Induced activity in tungsten as an ADSS target

Abstract

A part of India’s total electricity production is achieved from nuclear industry amounting to ~3000 MU per year during the last few years. The PHWR and BWR commissioned for the purpose employ U as the fuel and the spent fuel contains a large amount of transuranic (TRU) elements and actinides. Disposal of these long-lived high level wastes is a problem to the nuclear industry. Safe operation of the power reactors at near criticality is another problem to be mitigated. Accelerator driven sub-critical system (ADSS) has emerged as one of the preferred solutions to tackle both these problems. ADSS acts as a source of spallation neutrons which are supplied to the reactor core to sustain the fission chain reaction as well as for transmutation of long-lived isotopes. The neutronics of the system should ensure a hard neutron spectrum with high neutron yield, low yield of chemical and radio-toxicity, satisfying at the same time several other operational criteria [1]. This mandates a careful selection of the ADSS target. Different materials have been studied for their suitability to be used as ADSS target. Lead and lead-bismuth alloys have proved to be good choices for the purpose [2]. Of the other materials uranium and tungsten have high neutron yields [3] required for ADSS. Tungsten may be used as an ADSS target because besides having high cross section of neutron production it has low probability for production actinides by neutron capture [4]. In this work we have estimated the radioactivity produced in the tungsten target due to reactions induced by the primary proton beam at 400 MeV, 800 MeV and 1.2 GeV and by the secondary neutrons produced thereof.