Activation Analysis and Comparison of Bio-shield Under ITER and ASP Neutron Irradiation

Abstract

The leakage of fusion neutrons from ITER tokamak machine would cause bio-shield activation. Assessment of the shutdown dose rate from activated bio-shield is necessary from the standpoints of occupational safety. FISPACT inventory calculations have been performed for four different types of the bio-shield concrete under the neutron irradiation of ITER and ASP, which is a 14 MeV fusion neutron irradiation facility in UK. Shutdown contact dose rate and the dominant radioactive isotopes of each sample have been evaluated and cross compared for different concretes for ITER and ASP irradiations. The results show that activation products of same concrete are different under irradiation of predicted ITER moderated neutron source and ASP fast neutron source. Fast neutron activation leads to high dose rate dominated by 24Na for about 1 day after shutdown and it shows insignificant impact of impurities on dose rate. While moderated neutron activation leads concretes with impurities to a relative high dose rate for a long cooling time. These radiological hazard elements in impurity have been listed.