[en] Various flows to and from the boundary in a tokamak plasma are affected by the boundary conditions imposed by the metal plate of a limiter or diverter. For the charged particles, these conditions can be simplified to a perfect absorption in the ralevant range of the parameters. The loss regions in the phase space of the plasma due to the contact with the absorbing surface are effectively refilled within a short distance from the plate if the collisionality is high. However, a small effect is shown to extend from the plate and influence the outward diffusion of the plasma. In contrast to the weakly collisional models the analysis here is based on the determination of the eigenfunctions of the collision operator. (Auth.)