[en] Reactors based on DT fusion will impose certain requirements and pose challenges for diagnostics. These relate, for example, to the need for such facilities to address the safety aspects of using tritium and high neutron fluxes leading to activation and radiation fields. There are also implications arising from the need for high machine availability and hence reliability of critical diagnostics. This paper will focus on the safety and licensing implications using design issues for typical diagnostic types to illustrate the above