Chapter 3~Containing Underground Nuclear Explosions ¢ 43 point room, a muffler, a modified auxiliary closure Figure 3-6—Vessel| (MAC), a gas seal auxiliary closure (GSAC), and a Vessel 1 tunnel and pipe seal (TAPS). All these closures are End of stemming €— Bypass drift Mechanical hee HOS rift closurg Working point Mechanical closure (MAC) (TAPS) Mechanical closure (GSAC) Test chamber / End of stemming Key: GSAC =gas seal auxiliary closure; MAC = modified auxiliary closure; TAPS =Tunnel and pipe seal The HLOS Vessei | is designed to protect the experimental equipment after allowing radiation to trave! down the pipe. SOURCE: Modified trom Defense Nuclear Agency. the test chamber.24 The entire pipe is vacuum pumpedto simulate the conditions of space and to minimize the attenuation of radiation. The bypass drift (an access tunnel), located next to the line of sight pipe, is created to provide accessto the closures and to different parts of the tunnel system. These drifts allow for the nuclear device to be placed in the zero room and for late-time emplacementof test equipment. After the device has been emplaced at the working point, the bypass drift is completely filled with grout. After the experiment, parts of the bypass drift will be reexcavated to permit access to the tunnel system to recoverthe pipe and experimental equipment. The area around the HLOSpipe is also filled with grout, leaving only the HLOS pipe as a clear pathway between the explosion and the test chamber. Near the explosion, grout with properties similar to the surrounding rock is used so as notto interfere with the formation of the stress containment cage. Near the end of the pipe strong grout or concreteis used to support the pipe and closures. In between, the stemming is filled with super-lean grout designed to flow under moderate stress. The super-lean grout is designedto fill in and effectively plug any fractures that may form as the ground shock collapses the pipe and creates a stemmingplug. Asillustrated in figure 3-6, the principal components of an HLOSpipe system include a working 24On occasion, the diameterofthe pipe has increased to 20 feet. installed primarily to protect the experimental equipment. The closures are designed to shut off the pipe after the radiation created by the explosion has traveled down to the test chamber, but before material from the blast can fly down the pipe and destroy the equipment. The working point room is a box designed to house the nuclear device. The muffler is an expanded region of the HLOSpipethat is designed to reduce flow down the pipe by allowing expansion and creating turbulence and stagnation. The MAC (figure 3-7(a)) is a heavy steel housing that contains two 12-inch-thick forged-aluminum doors designed to close openings up to 84 inches in diameter. The doors are installed opposite each other, perpendicular to the pipe. The doors are shut by high pressure gas that is triggered at the time of detonation. Although the doors close completely within 0.03 seconds (overlapping so that each door fills the tunnel), in half that time they have metin the middle and obscure the pipe. The GSACis similar to the MACexceptthatit is designed to provide a gas-tight closure. The TAPS closure weighs 40 tons and the design (figure 3-7(b)) resembles a large toilet seat. The door, which weighsup to 9 tons, is hinged on the top edge and held in the horizontal (open) position. Whenthe dooris released, it swings down by gravity and slams shut in about 0.75 seconds. Any pressure remaining in the pipe pushes on the door making the seal tighter. The MAC and GSACwill withstand pressures up to 10,000 pounds per square inch. The TAPSis designed to withstand pressures up to !,000 pounds per square inch, and temperatures up to 1,000 °F. Whenthe explosion is detonated radiation travels down the HLOS pipe at the speed of light. The containmentprocess(figure 3-8(a-e), triggered at the time of detonation, occurs in the following sequence to protect experimental equipment and contain radioactive material produced by the explosion: e After 0.03 seconds(b), the cavity created by the explosion expands and the shock wave moves away from the working point and approaches the MAC. The shock wave collapses the pipe. squeezing it shut, and forms a stemming ‘*plug.’’ Both the MAC and the GSACshutoff