Development of flow and settling correlations for the transport of nuclear slurries in partially-filled pipes

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The transport of nuclear slurry through pipelines is an important, but currently poorly understood, physical process which is key to the safe and efficient clean out and decommissioning of pipelines within nuclear facilities. Partially-filled pipe flows, often gravity-driven, are present in a range of industrial applications and are often used to transport fluids with sediments or particulates, for example sewage and waste-water, as well as slurries in nuclear or mining operations. The partially-filled pipe geometry contains features of a full pipe and an open channel flow. However, in comparison to these flows, the scientific literature remains under-developed for partially-filled pipe flow with work often restricted to studies of water. When transporting fluids that contain solid particles, such as in slurry transport applications, there are two additional important considerations. Firstly, the fluids (now two-phase and non-Newtonian) do not follow the traditional flow correlations that were derived for water flows. And secondly, understanding the settling behaviour of the suspended particles (and its dependence of flow conditions) is critically important to avoid deposition and blockages, which are potentially disruptive and costly in applications that involve the transport of nuclear waste. The CDT project aims to address the following important challenges for partially-filled pipe flow of slurries: (1) an improved physical understanding of the flow, (2) the development and validation of accurate and reliable flow correlations, and (3) predicting transport behaviour (i.e. the likelihood of solids settling). This will be done through a combination of detailed experimental measurements of the flow (to help with physical understanding) and full-scale testing (for the empirical development and testing of correlations and sedimentation). The working fluids will have characteristics that are considered representative of nuclear waste slurries. As such, the work will support operations within nuclear plants and associated partially-filled pipelines during passive transfer operations. In these applications it is expected that fluids with less favourable transport properties will become prevalent in the future, as maximising solids loading minimises the quantity of waste that needs to be stored. Aim: To advance the physical understanding of the flow of complex fluids in partially-filled pipes in order to inform the safe and efficient clean-out of nuclear slurries through the development of transport correlations to characterise both the flow and the settling properties. Objectives: 1. To fully characterise, using laser diagnostics, the flow of model complex fluids in turbulent flow in a partially-filled pipe (at UoL). 2. To investigate the behaviour of non-active test materials (slurries) in a full-scale test rig (at NNL Workington). 3. To use the information from objectives 1 and 2 to develop transport correlations (for both flow and sedimentation) that can be used to design safe and efficient pipeline operations in nuclear facilities. Methodology and Approach: To achieve objective 1, the experiments will be conducted using the UoL Very Large-Scale Pipe Flow (VLSPF) facility. Model polymeric solutions (e.g. Carbopol and xanthan gum) will be used which imitate the key rheological properties of slurries (yield stress and shear-thinning). Unlike real slurries they will be transparent to provide optical access for high-speed stereoscopic particle image velocimetry measurements providing time-resolved, three-component velocity measurements in the cross-sectional plane. Reynolds numbers (Re) will be fully turbulent (around Re=104) and fill-heights ranging from 30% to 80% will be investigated, covering the range of primary interest to the nuclear industry. The principles of these experiment have been established by the supervisors of the CDT project for Newtonian fluids and will now be applied to the non-Newtonian