Development of nuclear emergency consequence assessment models for estuaries and coastal seas

Abstract

This work presents the coupled development of hydrodynamic, dispersion and dose assessment models to support nuclear emergency response consequence assessment. High resolution 2D depth averaged hydrodynamic models incorporating wetting and drying were developed for the Tamar estuary and Upper Firth of Clyde using the Thetis coastal ocean model and validation against available tidal elevation and velocity data showed very good agreement. To facilitate their use in emergencies, harmonic analysis was conducted to enable the rapid reconstruction of velocity and elevation fields. It was determined by sensitivity analysis that the loss of certain high frequency flow features in the reconstructed flow was significant to particle dispersion predictions. The novel application of Dynamic Mode Decomposition techniques was trialled to resolve these issues; however, training stability and the loss of temporal awareness using this technique were found to be limiting in its application. A 3D Lagrangian particle model has been developed over a base particle trajectory solver to enable the assessment of radioactive transport, including wind forcing, management of radioactive decay and kinetic exchange of radioactivity between water and sediment phases. A number of validation cases for the dispersion model are presented compared against a tracer study. A proof of concept directly coupled atmospheric and marine dispersion model was developed and demonstrated. Testing identified that such an approach may not be suitable for small domains due to the numerical limitations of Lagrangian simulations and representative exchange lengths between phases. Dose assessment tools have been developed, including the novel development of a full-field gamma shine assessment tool incorporating buildup and air attenuation. Some considerations for the best interpretation and communication of dose results in emergencies have also been provided. Sensitivity analysis of the combined model system has resulted in novel insights including the insensitivity of immediate response phase models to sediment dynamics.