Bacterial Diversity in the Hyperalkaline Allas Springs (Cyprus), a Natural Analogue for Cementitious Radioactive Waste Repository

The biogeochemical gradients that will develop across the interface between a highly alkaline cementitious geological disposal facility for intermediate level radioactive waste and the geosphere are poorly understood. In addition, there is a paucity of information about the microorganisms that may populate these environments and their role in biomineralization, gas consumption and generation, metal cycling, and on radionuclide speciation and solubility. In this study, we investigated the phylogenetic diversity of indigenous microbial communities and their potential for alkaline metal reduction in samples collected from a natural analogue for cementitious radioactive waste repositories, the hyperalkaline Allas Springs (pH up to 11.9), Troodos Mountains, Cyprus. The site is situated within an ophiolitic complex of ultrabasic rocks that are undergoing active low-temperature serpentinization, which results in hyperalkaline conditions. 16S rRNA cloning and sequencing showed that phylogenetically diverse microbial communities exist in this natural high pH environment, including Hydrogenophaga species. This indicates that alkali-tolerant hydrogen-oxidizing microorganisms could potentially colonize an alkaline geological repository, which is predicted to be rich in molecular H2, as a result of processes including steel corrosion and cellulose biodegradation within the wastes. Moreover, microbial metal reduction was confirmed at alkaline pH in this study by enrichment microcosms and by pure cultures of bacterial isolates affiliated to the Paenibacillus and Alkaliphilus genera. Overall, these data show that a diverse range of microbiological processes can occur in high pH environments, consistent with those expected during the geodisposal of intermediate level waste. Many of these, including gas metabolism and metal reduction, have clear implications for the long-term geological disposal of radioactive waste

Blast furnace slag-Mg(OH)(2) cements activated by sodium carbonate

The structural evolution of a sodium carbonate activated slag cement blended with varying quantities of Mg(OH)2 was assessed. The main reaction products of these blended cements were a calcium-sodium aluminosilicate hydrate type gel, an Mg-Al layered double hydroxide with a hydrotalcite type structure, calcite, and a hydrous calcium aluminate phase (tentatively identified as a carbonate-containing AFm structure), in proportions which varied with Na2O/slag ratios. Particles of Mg(OH)2 do not chemically react within these cements. Instead, Mg(OH)2 acts as a filler accelerating the hardening of sodium carbonate activated slags. Although increased Mg(OH)2 replacement reduced the compressive strength of these cements, pastes with 50 wt% Mg(OH)2 still reached strengths of ∼21 MPa. The chemical and mechanical characteristics of sodium carbonate activated slag/Mg(OH)2 cements makes them a potentially suitable matrix for encapsulation of high loadings of Mg(OH)2-bearing wastes such as Magnox sludge

Cost overruns – helping to define what they really mean

Civil engineers are often in the firing line for alleged cost overruns, particularly on major publicly funded infrastructure projects. This usually occurs when the final cost of a project is simply compared with the original estimate, even though this was published a long time ago, in different circumstances and for a quite different project to the one carried out. This paper proposes a systematic approach to ensure that cost overruns, should they occur, are more accurately defined in terms of when the initial and end costs are assessed, from which point of view, at which project stage, and including scope changes and financial assumptions. The paper refers to the UK’s £163 billion nuclear decommissioning programme

The participatory turn in radioactive waste management:Deliberation and the social-technical divide

National policies for long-term management of radioactive waste have for decades been driven by technical experts. The pursuit of these technocratic policies led in many countries to conflict with affected communities. Since the late 1990s, however, there has been a turn to more participatory approaches. This participatory turn reflects widespread acknowledgement in the discourse of policy actors and implementing organisations of the importance of social aspects of radioactive waste management and the need to involve citizens and their representatives in the process. This appears to be an important move towards democratisation of this particular field of technological decision making but, despite these developments, technical aspects are still most often brought into the public arena only after technical experts have defined the ‘problem’ and decided upon a ‘solution’. This maintains a notional divide between the treatment of technical and social aspects of radioactive waste management and raises pressing questions about the kind of choice affected communities are given if they are not able to debate fully the technical options. The article aims to contribute to better understanding and addressing this situation by exploring the complex entanglement of the social and the technical in radioactive waste management policy and practice, analysing the contingent configurations that emerge as sociotechnical combinations. Drawing upon empirical examples from four countries that have taken the participatory turn - Belgium, Slovenia, Sweden and the United Kingdom – the article describes the different ways in which sociotechnical combinations have been constructed, and discusses their implications for future practice