Pressurizer for a pressurized water nuclear power station, comprising an outer casing which delimits an inner space; a duct (11) which extends beneath the casing and which is capable of being tapped from the coolant system of the nuclear power station; a tap (18) which places the inner space of the casing in communication with the duct (11), this tap (18) being welded to the duct (11) by means of a weld seam (32); a sleeve (42) for protecting the weld seam (32), which sleeve is arranged inside the tap (18) and which has a lower peripheral edge (46) which is engaged in the duct (11), the sleeve (42) defining with the tap (18) and the duct (11) an annular space (74) which is capable of being filled with the primary liquid; wherein the annular space (74) is open along at least a portion of the lower peripheral edge (46) of the sleeve (42) and opens inside the duct (11).