Problems of heavy coolant technology for accelerator-driven systems

The title topic is discussed, and the activities of nuclides in the target gas system by 1 MW power after 6 months of work are tabulated. The following facts are stressed: Realization of traditional technology based mainly on cover gas replacement, release and feeding of gas mixtures into the loop is complicated and needs developing and applying devices for purification of the gases removed and radiation shielding of these devices at least. Such developments are especially urgent for ADS projects where coolant circulation is intensified by gas lift. Traditional technology is unable to solve a number of problems associated with the elimination of electropositive impurities (Au, Ag, Hg and others) that make a significant contribution to change compound and radio activity of ADS coolants. The task to remove such impurities was not set for traditional nuclear power plants, so that appropriate developments began only recently. New processes that could replace the developed processes have not been revealed in the course of investigations, however there is an opportunity of using new methods of their realization. For example, the processes of purification and regulation of coolant quality using chemically active gases can be implemented without using external gas systems. The solid hydride, metallooxide and other chemical compounds located in the gas volume or in the coolant loops of ADS can be the sources and absorbents of chemically active gas components. Applying to ADS conditions the emphasis of some processes goals can be slightly changed. For example: regulation of dissolved oxygen activity can be performed as well (probably, mainly) for oxygen refining of coolant by means of electronegative impurities transition into solid-phase oxide compounds; gas and coolant filtering can also be performed to localize radioactive impurities in the ADS circuit. Probably, the coolant technology can be employed to solve a number of tasks: to localize radioactive impurities in the ADS circuit, to limit radioactive releases during normal ADS operation, and to reduce the radioactivity of the coolant and loop as a whole. The most likely ways of heavy coolants technology development as applied to ADS are the following: development of the new processes and devices to remove the electronegative impurities from the coolant and to localize them in the circuit (sorption filtering, evaporation, condensation and others); development of the high effective methods to purify gases removed from the circuit; c) adaptation of the developed processes as applied to ADS; d) adaptation of the devices for processes realization, based mainly on the use of external systems for feeding and discharging the chemically active gases; e) development of new devices for processes realization without using external gas system. At present it is advisable to carry out the works in all directions mentioned above to determine their prospects.Further on, when developing particular ADS designs, it is possible to intensify the development in some directions