Estimation of Induced Activity in an ADSS Facility

Abstract

In order to meet the ever growing global demand for electricity, accelerator driven subcritical systems (ADSS) are emerging as one of the preferred choices. This is due to the fact that in ADSS, the neutrons required to sustain the fission chain reaction in a reactor is supplied from spallation reaction induced by high energy protons from an accelerator, on a heavy target. The spallation target is placed in the core of the reactor. The neutrons produced are used to drive the chain reaction as well as for transmutation of radioactive waste. When the accelerator beam is turned off the supply of neutrons is stopped and any criticality accident may be averted. So ensuring safety against any type of nuclear accident is easier in these facilities as compared to the conventional power reactors. In view of this, concentrated efforts in the field of nuclear engineering are being directed towards the development of ADSS facilities. Production of high flux of fast neutrons through high energy nuclear (spallation) reactions is the main aim of the booster accelerator in an ADSS. This is achieved through the interaction of high current high energy proton beams on suitable targets. Running a high energy accelerator incurs a considerable expenditure and the accelerator parameters are decided for optimizing the cost-benefit of the system (maximum neutron yield for certain beam energy and beam current). It has been found that the neutron economy is optimized around 1 GeV proton energy [1, 2]. However, various structural parameters, target stability, heat generation profile and other logistics are studied at much lower beam energies [3], which are easily available. Running a high energy machine at high currents would lead to the generation of considerable amount of radioactive waste depending on the target-projectile combination. So, in these high current machines one of the factors constraining the beam current and irradiation time is the production of induced radioand chemical toxicity.