SAFE Barriers - a Systems Approach For Engineered Barriers

Lead Research Organisation: University of Strathclyde
Department Name: Civil and Environmental Engineering

Abstract

Scientific objectives are:
1. To deploy and refine advanced monitoring technologies for simultaneous imaging of THMC variables (pH, temperature, pore-water pressure, swelling etc) within the laboratory. We will embed state-of-the-art micro-to-nano scale wireless devices into bentonite, and combine these with micro-scale geophysical and magnetic monitoring surveys, to illuminate 2D and 3D heterogeneities in THMC behaviour.
2. To integrate these monitoring technologies with experiments to gain a predictive understanding of the THMC evolution of clay-based engineered barriers, and their interfaces, up to the upper-bound of realistic environmental conditions. Interfaces will comprise joints within the clay as well as interfaces to the surrounding rock, cement and waste container. Experiments and modelling will focus on the effects of strong gradients in temperature (<150 degrees C), low pH cements and high salinity (10-40 g/l) across the EBS interfaces, and on the fingering of flow along joints and interfaces that may give rise to a heterogeneous THMC system response.

Planned Impact

Beneficiaries of this research fall into all four impact categories:
(i) Knowledge: a major contribution to the expanding global dialogue within the industry about engineered barrier systems (EBS), through development and maintenance of reciprocal relations with major industry-led, international programmes, as well as with other UK projects.
(ii) Society: working closely with the NDA public relations function, we propose to use dynamic, interactive theatre to explore the key issues in EBS implementation with communities in areas of the UK with active nuclear power stations and/or existing surface radwaste management facilities.
(iii) People: work closely with other NDA-sponsored projects (and international initiatives) to develop and implement an inter-institutional programme of 'additional professional formation' for project PhD students and postdocs, involving regular exposure to industrial practice (with NDA and others), and annual events in which young researchers will work in groups on realistic design formulated with our industrial counterparts.
(iv) Economy: We are confident that our 'whole system' approach will offer significant opportunities for cost savings, which we will identify and promote through regular dialogue with NDA planning and design staff.

Publications


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Feischl M (2016) An Abstract Analysis of Optimal Goal-Oriented Adaptivity in SIAM Journal on Numerical Analysis
Grassl P (2015) On a 2D hydro-mechanical lattice approach for modelling hydraulic fracture in Journal of the Mechanics and Physics of Solids
Grassl P (2013) CDPM2: A damage-plasticity approach to modelling the failure of concrete in International Journal of Solids and Structures
Grassl P (2014) Evaluation of nonlocal approaches for modelling fracture near nonconvex boundaries in International Journal of Solids and Structures
Grégoire D (2015) Mesoscale analysis of failure in quasi-brittle materials: comparison between lattice model and acoustic emission data. in International journal for numerical and analytical methods in geomechanics
 
Description Some key research findings from, and technologies delivered by, the SAFE Barriers project are highlighted below:

The bentonite/steel interface:
Exposure of bentonite to thermo-saline conditions and corrosion products derived from structural grade 275 carbon steel inhibits the swelling pressure, free swell capacity and ductility of the bentonite.  Whilst in the tests carried out, the measured values remained above the design limits set out in the SKB concept for mechanical and mass transport behaviour, in some cases, they dropped below the limit inhibiting microbial activity.

Colloidal silica grouting:
The physical erosion and chemical dissolution of solid silica grout increases with increasing flow rate, but remains constant under steady-state flow conditions. Scaling of the experimental results to repository conditions using a simple flow model indicates that erosion of fractured grouts under natural groundwater velocities is not significant. However, in cases where there is hydraulic communication between the surrounding geosphere and the open tunnel, erosion rates could be rapid and the grout may fail.

THMC processes under elevated temperatures:
Experiments show that application of a strong thermal gradient in the temperature (up to 150°C) did not deteriorate the thermal, hydraulic, mechanical and chemical response of the compacted bentonite barrier.

Bentonite, gas flow, temperature interactions:
Experiments demonstrate that permeability, total stress, swelling pressure and porewater pressure are strongly sensitive to changes in temperature. However, thermal loading up to 150°C has minimal long-term impact on the hydraulic permeability of the bentonite.

Bentonite buffer erosion:
The accessory minerals inherent in MX80 bentonite act as a barrier, inhibiting montmorillonite erosion through fractures in the surrounding rock. A ring of accessory minerals forms surrounding the bentonite buffer, that gradually thickens until montmorillonite erosion ceases. Simple upscaling calculations, based on these experiments, show that erosion rates are 1-2 orders of magnitude lower than those based on pure montmorillonite that are used within the SKB licence application. Using this new model of bentonite erosion, mass loss is shown to stay within acceptable limits for the safety of long-term disposal.

Application of MEMS technology in bentonite:
A successful encapsulation method has been developed for application of MEMS temperature and humidity sensors in hydrated bentonite. Results demonstrate that the encapsulated sensors are sufficiently robust to work under sustained swelling pressure over the long-term and that a new calibration algorithm, which accounts for simultaneous changes in temperature and humidity, can improve the sensor accuracy particularly in humidity conditions that are above 90%.


Development of magnetic sensors:
The sensitivity of permanent ferromagnets to corrosion in alkaline and saline fluids in the presence of re-saturating bentonite has been demonstrated. Nd-Fe-B 'neo magnets' show measurable (>90%) decreases in their magnetic field properties simultaneously with bentonite saturation, and other magnet types show slower but measurable corrosion and decreases in magnetisation. The presence of the corroding magnets has a negligible effect on the swelling properties of EBS bentonite. These results demonstrate that magnetic materials embedded within the EBS have significant potential for monitoring saturation of the bentonite buffer over various timescales.


Simulation of the behaviour of the bentonite:
A new framework for a hydro-mechanical network model for porous geomaterials describing fluid retention, conductivity and mechanical response at the capillary pore scale has been developed. This framework is one of the very few approaches available which couple transport and structural networks at the capillary pore scale, which is essential for being able to model reactive transport processes caused by mechanical changes of the material structures (e.g. due to constraint swelling). These techniques were used to demonstrate that the non-monotonic evolution of conductivity in constrained swelling tests is due to swelling induced reduction of void diameters, long before all voids are water filled.
Exploitation Route The data on bentonite barrier erosion can be used within assessments for the environmental safety case for nuclear waste disposal in the UK and outside.

The MEMS devices and the magnetic sensors may be suitable for application in an operational repository.

The data on elevated temperatures may be sufficient to allow disposal of wastes at higher temperatures, which will reduce the requirements for surface storage
Sectors Construction,Energy,Environment
 
Description The research project has developed prototype public engagement tools for Radioactive Waste Management Ltd to use in the 2017 siting process for a Geological Disposal Facility.
First Year Of Impact 2016
Impact Types Societal
 
Description Big Pitch: Ground Engineering
Amount £200,000 (GBP)
Funding ID EP/M016854/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Academic/University
Country United Kingdom of Great Britain & Northern Ireland (UK)
Start 12/2014 
End 12/2016
 
Description Collaboration with University of Stanford 
Organisation Stanford University
Country United States of America 
Sector Academic/University 
PI Contribution We are moving forward with several follow-on joint projects with Stanford. We will have research student exchange and will have access to their X-Ray CT scanner for a period of 1 year.
Collaborator Contribution Access to X-Ray CT scanner and multiphase flow apparatus.
Impact Journal paper currently in review. 4 joint PhD studentships 2 funded by strathclyde, 2 by Stanford
Start Year 2014
 
Description Joint research with NERC 
Organisation Natural Environment Research Council (NERC)
Country United Kingdom of Great Britain & Northern Ireland (UK) 
Sector Public 
PI Contribution University of Strathclyde researchers worked on this project with researchers from NERC
Start Year 2012
 
Description Joint research with SHEFFIELD UNIVERSITY 
Organisation University of Sheffield
Country United Kingdom of Great Britain & Northern Ireland (UK) 
Sector Academic/University 
PI Contribution University of Strathclyde researchers worked on this project with researchers from SHEFFIELD UNIVERSITY
Start Year 2010
 
Description Joint research with UNI OF EDINBURGH 
Organisation Durham University
Country United Kingdom of Great Britain & Northern Ireland (UK) 
Sector Academic/University 
PI Contribution University of Strathclyde researchers worked on this project with researchers from University of Durham
Start Year 2011
 
Description Joint research with UNI OF EDINBURGH 
Organisation University of Edinburgh
Country United Kingdom of Great Britain & Northern Ireland (UK) 
Sector Academic/University 
PI Contribution University of Strathclyde researchers worked on this project with researchers from UNI OF EDINBURGH
Start Year 2012
 
Description Joint research with UNIVERSITY OF GLASGOW 
Organisation University of Glasgow
Country United Kingdom of Great Britain & Northern Ireland (UK) 
Sector Academic/University 
PI Contribution University of Strathclyde researchers worked on this project with researchers from UNIVERSITY OF GLASGOW
Start Year 2012
 
Description Joint research with University of Nottingham 
Organisation University of Nottingham
Country United Kingdom of Great Britain & Northern Ireland (UK) 
Sector Academic/University 
PI Contribution University of Strathclyde researchers worked on this project with researchers from University of Nottingham
Start Year 2012
 
Description Appointed as expert hydrogeologist to the UK Committee for Radioactive Waste Management (CoRWM). 
Form Of Engagement Activity A formal working group, expert panel or dialogue
Part Of Official Scheme? Yes
Geographic Reach National
Primary Audience Policymakers/parliamentarians
Results and Impact My advice has contributed to a number of key decisions. Most recently, had a significant impact on the contents of the 2014 White Paper on Siting a Geological Disposal Facility in the UK

Changes to the recent White Paper
Year(s) Of Engagement Activity 2008,2009,2010,2011,2012
URL https://www.gov.uk/government/organisations/committee-on-radioactive-waste-management