A turbine shaft of a turbomachine extending along a longitudinal axis (A) includes a main tubular portion with a length L1 and a maximum outer main diameter. The shaft further includes a secondary tubular segment with a length L2 and a maximum outer secondary diameter greater than the maximum outer main diameter. The secondary tubular segment extends radially from the shaft such that the main tubular portion extends on either side of the secondary tubular segment along the longitudinal axis (A). The secondary tubular segment includes a weak point that is configured to break the shaft into two distinct parts when the value of a tangential stress applied to the shaft exceeds a predetermined threshold value, and thus cause retraction of the turbine.