Measuring shrinkage of holes to store radioactive waste - esp. holes in subterranean salt domes which are heated while capacitor monitors redn. in hole dia

The highly radioactive waste (HAW) gives off heat, so that after a long storage time the holes in subterranean salt formations employed for storing the HAW undergo shrinkage. The shrinkage is measured by applying a constant amt. of heat to the region of the hole for several weeks, and using a capacitor to monitor the change in hole dia. The capacitor uses two ring electrodes, one of which is fed with a sinusoidal voltage of known frequency; and the capacitor provides a signal voltage (Us) representing the dia. (2r) of the hole. The pref. appts. employes a probe contg. a heater for the hole and also the capacitor, which consists of an outer ring electrode with overlapping ends so the ring can shrink in dia. to correspond with the shrinkage of the hole. Holes are drilled in subterranean salt deposits for the long-time storage of HAW; and the holes are lined with tubes. The pressure caused by shrinkage of the salt must not cause the tube to shrink in dia. The HAW is contained in steel drums placed in the tubes.