Fixed bed or moving bed reactors with a radial flow of process stream to be treated, comprising improved internals

A reactor with a radial flow of process stream to be treated, comprising a shell (5), means for introducing process stream to be treated (4) and for effluents (11) to be removed, a zone for distributing said process stream (9), optional diplegs (6) for introducing catalyst, outer screens (3) and inner screens (2) to enable the process stream which is to be treated to move from an outer screen (3) to an inner screen (2) located substantially at the centre of the reactor, or conversely from the inner screen (2) to the outer screen (3), wherein said reactor further comprises at least one supplemental outer screen (13, 18) having a shape which is adapted to that of the bottom of the reactor or the head of the reactor, said supplemental screen (13, 18) being located in the extension of the outer screen (3).