Post-explosion environment resulting from the Salmon Event

Abstract

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.

Kinematic analysis of strong motion P and SV waves from the Sterling Event

“…In these kinds of models, the Sterling explosion simply reactivated dislocation, either tensional or shear, on one or more cracks. This fit is particularly interesting because one of the inferred fault planes coincides exactly with an observed shear zone below the shot point [see Rawson et al, 1966, Figure 1]. Figure 6 shows the observed first motions and a fit assuming a shear dislocation.…”

“…The primary goal of this series of tests was to evaluate the effect of source decoupling. Figure 1 shows a schematic of the Salmon cavity as determined from direct observations from boreholes and indirect observations using geophysical means [Rawson et al, 1966]. Figure 1 shows a schematic of the Salmon cavity as determined from direct observations from boreholes and indirect observations using geophysical means [Rawson et al, 1966].…”

“…The surrounding medium was pervasively cracked and fractured out to a distance of 3 to 5 cavity radii as seen from direct observation of forcefully injected radioactive melt and diffusion of other radioactive materials [Rawson et al, 1966]. The center of the cavity is located at 828-m depth.…”

Thermal stress state of rock massif with a spherical cavity taking into account inhomogeneity of the medium

“…As is known [1,6] using the method of forming explosive underground cavities, as well as drilling and blasting method for tunneling holes surrounding rock mass undergoing such changes (appearance of microcracks, compaction, sintering) that lead to mechanical inhomogeneity of material. At the same time there is local variation of the modulus of elasticity, which has a central symmetry.…”

“…Expanding the surface loads p в (T) and q в (T) (5) in series similar to (6), it is sufficient to restrict members to n = 3:…”