Impact of radiation measurements on hardening of TFTR diagnostics

Contrary to previous plans for the preparation of diagnostic systems for D-T break-even experiments in the Tokamak Fusion Test Reactor (TFTR), it now appears that a limited Q∼1 demonstration can be carried out without constructing a close-fitting igloo radiation shield around the tokamak. In order to assess the impact of D-T operation of TFTR without an igloo shield, particularly with regard to hardening of diagonstic systems, we have mapped neutron and gamma fluxes inside the test cell and test cell basement, using a variety of radiation measurements. The measurements are sufficiently detailed to resolve massive hardware components, such as neutral beams and shielded diagnostic systems, and can be used to predict local fluxes. By comparing the measurements with transport code calculations for the case of a bare tokamak, we conclude that the models have substantially overestimated fluxes both inside and outside the TFTR shield walls. It may be possible to eliminate an igloo shield, by taking credit for the shielding effectiveness of massive hardware around the tokamak. However, this will increase the need for local diagnostic shielding