Behavior of a steel liner-and-bolts system under very high thermal and mechanical loading

Abstract

This paper describes the execution of the CONVEX Liner Add-On to the DIAMOND FORTUNE low-yield cavity test of the Defense Nuclear Agency (DNA). CONVEX stands for COntained Nuclear Vessel EXperiment. It is a joint concept to three Department of Energy Laboratories (Lawrence Livermore National Laboratory, Los Alamos National Laboratory, and Sandia National Laboratories) and the DNA. It concerns the design of underground chambers where repeated low-yield nuclear explosions could be conducted. The approach proposed by the first author in the early 1980s was to engineer a steel-lined rock cavern where the steel liner would be pre-stressed against the rock by tendons and/or bolts. These would daylight in tunnels surrounding the main cavity. From there, they could be initially tensioned, and retensioned if needed, after each test. The CONVEX Liner Add-On to DIAMOND FORTUNE consisted of anchoring a 1.4m square, 2.5 cm thick steel plate to the wall of the cavity, using a 5.08 cm dia center bolt and four 2.54 cm dia corner bolts. The bolts daylighted in a “run-around” drift surrounding the cavity, and separated from it by a 9 m thick rock pillar. The liner plate, the bolts and the rock pillar were equipped with 23 gages to describe the thermal and mechanical response of the system during pretensioning, during the dynamic loading phase, and post-test. Particular emphasis was given to obtaining the response both upon loading and during the rebound of the system, in order to determine whether the plate ever separated from the rock. So, the main operational objectives of this project were to acquire response data of the system under nuclear loading and to ascertain the status of contact between the steel plate and the rock, as shown by plate-rock contact pressure data and bolt tension data. The instrumentation and data acquisition system performed extremely well. Data were recorded during the dynamic phase; plate temperature was monitored for several hours after the test; and the remaining tension was obtained run-around drift. The test data indicated that the operational objectives had been met and that the concept of a steel-lined rock cavity could provide for reusable test beds for repeated low yield nuclear events. The results of this experiment can be used to guide the design of liner systems subjected to very high mechanical and thermal loads.