Chapter 3—Containing Underground Nuclear Explosions « 41
Figure 3-4—‘‘Typicai”’ Stemming Plan
Cable fanouts
so that the grout and fines can seal between them.
Frequently, radiation detectors are installed between
plugs to monitor the post-shot flow of radiation
through the stemming column.
CONTAINING HORIZONTAL
TUNNEL TESTS
Emplacement pipe
(if used)
Sanded
gypsum
Plug
.
concrete
Fines
Coarse
Cable gas blocks
Both types of horizontal tunnel tests (effects tests
and cavity tests) use the same containment concept
of three redundant containment *‘vessels’* that nest
inside each other and are separated by plugs (figure
(Plug to
true scale)
The containment of a horizontal tunnel test is
different from the containmentofa vertical drill hole
test because the experimental apparatus is intended
to be recovered. In most tests, the objective is to
allow direct radiation from a nuclear explosion to
reach the experiment, but prevent the explosive
debris and fission products from destroying it.
Therefore, the containment is designed for two
tasks: 1) to prevent the uncontrolled release of
radioactive material into the atmosphere for public
safety, and 2) to prevent explosive debris from
reaching the experimental test chamber.
(Diagram not to scale)
Typical stemming sequence of coarse material, fine material, and
sanded gypsum plug used by Lawrence Livermore National
Laboratory for verticaldrill hoie tests.
SOURCE: Modified from Lawrence Livermore National Laboratory.
Livermore test with six sanded gypsum concrete
plugs.?? The plugs have two purposes: 1) to impede
gas flow, and 2) to serve as structural platformsthat
prevent the stemming from falling out if only a
partial collapse occurs. Under each plugis a layer of
sand-size fine material. The sand provides a base for
the plug. Alternating between the plugs and the
fines, coarse gravel is used to fill in the rest of the
stemming. The typical repeating pattern used for
stemming by Los ALamos, for example, is 50 feet of
gravel, 10 feet of sand, and a plug.
All the diagnostic cables from the nuclear device
are blocked to prevent gas from finding a pathway
throughthe cables and traveling to the surface. Cable
fan-out zones physically separate the cables at plugs
3-5).23 Each vessel is designed to independently
contain the nuclear explosion, even if the other
vessels fail. {f, for example, gas leaks from vesselI
into vessel II, vessel II has a volume large enough so
that the resulting gas temperatures and pressures
would be weil within the limits that the plugs are
designed to withstand. The vessels are organized as
follows:
Vessel I is designed to protect the experiment by
preventing damage to the equipment and allowing it
to be recovered.
Vessel II is designed to protect the tunnel system
so that it can be reused even if vessel I fails and the
experimental equipment is lost.
Vessel III is designed purely for containment,
such that even if the experimental equipment is lost
and the tunnel system contaminated. radioactive
material will not escape to the atmosphere.
In addition to the three containmentvessels, there
is a gas seal doorat the entrance of the tunnel system
that serves as an additional safety measure. The gas
seal door is closed prior to detonation and the area
22 Although Livermore and Los Alamos use the same general stemming philosophy, there are somedifferences: For example, Livermoreuses sanded
gypsum concrete plugs while Los Alamos uses plugs made of epoxy. Also, Livermore uses an emplacementpipe for lowering the device downhole, while
Los Alamos lowers the device and diagnostic cannister on a wire rope harness.
23See ch. 2 for a discussionof types of nuclear tests.