Predicting multiphase flow and tracer transport for an underground chemical explosive test

Area of Science:

• Geophysics
• Environmental Science
• Nuclear Nonproliferation

Background:

• Detecting radionuclide gas seepage from clandestine underground nuclear tests is crucial for nonproliferation efforts.
• Early-time gas transport (<6 days) driven by explosive pressure waves is poorly constrained due to limited field data.

Purpose of the Study:

• To simulate multi-phase gas transport in the vadose zone following an underground explosion.
• To improve the understanding of early-time gas migration dynamics and inform sensor placement for explosion monitoring.

Main Methods:

• Utilized pre-shot data from a chemical explosion in P-Tunnel at the Nevada National Security Site.
• Employed a simplified 2D-radial model to simulate multi-phase gas transport in the vadose zone.
• Compared model predictions of tracer arrival times with observational data.

Main Results:

• Model predictions of tracer arrival matched observations within one order-of-magnitude, despite using a simplified model.
• Demonstrated that transient blast forcing rapidly mobilizes gases from the explosion cavity into surrounding rock.
• Validated the model's capability to predict gas migration from underground explosions.

Conclusions:

• The integration of field data and modeling significantly enhances the ability to predict gas migration from underground explosions.
• Findings provide critical insights into the coupled dynamics of pressure waves and contaminant transport in the vadose zone.
• Results have broader implications for monitoring underground activities and assessing associated hazards.