Radiation environment for FIRE diagnostic ports

Two-dimensional neutronics calculations have been performed to determine the nuclear radiation environment at selected locations in the FIRE diagnostics penetrations and to assess the impact of streaming on average flux outside the port flange. The total neutron flux (integrated over all energies), the fast neutron flux (E > 0.1 MeV) and the total gamma flux were calculated at the front of the plug, along the penetrations, at the back of the plug and at the back of the port flange. In addition, the absorbed dose rates in silica (SiO₂) and alumina (Al₂O₃) were calculated. Two types of penetrations were assessed. These are straight and 4-bend penetrations. Radiation streaming calculations indicated that the port plug should be increased to 3.4 m, the location of the cryostat interface, to ensure that the dose rates after shutdown in the area behind the port flange are similar to the acceptable levels obtained in the 1.1-m plug without penetrations.