive analytical methods provides means to distinguish secondary features or in situ textures. It allows to eliminate false interpretations due to sample deformation and guides subsampling. Second, XCT images add the third dimension to analyses, allowing larger spatial coverage in less time. Overall, findings support the application of XCT for reducing uncertainties related to physical characterization of bentonite samples, both natural and industrial. They also show that XCT has potential to be developed to support quality assurance processes for bentonite sealant manufacturing.

Highlights

Utilizing clay materials in the geotechnical applications for geological disposal of high level radioactive waste has one major difference to all other environmental applications—the time frame of assessing the performance of the systems spans up to a million years
In order to assess longterm performance of these materials, geological formations of bentonite have been studied in the past, but no detailed large-scale textural analyses have been produced to date
The X-ray computed tomography (XCT) method is applied to bentonites, providing a new, structurally more profound way to interpret the results of physical and chemical analyses of samples

Summary

Introduction

Utilizing clay materials in the geotechnical applications for geological disposal of high level radioactive waste has one major difference to all other environmental applications—the time frame of assessing the performance of the systems spans up to a million years. This sets a requirement to understand processes that are beyond experimental timescales. Kawaragi et al (2009) used XCT to characterize both processed and natural bentonite samples, but for the use in large scale data acquisition for deposit-wide bentonite petrography, the method is yet to be employed ( other types of clay deposits have previously been studied, e.g. Boom Clay: Hemes 2015). The emphasis is set on identifying these artefacts via XCT and assessing their significance to the interpretation of the results (those presented in Alexander et al 2017)

Methods

Results

Discussion

Conclusion