Device and method for blocking an orifice of a tube wrapper of a steam generator of a nuclear reactor with pressurised water

The invention relates to a device (20) for closing an inner hole of a control sleeve of a steam generator, comprising: a movable shaft (21) which comprises a pair of lower half flanges (25, 26); a pair of upper half flanges (27, 28) which can be rotated by 180 degrees by the shaft (21) between a low position and a high position, at the low position, the pair of upper half flanges, facing the lower half flanges (25, 26), are used for being introduced into the hole of the control sleeve of the steam generator, and at the high position, the pair of upper half flanges are opposite to the lower half flanges (25, 26); and a mechanism (22) for clamping the lower half flanges (25, 26) and the upper half flanges (27, 28) to the circumferential edge disposed at any side of the inner hole so as to close the inner hole. The invention also relates to a closing method and a tool for mounting and removing the closing device.