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Transport of radioactive waste along the Sellafield shoreline: climate change impact and mitigation strategies through nature based solutions

About This PhD Project

Project Description

This proposal aims to build on previous collaboration across the Department of Geography and Planning and NNL on the ARCoES project. The proposed research will take existing assessments of flood risk to the next level by projecting coastal change due to erosion and sedimentation, thus providing new knowledge on the potential physical remobilization and transport of sediments contaminated by radioactive waste.

Numerical modelling will be applied to examine the relative significance of waves, storms and sea-level rise on coastal erosion and sediment transport for the wider Sellafield shoreline and adjacent waters. The fate of sediments labelled with Sellafield radionuclides will also be investigated to assess the effects of remobilized legacy waste on the environment. The numerical modelling environment will provide a tool for assessing the effectiveness of ‘nature-based’ interventions at the coast that aim to mitigate erosion and flood risk, thus providing a tool for stakeholders to explore different management options.

The student will spend time at NNL to understand the environmental and policy contexts within which decisions regarding the management and storage of nuclear waste are made. This will involve working alongside NNL colleague to become acquainted with the focus and demands of their research and assessment.

Hypothesis 1: Increasing storms occurrence will mostly affect the remobilization of sediments deposited on mud flats. Sea level rise will mostly affect the remobilization of contaminated material at the shoreline.

Aim 1: To identify the relative contribution of storms and sea level rise to the dispersal of legacy waste.

Aim 2: To identify uncertainties in the risk associated to the dispersal of contaminants for various climate change scenarios.

Objectives: Setup of numerical model simulating the hydrodynamic of the wider Sellafield shoreline and adjacent waters and accounting for sediment transport, vegetation processes, and different decay rates for radioactive material. Model calibration.
Ensemble simulations to test the influence of storms and sea level rise on the remobilization of legacy waste. Tracking of transport patterns and destinations along the coastline of contaminated tracers with different decays rate.

Methodology and Approach

We will use the fluid dynamics package Delft3D. Delft3D is a numerical model composed of a number of integrated modules. Together, they allow the simulation of hydrodynamic flow, sediment transport and related bed evolution, short-wave generation and propagation, and the modelling of water quality parameters. The Delft3D-FLOW module is able to solve the unsteady shallow-water equations in two and three dimensions. The sediment transport and morphology modules account for bed and suspended load transport of cohesive and non-cohesive sediments and for the exchange of sediments between the bed and the flow.

The numerical model will be adapted to include different decay rates to account for different radioactive elements.

We will conduct ensemble simulations to evaluate the contribution of different storms intensities and frequency and of various sea level rise scenarios to the remobilization of mudflat and shoreline sediments.

Field measurements and coring will be done for the evaluation of the spatial distribution of contaminants depending on the relative exposure to wind waves, and tidal currents.

Hypothesis 2: Coastal erosion will significantly increase the dispersion of radioactive material at a large scale. The contribution of coastal erosion to the dispersion of radioactive material will be spatially variable.

Aim 1: To identify the contribution of the erosion of different stretches of shoreline to the remobilization of legacy waste.

Aim 2: To inform decision makers about those locations whose protection from erosion should be prioritized to minimize the large scale remobilization of radioactive material.

Objectives: To identify the destination and preferential transport patters of legacy waste coming from sediments eroded along different portions of the Sellafield shoreline.
To identify the most dangerous sites whose erosion might significantly increase the export of legacy waste at distal locations

Methodology and Approach: We will utilize the numerical model mentioned above to simulate different erosion scenarios. We will use remote sensing and aerial images to assess the current state of vulnerability of the area to coastal erosion. Sediments and lab analysis will be done to evaluate the uncertainty of modelling results.

Hypothesis 3: “Nature based” solution include the use of salt-marshes and vegetated surfaces to protect the coastline. Nature-based interventions are effective solutions to prevent the remobilization of legacy waste along the coastal zone.

Aim 1: To provide stakeholders with the knowledge and tools necessary to make informed decisions on the use of nature based solutions as a management option to prevent the remobilization of contaminated material.

Aim 2: To find optimum vegetation spatial distribution and vegetation properties to maximize the trapping of contaminants.

Objectives: To test the direct impact of different vegetation spatial distributions and vegetation properties (e.g. stems height, density and flexibility) on the dispersal of legacy waste.
To test the indirect impact of vegetation on the transport of legacy waste through decrease in the risk of flooding and erosion.

General methodology and approach:
Building on the numerical model mentioned in the previous point, we will conduct ensemble simulations to account for the influence of vegetation properties and distribution on the trapping of contaminants.

Student Specific Training

The student will undertake a 6-month secondment with NNL. During this time they will receive training in the regulatory process and the demands of data (including the handling of variability and uncertainty) in providing the evidence base upon which decisions are based. The student will be embedded with the NNL team and will be exposed to all aspects of work in the nuclear waste regulation and management sector. They will be trained in the analysis of risk and uncertainty, and will experience direct engagement with a wide range of stakeholders.

Training at the University will include the acquisition of data from a variety of sources on topographic/bathymetric data, coastal hydrodynamics, sediment grain size and suspended concentration data, and radionuclide geochemistry in the environment.
Training will be assessed through production of two short written reports (one at half time and one at the end), one poster presentation, and one short oral presentation.


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