Colloidal Silica Grout for Stabilisation of Underground Structures and for the Formation of Hydraulic and Chemical Barriers for Inhibiting Contaminant Migration

Academic Institution: University of Strathclyde

Academic Supervisor: Professor Rebecca Lunn

Industry Partner: Nuclear Decommissioning Authority

PhD Student: David Morrison

Start Date: 1st December 2019

Abstract

The proposed PhD project, in partnership with the Nuclear Decommissioning Authority (NDA), will explore the potential for colloidal silica grout to support aspects of nuclear decommissioning and nuclear waste storage. The UK’s nuclear sites contain stored wastes in ponds and silos as well as large volumes of contaminated concrete and soil. During storage decommissioning and deconstruction operations, there are significant risks of radionuclide transport via groundwater and airborne particulate releases. Colloidal silica grout has the potential to reduce these risks to an almost negligible level. Experiments previously conducted at Strathclyde have shown that injection of colloidal silica into existing soils results in the formation of a chemical and a hydraulic ground barrier. The colloidal silica not only significantly decreases the soil permeability (below that of a clay) but also increases the in situ sorption capacity, thus trapping radionuclides.

The PhD will investigate the use of colloidal silica in support of nuclear decommissioning. The student (and supervision team) will work with the NDA to define priority applications for colloidal silica and, hence, to refine the proposed experimental programme to address both fundamental and applied research needs.

Fundamental challenges will include assessment of long-term mechanical and chemical grout stability, design of additives to increase grout sorption capacity for improved chemical containment, and investigating the potential for contaminant diffusion across grouted soil barriers.

Potential applications include inhibiting radionuclide migration from recently decommissioned structures during care and maintenance (e.g. silos and ponds from which wastes have already been retrieved); the development of primary or secondary barriers around existing radionuclide (or other) contaminated areas; and stabilisation of underground structures.

If experimental results prove promising, this PhD will be used in support of future safety case development to underpin future decommissioning applications for colloidal silica grout on the NDA’s nuclear sites across the UK.