Abstract: A nuclear reactor includes a pressure vessel having a bottom wall above which a core vessel is suspended with its lower end spaced above this bottom wall. In case the core vessel accidentally falls, it is intercepted by a construction transmitting the force of the falling core vessel to the pressure vessel's bottom wall throughout a plurality of widely interspaced positions so that the bottom wall does not have to withstand the force in a localized concentrated manner. Preferably these positions are adjacent to the pressure vessel's side wall, and the intercept construction is made of ductile metal having upper portions reduced in cross-sectional area so that these upper portions are stressed beyond their elastic limit and deform in a ductile shock-absorbing manner if required to intercept the falling core vessel. Various other features of construction are included.