Chapter 3—Containing Underground Nuclear Explosions ¢ 47
Photo creat David Graham
Fast acting closure.
Controlled Tunnel Purging
the explosion (called ‘‘gas sampling’’), and sealing
the drill back holes (called *‘cement back"’)
Controlled tunnel purgingis an intentional release
of radioactive material to recover experimental
equipment and ventilate test tunnels. During a
controlled tunnel purging, gases from the tunnel are
filtered, mixed with air to reduce the concentration,
and released over time when weatherconditions are
favorable for dispersion into sparsely populated
areas.
The containment of underground nuclear explosions is a process that has continually evolved
through learning, experimentation. and experience.
The record of containment illustrates the various
types of releases and their relative impact.
Operational Release
Containment Evaluation Panel
Operational releases are smallreleases of radioactivity resulting from operational aspects of vertical
drill hole tests. Activities that often result in
operational releases include: drilling back down to
the location of the explosion to collect core samples
(called **drill back’’), collecting gas sampies from
RECORD OF CONTAINMENT
The Containment Evaluation Panel defines suc-
cessful containment as no radioactivity detectable
offsite and no unanticipated release of activity
onsite. By this definition, the CEP has failed to
predict unsuccessful containment on four occasions
since 1970: