For a NET breeding blanket, consisting of canister type elements, the rupture of a helium coolant pipe within an element is a postulated accident to be analysed. In this paper the resulting structural response of this element has been investigated by advanced finite element calculations and a full scale experiment. Provided the ductility of the material of the element including the necessary weldings is sufficient, the elements are able to carry the pressure of the coolant (60 bar) escaping from the ruptured pipes.