Shielding aspects of a tokamak reaching ignition

The Ignitor experiment is designed to produce deuterium-tritium (DT) plasmas in which ignition can take place and the physics of α-particles can be studied. After a first period of a neutronic operation, a second phase in deuterium with 2.5 MeV neutron production rate up to 1017 n/s is planned. This will be followed by operations at increasing percentages of tritium, leading to short but intense 14 MeV neutron production, up to ∼ 3 x 1019 n/s. To calculate the neutron fluxes in all the machine components, a detailed description of the actual Ignitor machine is implemented in the MCNP-4B Monte Carlo code. These fluxes are then used as input for the FISPACT-99 code for the analysis of the activation at the end of life (EOL) and at intermediate times for safety assessment purposes. The estimated neutron emission pulse results in rather modest neutron fluences (∼ 1018 n/cm2 on the first wall at EOL). The shielding strategy and possible solutions to prevent/reduce the activation of the cryostat are presented. (authors)