AbstractThe influence of plasma thermal instability on the safety of a D—T tokamak breeder reactor is examined, by coupling (a) a one-dimensional tokamak transport model which includes a radial motion, and (b) thermal-hydraulic equations for the blanket materials. The plasma is operated at a volume-averaged temperature of 15 keV and at a nearly-ignited state (Qp ∼ 100). The blanket uses a mobile form of uranium pebble-bed configurations with helium cooling. If one takes appropriate positive values for the vertical field decay index, then the thermal instability and its influence can be considerably suppressed. However, the actual field decay index is negative because a D-shaped plasma is supposed. In this case the effect of radial motion decreases and unfavorable changes in plasma/blanket parameters are observed. For successful operation one must provide the plasma with some control. The plasma thermal instability and its influence on the blanket can be completely eliminated by applying a vertical-field regulation.