The anomalous groundwater mound and resulting flow regime associated with the Aardvark underground nuclear explosion have been examined. The initial anomalous groundwater mound was estimated to be about 200 m high and 250 m in radius with a central depression. The major mechanism for mound development was probably compaction of nearly saturated rock surrounding the explosion. Results of the calculations indicate that water first flowed into the collapsed zone, then radially outward with early velocities approximately 200 times preshot flow velocities. After about 400 days the magnitude of the anomalous flow had declined to or below the magnitude of the preshot groundwater flow rates. Ideally ‘traced tagged’ water particles initially near the edge of the collapsed zone are estimated to have moved outward about 6.2 m during the first 100 days after the explosion. It is shown that the anomalous mound does not significantly increase the migration of radionuclides from this explosion environment.
A summary of some results of the Gnome underground nuclear explosion in bedded salt is presented. The report deals primarily with the environment produced by the explosion, touches also on isotope production feasibility, feasibility of power production, seismic measurements, shock studies, and neutron experimentation, and discusses the venting which accompanied the explosion.
The Salmon event was a 5.3 _ 0.5 kt nuclear detonation at a depth of 827.8 m in the Tatum salt dome in Mississippi. The explosion created a nearly spherical cavity of radius 17.4 _ 0.6 m and vaporized and melted approximately 5.4 X 106 kg of rock which formed a puddle of recrystallized salt. At the time of penetration the cavity was under a partial vacuum with a pressure of less than 313 mb, and the temperature of its gases was about 205øC. Most of the explosion energy was in the form of heat distributed within 45 m of the shot point. Radioactive melt injected into cracks was observed as far as 37 m from the shot point, and radioactivity increased above background as far as 64 m. The wall rock was highly microfractured and contained some macrofractures. The most broken portion of the rock surrounding the cavity was observed in the region 39 to 50 m below shot point. The puddle at the base of the cavity was highly fractionareal, with a high concentration of refractory radioactive species in the bottom few centimeters. Separation of Xe TM in the cavity gas from the parent I • found in the puddle indicates that the puddle took 24 to 32 days to solidify. It is concluded that the resulting cavity is stable and could be used for an experimental investigation of full or partial decoupling; however, the material surrounding the cavity is less competent than it was before the shot, and the present strength and stress distribution of the rock are not known. [1966]. The medium in the vicinity of the explosion is characterized by 90% NaC1, 10% CaSO•, and a very low water content (•0.001% by weight). The average in situ bulk density of the salt is about 2.24 g/cm • and the average compressional and shear velocities are about 4550 and 2520 m/sec [Rawson, to be published]. Major obiectives of the Salmon event that depended upon postshot exploration were to determine the condition of the cavity generated by the explosion, to assess the feasibility of re-use of the cavity for subsequent explosions, and to obtain samples of the recrystallized melt for radiochemical yield determination. The exploration basically consisted in drill-ing two holes, PS 1 and PS 2. An additional hole was 'whipstocked' off each main hole. Figure 1, a plan and vertical section of the postshot drillholes, displays pertinent data obtained from these holes about the rock surrounding the cavity. Core drilling provided samples and made possible geophysical logging, gas sampling, television observations of borehole and cavity,and radiation and temperature logging. In conjunction with re-entry drilling, a chemical processing plant was used to control the release of radioactive cavity gases and to monitor the pressure, temperature, and gas composition.
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