Analysis of water activation in fusion and fission nuclear facilities

摘要

Water is used as a cooling fluid of certain systems in operational fusion reactors and will also be used in the ITER tokamak. During cooling the water is exposed to high energy neutrons emitted from fusion of deuterium and tritium and becomes activated. The main contributors to the activity of the cooling water are radioactive isotopes of oxygen and nitrogen produced by activation of oxygen isotopes in the cooling water, i.e. N-16, N-17 and( )(19)O. As currently few experiments for water activation in fusion reactors exist, computational methods are needed to determine water activation and consequent dose rates in fusion reactors. The calculated activation of oxygen isotopes strongly depends on the cross sections in evaluated nuclear data libraries. For fusion reactors there are two reference nuclear data libraries: FENDL-2.1 and FENFL-3.1b. The calculated activities of nuclides in water have an uncertainty, which depend on the uncertainty of calculated neutron spectra and uncertainty in reaction cross sections. For the reference fusion libraries the uncertainty for activation of water isotopes, due to uncertainty in reaction cross section, is around 8% for isotope O-16, around 12% for the isotope O-17 and around 12% for isotope O-18. The uncertainty in oxygen activation due to the uncertainty of activation cross sections is thus in the order of several percent. Hence statistical uncertainty of neutron fluxes calculated with the Monte Carlo method can be of the same order of magnitude.