Radiological properties of heavy liquid metal targets of accelerator driven systems

The long-lived radioactivity of lead-bismuth coolant (LBC) inside the targets of the accelerator driven systems (ADS) is estimated. It is determined by both spallation and fission products of lead and bismuth nuclides. Based on US safety standards the radiotoxicity of targets was calculated for different cooling down periods. In order to estimate the total radioactivity of 1-MW power target circuit (TC), which is developing now at IPPE, the contribution of its main components are preliminarily analyzed. The following conclusions were made: (1) Preliminary analysis has shown that 2 years after the stop of the ADS operation its coolant radiotoxicity in comparison with that of reactor installations is higher in the all cooling interval in question and reaches the radiotoxicity of natural uranium only in approximately 300 years. (2) Under effect of accelerator proton beam with energy Ep = 800 MeV, as a result of nuclear reactions in the LBC volume of the TC of 1-MW power, a wide spectrum of radionuclides is formed and accumulated. The total specific coolant activity to the end of operation time under nominal power proved to be as much as about 500 Ci/kg and reduces to 2.7 Ci/kg in 5 years. (3) The most dangerous are gaseous and volatile radionuclides, that due to thermal diffusion and evaporation partly are transmitting from the lead-bismuth mirror of volume compensator into protective gas system (helium). Among them there are noble gases krypton and xenon, radionuclides of polonium, mercury, cesium, iodine, bromine, and rubidium. (4) Only nuclides with half-lives no lower than 10 hours were included in the calculations. The short-lived nuclides were not taken into account as structurally the TC is installed in a hermetic container under biological shielding. Even in case of break of the membrane (the window of the target active part) with coolant leakage into the container volume and its further freezing, any direct danger for operation personal is fully excluded