Fugitive Emission Rates Using Sampling and CFD
Project: The determination of fugitive emission rates using high volume size separated sampling and CFD modelling
Client: Sellafield Limited, Sellafield
The Challenge
The Environment Agency (EA) required as part of the Sellafield Authorisation for the Disposal of Radioactive Waste, that Sellafield Ltd. developed and implemented monitoring arrangements to measure the discharges of particulate radionuclides from the surfaces of open ponds.
The Solution
- WSC developed a new method for estimating these emission rates based on measurements of upwind and downwind air concentrations and numerical modelling of atmospheric dispersion. The measurement collection methods, time resolution of the sampling and modelling methodologies represented significant improvementsover those previously implemented.
- A Computational Fluid Dynamics (CFD) model was applied to resolve the complex flows and dispersion that affect releases from the ponds. Predictions of wind flows and turbulence over the Sellafield site were validated using meteorological data collected on-site. Additionally, advanced Gaussian Plume were applied to determine the contribution of stack releases to the measured air concentrations. The contribution of stack sources to measured air concentrations of radioactive particles was further assessed at the downwind site by size fractionating the material using a high-volume cascade impactor. Due to the filtering of stack releases it was expected that the contributions from these sources would be associated with a finer size fraction than the releases from the pond surfaces.
- The measured and modelled data were thus used to “backcalculate” the emission rates of fugitive radionuclides from the
ponds. Using the CFD dispersion factors, a boot-strap resampling statistical method was applied to derive emission rates and the
corresponding upper and lower confidence limits.
The Benefits
· The Environment Agency Requirement was fully met.