Characterization of TFTR shielding penetrations of ITER-relevance in D-T neutron field

D-T operation of TFTR began successfully with trace tritium discharges in mid-November 1993. During the next year, the TFTR plasma tritium fraction is scheduled to be increased to at least 50%. The availability of larger amounts of D-T fusion neutrons in the high power D-T plasma phase of TFTR provides a useful opportunity to characterize tokamak shielding-penetration geometries of potential interest to ITER. These types of measurements can provide direct experimental data on the degree of enhancement of transmitted neutron flux along or across a realistic penetration and, as such, can be used to validate, calculational methods and to meet fusion reactor licensing requirements. The enhancement of neutron streaming in the shielding penetrations has the following significant consequences from the ITER viewpoint: (1) increased radiation damage to plasma diagnostics/detectors, (2) increased biological dose rates behind the shield, (3) increased radiation damage to the superconducting magnet on the inboard side. TFTR has penetrations of different varieties inside the vacuum vessel, the test cell, and the adjoining hot cell. In the initial stage, the authors have chosen to characterize three different types of penetrations in and around the TFTR test cell: (1) a straight hollow pipe coming out of the test cell concrete wall on east side of the test cell into the hot cell, (2) a bent pipe coming out of the test cell through the north concrete wall, and (3) a labyrinth in the north-west end of the test cell