Radioisotope Fume Hood Stack Design
Derrick Ko, Rowan Williams Davies & Irwin, Inc.
Re-entrainment of laboratory exhaust is a continuing challenge for building designers. Laboratory exhaust containing vapors and gases must be dispersed to a safe level so that when it impinges on a sensitive area or individual, it does not endanger or discomfort building occupants or neighbors. The concerns with re-entrainment are even more marked when the laboratory exhaust contains radioisotope emissions. The radiation hazard posed by airborne radioisotopes can result in both acute and chronic health problems in exposed individuals.
Two limits are typically considered when evaluating radioisotope emissions. The first is the Maximum Permissible Concentration (MPC); this regulates the allowable concentrations of radioisotopes in an exhaust. MPC is calculated separately for each radionuclide. The second is the annual dosage limit (ADL); this regulates the maximum levels of exposure for different potential receptors. This is affected by both the emitted concentration and the dispersion achieved by the exhaust stack and intake design.
Typically, models such as COMPLY and CAP88 are used to evaluate radiation exposures and demonstrate compliance for radionuclide emissions. While these models are convenient for calculating exposures, they are not well suited for estimating near-field dispersion, particularly in highly urbanized environments. This can result in very conservative stack and intake designs.
Instead of modeling dispersion through these regulatory models, dedicated wind tunnel and numerical dispersion models could be used to develop more accurate dispersion estimates. This leads to stack and intake designs that can meet exposure limits while potentially being less costly than designs based on regulatory modeling.
Better design practices can help to meet both of these regulations. The following objectives will be achieved with this presentation:
- Identify concepts for understanding of radioisotope regulatory limits.
- Demonstrate how radioisotope hood stack designs can benefit from improved dispersion modeling.
- Compare the advantages and disadvantages of different design strategies for meeting the regulatory limits.
Biography:
Derrick Ko is a technical coordinator in the exhaust re-entrainment group at Rowan Williams Davies & Irwin, Inc. His technical specialization has been in evaluating exhaust dispersion with wind tunnel and numerical models. Recently, his projects have focused on providing design guidance for healthcare, transportation, and central utility facilities. Mr. Ko holds a Bachelor of Applied Science degree in chemical engineering from the University of Waterloo.