Westinghouse Electric Corporation

Thomas R Freeman

John F Wilson

Donald G Sherwood

Thomas M Camden, Jr

Pratap K Doshi

Ronald P Knott

Claude M Mildrum

Brian H Alsop

William L Orr

A nuclear fuel rod has an elongated hollow cladding tube with a pair of end plugs and fuel pellets contained in the tube and extending between the end plugs. All pellets are composed of fissile material having a single enrichment. The pellets are provided in an axial stack having a length slightly less than the distance between the end plugs such that when the tube is disposed in a vertical orientation the stack of pellets at a lower end rests on the lower end plug and at an upper end is spaced from upper end plug by a gap. The gap is devoid of any structure restraining the stack from movement toward the upper end plug. The pellets in the stack are provided in an arrangement of axial regions which includes a pair of first opposite end axial regions and second and third tandemly-disposed middle axial regions between the first axial regions. The pellets in the first opposite end axial regions are identical in number and have annular configurations with an annulus of a first void size. Pellets in the second axial region have annular configurations with an annulus of a second void size smaller than the first void size of the annulus of pellet in the first axial regions. Pellets in the third axial region have solid configurations.

Fuel rod with axial regions of annular and standard fuel pellets

A control rod for use in a nuclear reactor core to provide xenon compensation includes an elongated inner cylindrical member and an elongated outer cylindrical member surrounding the inner member. Each of the members is composed of axially-extending, alternating black poison and nonpoison regions. Also, the inner member is axially movable relative to the outer member to adjust the degree to which the poison regions of the members overlap with the nonpoison regions thereof and thereby change the overall worth of the rod in an axially uniform manner. The inner cylindrical member has a solid cross-sectional configuration, whereas the outer cylindrical member has an annular cross-sectional configuration and concentrically surrounds the inner member. Each of the poison regions in the members is about the same axial height, while each of the nonpoison regions is about the same axial height. The guide thimble of a fuel assembly in which the control rod is placed has an annular stop being sized to support a lower end of the outer member for retaining the outer member in a stationary position therein, whereas the stop has a central hole sized to allow passage of a lower end of the inner member therethrough in order to move the inner member axially relative to the outer member to adjust the degree to which the poison regions of the members overlap with the nonpoison regions thereof and thereby change the overall worth of the rod.

Nuclear reactor control rod with uniformly changeable axial worth

A radial neutron reflector is disclosed for a light water nuclear reactor. The irregular space between the core periphery and the core barrel surrounding the core is filled with a structure comprising material other than hydrogen such as zirconia or stainless steel so as to displace the reactor water coolant in this region. The structure is provided with appropriately sized flow holes to pass reactor coolant therethrough and to balance the pressure within the structure to substantially coincide with the axial pressure profile at the core periphery.

Radial neutron reflector

A control rod for use in a nuclear reactor core to provide xenon compensation includes an elongated inner cylindrical member and an elongated outer cylindrical member surrounding the inner member. Each of the members is composed of axially-extending, alternating black poison and nonpoison regions. Also, the inner member is axially movable relative to the outer member to adjust the degree to which the poison regions of the members overlap with the nonpoison regions thereof and thereby change the overall worth of the rod in an axially uniform manner. The inner cylindrical member has a solid cross-sectional configuration, whereas the outer cylindrical member has an annular cross-sectional configuration and concentrically surrounds the inner member. Each of the poison regions in the members is about the same axial height, while each of the nonpoison regions is about the same axial height. The guide thimble of a fuel assembly in which the control rod is placed has an annular stop being sized to support a lower end of the outer member for retaining the outer member in a stationary position therein, whereas the stop has a central hole sized to allow passage of a lower end of the inner member therethrough in order to move the inner member axially relative the outer member to adjust the degree to which the poison regions of the members overlap with the nonpoison regions thereof and thereby change the overall worth of the rod.

A control arrangement which provides enthalpy rise compensation upon reduction of core power includes control rodlets arranged in a cluster. Each control rod cluster has a higher axial worth at an upper portion than at a lower portion thereof. Several different embodiments of control rod clusters are provided. In one embodiment, the worth of the control rod cluster varies in accordance with different lengths of the absorber material contained within its rodlets. In another embodiment, the worth of the control rod cluster varies in accordance with different variations in densities of the absorber material within its rodlets. In a third embodiment, the worth of the control rod cluster varies in accordance with different kinds of the absorber material within the rodlets. In a final embodiment, the worth of the control rod cluster varies in accordance with different variations in diameters of the absorber material within its rodlets.

Nuclear reactor control rod cluster for enthalpy rise compensation

A fuel assembly, particularly advantageous for use with a BWR, wherein the fuel bundle is adapted to be inserted into an envelope formed from a flow channel and a lower nozzle assembly. The fuel bundle is essentially axially symmetrical having identical top and bottom tie plates. Within the fuel bundle, alternate fission gas plenums are disposed at the top and bottom of the bundle respectively. During the refueling operation, the fuel bundle is removed from the reactor core, axially inverted and reinserted into the core for continued burn up. The invention takes advantage of the reactivity increase possible in a BWR when a partially burned fuel bundle is inverted.

Reversible BWR fuel assembly and method of using same

A control rod assembly arrangement is disclosed for a light water nuclear reactor. Absorber rods are combined with stainless steel rods to achieve a more homogeneous poison distribution effect which reduces power depression within associated fuel assemblies and thereby flattens the overall power distribution within the core. In addition to improved load follow performance, safety analysis margins are improved due to the reduction in control rod reactivity worth.

Control rod cluster arrangement

A nuclear fuel assembly, particularly advantageous for use in a pressurized water reactor, wherein each alternate fuel rod in the assembly is positioned with its fission gas plenum zone at the top of the assembly and the intervening alternate fuel rods are positioned with their fission gas plenum zones at the bottom of the assembly. All of the fuel rods are preferably axially coextensive. An axial blanket region may be formed by providing the fuel zone of each fuel rod with a small zone of natural or depleted uranium at a part of the fuel zone furthest from the fission gas plenum zone. A method of effectively lengthening the active length of a nuclear fuel assembly is also described.

Growing community of inventors

Greensburg, PA, United States of America

Thomas R Freeman