Abstract: A liquid level sensing apparatus (32) senses the level of liquid surrounding the apparatus. A plurality of axially spaced sensors (36) are enclosed in a separator tube (86). The separator tube (86) tends to collapse the level of a two-phase fluid within the separator tube into essentially a liquid phase and a gaseous phase where the collapsed level bears a relationship to the coolant inventory outside the separator tube. The level of the liquid phase is sensed by level sensing apparatus (32). The separator tube (86) contains inlet-outlet ports (90,92) near the top and bottom thereof to equalize the liquid level inside and outside the separator tube (86) when the level fluctuates or the water within the separator tube (86) flashes to steam. Each sensor (36) is comprised of a heater (64), a heated thermocouple junction (68) and an unheated thermocouple junction (66) within an elongated heat conductive housing (62).

Abstract: The oscillatory forces acting on an eccentric rod within a diffuser are reduced by an annular bypass collar around the rod immediately upstream of the diffuser region. The collar includes a sleeve portion that completely surrounds the rod and a bypass channel outside the sleeve which carries most of the fluid into the diffuser region on a path parallel to but spaced from the rod. The collar is most effective when a multiplicity of discrete bypass channels are provided.

Abstract: An enclosed reservoir is sized and located in relation to the steam generator of a pressurized water nuclear reactor power plant so that upon a loss of feedwater flow to the steam generator, a gravity induced supplementary flow into the steam generator is automatically initiated to dissipate the residual heat generated in the reactor. The height of the reservoir is the same as the distance between upper and lower design limits on steam generator feedwater level. The top of the steam generator is fluidly connected to the top of the reservoir to equalize the pressure therebetween. The gravity induced flow from the reservoir to the steam generator produces a water level in the steam generator that stays within the upper and lower design limits.

Abstract: A method and apparatus for the storage of fuel in a stainless steel egg crate structure within a storage pool. Fuel is initially stored in a checkerboard pattern or in each opening if the fuel is of low enrichment. Additional fuel (or fuel of higher enrichment) is later stored by adding stainless steel angled plates within each opening, thereby forming flux traps between the openings. Still higher enrichment fuel is later stored by adding poison plates either with or without the stainless steel angles.

Abstract: A new part length rod is provided which may be used to not only control xenon induced power oscillations but also to contribute to shutdown reactivity when a rapid shutdown of the reactor is required. The part length rod consists of a control rod with three regions. The lower control region is a longer weaker active portion separated from an upper stronger shorter poison section by an intermediate section which is a relative non-absorber of neutrons. The combination of the longer weaker control section with the upper high worth poison section permits the part length rod of this invention to be scrammed into the core. When a reactor shutdown is required but also permits the control rod to be used as a tool to control power distribution in both the axial and radial directions during normal operation.

Abstract: A new part length rod is provided which may be used to not only control xenon induced power oscillations but also to contribute to shutdown reactivity when a rapid shutdown of the reactor is required. The part length rod consists of a control rod with three regions. The lower control region is a longer weaker active portion separated from an upper stronger shorter poison section by an intermediate section which is a relative non-absorber of neutrons. The combination of the longer weaker control section with the upper high worth poison section permits the part length rod of this invention to be scrammed into the core. When a reactor shutdown is required but also permits the control rod to be used as a tool to control power distribution in both the axial and radial directions during normal operation.

Abstract: A lock down device for restraining a nuclear fuel assembly against hydraulic flow forces having cantilever leaf springs on the fuel assembly lower end fitting which lock into recesses in the fuel alignment pins located on the core support plate.

Abstract: A bottom actuated hydraulic reactor control system including absorber element blow-out protection means and wherein cooling flow for neutron absorber elements is derived from the pressure vessel coolant via an external system.

Abstract: A pressurized nuclear reactor having an instrument assembly sheathed in a metallic tube which is extended vertically upward into the reactor core by traversing a metallic guide tube which is welded to the wall of the vessel. Sensors in each instrument assembly are connected to instruments outside the vessel to manifest the conditions within the core. Each instrument assembly probe is moved into position within a metallic guide channel. The guide channel penetrates the wall of the vessel and forms part of the barrier to the environment within the pressure vessel. Each channel includes a ball check valve which is opened by the instrument assembly probe when the probe passes through the valve. A ball valve element is moved from its seat by the probe to a position lateral of the bore of the channel and is guided to its seat along a sloped path within the valve body when the probe is removed.

Abstract: A new part length rod is provided which may be used to not only control xenon induced power oscillations but also to contribute to shutdown reactivity when a rapid shutdown of the reactor is required. The part length rod consists of a control rod with three regions. The lower control region is a longer weaker active portion separated from an upper stronger shorter poison section by an intermediate section which is a relative non-absorber of neutrons. The combination of the longer weaker control section with the upper high worth poison section permits the part length rod of this invention to be scrammed into the core, when a reactor shutdown is required but also permits the control rod to be used as a tool to control power distribution in both the axial and radial directions during normal operation.

Abstract: An apparatus for the safe storage of a plurality of fissionable masses including an array of discrete neutron absorbing shields which utilizes the principle of the neutron trap to reduce the multipication factor of the storage array to a subcritical value when immersed in a neutron moderating medium. Each discrete neutron absorbing shield is designed to perimetrically encircle each of the stored fissionable masses. Each shield is spaced such that the encircled fissionable mass is spaced from the next adjacent neutron absorbing shield by a distance determined by the enrichment of the fissionable masses and attenuation of the moderating medium.

Abstract: A shock buffer is provided for the gradual deceleration of a rapidly descending control element assembly in a nuclear reactor. The interactive buffer components are associated respectively with the movable control element assembly and part of the upper guide structure independent of and spaced from the fuel assemblies of the reactor.Preferably, the buffer is of the piston and cylinder type, with a piston extending upward from a tube sheet of the upper guide structure and a cylinder opening downward and carried by the control element assembly near its upper end. The cylinder descends about the buffer piston near the lower extent of control element assembly travel. Liquid naturally occupying the buffer cylinder, as the reactor coolant at the ambient pressure within the reactor, provides hydraulic decelerating forces on the control element assembly when relative insertion of the piston in the cylinder occurs.

Abstract: An apparatus for the safe storage of a plurality of fissionable masses including an array of discrete neutron absorbing shields which utilizes the principle of the neutron trap to reduce the multiplication factor of the storage array to a subcritical value when immersed in a neutron moderating medium. Each discrete neutron absorbing shield is spaced such that the encircled fissionable mass is spaced from the next adjacent neutron absorbing shield by a distance determined by the enrichment of the fissonable masses and attenuation of the moderating medium.

Abstract: An apparatus for the safe storage of a plurality of fissionable masses including an array of discrete neutron absorbing shields which utilizes the principle of the neutron trap to reduce the multiplication factor of the storage array to a subcritical value when immersed in a neutron moderating medium. Each discrete neutron absorbing shield is designed to perimetrically encircle each of the stored fissionable masses. Each shield is spaced such that the encircled fissionable mass is spaced from the next adjacent neutron absorbing shield by a distance determined by the enrichment of the fissionable masses and attenuation of the moderating medium.

Abstract: An emergency core cooling system for a nuclear reactor in which an emergency cooling injection manifold is integrally formed with the guide structure which guides control elements into the reactor core. The guide structure comprises two vertically spaced plates each of which substantially overlies the entire core and which are interconnected by a control element guidance means. A third plate is supported in vertical spaced relationship from one of the plates of the guide structure to define the manifold therebetween. Means are provided for substantially sealing the plenum from the main coolant flow path of the reactor. Means are also provided for introducing emergency coolant into the injection manifold and for dispersing coolant fluid therein into the core in the event of a loss of coolant accident.

Abstract: A method and apparatus for increasing the reliability of linear drive devices of a nuclear reactor to scram the control elements held in a raised position thereby. Each of the plurality of linear drive devices includes a first type of holding means associated with the drive means of the linear drive device and a second type of holding means distinct and operatively dissimilar from the first type. The system of linear drive devices having both types of holding means are operated in such a manner that the control elements of a portion of the linear drive devices are only held in a raised position by the first holding means and the control elements of the remaining portion of linear drive devices are held in a raised position by only the second type of holding means. Since the two types of holding means are distinct from one another and are operatively dissimilar, the probability of failure of both systems to scram as a result of common mode failure will be minimized.