Efficiency of a borehole seal by means of pre-compacted bentonite blocks

The backfilling and sealing of shafts and galleries is an essential part of the design of underground repositories for high-level radioactive waste. Part of the EC funded project RESEAL studied the feasibility of sealing off a borehole in plastic Boom Clay by means of pre-compacted bentonite blocks. Two bentonites, namely the FoCa and Serrata clay, have been used. Based on laboratory tests, the bentonite blocks had an initial dry density of about 1.8 g/cm3 to obtain a swelling pressure of about 4.4 MPa, corresponding to the in situ lithostatic stress, at full saturation. The set-up was equipped with several sensors to follow-up the behaviour of the seal and the surrounding host rock during hydration. Full saturation was reached after five months and was mainly reached by natural hydration. Swelling pressure was lower than originally foreseen due to the slow reconsolidation of the host rock. Later on, the efficiency of the seal with respect to water, gas and radionuclide migration was tested. The in situ measured permeability of the seals was about 5 × 10-13 m/s. A gas breakthrough experiment did not show any preferential gas migration through the seal. No evidences of a preferential pathway could be detected from 125I tracer test result

RESEAL II: a large-scale in situ demonstration for repository sealing in an argillaceous host rock: phase II

Final ReportPreprin

Mycobacterium tuberculosis volatiles for diagnosis of tuberculosis by Cricetomys rats.

Tuberculosis (TB) diagnosis in regions with limited resources depends on microscopy with insufficient sensitivity. Rapid diagnostic tests of low cost but high sensitivity and specificity are needed for better point-of-care management of TB. Trained African giant pouched rats (Cricetomys sp.) can diagnose pulmonary TB in sputum but the relevant Mycobacterium tuberculosis (Mtb)-specific volatile compounds remain unknown. We investigated the odour volatiles of Mtb detected by rats in reference Mtb, nontuberculous mycobacteria, Nocardia sp., Streptomyces sp., Rhodococcus sp., and other respiratory tract microorganisms spiked into Mtb-negative sputum. Thirteen compounds were specific to Mtb and 13 were shared with other microorganisms. Rats discriminated a blend of Mtb-specific volatiles from individual, and blends of shared, compounds (P = 0.001). The rats' sensitivity for typical TB-positive sputa was 99.15% with 92.23% specificity and 93.14% accuracy. These findings underline the potential of trained Cricetomys rats for rapid TB diagnosis in resource-limited settings, particularly in Africa where Cricetomys rats occur widely and the burden of TB is high

Benchmarking as Key Element of Confidence Building in Safety Assessments for Radioactive Waste Disposal

Abstract: In safety cases for disposal of radioactive waste, currently in development in several countries worldwide, verification of the codes applied for assessment of the long-term repository safety is typically one of the quality assurance requirements demanded by regulatory bodies. Code verification can be done by performing benchmark calculations between two numerical codes. In this paper, an internationally organized benchmark exercise is presented, in which the intercomparison was carried out for a selection of key radionuclides, among which an actinide chain. Besides a strict comparison of the calculated output, both applied codes were evaluated on the feasibility of implementation of processes, especially focusing on realism in the source term formulation. The examples presented in this paper show that COMSOL Multiphysics can be a valuable complementary modelling tool, adequately representing most of the processes of importance in a radioactive waste repository, for varying and even extreme timescales

The volatiles of pathogenic and nonpathogenic mycobacteria and related bacteria

Beilstein Journal of Organic Chemistry. 2012, 8: 290–299.Volatiles released by pathogenic and nonpathogenic mycobacteria, as well as by mycobacteria-related Nocardia spp., were analyzed. Bacteria were cultivated on solid and in liquid media, and headspace samples were collected at various times during the bacterial lifecycle to elucidate the conditions giving optimal volatile emission. Emitted volatiles were collected by using closedloop stripping analysis (CLSA) and were analyzed by gas-chromatography–mass-spectrometry. A wide range of compounds was produced, although the absolute amount was small. Nevertheless, characteristic bouquets of compounds could be identified. Predominantly aromatic compounds and fatty-acid derivatives were released by pathogenic/nonpathogenic mycobacteria, while the two Nocardia spp. (N. asteroides and N. africana) emitted the sesquiterpene aciphyllene. Pathogenic Mycobacterium tuberculosis strains grown on agar plates produced a distinct bouquet with different volatiles, while liquid cultures produce less compounds but sometimes an earlier onset of volatile production because of their steeper growth curves under this conditions. This behavior differentiates M. tuberculosis from other mycobacteria, which generally produced fewer compounds in seemingly lower amounts. Knowledge of the production of volatiles by M. tuberculosis can facilitate the rational design of alternative and faster diagnostic measures for tuberculosis

Consequences of the thermal transient on the evolution of the damaged zone around a repository for heat-emitting high-level radioactive waste in a clay formation: a performance assessment perspective

International audienceA proper evaluation of the perturbations of the host rock induced by the excavation and the emplacement of exothermic wastes is essential for the assessment of the long-term safety of high-level radioactive waste disposals in clay formations. The impact of the periodthermal transient on the evolution of the damaged zone (DZ) has been explored in a recent European Commission project called TIMODAZ (Thermal Impact on the Damaged Zone Around a Radioactive Waste Disposal in Clay Host Rocks, 2006 — 2010). This paper integrates the scientific results of the TIMODAZ project from a performance assessment (PA) point of view, showing how these results support and justify key PA assumptions and the values of PA model parameters. This paper also contextualises the significance of the thermal impact on the DZ from a safety case perspective, highlighting how the project outcomes result into an improved understanding of the Thermo-Hydro-Mechanical behaviour of the host clays.The results obtained in the TIMODAZ project strengthen the assessment basis of the safety evaluation of the current repository designs. There was no evidence throughout the TIMODAZ experimental observations of a temperature-induced additional opening of fractures or of a significant permeability increase of the DZ. Instead, thermal-induced plasticity, swelling and creep behaviour seem to be beneficial to the sealing of fractures and to the recovery of a very low permeability in the DZ, close to that of an undisturbed clay host rock. Results from the TIMODAZ project indicate that the favourable properties of the clay host rock that guarantee the effectiveness of the safety functions of the repository system are expected to be maintained after the heating-cooling cycle. Hence, the basic assumptions usually made in PA calculations so far are expected to remain valid and the performance of the system should not be affected in a negative way by the thermal evolution of the DZ around a radioactive waste repository in clay host rock