The response of compact bentonite during a 1-D gas flow test

This report describes the results of a 1-D gas injection test on compact Mx80 bentonite. The test comprises the first dataset for Stage 1A of Task A of the DECOVALEX-2019 programme, which has been designed to improve our understanding of the migration of repository gases through clay-based materials. Over the duration of the testing period, pressurised helium gas was applied to the face of the injection end of the clay sample, and the gas pressure was increased until the entry pressure was exceeded and gas entered the sample. The gas then migrated through the clay and changes in porewater pressure, swelling pressure and flowrate were observed by the instrumentation around the sample. Gas breakthrough occurred as outflow was recorded by the backpressure pump that corresponded with the changes in pressure. The data presented in this study shows that dynamic processes operate within the clay causing differing responses to be recorded on the monitoring instruments. The recorded response of the clay highlights the spatial and temporal development of permeability within the clay sample over the duration of the test

The current state of CCS: Ongoing research at the University of Cambridge with application to the UK policy framework

The Earth's climate is changing and the release of carbon dioxide (CO2) is recognised as the principal cause. To meet legally binding targets, UK GHG emissions need to be cut by at least 80% of the 1990 levels by 2050. With an increase in future fossil fuel use, Carbon Capture and Storage (CCS) is the only method of meeting these targets. Some key challenges face the deployment of CCS including cost, uncertainty of CCS deployment, the risks of long-term CO2 storage, public communication and scale. Research at the University of Cambridge is resolving these issues and assisting the deployment of CCS technology. The right regulatory framework also needs to be set so that the technology is commercially deployed. The current UK policy framework for CCS is outlined in this document and the immediate barriers to deployment are highlighted. The ongoing CCS research taking place primarily at the University of Cambridge is described. There are many steps that need to be taken if CCS deployment is to ultimately succeed; this document attempts to highlight these steps and address them.Carbon Capture Technologie

Bentonite homogenisation during the closure of void spaces

In a geological repository, the disposal of radioactive waste will result in the creation of engineering voids. Bentonite is commonly proposed as a sealing material as a result of its high swelling capacity. As the bentonite expands, the non-uniform development of porewater pressure and its coupling to total stress within the bentonite, may impair homogenisation. In this study we present results from five laboratory tests performed on sodium- and calcium-based bentonites to examine their swelling potential and capacity to homogenise over extreme bentonite-to-void ratios. Results demonstrate that even under these extreme ratios, the bentonite is able to swell and ultimately fill each void, creating a small swelling pressure. The swelling pressure development is spatially complex and time-consuming, and does not appear to be influenced by friction. Instead, it is characterised by plastic yielding of the clay with 70%–80% of the volume change associated with clay expansion adjacent to the void. This leads to heterogeneity illustrated by the presence of persistent differential stresses and the non-uniform distribution of moisture contents. Increases in the moisture content were measured but did not always correlate with the development of swelling pressure. This disequilibrium of the system is likely a reflection of the test durations and the slow evolution in the rates of change in swelling and porewater pressure beyond 130 days. Given the length of the experimental tests presented here, the time required to achieve full homogenisation of the clay is likely to be many years, if it occurs at all. Gravity segregation was also present in horizontal tests, further impairing clay homogenisation. However, as presented in this paper, it is possible to define functional relationships describing the bentonite swelling potential across engineering voids of differing size. This information will assist in establishing a safety case for bentonite usage in geological radioactive waste disposal

Closing repository void spaces using bentonite: does heat make a difference?

Bentonites are commonly proposed for use in the geological disposal of high heat generating radioactive wastes. Repository designs include bentonite as a buffer to occupy the void space around the waste canisters because of the favourable properties it can exhibit that enhance the isolation and containment functionality of the repository. Many repository concepts introduce small voids within the bentonite because the buffer is incorporated as individual bricks stacked around the waste canisters. These voids must be closed to prevent the persistence of high permeability pathways for fluids. As bentonite hydrates, it expands and can exert a considerable swelling pressure on the surrounding host rock. The bentonite also expands to fill the engineering cavities inherently present in the repository, but the non-uniform development of total stress and pore pressure could cause persistent material heterogeneities to occur. This is likely to be exacerbated by the thermal gradients existing between the hot waste and the temperature of the surrounding host rock in the early stages of repository post-closure. Whilst this is an area of ongoing research, the final extent of bentonite homogenisation within the repository and for how long property variations persist, is not well understood. In this study, four tests were conducted on pre-compacted, sodium-activated MX80 bentonite samples placed next to a water-filled engineering void, to examine the effect of elevated temperature on the development of swelling and swelling pressure as a function of sample size. The sample lengths were chosen to give small bentonite-to-void ratios, and to represent extremities of behaviour, such that an acceptable upper limit of void size might be established. The results demonstrated that even under extreme bentonite-to-void ratios, the bentonite was able to swell and completely fill the void space, exerting a small but measurable swelling pressure. Under the conditions of this study, the results have shown larger end-of-test swelling pressures and higher final dry densities along their entire length than shown in equivalent tests conducted at ambient temperature. In addition, the elevated temperature tests showed a rapid initial increase and then decrease in swelling pressure at the start of testing, approaching an asymptote in swelling pressure more quickly, whilst uptaking less water than in the ambient temperature case. This implied that heating the bentonite reduced the test duration by about 60%, which is most likely explained by a reduction in the viscosity of the test permeant at higher temperatures

Scoping study examining the behaviour of Boom Clay at disposal depths investigated in OPERA

The Onderzoeks Programma Eindberging Radioactief Afval (OPERA) is the third national research programme for the geological disposal of radioactive waste in the Netherlands, operating during the period 2011 to 2017. The rock types to host a geological disposal facility that are currently being considered in the Netherlands are salt and clay. Earlier Dutch work focussed mostly on salt, but the present programme OPERA is focused on a specific clay formation the Boom Clay. Previous studies have primarily focused on examining behaviour at the Belgium reference depth (~220m). The work presented in this study extends this knowledge-base to repository depths of potential interest in the Netherlands (~500m). In this report, results from a scoping study examining the hydromechanical properties of Boom Clay are presented, including investigations on consolidation, swelling, hydraulic, gas and deformation behaviour. These were performed on preserved core material retrieved from the HADES underground research laboratory, Belgium. Sections of core were then consolidated to a depth representative of the Netherlands. Permeability was sensitive to stress state and thermal load, though incremental changes in NaCl concentration had minimal impact. Hysteresis was observed in thermally induced changes in permeability. Gas entry was closely linked to the minimum principal stress component, with mass and volume changes of samples observed as a result of gas migration. Stress, porewater pressure and gas flow were integrally linked with pathways evolving temporally and spatially. A transition from brittle to ductile deformation was noted with increasing stress in both compression and shear. Boom Clay is both complex and anisotropic in its behaviour

Conformational dynamics of cohesin/Scc2 loading complex are regulated by Smc3 acetylation and ATP binding

The ring-shaped cohesin complex is a key player in sister chromatid cohesion, DNA repair, and gene transcription. The loading of cohesin to chromosomes requires the loader Scc2 and is regulated by ATP. This process is hindered by Smc3 acetylation. However, the molecular mechanism underlying this inhibition remains mysterious. Here, using Saccharomyces cerevisiae as a model system, we identify a novel configuration of Scc2 with pre-engaged cohesin and reveal dynamic conformations of the cohesin/Scc2 complex in the loading reaction. We demonstrate that Smc3 acetylation blocks the association of Scc2 with pre-engaged cohesin by impairing the interaction of Scc2 with Smc3’s head. Lastly, we show that ATP binding induces the cohesin/Scc2 complex to clamp DNA by promoting the interaction between Scc2 and Smc3 coiled coil. Our results illuminate a dynamic reconfiguration of the cohesin/Scc2 complex during loading and indicate how Smc3 acetylation and ATP regulate this process

Prevalence of intellectual disability among eight-year-old children from selected communities in the United States, 2014

Background: Children with intellectual disability (ID), characterized by impairments in intellectual functioning and adaptive behavior, benefit from early identification and access to services. Previous U.S. estimates used administrative data or parent report with limited information for demographic subgroups. Objective: Using empiric measures we examined ID characteristics among 8-year-old children and estimated prevalence by sex, race/ethnicity, geographic area and socioeconomic status (SES) area indicators. Methods: We analyzed data for 8-year-old children in 9 geographic areas participating in the 2014 Autism and Developmental Disabilities Monitoring Network. Children with ID were identified through record review of IQ test data. Census and American Community Survey data were used to estimate the denominator. Results: Overall, 11.8 per 1,000 (1.2%) had ID (IQ ≤ 70), of whom 39% (n = 998) also had autism spectrum disorder. Among children with ID, 1,823 had adaptive behavior test scores for which 64% were characterized as impaired. ID prevalence per 1,000 was 15.8 (95% confidence interval [95% CI], 15.0–16.5) among males and 7.7 (95% CI, 7.2–8.2) among females. ID prevalence was 17.7 (95% CI, 16.6–18.9) among children who were non-Hispanic black; 12.0 (95% CI, 11.1–13.0), among Hispanic; 8.6 (95% CI, 7.1–10.4), among non-Hispanic Asian; and 8.0 (95% CI, 7.5–8.6), among non-Hispanic white. Prevalence varied across geographic areas and was inversely associated with SES. Conclusions: ID prevalence varied substantively among racial, ethnic, geographic, and SES groups. Results can inform strategies to enhance identification and improve access to services particularly for children who are minorities or living in areas with lower SES

CONTAIN D11 : integrated final results and conclusions

Carbon capture and storage is a technology capable of reducing CO2 outputs on a large scale; the concept usually requires CO2 to be removed from post-combustion flue gases and sequestered in geological formations. Depleted gas fields constitute “the most important storage type for the UK” and will provide a large and important potential future offshore storage capacity (DECC, 2012). Over the last 4 years, the CONTAIN research project has focussed on the geomechanical behaviour of depleted hydrocarbon fields in response to injection with CO2, combining a modelling and experimental approach with the public perceptions of CCS into three work packages. The project has provided a better understanding of the hydromechanical impacts of depletion on caprocks and the effect of subsequent CO2 injection, in order to assist with the implementation of CCS in this type of reservoir. Work package 1 outlined a phenomenological approach to assessing possible deformation during operation. Focus was placed on rock mechanics and transport experiments on material from the geologies of target formations in the North Sea, providing information that could be incorporated into numerical simulations. Work package 2 expanded this understanding by considering fractured caprock. Numerical modelling was used to study the deformation of an initially intact caprock caused by the depletion of an underlying reservoir during oil extraction. Deformation and flow were geomechanically modelled in three dimensions using a fully coupled poroelastic model, incorporating discrete fractures and faults into the caprock. Work package 3 offered new and valuable insight on future public awareness campaigns aimed at gaining acceptance of CCS. Qualitative expert interviews have been used, a CCS expert survey and a public survey across four countries to gain an understanding of perceptions of CCS risks and benefits, and has allowed for comparison of views on CCS between experts and public. In addition, the work package has explored the impact of different message framings on CCS attitudes. The findings of each work package are summarised in this report, with each work package represented by a report chapter. A synthesis of the findings and discussion of the work as a whole follows

The influence of T cell development on pathogen specificity and autoreactivity

T cells orchestrate adaptive immune responses upon activation. T cell activation requires sufficiently strong binding of T cell receptors on their surface to short peptides derived from foreign proteins bound to protein products of the major histocompatibility (MHC) gene products, which are displayed on the surface of antigen presenting cells. T cells can also interact with peptide-MHC complexes, where the peptide is derived from host (self) proteins. A diverse repertoire of relatively self-tolerant T cell receptors is selected in the thymus. We study a model, computationally and analytically, to describe how thymic selection shapes the repertoire of T cell receptors, such that T cell receptor recognition of pathogenic peptides is both specific and degenerate. We also discuss the escape probability of autoimmune T cells from the thymus.Comment: 12 pages, 7 figure