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Time Domain Reflectometry with Waveguides

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Fact Sheets:
AR #2244

 

Tech ID: 704
Project Overview
The objective of this task is to design a sub-surface barrier performance monitoring system which will indicate liquid contaminants are migrating past the barrier system so that corrective actions can be taken. Sub-surface barrier systems will operate below underground waste disposal structures at various DOE sites to prevent the transport of chemical and radioactive contaminants into soil and water table. State and federal regulators are requiring that the sub-surface barrier system have a detection or performance monitoring verification system in place. The sub-surface barrier performance monitoring system will detect moisture increases above baseline after the barrier system has been installed.

This technology provides real-time monitoring of barriers on surface and subsurface. This monitoring system will give the regulators, waste disposal structure operators/owners, and the public assurance that the barrier system is performing as designed.

Technology Description
 The system consists of: 1) sensors or waveguides constructed of stainless steel emplaced adjacent to or within the barrier material spaced a few feet apart, and 2) electronics devices which are connected to the sensors. The electronics package sends a pulse into the sensor and measures the difference between the input pulse and reflected pulse. This difference translates into changes in moisture near the sensor. The correlation to moisture content in soil was shown to be accurate by experimentation/comparison to other reliable moisture detection systems. If the sensors detect moisture content above that of background via the electronics package, the computer software can then alert operators that corrective actions are necessary. The system inherently allows a diagnostic assessment method to be performed because adjacent sensors can be individually analyzed to determine operability. In a cement based sub-surface barrier, the sensor system satisfies multiple objectives. Sensors embedded into the cement-like barrier provide: 1) a 'yes/no' moisture detection capability which will alert operators to moisture conditions prior to any moisture penetrating past the barrier, 2) barrier emplacement quality control so that any discontinuities, windows, or pockets in the barrier can be detected and located, 3) a method to determine where and if discontinuities occurred after a seismic event, and 4) a method to allow a more detailed determination of the amounts of moisture (if any) passing through the barrier in the vicinity of the sensors using the same electronic package.

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