Atmospheric Dispersion Modeling

PNNL-25654, Rev. 1, Atmospheric Dispersion Modeling Tools for Hanford Tank Farms Applications

Washington River Protection Solutions (WRPS) contracted with Pacific Northwest National Laboratory (PNNL) to conduct a study to evaluate several atmospheric dispersion models for Hanford tank farms applications. This information will lead to a better understanding of how chemical vapors may move through the air at the Hanford Site. Atmospheric dispersion models simulate the concentration of vapors over time and distance from user-prescribed sources.

There are four basic classes of dispersion models that may be used to simulate atmospheric dispersion. They are listed here in order of increasing complexity:

• The Plume model, which assumes a continuous release from a source and steady meteorological conditions,
• The Puff model, which simulates a release as a series of discrete puffs and can incorporate atmospheric changes and terrain effects,
• The Particle model, which simulates by tracking a large number of particle trajectories and can incorporate terrain and wind effects, and
• Computational Fluid Dynamics (CFD) models, which utilize differential equations to calculate material transport and concentration change across a grid.

The compatibility of specific atmospheric dispersion models was evaluated against the modeling needs of the Hanford tank farms. The report reviewed four different application areas where atmospheric dispersion models are used:

• Real-time response
• Worker Safety and Emergency planning
• Regulatory compliance, and
• Engineering and research applications.

WRPS has used or has previously considered seven different dispersion models that relate to these application areas:

• AERMOD, a plume model used for regulatory and engineering and research needs

• CFX, a CFD model used in engineering and research
• FDS, a CFD model used in worker safety and emergency planning
• EPIcode, a plume model used in worker safety and emergency planning
• AIHA-Eddy, a puff model used in worker safety and emergency planning
• APGEMS, a puff model used in worker safety and emergency planning, real-time response, and engineering and research application, and
• SAFER, a plume model that was considered for use in real-time response.

In the report, PNNL recommended the use of certain models for Hanford specific applications as shown in the table below.

The full Atmospheric Dispersion Modeling Tools for Hanford Tank Farms Application report can be found here.