46 © The Containment of Underground Nuclear Explosions locks in the residual stress field, thereby forming a containment cage. The shock wave passesthe test chamber. e After 0.75 seconds(e), the final mechanicalseal (TAPS) closes, preventing late-time explosive and radioactive gases from entering the test chamber. The entire closure process for containment takes Figure 3-9—Typical Post-Shot Configuration —_ —. a ~ tL SO tnKe Approximate chimney boundary less than 3/4 of a second. Because the tests are typically buried at a depth greater than necessary for containment, the chimney does not reach the surface and a collapse crater normally does not form. A typical post-shot chimney configuration with its approximate boundaries is shownin figure 3-9. 400 m T ynnel LOS pipe reser In lower yield tests, such as those conductedin the P-tunnel complex, the first mechanical closure is a = te Stemming Fast Acting Closure (FAC) rather than a MAC.® plug The FAC (figure 3-7(c)) closes in 0.001 seconds and complex can withstand pressures of 30,000 pounds per square inch. The FAC acts like a cork, blocking off the HLOSpipe early, and preventing debris and stemming material from flying downthe pipe. A similar closure is currently being developed for larger yield tunneltests. Tunnel shots are typically overburied and the collapse chimney rarely extends to the surface. TYPES OF RADIATION RELEASES leases of radioactive material. They are characterized as active releases under pressure, such as when radioactive material is driven out of the ground by steam or gas. ‘‘Baneberry,”’ in 1970. ts ithe lise example of an explosion that “‘vented.”’ Terms describing the release or containment of underground nuciear explosions have been refined to account for the volume of the material and the conditionsof the release. The commonly used terms are described below. Containment Failure Containment failures are releases of radioactive material that do not fall within thestrict definition of successful containment, which is described by the Department of Energyas: Containmentsuch that a test results in no radioactivity detectable off site as measured by normal monitoring equipment and no unanticipated release of radioactivity onsite. Detection of noble gases that appear onsite long after an event, due to changing atmospheric conditions, is not unanticipated. Anticipated releases will be designed to conform to specific guidance from DOE/HQ.*6 Containment failures are commonly described as: SOURCE: Modified from Defense Nuciear Agency. Ventings Ventings are prompt, massive, unconwolled re- Seeps Seeps, which are notvisible, can only be detected by measuring for radiation. Seeps are charactenzed as uncontrolled slow releases of radioactive matenal with little or no energy. Late-Time Seep Late-time seeps are small releases of noncondensable gases that usually occur days or weeks after 4 vertical drill hole test. The noncondensable gases diffuse up through the pore spaces of the overlying rock and are thought to be drawn to the surface by a decrease in atmospheric pressure (called ‘“atmospheric pumping’’). 25The P-tunne! complex 1s mined in Aqueduct Mesa and has less overburden than the N-tunne!l complex in Rainier Mesa. Theretore, P tunnel 1s generally used for loweryield tests. Section VIIL.F, Containment Evaluation Panel Charter.