Modelling Particle Transport from Decommissioned and Operational Pipelines Case Study
Client: British Nuclear Group Sellafield Limited & NNC Limited
The Challenge
The clients were involved in decommissioning an effluent discharge pipeline. The plan was to cut the pipeline into small sections and then remove them to a barge for transfer and disposal at the Low Level Waste Repository at Drigg. In cutting the pipeline, there was concern that contaminated sediment within the pipeline would become re-suspended within the water column and could potentially be transported to local beaches. The clients needed a modelling tool to predict where sediment might be dispersed during pipeline cutting operation under a variety of weather and tidal conditions.
The Solution
Using Mike21 a simple 2D hydrodynamic model for the local coastal area was set up to investigate the Lagrangian transport and movement of particles from the pipeline cutting site during a range of tidal and weather conditions. This resulted in an atlas of potential impact scenarios for local beaches and a tool the operators could use to determine the most appropriate cutting regime, which would have the least impact for particle re-suspension and deposition on local beaches.
Using the initial hydrodynamic model set-up, a more complex particle-tracking model was then derived to investigate the probability of particle deposition on the local beaches for historic discharges from an operational pipeline. The results of this work were used to design a focused sampling campaign for the investigation of near-field deposition of particulate material that could be discharged from the pipeline.
This model has also applied to:
• Investigating the impact of extreme storm events on the accidental lose of pipeline sections from the cutting barge;
• Probability mapping for hot particle finds on Cumbrian beaches;
• Emergency discharge modelling of particles from operational pipelines;
• Use of biocidal chemicals to remove bio-films and associated particulate during pipeline cleaning operations; and
• Human and biota dose assessment for particulate discharges.
The Benefits
The client was able to use the particle-tracking atlas, to determine the best times for pipeline cutting operations during specific weather conditions, which would result in lowest probability for beach impacts of re-suspended particles. The model developed for this work is suitable for investigation of both historic and emergency discharges from historic and operational pipelines.