One method of low and intermediate concentrate disposal to the ground that maintains control of wastes is hydrofracture. In this method, a well is drilled to the desired geological formation and cased. Then, the casing is perforated at the specific depth desired, pressure is applied, and the formation is fractured. After the formation is fractured, a radioactive waste mixture containing portland cement, fly ash, attapulgite, illite, delta gluconolactone, and trib-utyl phosphate is injected into the space and spread as a thin sheet parallel to the bedding (Figure 8.7.2). The radioactive waste forms a dense solid with improved cesium retention on the illite and improved strontium retention on the fly ash. The delta gluconolactone retards set times, and the attapulgite is a suspender, reducing the quantity of cement required.

This technique was first used in December 1966, when the first ultimate disposal of radioactive waste took place with the injection of 72,000 gal of intermediate waste containing 20,000 curies of cesium-137 in a shale formation 870 ft below the ground surface. The method was also routinely used at Oak Ridge National Laboratory and was demonstrated at the Nuclear Fuel Services site.

Hydrofracture techniques are used where there are thick formations of shale in flat-lying, well-bedded, sedimentary rock for intermediate activity wastes and possibly for low and high activity wastes with suitable modifications.

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