Diaphragm-like protection for equipping a sheath lining a passage through a wall

Biological protection for closing an opening in a containment wall of a radioactive zone, this protection comprising an iris-type diaphragm including a base in the form of a flat disc directly supporting a contact surface of petals, the petals being formed by flat plates having substantially triangular contours and made of at least one material protecting from ionising radiation, which petals are capable of being displaced parallel to the base between an open state in which these petals jointly delimit a central opening and a closed state in which these petals are brought together to jointly form a continuous closed wall, wherein each petal comprises ball bearings in order to limit the friction forces generated between the petals and the base during the displacement of these petals, wherein at least one of the ball bearings comprises the contact surface.