Characterization of Cement Microstructure for the Immobilization of Nuclear Waste Using Advanced Imaging Methods
- PDF / 328,005 Bytes
- 6 Pages / 432 x 648 pts Page_size
- 105 Downloads / 220 Views
Characterization of Cement Microstructure for the Immobilization of Nuclear Waste Using Advanced Imaging Methods D.L. Engelberg 1,2, J.A. Duff 1, L. Murray 2, L. Dodds 2, N. Mobasher 2, P.J. Withers 3 1
Research Centre for Radwaste & Decommissioning, School of Materials, University of Manchester, M13 9PL, Manchester, UK 2 Nuclear FiRST CDT, University of Manchester & University of Sheffield, UK 3 Henry Moseley X-ray Imaging Facility (HMXIF), School of Materials, University of Manchester, M13 9PL, Manchester, UK ABSTRACT A range of advanced imaging techniques have been brought together to provide a comprehensive picture of cement microstructure for nuclear waste immobilization. Image analysis of Nirex Reference Vault Backfill (NRVB) has been used to characterize the CalciumSilicate-Hydrate (C-S-H) matrix fraction. Through weight loss measurements and digital image correlation of OPC-based cement blends we have quantified the development of microstructure surface strains during the initial 48 hrs hardening period. The build-up of displacements on the microstructure scale indicated grain-like compressive areas, surrounded by a network of tensile regions. Serial sectioning of NRVB using ultra-microtome cutting has been explored for advanced high-resolution 3D microstructure characterization, while X-ray Computed Tomography (XCT) has been used to obtain information of the 3-D pore space and size distribution of air pores in NRVB non-destructively. INTRODUCTION Blended cements play a major role in the UK’s programme for the immobilization of intermediate level radioactive waste (ILW) [1]. Cementitious materials have been selected based on their ability to chemically retain radio-nuclides, to maintain the integrity of waste containers, and to stabilize the host-rock near-field environment after repository closure. A broad variety of ordinary Portland cement (OPC) based blends are generally considered, in order to accommodate waste-specific requirements, such as blast furnace slag (BFS) modified grouts [2], low-pH cements for waste streams containing reactive metals [3], or the NIREX reference vault backfill (NRVB) for backfilling/sealing the deep geological repository [1]. Understanding cement microstructure is therefore important for optimizing long-term material performance. Modeling cement integrity and permeability, in combination with predicting the fracture behavior so as to prevent radio-nuclide migration through the microstructure, as well as the prediction of localized corrosion as a function of cement weathering are just some examples where microstructure information can be used for improving cement durability. This paper aims to provide insight into the application of novel microstructure characterization approaches for cementitious materials, relevant to the immobilization of nuclear waste. A range of imaging-based analysis techniques are introduced and typical applications briefly outlined, including digital image correlation and analysis, 3D microtome sectioning, and X-ray computed tomography.
521
EXPERIM
Data Loading...
