bility. By this method, liquid wastes are injected into a deep underground cavity with mineral treatment and allowed to self-boil. The resulting steam is processed at ground level and recycled in a closed system. When waste addition is terminated, the chimney is allowed to boil dry. The heat generated by the radioactive wastes then melts the surrounding rock, thus dissolving the wastes. When waste and water addition stop, the cavity temperature would rise to the melting point of the rock. As the molten rock mass increases in size, so does the surface area. This results in a higher rate of conductive heat loss to the surrounding rock. Concurrently the heat production rate of radioactivity diminishes because of decay. When the heat loss rate exceeds that of input, the molten rock will begin to cool and solidify. Finally the rock refreezes, trapping the radioactivity in an insoluble rock matrix deep underground. The heat surrounding the radioactivity would prevent the intrusion of ground water. After all, the steam and vapour are no longer released. The outlet hole would be sealed. To go a little deeper into this concept, the treatment of the wastes before injection is very important. To avoid breakdown of the rock that constitutes the formation, the acidity of he wastes has to be reduced. It has been established experimentally that pH values of 6.5 to 9.5 are the best for all receiving formations. With such a pH range, breakdown of the formation rock and dissociation of the formation water are avoided. The stability of waste containing metal cations which become hydrolysed in acid can be guaranteed only by complexing agents which form 'water-soluble complexes' with cations in the relevant pH range. The importance of complexing in the preparation of wastes increases because raising of the waste solution pH to neutrality, or slight alkalinity results in increased sorption by the formation rock of radioisotopes present in the form of free ca...
