Abstract: A nuclear reactor is disclosed wherein hydraulic drive mechanisms for control rods are provided with a positive mechanical latching arrangement to maintain the control rods in a withdrawn position with respect to the core. With this arrangement, the coil of an associated electromagnet must be deliberately energized in order to insert the control rod into the core thus making accidental tripping highly unlikely. The drive mechanism is further provided with a hydraulic decelerating device which uses reactor coolant water to smoothly decelerate the control rod as it approaches the fully withdrawn position.

Abstract: A nuclear reactor internals arrangement is disclosed which facilitates reactor refueling. A reactor vessel and a nuclear core is utilized in conjunction with an upper core support arrangement having means for storing withdrawn control rods therein. The upper core support mounted to the underside of the reactor vessel closure head so that upon withdrawal of the control rods into the upper core support, the closure head, the upper core support and the control rods are removed as a single unit thereby directly exposing the core for purposes of refueling.

Abstract: Upon the occasion of loss of coolant in a nuclear reactor as when a coolant supply or return line breaks, or both lines break, borated liquid coolant from an emergency source is supplied in an amount to absorb heat being generated in the reactor even after the control rods have been inserted. The liquid coolant flows from pressurized storage vessels outside the reactor to an internal manifold from which it is distributed to unused control rod guide thimbles in the reactor fuel assemblies. Since the guide thimbles are mounted at predetermined positions relative to heat generating fuel elements in the fuel assemblies, holes bored at selected locations in the guide thimble walls, sprays the coolant against the reactor fuel elements which continue to dissipate heat but at a reduced level.

Abstract: A system is provided for determining during operation of a nuclear reactor having fluid pressure operated control rod mechanisms the exact location of a fuel assembly with a defective fuel rod. The construction of the reactor internals is simplified in a manner to facilitate the testing for defective fuel rods and to reduce the cost of producing the upper internals of the reactor.