New radioactive nuclides accumulation in chloride target of accelerator-driven system

The change of isotopic composition, accumulation of new radionuclides (S, Tl, Po), and radiation characteristics (activity.and radiotoxicity) are calculated for chloride salt neutron-producing target of ADS. Only action of low-energy neutrons of subcritical blanket and high-energy neutrons produced in the target are considered. The target material is chloride salt mixture composed of sodium chloride and lead chloride. The flux density of thermal neutrons of blanket from 1013 to 1015 neutron/cm2s and those of high-energy neutrons of the target itself from 1015 to 1016 neutron/cm2s are taken into account. It is shown that the activity of target with dimension about 50 cm: irradiated by thermal neutron flux 1014 neutron/cm2s during a time of 1 year is about 1.5 Curie/gram. The major part in activity and radiotoxicity is contributed by radionuclide S-35. The new radionuclides under irradiation by high-energy neutron of the target itself are produced not only by (n, γ) but also by (n,2n), (n,3n) reactions with neutrons of energies over 10-20 MeV. The activity and radiotoxicity are about 10-25 times higher then those produced by thermal neutrons of blanket. The major portion is contributed by S-35. This result shows the importance of the high energy neutrons of the target itself in production of those radionuclides that determine the basic radiation characteristics if the irradiated target. The investigation was performed in the framework of the project ISTC No. 477. (author)