Assessment of gas capture via tunnel ventilation following an underground chemical explosion

In October 2023 an underground chemical explosive test, Physics Experiment 1-A, was executed in a tunnel at the Nevada National Security Site. This test was part of a series of multi-physics experiments focused on enhancing nuclear explosion monitoring techniques. Part of the experiment included monitoring ga movement. As part of the facility operations, there were two events during the first five days of the experiment where the ventilation system was operated to purge gases from the facility. These events afforded an opportunity to evaluate the mass of gases emitted to the atmosphere during these ventilation events and compare to the total mass produced during the experiment. This provides a basis for estimating the fraction of gas produced in an underground test that might be expected to be released through natural and engineered pathways. Using several approaches, an estimate of between 1 and 9% of the total gas produced by the experiment was captured and discharged to the atmosphere during these events. The percentage of gas captured was nominally equal to the percentage of the plume volume that was bisected by the facility tunnels and represents a similar fraction to that assumed as potential releases for underground nuclear tests.