Structural and stochastical modelling of possible contaminant pathways below nuclear installations

Structural and stochastical modelling of possible contaminant pathways below nuclear installations 1Richard Haslam, 1Stuart Clarke, 1Peter Styles & 2Clive Auton 1Earth Sciences and Geography, School of Physical and Geographical Sciences, Keele University, Keele, Staffordshire, ST5 5BG, United Kingdom 2British Geological Survey, Murchison House, West Mains Road, Edinburgh, EH9 3LA, United Kingdom Dounreay Nuclear Power station is situated on the northern coast of Caithness, Scotland on complex normally faulted Devonian sedimentary rocks with a thin, intermittent cover of superficial deposits, predominantly comprising glacial tills of varying provenance. Bedrock structure, fracture patterns and the relationships between bedrock and the superficial deposits have a considerable impact on the transmissivity of any possible contaminants. Consequently, an understanding of the bedrock-superficial boundary and how fractures and faults influence and control the transport of fluids are a key concern. The principal aims of this work are to gain an understanding of the processes and controls on fluid flow pathways within such complex geological terrains, and develop methods of stochastatically evaluating likely contamination transport within the subsurface. This work focuses on the near-surface bedrock geology and superficial deposits. The near surface geology of the Dounreay site comprises cyclic sequences of lacustrine rocks; their cyclicity has enabled a reference stratigraphy to be created and correlated across the site. This stratigraphy, the coastal exposures and the extensive amount of borehole data available, provide a unique opportunity to construct and constrain a three-dimensional bedrock model; the interpretive element of which has been robustly test using structural restoration techniques. In the bedrock of Dounreay, three principal fracture sets have been identified. The first two sets of fractures are approximately orthogonal, trending north-northwest and west-southwest respectively; they represent the regional fracture set. It is proposed that these fractures where produced during loading and burial of the Devonian sediments. The final fracture set is predominantly parallel to bedding of the laminated sediments; it gives the Caithness Flagstones their ‘flaggy’ nature. The regional fracture sets are approximately constant over the site area and vary little with depth, whereas the bedding parallel fracture set shows a marked decrease in the number of fractures per meter with depth, on a logarithmic trend. This relationship is also visible in the Rock Quality Designation (RQD) values and hydraulic conductivity data from boreholes. It follows that the bedding parallel fractures are the major controlling factor of flow in the shallow subsurface and that the RQD values can be used as a proxy for fracture density. RQD values are a commonly collected during borehole drilling and the relationship between hydraulic conductivity and RQD values offer a method for stochastically populating a 3D geological model with hydraulic conductivity values. Current geological interpretations of the superficial deposits are based primarily on their genesis. Consequently, subdivisions based on the origin of the sediments do not relate directly to their fluid transmissivity. The superficial deposits generally have a very low hydraulic conductivity, compared to that of the bedrock, impeding the flow of water from the surface to the groundwater system at depth. A combination of driller’s description and comparisons of grain-size distribution enables subdivisions of the Quaternary strata to be established based on their properties instead of their genesis. These properties can then be stochastically interpolated throughout the 3D geological model. This work provides a framework from which likely contamination scenarios can be modelled, both in the well-constrained subsurface of Dounreay, and at other nuclear installations where the nature of the subsurface is less well constrained

Potential migration of buoyant LNAPL from Intermediate Level Waste (ILW) emplaced in a geological disposal facility (GDF) for UK radioactive waste

A safety case for the disposal of Intermediate Level (radioactive) Waste (ILW) in a deep geological disposal facility (GDF) requires consideration of the potential for waste-derived light non-aqueous phase liquid (LNAPL) to migrate under positive buoyancy from disposed waste packages. Were entrainment of waste-derived radionuclides in LNAPL to occur, such migration could result in a shorter overall travel time to environmental or human receptors than radionuclide migration solely associated with the movement of groundwater. This paper provides a contribution to the assessment of this issue through multiphase-flow numerical modelling underpinned by a review of the UK's ILW inventory and literature to define the nature of the associated ILW LNAPL source term. Examination has been at the waste package-local GDF environment scale to determine whether proposed disposal of ILW would lead to significant likelihood of LNAPL migration, both from waste packages and from a GDF vault into the local host rock. Our review and numerical modelling support the proposition that the release of a discrete free phase LNAPL from ILW would not present a significant challenge to the safety case even with conservative approximations. 'As-disposed' LNAPL emplaced with the waste is not expected to pose a significant issue. 'Secondary LNAPL' generated in situ within the disposed ILW, arising from the decomposition of plastics, in particular PVC (polyvinyl chloride), could form the predominant LNAPL source term. Released high molecular weight phthalate plasticizers are judged to be the primary LNAPL potentially generated. These are expected to have low buoyancy-based mobility due to their very low density contrast with water and high viscosity. Due to the inherent uncertainties, significant conservatisms were adopted within the numerical modelling approach, including: the simulation of a deliberately high organic material - PVC content wastestream (2D03) within an annular grouted waste package vulnerable to LNAPL release; upper bound inventory estimates of LNAPLs; incorporating the lack of any hydraulic resistance of the package vent; the lack of any degradation of dissolved LNAPL; and, significantly, the small threshold displacement pressure assumed at which LNAPL is able to enter initially water-saturated pores. Initial scoping calculations on the latter suggested that the rate at which LNAPL is able to migrate from a waste package is likely to be very small and insignificant for likely representative displacement pressure data: this represents a key result. Adopting a conservative displacement pressure, however, allowed the effect of other features and processes in the system to be assessed. High LNAPL viscosity together with low density contrast with water reduces LNAPL migration potential. Migration to the host rock is less likely if waste package vent fluxes are small, solubility limits are high and path lengths through the backfill are short. The capacity of the system to dissolve all of the free LNAPL will, however, depend on groundwater availability. Even with the conservatisms invoked, the overall conclusion of model simulations of intact and compromised (cracked or corroded) waste packages, for a range of realistic ILW LNAPL scenarios, is that it is unlikely that significant LNAPL would be able to migrate from the waste packages and even more unlikely it would be sufficiently persistent to reach the host rock immediately beyond the GDF

Microbial impacts on 99mTc migration through sandstone under highly alkaline conditions relevant to radioactive waste disposal

Geological disposal of intermediate level radioactive waste in the UK is planned to involve the use of cementitious materials, facilitating the formation of an alkali-disturbed zone within the host rock. The biogeochemical processes that will occur in this environment, and the extent to which they will impact on radionuclide migration, are currently poorly understood. This study investigates the impact of biogeochemical processes on the mobility of the radionuclide technetium, in column experiments designed to be representative of aspects of the alkali-disturbed zone. Results indicate that microbial processes were capable of inhibiting 99mTc migration through columns, and X-ray radiography demonstrated that extensive physical changes had occurred to the material within columns where microbiological activity had been stimulated. The utilisation of organic acids under highly alkaline conditions, generating H2 and CO2, may represent a mechanism by which microbial processes may alter the hydraulic conductivity of a geological environment. Column sediments were dominated by obligately alkaliphilic H2-oxidising bacteria, suggesting that the enrichment of these bacteria may have occurred as a result of H2 generation during organic acid metabolism. The results from these experiments show that microorganisms are able to carry out a number of processes under highly alkaline conditions that could potentially impact on the properties of the host rock surrounding a geological disposal facility for intermediate level radioactive waste

Об уровнях готовности технологий и применении Калькулятора УГТ для их оценивания

The article presents the issues of qualitative and quantitative assessment of readiness for research and development in the field of aviation technology.В статье рассматриваются вопросы качественной и количественной оценки готовности технологий в контексте управления процессом исследований и разработок в области авиации с использованием метода системной интеграции технологий

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

The challenges of nuclear waste management from a life cycle perspective

As nuclear industry grows and expands, the yearly amount of waste produced increases and it adds to the large quantity of nuclear wastes generated, and not yet disposed, in the last 50 years from existing plants. Consequently, the development of an international agreed policy to manage nuclear wastes is key to support such growth. Many countries, such as USA, Sweden, Canada, have opted for a direct disposal of Spent Nuclear Fuel (SNF) (Open Cycle); whilst others, such as the UK, Japan and France, have preferred reprocessing SNF (Closed Cycle). Other countries are yet to take a final decision (e.g. Spain, Argentina) and wait for future development in nuclear R&D. Economically an open cycle is much more advantageous than a closed cycle, but what about the environmental concerns? Life Cycle Assessment (LCA) approach may come to help to the Nuclear Industry as a means of evaluating and comparing alternative strategies on the basis of their environmental performances. Therefore, LCA studies carried in the nuclear field may be used to support the decision-making process when choosing between different Nuclear Fuel Cycles or Nuclear Waste Management strategies. Furthermore, the results of such LCA studies might serve to improve public attitudes towards the Nuclear Energy, provided that they are used in an open and transparent way. Up to the present very few LCA studies have been carried out in the nuclear context: the main cause for this shortage is the lack of a standard and consistent approach for the inclusion of ionising radiation within the Life Cycle Impact Assessment (LCIA) step. In that regard, not one reported LCA study has considered the impacts of radionuclide releases from operation of nuclear reactors nor from management of nuclear waste. The present study addresses this issue by proposing a novel approach for the assessment of the impact of radionuclide releases both as direct discharges (i.e. liquid and aerial) and from management of solid wastes in a Geological Disposal Facility. The approach is based on a risk methodology which relies on two generic models, publicly available, developed by the IAEA (International Atomic Energy Agency) and the NDA (Nuclear Decommissioning Authority). The proposed methodology will then be applied to the UK Nuclear Waste Management process for a complete LCA study where, along with ionising radiation impact, several other environmental impact factors will be evaluated. Real data, collated on field from UK nuclear facilities, will be used for the foreground system. The management of the amount of AGR/LWR fuel assemblies used to produce 1 TJ of electricity has been chosen as functional unit. Results of the study will show the overall environmental footprint of the UK reprocessing step of spent nuclear fuel both in terms of radiological and non-radiological impacts. Preliminary results will be presented at the conference

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

Making Distant Futures: Implementing Geological Disposal of Nuclear Waste in the UK and Finland

This thesis explores the making of distant futures through two nuclear waste disposal projects. Geological disposal of nuclear waste (GD) has enjoyed a technopolitical consensus for decades as the best available method for the long-term management of hazardous radioactive material, yet, to date, no geological repository facilities exist anywhere in the world. These ‘disposal facilities’ are expected to seclude nuclear waste from the environment for up to one million years, raising challenges for technical knowledge production, policy implementation and public expectations. Examining the proposed implementation of GD in the UK and Finland, this thesis focuses on the ways in which the management of nuclear waste is crafted in the present day and projected on, million of years into the future, as necessitated by the waste half- lives and as demanded by regulatory practice. In exploring these two national contexts, the thesis traces how knowledge is made about distant futures that exist beyond contemporary knowledge making capacity. As a contribution to limited ethnographic discussion on nuclear waste matters, the making of distant nuclear futures is examined in spaces that have been overlooked in sociological literatures on GD e.g. materials science laboratories. The thesis draws from actor-network approaches, sociology of time and feminist STS literature to develop a ‘comparative-conversationalist’ framework. This approach enabled the comparison of wildly different cases by bringing them into conversation rather than direct comparison with each other. Based on participant-observations in two university research labs; interviews with civil servants, university researchers, technical consultants, regulators and industry representatives; and documentary analysis, I trace practices through which the future is made safe, and, nuclear wastes crafted as manageable. The thesis will demonstrate how future making around nuclear waste varies over time and space. I propose that, because of the very distant future that GD concerns, we should discuss the safety aspects of GD and the ability of disposal facilities to contain wastes as ‘real unrealised present possibilities’. Towards this, I develop the notion of contain-ability. Contain-ability directs attention towards the relational makings of safety in the present, and the uncertainty of containment in the very distant future. It underlines safety as an emergent feature rather than an inherent property of disposal concepts and facilities achieved by engineers. 3 Overall then, the thesis demonstrates that a distant nuclear future is a crafted through situated makings that depend on available sociotechnical conditions, including: geological environments; the scale and complexity of nuclear industries and waste inventories; available financial resources and cultural reserves; and imaginations of wastes, nuclear futures and pasts. The successes and failures of policies for the implementation of GD cannot be construed simply through public acceptance or opposition arguments and more attention needs to be directed to the contingencies of scientific knowledge production and future making

An alternative approach to railway asset management value analysis: application to a UK railway corridor

Railway networks are complex systems and the management of such systems is a challenging task for railway asset managers. It is their responsibility to ensure that the network delivers the highest level of performance for all stakeholders, whilst adhering to strict safety regulations and financial constraints. Historically, Reliability, Availability, Maintainability and Safety (RAMS) analysis has been used to assess the performance and safety of railway networks, nonetheless there is a lack of consistency in approaches across the industry, with analysis often influenced by the key stakeholders at the time. This research demonstrates an application of an Extended RAMS framework on the UK Railway Network, the Extended RAMS frameworks aims to consolidate various extensions to the traditional RAMS approach in to a single universal approach, which is beneficial to all stakeholders. This paper explores the data currently available within the rail industry and how it can be used to assess the ten metrics within the framework. The final part of the paper explores how the parameters within the ExRAMS framework can be used as the bases of a value analysis, which can be used to assist with asset management decisions