Refiner segment in a fiber refiner

A refiner segment (4) for a refiner (1) comprises one or more refining zones (Z(x)) and is provided with a pattern of bars (10) arranged at a respective pumping feeding angle (β) within a respective refining zone (Z(x))， and intermediate grooves (11) between the bars (10)， and dams (12) extending between the bars (10) and protruding above the surface of the grooves (11). The dams are arranged at least at the ends of at least some of the bars (10) at the borders between the refining zones (Z(x)) such that openings (13) are formed at the borders between the refining zones (Z(x))， radially outside of the dams (12)， where the openings (13) are arranged such that a respective angle (Y) between an imaginary line connecting the openings (13) at a radially inner border of a respective refining zone (Z(x)) and a line which is perpendicular to a radius (r) of the refiner segment (4) is directed towards the inner edge of the refiner segment (4)， thereby allowing steam (8) to pass through the openings (13) and flow towards an inner edge (41) of the refiner segment (4).